xref: /external/clang/lib/AST/ExprConstant.cpp

//===--- ExprConstant.cpp - Expression Constant Evaluator -----------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the Expr constant evaluator.
//
// Constant expression evaluation produces four main results:
//
//  * A success/failure flag indicating whether constant folding was successful.
//    This is the 'bool' return value used by most of the code in this file. A
//    'false' return value indicates that constant folding has failed, and any
//    appropriate diagnostic has already been produced.
//
//  * An evaluated result, valid only if constant folding has not failed.
//
//  * A flag indicating if evaluation encountered (unevaluated) side-effects.
//    These arise in cases such as (sideEffect(), 0) and (sideEffect() || 1),
//    where it is possible to determine the evaluated result regardless.
//
//  * A set of notes indicating why the evaluation was not a constant expression
//    (under the C++11 / C++1y rules only, at the moment), or, if folding failed
//    too, why the expression could not be folded.
//
// If we are checking for a potential constant expression, failure to constant
// fold a potential constant sub-expression will be indicated by a 'false'
// return value (the expression could not be folded) and no diagnostic (the
// expression is not necessarily non-constant).
//
//===----------------------------------------------------------------------===//

#include "clang/AST/APValue.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/ASTDiagnostic.h"
#include "clang/AST/CharUnits.h"
#include "clang/AST/Expr.h"
#include "clang/AST/RecordLayout.h"
#include "clang/AST/StmtVisitor.h"
#include "clang/AST/TypeLoc.h"
#include "clang/Basic/Builtins.h"
#include "clang/Basic/TargetInfo.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/Support/raw_ostream.h"
#include <cstring>
#include <functional>

using namespace clang;
using llvm::APSInt;
using llvm::APFloat;

static bool IsGlobalLValue(APValue::LValueBase B);

namespace {
  struct LValue;
  struct CallStackFrame;
  struct EvalInfo;

  static QualType getType(APValue::LValueBase B) {
    if (!B) return QualType();
    if (const ValueDecl *D = B.dyn_cast<const ValueDecl*>())
      return D->getType();

    const Expr *Base = B.get<const Expr*>();

    // For a materialized temporary, the type of the temporary we materialized
    // may not be the type of the expression.
    if (const MaterializeTemporaryExpr *MTE =
            dyn_cast<MaterializeTemporaryExpr>(Base)) {
      SmallVector<const Expr *, 2> CommaLHSs;
      SmallVector<SubobjectAdjustment, 2> Adjustments;
      const Expr *Temp = MTE->GetTemporaryExpr();
      const Expr *Inner = Temp->skipRValueSubobjectAdjustments(CommaLHSs,
                                                               Adjustments);
      // Keep any cv-qualifiers from the reference if we generated a temporary
      // for it.
      if (Inner != Temp)
        return Inner->getType();
    }

    return Base->getType();
  }

  /// Get an LValue path entry, which is known to not be an array index, as a
  /// field or base class.
  static
  APValue::BaseOrMemberType getAsBaseOrMember(APValue::LValuePathEntry E) {
    APValue::BaseOrMemberType Value;
    Value.setFromOpaqueValue(E.BaseOrMember);
    return Value;
  }

  /// Get an LValue path entry, which is known to not be an array index, as a
  /// field declaration.
  static const FieldDecl *getAsField(APValue::LValuePathEntry E) {
    return dyn_cast<FieldDecl>(getAsBaseOrMember(E).getPointer());
  }
  /// Get an LValue path entry, which is known to not be an array index, as a
  /// base class declaration.
  static const CXXRecordDecl *getAsBaseClass(APValue::LValuePathEntry E) {
    return dyn_cast<CXXRecordDecl>(getAsBaseOrMember(E).getPointer());
  }
  /// Determine whether this LValue path entry for a base class names a virtual
  /// base class.
  static bool isVirtualBaseClass(APValue::LValuePathEntry E) {
    return getAsBaseOrMember(E).getInt();
  }

  /// Find the path length and type of the most-derived subobject in the given
  /// path, and find the size of the containing array, if any.
  static
  unsigned findMostDerivedSubobject(ASTContext &Ctx, QualType Base,
                                    ArrayRef<APValue::LValuePathEntry> Path,
                                    uint64_t &ArraySize, QualType &Type) {
    unsigned MostDerivedLength = 0;
    Type = Base;
    for (unsigned I = 0, N = Path.size(); I != N; ++I) {
      if (Type->isArrayType()) {
        const ConstantArrayType *CAT =
          cast<ConstantArrayType>(Ctx.getAsArrayType(Type));
        Type = CAT->getElementType();
        ArraySize = CAT->getSize().getZExtValue();
        MostDerivedLength = I + 1;
      } else if (Type->isAnyComplexType()) {
        const ComplexType *CT = Type->castAs<ComplexType>();
        Type = CT->getElementType();
        ArraySize = 2;
        MostDerivedLength = I + 1;
      } else if (const FieldDecl *FD = getAsField(Path[I])) {
        Type = FD->getType();
        ArraySize = 0;
        MostDerivedLength = I + 1;
      } else {
        // Path[I] describes a base class.
        ArraySize = 0;
      }
    }
    return MostDerivedLength;
  }

  // The order of this enum is important for diagnostics.
  enum CheckSubobjectKind {
    CSK_Base, CSK_Derived, CSK_Field, CSK_ArrayToPointer, CSK_ArrayIndex,
    CSK_This, CSK_Real, CSK_Imag
  };

  /// A path from a glvalue to a subobject of that glvalue.
  struct SubobjectDesignator {
    /// True if the subobject was named in a manner not supported by C++11. Such
    /// lvalues can still be folded, but they are not core constant expressions
    /// and we cannot perform lvalue-to-rvalue conversions on them.
    bool Invalid : 1;

    /// Is this a pointer one past the end of an object?
    bool IsOnePastTheEnd : 1;

    /// The length of the path to the most-derived object of which this is a
    /// subobject.
    unsigned MostDerivedPathLength : 30;

    /// The size of the array of which the most-derived object is an element, or
    /// 0 if the most-derived object is not an array element.
    uint64_t MostDerivedArraySize;

    /// The type of the most derived object referred to by this address.
    QualType MostDerivedType;

    typedef APValue::LValuePathEntry PathEntry;

    /// The entries on the path from the glvalue to the designated subobject.
    SmallVector<PathEntry, 8> Entries;

    SubobjectDesignator() : Invalid(true) {}

    explicit SubobjectDesignator(QualType T)
      : Invalid(false), IsOnePastTheEnd(false), MostDerivedPathLength(0),
        MostDerivedArraySize(0), MostDerivedType(T) {}

    SubobjectDesignator(ASTContext &Ctx, const APValue &V)
      : Invalid(!V.isLValue() || !V.hasLValuePath()), IsOnePastTheEnd(false),
        MostDerivedPathLength(0), MostDerivedArraySize(0) {
      if (!Invalid) {
        IsOnePastTheEnd = V.isLValueOnePastTheEnd();
        ArrayRef<PathEntry> VEntries = V.getLValuePath();
        Entries.insert(Entries.end(), VEntries.begin(), VEntries.end());
        if (V.getLValueBase())
          MostDerivedPathLength =
              findMostDerivedSubobject(Ctx, getType(V.getLValueBase()),
                                       V.getLValuePath(), MostDerivedArraySize,
                                       MostDerivedType);
      }
    }

    void setInvalid() {
      Invalid = true;
      Entries.clear();
    }

    /// Determine whether this is a one-past-the-end pointer.
    bool isOnePastTheEnd() const {
      if (IsOnePastTheEnd)
        return true;
      if (MostDerivedArraySize &&
          Entries[MostDerivedPathLength - 1].ArrayIndex == MostDerivedArraySize)
        return true;
      return false;
    }

    /// Check that this refers to a valid subobject.
    bool isValidSubobject() const {
      if (Invalid)
        return false;
      return !isOnePastTheEnd();
    }
    /// Check that this refers to a valid subobject, and if not, produce a
    /// relevant diagnostic and set the designator as invalid.
    bool checkSubobject(EvalInfo &Info, const Expr *E, CheckSubobjectKind CSK);

    /// Update this designator to refer to the first element within this array.
    void addArrayUnchecked(const ConstantArrayType *CAT) {
      PathEntry Entry;
      Entry.ArrayIndex = 0;
      Entries.push_back(Entry);

      // This is a most-derived object.
      MostDerivedType = CAT->getElementType();
      MostDerivedArraySize = CAT->getSize().getZExtValue();
      MostDerivedPathLength = Entries.size();
    }
    /// Update this designator to refer to the given base or member of this
    /// object.
    void addDeclUnchecked(const Decl *D, bool Virtual = false) {
      PathEntry Entry;
      APValue::BaseOrMemberType Value(D, Virtual);
      Entry.BaseOrMember = Value.getOpaqueValue();
      Entries.push_back(Entry);

      // If this isn't a base class, it's a new most-derived object.
      if (const FieldDecl *FD = dyn_cast<FieldDecl>(D)) {
        MostDerivedType = FD->getType();
        MostDerivedArraySize = 0;
        MostDerivedPathLength = Entries.size();
      }
    }
    /// Update this designator to refer to the given complex component.
    void addComplexUnchecked(QualType EltTy, bool Imag) {
      PathEntry Entry;
      Entry.ArrayIndex = Imag;
      Entries.push_back(Entry);

      // This is technically a most-derived object, though in practice this
      // is unlikely to matter.
      MostDerivedType = EltTy;
      MostDerivedArraySize = 2;
      MostDerivedPathLength = Entries.size();
    }
    void diagnosePointerArithmetic(EvalInfo &Info, const Expr *E, uint64_t N);
    /// Add N to the address of this subobject.
    void adjustIndex(EvalInfo &Info, const Expr *E, uint64_t N) {
      if (Invalid) return;
      if (MostDerivedPathLength == Entries.size() && MostDerivedArraySize) {
        Entries.back().ArrayIndex += N;
        if (Entries.back().ArrayIndex > MostDerivedArraySize) {
          diagnosePointerArithmetic(Info, E, Entries.back().ArrayIndex);
          setInvalid();
        }
        return;
      }
      // [expr.add]p4: For the purposes of these operators, a pointer to a
      // nonarray object behaves the same as a pointer to the first element of
      // an array of length one with the type of the object as its element type.
      if (IsOnePastTheEnd && N == (uint64_t)-1)
        IsOnePastTheEnd = false;
      else if (!IsOnePastTheEnd && N == 1)
        IsOnePastTheEnd = true;
      else if (N != 0) {
        diagnosePointerArithmetic(Info, E, uint64_t(IsOnePastTheEnd) + N);
        setInvalid();
      }
    }
  };

  /// A stack frame in the constexpr call stack.
  struct CallStackFrame {
    EvalInfo &Info;

    /// Parent - The caller of this stack frame.
    CallStackFrame *Caller;

    /// CallLoc - The location of the call expression for this call.
    SourceLocation CallLoc;

    /// Callee - The function which was called.
    const FunctionDecl *Callee;

    /// Index - The call index of this call.
    unsigned Index;

    /// This - The binding for the this pointer in this call, if any.
    const LValue *This;

    /// Arguments - Parameter bindings for this function call, indexed by
    /// parameters' function scope indices.
    APValue *Arguments;

    // Note that we intentionally use std::map here so that references to
    // values are stable.
    typedef std::map<const void*, APValue> MapTy;
    typedef MapTy::const_iterator temp_iterator;
    /// Temporaries - Temporary lvalues materialized within this stack frame.
    MapTy Temporaries;

    CallStackFrame(EvalInfo &Info, SourceLocation CallLoc,
                   const FunctionDecl *Callee, const LValue *This,
                   APValue *Arguments);
    ~CallStackFrame();

    APValue *getTemporary(const void *Key) {
      MapTy::iterator I = Temporaries.find(Key);
      return I == Temporaries.end() ? nullptr : &I->second;
    }
    APValue &createTemporary(const void *Key, bool IsLifetimeExtended);
  };

  /// Temporarily override 'this'.
  class ThisOverrideRAII {
  public:
    ThisOverrideRAII(CallStackFrame &Frame, const LValue *NewThis, bool Enable)
        : Frame(Frame), OldThis(Frame.This) {
      if (Enable)
        Frame.This = NewThis;
    }
    ~ThisOverrideRAII() {
      Frame.This = OldThis;
    }
  private:
    CallStackFrame &Frame;
    const LValue *OldThis;
  };

  /// A partial diagnostic which we might know in advance that we are not going
  /// to emit.
  class OptionalDiagnostic {
    PartialDiagnostic *Diag;

  public:
    explicit OptionalDiagnostic(PartialDiagnostic *Diag = nullptr)
      : Diag(Diag) {}

    template<typename T>
    OptionalDiagnostic &operator<<(const T &v) {
      if (Diag)
        *Diag << v;
      return *this;
    }

    OptionalDiagnostic &operator<<(const APSInt &I) {
      if (Diag) {
        SmallVector<char, 32> Buffer;
        I.toString(Buffer);
        *Diag << StringRef(Buffer.data(), Buffer.size());
      }
      return *this;
    }

    OptionalDiagnostic &operator<<(const APFloat &F) {
      if (Diag) {
        // FIXME: Force the precision of the source value down so we don't
        // print digits which are usually useless (we don't really care here if
        // we truncate a digit by accident in edge cases).  Ideally,
        // APFloat::toString would automatically print the shortest
        // representation which rounds to the correct value, but it's a bit
        // tricky to implement.
        unsigned precision =
            llvm::APFloat::semanticsPrecision(F.getSemantics());
        precision = (precision * 59 + 195) / 196;
        SmallVector<char, 32> Buffer;
        F.toString(Buffer, precision);
        *Diag << StringRef(Buffer.data(), Buffer.size());
      }
      return *this;
    }
  };

  /// A cleanup, and a flag indicating whether it is lifetime-extended.
  class Cleanup {
    llvm::PointerIntPair<APValue*, 1, bool> Value;

  public:
    Cleanup(APValue *Val, bool IsLifetimeExtended)
        : Value(Val, IsLifetimeExtended) {}

    bool isLifetimeExtended() const { return Value.getInt(); }
    void endLifetime() {
      *Value.getPointer() = APValue();
    }
  };

  /// EvalInfo - This is a private struct used by the evaluator to capture
  /// information about a subexpression as it is folded.  It retains information
  /// about the AST context, but also maintains information about the folded
  /// expression.
  ///
  /// If an expression could be evaluated, it is still possible it is not a C
  /// "integer constant expression" or constant expression.  If not, this struct
  /// captures information about how and why not.
  ///
  /// One bit of information passed *into* the request for constant folding
  /// indicates whether the subexpression is "evaluated" or not according to C
  /// rules.  For example, the RHS of (0 && foo()) is not evaluated.  We can
  /// evaluate the expression regardless of what the RHS is, but C only allows
  /// certain things in certain situations.
  struct EvalInfo {
    ASTContext &Ctx;

    /// EvalStatus - Contains information about the evaluation.
    Expr::EvalStatus &EvalStatus;

    /// CurrentCall - The top of the constexpr call stack.
    CallStackFrame *CurrentCall;

    /// CallStackDepth - The number of calls in the call stack right now.
    unsigned CallStackDepth;

    /// NextCallIndex - The next call index to assign.
    unsigned NextCallIndex;

    /// StepsLeft - The remaining number of evaluation steps we're permitted
    /// to perform. This is essentially a limit for the number of statements
    /// we will evaluate.
    unsigned StepsLeft;

    /// BottomFrame - The frame in which evaluation started. This must be
    /// initialized after CurrentCall and CallStackDepth.
    CallStackFrame BottomFrame;

    /// A stack of values whose lifetimes end at the end of some surrounding
    /// evaluation frame.
    llvm::SmallVector<Cleanup, 16> CleanupStack;

    /// EvaluatingDecl - This is the declaration whose initializer is being
    /// evaluated, if any.
    APValue::LValueBase EvaluatingDecl;

    /// EvaluatingDeclValue - This is the value being constructed for the
    /// declaration whose initializer is being evaluated, if any.
    APValue *EvaluatingDeclValue;

    /// HasActiveDiagnostic - Was the previous diagnostic stored? If so, further
    /// notes attached to it will also be stored, otherwise they will not be.
    bool HasActiveDiagnostic;

    enum EvaluationMode {
      /// Evaluate as a constant expression. Stop if we find that the expression
      /// is not a constant expression.
      EM_ConstantExpression,

      /// Evaluate as a potential constant expression. Keep going if we hit a
      /// construct that we can't evaluate yet (because we don't yet know the
      /// value of something) but stop if we hit something that could never be
      /// a constant expression.
      EM_PotentialConstantExpression,

      /// Fold the expression to a constant. Stop if we hit a side-effect that
      /// we can't model.
      EM_ConstantFold,

      /// Evaluate the expression looking for integer overflow and similar
      /// issues. Don't worry about side-effects, and try to visit all
      /// subexpressions.
      EM_EvaluateForOverflow,

      /// Evaluate in any way we know how. Don't worry about side-effects that
      /// can't be modeled.
      EM_IgnoreSideEffects,

      /// Evaluate as a constant expression. Stop if we find that the expression
      /// is not a constant expression. Some expressions can be retried in the
      /// optimizer if we don't constant fold them here, but in an unevaluated
      /// context we try to fold them immediately since the optimizer never
      /// gets a chance to look at it.
      EM_ConstantExpressionUnevaluated,

      /// Evaluate as a potential constant expression. Keep going if we hit a
      /// construct that we can't evaluate yet (because we don't yet know the
      /// value of something) but stop if we hit something that could never be
      /// a constant expression. Some expressions can be retried in the
      /// optimizer if we don't constant fold them here, but in an unevaluated
      /// context we try to fold them immediately since the optimizer never
      /// gets a chance to look at it.
      EM_PotentialConstantExpressionUnevaluated
    } EvalMode;

    /// Are we checking whether the expression is a potential constant
    /// expression?
    bool checkingPotentialConstantExpression() const {
      return EvalMode == EM_PotentialConstantExpression ||
             EvalMode == EM_PotentialConstantExpressionUnevaluated;
    }

    /// Are we checking an expression for overflow?
    // FIXME: We should check for any kind of undefined or suspicious behavior
    // in such constructs, not just overflow.
    bool checkingForOverflow() { return EvalMode == EM_EvaluateForOverflow; }

    EvalInfo(const ASTContext &C, Expr::EvalStatus &S, EvaluationMode Mode)
      : Ctx(const_cast<ASTContext &>(C)), EvalStatus(S), CurrentCall(nullptr),
        CallStackDepth(0), NextCallIndex(1),
        StepsLeft(getLangOpts().ConstexprStepLimit),
        BottomFrame(*this, SourceLocation(), nullptr, nullptr, nullptr),
        EvaluatingDecl((const ValueDecl *)nullptr),
        EvaluatingDeclValue(nullptr), HasActiveDiagnostic(false),
        EvalMode(Mode) {}

    void setEvaluatingDecl(APValue::LValueBase Base, APValue &Value) {
      EvaluatingDecl = Base;
      EvaluatingDeclValue = &Value;
    }

    const LangOptions &getLangOpts() const { return Ctx.getLangOpts(); }

    bool CheckCallLimit(SourceLocation Loc) {
      // Don't perform any constexpr calls (other than the call we're checking)
      // when checking a potential constant expression.
      if (checkingPotentialConstantExpression() && CallStackDepth > 1)
        return false;
      if (NextCallIndex == 0) {
        // NextCallIndex has wrapped around.
        Diag(Loc, diag::note_constexpr_call_limit_exceeded);
        return false;
      }
      if (CallStackDepth <= getLangOpts().ConstexprCallDepth)
        return true;
      Diag(Loc, diag::note_constexpr_depth_limit_exceeded)
        << getLangOpts().ConstexprCallDepth;
      return false;
    }

    CallStackFrame *getCallFrame(unsigned CallIndex) {
      assert(CallIndex && "no call index in getCallFrame");
      // We will eventually hit BottomFrame, which has Index 1, so Frame can't
      // be null in this loop.
      CallStackFrame *Frame = CurrentCall;
      while (Frame->Index > CallIndex)
        Frame = Frame->Caller;
      return (Frame->Index == CallIndex) ? Frame : nullptr;
    }

    bool nextStep(const Stmt *S) {
      if (!StepsLeft) {
        Diag(S->getLocStart(), diag::note_constexpr_step_limit_exceeded);
        return false;
      }
      --StepsLeft;
      return true;
    }

  private:
    /// Add a diagnostic to the diagnostics list.
    PartialDiagnostic &addDiag(SourceLocation Loc, diag::kind DiagId) {
      PartialDiagnostic PD(DiagId, Ctx.getDiagAllocator());
      EvalStatus.Diag->push_back(std::make_pair(Loc, PD));
      return EvalStatus.Diag->back().second;
    }

    /// Add notes containing a call stack to the current point of evaluation.
    void addCallStack(unsigned Limit);

  public:
    /// Diagnose that the evaluation cannot be folded.
    OptionalDiagnostic Diag(SourceLocation Loc, diag::kind DiagId
                              = diag::note_invalid_subexpr_in_const_expr,
                            unsigned ExtraNotes = 0) {
      if (EvalStatus.Diag) {
        // If we have a prior diagnostic, it will be noting that the expression
        // isn't a constant expression. This diagnostic is more important,
        // unless we require this evaluation to produce a constant expression.
        //
        // FIXME: We might want to show both diagnostics to the user in
        // EM_ConstantFold mode.
        if (!EvalStatus.Diag->empty()) {
          switch (EvalMode) {
          case EM_ConstantFold:
          case EM_IgnoreSideEffects:
          case EM_EvaluateForOverflow:
            if (!EvalStatus.HasSideEffects)
              break;
            // We've had side-effects; we want the diagnostic from them, not
            // some later problem.
          case EM_ConstantExpression:
          case EM_PotentialConstantExpression:
          case EM_ConstantExpressionUnevaluated:
          case EM_PotentialConstantExpressionUnevaluated:
            HasActiveDiagnostic = false;
            return OptionalDiagnostic();
          }
        }

        unsigned CallStackNotes = CallStackDepth - 1;
        unsigned Limit = Ctx.getDiagnostics().getConstexprBacktraceLimit();
        if (Limit)
          CallStackNotes = std::min(CallStackNotes, Limit + 1);
        if (checkingPotentialConstantExpression())
          CallStackNotes = 0;

        HasActiveDiagnostic = true;
        EvalStatus.Diag->clear();
        EvalStatus.Diag->reserve(1 + ExtraNotes + CallStackNotes);
        addDiag(Loc, DiagId);
        if (!checkingPotentialConstantExpression())
          addCallStack(Limit);
        return OptionalDiagnostic(&(*EvalStatus.Diag)[0].second);
      }
      HasActiveDiagnostic = false;
      return OptionalDiagnostic();
    }

    OptionalDiagnostic Diag(const Expr *E, diag::kind DiagId
                              = diag::note_invalid_subexpr_in_const_expr,
                            unsigned ExtraNotes = 0) {
      if (EvalStatus.Diag)
        return Diag(E->getExprLoc(), DiagId, ExtraNotes);
      HasActiveDiagnostic = false;
      return OptionalDiagnostic();
    }

    /// Diagnose that the evaluation does not produce a C++11 core constant
    /// expression.
    ///
    /// FIXME: Stop evaluating if we're in EM_ConstantExpression or
    /// EM_PotentialConstantExpression mode and we produce one of these.
    template<typename LocArg>
    OptionalDiagnostic CCEDiag(LocArg Loc, diag::kind DiagId
                                 = diag::note_invalid_subexpr_in_const_expr,
                               unsigned ExtraNotes = 0) {
      // Don't override a previous diagnostic. Don't bother collecting
      // diagnostics if we're evaluating for overflow.
      if (!EvalStatus.Diag || !EvalStatus.Diag->empty()) {
        HasActiveDiagnostic = false;
        return OptionalDiagnostic();
      }
      return Diag(Loc, DiagId, ExtraNotes);
    }

    /// Add a note to a prior diagnostic.
    OptionalDiagnostic Note(SourceLocation Loc, diag::kind DiagId) {
      if (!HasActiveDiagnostic)
        return OptionalDiagnostic();
      return OptionalDiagnostic(&addDiag(Loc, DiagId));
    }

    /// Add a stack of notes to a prior diagnostic.
    void addNotes(ArrayRef<PartialDiagnosticAt> Diags) {
      if (HasActiveDiagnostic) {
        EvalStatus.Diag->insert(EvalStatus.Diag->end(),
                                Diags.begin(), Diags.end());
      }
    }

    /// Should we continue evaluation after encountering a side-effect that we
    /// couldn't model?
    bool keepEvaluatingAfterSideEffect() {
      switch (EvalMode) {
      case EM_PotentialConstantExpression:
      case EM_PotentialConstantExpressionUnevaluated:
      case EM_EvaluateForOverflow:
      case EM_IgnoreSideEffects:
        return true;

      case EM_ConstantExpression:
      case EM_ConstantExpressionUnevaluated:
      case EM_ConstantFold:
        return false;
      }
      llvm_unreachable("Missed EvalMode case");
    }

    /// Note that we have had a side-effect, and determine whether we should
    /// keep evaluating.
    bool noteSideEffect() {
      EvalStatus.HasSideEffects = true;
      return keepEvaluatingAfterSideEffect();
    }

    /// Should we continue evaluation as much as possible after encountering a
    /// construct which can't be reduced to a value?
    bool keepEvaluatingAfterFailure() {
      if (!StepsLeft)
        return false;

      switch (EvalMode) {
      case EM_PotentialConstantExpression:
      case EM_PotentialConstantExpressionUnevaluated:
      case EM_EvaluateForOverflow:
        return true;

      case EM_ConstantExpression:
      case EM_ConstantExpressionUnevaluated:
      case EM_ConstantFold:
      case EM_IgnoreSideEffects:
        return false;
      }
      llvm_unreachable("Missed EvalMode case");
    }
  };

  /// Object used to treat all foldable expressions as constant expressions.
  struct FoldConstant {
    EvalInfo &Info;
    bool Enabled;
    bool HadNoPriorDiags;
    EvalInfo::EvaluationMode OldMode;

    explicit FoldConstant(EvalInfo &Info, bool Enabled)
      : Info(Info),
        Enabled(Enabled),
        HadNoPriorDiags(Info.EvalStatus.Diag &&
                        Info.EvalStatus.Diag->empty() &&
                        !Info.EvalStatus.HasSideEffects),
        OldMode(Info.EvalMode) {
      if (Enabled &&
          (Info.EvalMode == EvalInfo::EM_ConstantExpression ||
           Info.EvalMode == EvalInfo::EM_ConstantExpressionUnevaluated))
        Info.EvalMode = EvalInfo::EM_ConstantFold;
    }
    void keepDiagnostics() { Enabled = false; }
    ~FoldConstant() {
      if (Enabled && HadNoPriorDiags && !Info.EvalStatus.Diag->empty() &&
          !Info.EvalStatus.HasSideEffects)
        Info.EvalStatus.Diag->clear();
      Info.EvalMode = OldMode;
    }
  };

  /// RAII object used to suppress diagnostics and side-effects from a
  /// speculative evaluation.
  class SpeculativeEvaluationRAII {
    EvalInfo &Info;
    Expr::EvalStatus Old;

  public:
    SpeculativeEvaluationRAII(EvalInfo &Info,
                        SmallVectorImpl<PartialDiagnosticAt> *NewDiag = nullptr)
      : Info(Info), Old(Info.EvalStatus) {
      Info.EvalStatus.Diag = NewDiag;
      // If we're speculatively evaluating, we may have skipped over some
      // evaluations and missed out a side effect.
      Info.EvalStatus.HasSideEffects = true;
    }
    ~SpeculativeEvaluationRAII() {
      Info.EvalStatus = Old;
    }
  };

  /// RAII object wrapping a full-expression or block scope, and handling
  /// the ending of the lifetime of temporaries created within it.
  template<bool IsFullExpression>
  class ScopeRAII {
    EvalInfo &Info;
    unsigned OldStackSize;
  public:
    ScopeRAII(EvalInfo &Info)
        : Info(Info), OldStackSize(Info.CleanupStack.size()) {}
    ~ScopeRAII() {
      // Body moved to a static method to encourage the compiler to inline away
      // instances of this class.
      cleanup(Info, OldStackSize);
    }
  private:
    static void cleanup(EvalInfo &Info, unsigned OldStackSize) {
      unsigned NewEnd = OldStackSize;
      for (unsigned I = OldStackSize, N = Info.CleanupStack.size();
           I != N; ++I) {
        if (IsFullExpression && Info.CleanupStack[I].isLifetimeExtended()) {
          // Full-expression cleanup of a lifetime-extended temporary: nothing
          // to do, just move this cleanup to the right place in the stack.
          std::swap(Info.CleanupStack[I], Info.CleanupStack[NewEnd]);
          ++NewEnd;
        } else {
          // End the lifetime of the object.
          Info.CleanupStack[I].endLifetime();
        }
      }
      Info.CleanupStack.erase(Info.CleanupStack.begin() + NewEnd,
                              Info.CleanupStack.end());
    }
  };
  typedef ScopeRAII<false> BlockScopeRAII;
  typedef ScopeRAII<true> FullExpressionRAII;
}

bool SubobjectDesignator::checkSubobject(EvalInfo &Info, const Expr *E,
                                         CheckSubobjectKind CSK) {
  if (Invalid)
    return false;
  if (isOnePastTheEnd()) {
    Info.CCEDiag(E, diag::note_constexpr_past_end_subobject)
      << CSK;
    setInvalid();
    return false;
  }
  return true;
}

void SubobjectDesignator::diagnosePointerArithmetic(EvalInfo &Info,
                                                    const Expr *E, uint64_t N) {
  if (MostDerivedPathLength == Entries.size() && MostDerivedArraySize)
    Info.CCEDiag(E, diag::note_constexpr_array_index)
      << static_cast<int>(N) << /*array*/ 0
      << static_cast<unsigned>(MostDerivedArraySize);
  else
    Info.CCEDiag(E, diag::note_constexpr_array_index)
      << static_cast<int>(N) << /*non-array*/ 1;
  setInvalid();
}

CallStackFrame::CallStackFrame(EvalInfo &Info, SourceLocation CallLoc,
                               const FunctionDecl *Callee, const LValue *This,
                               APValue *Arguments)
    : Info(Info), Caller(Info.CurrentCall), CallLoc(CallLoc), Callee(Callee),
      Index(Info.NextCallIndex++), This(This), Arguments(Arguments) {
  Info.CurrentCall = this;
  ++Info.CallStackDepth;
}

CallStackFrame::~CallStackFrame() {
  assert(Info.CurrentCall == this && "calls retired out of order");
  --Info.CallStackDepth;
  Info.CurrentCall = Caller;
}

APValue &CallStackFrame::createTemporary(const void *Key,
                                         bool IsLifetimeExtended) {
  APValue &Result = Temporaries[Key];
  assert(Result.isUninit() && "temporary created multiple times");
  Info.CleanupStack.push_back(Cleanup(&Result, IsLifetimeExtended));
  return Result;
}

static void describeCall(CallStackFrame *Frame, raw_ostream &Out);

void EvalInfo::addCallStack(unsigned Limit) {
  // Determine which calls to skip, if any.
  unsigned ActiveCalls = CallStackDepth - 1;
  unsigned SkipStart = ActiveCalls, SkipEnd = SkipStart;
  if (Limit && Limit < ActiveCalls) {
    SkipStart = Limit / 2 + Limit % 2;
    SkipEnd = ActiveCalls - Limit / 2;
  }

  // Walk the call stack and add the diagnostics.
  unsigned CallIdx = 0;
  for (CallStackFrame *Frame = CurrentCall; Frame != &BottomFrame;
       Frame = Frame->Caller, ++CallIdx) {
    // Skip this call?
    if (CallIdx >= SkipStart && CallIdx < SkipEnd) {
      if (CallIdx == SkipStart) {
        // Note that we're skipping calls.
        addDiag(Frame->CallLoc, diag::note_constexpr_calls_suppressed)
          << unsigned(ActiveCalls - Limit);
      }
      continue;
    }

    SmallVector<char, 128> Buffer;
    llvm::raw_svector_ostream Out(Buffer);
    describeCall(Frame, Out);
    addDiag(Frame->CallLoc, diag::note_constexpr_call_here) << Out.str();
  }
}

namespace {
  struct ComplexValue {
  private:
    bool IsInt;

  public:
    APSInt IntReal, IntImag;
    APFloat FloatReal, FloatImag;

    ComplexValue() : FloatReal(APFloat::Bogus), FloatImag(APFloat::Bogus) {}

    void makeComplexFloat() { IsInt = false; }
    bool isComplexFloat() const { return !IsInt; }
    APFloat &getComplexFloatReal() { return FloatReal; }
    APFloat &getComplexFloatImag() { return FloatImag; }

    void makeComplexInt() { IsInt = true; }
    bool isComplexInt() const { return IsInt; }
    APSInt &getComplexIntReal() { return IntReal; }
    APSInt &getComplexIntImag() { return IntImag; }

    void moveInto(APValue &v) const {
      if (isComplexFloat())
        v = APValue(FloatReal, FloatImag);
      else
        v = APValue(IntReal, IntImag);
    }
    void setFrom(const APValue &v) {
      assert(v.isComplexFloat() || v.isComplexInt());
      if (v.isComplexFloat()) {
        makeComplexFloat();
        FloatReal = v.getComplexFloatReal();
        FloatImag = v.getComplexFloatImag();
      } else {
        makeComplexInt();
        IntReal = v.getComplexIntReal();
        IntImag = v.getComplexIntImag();
      }
    }
  };

  struct LValue {
    APValue::LValueBase Base;
    CharUnits Offset;
    unsigned CallIndex;
    SubobjectDesignator Designator;

    const APValue::LValueBase getLValueBase() const { return Base; }
    CharUnits &getLValueOffset() { return Offset; }
    const CharUnits &getLValueOffset() const { return Offset; }
    unsigned getLValueCallIndex() const { return CallIndex; }
    SubobjectDesignator &getLValueDesignator() { return Designator; }
    const SubobjectDesignator &getLValueDesignator() const { return Designator;}

    void moveInto(APValue &V) const {
      if (Designator.Invalid)
        V = APValue(Base, Offset, APValue::NoLValuePath(), CallIndex);
      else
        V = APValue(Base, Offset, Designator.Entries,
                    Designator.IsOnePastTheEnd, CallIndex);
    }
    void setFrom(ASTContext &Ctx, const APValue &V) {
      assert(V.isLValue());
      Base = V.getLValueBase();
      Offset = V.getLValueOffset();
      CallIndex = V.getLValueCallIndex();
      Designator = SubobjectDesignator(Ctx, V);
    }

    void set(APValue::LValueBase B, unsigned I = 0) {
      Base = B;
      Offset = CharUnits::Zero();
      CallIndex = I;
      Designator = SubobjectDesignator(getType(B));
    }

    // Check that this LValue is not based on a null pointer. If it is, produce
    // a diagnostic and mark the designator as invalid.
    bool checkNullPointer(EvalInfo &Info, const Expr *E,
                          CheckSubobjectKind CSK) {
      if (Designator.Invalid)
        return false;
      if (!Base) {
        Info.CCEDiag(E, diag::note_constexpr_null_subobject)
          << CSK;
        Designator.setInvalid();
        return false;
      }
      return true;
    }

    // Check this LValue refers to an object. If not, set the designator to be
    // invalid and emit a diagnostic.
    bool checkSubobject(EvalInfo &Info, const Expr *E, CheckSubobjectKind CSK) {
      // Outside C++11, do not build a designator referring to a subobject of
      // any object: we won't use such a designator for anything.
      if (!Info.getLangOpts().CPlusPlus11)
        Designator.setInvalid();
      return (CSK == CSK_ArrayToPointer || checkNullPointer(Info, E, CSK)) &&
             Designator.checkSubobject(Info, E, CSK);
    }

    void addDecl(EvalInfo &Info, const Expr *E,
                 const Decl *D, bool Virtual = false) {
      if (checkSubobject(Info, E, isa<FieldDecl>(D) ? CSK_Field : CSK_Base))
        Designator.addDeclUnchecked(D, Virtual);
    }
    void addArray(EvalInfo &Info, const Expr *E, const ConstantArrayType *CAT) {
      if (checkSubobject(Info, E, CSK_ArrayToPointer))
        Designator.addArrayUnchecked(CAT);
    }
    void addComplex(EvalInfo &Info, const Expr *E, QualType EltTy, bool Imag) {
      if (checkSubobject(Info, E, Imag ? CSK_Imag : CSK_Real))
        Designator.addComplexUnchecked(EltTy, Imag);
    }
    void adjustIndex(EvalInfo &Info, const Expr *E, uint64_t N) {
      if (N && checkNullPointer(Info, E, CSK_ArrayIndex))
        Designator.adjustIndex(Info, E, N);
    }
  };

  struct MemberPtr {
    MemberPtr() {}
    explicit MemberPtr(const ValueDecl *Decl) :
      DeclAndIsDerivedMember(Decl, false), Path() {}

    /// The member or (direct or indirect) field referred to by this member
    /// pointer, or 0 if this is a null member pointer.
    const ValueDecl *getDecl() const {
      return DeclAndIsDerivedMember.getPointer();
    }
    /// Is this actually a member of some type derived from the relevant class?
    bool isDerivedMember() const {
      return DeclAndIsDerivedMember.getInt();
    }
    /// Get the class which the declaration actually lives in.
    const CXXRecordDecl *getContainingRecord() const {
      return cast<CXXRecordDecl>(
          DeclAndIsDerivedMember.getPointer()->getDeclContext());
    }

    void moveInto(APValue &V) const {
      V = APValue(getDecl(), isDerivedMember(), Path);
    }
    void setFrom(const APValue &V) {
      assert(V.isMemberPointer());
      DeclAndIsDerivedMember.setPointer(V.getMemberPointerDecl());
      DeclAndIsDerivedMember.setInt(V.isMemberPointerToDerivedMember());
      Path.clear();
      ArrayRef<const CXXRecordDecl*> P = V.getMemberPointerPath();
      Path.insert(Path.end(), P.begin(), P.end());
    }

    /// DeclAndIsDerivedMember - The member declaration, and a flag indicating
    /// whether the member is a member of some class derived from the class type
    /// of the member pointer.
    llvm::PointerIntPair<const ValueDecl*, 1, bool> DeclAndIsDerivedMember;
    /// Path - The path of base/derived classes from the member declaration's
    /// class (exclusive) to the class type of the member pointer (inclusive).
    SmallVector<const CXXRecordDecl*, 4> Path;

    /// Perform a cast towards the class of the Decl (either up or down the
    /// hierarchy).
    bool castBack(const CXXRecordDecl *Class) {
      assert(!Path.empty());
      const CXXRecordDecl *Expected;
      if (Path.size() >= 2)
        Expected = Path[Path.size() - 2];
      else
        Expected = getContainingRecord();
      if (Expected->getCanonicalDecl() != Class->getCanonicalDecl()) {
        // C++11 [expr.static.cast]p12: In a conversion from (D::*) to (B::*),
        // if B does not contain the original member and is not a base or
        // derived class of the class containing the original member, the result
        // of the cast is undefined.
        // C++11 [conv.mem]p2 does not cover this case for a cast from (B::*) to
        // (D::*). We consider that to be a language defect.
        return false;
      }
      Path.pop_back();
      return true;
    }
    /// Perform a base-to-derived member pointer cast.
    bool castToDerived(const CXXRecordDecl *Derived) {
      if (!getDecl())
        return true;
      if (!isDerivedMember()) {
        Path.push_back(Derived);
        return true;
      }
      if (!castBack(Derived))
        return false;
      if (Path.empty())
        DeclAndIsDerivedMember.setInt(false);
      return true;
    }
    /// Perform a derived-to-base member pointer cast.
    bool castToBase(const CXXRecordDecl *Base) {
      if (!getDecl())
        return true;
      if (Path.empty())
        DeclAndIsDerivedMember.setInt(true);
      if (isDerivedMember()) {
        Path.push_back(Base);
        return true;
      }
      return castBack(Base);
    }
  };

  /// Compare two member pointers, which are assumed to be of the same type.
  static bool operator==(const MemberPtr &LHS, const MemberPtr &RHS) {
    if (!LHS.getDecl() || !RHS.getDecl())
      return !LHS.getDecl() && !RHS.getDecl();
    if (LHS.getDecl()->getCanonicalDecl() != RHS.getDecl()->getCanonicalDecl())
      return false;
    return LHS.Path == RHS.Path;
  }
}

static bool Evaluate(APValue &Result, EvalInfo &Info, const Expr *E);
static bool EvaluateInPlace(APValue &Result, EvalInfo &Info,
                            const LValue &This, const Expr *E,
                            bool AllowNonLiteralTypes = false);
static bool EvaluateLValue(const Expr *E, LValue &Result, EvalInfo &Info);
static bool EvaluatePointer(const Expr *E, LValue &Result, EvalInfo &Info);
static bool EvaluateMemberPointer(const Expr *E, MemberPtr &Result,
                                  EvalInfo &Info);
static bool EvaluateTemporary(const Expr *E, LValue &Result, EvalInfo &Info);
static bool EvaluateInteger(const Expr *E, APSInt  &Result, EvalInfo &Info);
static bool EvaluateIntegerOrLValue(const Expr *E, APValue &Result,
                                    EvalInfo &Info);
static bool EvaluateFloat(const Expr *E, APFloat &Result, EvalInfo &Info);
static bool EvaluateComplex(const Expr *E, ComplexValue &Res, EvalInfo &Info);
static bool EvaluateAtomic(const Expr *E, APValue &Result, EvalInfo &Info);

//===----------------------------------------------------------------------===//
// Misc utilities
//===----------------------------------------------------------------------===//

/// Produce a string describing the given constexpr call.
static void describeCall(CallStackFrame *Frame, raw_ostream &Out) {
  unsigned ArgIndex = 0;
  bool IsMemberCall = isa<CXXMethodDecl>(Frame->Callee) &&
                      !isa<CXXConstructorDecl>(Frame->Callee) &&
                      cast<CXXMethodDecl>(Frame->Callee)->isInstance();

  if (!IsMemberCall)
    Out << *Frame->Callee << '(';

  if (Frame->This && IsMemberCall) {
    APValue Val;
    Frame->This->moveInto(Val);
    Val.printPretty(Out, Frame->Info.Ctx,
                    Frame->This->Designator.MostDerivedType);
    // FIXME: Add parens around Val if needed.
    Out << "->" << *Frame->Callee << '(';
    IsMemberCall = false;
  }

  for (FunctionDecl::param_const_iterator I = Frame->Callee->param_begin(),
       E = Frame->Callee->param_end(); I != E; ++I, ++ArgIndex) {
    if (ArgIndex > (unsigned)IsMemberCall)
      Out << ", ";

    const ParmVarDecl *Param = *I;
    const APValue &Arg = Frame->Arguments[ArgIndex];
    Arg.printPretty(Out, Frame->Info.Ctx, Param->getType());

    if (ArgIndex == 0 && IsMemberCall)
      Out << "->" << *Frame->Callee << '(';
  }

  Out << ')';
}

/// Evaluate an expression to see if it had side-effects, and discard its
/// result.
/// \return \c true if the caller should keep evaluating.
static bool EvaluateIgnoredValue(EvalInfo &Info, const Expr *E) {
  APValue Scratch;
  if (!Evaluate(Scratch, Info, E))
    // We don't need the value, but we might have skipped a side effect here.
    return Info.noteSideEffect();
  return true;
}

/// Sign- or zero-extend a value to 64 bits. If it's already 64 bits, just
/// return its existing value.
static int64_t getExtValue(const APSInt &Value) {
  return Value.isSigned() ? Value.getSExtValue()
                          : static_cast<int64_t>(Value.getZExtValue());
}

/// Should this call expression be treated as a string literal?
static bool IsStringLiteralCall(const CallExpr *E) {
  unsigned Builtin = E->getBuiltinCallee();
  return (Builtin == Builtin::BI__builtin___CFStringMakeConstantString ||
          Builtin == Builtin::BI__builtin___NSStringMakeConstantString);
}

static bool IsGlobalLValue(APValue::LValueBase B) {
  // C++11 [expr.const]p3 An address constant expression is a prvalue core
  // constant expression of pointer type that evaluates to...

  // ... a null pointer value, or a prvalue core constant expression of type
  // std::nullptr_t.
  if (!B) return true;

  if (const ValueDecl *D = B.dyn_cast<const ValueDecl*>()) {
    // ... the address of an object with static storage duration,
    if (const VarDecl *VD = dyn_cast<VarDecl>(D))
      return VD->hasGlobalStorage();
    // ... the address of a function,
    return isa<FunctionDecl>(D);
  }

  const Expr *E = B.get<const Expr*>();
  switch (E->getStmtClass()) {
  default:
    return false;
  case Expr::CompoundLiteralExprClass: {
    const CompoundLiteralExpr *CLE = cast<CompoundLiteralExpr>(E);
    return CLE->isFileScope() && CLE->isLValue();
  }
  case Expr::MaterializeTemporaryExprClass:
    // A materialized temporary might have been lifetime-extended to static
    // storage duration.
    return cast<MaterializeTemporaryExpr>(E)->getStorageDuration() == SD_Static;
  // A string literal has static storage duration.
  case Expr::StringLiteralClass:
  case Expr::PredefinedExprClass:
  case Expr::ObjCStringLiteralClass:
  case Expr::ObjCEncodeExprClass:
  case Expr::CXXTypeidExprClass:
  case Expr::CXXUuidofExprClass:
    return true;
  case Expr::CallExprClass:
    return IsStringLiteralCall(cast<CallExpr>(E));
  // For GCC compatibility, &&label has static storage duration.
  case Expr::AddrLabelExprClass:
    return true;
  // A Block literal expression may be used as the initialization value for
  // Block variables at global or local static scope.
  case Expr::BlockExprClass:
    return !cast<BlockExpr>(E)->getBlockDecl()->hasCaptures();
  case Expr::ImplicitValueInitExprClass:
    // FIXME:
    // We can never form an lvalue with an implicit value initialization as its
    // base through expression evaluation, so these only appear in one case: the
    // implicit variable declaration we invent when checking whether a constexpr
    // constructor can produce a constant expression. We must assume that such
    // an expression might be a global lvalue.
    return true;
  }
}

static void NoteLValueLocation(EvalInfo &Info, APValue::LValueBase Base) {
  assert(Base && "no location for a null lvalue");
  const ValueDecl *VD = Base.dyn_cast<const ValueDecl*>();
  if (VD)
    Info.Note(VD->getLocation(), diag::note_declared_at);
  else
    Info.Note(Base.get<const Expr*>()->getExprLoc(),
              diag::note_constexpr_temporary_here);
}

/// Check that this reference or pointer core constant expression is a valid
/// value for an address or reference constant expression. Return true if we
/// can fold this expression, whether or not it's a constant expression.
static bool CheckLValueConstantExpression(EvalInfo &Info, SourceLocation Loc,
                                          QualType Type, const LValue &LVal) {
  bool IsReferenceType = Type->isReferenceType();

  APValue::LValueBase Base = LVal.getLValueBase();
  const SubobjectDesignator &Designator = LVal.getLValueDesignator();

  // Check that the object is a global. Note that the fake 'this' object we
  // manufacture when checking potential constant expressions is conservatively
  // assumed to be global here.
  if (!IsGlobalLValue(Base)) {
    if (Info.getLangOpts().CPlusPlus11) {
      const ValueDecl *VD = Base.dyn_cast<const ValueDecl*>();
      Info.Diag(Loc, diag::note_constexpr_non_global, 1)
        << IsReferenceType << !Designator.Entries.empty()
        << !!VD << VD;
      NoteLValueLocation(Info, Base);
    } else {
      Info.Diag(Loc);
    }
    // Don't allow references to temporaries to escape.
    return false;
  }
  assert((Info.checkingPotentialConstantExpression() ||
          LVal.getLValueCallIndex() == 0) &&
         "have call index for global lvalue");

  if (const ValueDecl *VD = Base.dyn_cast<const ValueDecl*>()) {
    if (const VarDecl *Var = dyn_cast<const VarDecl>(VD)) {
      // Check if this is a thread-local variable.
      if (Var->getTLSKind())
        return false;

      // A dllimport variable never acts like a constant.
      if (Var->hasAttr<DLLImportAttr>())
        return false;
    }
    if (const auto *FD = dyn_cast<const FunctionDecl>(VD)) {
      // __declspec(dllimport) must be handled very carefully:
      // We must never initialize an expression with the thunk in C++.
      // Doing otherwise would allow the same id-expression to yield
      // different addresses for the same function in different translation
      // units.  However, this means that we must dynamically initialize the
      // expression with the contents of the import address table at runtime.
      //
      // The C language has no notion of ODR; furthermore, it has no notion of
      // dynamic initialization.  This means that we are permitted to
      // perform initialization with the address of the thunk.
      if (Info.getLangOpts().CPlusPlus && FD->hasAttr<DLLImportAttr>())
        return false;
    }
  }

  // Allow address constant expressions to be past-the-end pointers. This is
  // an extension: the standard requires them to point to an object.
  if (!IsReferenceType)
    return true;

  // A reference constant expression must refer to an object.
  if (!Base) {
    // FIXME: diagnostic
    Info.CCEDiag(Loc);
    return true;
  }

  // Does this refer one past the end of some object?
  if (Designator.isOnePastTheEnd()) {
    const ValueDecl *VD = Base.dyn_cast<const ValueDecl*>();
    Info.Diag(Loc, diag::note_constexpr_past_end, 1)
      << !Designator.Entries.empty() << !!VD << VD;
    NoteLValueLocation(Info, Base);
  }

  return true;
}

/// Check that this core constant expression is of literal type, and if not,
/// produce an appropriate diagnostic.
static bool CheckLiteralType(EvalInfo &Info, const Expr *E,
                             const LValue *This = nullptr) {
  if (!E->isRValue() || E->getType()->isLiteralType(Info.Ctx))
    return true;

  // C++1y: A constant initializer for an object o [...] may also invoke
  // constexpr constructors for o and its subobjects even if those objects
  // are of non-literal class types.
  if (Info.getLangOpts().CPlusPlus1y && This &&
      Info.EvaluatingDecl == This->getLValueBase())
    return true;

  // Prvalue constant expressions must be of literal types.
  if (Info.getLangOpts().CPlusPlus11)
    Info.Diag(E, diag::note_constexpr_nonliteral)
      << E->getType();
  else
    Info.Diag(E, diag::note_invalid_subexpr_in_const_expr);
  return false;
}

/// Check that this core constant expression value is a valid value for a
/// constant expression. If not, report an appropriate diagnostic. Does not
/// check that the expression is of literal type.
static bool CheckConstantExpression(EvalInfo &Info, SourceLocation DiagLoc,
                                    QualType Type, const APValue &Value) {
  if (Value.isUninit()) {
    Info.Diag(DiagLoc, diag::note_constexpr_uninitialized)
      << true << Type;
    return false;
  }

  // Core issue 1454: For a literal constant expression of array or class type,
  // each subobject of its value shall have been initialized by a constant
  // expression.
  if (Value.isArray()) {
    QualType EltTy = Type->castAsArrayTypeUnsafe()->getElementType();
    for (unsigned I = 0, N = Value.getArrayInitializedElts(); I != N; ++I) {
      if (!CheckConstantExpression(Info, DiagLoc, EltTy,
                                   Value.getArrayInitializedElt(I)))
        return false;
    }
    if (!Value.hasArrayFiller())
      return true;
    return CheckConstantExpression(Info, DiagLoc, EltTy,
                                   Value.getArrayFiller());
  }
  if (Value.isUnion() && Value.getUnionField()) {
    return CheckConstantExpression(Info, DiagLoc,
                                   Value.getUnionField()->getType(),
                                   Value.getUnionValue());
  }
  if (Value.isStruct()) {
    RecordDecl *RD = Type->castAs<RecordType>()->getDecl();
    if (const CXXRecordDecl *CD = dyn_cast<CXXRecordDecl>(RD)) {
      unsigned BaseIndex = 0;
      for (CXXRecordDecl::base_class_const_iterator I = CD->bases_begin(),
             End = CD->bases_end(); I != End; ++I, ++BaseIndex) {
        if (!CheckConstantExpression(Info, DiagLoc, I->getType(),
                                     Value.getStructBase(BaseIndex)))
          return false;
      }
    }
    for (const auto *I : RD->fields()) {
      if (!CheckConstantExpression(Info, DiagLoc, I->getType(),
                                   Value.getStructField(I->getFieldIndex())))
        return false;
    }
  }

  if (Value.isLValue()) {
    LValue LVal;
    LVal.setFrom(Info.Ctx, Value);
    return CheckLValueConstantExpression(Info, DiagLoc, Type, LVal);
  }

  // Everything else is fine.
  return true;
}

const ValueDecl *GetLValueBaseDecl(const LValue &LVal) {
  return LVal.Base.dyn_cast<const ValueDecl*>();
}

static bool IsLiteralLValue(const LValue &Value) {
  if (Value.CallIndex)
    return false;
  const Expr *E = Value.Base.dyn_cast<const Expr*>();
  return E && !isa<MaterializeTemporaryExpr>(E);
}

static bool IsWeakLValue(const LValue &Value) {
  const ValueDecl *Decl = GetLValueBaseDecl(Value);
  return Decl && Decl->isWeak();
}

static bool EvalPointerValueAsBool(const APValue &Value, bool &Result) {
  // A null base expression indicates a null pointer.  These are always
  // evaluatable, and they are false unless the offset is zero.
  if (!Value.getLValueBase()) {
    Result = !Value.getLValueOffset().isZero();
    return true;
  }

  // We have a non-null base.  These are generally known to be true, but if it's
  // a weak declaration it can be null at runtime.
  Result = true;
  const ValueDecl *Decl = Value.getLValueBase().dyn_cast<const ValueDecl*>();
  return !Decl || !Decl->isWeak();
}

static bool HandleConversionToBool(const APValue &Val, bool &Result) {
  switch (Val.getKind()) {
  case APValue::Uninitialized:
    return false;
  case APValue::Int:
    Result = Val.getInt().getBoolValue();
    return true;
  case APValue::Float:
    Result = !Val.getFloat().isZero();
    return true;
  case APValue::ComplexInt:
    Result = Val.getComplexIntReal().getBoolValue() ||
             Val.getComplexIntImag().getBoolValue();
    return true;
  case APValue::ComplexFloat:
    Result = !Val.getComplexFloatReal().isZero() ||
             !Val.getComplexFloatImag().isZero();
    return true;
  case APValue::LValue:
    return EvalPointerValueAsBool(Val, Result);
  case APValue::MemberPointer:
    Result = Val.getMemberPointerDecl();
    return true;
  case APValue::Vector:
  case APValue::Array:
  case APValue::Struct:
  case APValue::Union:
  case APValue::AddrLabelDiff:
    return false;
  }

  llvm_unreachable("unknown APValue kind");
}

static bool EvaluateAsBooleanCondition(const Expr *E, bool &Result,
                                       EvalInfo &Info) {
  assert(E->isRValue() && "missing lvalue-to-rvalue conv in bool condition");
  APValue Val;
  if (!Evaluate(Val, Info, E))
    return false;
  return HandleConversionToBool(Val, Result);
}

template<typename T>
static void HandleOverflow(EvalInfo &Info, const Expr *E,
                           const T &SrcValue, QualType DestType) {
  Info.CCEDiag(E, diag::note_constexpr_overflow)
    << SrcValue << DestType;
}

static bool HandleFloatToIntCast(EvalInfo &Info, const Expr *E,
                                 QualType SrcType, const APFloat &Value,
                                 QualType DestType, APSInt &Result) {
  unsigned DestWidth = Info.Ctx.getIntWidth(DestType);
  // Determine whether we are converting to unsigned or signed.
  bool DestSigned = DestType->isSignedIntegerOrEnumerationType();

  Result = APSInt(DestWidth, !DestSigned);
  bool ignored;
  if (Value.convertToInteger(Result, llvm::APFloat::rmTowardZero, &ignored)
      & APFloat::opInvalidOp)
    HandleOverflow(Info, E, Value, DestType);
  return true;
}

static bool HandleFloatToFloatCast(EvalInfo &Info, const Expr *E,
                                   QualType SrcType, QualType DestType,
                                   APFloat &Result) {
  APFloat Value = Result;
  bool ignored;
  if (Result.convert(Info.Ctx.getFloatTypeSemantics(DestType),
                     APFloat::rmNearestTiesToEven, &ignored)
      & APFloat::opOverflow)
    HandleOverflow(Info, E, Value, DestType);
  return true;
}

static APSInt HandleIntToIntCast(EvalInfo &Info, const Expr *E,
                                 QualType DestType, QualType SrcType,
                                 APSInt &Value) {
  unsigned DestWidth = Info.Ctx.getIntWidth(DestType);
  APSInt Result = Value;
  // Figure out if this is a truncate, extend or noop cast.
  // If the input is signed, do a sign extend, noop, or truncate.
  Result = Result.extOrTrunc(DestWidth);
  Result.setIsUnsigned(DestType->isUnsignedIntegerOrEnumerationType());
  return Result;
}

static bool HandleIntToFloatCast(EvalInfo &Info, const Expr *E,
                                 QualType SrcType, const APSInt &Value,
                                 QualType DestType, APFloat &Result) {
  Result = APFloat(Info.Ctx.getFloatTypeSemantics(DestType), 1);
  if (Result.convertFromAPInt(Value, Value.isSigned(),
                              APFloat::rmNearestTiesToEven)
      & APFloat::opOverflow)
    HandleOverflow(Info, E, Value, DestType);
  return true;
}

static bool truncateBitfieldValue(EvalInfo &Info, const Expr *E,
                                  APValue &Value, const FieldDecl *FD) {
  assert(FD->isBitField() && "truncateBitfieldValue on non-bitfield");

  if (!Value.isInt()) {
    // Trying to store a pointer-cast-to-integer into a bitfield.
    // FIXME: In this case, we should provide the diagnostic for casting
    // a pointer to an integer.
    assert(Value.isLValue() && "integral value neither int nor lvalue?");
    Info.Diag(E);
    return false;
  }

  APSInt &Int = Value.getInt();
  unsigned OldBitWidth = Int.getBitWidth();
  unsigned NewBitWidth = FD->getBitWidthValue(Info.Ctx);
  if (NewBitWidth < OldBitWidth)
    Int = Int.trunc(NewBitWidth).extend(OldBitWidth);
  return true;
}

static bool EvalAndBitcastToAPInt(EvalInfo &Info, const Expr *E,
                                  llvm::APInt &Res) {
  APValue SVal;
  if (!Evaluate(SVal, Info, E))
    return false;
  if (SVal.isInt()) {
    Res = SVal.getInt();
    return true;
  }
  if (SVal.isFloat()) {
    Res = SVal.getFloat().bitcastToAPInt();
    return true;
  }
  if (SVal.isVector()) {
    QualType VecTy = E->getType();
    unsigned VecSize = Info.Ctx.getTypeSize(VecTy);
    QualType EltTy = VecTy->castAs<VectorType>()->getElementType();
    unsigned EltSize = Info.Ctx.getTypeSize(EltTy);
    bool BigEndian = Info.Ctx.getTargetInfo().isBigEndian();
    Res = llvm::APInt::getNullValue(VecSize);
    for (unsigned i = 0; i < SVal.getVectorLength(); i++) {
      APValue &Elt = SVal.getVectorElt(i);
      llvm::APInt EltAsInt;
      if (Elt.isInt()) {
        EltAsInt = Elt.getInt();
      } else if (Elt.isFloat()) {
        EltAsInt = Elt.getFloat().bitcastToAPInt();
      } else {
        // Don't try to handle vectors of anything other than int or float
        // (not sure if it's possible to hit this case).
        Info.Diag(E, diag::note_invalid_subexpr_in_const_expr);
        return false;
      }
      unsigned BaseEltSize = EltAsInt.getBitWidth();
      if (BigEndian)
        Res |= EltAsInt.zextOrTrunc(VecSize).rotr(i*EltSize+BaseEltSize);
      else
        Res |= EltAsInt.zextOrTrunc(VecSize).rotl(i*EltSize);
    }
    return true;
  }
  // Give up if the input isn't an int, float, or vector.  For example, we
  // reject "(v4i16)(intptr_t)&a".
  Info.Diag(E, diag::note_invalid_subexpr_in_const_expr);
  return false;
}

/// Perform the given integer operation, which is known to need at most BitWidth
/// bits, and check for overflow in the original type (if that type was not an
/// unsigned type).
template<typename Operation>
static APSInt CheckedIntArithmetic(EvalInfo &Info, const Expr *E,
                                   const APSInt &LHS, const APSInt &RHS,
                                   unsigned BitWidth, Operation Op) {
  if (LHS.isUnsigned())
    return Op(LHS, RHS);

  APSInt Value(Op(LHS.extend(BitWidth), RHS.extend(BitWidth)), false);
  APSInt Result = Value.trunc(LHS.getBitWidth());
  if (Result.extend(BitWidth) != Value) {
    if (Info.checkingForOverflow())
      Info.Ctx.getDiagnostics().Report(E->getExprLoc(),
        diag::warn_integer_constant_overflow)
          << Result.toString(10) << E->getType();
    else
      HandleOverflow(Info, E, Value, E->getType());
  }
  return Result;
}

/// Perform the given binary integer operation.
static bool handleIntIntBinOp(EvalInfo &Info, const Expr *E, const APSInt &LHS,
                              BinaryOperatorKind Opcode, APSInt RHS,
                              APSInt &Result) {
  switch (Opcode) {
  default:
    Info.Diag(E);
    return false;
  case BO_Mul:
    Result = CheckedIntArithmetic(Info, E, LHS, RHS, LHS.getBitWidth() * 2,
                                  std::multiplies<APSInt>());
    return true;
  case BO_Add:
    Result = CheckedIntArithmetic(Info, E, LHS, RHS, LHS.getBitWidth() + 1,
                                  std::plus<APSInt>());
    return true;
  case BO_Sub:
    Result = CheckedIntArithmetic(Info, E, LHS, RHS, LHS.getBitWidth() + 1,
                                  std::minus<APSInt>());
    return true;
  case BO_And: Result = LHS & RHS; return true;
  case BO_Xor: Result = LHS ^ RHS; return true;
  case BO_Or:  Result = LHS | RHS; return true;
  case BO_Div:
  case BO_Rem:
    if (RHS == 0) {
      Info.Diag(E, diag::note_expr_divide_by_zero);
      return false;
    }
    // Check for overflow case: INT_MIN / -1 or INT_MIN % -1.
    if (RHS.isNegative() && RHS.isAllOnesValue() &&
        LHS.isSigned() && LHS.isMinSignedValue())
      HandleOverflow(Info, E, -LHS.extend(LHS.getBitWidth() + 1), E->getType());
    Result = (Opcode == BO_Rem ? LHS % RHS : LHS / RHS);
    return true;
  case BO_Shl: {
    if (Info.getLangOpts().OpenCL)
      // OpenCL 6.3j: shift values are effectively % word size of LHS.
      RHS &= APSInt(llvm::APInt(RHS.getBitWidth(),
                    static_cast<uint64_t>(LHS.getBitWidth() - 1)),
                    RHS.isUnsigned());
    else if (RHS.isSigned() && RHS.isNegative()) {
      // During constant-folding, a negative shift is an opposite shift. Such
      // a shift is not a constant expression.
      Info.CCEDiag(E, diag::note_constexpr_negative_shift) << RHS;
      RHS = -RHS;
      goto shift_right;
    }
  shift_left:
    // C++11 [expr.shift]p1: Shift width must be less than the bit width of
    // the shifted type.
    unsigned SA = (unsigned) RHS.getLimitedValue(LHS.getBitWidth()-1);
    if (SA != RHS) {
      Info.CCEDiag(E, diag::note_constexpr_large_shift)
        << RHS << E->getType() << LHS.getBitWidth();
    } else if (LHS.isSigned()) {
      // C++11 [expr.shift]p2: A signed left shift must have a non-negative
      // operand, and must not overflow the corresponding unsigned type.
      if (LHS.isNegative())
        Info.CCEDiag(E, diag::note_constexpr_lshift_of_negative) << LHS;
      else if (LHS.countLeadingZeros() < SA)
        Info.CCEDiag(E, diag::note_constexpr_lshift_discards);
    }
    Result = LHS << SA;
    return true;
  }
  case BO_Shr: {
    if (Info.getLangOpts().OpenCL)
      // OpenCL 6.3j: shift values are effectively % word size of LHS.
      RHS &= APSInt(llvm::APInt(RHS.getBitWidth(),
                    static_cast<uint64_t>(LHS.getBitWidth() - 1)),
                    RHS.isUnsigned());
    else if (RHS.isSigned() && RHS.isNegative()) {
      // During constant-folding, a negative shift is an opposite shift. Such a
      // shift is not a constant expression.
      Info.CCEDiag(E, diag::note_constexpr_negative_shift) << RHS;
      RHS = -RHS;
      goto shift_left;
    }
  shift_right:
    // C++11 [expr.shift]p1: Shift width must be less than the bit width of the
    // shifted type.
    unsigned SA = (unsigned) RHS.getLimitedValue(LHS.getBitWidth()-1);
    if (SA != RHS)
      Info.CCEDiag(E, diag::note_constexpr_large_shift)
        << RHS << E->getType() << LHS.getBitWidth();
    Result = LHS >> SA;
    return true;
  }

  case BO_LT: Result = LHS < RHS; return true;
  case BO_GT: Result = LHS > RHS; return true;
  case BO_LE: Result = LHS <= RHS; return true;
  case BO_GE: Result = LHS >= RHS; return true;
  case BO_EQ: Result = LHS == RHS; return true;
  case BO_NE: Result = LHS != RHS; return true;
  }
}

/// Perform the given binary floating-point operation, in-place, on LHS.
static bool handleFloatFloatBinOp(EvalInfo &Info, const Expr *E,
                                  APFloat &LHS, BinaryOperatorKind Opcode,
                                  const APFloat &RHS) {
  switch (Opcode) {
  default:
    Info.Diag(E);
    return false;
  case BO_Mul:
    LHS.multiply(RHS, APFloat::rmNearestTiesToEven);
    break;
  case BO_Add:
    LHS.add(RHS, APFloat::rmNearestTiesToEven);
    break;
  case BO_Sub:
    LHS.subtract(RHS, APFloat::rmNearestTiesToEven);
    break;
  case BO_Div:
    LHS.divide(RHS, APFloat::rmNearestTiesToEven);
    break;
  }

  if (LHS.isInfinity() || LHS.isNaN())
    Info.CCEDiag(E, diag::note_constexpr_float_arithmetic) << LHS.isNaN();
  return true;
}

/// Cast an lvalue referring to a base subobject to a derived class, by
/// truncating the lvalue's path to the given length.
static bool CastToDerivedClass(EvalInfo &Info, const Expr *E, LValue &Result,
                               const RecordDecl *TruncatedType,
                               unsigned TruncatedElements) {
  SubobjectDesignator &D = Result.Designator;

  // Check we actually point to a derived class object.
  if (TruncatedElements == D.Entries.size())
    return true;
  assert(TruncatedElements >= D.MostDerivedPathLength &&
         "not casting to a derived class");
  if (!Result.checkSubobject(Info, E, CSK_Derived))
    return false;

  // Truncate the path to the subobject, and remove any derived-to-base offsets.
  const RecordDecl *RD = TruncatedType;
  for (unsigned I = TruncatedElements, N = D.Entries.size(); I != N; ++I) {
    if (RD->isInvalidDecl()) return false;
    const ASTRecordLayout &Layout = Info.Ctx.getASTRecordLayout(RD);
    const CXXRecordDecl *Base = getAsBaseClass(D.Entries[I]);
    if (isVirtualBaseClass(D.Entries[I]))
      Result.Offset -= Layout.getVBaseClassOffset(Base);
    else
      Result.Offset -= Layout.getBaseClassOffset(Base);
    RD = Base;
  }
  D.Entries.resize(TruncatedElements);
  return true;
}

static bool HandleLValueDirectBase(EvalInfo &Info, const Expr *E, LValue &Obj,
                                   const CXXRecordDecl *Derived,
                                   const CXXRecordDecl *Base,
                                   const ASTRecordLayout *RL = nullptr) {
  if (!RL) {
    if (Derived->isInvalidDecl()) return false;
    RL = &Info.Ctx.getASTRecordLayout(Derived);
  }

  Obj.getLValueOffset() += RL->getBaseClassOffset(Base);
  Obj.addDecl(Info, E, Base, /*Virtual*/ false);
  return true;
}

static bool HandleLValueBase(EvalInfo &Info, const Expr *E, LValue &Obj,
                             const CXXRecordDecl *DerivedDecl,
                             const CXXBaseSpecifier *Base) {
  const CXXRecordDecl *BaseDecl = Base->getType()->getAsCXXRecordDecl();

  if (!Base->isVirtual())
    return HandleLValueDirectBase(Info, E, Obj, DerivedDecl, BaseDecl);

  SubobjectDesignator &D = Obj.Designator;
  if (D.Invalid)
    return false;

  // Extract most-derived object and corresponding type.
  DerivedDecl = D.MostDerivedType->getAsCXXRecordDecl();
  if (!CastToDerivedClass(Info, E, Obj, DerivedDecl, D.MostDerivedPathLength))
    return false;

  // Find the virtual base class.
  if (DerivedDecl->isInvalidDecl()) return false;
  const ASTRecordLayout &Layout = Info.Ctx.getASTRecordLayout(DerivedDecl);
  Obj.getLValueOffset() += Layout.getVBaseClassOffset(BaseDecl);
  Obj.addDecl(Info, E, BaseDecl, /*Virtual*/ true);
  return true;
}

static bool HandleLValueBasePath(EvalInfo &Info, const CastExpr *E,
                                 QualType Type, LValue &Result) {
  for (CastExpr::path_const_iterator PathI = E->path_begin(),
                                     PathE = E->path_end();
       PathI != PathE; ++PathI) {
    if (!HandleLValueBase(Info, E, Result, Type->getAsCXXRecordDecl(),
                          *PathI))
      return false;
    Type = (*PathI)->getType();
  }
  return true;
}

/// Update LVal to refer to the given field, which must be a member of the type
/// currently described by LVal.
static bool HandleLValueMember(EvalInfo &Info, const Expr *E, LValue &LVal,
                               const FieldDecl *FD,
                               const ASTRecordLayout *RL = nullptr) {
  if (!RL) {
    if (FD->getParent()->isInvalidDecl()) return false;
    RL = &Info.Ctx.getASTRecordLayout(FD->getParent());
  }

  unsigned I = FD->getFieldIndex();
  LVal.Offset += Info.Ctx.toCharUnitsFromBits(RL->getFieldOffset(I));
  LVal.addDecl(Info, E, FD);
  return true;
}

/// Update LVal to refer to the given indirect field.
static bool HandleLValueIndirectMember(EvalInfo &Info, const Expr *E,
                                       LValue &LVal,
                                       const IndirectFieldDecl *IFD) {
  for (const auto *C : IFD->chain())
    if (!HandleLValueMember(Info, E, LVal, cast<FieldDecl>(C)))
      return false;
  return true;
}

/// Get the size of the given type in char units.
static bool HandleSizeof(EvalInfo &Info, SourceLocation Loc,
                         QualType Type, CharUnits &Size) {
  // sizeof(void), __alignof__(void), sizeof(function) = 1 as a gcc
  // extension.
  if (Type->isVoidType() || Type->isFunctionType()) {
    Size = CharUnits::One();
    return true;
  }

  if (!Type->isConstantSizeType()) {
    // sizeof(vla) is not a constantexpr: C99 6.5.3.4p2.
    // FIXME: Better diagnostic.
    Info.Diag(Loc);
    return false;
  }

  Size = Info.Ctx.getTypeSizeInChars(Type);
  return true;
}

/// Update a pointer value to model pointer arithmetic.
/// \param Info - Information about the ongoing evaluation.
/// \param E - The expression being evaluated, for diagnostic purposes.
/// \param LVal - The pointer value to be updated.
/// \param EltTy - The pointee type represented by LVal.
/// \param Adjustment - The adjustment, in objects of type EltTy, to add.
static bool HandleLValueArrayAdjustment(EvalInfo &Info, const Expr *E,
                                        LValue &LVal, QualType EltTy,
                                        int64_t Adjustment) {
  CharUnits SizeOfPointee;
  if (!HandleSizeof(Info, E->getExprLoc(), EltTy, SizeOfPointee))
    return false;

  // Compute the new offset in the appropriate width.
  LVal.Offset += Adjustment * SizeOfPointee;
  LVal.adjustIndex(Info, E, Adjustment);
  return true;
}

/// Update an lvalue to refer to a component of a complex number.
/// \param Info - Information about the ongoing evaluation.
/// \param LVal - The lvalue to be updated.
/// \param EltTy - The complex number's component type.
/// \param Imag - False for the real component, true for the imaginary.
static bool HandleLValueComplexElement(EvalInfo &Info, const Expr *E,
                                       LValue &LVal, QualType EltTy,
                                       bool Imag) {
  if (Imag) {
    CharUnits SizeOfComponent;
    if (!HandleSizeof(Info, E->getExprLoc(), EltTy, SizeOfComponent))
      return false;
    LVal.Offset += SizeOfComponent;
  }
  LVal.addComplex(Info, E, EltTy, Imag);
  return true;
}

/// Try to evaluate the initializer for a variable declaration.
///
/// \param Info   Information about the ongoing evaluation.
/// \param E      An expression to be used when printing diagnostics.
/// \param VD     The variable whose initializer should be obtained.
/// \param Frame  The frame in which the variable was created. Must be null
///               if this variable is not local to the evaluation.
/// \param Result Filled in with a pointer to the value of the variable.
static bool evaluateVarDeclInit(EvalInfo &Info, const Expr *E,
                                const VarDecl *VD, CallStackFrame *Frame,
                                APValue *&Result) {
  // If this is a parameter to an active constexpr function call, perform
  // argument substitution.
  if (const ParmVarDecl *PVD = dyn_cast<ParmVarDecl>(VD)) {
    // Assume arguments of a potential constant expression are unknown
    // constant expressions.
    if (Info.checkingPotentialConstantExpression())
      return false;
    if (!Frame || !Frame->Arguments) {
      Info.Diag(E, diag::note_invalid_subexpr_in_const_expr);
      return false;
    }
    Result = &Frame->Arguments[PVD->getFunctionScopeIndex()];
    return true;
  }

  // If this is a local variable, dig out its value.
  if (Frame) {
    Result = Frame->getTemporary(VD);
    assert(Result && "missing value for local variable");
    return true;
  }

  // Dig out the initializer, and use the declaration which it's attached to.
  const Expr *Init = VD->getAnyInitializer(VD);
  if (!Init || Init->isValueDependent()) {
    // If we're checking a potential constant expression, the variable could be
    // initialized later.
    if (!Info.checkingPotentialConstantExpression())
      Info.Diag(E, diag::note_invalid_subexpr_in_const_expr);
    return false;
  }

  // If we're currently evaluating the initializer of this declaration, use that
  // in-flight value.
  if (Info.EvaluatingDecl.dyn_cast<const ValueDecl*>() == VD) {
    Result = Info.EvaluatingDeclValue;
    return true;
  }

  // Never evaluate the initializer of a weak variable. We can't be sure that
  // this is the definition which will be used.
  if (VD->isWeak()) {
    Info.Diag(E, diag::note_invalid_subexpr_in_const_expr);
    return false;
  }

  // Check that we can fold the initializer. In C++, we will have already done
  // this in the cases where it matters for conformance.
  SmallVector<PartialDiagnosticAt, 8> Notes;
  if (!VD->evaluateValue(Notes)) {
    Info.Diag(E, diag::note_constexpr_var_init_non_constant,
              Notes.size() + 1) << VD;
    Info.Note(VD->getLocation(), diag::note_declared_at);
    Info.addNotes(Notes);
    return false;
  } else if (!VD->checkInitIsICE()) {
    Info.CCEDiag(E, diag::note_constexpr_var_init_non_constant,
                 Notes.size() + 1) << VD;
    Info.Note(VD->getLocation(), diag::note_declared_at);
    Info.addNotes(Notes);
  }

  Result = VD->getEvaluatedValue();
  return true;
}

static bool IsConstNonVolatile(QualType T) {
  Qualifiers Quals = T.getQualifiers();
  return Quals.hasConst() && !Quals.hasVolatile();
}

/// Get the base index of the given base class within an APValue representing
/// the given derived class.
static unsigned getBaseIndex(const CXXRecordDecl *Derived,
                             const CXXRecordDecl *Base) {
  Base = Base->getCanonicalDecl();
  unsigned Index = 0;
  for (CXXRecordDecl::base_class_const_iterator I = Derived->bases_begin(),
         E = Derived->bases_end(); I != E; ++I, ++Index) {
    if (I->getType()->getAsCXXRecordDecl()->getCanonicalDecl() == Base)
      return Index;
  }

  llvm_unreachable("base class missing from derived class's bases list");
}

/// Extract the value of a character from a string literal.
static APSInt extractStringLiteralCharacter(EvalInfo &Info, const Expr *Lit,
                                            uint64_t Index) {
  // FIXME: Support PredefinedExpr, ObjCEncodeExpr, MakeStringConstant
  const StringLiteral *S = cast<StringLiteral>(Lit);
  const ConstantArrayType *CAT =
      Info.Ctx.getAsConstantArrayType(S->getType());
  assert(CAT && "string literal isn't an array");
  QualType CharType = CAT->getElementType();
  assert(CharType->isIntegerType() && "unexpected character type");

  APSInt Value(S->getCharByteWidth() * Info.Ctx.getCharWidth(),
               CharType->isUnsignedIntegerType());
  if (Index < S->getLength())
    Value = S->getCodeUnit(Index);
  return Value;
}

// Expand a string literal into an array of characters.
static void expandStringLiteral(EvalInfo &Info, const Expr *Lit,
                                APValue &Result) {
  const StringLiteral *S = cast<StringLiteral>(Lit);
  const ConstantArrayType *CAT =
      Info.Ctx.getAsConstantArrayType(S->getType());
  assert(CAT && "string literal isn't an array");
  QualType CharType = CAT->getElementType();
  assert(CharType->isIntegerType() && "unexpected character type");

  unsigned Elts = CAT->getSize().getZExtValue();
  Result = APValue(APValue::UninitArray(),
                   std::min(S->getLength(), Elts), Elts);
  APSInt Value(S->getCharByteWidth() * Info.Ctx.getCharWidth(),
               CharType->isUnsignedIntegerType());
  if (Result.hasArrayFiller())
    Result.getArrayFiller() = APValue(Value);
  for (unsigned I = 0, N = Result.getArrayInitializedElts(); I != N; ++I) {
    Value = S->getCodeUnit(I);
    Result.getArrayInitializedElt(I) = APValue(Value);
  }
}

// Expand an array so that it has more than Index filled elements.
static void expandArray(APValue &Array, unsigned Index) {
  unsigned Size = Array.getArraySize();
  assert(Index < Size);

  // Always at least double the number of elements for which we store a value.
  unsigned OldElts = Array.getArrayInitializedElts();
  unsigned NewElts = std::max(Index+1, OldElts * 2);
  NewElts = std::min(Size, std::max(NewElts, 8u));

  // Copy the data across.
  APValue NewValue(APValue::UninitArray(), NewElts, Size);
  for (unsigned I = 0; I != OldElts; ++I)
    NewValue.getArrayInitializedElt(I).swap(Array.getArrayInitializedElt(I));
  for (unsigned I = OldElts; I != NewElts; ++I)
    NewValue.getArrayInitializedElt(I) = Array.getArrayFiller();
  if (NewValue.hasArrayFiller())
    NewValue.getArrayFiller() = Array.getArrayFiller();
  Array.swap(NewValue);
}

/// Kinds of access we can perform on an object, for diagnostics.
enum AccessKinds {
  AK_Read,
  AK_Assign,
  AK_Increment,
  AK_Decrement
};

/// A handle to a complete object (an object that is not a subobject of
/// another object).
struct CompleteObject {
  /// The value of the complete object.
  APValue *Value;
  /// The type of the complete object.
  QualType Type;

  CompleteObject() : Value(nullptr) {}
  CompleteObject(APValue *Value, QualType Type)
      : Value(Value), Type(Type) {
    assert(Value && "missing value for complete object");
  }

  LLVM_EXPLICIT operator bool() const { return Value; }
};

/// Find the designated sub-object of an rvalue.
template<typename SubobjectHandler>
typename SubobjectHandler::result_type
findSubobject(EvalInfo &Info, const Expr *E, const CompleteObject &Obj,
              const SubobjectDesignator &Sub, SubobjectHandler &handler) {
  if (Sub.Invalid)
    // A diagnostic will have already been produced.
    return handler.failed();
  if (Sub.isOnePastTheEnd()) {
    if (Info.getLangOpts().CPlusPlus11)
      Info.Diag(E, diag::note_constexpr_access_past_end)
        << handler.AccessKind;
    else
      Info.Diag(E);
    return handler.failed();
  }

  APValue *O = Obj.Value;
  QualType ObjType = Obj.Type;
  const FieldDecl *LastField = nullptr;

  // Walk the designator's path to find the subobject.
  for (unsigned I = 0, N = Sub.Entries.size(); /**/; ++I) {
    if (O->isUninit()) {
      if (!Info.checkingPotentialConstantExpression())
        Info.Diag(E, diag::note_constexpr_access_uninit) << handler.AccessKind;
      return handler.failed();
    }

    if (I == N) {
      if (!handler.found(*O, ObjType))
        return false;

      // If we modified a bit-field, truncate it to the right width.
      if (handler.AccessKind != AK_Read &&
          LastField && LastField->isBitField() &&
          !truncateBitfieldValue(Info, E, *O, LastField))
        return false;

      return true;
    }

    LastField = nullptr;
    if (ObjType->isArrayType()) {
      // Next subobject is an array element.
      const ConstantArrayType *CAT = Info.Ctx.getAsConstantArrayType(ObjType);
      assert(CAT && "vla in literal type?");
      uint64_t Index = Sub.Entries[I].ArrayIndex;
      if (CAT->getSize().ule(Index)) {
        // Note, it should not be possible to form a pointer with a valid
        // designator which points more than one past the end of the array.
        if (Info.getLangOpts().CPlusPlus11)
          Info.Diag(E, diag::note_constexpr_access_past_end)
            << handler.AccessKind;
        else
          Info.Diag(E);
        return handler.failed();
      }

      ObjType = CAT->getElementType();

      // An array object is represented as either an Array APValue or as an
      // LValue which refers to a string literal.
      if (O->isLValue()) {
        assert(I == N - 1 && "extracting subobject of character?");
        assert(!O->hasLValuePath() || O->getLValuePath().empty());
        if (handler.AccessKind != AK_Read)
          expandStringLiteral(Info, O->getLValueBase().get<const Expr *>(),
                              *O);
        else
          return handler.foundString(*O, ObjType, Index);
      }

      if (O->getArrayInitializedElts() > Index)
        O = &O->getArrayInitializedElt(Index);
      else if (handler.AccessKind != AK_Read) {
        expandArray(*O, Index);
        O = &O->getArrayInitializedElt(Index);
      } else
        O = &O->getArrayFiller();
    } else if (ObjType->isAnyComplexType()) {
      // Next subobject is a complex number.
      uint64_t Index = Sub.Entries[I].ArrayIndex;
      if (Index > 1) {
        if (Info.getLangOpts().CPlusPlus11)
          Info.Diag(E, diag::note_constexpr_access_past_end)
            << handler.AccessKind;
        else
          Info.Diag(E);
        return handler.failed();
      }

      bool WasConstQualified = ObjType.isConstQualified();
      ObjType = ObjType->castAs<ComplexType>()->getElementType();
      if (WasConstQualified)
        ObjType.addConst();

      assert(I == N - 1 && "extracting subobject of scalar?");
      if (O->isComplexInt()) {
        return handler.found(Index ? O->getComplexIntImag()
                                   : O->getComplexIntReal(), ObjType);
      } else {
        assert(O->isComplexFloat());
        return handler.found(Index ? O->getComplexFloatImag()
                                   : O->getComplexFloatReal(), ObjType);
      }
    } else if (const FieldDecl *Field = getAsField(Sub.Entries[I])) {
      if (Field->isMutable() && handler.AccessKind == AK_Read) {
        Info.Diag(E, diag::note_constexpr_ltor_mutable, 1)
          << Field;
        Info.Note(Field->getLocation(), diag::note_declared_at);
        return handler.failed();
      }

      // Next subobject is a class, struct or union field.
      RecordDecl *RD = ObjType->castAs<RecordType>()->getDecl();
      if (RD->isUnion()) {
        const FieldDecl *UnionField = O->getUnionField();
        if (!UnionField ||
            UnionField->getCanonicalDecl() != Field->getCanonicalDecl()) {
          Info.Diag(E, diag::note_constexpr_access_inactive_union_member)
            << handler.AccessKind << Field << !UnionField << UnionField;
          return handler.failed();
        }
        O = &O->getUnionValue();
      } else
        O = &O->getStructField(Field->getFieldIndex());

      bool WasConstQualified = ObjType.isConstQualified();
      ObjType = Field->getType();
      if (WasConstQualified && !Field->isMutable())
        ObjType.addConst();

      if (ObjType.isVolatileQualified()) {
        if (Info.getLangOpts().CPlusPlus) {
          // FIXME: Include a description of the path to the volatile subobject.
          Info.Diag(E, diag::note_constexpr_access_volatile_obj, 1)
            << handler.AccessKind << 2 << Field;
          Info.Note(Field->getLocation(), diag::note_declared_at);
        } else {
          Info.Diag(E, diag::note_invalid_subexpr_in_const_expr);
        }
        return handler.failed();
      }

      LastField = Field;
    } else {
      // Next subobject is a base class.
      const CXXRecordDecl *Derived = ObjType->getAsCXXRecordDecl();
      const CXXRecordDecl *Base = getAsBaseClass(Sub.Entries[I]);
      O = &O->getStructBase(getBaseIndex(Derived, Base));

      bool WasConstQualified = ObjType.isConstQualified();
      ObjType = Info.Ctx.getRecordType(Base);
      if (WasConstQualified)
        ObjType.addConst();
    }
  }
}

namespace {
struct ExtractSubobjectHandler {
  EvalInfo &Info;
  APValue &Result;

  static const AccessKinds AccessKind = AK_Read;

  typedef bool result_type;
  bool failed() { return false; }
  bool found(APValue &Subobj, QualType SubobjType) {
    Result = Subobj;
    return true;
  }
  bool found(APSInt &Value, QualType SubobjType) {
    Result = APValue(Value);
    return true;
  }
  bool found(APFloat &Value, QualType SubobjType) {
    Result = APValue(Value);
    return true;
  }
  bool foundString(APValue &Subobj, QualType SubobjType, uint64_t Character) {
    Result = APValue(extractStringLiteralCharacter(
        Info, Subobj.getLValueBase().get<const Expr *>(), Character));
    return true;
  }
};
} // end anonymous namespace

const AccessKinds ExtractSubobjectHandler::AccessKind;

/// Extract the designated sub-object of an rvalue.
static bool extractSubobject(EvalInfo &Info, const Expr *E,
                             const CompleteObject &Obj,
                             const SubobjectDesignator &Sub,
                             APValue &Result) {
  ExtractSubobjectHandler Handler = { Info, Result };
  return findSubobject(Info, E, Obj, Sub, Handler);
}

namespace {
struct ModifySubobjectHandler {
  EvalInfo &Info;
  APValue &NewVal;
  const Expr *E;

  typedef bool result_type;
  static const AccessKinds AccessKind = AK_Assign;

  bool checkConst(QualType QT) {
    // Assigning to a const object has undefined behavior.
    if (QT.isConstQualified()) {
      Info.Diag(E, diag::note_constexpr_modify_const_type) << QT;
      return false;
    }
    return true;
  }

  bool failed() { return false; }
  bool found(APValue &Subobj, QualType SubobjType) {
    if (!checkConst(SubobjType))
      return false;
    // We've been given ownership of NewVal, so just swap it in.
    Subobj.swap(NewVal);
    return true;
  }
  bool found(APSInt &Value, QualType SubobjType) {
    if (!checkConst(SubobjType))
      return false;
    if (!NewVal.isInt()) {
      // Maybe trying to write a cast pointer value into a complex?
      Info.Diag(E);
      return false;
    }
    Value = NewVal.getInt();
    return true;
  }
  bool found(APFloat &Value, QualType SubobjType) {
    if (!checkConst(SubobjType))
      return false;
    Value = NewVal.getFloat();
    return true;
  }
  bool foundString(APValue &Subobj, QualType SubobjType, uint64_t Character) {
    llvm_unreachable("shouldn't encounter string elements with ExpandArrays");
  }
};
} // end anonymous namespace

const AccessKinds ModifySubobjectHandler::AccessKind;

/// Update the designated sub-object of an rvalue to the given value.
static bool modifySubobject(EvalInfo &Info, const Expr *E,
                            const CompleteObject &Obj,
                            const SubobjectDesignator &Sub,
                            APValue &NewVal) {
  ModifySubobjectHandler Handler = { Info, NewVal, E };
  return findSubobject(Info, E, Obj, Sub, Handler);
}

/// Find the position where two subobject designators diverge, or equivalently
/// the length of the common initial subsequence.
static unsigned FindDesignatorMismatch(QualType ObjType,
                                       const SubobjectDesignator &A,
                                       const SubobjectDesignator &B,
                                       bool &WasArrayIndex) {
  unsigned I = 0, N = std::min(A.Entries.size(), B.Entries.size());
  for (/**/; I != N; ++I) {
    if (!ObjType.isNull() &&
        (ObjType->isArrayType() || ObjType->isAnyComplexType())) {
      // Next subobject is an array element.
      if (A.Entries[I].ArrayIndex != B.Entries[I].ArrayIndex) {
        WasArrayIndex = true;
        return I;
      }
      if (ObjType->isAnyComplexType())
        ObjType = ObjType->castAs<ComplexType>()->getElementType();
      else
        ObjType = ObjType->castAsArrayTypeUnsafe()->getElementType();
    } else {
      if (A.Entries[I].BaseOrMember != B.Entries[I].BaseOrMember) {
        WasArrayIndex = false;
        return I;
      }
      if (const FieldDecl *FD = getAsField(A.Entries[I]))
        // Next subobject is a field.
        ObjType = FD->getType();
      else
        // Next subobject is a base class.
        ObjType = QualType();
    }
  }
  WasArrayIndex = false;
  return I;
}

/// Determine whether the given subobject designators refer to elements of the
/// same array object.
static bool AreElementsOfSameArray(QualType ObjType,
                                   const SubobjectDesignator &A,
                                   const SubobjectDesignator &B) {
  if (A.Entries.size() != B.Entries.size())
    return false;

  bool IsArray = A.MostDerivedArraySize != 0;
  if (IsArray && A.MostDerivedPathLength != A.Entries.size())
    // A is a subobject of the array element.
    return false;

  // If A (and B) designates an array element, the last entry will be the array
  // index. That doesn't have to match. Otherwise, we're in the 'implicit array
  // of length 1' case, and the entire path must match.
  bool WasArrayIndex;
  unsigned CommonLength = FindDesignatorMismatch(ObjType, A, B, WasArrayIndex);
  return CommonLength >= A.Entries.size() - IsArray;
}

/// Find the complete object to which an LValue refers.
CompleteObject findCompleteObject(EvalInfo &Info, const Expr *E, AccessKinds AK,
                                  const LValue &LVal, QualType LValType) {
  if (!LVal.Base) {
    Info.Diag(E, diag::note_constexpr_access_null) << AK;
    return CompleteObject();
  }

  CallStackFrame *Frame = nullptr;
  if (LVal.CallIndex) {
    Frame = Info.getCallFrame(LVal.CallIndex);
    if (!Frame) {
      Info.Diag(E, diag::note_constexpr_lifetime_ended, 1)
        << AK << LVal.Base.is<const ValueDecl*>();
      NoteLValueLocation(Info, LVal.Base);
      return CompleteObject();
    }
  }

  // C++11 DR1311: An lvalue-to-rvalue conversion on a volatile-qualified type
  // is not a constant expression (even if the object is non-volatile). We also
  // apply this rule to C++98, in order to conform to the expected 'volatile'
  // semantics.
  if (LValType.isVolatileQualified()) {
    if (Info.getLangOpts().CPlusPlus)
      Info.Diag(E, diag::note_constexpr_access_volatile_type)
        << AK << LValType;
    else
      Info.Diag(E);
    return CompleteObject();
  }

  // Compute value storage location and type of base object.
  APValue *BaseVal = nullptr;
  QualType BaseType = getType(LVal.Base);

  if (const ValueDecl *D = LVal.Base.dyn_cast<const ValueDecl*>()) {
    // In C++98, const, non-volatile integers initialized with ICEs are ICEs.
    // In C++11, constexpr, non-volatile variables initialized with constant
    // expressions are constant expressions too. Inside constexpr functions,
    // parameters are constant expressions even if they're non-const.
    // In C++1y, objects local to a constant expression (those with a Frame) are
    // both readable and writable inside constant expressions.
    // In C, such things can also be folded, although they are not ICEs.
    const VarDecl *VD = dyn_cast<VarDecl>(D);
    if (VD) {
      if (const VarDecl *VDef = VD->getDefinition(Info.Ctx))
        VD = VDef;
    }
    if (!VD || VD->isInvalidDecl()) {
      Info.Diag(E);
      return CompleteObject();
    }

    // Accesses of volatile-qualified objects are not allowed.
    if (BaseType.isVolatileQualified()) {
      if (Info.getLangOpts().CPlusPlus) {
        Info.Diag(E, diag::note_constexpr_access_volatile_obj, 1)
          << AK << 1 << VD;
        Info.Note(VD->getLocation(), diag::note_declared_at);
      } else {
        Info.Diag(E);
      }
      return CompleteObject();
    }

    // Unless we're looking at a local variable or argument in a constexpr call,
    // the variable we're reading must be const.
    if (!Frame) {
      if (Info.getLangOpts().CPlusPlus1y &&
          VD == Info.EvaluatingDecl.dyn_cast<const ValueDecl *>()) {
        // OK, we can read and modify an object if we're in the process of
        // evaluating its initializer, because its lifetime began in this
        // evaluation.
      } else if (AK != AK_Read) {
        // All the remaining cases only permit reading.
        Info.Diag(E, diag::note_constexpr_modify_global);
        return CompleteObject();
      } else if (VD->isConstexpr()) {
        // OK, we can read this variable.
      } else if (BaseType->isIntegralOrEnumerationType()) {
        if (!BaseType.isConstQualified()) {
          if (Info.getLangOpts().CPlusPlus) {
            Info.Diag(E, diag::note_constexpr_ltor_non_const_int, 1) << VD;
            Info.Note(VD->getLocation(), diag::note_declared_at);
          } else {
            Info.Diag(E);
          }
          return CompleteObject();
        }
      } else if (BaseType->isFloatingType() && BaseType.isConstQualified()) {
        // We support folding of const floating-point types, in order to make
        // static const data members of such types (supported as an extension)
        // more useful.
        if (Info.getLangOpts().CPlusPlus11) {
          Info.CCEDiag(E, diag::note_constexpr_ltor_non_constexpr, 1) << VD;
          Info.Note(VD->getLocation(), diag::note_declared_at);
        } else {
          Info.CCEDiag(E);
        }
      } else {
        // FIXME: Allow folding of values of any literal type in all languages.
        if (Info.getLangOpts().CPlusPlus11) {
          Info.Diag(E, diag::note_constexpr_ltor_non_constexpr, 1) << VD;
          Info.Note(VD->getLocation(), diag::note_declared_at);
        } else {
          Info.Diag(E);
        }
        return CompleteObject();
      }
    }

    if (!evaluateVarDeclInit(Info, E, VD, Frame, BaseVal))
      return CompleteObject();
  } else {
    const Expr *Base = LVal.Base.dyn_cast<const Expr*>();

    if (!Frame) {
      if (const MaterializeTemporaryExpr *MTE =
              dyn_cast<MaterializeTemporaryExpr>(Base)) {
        assert(MTE->getStorageDuration() == SD_Static &&
               "should have a frame for a non-global materialized temporary");

        // Per C++1y [expr.const]p2:
        //  an lvalue-to-rvalue conversion [is not allowed unless it applies to]
        //   - a [...] glvalue of integral or enumeration type that refers to
        //     a non-volatile const object [...]
        //   [...]
        //   - a [...] glvalue of literal type that refers to a non-volatile
        //     object whose lifetime began within the evaluation of e.
        //
        // C++11 misses the 'began within the evaluation of e' check and
        // instead allows all temporaries, including things like:
        //   int &&r = 1;
        //   int x = ++r;
        //   constexpr int k = r;
        // Therefore we use the C++1y rules in C++11 too.
        const ValueDecl *VD = Info.EvaluatingDecl.dyn_cast<const ValueDecl*>();
        const ValueDecl *ED = MTE->getExtendingDecl();
        if (!(BaseType.isConstQualified() &&
              BaseType->isIntegralOrEnumerationType()) &&
            !(VD && VD->getCanonicalDecl() == ED->getCanonicalDecl())) {
          Info.Diag(E, diag::note_constexpr_access_static_temporary, 1) << AK;
          Info.Note(MTE->getExprLoc(), diag::note_constexpr_temporary_here);
          return CompleteObject();
        }

        BaseVal = Info.Ctx.getMaterializedTemporaryValue(MTE, false);
        assert(BaseVal && "got reference to unevaluated temporary");
      } else {
        Info.Diag(E);
        return CompleteObject();
      }
    } else {
      BaseVal = Frame->getTemporary(Base);
      assert(BaseVal && "missing value for temporary");
    }

    // Volatile temporary objects cannot be accessed in constant expressions.
    if (BaseType.isVolatileQualified()) {
      if (Info.getLangOpts().CPlusPlus) {
        Info.Diag(E, diag::note_constexpr_access_volatile_obj, 1)
          << AK << 0;
        Info.Note(Base->getExprLoc(), diag::note_constexpr_temporary_here);
      } else {
        Info.Diag(E);
      }
      return CompleteObject();
    }
  }

  // During the construction of an object, it is not yet 'const'.
  // FIXME: We don't set up EvaluatingDecl for local variables or temporaries,
  // and this doesn't do quite the right thing for const subobjects of the
  // object under construction.
  if (LVal.getLValueBase() == Info.EvaluatingDecl) {
    BaseType = Info.Ctx.getCanonicalType(BaseType);
    BaseType.removeLocalConst();
  }

  // In C++1y, we can't safely access any mutable state when we might be
  // evaluating after an unmodeled side effect or an evaluation failure.
  //
  // FIXME: Not all local state is mutable. Allow local constant subobjects
  // to be read here (but take care with 'mutable' fields).
  if (Frame && Info.getLangOpts().CPlusPlus1y &&
      (Info.EvalStatus.HasSideEffects || Info.keepEvaluatingAfterFailure()))
    return CompleteObject();

  return CompleteObject(BaseVal, BaseType);
}

/// \brief Perform an lvalue-to-rvalue conversion on the given glvalue. This
/// can also be used for 'lvalue-to-lvalue' conversions for looking up the
/// glvalue referred to by an entity of reference type.
///
/// \param Info - Information about the ongoing evaluation.
/// \param Conv - The expression for which we are performing the conversion.
///               Used for diagnostics.
/// \param Type - The type of the glvalue (before stripping cv-qualifiers in the
///               case of a non-class type).
/// \param LVal - The glvalue on which we are attempting to perform this action.
/// \param RVal - The produced value will be placed here.
static bool handleLValueToRValueConversion(EvalInfo &Info, const Expr *Conv,
                                           QualType Type,
                                           const LValue &LVal, APValue &RVal) {
  if (LVal.Designator.Invalid)
    return false;

  // Check for special cases where there is no existing APValue to look at.
  const Expr *Base = LVal.Base.dyn_cast<const Expr*>();
  if (!LVal.Designator.Invalid && Base && !LVal.CallIndex &&
      !Type.isVolatileQualified()) {
    if (const CompoundLiteralExpr *CLE = dyn_cast<CompoundLiteralExpr>(Base)) {
      // In C99, a CompoundLiteralExpr is an lvalue, and we defer evaluating the
      // initializer until now for such expressions. Such an expression can't be
      // an ICE in C, so this only matters for fold.
      assert(!Info.getLangOpts().CPlusPlus && "lvalue compound literal in c++?");
      if (Type.isVolatileQualified()) {
        Info.Diag(Conv);
        return false;
      }
      APValue Lit;
      if (!Evaluate(Lit, Info, CLE->getInitializer()))
        return false;
      CompleteObject LitObj(&Lit, Base->getType());
      return extractSubobject(Info, Conv, LitObj, LVal.Designator, RVal);
    } else if (isa<StringLiteral>(Base)) {
      // We represent a string literal array as an lvalue pointing at the
      // corresponding expression, rather than building an array of chars.
      // FIXME: Support PredefinedExpr, ObjCEncodeExpr, MakeStringConstant
      APValue Str(Base, CharUnits::Zero(), APValue::NoLValuePath(), 0);
      CompleteObject StrObj(&Str, Base->getType());
      return extractSubobject(Info, Conv, StrObj, LVal.Designator, RVal);
    }
  }

  CompleteObject Obj = findCompleteObject(Info, Conv, AK_Read, LVal, Type);
  return Obj && extractSubobject(Info, Conv, Obj, LVal.Designator, RVal);
}

/// Perform an assignment of Val to LVal. Takes ownership of Val.
static bool handleAssignment(EvalInfo &Info, const Expr *E, const LValue &LVal,
                             QualType LValType, APValue &Val) {
  if (LVal.Designator.Invalid)
    return false;

  if (!Info.getLangOpts().CPlusPlus1y) {
    Info.Diag(E);
    return false;
  }

  CompleteObject Obj = findCompleteObject(Info, E, AK_Assign, LVal, LValType);
  return Obj && modifySubobject(Info, E, Obj, LVal.Designator, Val);
}

static bool isOverflowingIntegerType(ASTContext &Ctx, QualType T) {
  return T->isSignedIntegerType() &&
         Ctx.getIntWidth(T) >= Ctx.getIntWidth(Ctx.IntTy);
}

namespace {
struct CompoundAssignSubobjectHandler {
  EvalInfo &Info;
  const Expr *E;
  QualType PromotedLHSType;
  BinaryOperatorKind Opcode;
  const APValue &RHS;

  static const AccessKinds AccessKind = AK_Assign;

  typedef bool result_type;

  bool checkConst(QualType QT) {
    // Assigning to a const object has undefined behavior.
    if (QT.isConstQualified()) {
      Info.Diag(E, diag::note_constexpr_modify_const_type) << QT;
      return false;
    }
    return true;
  }

  bool failed() { return false; }
  bool found(APValue &Subobj, QualType SubobjType) {
    switch (Subobj.getKind()) {
    case APValue::Int:
      return found(Subobj.getInt(), SubobjType);
    case APValue::Float:
      return found(Subobj.getFloat(), SubobjType);
    case APValue::ComplexInt:
    case APValue::ComplexFloat:
      // FIXME: Implement complex compound assignment.
      Info.Diag(E);
      return false;
    case APValue::LValue:
      return foundPointer(Subobj, SubobjType);
    default:
      // FIXME: can this happen?
      Info.Diag(E);
      return false;
    }
  }
  bool found(APSInt &Value, QualType SubobjType) {
    if (!checkConst(SubobjType))
      return false;

    if (!SubobjType->isIntegerType() || !RHS.isInt()) {
      // We don't support compound assignment on integer-cast-to-pointer
      // values.
      Info.Diag(E);
      return false;
    }

    APSInt LHS = HandleIntToIntCast(Info, E, PromotedLHSType,
                                    SubobjType, Value);
    if (!handleIntIntBinOp(Info, E, LHS, Opcode, RHS.getInt(), LHS))
      return false;
    Value = HandleIntToIntCast(Info, E, SubobjType, PromotedLHSType, LHS);
    return true;
  }
  bool found(APFloat &Value, QualType SubobjType) {
    return checkConst(SubobjType) &&
           HandleFloatToFloatCast(Info, E, SubobjType, PromotedLHSType,
                                  Value) &&
           handleFloatFloatBinOp(Info, E, Value, Opcode, RHS.getFloat()) &&
           HandleFloatToFloatCast(Info, E, PromotedLHSType, SubobjType, Value);
  }
  bool foundPointer(APValue &Subobj, QualType SubobjType) {
    if (!checkConst(SubobjType))
      return false;

    QualType PointeeType;
    if (const PointerType *PT = SubobjType->getAs<PointerType>())
      PointeeType = PT->getPointeeType();

    if (PointeeType.isNull() || !RHS.isInt() ||
        (Opcode != BO_Add && Opcode != BO_Sub)) {
      Info.Diag(E);
      return false;
    }

    int64_t Offset = getExtValue(RHS.getInt());
    if (Opcode == BO_Sub)
      Offset = -Offset;

    LValue LVal;
    LVal.setFrom(Info.Ctx, Subobj);
    if (!HandleLValueArrayAdjustment(Info, E, LVal, PointeeType, Offset))
      return false;
    LVal.moveInto(Subobj);
    return true;
  }
  bool foundString(APValue &Subobj, QualType SubobjType, uint64_t Character) {
    llvm_unreachable("shouldn't encounter string elements here");
  }
};
} // end anonymous namespace

const AccessKinds CompoundAssignSubobjectHandler::AccessKind;

/// Perform a compound assignment of LVal <op>= RVal.
static bool handleCompoundAssignment(
    EvalInfo &Info, const Expr *E,
    const LValue &LVal, QualType LValType, QualType PromotedLValType,
    BinaryOperatorKind Opcode, const APValue &RVal) {
  if (LVal.Designator.Invalid)
    return false;

  if (!Info.getLangOpts().CPlusPlus1y) {
    Info.Diag(E);
    return false;
  }

  CompleteObject Obj = findCompleteObject(Info, E, AK_Assign, LVal, LValType);
  CompoundAssignSubobjectHandler Handler = { Info, E, PromotedLValType, Opcode,
                                             RVal };
  return Obj && findSubobject(Info, E, Obj, LVal.Designator, Handler);
}

namespace {
struct IncDecSubobjectHandler {
  EvalInfo &Info;
  const Expr *E;
  AccessKinds AccessKind;
  APValue *Old;

  typedef bool result_type;

  bool checkConst(QualType QT) {
    // Assigning to a const object has undefined behavior.
    if (QT.isConstQualified()) {
      Info.Diag(E, diag::note_constexpr_modify_const_type) << QT;
      return false;
    }
    return true;
  }

  bool failed() { return false; }
  bool found(APValue &Subobj, QualType SubobjType) {
    // Stash the old value. Also clear Old, so we don't clobber it later
    // if we're post-incrementing a complex.
    if (Old) {
      *Old = Subobj;
      Old = nullptr;
    }

    switch (Subobj.getKind()) {
    case APValue::Int:
      return found(Subobj.getInt(), SubobjType);
    case APValue::Float:
      return found(Subobj.getFloat(), SubobjType);
    case APValue::ComplexInt:
      return found(Subobj.getComplexIntReal(),
                   SubobjType->castAs<ComplexType>()->getElementType()
                     .withCVRQualifiers(SubobjType.getCVRQualifiers()));
    case APValue::ComplexFloat:
      return found(Subobj.getComplexFloatReal(),
                   SubobjType->castAs<ComplexType>()->getElementType()
                     .withCVRQualifiers(SubobjType.getCVRQualifiers()));
    case APValue::LValue:
      return foundPointer(Subobj, SubobjType);
    default:
      // FIXME: can this happen?
      Info.Diag(E);
      return false;
    }
  }
  bool found(APSInt &Value, QualType SubobjType) {
    if (!checkConst(SubobjType))
      return false;

    if (!SubobjType->isIntegerType()) {
      // We don't support increment / decrement on integer-cast-to-pointer
      // values.
      Info.Diag(E);
      return false;
    }

    if (Old) *Old = APValue(Value);

    // bool arithmetic promotes to int, and the conversion back to bool
    // doesn't reduce mod 2^n, so special-case it.
    if (SubobjType->isBooleanType()) {
      if (AccessKind == AK_Increment)
        Value = 1;
      else
        Value = !Value;
      return true;
    }

    bool WasNegative = Value.isNegative();
    if (AccessKind == AK_Increment) {
      ++Value;

      if (!WasNegative && Value.isNegative() &&
          isOverflowingIntegerType(Info.Ctx, SubobjType)) {
        APSInt ActualValue(Value, /*IsUnsigned*/true);
        HandleOverflow(Info, E, ActualValue, SubobjType);
      }
    } else {
      --Value;

      if (WasNegative && !Value.isNegative() &&
          isOverflowingIntegerType(Info.Ctx, SubobjType)) {
        unsigned BitWidth = Value.getBitWidth();
        APSInt ActualValue(Value.sext(BitWidth + 1), /*IsUnsigned*/false);
        ActualValue.setBit(BitWidth);
        HandleOverflow(Info, E, ActualValue, SubobjType);
      }
    }
    return true;
  }
  bool found(APFloat &Value, QualType SubobjType) {
    if (!checkConst(SubobjType))
      return false;

    if (Old) *Old = APValue(Value);

    APFloat One(Value.getSemantics(), 1);
    if (AccessKind == AK_Increment)
      Value.add(One, APFloat::rmNearestTiesToEven);
    else
      Value.subtract(One, APFloat::rmNearestTiesToEven);
    return true;
  }
  bool foundPointer(APValue &Subobj, QualType SubobjType) {
    if (!checkConst(SubobjType))
      return false;

    QualType PointeeType;
    if (const PointerType *PT = SubobjType->getAs<PointerType>())
      PointeeType = PT->getPointeeType();
    else {
      Info.Diag(E);
      return false;
    }

    LValue LVal;
    LVal.setFrom(Info.Ctx, Subobj);
    if (!HandleLValueArrayAdjustment(Info, E, LVal, PointeeType,
                                     AccessKind == AK_Increment ? 1 : -1))
      return false;
    LVal.moveInto(Subobj);
    return true;
  }
  bool foundString(APValue &Subobj, QualType SubobjType, uint64_t Character) {
    llvm_unreachable("shouldn't encounter string elements here");
  }
};
} // end anonymous namespace

/// Perform an increment or decrement on LVal.
static bool handleIncDec(EvalInfo &Info, const Expr *E, const LValue &LVal,
                         QualType LValType, bool IsIncrement, APValue *Old) {
  if (LVal.Designator.Invalid)
    return false;

  if (!Info.getLangOpts().CPlusPlus1y) {
    Info.Diag(E);
    return false;
  }

  AccessKinds AK = IsIncrement ? AK_Increment : AK_Decrement;
  CompleteObject Obj = findCompleteObject(Info, E, AK, LVal, LValType);
  IncDecSubobjectHandler Handler = { Info, E, AK, Old };
  return Obj && findSubobject(Info, E, Obj, LVal.Designator, Handler);
}

/// Build an lvalue for the object argument of a member function call.
static bool EvaluateObjectArgument(EvalInfo &Info, const Expr *Object,
                                   LValue &This) {
  if (Object->getType()->isPointerType())
    return EvaluatePointer(Object, This, Info);

  if (Object->isGLValue())
    return EvaluateLValue(Object, This, Info);

  if (Object->getType()->isLiteralType(Info.Ctx))
    return EvaluateTemporary(Object, This, Info);

  Info.Diag(Object, diag::note_constexpr_nonliteral) << Object->getType();
  return false;
}

/// HandleMemberPointerAccess - Evaluate a member access operation and build an
/// lvalue referring to the result.
///
/// \param Info - Information about the ongoing evaluation.
/// \param LV - An lvalue referring to the base of the member pointer.
/// \param RHS - The member pointer expression.
/// \param IncludeMember - Specifies whether the member itself is included in
///        the resulting LValue subobject designator. This is not possible when
///        creating a bound member function.
/// \return The field or method declaration to which the member pointer refers,
///         or 0 if evaluation fails.
static const ValueDecl *HandleMemberPointerAccess(EvalInfo &Info,
                                                  QualType LVType,
                                                  LValue &LV,
                                                  const Expr *RHS,
                                                  bool IncludeMember = true) {
  MemberPtr MemPtr;
  if (!EvaluateMemberPointer(RHS, MemPtr, Info))
    return nullptr;

  // C++11 [expr.mptr.oper]p6: If the second operand is the null pointer to
  // member value, the behavior is undefined.
  if (!MemPtr.getDecl()) {
    // FIXME: Specific diagnostic.
    Info.Diag(RHS);
    return nullptr;
  }

  if (MemPtr.isDerivedMember()) {
    // This is a member of some derived class. Truncate LV appropriately.
    // The end of the derived-to-base path for the base object must match the
    // derived-to-base path for the member pointer.
    if (LV.Designator.MostDerivedPathLength + MemPtr.Path.size() >
        LV.Designator.Entries.size()) {
      Info.Diag(RHS);
      return nullptr;
    }
    unsigned PathLengthToMember =
        LV.Designator.Entries.size() - MemPtr.Path.size();
    for (unsigned I = 0, N = MemPtr.Path.size(); I != N; ++I) {
      const CXXRecordDecl *LVDecl = getAsBaseClass(
          LV.Designator.Entries[PathLengthToMember + I]);
      const CXXRecordDecl *MPDecl = MemPtr.Path[I];
      if (LVDecl->getCanonicalDecl() != MPDecl->getCanonicalDecl()) {
        Info.Diag(RHS);
        return nullptr;
      }
    }

    // Truncate the lvalue to the appropriate derived class.
    if (!CastToDerivedClass(Info, RHS, LV, MemPtr.getContainingRecord(),
                            PathLengthToMember))
      return nullptr;
  } else if (!MemPtr.Path.empty()) {
    // Extend the LValue path with the member pointer's path.
    LV.Designator.Entries.reserve(LV.Designator.Entries.size() +
                                  MemPtr.Path.size() + IncludeMember);

    // Walk down to the appropriate base class.
    if (const PointerType *PT = LVType->getAs<PointerType>())
      LVType = PT->getPointeeType();
    const CXXRecordDecl *RD = LVType->getAsCXXRecordDecl();
    assert(RD && "member pointer access on non-class-type expression");
    // The first class in the path is that of the lvalue.
    for (unsigned I = 1, N = MemPtr.Path.size(); I != N; ++I) {
      const CXXRecordDecl *Base = MemPtr.Path[N - I - 1];
      if (!HandleLValueDirectBase(Info, RHS, LV, RD, Base))
        return nullptr;
      RD = Base;
    }
    // Finally cast to the class containing the member.
    if (!HandleLValueDirectBase(Info, RHS, LV, RD,
                                MemPtr.getContainingRecord()))
      return nullptr;
  }

  // Add the member. Note that we cannot build bound member functions here.
  if (IncludeMember) {
    if (const FieldDecl *FD = dyn_cast<FieldDecl>(MemPtr.getDecl())) {
      if (!HandleLValueMember(Info, RHS, LV, FD))
        return nullptr;
    } else if (const IndirectFieldDecl *IFD =
                 dyn_cast<IndirectFieldDecl>(MemPtr.getDecl())) {
      if (!HandleLValueIndirectMember(Info, RHS, LV, IFD))
        return nullptr;
    } else {
      llvm_unreachable("can't construct reference to bound member function");
    }
  }

  return MemPtr.getDecl();
}

static const ValueDecl *HandleMemberPointerAccess(EvalInfo &Info,
                                                  const BinaryOperator *BO,
                                                  LValue &LV,
                                                  bool IncludeMember = true) {
  assert(BO->getOpcode() == BO_PtrMemD || BO->getOpcode() == BO_PtrMemI);

  if (!EvaluateObjectArgument(Info, BO->getLHS(), LV)) {
    if (Info.keepEvaluatingAfterFailure()) {
      MemberPtr MemPtr;
      EvaluateMemberPointer(BO->getRHS(), MemPtr, Info);
    }
    return nullptr;
  }

  return HandleMemberPointerAccess(Info, BO->getLHS()->getType(), LV,
                                   BO->getRHS(), IncludeMember);
}

/// HandleBaseToDerivedCast - Apply the given base-to-derived cast operation on
/// the provided lvalue, which currently refers to the base object.
static bool HandleBaseToDerivedCast(EvalInfo &Info, const CastExpr *E,
                                    LValue &Result) {
  SubobjectDesignator &D = Result.Designator;
  if (D.Invalid || !Result.checkNullPointer(Info, E, CSK_Derived))
    return false;

  QualType TargetQT = E->getType();
  if (const PointerType *PT = TargetQT->getAs<PointerType>())
    TargetQT = PT->getPointeeType();

  // Check this cast lands within the final derived-to-base subobject path.
  if (D.MostDerivedPathLength + E->path_size() > D.Entries.size()) {
    Info.CCEDiag(E, diag::note_constexpr_invalid_downcast)
      << D.MostDerivedType << TargetQT;
    return false;
  }

  // Check the type of the final cast. We don't need to check the path,
  // since a cast can only be formed if the path is unique.
  unsigned NewEntriesSize = D.Entries.size() - E->path_size();
  const CXXRecordDecl *TargetType = TargetQT->getAsCXXRecordDecl();
  const CXXRecordDecl *FinalType;
  if (NewEntriesSize == D.MostDerivedPathLength)
    FinalType = D.MostDerivedType->getAsCXXRecordDecl();
  else
    FinalType = getAsBaseClass(D.Entries[NewEntriesSize - 1]);
  if (FinalType->getCanonicalDecl() != TargetType->getCanonicalDecl()) {
    Info.CCEDiag(E, diag::note_constexpr_invalid_downcast)
      << D.MostDerivedType << TargetQT;
    return false;
  }

  // Truncate the lvalue to the appropriate derived class.
  return CastToDerivedClass(Info, E, Result, TargetType, NewEntriesSize);
}

namespace {
enum EvalStmtResult {
  /// Evaluation failed.
  ESR_Failed,
  /// Hit a 'return' statement.
  ESR_Returned,
  /// Evaluation succeeded.
  ESR_Succeeded,
  /// Hit a 'continue' statement.
  ESR_Continue,
  /// Hit a 'break' statement.
  ESR_Break,
  /// Still scanning for 'case' or 'default' statement.
  ESR_CaseNotFound
};
}

static bool EvaluateDecl(EvalInfo &Info, const Decl *D) {
  if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {
    // We don't need to evaluate the initializer for a static local.
    if (!VD->hasLocalStorage())
      return true;

    LValue Result;
    Result.set(VD, Info.CurrentCall->Index);
    APValue &Val = Info.CurrentCall->createTemporary(VD, true);

    const Expr *InitE = VD->getInit();
    if (!InitE) {
      Info.Diag(D->getLocStart(), diag::note_constexpr_uninitialized)
        << false << VD->getType();
      Val = APValue();
      return false;
    }

    if (InitE->isValueDependent())
      return false;

    if (!EvaluateInPlace(Val, Info, Result, InitE)) {
      // Wipe out any partially-computed value, to allow tracking that this
      // evaluation failed.
      Val = APValue();
      return false;
    }
  }

  return true;
}

/// Evaluate a condition (either a variable declaration or an expression).
static bool EvaluateCond(EvalInfo &Info, const VarDecl *CondDecl,
                         const Expr *Cond, bool &Result) {
  FullExpressionRAII Scope(Info);
  if (CondDecl && !EvaluateDecl(Info, CondDecl))
    return false;
  return EvaluateAsBooleanCondition(Cond, Result, Info);
}

static EvalStmtResult EvaluateStmt(APValue &Result, EvalInfo &Info,
                                   const Stmt *S,
                                   const SwitchCase *SC = nullptr);

/// Evaluate the body of a loop, and translate the result as appropriate.
static EvalStmtResult EvaluateLoopBody(APValue &Result, EvalInfo &Info,
                                       const Stmt *Body,
                                       const SwitchCase *Case = nullptr) {
  BlockScopeRAII Scope(Info);
  switch (EvalStmtResult ESR = EvaluateStmt(Result, Info, Body, Case)) {
  case ESR_Break:
    return ESR_Succeeded;
  case ESR_Succeeded:
  case ESR_Continue:
    return ESR_Continue;
  case ESR_Failed:
  case ESR_Returned:
  case ESR_CaseNotFound:
    return ESR;
  }
  llvm_unreachable("Invalid EvalStmtResult!");
}

/// Evaluate a switch statement.
static EvalStmtResult EvaluateSwitch(APValue &Result, EvalInfo &Info,
                                     const SwitchStmt *SS) {
  BlockScopeRAII Scope(Info);

  // Evaluate the switch condition.
  APSInt Value;
  {
    FullExpressionRAII Scope(Info);
    if (SS->getConditionVariable() &&
        !EvaluateDecl(Info, SS->getConditionVariable()))
      return ESR_Failed;
    if (!EvaluateInteger(SS->getCond(), Value, Info))
      return ESR_Failed;
  }

  // Find the switch case corresponding to the value of the condition.
  // FIXME: Cache this lookup.
  const SwitchCase *Found = nullptr;
  for (const SwitchCase *SC = SS->getSwitchCaseList(); SC;
       SC = SC->getNextSwitchCase()) {
    if (isa<DefaultStmt>(SC)) {
      Found = SC;
      continue;
    }

    const CaseStmt *CS = cast<CaseStmt>(SC);
    APSInt LHS = CS->getLHS()->EvaluateKnownConstInt(Info.Ctx);
    APSInt RHS = CS->getRHS() ? CS->getRHS()->EvaluateKnownConstInt(Info.Ctx)
                              : LHS;
    if (LHS <= Value && Value <= RHS) {
      Found = SC;
      break;
    }
  }

  if (!Found)
    return ESR_Succeeded;

  // Search the switch body for the switch case and evaluate it from there.
  switch (EvalStmtResult ESR = EvaluateStmt(Result, Info, SS->getBody(), Found)) {
  case ESR_Break:
    return ESR_Succeeded;
  case ESR_Succeeded:
  case ESR_Continue:
  case ESR_Failed:
  case ESR_Returned:
    return ESR;
  case ESR_CaseNotFound:
    // This can only happen if the switch case is nested within a statement
    // expression. We have no intention of supporting that.
    Info.Diag(Found->getLocStart(), diag::note_constexpr_stmt_expr_unsupported);
    return ESR_Failed;
  }
  llvm_unreachable("Invalid EvalStmtResult!");
}

// Evaluate a statement.
static EvalStmtResult EvaluateStmt(APValue &Result, EvalInfo &Info,
                                   const Stmt *S, const SwitchCase *Case) {
  if (!Info.nextStep(S))
    return ESR_Failed;

  // If we're hunting down a 'case' or 'default' label, recurse through
  // substatements until we hit the label.
  if (Case) {
    // FIXME: We don't start the lifetime of objects whose initialization we
    // jump over. However, such objects must be of class type with a trivial
    // default constructor that initialize all subobjects, so must be empty,
    // so this almost never matters.
    switch (S->getStmtClass()) {
    case Stmt::CompoundStmtClass:
      // FIXME: Precompute which substatement of a compound statement we
      // would jump to, and go straight there rather than performing a
      // linear scan each time.
    case Stmt::LabelStmtClass:
    case Stmt::AttributedStmtClass:
    case Stmt::DoStmtClass:
      break;

    case Stmt::CaseStmtClass:
    case Stmt::DefaultStmtClass:
      if (Case == S)
        Case = nullptr;
      break;

    case Stmt::IfStmtClass: {
      // FIXME: Precompute which side of an 'if' we would jump to, and go
      // straight there rather than scanning both sides.
      const IfStmt *IS = cast<IfStmt>(S);

      // Wrap the evaluation in a block scope, in case it's a DeclStmt
      // preceded by our switch label.
      BlockScopeRAII Scope(Info);

      EvalStmtResult ESR = EvaluateStmt(Result, Info, IS->getThen(), Case);
      if (ESR != ESR_CaseNotFound || !IS->getElse())
        return ESR;
      return EvaluateStmt(Result, Info, IS->getElse(), Case);
    }

    case Stmt::WhileStmtClass: {
      EvalStmtResult ESR =
          EvaluateLoopBody(Result, Info, cast<WhileStmt>(S)->getBody(), Case);
      if (ESR != ESR_Continue)
        return ESR;
      break;
    }

    case Stmt::ForStmtClass: {
      const ForStmt *FS = cast<ForStmt>(S);
      EvalStmtResult ESR =
          EvaluateLoopBody(Result, Info, FS->getBody(), Case);
      if (ESR != ESR_Continue)
        return ESR;
      if (FS->getInc()) {
        FullExpressionRAII IncScope(Info);
        if (!EvaluateIgnoredValue(Info, FS->getInc()))
          return ESR_Failed;
      }
      break;
    }

    case Stmt::DeclStmtClass:
      // FIXME: If the variable has initialization that can't be jumped over,
      // bail out of any immediately-surrounding compound-statement too.
    default:
      return ESR_CaseNotFound;
    }
  }

  switch (S->getStmtClass()) {
  default:
    if (const Expr *E = dyn_cast<Expr>(S)) {
      // Don't bother evaluating beyond an expression-statement which couldn't
      // be evaluated.
      FullExpressionRAII Scope(Info);
      if (!EvaluateIgnoredValue(Info, E))
        return ESR_Failed;
      return ESR_Succeeded;
    }

    Info.Diag(S->getLocStart());
    return ESR_Failed;

  case Stmt::NullStmtClass:
    return ESR_Succeeded;

  case Stmt::DeclStmtClass: {
    const DeclStmt *DS = cast<DeclStmt>(S);
    for (const auto *DclIt : DS->decls()) {
      // Each declaration initialization is its own full-expression.
      // FIXME: This isn't quite right; if we're performing aggregate
      // initialization, each braced subexpression is its own full-expression.
      FullExpressionRAII Scope(Info);
      if (!EvaluateDecl(Info, DclIt) && !Info.keepEvaluatingAfterFailure())
        return ESR_Failed;
    }
    return ESR_Succeeded;
  }

  case Stmt::ReturnStmtClass: {
    const Expr *RetExpr = cast<ReturnStmt>(S)->getRetValue();
    FullExpressionRAII Scope(Info);
    if (RetExpr && !Evaluate(Result, Info, RetExpr))
      return ESR_Failed;
    return ESR_Returned;
  }

  case Stmt::CompoundStmtClass: {
    BlockScopeRAII Scope(Info);

    const CompoundStmt *CS = cast<CompoundStmt>(S);
    for (const auto *BI : CS->body()) {
      EvalStmtResult ESR = EvaluateStmt(Result, Info, BI, Case);
      if (ESR == ESR_Succeeded)
        Case = nullptr;
      else if (ESR != ESR_CaseNotFound)
        return ESR;
    }
    return Case ? ESR_CaseNotFound : ESR_Succeeded;
  }

  case Stmt::IfStmtClass: {
    const IfStmt *IS = cast<IfStmt>(S);

    // Evaluate the condition, as either a var decl or as an expression.
    BlockScopeRAII Scope(Info);
    bool Cond;
    if (!EvaluateCond(Info, IS->getConditionVariable(), IS->getCond(), Cond))
      return ESR_Failed;

    if (const Stmt *SubStmt = Cond ? IS->getThen() : IS->getElse()) {
      EvalStmtResult ESR = EvaluateStmt(Result, Info, SubStmt);
      if (ESR != ESR_Succeeded)
        return ESR;
    }
    return ESR_Succeeded;
  }

  case Stmt::WhileStmtClass: {
    const WhileStmt *WS = cast<WhileStmt>(S);
    while (true) {
      BlockScopeRAII Scope(Info);
      bool Continue;
      if (!EvaluateCond(Info, WS->getConditionVariable(), WS->getCond(),
                        Continue))
        return ESR_Failed;
      if (!Continue)
        break;

      EvalStmtResult ESR = EvaluateLoopBody(Result, Info, WS->getBody());
      if (ESR != ESR_Continue)
        return ESR;
    }
    return ESR_Succeeded;
  }

  case Stmt::DoStmtClass: {
    const DoStmt *DS = cast<DoStmt>(S);
    bool Continue;
    do {
      EvalStmtResult ESR = EvaluateLoopBody(Result, Info, DS->getBody(), Case);
      if (ESR != ESR_Continue)
        return ESR;
      Case = nullptr;

      FullExpressionRAII CondScope(Info);
      if (!EvaluateAsBooleanCondition(DS->getCond(), Continue, Info))
        return ESR_Failed;
    } while (Continue);
    return ESR_Succeeded;
  }

  case Stmt::ForStmtClass: {
    const ForStmt *FS = cast<ForStmt>(S);
    BlockScopeRAII Scope(Info);
    if (FS->getInit()) {
      EvalStmtResult ESR = EvaluateStmt(Result, Info, FS->getInit());
      if (ESR != ESR_Succeeded)
        return ESR;
    }
    while (true) {
      BlockScopeRAII Scope(Info);
      bool Continue = true;
      if (FS->getCond() && !EvaluateCond(Info, FS->getConditionVariable(),
                                         FS->getCond(), Continue))
        return ESR_Failed;
      if (!Continue)
        break;

      EvalStmtResult ESR = EvaluateLoopBody(Result, Info, FS->getBody());
      if (ESR != ESR_Continue)
        return ESR;

      if (FS->getInc()) {
        FullExpressionRAII IncScope(Info);
        if (!EvaluateIgnoredValue(Info, FS->getInc()))
          return ESR_Failed;
      }
    }
    return ESR_Succeeded;
  }

  case Stmt::CXXForRangeStmtClass: {
    const CXXForRangeStmt *FS = cast<CXXForRangeStmt>(S);
    BlockScopeRAII Scope(Info);

    // Initialize the __range variable.
    EvalStmtResult ESR = EvaluateStmt(Result, Info, FS->getRangeStmt());
    if (ESR != ESR_Succeeded)
      return ESR;

    // Create the __begin and __end iterators.
    ESR = EvaluateStmt(Result, Info, FS->getBeginEndStmt());
    if (ESR != ESR_Succeeded)
      return ESR;

    while (true) {
      // Condition: __begin != __end.
      {
        bool Continue = true;
        FullExpressionRAII CondExpr(Info);
        if (!EvaluateAsBooleanCondition(FS->getCond(), Continue, Info))
          return ESR_Failed;
        if (!Continue)
          break;
      }

      // User's variable declaration, initialized by *__begin.
      BlockScopeRAII InnerScope(Info);
      ESR = EvaluateStmt(Result, Info, FS->getLoopVarStmt());
      if (ESR != ESR_Succeeded)
        return ESR;

      // Loop body.
      ESR = EvaluateLoopBody(Result, Info, FS->getBody());
      if (ESR != ESR_Continue)
        return ESR;

      // Increment: ++__begin
      if (!EvaluateIgnoredValue(Info, FS->getInc()))
        return ESR_Failed;
    }

    return ESR_Succeeded;
  }

  case Stmt::SwitchStmtClass:
    return EvaluateSwitch(Result, Info, cast<SwitchStmt>(S));

  case Stmt::ContinueStmtClass:
    return ESR_Continue;

  case Stmt::BreakStmtClass:
    return ESR_Break;

  case Stmt::LabelStmtClass:
    return EvaluateStmt(Result, Info, cast<LabelStmt>(S)->getSubStmt(), Case);

  case Stmt::AttributedStmtClass:
    // As a general principle, C++11 attributes can be ignored without
    // any semantic impact.
    return EvaluateStmt(Result, Info, cast<AttributedStmt>(S)->getSubStmt(),
                        Case);

  case Stmt::CaseStmtClass:
  case Stmt::DefaultStmtClass:
    return EvaluateStmt(Result, Info, cast<SwitchCase>(S)->getSubStmt(), Case);
  }
}

/// CheckTrivialDefaultConstructor - Check whether a constructor is a trivial
/// default constructor. If so, we'll fold it whether or not it's marked as
/// constexpr. If it is marked as constexpr, we will never implicitly define it,
/// so we need special handling.
static bool CheckTrivialDefaultConstructor(EvalInfo &Info, SourceLocation Loc,
                                           const CXXConstructorDecl *CD,
                                           bool IsValueInitialization) {
  if (!CD->isTrivial() || !CD->isDefaultConstructor())
    return false;

  // Value-initialization does not call a trivial default constructor, so such a
  // call is a core constant expression whether or not the constructor is
  // constexpr.
  if (!CD->isConstexpr() && !IsValueInitialization) {
    if (Info.getLangOpts().CPlusPlus11) {
      // FIXME: If DiagDecl is an implicitly-declared special member function,
      // we should be much more explicit about why it's not constexpr.
      Info.CCEDiag(Loc, diag::note_constexpr_invalid_function, 1)
        << /*IsConstexpr*/0 << /*IsConstructor*/1 << CD;
      Info.Note(CD->getLocation(), diag::note_declared_at);
    } else {
      Info.CCEDiag(Loc, diag::note_invalid_subexpr_in_const_expr);
    }
  }
  return true;
}

/// CheckConstexprFunction - Check that a function can be called in a constant
/// expression.
static bool CheckConstexprFunction(EvalInfo &Info, SourceLocation CallLoc,
                                   const FunctionDecl *Declaration,
                                   const FunctionDecl *Definition) {
  // Potential constant expressions can contain calls to declared, but not yet
  // defined, constexpr functions.
  if (Info.checkingPotentialConstantExpression() && !Definition &&
      Declaration->isConstexpr())
    return false;

  // Bail out with no diagnostic if the function declaration itself is invalid.
  // We will have produced a relevant diagnostic while parsing it.
  if (Declaration->isInvalidDecl())
    return false;

  // Can we evaluate this function call?
  if (Definition && Definition->isConstexpr() && !Definition->isInvalidDecl())
    return true;

  if (Info.getLangOpts().CPlusPlus11) {
    const FunctionDecl *DiagDecl = Definition ? Definition : Declaration;
    // FIXME: If DiagDecl is an implicitly-declared special member function, we
    // should be much more explicit about why it's not constexpr.
    Info.Diag(CallLoc, diag::note_constexpr_invalid_function, 1)
      << DiagDecl->isConstexpr() << isa<CXXConstructorDecl>(DiagDecl)
      << DiagDecl;
    Info.Note(DiagDecl->getLocation(), diag::note_declared_at);
  } else {
    Info.Diag(CallLoc, diag::note_invalid_subexpr_in_const_expr);
  }
  return false;
}

namespace {
typedef SmallVector<APValue, 8> ArgVector;
}

/// EvaluateArgs - Evaluate the arguments to a function call.
static bool EvaluateArgs(ArrayRef<const Expr*> Args, ArgVector &ArgValues,
                         EvalInfo &Info) {
  bool Success = true;
  for (ArrayRef<const Expr*>::iterator I = Args.begin(), E = Args.end();
       I != E; ++I) {
    if (!Evaluate(ArgValues[I - Args.begin()], Info, *I)) {
      // If we're checking for a potential constant expression, evaluate all
      // initializers even if some of them fail.
      if (!Info.keepEvaluatingAfterFailure())
        return false;
      Success = false;
    }
  }
  return Success;
}

/// Evaluate a function call.
static bool HandleFunctionCall(SourceLocation CallLoc,
                               const FunctionDecl *Callee, const LValue *This,
                               ArrayRef<const Expr*> Args, const Stmt *Body,
                               EvalInfo &Info, APValue &Result) {
  ArgVector ArgValues(Args.size());
  if (!EvaluateArgs(Args, ArgValues, Info))
    return false;

  if (!Info.CheckCallLimit(CallLoc))
    return false;

  CallStackFrame Frame(Info, CallLoc, Callee, This, ArgValues.data());

  // For a trivial copy or move assignment, perform an APValue copy. This is
  // essential for unions, where the operations performed by the assignment
  // operator cannot be represented as statements.
  const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(Callee);
  if (MD && MD->isDefaulted() && MD->isTrivial()) {
    assert(This &&
           (MD->isCopyAssignmentOperator() || MD->isMoveAssignmentOperator()));
    LValue RHS;
    RHS.setFrom(Info.Ctx, ArgValues[0]);
    APValue RHSValue;
    if (!handleLValueToRValueConversion(Info, Args[0], Args[0]->getType(),
                                        RHS, RHSValue))
      return false;
    if (!handleAssignment(Info, Args[0], *This, MD->getThisType(Info.Ctx),
                          RHSValue))
      return false;
    This->moveInto(Result);
    return true;
  }

  EvalStmtResult ESR = EvaluateStmt(Result, Info, Body);
  if (ESR == ESR_Succeeded) {
    if (Callee->getReturnType()->isVoidType())
      return true;
    Info.Diag(Callee->getLocEnd(), diag::note_constexpr_no_return);
  }
  return ESR == ESR_Returned;
}

/// Evaluate a constructor call.
static bool HandleConstructorCall(SourceLocation CallLoc, const LValue &This,
                                  ArrayRef<const Expr*> Args,
                                  const CXXConstructorDecl *Definition,
                                  EvalInfo &Info, APValue &Result) {
  ArgVector ArgValues(Args.size());
  if (!EvaluateArgs(Args, ArgValues, Info))
    return false;

  if (!Info.CheckCallLimit(CallLoc))
    return false;

  const CXXRecordDecl *RD = Definition->getParent();
  if (RD->getNumVBases()) {
    Info.Diag(CallLoc, diag::note_constexpr_virtual_base) << RD;
    return false;
  }

  CallStackFrame Frame(Info, CallLoc, Definition, &This, ArgValues.data());

  // If it's a delegating constructor, just delegate.
  if (Definition->isDelegatingConstructor()) {
    CXXConstructorDecl::init_const_iterator I = Definition->init_begin();
    {
      FullExpressionRAII InitScope(Info);
      if (!EvaluateInPlace(Result, Info, This, (*I)->getInit()))
        return false;
    }
    return EvaluateStmt(Result, Info, Definition->getBody()) != ESR_Failed;
  }

  // For a trivial copy or move constructor, perform an APValue copy. This is
  // essential for unions, where the operations performed by the constructor
  // cannot be represented by ctor-initializers.
  if (Definition->isDefaulted() &&
      ((Definition->isCopyConstructor() && Definition->isTrivial()) ||
       (Definition->isMoveConstructor() && Definition->isTrivial()))) {
    LValue RHS;
    RHS.setFrom(Info.Ctx, ArgValues[0]);
    return handleLValueToRValueConversion(Info, Args[0], Args[0]->getType(),
                                          RHS, Result);
  }

  // Reserve space for the struct members.
  if (!RD->isUnion() && Result.isUninit())
    Result = APValue(APValue::UninitStruct(), RD->getNumBases(),
                     std::distance(RD->field_begin(), RD->field_end()));

  if (RD->isInvalidDecl()) return false;
  const ASTRecordLayout &Layout = Info.Ctx.getASTRecordLayout(RD);

  // A scope for temporaries lifetime-extended by reference members.
  BlockScopeRAII LifetimeExtendedScope(Info);

  bool Success = true;
  unsigned BasesSeen = 0;
#ifndef NDEBUG
  CXXRecordDecl::base_class_const_iterator BaseIt = RD->bases_begin();
#endif
  for (const auto *I : Definition->inits()) {
    LValue Subobject = This;
    APValue *Value = &Result;

    // Determine the subobject to initialize.
    FieldDecl *FD = nullptr;
    if (I->isBaseInitializer()) {
      QualType BaseType(I->getBaseClass(), 0);
#ifndef NDEBUG
      // Non-virtual base classes are initialized in the order in the class
      // definition. We have already checked for virtual base classes.
      assert(!BaseIt->isVirtual() && "virtual base for literal type");
      assert(Info.Ctx.hasSameType(BaseIt->getType(), BaseType) &&
             "base class initializers not in expected order");
      ++BaseIt;
#endif
      if (!HandleLValueDirectBase(Info, I->getInit(), Subobject, RD,
                                  BaseType->getAsCXXRecordDecl(), &Layout))
        return false;
      Value = &Result.getStructBase(BasesSeen++);
    } else if ((FD = I->getMember())) {
      if (!HandleLValueMember(Info, I->getInit(), Subobject, FD, &Layout))
        return false;
      if (RD->isUnion()) {
        Result = APValue(FD);
        Value = &Result.getUnionValue();
      } else {
        Value = &Result.getStructField(FD->getFieldIndex());
      }
    } else if (IndirectFieldDecl *IFD = I->getIndirectMember()) {
      // Walk the indirect field decl's chain to find the object to initialize,
      // and make sure we've initialized every step along it.
      for (auto *C : IFD->chain()) {
        FD = cast<FieldDecl>(C);
        CXXRecordDecl *CD = cast<CXXRecordDecl>(FD->getParent());
        // Switch the union field if it differs. This happens if we had
        // preceding zero-initialization, and we're now initializing a union
        // subobject other than the first.
        // FIXME: In this case, the values of the other subobjects are
        // specified, since zero-initialization sets all padding bits to zero.
        if (Value->isUninit() ||
            (Value->isUnion() && Value->getUnionField() != FD)) {
          if (CD->isUnion())
            *Value = APValue(FD);
          else
            *Value = APValue(APValue::UninitStruct(), CD->getNumBases(),
                             std::distance(CD->field_begin(), CD->field_end()));
        }
        if (!HandleLValueMember(Info, I->getInit(), Subobject, FD))
          return false;
        if (CD->isUnion())
          Value = &Value->getUnionValue();
        else
          Value = &Value->getStructField(FD->getFieldIndex());
      }
    } else {
      llvm_unreachable("unknown base initializer kind");
    }

    FullExpressionRAII InitScope(Info);
    if (!EvaluateInPlace(*Value, Info, Subobject, I->getInit()) ||
        (FD && FD->isBitField() && !truncateBitfieldValue(Info, I->getInit(),
                                                          *Value, FD))) {
      // If we're checking for a potential constant expression, evaluate all
      // initializers even if some of them fail.
      if (!Info.keepEvaluatingAfterFailure())
        return false;
      Success = false;
    }
  }

  return Success &&
         EvaluateStmt(Result, Info, Definition->getBody()) != ESR_Failed;
}

//===----------------------------------------------------------------------===//
// Generic Evaluation
//===----------------------------------------------------------------------===//
namespace {

template <class Derived>
class ExprEvaluatorBase
  : public ConstStmtVisitor<Derived, bool> {
private:
  bool DerivedSuccess(const APValue &V, const Expr *E) {
    return static_cast<Derived*>(this)->Success(V, E);
  }
  bool DerivedZeroInitialization(const Expr *E) {
    return static_cast<Derived*>(this)->ZeroInitialization(E);
  }

  // Check whether a conditional operator with a non-constant condition is a
  // potential constant expression. If neither arm is a potential constant
  // expression, then the conditional operator is not either.
  template<typename ConditionalOperator>
  void CheckPotentialConstantConditional(const ConditionalOperator *E) {
    assert(Info.checkingPotentialConstantExpression());

    // Speculatively evaluate both arms.
    {
      SmallVector<PartialDiagnosticAt, 8> Diag;
      SpeculativeEvaluationRAII Speculate(Info, &Diag);

      StmtVisitorTy::Visit(E->getFalseExpr());
      if (Diag.empty())
        return;

      Diag.clear();
      StmtVisitorTy::Visit(E->getTrueExpr());
      if (Diag.empty())
        return;
    }

    Error(E, diag::note_constexpr_conditional_never_const);
  }


  template<typename ConditionalOperator>
  bool HandleConditionalOperator(const ConditionalOperator *E) {
    bool BoolResult;
    if (!EvaluateAsBooleanCondition(E->getCond(), BoolResult, Info)) {
      if (Info.checkingPotentialConstantExpression())
        CheckPotentialConstantConditional(E);
      return false;
    }

    Expr *EvalExpr = BoolResult ? E->getTrueExpr() : E->getFalseExpr();
    return StmtVisitorTy::Visit(EvalExpr);
  }

protected:
  EvalInfo &Info;
  typedef ConstStmtVisitor<Derived, bool> StmtVisitorTy;
  typedef ExprEvaluatorBase ExprEvaluatorBaseTy;

  OptionalDiagnostic CCEDiag(const Expr *E, diag::kind D) {
    return Info.CCEDiag(E, D);
  }

  bool ZeroInitialization(const Expr *E) { return Error(E); }

public:
  ExprEvaluatorBase(EvalInfo &Info) : Info(Info) {}

  EvalInfo &getEvalInfo() { return Info; }

  /// Report an evaluation error. This should only be called when an error is
  /// first discovered. When propagating an error, just return false.
  bool Error(const Expr *E, diag::kind D) {
    Info.Diag(E, D);
    return false;
  }
  bool Error(const Expr *E) {
    return Error(E, diag::note_invalid_subexpr_in_const_expr);
  }

  bool VisitStmt(const Stmt *) {
    llvm_unreachable("Expression evaluator should not be called on stmts");
  }
  bool VisitExpr(const Expr *E) {
    return Error(E);
  }

  bool VisitParenExpr(const ParenExpr *E)
    { return StmtVisitorTy::Visit(E->getSubExpr()); }
  bool VisitUnaryExtension(const UnaryOperator *E)
    { return StmtVisitorTy::Visit(E->getSubExpr()); }
  bool VisitUnaryPlus(const UnaryOperator *E)
    { return StmtVisitorTy::Visit(E->getSubExpr()); }
  bool VisitChooseExpr(const ChooseExpr *E)
    { return StmtVisitorTy::Visit(E->getChosenSubExpr()); }
  bool VisitGenericSelectionExpr(const GenericSelectionExpr *E)
    { return StmtVisitorTy::Visit(E->getResultExpr()); }
  bool VisitSubstNonTypeTemplateParmExpr(const SubstNonTypeTemplateParmExpr *E)
    { return StmtVisitorTy::Visit(E->getReplacement()); }
  bool VisitCXXDefaultArgExpr(const CXXDefaultArgExpr *E)
    { return StmtVisitorTy::Visit(E->getExpr()); }
  bool VisitCXXDefaultInitExpr(const CXXDefaultInitExpr *E) {
    // The initializer may not have been parsed yet, or might be erroneous.
    if (!E->getExpr())
      return Error(E);
    return StmtVisitorTy::Visit(E->getExpr());
  }
  // We cannot create any objects for which cleanups are required, so there is
  // nothing to do here; all cleanups must come from unevaluated subexpressions.
  bool VisitExprWithCleanups(const ExprWithCleanups *E)
    { return StmtVisitorTy::Visit(E->getSubExpr()); }

  bool VisitCXXReinterpretCastExpr(const CXXReinterpretCastExpr *E) {
    CCEDiag(E, diag::note_constexpr_invalid_cast) << 0;
    return static_cast<Derived*>(this)->VisitCastExpr(E);
  }
  bool VisitCXXDynamicCastExpr(const CXXDynamicCastExpr *E) {
    CCEDiag(E, diag::note_constexpr_invalid_cast) << 1;
    return static_cast<Derived*>(this)->VisitCastExpr(E);
  }

  bool VisitBinaryOperator(const BinaryOperator *E) {
    switch (E->getOpcode()) {
    default:
      return Error(E);

    case BO_Comma:
      VisitIgnoredValue(E->getLHS());
      return StmtVisitorTy::Visit(E->getRHS());

    case BO_PtrMemD:
    case BO_PtrMemI: {
      LValue Obj;
      if (!HandleMemberPointerAccess(Info, E, Obj))
        return false;
      APValue Result;
      if (!handleLValueToRValueConversion(Info, E, E->getType(), Obj, Result))
        return false;
      return DerivedSuccess(Result, E);
    }
    }
  }

  bool VisitBinaryConditionalOperator(const BinaryConditionalOperator *E) {
    // Evaluate and cache the common expression. We treat it as a temporary,
    // even though it's not quite the same thing.
    if (!Evaluate(Info.CurrentCall->createTemporary(E->getOpaqueValue(), false),
                  Info, E->getCommon()))
      return false;

    return HandleConditionalOperator(E);
  }

  bool VisitConditionalOperator(const ConditionalOperator *E) {
    bool IsBcpCall = false;
    // If the condition (ignoring parens) is a __builtin_constant_p call,
    // the result is a constant expression if it can be folded without
    // side-effects. This is an important GNU extension. See GCC PR38377
    // for discussion.
    if (const CallExpr *CallCE =
          dyn_cast<CallExpr>(E->getCond()->IgnoreParenCasts()))
      if (CallCE->getBuiltinCallee() == Builtin::BI__builtin_constant_p)
        IsBcpCall = true;

    // Always assume __builtin_constant_p(...) ? ... : ... is a potential
    // constant expression; we can't check whether it's potentially foldable.
    if (Info.checkingPotentialConstantExpression() && IsBcpCall)
      return false;

    FoldConstant Fold(Info, IsBcpCall);
    if (!HandleConditionalOperator(E)) {
      Fold.keepDiagnostics();
      return false;
    }

    return true;
  }

  bool VisitOpaqueValueExpr(const OpaqueValueExpr *E) {
    if (APValue *Value = Info.CurrentCall->getTemporary(E))
      return DerivedSuccess(*Value, E);

    const Expr *Source = E->getSourceExpr();
    if (!Source)
      return Error(E);
    if (Source == E) { // sanity checking.
      assert(0 && "OpaqueValueExpr recursively refers to itself");
      return Error(E);
    }
    return StmtVisitorTy::Visit(Source);
  }

  bool VisitCallExpr(const CallExpr *E) {
    const Expr *Callee = E->getCallee()->IgnoreParens();
    QualType CalleeType = Callee->getType();

    const FunctionDecl *FD = nullptr;
    LValue *This = nullptr, ThisVal;
    ArrayRef<const Expr *> Args(E->getArgs(), E->getNumArgs());
    bool HasQualifier = false;

    // Extract function decl and 'this' pointer from the callee.
    if (CalleeType->isSpecificBuiltinType(BuiltinType::BoundMember)) {
      const ValueDecl *Member = nullptr;
      if (const MemberExpr *ME = dyn_cast<MemberExpr>(Callee)) {
        // Explicit bound member calls, such as x.f() or p->g();
        if (!EvaluateObjectArgument(Info, ME->getBase(), ThisVal))
          return false;
        Member = ME->getMemberDecl();
        This = &ThisVal;
        HasQualifier = ME->hasQualifier();
      } else if (const BinaryOperator *BE = dyn_cast<BinaryOperator>(Callee)) {
        // Indirect bound member calls ('.*' or '->*').
        Member = HandleMemberPointerAccess(Info, BE, ThisVal, false);
        if (!Member) return false;
        This = &ThisVal;
      } else
        return Error(Callee);

      FD = dyn_cast<FunctionDecl>(Member);
      if (!FD)
        return Error(Callee);
    } else if (CalleeType->isFunctionPointerType()) {
      LValue Call;
      if (!EvaluatePointer(Callee, Call, Info))
        return false;

      if (!Call.getLValueOffset().isZero())
        return Error(Callee);
      FD = dyn_cast_or_null<FunctionDecl>(
                             Call.getLValueBase().dyn_cast<const ValueDecl*>());
      if (!FD)
        return Error(Callee);

      // Overloaded operator calls to member functions are represented as normal
      // calls with '*this' as the first argument.
      const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(FD);
      if (MD && !MD->isStatic()) {
        // FIXME: When selecting an implicit conversion for an overloaded
        // operator delete, we sometimes try to evaluate calls to conversion
        // operators without a 'this' parameter!
        if (Args.empty())
          return Error(E);

        if (!EvaluateObjectArgument(Info, Args[0], ThisVal))
          return false;
        This = &ThisVal;
        Args = Args.slice(1);
      }

      // Don't call function pointers which have been cast to some other type.
      if (!Info.Ctx.hasSameType(CalleeType->getPointeeType(), FD->getType()))
        return Error(E);
    } else
      return Error(E);

    if (This && !This->checkSubobject(Info, E, CSK_This))
      return false;

    // DR1358 allows virtual constexpr functions in some cases. Don't allow
    // calls to such functions in constant expressions.
    if (This && !HasQualifier &&
        isa<CXXMethodDecl>(FD) && cast<CXXMethodDecl>(FD)->isVirtual())
      return Error(E, diag::note_constexpr_virtual_call);

    const FunctionDecl *Definition = nullptr;
    Stmt *Body = FD->getBody(Definition);
    APValue Result;

    if (!CheckConstexprFunction(Info, E->getExprLoc(), FD, Definition) ||
        !HandleFunctionCall(E->getExprLoc(), Definition, This, Args, Body,
                            Info, Result))
      return false;

    return DerivedSuccess(Result, E);
  }

  bool VisitCompoundLiteralExpr(const CompoundLiteralExpr *E) {
    return StmtVisitorTy::Visit(E->getInitializer());
  }
  bool VisitInitListExpr(const InitListExpr *E) {
    if (E->getNumInits() == 0)
      return DerivedZeroInitialization(E);
    if (E->getNumInits() == 1)
      return StmtVisitorTy::Visit(E->getInit(0));
    return Error(E);
  }
  bool VisitImplicitValueInitExpr(const ImplicitValueInitExpr *E) {
    return DerivedZeroInitialization(E);
  }
  bool VisitCXXScalarValueInitExpr(const CXXScalarValueInitExpr *E) {
    return DerivedZeroInitialization(E);
  }
  bool VisitCXXNullPtrLiteralExpr(const CXXNullPtrLiteralExpr *E) {
    return DerivedZeroInitialization(E);
  }

  /// A member expression where the object is a prvalue is itself a prvalue.
  bool VisitMemberExpr(const MemberExpr *E) {
    assert(!E->isArrow() && "missing call to bound member function?");

    APValue Val;
    if (!Evaluate(Val, Info, E->getBase()))
      return false;

    QualType BaseTy = E->getBase()->getType();

    const FieldDecl *FD = dyn_cast<FieldDecl>(E->getMemberDecl());
    if (!FD) return Error(E);
    assert(!FD->getType()->isReferenceType() && "prvalue reference?");
    assert(BaseTy->castAs<RecordType>()->getDecl()->getCanonicalDecl() ==
           FD->getParent()->getCanonicalDecl() && "record / field mismatch");

    CompleteObject Obj(&Val, BaseTy);
    SubobjectDesignator Designator(BaseTy);
    Designator.addDeclUnchecked(FD);

    APValue Result;
    return extractSubobject(Info, E, Obj, Designator, Result) &&
           DerivedSuccess(Result, E);
  }

  bool VisitCastExpr(const CastExpr *E) {
    switch (E->getCastKind()) {
    default:
      break;

    case CK_AtomicToNonAtomic: {
      APValue AtomicVal;
      if (!EvaluateAtomic(E->getSubExpr(), AtomicVal, Info))
        return false;
      return DerivedSuccess(AtomicVal, E);
    }

    case CK_NoOp:
    case CK_UserDefinedConversion:
      return StmtVisitorTy::Visit(E->getSubExpr());

    case CK_LValueToRValue: {
      LValue LVal;
      if (!EvaluateLValue(E->getSubExpr(), LVal, Info))
        return false;
      APValue RVal;
      // Note, we use the subexpression's type in order to retain cv-qualifiers.
      if (!handleLValueToRValueConversion(Info, E, E->getSubExpr()->getType(),
                                          LVal, RVal))
        return false;
      return DerivedSuccess(RVal, E);
    }
    }

    return Error(E);
  }

  bool VisitUnaryPostInc(const UnaryOperator *UO) {
    return VisitUnaryPostIncDec(UO);
  }
  bool VisitUnaryPostDec(const UnaryOperator *UO) {
    return VisitUnaryPostIncDec(UO);
  }
  bool VisitUnaryPostIncDec(const UnaryOperator *UO) {
    if (!Info.getLangOpts().CPlusPlus1y && !Info.keepEvaluatingAfterFailure())
      return Error(UO);

    LValue LVal;
    if (!EvaluateLValue(UO->getSubExpr(), LVal, Info))
      return false;
    APValue RVal;
    if (!handleIncDec(this->Info, UO, LVal, UO->getSubExpr()->getType(),
                      UO->isIncrementOp(), &RVal))
      return false;
    return DerivedSuccess(RVal, UO);
  }

  bool VisitStmtExpr(const StmtExpr *E) {
    // We will have checked the full-expressions inside the statement expression
    // when they were completed, and don't need to check them again now.
    if (Info.checkingForOverflow())
      return Error(E);

    BlockScopeRAII Scope(Info);
    const CompoundStmt *CS = E->getSubStmt();
    for (CompoundStmt::const_body_iterator BI = CS->body_begin(),
                                           BE = CS->body_end();
         /**/; ++BI) {
      if (BI + 1 == BE) {
        const Expr *FinalExpr = dyn_cast<Expr>(*BI);
        if (!FinalExpr) {
          Info.Diag((*BI)->getLocStart(),
                    diag::note_constexpr_stmt_expr_unsupported);
          return false;
        }
        return this->Visit(FinalExpr);
      }

      APValue ReturnValue;
      EvalStmtResult ESR = EvaluateStmt(ReturnValue, Info, *BI);
      if (ESR != ESR_Succeeded) {
        // FIXME: If the statement-expression terminated due to 'return',
        // 'break', or 'continue', it would be nice to propagate that to
        // the outer statement evaluation rather than bailing out.
        if (ESR != ESR_Failed)
          Info.Diag((*BI)->getLocStart(),
                    diag::note_constexpr_stmt_expr_unsupported);
        return false;
      }
    }
  }

  /// Visit a value which is evaluated, but whose value is ignored.
  void VisitIgnoredValue(const Expr *E) {
    EvaluateIgnoredValue(Info, E);
  }
};

}

//===----------------------------------------------------------------------===//
// Common base class for lvalue and temporary evaluation.
//===----------------------------------------------------------------------===//
namespace {
template<class Derived>
class LValueExprEvaluatorBase
  : public ExprEvaluatorBase<Derived> {
protected:
  LValue &Result;
  typedef LValueExprEvaluatorBase LValueExprEvaluatorBaseTy;
  typedef ExprEvaluatorBase<Derived> ExprEvaluatorBaseTy;

  bool Success(APValue::LValueBase B) {
    Result.set(B);
    return true;
  }

public:
  LValueExprEvaluatorBase(EvalInfo &Info, LValue &Result) :
    ExprEvaluatorBaseTy(Info), Result(Result) {}

  bool Success(const APValue &V, const Expr *E) {
    Result.setFrom(this->Info.Ctx, V);
    return true;
  }

  bool VisitMemberExpr(const MemberExpr *E) {
    // Handle non-static data members.
    QualType BaseTy;
    if (E->isArrow()) {
      if (!EvaluatePointer(E->getBase(), Result, this->Info))
        return false;
      BaseTy = E->getBase()->getType()->castAs<PointerType>()->getPointeeType();
    } else if (E->getBase()->isRValue()) {
      assert(E->getBase()->getType()->isRecordType());
      if (!EvaluateTemporary(E->getBase(), Result, this->Info))
        return false;
      BaseTy = E->getBase()->getType();
    } else {
      if (!this->Visit(E->getBase()))
        return false;
      BaseTy = E->getBase()->getType();
    }

    const ValueDecl *MD = E->getMemberDecl();
    if (const FieldDecl *FD = dyn_cast<FieldDecl>(E->getMemberDecl())) {
      assert(BaseTy->getAs<RecordType>()->getDecl()->getCanonicalDecl() ==
             FD->getParent()->getCanonicalDecl() && "record / field mismatch");
      (void)BaseTy;
      if (!HandleLValueMember(this->Info, E, Result, FD))
        return false;
    } else if (const IndirectFieldDecl *IFD = dyn_cast<IndirectFieldDecl>(MD)) {
      if (!HandleLValueIndirectMember(this->Info, E, Result, IFD))
        return false;
    } else
      return this->Error(E);

    if (MD->getType()->isReferenceType()) {
      APValue RefValue;
      if (!handleLValueToRValueConversion(this->Info, E, MD->getType(), Result,
                                          RefValue))
        return false;
      return Success(RefValue, E);
    }
    return true;
  }

  bool VisitBinaryOperator(const BinaryOperator *E) {
    switch (E->getOpcode()) {
    default:
      return ExprEvaluatorBaseTy::VisitBinaryOperator(E);

    case BO_PtrMemD:
    case BO_PtrMemI:
      return HandleMemberPointerAccess(this->Info, E, Result);
    }
  }

  bool VisitCastExpr(const CastExpr *E) {
    switch (E->getCastKind()) {
    default:
      return ExprEvaluatorBaseTy::VisitCastExpr(E);

    case CK_DerivedToBase:
    case CK_UncheckedDerivedToBase:
      if (!this->Visit(E->getSubExpr()))
        return false;

      // Now figure out the necessary offset to add to the base LV to get from
      // the derived class to the base class.
      return HandleLValueBasePath(this->Info, E, E->getSubExpr()->getType(),
                                  Result);
    }
  }
};
}

//===----------------------------------------------------------------------===//
// LValue Evaluation
//
// This is used for evaluating lvalues (in C and C++), xvalues (in C++11),
// function designators (in C), decl references to void objects (in C), and
// temporaries (if building with -Wno-address-of-temporary).
//
// LValue evaluation produces values comprising a base expression of one of the
// following types:
// - Declarations
//  * VarDecl
//  * FunctionDecl
// - Literals
//  * CompoundLiteralExpr in C
//  * StringLiteral
//  * CXXTypeidExpr
//  * PredefinedExpr
//  * ObjCStringLiteralExpr
//  * ObjCEncodeExpr
//  * AddrLabelExpr
//  * BlockExpr
//  * CallExpr for a MakeStringConstant builtin
// - Locals and temporaries
//  * MaterializeTemporaryExpr
//  * Any Expr, with a CallIndex indicating the function in which the temporary
//    was evaluated, for cases where the MaterializeTemporaryExpr is missing
//    from the AST (FIXME).
//  * A MaterializeTemporaryExpr that has static storage duration, with no
//    CallIndex, for a lifetime-extended temporary.
// plus an offset in bytes.
//===----------------------------------------------------------------------===//
namespace {
class LValueExprEvaluator
  : public LValueExprEvaluatorBase<LValueExprEvaluator> {
public:
  LValueExprEvaluator(EvalInfo &Info, LValue &Result) :
    LValueExprEvaluatorBaseTy(Info, Result) {}

  bool VisitVarDecl(const Expr *E, const VarDecl *VD);
  bool VisitUnaryPreIncDec(const UnaryOperator *UO);

  bool VisitDeclRefExpr(const DeclRefExpr *E);
  bool VisitPredefinedExpr(const PredefinedExpr *E) { return Success(E); }
  bool VisitMaterializeTemporaryExpr(const MaterializeTemporaryExpr *E);
  bool VisitCompoundLiteralExpr(const CompoundLiteralExpr *E);
  bool VisitMemberExpr(const MemberExpr *E);
  bool VisitStringLiteral(const StringLiteral *E) { return Success(E); }
  bool VisitObjCEncodeExpr(const ObjCEncodeExpr *E) { return Success(E); }
  bool VisitCXXTypeidExpr(const CXXTypeidExpr *E);
  bool VisitCXXUuidofExpr(const CXXUuidofExpr *E);
  bool VisitArraySubscriptExpr(const ArraySubscriptExpr *E);
  bool VisitUnaryDeref(const UnaryOperator *E);
  bool VisitUnaryReal(const UnaryOperator *E);
  bool VisitUnaryImag(const UnaryOperator *E);
  bool VisitUnaryPreInc(const UnaryOperator *UO) {
    return VisitUnaryPreIncDec(UO);
  }
  bool VisitUnaryPreDec(const UnaryOperator *UO) {
    return VisitUnaryPreIncDec(UO);
  }
  bool VisitBinAssign(const BinaryOperator *BO);
  bool VisitCompoundAssignOperator(const CompoundAssignOperator *CAO);

  bool VisitCastExpr(const CastExpr *E) {
    switch (E->getCastKind()) {
    default:
      return LValueExprEvaluatorBaseTy::VisitCastExpr(E);

    case CK_LValueBitCast:
      this->CCEDiag(E, diag::note_constexpr_invalid_cast) << 2;
      if (!Visit(E->getSubExpr()))
        return false;
      Result.Designator.setInvalid();
      return true;

    case CK_BaseToDerived:
      if (!Visit(E->getSubExpr()))
        return false;
      return HandleBaseToDerivedCast(Info, E, Result);
    }
  }
};
} // end anonymous namespace

/// Evaluate an expression as an lvalue. This can be legitimately called on
/// expressions which are not glvalues, in two cases:
///  * function designators in C, and
///  * "extern void" objects
static bool EvaluateLValue(const Expr *E, LValue &Result, EvalInfo &Info) {
  assert(E->isGLValue() || E->getType()->isFunctionType() ||
         E->getType()->isVoidType());
  return LValueExprEvaluator(Info, Result).Visit(E);
}

bool LValueExprEvaluator::VisitDeclRefExpr(const DeclRefExpr *E) {
  if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(E->getDecl()))
    return Success(FD);
  if (const VarDecl *VD = dyn_cast<VarDecl>(E->getDecl()))
    return VisitVarDecl(E, VD);
  return Error(E);
}

bool LValueExprEvaluator::VisitVarDecl(const Expr *E, const VarDecl *VD) {
  CallStackFrame *Frame = nullptr;
  if (VD->hasLocalStorage() && Info.CurrentCall->Index > 1)
    Frame = Info.CurrentCall;

  if (!VD->getType()->isReferenceType()) {
    if (Frame) {
      Result.set(VD, Frame->Index);
      return true;
    }
    return Success(VD);
  }

  APValue *V;
  if (!evaluateVarDeclInit(Info, E, VD, Frame, V))
    return false;
  if (V->isUninit()) {
    if (!Info.checkingPotentialConstantExpression())
      Info.Diag(E, diag::note_constexpr_use_uninit_reference);
    return false;
  }
  return Success(*V, E);
}

bool LValueExprEvaluator::VisitMaterializeTemporaryExpr(
    const MaterializeTemporaryExpr *E) {
  // Walk through the expression to find the materialized temporary itself.
  SmallVector<const Expr *, 2> CommaLHSs;
  SmallVector<SubobjectAdjustment, 2> Adjustments;
  const Expr *Inner = E->GetTemporaryExpr()->
      skipRValueSubobjectAdjustments(CommaLHSs, Adjustments);

  // If we passed any comma operators, evaluate their LHSs.
  for (unsigned I = 0, N = CommaLHSs.size(); I != N; ++I)
    if (!EvaluateIgnoredValue(Info, CommaLHSs[I]))
      return false;

  // A materialized temporary with static storage duration can appear within the
  // result of a constant expression evaluation, so we need to preserve its
  // value for use outside this evaluation.
  APValue *Value;
  if (E->getStorageDuration() == SD_Static) {
    Value = Info.Ctx.getMaterializedTemporaryValue(E, true);
    *Value = APValue();
    Result.set(E);
  } else {
    Value = &Info.CurrentCall->
        createTemporary(E, E->getStorageDuration() == SD_Automatic);
    Result.set(E, Info.CurrentCall->Index);
  }

  QualType Type = Inner->getType();

  // Materialize the temporary itself.
  if (!EvaluateInPlace(*Value, Info, Result, Inner) ||
      (E->getStorageDuration() == SD_Static &&
       !CheckConstantExpression(Info, E->getExprLoc(), Type, *Value))) {
    *Value = APValue();
    return false;
  }

  // Adjust our lvalue to refer to the desired subobject.
  for (unsigned I = Adjustments.size(); I != 0; /**/) {
    --I;
    switch (Adjustments[I].Kind) {
    case SubobjectAdjustment::DerivedToBaseAdjustment:
      if (!HandleLValueBasePath(Info, Adjustments[I].DerivedToBase.BasePath,
                                Type, Result))
        return false;
      Type = Adjustments[I].DerivedToBase.BasePath->getType();
      break;

    case SubobjectAdjustment::FieldAdjustment:
      if (!HandleLValueMember(Info, E, Result, Adjustments[I].Field))
        return false;
      Type = Adjustments[I].Field->getType();
      break;

    case SubobjectAdjustment::MemberPointerAdjustment:
      if (!HandleMemberPointerAccess(this->Info, Type, Result,
                                     Adjustments[I].Ptr.RHS))
        return false;
      Type = Adjustments[I].Ptr.MPT->getPointeeType();
      break;
    }
  }

  return true;
}

bool
LValueExprEvaluator::VisitCompoundLiteralExpr(const CompoundLiteralExpr *E) {
  assert(!Info.getLangOpts().CPlusPlus && "lvalue compound literal in c++?");
  // Defer visiting the literal until the lvalue-to-rvalue conversion. We can
  // only see this when folding in C, so there's no standard to follow here.
  return Success(E);
}

bool LValueExprEvaluator::VisitCXXTypeidExpr(const CXXTypeidExpr *E) {
  if (!E->isPotentiallyEvaluated())
    return Success(E);

  Info.Diag(E, diag::note_constexpr_typeid_polymorphic)
    << E->getExprOperand()->getType()
    << E->getExprOperand()->getSourceRange();
  return false;
}

bool LValueExprEvaluator::VisitCXXUuidofExpr(const CXXUuidofExpr *E) {
  return Success(E);
}

bool LValueExprEvaluator::VisitMemberExpr(const MemberExpr *E) {
  // Handle static data members.
  if (const VarDecl *VD = dyn_cast<VarDecl>(E->getMemberDecl())) {
    VisitIgnoredValue(E->getBase());
    return VisitVarDecl(E, VD);
  }

  // Handle static member functions.
  if (const CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(E->getMemberDecl())) {
    if (MD->isStatic()) {
      VisitIgnoredValue(E->getBase());
      return Success(MD);
    }
  }

  // Handle non-static data members.
  return LValueExprEvaluatorBaseTy::VisitMemberExpr(E);
}

bool LValueExprEvaluator::VisitArraySubscriptExpr(const ArraySubscriptExpr *E) {
  // FIXME: Deal with vectors as array subscript bases.
  if (E->getBase()->getType()->isVectorType())
    return Error(E);

  if (!EvaluatePointer(E->getBase(), Result, Info))
    return false;

  APSInt Index;
  if (!EvaluateInteger(E->getIdx(), Index, Info))
    return false;

  return HandleLValueArrayAdjustment(Info, E, Result, E->getType(),
                                     getExtValue(Index));
}

bool LValueExprEvaluator::VisitUnaryDeref(const UnaryOperator *E) {
  return EvaluatePointer(E->getSubExpr(), Result, Info);
}

bool LValueExprEvaluator::VisitUnaryReal(const UnaryOperator *E) {
  if (!Visit(E->getSubExpr()))
    return false;
  // __real is a no-op on scalar lvalues.
  if (E->getSubExpr()->getType()->isAnyComplexType())
    HandleLValueComplexElement(Info, E, Result, E->getType(), false);
  return true;
}

bool LValueExprEvaluator::VisitUnaryImag(const UnaryOperator *E) {
  assert(E->getSubExpr()->getType()->isAnyComplexType() &&
         "lvalue __imag__ on scalar?");
  if (!Visit(E->getSubExpr()))
    return false;
  HandleLValueComplexElement(Info, E, Result, E->getType(), true);
  return true;
}

bool LValueExprEvaluator::VisitUnaryPreIncDec(const UnaryOperator *UO) {
  if (!Info.getLangOpts().CPlusPlus1y && !Info.keepEvaluatingAfterFailure())
    return Error(UO);

  if (!this->Visit(UO->getSubExpr()))
    return false;

  return handleIncDec(
      this->Info, UO, Result, UO->getSubExpr()->getType(),
      UO->isIncrementOp(), nullptr);
}

bool LValueExprEvaluator::VisitCompoundAssignOperator(
    const CompoundAssignOperator *CAO) {
  if (!Info.getLangOpts().CPlusPlus1y && !Info.keepEvaluatingAfterFailure())
    return Error(CAO);

  APValue RHS;

  // The overall lvalue result is the result of evaluating the LHS.
  if (!this->Visit(CAO->getLHS())) {
    if (Info.keepEvaluatingAfterFailure())
      Evaluate(RHS, this->Info, CAO->getRHS());
    return false;
  }

  if (!Evaluate(RHS, this->Info, CAO->getRHS()))
    return false;

  return handleCompoundAssignment(
      this->Info, CAO,
      Result, CAO->getLHS()->getType(), CAO->getComputationLHSType(),
      CAO->getOpForCompoundAssignment(CAO->getOpcode()), RHS);
}

bool LValueExprEvaluator::VisitBinAssign(const BinaryOperator *E) {
  if (!Info.getLangOpts().CPlusPlus1y && !Info.keepEvaluatingAfterFailure())
    return Error(E);

  APValue NewVal;

  if (!this->Visit(E->getLHS())) {
    if (Info.keepEvaluatingAfterFailure())
      Evaluate(NewVal, this->Info, E->getRHS());
    return false;
  }

  if (!Evaluate(NewVal, this->Info, E->getRHS()))
    return false;

  return handleAssignment(this->Info, E, Result, E->getLHS()->getType(),
                          NewVal);
}

//===----------------------------------------------------------------------===//
// Pointer Evaluation
//===----------------------------------------------------------------------===//

namespace {
class PointerExprEvaluator
  : public ExprEvaluatorBase<PointerExprEvaluator> {
  LValue &Result;

  bool Success(const Expr *E) {
    Result.set(E);
    return true;
  }
public:

  PointerExprEvaluator(EvalInfo &info, LValue &Result)
    : ExprEvaluatorBaseTy(info), Result(Result) {}

  bool Success(const APValue &V, const Expr *E) {
    Result.setFrom(Info.Ctx, V);
    return true;
  }
  bool ZeroInitialization(const Expr *E) {
    return Success((Expr*)nullptr);
  }

  bool VisitBinaryOperator(const BinaryOperator *E);
  bool VisitCastExpr(const CastExpr* E);
  bool VisitUnaryAddrOf(const UnaryOperator *E);
  bool VisitObjCStringLiteral(const ObjCStringLiteral *E)
      { return Success(E); }
  bool VisitObjCBoxedExpr(const ObjCBoxedExpr *E)
      { return Success(E); }
  bool VisitAddrLabelExpr(const AddrLabelExpr *E)
      { return Success(E); }
  bool VisitCallExpr(const CallExpr *E);
  bool VisitBlockExpr(const BlockExpr *E) {
    if (!E->getBlockDecl()->hasCaptures())
      return Success(E);
    return Error(E);
  }
  bool VisitCXXThisExpr(const CXXThisExpr *E) {
    // Can't look at 'this' when checking a potential constant expression.
    if (Info.checkingPotentialConstantExpression())
      return false;
    if (!Info.CurrentCall->This) {
      if (Info.getLangOpts().CPlusPlus11)
        Info.Diag(E, diag::note_constexpr_this) << E->isImplicit();
      else
        Info.Diag(E);
      return false;
    }
    Result = *Info.CurrentCall->This;
    return true;
  }

  // FIXME: Missing: @protocol, @selector
};
} // end anonymous namespace

static bool EvaluatePointer(const Expr* E, LValue& Result, EvalInfo &Info) {
  assert(E->isRValue() && E->getType()->hasPointerRepresentation());
  return PointerExprEvaluator(Info, Result).Visit(E);
}

bool PointerExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) {
  if (E->getOpcode() != BO_Add &&
      E->getOpcode() != BO_Sub)
    return ExprEvaluatorBaseTy::VisitBinaryOperator(E);

  const Expr *PExp = E->getLHS();
  const Expr *IExp = E->getRHS();
  if (IExp->getType()->isPointerType())
    std::swap(PExp, IExp);

  bool EvalPtrOK = EvaluatePointer(PExp, Result, Info);
  if (!EvalPtrOK && !Info.keepEvaluatingAfterFailure())
    return false;

  llvm::APSInt Offset;
  if (!EvaluateInteger(IExp, Offset, Info) || !EvalPtrOK)
    return false;

  int64_t AdditionalOffset = getExtValue(Offset);
  if (E->getOpcode() == BO_Sub)
    AdditionalOffset = -AdditionalOffset;

  QualType Pointee = PExp->getType()->castAs<PointerType>()->getPointeeType();
  return HandleLValueArrayAdjustment(Info, E, Result, Pointee,
                                     AdditionalOffset);
}

bool PointerExprEvaluator::VisitUnaryAddrOf(const UnaryOperator *E) {
  return EvaluateLValue(E->getSubExpr(), Result, Info);
}

bool PointerExprEvaluator::VisitCastExpr(const CastExpr* E) {
  const Expr* SubExpr = E->getSubExpr();

  switch (E->getCastKind()) {
  default:
    break;

  case CK_BitCast:
  case CK_CPointerToObjCPointerCast:
  case CK_BlockPointerToObjCPointerCast:
  case CK_AnyPointerToBlockPointerCast:
    if (!Visit(SubExpr))
      return false;
    // Bitcasts to cv void* are static_casts, not reinterpret_casts, so are
    // permitted in constant expressions in C++11. Bitcasts from cv void* are
    // also static_casts, but we disallow them as a resolution to DR1312.
    if (!E->getType()->isVoidPointerType()) {
      Result.Designator.setInvalid();
      if (SubExpr->getType()->isVoidPointerType())
        CCEDiag(E, diag::note_constexpr_invalid_cast)
          << 3 << SubExpr->getType();
      else
        CCEDiag(E, diag::note_constexpr_invalid_cast) << 2;
    }
    return true;

  case CK_DerivedToBase:
  case CK_UncheckedDerivedToBase:
    if (!EvaluatePointer(E->getSubExpr(), Result, Info))
      return false;
    if (!Result.Base && Result.Offset.isZero())
      return true;

    // Now figure out the necessary offset to add to the base LV to get from
    // the derived class to the base class.
    return HandleLValueBasePath(Info, E, E->getSubExpr()->getType()->
                                  castAs<PointerType>()->getPointeeType(),
                                Result);

  case CK_BaseToDerived:
    if (!Visit(E->getSubExpr()))
      return false;
    if (!Result.Base && Result.Offset.isZero())
      return true;
    return HandleBaseToDerivedCast(Info, E, Result);

  case CK_NullToPointer:
    VisitIgnoredValue(E->getSubExpr());
    return ZeroInitialization(E);

  case CK_IntegralToPointer: {
    CCEDiag(E, diag::note_constexpr_invalid_cast) << 2;

    APValue Value;
    if (!EvaluateIntegerOrLValue(SubExpr, Value, Info))
      break;

    if (Value.isInt()) {
      unsigned Size = Info.Ctx.getTypeSize(E->getType());
      uint64_t N = Value.getInt().extOrTrunc(Size).getZExtValue();
      Result.Base = (Expr*)nullptr;
      Result.Offset = CharUnits::fromQuantity(N);
      Result.CallIndex = 0;
      Result.Designator.setInvalid();
      return true;
    } else {
      // Cast is of an lvalue, no need to change value.
      Result.setFrom(Info.Ctx, Value);
      return true;
    }
  }
  case CK_ArrayToPointerDecay:
    if (SubExpr->isGLValue()) {
      if (!EvaluateLValue(SubExpr, Result, Info))
        return false;
    } else {
      Result.set(SubExpr, Info.CurrentCall->Index);
      if (!EvaluateInPlace(Info.CurrentCall->createTemporary(SubExpr, false),
                           Info, Result, SubExpr))
        return false;
    }
    // The result is a pointer to the first element of the array.
    if (const ConstantArrayType *CAT
          = Info.Ctx.getAsConstantArrayType(SubExpr->getType()))
      Result.addArray(Info, E, CAT);
    else
      Result.Designator.setInvalid();
    return true;

  case CK_FunctionToPointerDecay:
    return EvaluateLValue(SubExpr, Result, Info);
  }

  return ExprEvaluatorBaseTy::VisitCastExpr(E);
}

bool PointerExprEvaluator::VisitCallExpr(const CallExpr *E) {
  if (IsStringLiteralCall(E))
    return Success(E);

  switch (E->getBuiltinCallee()) {
  case Builtin::BI__builtin_addressof:
    return EvaluateLValue(E->getArg(0), Result, Info);

  default:
    return ExprEvaluatorBaseTy::VisitCallExpr(E);
  }
}

//===----------------------------------------------------------------------===//
// Member Pointer Evaluation
//===----------------------------------------------------------------------===//

namespace {
class MemberPointerExprEvaluator
  : public ExprEvaluatorBase<MemberPointerExprEvaluator> {
  MemberPtr &Result;

  bool Success(const ValueDecl *D) {
    Result = MemberPtr(D);
    return true;
  }
public:

  MemberPointerExprEvaluator(EvalInfo &Info, MemberPtr &Result)
    : ExprEvaluatorBaseTy(Info), Result(Result) {}

  bool Success(const APValue &V, const Expr *E) {
    Result.setFrom(V);
    return true;
  }
  bool ZeroInitialization(const Expr *E) {
    return Success((const ValueDecl*)nullptr);
  }

  bool VisitCastExpr(const CastExpr *E);
  bool VisitUnaryAddrOf(const UnaryOperator *E);
};
} // end anonymous namespace

static bool EvaluateMemberPointer(const Expr *E, MemberPtr &Result,
                                  EvalInfo &Info) {
  assert(E->isRValue() && E->getType()->isMemberPointerType());
  return MemberPointerExprEvaluator(Info, Result).Visit(E);
}

bool MemberPointerExprEvaluator::VisitCastExpr(const CastExpr *E) {
  switch (E->getCastKind()) {
  default:
    return ExprEvaluatorBaseTy::VisitCastExpr(E);

  case CK_NullToMemberPointer:
    VisitIgnoredValue(E->getSubExpr());
    return ZeroInitialization(E);

  case CK_BaseToDerivedMemberPointer: {
    if (!Visit(E->getSubExpr()))
      return false;
    if (E->path_empty())
      return true;
    // Base-to-derived member pointer casts store the path in derived-to-base
    // order, so iterate backwards. The CXXBaseSpecifier also provides us with
    // the wrong end of the derived->base arc, so stagger the path by one class.
    typedef std::reverse_iterator<CastExpr::path_const_iterator> ReverseIter;
    for (ReverseIter PathI(E->path_end() - 1), PathE(E->path_begin());
         PathI != PathE; ++PathI) {
      assert(!(*PathI)->isVirtual() && "memptr cast through vbase");
      const CXXRecordDecl *Derived = (*PathI)->getType()->getAsCXXRecordDecl();
      if (!Result.castToDerived(Derived))
        return Error(E);
    }
    const Type *FinalTy = E->getType()->castAs<MemberPointerType>()->getClass();
    if (!Result.castToDerived(FinalTy->getAsCXXRecordDecl()))
      return Error(E);
    return true;
  }

  case CK_DerivedToBaseMemberPointer:
    if (!Visit(E->getSubExpr()))
      return false;
    for (CastExpr::path_const_iterator PathI = E->path_begin(),
         PathE = E->path_end(); PathI != PathE; ++PathI) {
      assert(!(*PathI)->isVirtual() && "memptr cast through vbase");
      const CXXRecordDecl *Base = (*PathI)->getType()->getAsCXXRecordDecl();
      if (!Result.castToBase(Base))
        return Error(E);
    }
    return true;
  }
}

bool MemberPointerExprEvaluator::VisitUnaryAddrOf(const UnaryOperator *E) {
  // C++11 [expr.unary.op]p3 has very strict rules on how the address of a
  // member can be formed.
  return Success(cast<DeclRefExpr>(E->getSubExpr())->getDecl());
}

//===----------------------------------------------------------------------===//
// Record Evaluation
//===----------------------------------------------------------------------===//

namespace {
  class RecordExprEvaluator
  : public ExprEvaluatorBase<RecordExprEvaluator> {
    const LValue &This;
    APValue &Result;
  public:

    RecordExprEvaluator(EvalInfo &info, const LValue &This, APValue &Result)
      : ExprEvaluatorBaseTy(info), This(This), Result(Result) {}

    bool Success(const APValue &V, const Expr *E) {
      Result = V;
      return true;
    }
    bool ZeroInitialization(const Expr *E);

    bool VisitCastExpr(const CastExpr *E);
    bool VisitInitListExpr(const InitListExpr *E);
    bool VisitCXXConstructExpr(const CXXConstructExpr *E);
    bool VisitCXXStdInitializerListExpr(const CXXStdInitializerListExpr *E);
  };
}

/// Perform zero-initialization on an object of non-union class type.
/// C++11 [dcl.init]p5:
///  To zero-initialize an object or reference of type T means:
///    [...]
///    -- if T is a (possibly cv-qualified) non-union class type,
///       each non-static data member and each base-class subobject is
///       zero-initialized
static bool HandleClassZeroInitialization(EvalInfo &Info, const Expr *E,
                                          const RecordDecl *RD,
                                          const LValue &This, APValue &Result) {
  assert(!RD->isUnion() && "Expected non-union class type");
  const CXXRecordDecl *CD = dyn_cast<CXXRecordDecl>(RD);
  Result = APValue(APValue::UninitStruct(), CD ? CD->getNumBases() : 0,
                   std::distance(RD->field_begin(), RD->field_end()));

  if (RD->isInvalidDecl()) return false;
  const ASTRecordLayout &Layout = Info.Ctx.getASTRecordLayout(RD);

  if (CD) {
    unsigned Index = 0;
    for (CXXRecordDecl::base_class_const_iterator I = CD->bases_begin(),
           End = CD->bases_end(); I != End; ++I, ++Index) {
      const CXXRecordDecl *Base = I->getType()->getAsCXXRecordDecl();
      LValue Subobject = This;
      if (!HandleLValueDirectBase(Info, E, Subobject, CD, Base, &Layout))
        return false;
      if (!HandleClassZeroInitialization(Info, E, Base, Subobject,
                                         Result.getStructBase(Index)))
        return false;
    }
  }

  for (const auto *I : RD->fields()) {
    // -- if T is a reference type, no initialization is performed.
    if (I->getType()->isReferenceType())
      continue;

    LValue Subobject = This;
    if (!HandleLValueMember(Info, E, Subobject, I, &Layout))
      return false;

    ImplicitValueInitExpr VIE(I->getType());
    if (!EvaluateInPlace(
          Result.getStructField(I->getFieldIndex()), Info, Subobject, &VIE))
      return false;
  }

  return true;
}

bool RecordExprEvaluator::ZeroInitialization(const Expr *E) {
  const RecordDecl *RD = E->getType()->castAs<RecordType>()->getDecl();
  if (RD->isInvalidDecl()) return false;
  if (RD->isUnion()) {
    // C++11 [dcl.init]p5: If T is a (possibly cv-qualified) union type, the
    // object's first non-static named data member is zero-initialized
    RecordDecl::field_iterator I = RD->field_begin();
    if (I == RD->field_end()) {
      Result = APValue((const FieldDecl*)nullptr);
      return true;
    }

    LValue Subobject = This;
    if (!HandleLValueMember(Info, E, Subobject, *I))
      return false;
    Result = APValue(*I);
    ImplicitValueInitExpr VIE(I->getType());
    return EvaluateInPlace(Result.getUnionValue(), Info, Subobject, &VIE);
  }

  if (isa<CXXRecordDecl>(RD) && cast<CXXRecordDecl>(RD)->getNumVBases()) {
    Info.Diag(E, diag::note_constexpr_virtual_base) << RD;
    return false;
  }

  return HandleClassZeroInitialization(Info, E, RD, This, Result);
}

bool RecordExprEvaluator::VisitCastExpr(const CastExpr *E) {
  switch (E->getCastKind()) {
  default:
    return ExprEvaluatorBaseTy::VisitCastExpr(E);

  case CK_ConstructorConversion:
    return Visit(E->getSubExpr());

  case CK_DerivedToBase:
  case CK_UncheckedDerivedToBase: {
    APValue DerivedObject;
    if (!Evaluate(DerivedObject, Info, E->getSubExpr()))
      return false;
    if (!DerivedObject.isStruct())
      return Error(E->getSubExpr());

    // Derived-to-base rvalue conversion: just slice off the derived part.
    APValue *Value = &DerivedObject;
    const CXXRecordDecl *RD = E->getSubExpr()->getType()->getAsCXXRecordDecl();
    for (CastExpr::path_const_iterator PathI = E->path_begin(),
         PathE = E->path_end(); PathI != PathE; ++PathI) {
      assert(!(*PathI)->isVirtual() && "record rvalue with virtual base");
      const CXXRecordDecl *Base = (*PathI)->getType()->getAsCXXRecordDecl();
      Value = &Value->getStructBase(getBaseIndex(RD, Base));
      RD = Base;
    }
    Result = *Value;
    return true;
  }
  }
}

bool RecordExprEvaluator::VisitInitListExpr(const InitListExpr *E) {
  const RecordDecl *RD = E->getType()->castAs<RecordType>()->getDecl();
  if (RD->isInvalidDecl()) return false;
  const ASTRecordLayout &Layout = Info.Ctx.getASTRecordLayout(RD);

  if (RD->isUnion()) {
    const FieldDecl *Field = E->getInitializedFieldInUnion();
    Result = APValue(Field);
    if (!Field)
      return true;

    // If the initializer list for a union does not contain any elements, the
    // first element of the union is value-initialized.
    // FIXME: The element should be initialized from an initializer list.
    //        Is this difference ever observable for initializer lists which
    //        we don't build?
    ImplicitValueInitExpr VIE(Field->getType());
    const Expr *InitExpr = E->getNumInits() ? E->getInit(0) : &VIE;

    LValue Subobject = This;
    if (!HandleLValueMember(Info, InitExpr, Subobject, Field, &Layout))
      return false;

    // Temporarily override This, in case there's a CXXDefaultInitExpr in here.
    ThisOverrideRAII ThisOverride(*Info.CurrentCall, &This,
                                  isa<CXXDefaultInitExpr>(InitExpr));

    return EvaluateInPlace(Result.getUnionValue(), Info, Subobject, InitExpr);
  }

  assert((!isa<CXXRecordDecl>(RD) || !cast<CXXRecordDecl>(RD)->getNumBases()) &&
         "initializer list for class with base classes");
  Result = APValue(APValue::UninitStruct(), 0,
                   std::distance(RD->field_begin(), RD->field_end()));
  unsigned ElementNo = 0;
  bool Success = true;
  for (const auto *Field : RD->fields()) {
    // Anonymous bit-fields are not considered members of the class for
    // purposes of aggregate initialization.
    if (Field->isUnnamedBitfield())
      continue;

    LValue Subobject = This;

    bool HaveInit = ElementNo < E->getNumInits();

    // FIXME: Diagnostics here should point to the end of the initializer
    // list, not the start.
    if (!HandleLValueMember(Info, HaveInit ? E->getInit(ElementNo) : E,
                            Subobject, Field, &Layout))
      return false;

    // Perform an implicit value-initialization for members beyond the end of
    // the initializer list.
    ImplicitValueInitExpr VIE(HaveInit ? Info.Ctx.IntTy : Field->getType());
    const Expr *Init = HaveInit ? E->getInit(ElementNo++) : &VIE;

    // Temporarily override This, in case there's a CXXDefaultInitExpr in here.
    ThisOverrideRAII ThisOverride(*Info.CurrentCall, &This,
                                  isa<CXXDefaultInitExpr>(Init));

    APValue &FieldVal = Result.getStructField(Field->getFieldIndex());
    if (!EvaluateInPlace(FieldVal, Info, Subobject, Init) ||
        (Field->isBitField() && !truncateBitfieldValue(Info, Init,
                                                       FieldVal, Field))) {
      if (!Info.keepEvaluatingAfterFailure())
        return false;
      Success = false;
    }
  }

  return Success;
}

bool RecordExprEvaluator::VisitCXXConstructExpr(const CXXConstructExpr *E) {
  const CXXConstructorDecl *FD = E->getConstructor();
  if (FD->isInvalidDecl() || FD->getParent()->isInvalidDecl()) return false;

  bool ZeroInit = E->requiresZeroInitialization();
  if (CheckTrivialDefaultConstructor(Info, E->getExprLoc(), FD, ZeroInit)) {
    // If we've already performed zero-initialization, we're already done.
    if (!Result.isUninit())
      return true;

    // We can get here in two different ways:
    //  1) We're performing value-initialization, and should zero-initialize
    //     the object, or
    //  2) We're performing default-initialization of an object with a trivial
    //     constexpr default constructor, in which case we should start the
    //     lifetimes of all the base subobjects (there can be no data member
    //     subobjects in this case) per [basic.life]p1.
    // Either way, ZeroInitialization is appropriate.
    return ZeroInitialization(E);
  }

  const FunctionDecl *Definition = nullptr;
  FD->getBody(Definition);

  if (!CheckConstexprFunction(Info, E->getExprLoc(), FD, Definition))
    return false;

  // Avoid materializing a temporary for an elidable copy/move constructor.
  if (E->isElidable() && !ZeroInit)
    if (const MaterializeTemporaryExpr *ME
          = dyn_cast<MaterializeTemporaryExpr>(E->getArg(0)))
      return Visit(ME->GetTemporaryExpr());

  if (ZeroInit && !ZeroInitialization(E))
    return false;

  ArrayRef<const Expr *> Args(E->getArgs(), E->getNumArgs());
  return HandleConstructorCall(E->getExprLoc(), This, Args,
                               cast<CXXConstructorDecl>(Definition), Info,
                               Result);
}

bool RecordExprEvaluator::VisitCXXStdInitializerListExpr(
    const CXXStdInitializerListExpr *E) {
  const ConstantArrayType *ArrayType =
      Info.Ctx.getAsConstantArrayType(E->getSubExpr()->getType());

  LValue Array;
  if (!EvaluateLValue(E->getSubExpr(), Array, Info))
    return false;

  // Get a pointer to the first element of the array.
  Array.addArray(Info, E, ArrayType);

  // FIXME: Perform the checks on the field types in SemaInit.
  RecordDecl *Record = E->getType()->castAs<RecordType>()->getDecl();
  RecordDecl::field_iterator Field = Record->field_begin();
  if (Field == Record->field_end())
    return Error(E);

  // Start pointer.
  if (!Field->getType()->isPointerType() ||
      !Info.Ctx.hasSameType(Field->getType()->getPointeeType(),
                            ArrayType->getElementType()))
    return Error(E);

  // FIXME: What if the initializer_list type has base classes, etc?
  Result = APValue(APValue::UninitStruct(), 0, 2);
  Array.moveInto(Result.getStructField(0));

  if (++Field == Record->field_end())
    return Error(E);

  if (Field->getType()->isPointerType() &&
      Info.Ctx.hasSameType(Field->getType()->getPointeeType(),
                           ArrayType->getElementType())) {
    // End pointer.
    if (!HandleLValueArrayAdjustment(Info, E, Array,
                                     ArrayType->getElementType(),
                                     ArrayType->getSize().getZExtValue()))
      return false;
    Array.moveInto(Result.getStructField(1));
  } else if (Info.Ctx.hasSameType(Field->getType(), Info.Ctx.getSizeType()))
    // Length.
    Result.getStructField(1) = APValue(APSInt(ArrayType->getSize()));
  else
    return Error(E);

  if (++Field != Record->field_end())
    return Error(E);

  return true;
}

static bool EvaluateRecord(const Expr *E, const LValue &This,
                           APValue &Result, EvalInfo &Info) {
  assert(E->isRValue() && E->getType()->isRecordType() &&
         "can't evaluate expression as a record rvalue");
  return RecordExprEvaluator(Info, This, Result).Visit(E);
}

//===----------------------------------------------------------------------===//
// Temporary Evaluation
//
// Temporaries are represented in the AST as rvalues, but generally behave like
// lvalues. The full-object of which the temporary is a subobject is implicitly
// materialized so that a reference can bind to it.
//===----------------------------------------------------------------------===//
namespace {
class TemporaryExprEvaluator
  : public LValueExprEvaluatorBase<TemporaryExprEvaluator> {
public:
  TemporaryExprEvaluator(EvalInfo &Info, LValue &Result) :
    LValueExprEvaluatorBaseTy(Info, Result) {}

  /// Visit an expression which constructs the value of this temporary.
  bool VisitConstructExpr(const Expr *E) {
    Result.set(E, Info.CurrentCall->Index);
    return EvaluateInPlace(Info.CurrentCall->createTemporary(E, false),
                           Info, Result, E);
  }

  bool VisitCastExpr(const CastExpr *E) {
    switch (E->getCastKind()) {
    default:
      return LValueExprEvaluatorBaseTy::VisitCastExpr(E);

    case CK_ConstructorConversion:
      return VisitConstructExpr(E->getSubExpr());
    }
  }
  bool VisitInitListExpr(const InitListExpr *E) {
    return VisitConstructExpr(E);
  }
  bool VisitCXXConstructExpr(const CXXConstructExpr *E) {
    return VisitConstructExpr(E);
  }
  bool VisitCallExpr(const CallExpr *E) {
    return VisitConstructExpr(E);
  }
};
} // end anonymous namespace

/// Evaluate an expression of record type as a temporary.
static bool EvaluateTemporary(const Expr *E, LValue &Result, EvalInfo &Info) {
  assert(E->isRValue() && E->getType()->isRecordType());
  return TemporaryExprEvaluator(Info, Result).Visit(E);
}

//===----------------------------------------------------------------------===//
// Vector Evaluation
//===----------------------------------------------------------------------===//

namespace {
  class VectorExprEvaluator
  : public ExprEvaluatorBase<VectorExprEvaluator> {
    APValue &Result;
  public:

    VectorExprEvaluator(EvalInfo &info, APValue &Result)
      : ExprEvaluatorBaseTy(info), Result(Result) {}

    bool Success(const ArrayRef<APValue> &V, const Expr *E) {
      assert(V.size() == E->getType()->castAs<VectorType>()->getNumElements());
      // FIXME: remove this APValue copy.
      Result = APValue(V.data(), V.size());
      return true;
    }
    bool Success(const APValue &V, const Expr *E) {
      assert(V.isVector());
      Result = V;
      return true;
    }
    bool ZeroInitialization(const Expr *E);

    bool VisitUnaryReal(const UnaryOperator *E)
      { return Visit(E->getSubExpr()); }
    bool VisitCastExpr(const CastExpr* E);
    bool VisitInitListExpr(const InitListExpr *E);
    bool VisitUnaryImag(const UnaryOperator *E);
    // FIXME: Missing: unary -, unary ~, binary add/sub/mul/div,
    //                 binary comparisons, binary and/or/xor,
    //                 shufflevector, ExtVectorElementExpr
  };
} // end anonymous namespace

static bool EvaluateVector(const Expr* E, APValue& Result, EvalInfo &Info) {
  assert(E->isRValue() && E->getType()->isVectorType() &&"not a vector rvalue");
  return VectorExprEvaluator(Info, Result).Visit(E);
}

bool VectorExprEvaluator::VisitCastExpr(const CastExpr* E) {
  const VectorType *VTy = E->getType()->castAs<VectorType>();
  unsigned NElts = VTy->getNumElements();

  const Expr *SE = E->getSubExpr();
  QualType SETy = SE->getType();

  switch (E->getCastKind()) {
  case CK_VectorSplat: {
    APValue Val = APValue();
    if (SETy->isIntegerType()) {
      APSInt IntResult;
      if (!EvaluateInteger(SE, IntResult, Info))
         return false;
      Val = APValue(IntResult);
    } else if (SETy->isRealFloatingType()) {
       APFloat F(0.0);
       if (!EvaluateFloat(SE, F, Info))
         return false;
       Val = APValue(F);
    } else {
      return Error(E);
    }

    // Splat and create vector APValue.
    SmallVector<APValue, 4> Elts(NElts, Val);
    return Success(Elts, E);
  }
  case CK_BitCast: {
    // Evaluate the operand into an APInt we can extract from.
    llvm::APInt SValInt;
    if (!EvalAndBitcastToAPInt(Info, SE, SValInt))
      return false;
    // Extract the elements
    QualType EltTy = VTy->getElementType();
    unsigned EltSize = Info.Ctx.getTypeSize(EltTy);
    bool BigEndian = Info.Ctx.getTargetInfo().isBigEndian();
    SmallVector<APValue, 4> Elts;
    if (EltTy->isRealFloatingType()) {
      const llvm::fltSemantics &Sem = Info.Ctx.getFloatTypeSemantics(EltTy);
      unsigned FloatEltSize = EltSize;
      if (&Sem == &APFloat::x87DoubleExtended)
        FloatEltSize = 80;
      for (unsigned i = 0; i < NElts; i++) {
        llvm::APInt Elt;
        if (BigEndian)
          Elt = SValInt.rotl(i*EltSize+FloatEltSize).trunc(FloatEltSize);
        else
          Elt = SValInt.rotr(i*EltSize).trunc(FloatEltSize);
        Elts.push_back(APValue(APFloat(Sem, Elt)));
      }
    } else if (EltTy->isIntegerType()) {
      for (unsigned i = 0; i < NElts; i++) {
        llvm::APInt Elt;
        if (BigEndian)
          Elt = SValInt.rotl(i*EltSize+EltSize).zextOrTrunc(EltSize);
        else
          Elt = SValInt.rotr(i*EltSize).zextOrTrunc(EltSize);
        Elts.push_back(APValue(APSInt(Elt, EltTy->isSignedIntegerType())));
      }
    } else {
      return Error(E);
    }
    return Success(Elts, E);
  }
  default:
    return ExprEvaluatorBaseTy::VisitCastExpr(E);
  }
}

bool
VectorExprEvaluator::VisitInitListExpr(const InitListExpr *E) {
  const VectorType *VT = E->getType()->castAs<VectorType>();
  unsigned NumInits = E->getNumInits();
  unsigned NumElements = VT->getNumElements();

  QualType EltTy = VT->getElementType();
  SmallVector<APValue, 4> Elements;

  // The number of initializers can be less than the number of
  // vector elements. For OpenCL, this can be due to nested vector
  // initialization. For GCC compatibility, missing trailing elements
  // should be initialized with zeroes.
  unsigned CountInits = 0, CountElts = 0;
  while (CountElts < NumElements) {
    // Handle nested vector initialization.
    if (CountInits < NumInits
        && E->getInit(CountInits)->getType()->isVectorType()) {
      APValue v;
      if (!EvaluateVector(E->getInit(CountInits), v, Info))
        return Error(E);
      unsigned vlen = v.getVectorLength();
      for (unsigned j = 0; j < vlen; j++)
        Elements.push_back(v.getVectorElt(j));
      CountElts += vlen;
    } else if (EltTy->isIntegerType()) {
      llvm::APSInt sInt(32);
      if (CountInits < NumInits) {
        if (!EvaluateInteger(E->getInit(CountInits), sInt, Info))
          return false;
      } else // trailing integer zero.
        sInt = Info.Ctx.MakeIntValue(0, EltTy);
      Elements.push_back(APValue(sInt));
      CountElts++;
    } else {
      llvm::APFloat f(0.0);
      if (CountInits < NumInits) {
        if (!EvaluateFloat(E->getInit(CountInits), f, Info))
          return false;
      } else // trailing float zero.
        f = APFloat::getZero(Info.Ctx.getFloatTypeSemantics(EltTy));
      Elements.push_back(APValue(f));
      CountElts++;
    }
    CountInits++;
  }
  return Success(Elements, E);
}

bool
VectorExprEvaluator::ZeroInitialization(const Expr *E) {
  const VectorType *VT = E->getType()->getAs<VectorType>();
  QualType EltTy = VT->getElementType();
  APValue ZeroElement;
  if (EltTy->isIntegerType())
    ZeroElement = APValue(Info.Ctx.MakeIntValue(0, EltTy));
  else
    ZeroElement =
        APValue(APFloat::getZero(Info.Ctx.getFloatTypeSemantics(EltTy)));

  SmallVector<APValue, 4> Elements(VT->getNumElements(), ZeroElement);
  return Success(Elements, E);
}

bool VectorExprEvaluator::VisitUnaryImag(const UnaryOperator *E) {
  VisitIgnoredValue(E->getSubExpr());
  return ZeroInitialization(E);
}

//===----------------------------------------------------------------------===//
// Array Evaluation
//===----------------------------------------------------------------------===//

namespace {
  class ArrayExprEvaluator
  : public ExprEvaluatorBase<ArrayExprEvaluator> {
    const LValue &This;
    APValue &Result;
  public:

    ArrayExprEvaluator(EvalInfo &Info, const LValue &This, APValue &Result)
      : ExprEvaluatorBaseTy(Info), This(This), Result(Result) {}

    bool Success(const APValue &V, const Expr *E) {
      assert((V.isArray() || V.isLValue()) &&
             "expected array or string literal");
      Result = V;
      return true;
    }

    bool ZeroInitialization(const Expr *E) {
      const ConstantArrayType *CAT =
          Info.Ctx.getAsConstantArrayType(E->getType());
      if (!CAT)
        return Error(E);

      Result = APValue(APValue::UninitArray(), 0,
                       CAT->getSize().getZExtValue());
      if (!Result.hasArrayFiller()) return true;

      // Zero-initialize all elements.
      LValue Subobject = This;
      Subobject.addArray(Info, E, CAT);
      ImplicitValueInitExpr VIE(CAT->getElementType());
      return EvaluateInPlace(Result.getArrayFiller(), Info, Subobject, &VIE);
    }

    bool VisitInitListExpr(const InitListExpr *E);
    bool VisitCXXConstructExpr(const CXXConstructExpr *E);
    bool VisitCXXConstructExpr(const CXXConstructExpr *E,
                               const LValue &Subobject,
                               APValue *Value, QualType Type);
  };
} // end anonymous namespace

static bool EvaluateArray(const Expr *E, const LValue &This,
                          APValue &Result, EvalInfo &Info) {
  assert(E->isRValue() && E->getType()->isArrayType() && "not an array rvalue");
  return ArrayExprEvaluator(Info, This, Result).Visit(E);
}

bool ArrayExprEvaluator::VisitInitListExpr(const InitListExpr *E) {
  const ConstantArrayType *CAT = Info.Ctx.getAsConstantArrayType(E->getType());
  if (!CAT)
    return Error(E);

  // C++11 [dcl.init.string]p1: A char array [...] can be initialized by [...]
  // an appropriately-typed string literal enclosed in braces.
  if (E->isStringLiteralInit()) {
    LValue LV;
    if (!EvaluateLValue(E->getInit(0), LV, Info))
      return false;
    APValue Val;
    LV.moveInto(Val);
    return Success(Val, E);
  }

  bool Success = true;

  assert((!Result.isArray() || Result.getArrayInitializedElts() == 0) &&
         "zero-initialized array shouldn't have any initialized elts");
  APValue Filler;
  if (Result.isArray() && Result.hasArrayFiller())
    Filler = Result.getArrayFiller();

  unsigned NumEltsToInit = E->getNumInits();
  unsigned NumElts = CAT->getSize().getZExtValue();
  const Expr *FillerExpr = E->hasArrayFiller() ? E->getArrayFiller() : nullptr;

  // If the initializer might depend on the array index, run it for each
  // array element. For now, just whitelist non-class value-initialization.
  if (NumEltsToInit != NumElts && !isa<ImplicitValueInitExpr>(FillerExpr))
    NumEltsToInit = NumElts;

  Result = APValue(APValue::UninitArray(), NumEltsToInit, NumElts);

  // If the array was previously zero-initialized, preserve the
  // zero-initialized values.
  if (!Filler.isUninit()) {
    for (unsigned I = 0, E = Result.getArrayInitializedElts(); I != E; ++I)
      Result.getArrayInitializedElt(I) = Filler;
    if (Result.hasArrayFiller())
      Result.getArrayFiller() = Filler;
  }

  LValue Subobject = This;
  Subobject.addArray(Info, E, CAT);
  for (unsigned Index = 0; Index != NumEltsToInit; ++Index) {
    const Expr *Init =
        Index < E->getNumInits() ? E->getInit(Index) : FillerExpr;
    if (!EvaluateInPlace(Result.getArrayInitializedElt(Index),
                         Info, Subobject, Init) ||
        !HandleLValueArrayAdjustment(Info, Init, Subobject,
                                     CAT->getElementType(), 1)) {
      if (!Info.keepEvaluatingAfterFailure())
        return false;
      Success = false;
    }
  }

  if (!Result.hasArrayFiller())
    return Success;

  // If we get here, we have a trivial filler, which we can just evaluate
  // once and splat over the rest of the array elements.
  assert(FillerExpr && "no array filler for incomplete init list");
  return EvaluateInPlace(Result.getArrayFiller(), Info, Subobject,
                         FillerExpr) && Success;
}

bool ArrayExprEvaluator::VisitCXXConstructExpr(const CXXConstructExpr *E) {
  return VisitCXXConstructExpr(E, This, &Result, E->getType());
}

bool ArrayExprEvaluator::VisitCXXConstructExpr(const CXXConstructExpr *E,
                                               const LValue &Subobject,
                                               APValue *Value,
                                               QualType Type) {
  bool HadZeroInit = !Value->isUninit();

  if (const ConstantArrayType *CAT = Info.Ctx.getAsConstantArrayType(Type)) {
    unsigned N = CAT->getSize().getZExtValue();

    // Preserve the array filler if we had prior zero-initialization.
    APValue Filler =
      HadZeroInit && Value->hasArrayFiller() ? Value->getArrayFiller()
                                             : APValue();

    *Value = APValue(APValue::UninitArray(), N, N);

    if (HadZeroInit)
      for (unsigned I = 0; I != N; ++I)
        Value->getArrayInitializedElt(I) = Filler;

    // Initialize the elements.
    LValue ArrayElt = Subobject;
    ArrayElt.addArray(Info, E, CAT);
    for (unsigned I = 0; I != N; ++I)
      if (!VisitCXXConstructExpr(E, ArrayElt, &Value->getArrayInitializedElt(I),
                                 CAT->getElementType()) ||
          !HandleLValueArrayAdjustment(Info, E, ArrayElt,
                                       CAT->getElementType(), 1))
        return false;

    return true;
  }

  if (!Type->isRecordType())
    return Error(E);

  const CXXConstructorDecl *FD = E->getConstructor();

  bool ZeroInit = E->requiresZeroInitialization();
  if (CheckTrivialDefaultConstructor(Info, E->getExprLoc(), FD, ZeroInit)) {
    if (HadZeroInit)
      return true;

    // See RecordExprEvaluator::VisitCXXConstructExpr for explanation.
    ImplicitValueInitExpr VIE(Type);
    return EvaluateInPlace(*Value, Info, Subobject, &VIE);
  }

  const FunctionDecl *Definition = nullptr;
  FD->getBody(Definition);

  if (!CheckConstexprFunction(Info, E->getExprLoc(), FD, Definition))
    return false;

  if (ZeroInit && !HadZeroInit) {
    ImplicitValueInitExpr VIE(Type);
    if (!EvaluateInPlace(*Value, Info, Subobject, &VIE))
      return false;
  }

  ArrayRef<const Expr *> Args(E->getArgs(), E->getNumArgs());
  return HandleConstructorCall(E->getExprLoc(), Subobject, Args,
                               cast<CXXConstructorDecl>(Definition),
                               Info, *Value);
}

//===----------------------------------------------------------------------===//
// Integer Evaluation
//
// As a GNU extension, we support casting pointers to sufficiently-wide integer
// types and back in constant folding. Integer values are thus represented
// either as an integer-valued APValue, or as an lvalue-valued APValue.
//===----------------------------------------------------------------------===//

namespace {
class IntExprEvaluator
  : public ExprEvaluatorBase<IntExprEvaluator> {
  APValue &Result;
public:
  IntExprEvaluator(EvalInfo &info, APValue &result)
    : ExprEvaluatorBaseTy(info), Result(result) {}

  bool Success(const llvm::APSInt &SI, const Expr *E, APValue &Result) {
    assert(E->getType()->isIntegralOrEnumerationType() &&
           "Invalid evaluation result.");
    assert(SI.isSigned() == E->getType()->isSignedIntegerOrEnumerationType() &&
           "Invalid evaluation result.");
    assert(SI.getBitWidth() == Info.Ctx.getIntWidth(E->getType()) &&
           "Invalid evaluation result.");
    Result = APValue(SI);
    return true;
  }
  bool Success(const llvm::APSInt &SI, const Expr *E) {
    return Success(SI, E, Result);
  }

  bool Success(const llvm::APInt &I, const Expr *E, APValue &Result) {
    assert(E->getType()->isIntegralOrEnumerationType() &&
           "Invalid evaluation result.");
    assert(I.getBitWidth() == Info.Ctx.getIntWidth(E->getType()) &&
           "Invalid evaluation result.");
    Result = APValue(APSInt(I));
    Result.getInt().setIsUnsigned(
                            E->getType()->isUnsignedIntegerOrEnumerationType());
    return true;
  }
  bool Success(const llvm::APInt &I, const Expr *E) {
    return Success(I, E, Result);
  }

  bool Success(uint64_t Value, const Expr *E, APValue &Result) {
    assert(E->getType()->isIntegralOrEnumerationType() &&
           "Invalid evaluation result.");
    Result = APValue(Info.Ctx.MakeIntValue(Value, E->getType()));
    return true;
  }
  bool Success(uint64_t Value, const Expr *E) {
    return Success(Value, E, Result);
  }

  bool Success(CharUnits Size, const Expr *E) {
    return Success(Size.getQuantity(), E);
  }

  bool Success(const APValue &V, const Expr *E) {
    if (V.isLValue() || V.isAddrLabelDiff()) {
      Result = V;
      return true;
    }
    return Success(V.getInt(), E);
  }

  bool ZeroInitialization(const Expr *E) { return Success(0, E); }

  //===--------------------------------------------------------------------===//
  //                            Visitor Methods
  //===--------------------------------------------------------------------===//

  bool VisitIntegerLiteral(const IntegerLiteral *E) {
    return Success(E->getValue(), E);
  }
  bool VisitCharacterLiteral(const CharacterLiteral *E) {
    return Success(E->getValue(), E);
  }

  bool CheckReferencedDecl(const Expr *E, const Decl *D);
  bool VisitDeclRefExpr(const DeclRefExpr *E) {
    if (CheckReferencedDecl(E, E->getDecl()))
      return true;

    return ExprEvaluatorBaseTy::VisitDeclRefExpr(E);
  }
  bool VisitMemberExpr(const MemberExpr *E) {
    if (CheckReferencedDecl(E, E->getMemberDecl())) {
      VisitIgnoredValue(E->getBase());
      return true;
    }

    return ExprEvaluatorBaseTy::VisitMemberExpr(E);
  }

  bool VisitCallExpr(const CallExpr *E);
  bool VisitBinaryOperator(const BinaryOperator *E);
  bool VisitOffsetOfExpr(const OffsetOfExpr *E);
  bool VisitUnaryOperator(const UnaryOperator *E);

  bool VisitCastExpr(const CastExpr* E);
  bool VisitUnaryExprOrTypeTraitExpr(const UnaryExprOrTypeTraitExpr *E);

  bool VisitCXXBoolLiteralExpr(const CXXBoolLiteralExpr *E) {
    return Success(E->getValue(), E);
  }

  bool VisitObjCBoolLiteralExpr(const ObjCBoolLiteralExpr *E) {
    return Success(E->getValue(), E);
  }

  // Note, GNU defines __null as an integer, not a pointer.
  bool VisitGNUNullExpr(const GNUNullExpr *E) {
    return ZeroInitialization(E);
  }

  bool VisitTypeTraitExpr(const TypeTraitExpr *E) {
    return Success(E->getValue(), E);
  }

  bool VisitArrayTypeTraitExpr(const ArrayTypeTraitExpr *E) {
    return Success(E->getValue(), E);
  }

  bool VisitExpressionTraitExpr(const ExpressionTraitExpr *E) {
    return Success(E->getValue(), E);
  }

  bool VisitUnaryReal(const UnaryOperator *E);
  bool VisitUnaryImag(const UnaryOperator *E);

  bool VisitCXXNoexceptExpr(const CXXNoexceptExpr *E);
  bool VisitSizeOfPackExpr(const SizeOfPackExpr *E);

private:
  CharUnits GetAlignOfExpr(const Expr *E);
  CharUnits GetAlignOfType(QualType T);
  static QualType GetObjectType(APValue::LValueBase B);
  bool TryEvaluateBuiltinObjectSize(const CallExpr *E);
  // FIXME: Missing: array subscript of vector, member of vector
};
} // end anonymous namespace

/// EvaluateIntegerOrLValue - Evaluate an rvalue integral-typed expression, and
/// produce either the integer value or a pointer.
///
/// GCC has a heinous extension which folds casts between pointer types and
/// pointer-sized integral types. We support this by allowing the evaluation of
/// an integer rvalue to produce a pointer (represented as an lvalue) instead.
/// Some simple arithmetic on such values is supported (they are treated much
/// like char*).
static bool EvaluateIntegerOrLValue(const Expr *E, APValue &Result,
                                    EvalInfo &Info) {
  assert(E->isRValue() && E->getType()->isIntegralOrEnumerationType());
  return IntExprEvaluator(Info, Result).Visit(E);
}

static bool EvaluateInteger(const Expr *E, APSInt &Result, EvalInfo &Info) {
  APValue Val;
  if (!EvaluateIntegerOrLValue(E, Val, Info))
    return false;
  if (!Val.isInt()) {
    // FIXME: It would be better to produce the diagnostic for casting
    //        a pointer to an integer.
    Info.Diag(E, diag::note_invalid_subexpr_in_const_expr);
    return false;
  }
  Result = Val.getInt();
  return true;
}

/// Check whether the given declaration can be directly converted to an integral
/// rvalue. If not, no diagnostic is produced; there are other things we can
/// try.
bool IntExprEvaluator::CheckReferencedDecl(const Expr* E, const Decl* D) {
  // Enums are integer constant exprs.
  if (const EnumConstantDecl *ECD = dyn_cast<EnumConstantDecl>(D)) {
    // Check for signedness/width mismatches between E type and ECD value.
    bool SameSign = (ECD->getInitVal().isSigned()
                     == E->getType()->isSignedIntegerOrEnumerationType());
    bool SameWidth = (ECD->getInitVal().getBitWidth()
                      == Info.Ctx.getIntWidth(E->getType()));
    if (SameSign && SameWidth)
      return Success(ECD->getInitVal(), E);
    else {
      // Get rid of mismatch (otherwise Success assertions will fail)
      // by computing a new value matching the type of E.
      llvm::APSInt Val = ECD->getInitVal();
      if (!SameSign)
        Val.setIsSigned(!ECD->getInitVal().isSigned());
      if (!SameWidth)
        Val = Val.extOrTrunc(Info.Ctx.getIntWidth(E->getType()));
      return Success(Val, E);
    }
  }
  return false;
}

/// EvaluateBuiltinClassifyType - Evaluate __builtin_classify_type the same way
/// as GCC.
static int EvaluateBuiltinClassifyType(const CallExpr *E) {
  // The following enum mimics the values returned by GCC.
  // FIXME: Does GCC differ between lvalue and rvalue references here?
  enum gcc_type_class {
    no_type_class = -1,
    void_type_class, integer_type_class, char_type_class,
    enumeral_type_class, boolean_type_class,
    pointer_type_class, reference_type_class, offset_type_class,
    real_type_class, complex_type_class,
    function_type_class, method_type_class,
    record_type_class, union_type_class,
    array_type_class, string_type_class,
    lang_type_class
  };

  // If no argument was supplied, default to "no_type_class". This isn't
  // ideal, however it is what gcc does.
  if (E->getNumArgs() == 0)
    return no_type_class;

  QualType ArgTy = E->getArg(0)->getType();
  if (ArgTy->isVoidType())
    return void_type_class;
  else if (ArgTy->isEnumeralType())
    return enumeral_type_class;
  else if (ArgTy->isBooleanType())
    return boolean_type_class;
  else if (ArgTy->isCharType())
    return string_type_class; // gcc doesn't appear to use char_type_class
  else if (ArgTy->isIntegerType())
    return integer_type_class;
  else if (ArgTy->isPointerType())
    return pointer_type_class;
  else if (ArgTy->isReferenceType())
    return reference_type_class;
  else if (ArgTy->isRealType())
    return real_type_class;
  else if (ArgTy->isComplexType())
    return complex_type_class;
  else if (ArgTy->isFunctionType())
    return function_type_class;
  else if (ArgTy->isStructureOrClassType())
    return record_type_class;
  else if (ArgTy->isUnionType())
    return union_type_class;
  else if (ArgTy->isArrayType())
    return array_type_class;
  else if (ArgTy->isUnionType())
    return union_type_class;
  else  // FIXME: offset_type_class, method_type_class, & lang_type_class?
    llvm_unreachable("CallExpr::isBuiltinClassifyType(): unimplemented type");
}

/// EvaluateBuiltinConstantPForLValue - Determine the result of
/// __builtin_constant_p when applied to the given lvalue.
///
/// An lvalue is only "constant" if it is a pointer or reference to the first
/// character of a string literal.
template<typename LValue>
static bool EvaluateBuiltinConstantPForLValue(const LValue &LV) {
  const Expr *E = LV.getLValueBase().template dyn_cast<const Expr*>();
  return E && isa<StringLiteral>(E) && LV.getLValueOffset().isZero();
}

/// EvaluateBuiltinConstantP - Evaluate __builtin_constant_p as similarly to
/// GCC as we can manage.
static bool EvaluateBuiltinConstantP(ASTContext &Ctx, const Expr *Arg) {
  QualType ArgType = Arg->getType();

  // __builtin_constant_p always has one operand. The rules which gcc follows
  // are not precisely documented, but are as follows:
  //
  //  - If the operand is of integral, floating, complex or enumeration type,
  //    and can be folded to a known value of that type, it returns 1.
  //  - If the operand and can be folded to a pointer to the first character
  //    of a string literal (or such a pointer cast to an integral type), it
  //    returns 1.
  //
  // Otherwise, it returns 0.
  //
  // FIXME: GCC also intends to return 1 for literals of aggregate types, but
  // its support for this does not currently work.
  if (ArgType->isIntegralOrEnumerationType()) {
    Expr::EvalResult Result;
    if (!Arg->EvaluateAsRValue(Result, Ctx) || Result.HasSideEffects)
      return false;

    APValue &V = Result.Val;
    if (V.getKind() == APValue::Int)
      return true;

    return EvaluateBuiltinConstantPForLValue(V);
  } else if (ArgType->isFloatingType() || ArgType->isAnyComplexType()) {
    return Arg->isEvaluatable(Ctx);
  } else if (ArgType->isPointerType() || Arg->isGLValue()) {
    LValue LV;
    Expr::EvalStatus Status;
    EvalInfo Info(Ctx, Status, EvalInfo::EM_ConstantFold);
    if ((Arg->isGLValue() ? EvaluateLValue(Arg, LV, Info)
                          : EvaluatePointer(Arg, LV, Info)) &&
        !Status.HasSideEffects)
      return EvaluateBuiltinConstantPForLValue(LV);
  }

  // Anything else isn't considered to be sufficiently constant.
  return false;
}

/// Retrieves the "underlying object type" of the given expression,
/// as used by __builtin_object_size.
QualType IntExprEvaluator::GetObjectType(APValue::LValueBase B) {
  if (const ValueDecl *D = B.dyn_cast<const ValueDecl*>()) {
    if (const VarDecl *VD = dyn_cast<VarDecl>(D))
      return VD->getType();
  } else if (const Expr *E = B.get<const Expr*>()) {
    if (isa<CompoundLiteralExpr>(E))
      return E->getType();
  }

  return QualType();
}

bool IntExprEvaluator::TryEvaluateBuiltinObjectSize(const CallExpr *E) {
  LValue Base;

  {
    // The operand of __builtin_object_size is never evaluated for side-effects.
    // If there are any, but we can determine the pointed-to object anyway, then
    // ignore the side-effects.
    SpeculativeEvaluationRAII SpeculativeEval(Info);
    if (!EvaluatePointer(E->getArg(0), Base, Info))
      return false;
  }

  // If we can prove the base is null, lower to zero now.
  if (!Base.getLValueBase()) return Success(0, E);

  QualType T = GetObjectType(Base.getLValueBase());
  if (T.isNull() ||
      T->isIncompleteType() ||
      T->isFunctionType() ||
      T->isVariablyModifiedType() ||
      T->isDependentType())
    return Error(E);

  CharUnits Size = Info.Ctx.getTypeSizeInChars(T);
  CharUnits Offset = Base.getLValueOffset();

  if (!Offset.isNegative() && Offset <= Size)
    Size -= Offset;
  else
    Size = CharUnits::Zero();
  return Success(Size, E);
}

bool IntExprEvaluator::VisitCallExpr(const CallExpr *E) {
  switch (unsigned BuiltinOp = E->getBuiltinCallee()) {
  default:
    return ExprEvaluatorBaseTy::VisitCallExpr(E);

  case Builtin::BI__builtin_object_size: {
    if (TryEvaluateBuiltinObjectSize(E))
      return true;

    // If evaluating the argument has side-effects, we can't determine the size
    // of the object, and so we lower it to unknown now. CodeGen relies on us to
    // handle all cases where the expression has side-effects.
    if (E->getArg(0)->HasSideEffects(Info.Ctx)) {
      if (E->getArg(1)->EvaluateKnownConstInt(Info.Ctx).getZExtValue() <= 1)
        return Success(-1ULL, E);
      return Success(0, E);
    }

    // Expression had no side effects, but we couldn't statically determine the
    // size of the referenced object.
    switch (Info.EvalMode) {
    case EvalInfo::EM_ConstantExpression:
    case EvalInfo::EM_PotentialConstantExpression:
    case EvalInfo::EM_ConstantFold:
    case EvalInfo::EM_EvaluateForOverflow:
    case EvalInfo::EM_IgnoreSideEffects:
      return Error(E);
    case EvalInfo::EM_ConstantExpressionUnevaluated:
    case EvalInfo::EM_PotentialConstantExpressionUnevaluated:
      return Success(-1ULL, E);
    }
  }

  case Builtin::BI__builtin_bswap16:
  case Builtin::BI__builtin_bswap32:
  case Builtin::BI__builtin_bswap64: {
    APSInt Val;
    if (!EvaluateInteger(E->getArg(0), Val, Info))
      return false;

    return Success(Val.byteSwap(), E);
  }

  case Builtin::BI__builtin_classify_type:
    return Success(EvaluateBuiltinClassifyType(E), E);

  // FIXME: BI__builtin_clrsb
  // FIXME: BI__builtin_clrsbl
  // FIXME: BI__builtin_clrsbll

  case Builtin::BI__builtin_clz:
  case Builtin::BI__builtin_clzl:
  case Builtin::BI__builtin_clzll:
  case Builtin::BI__builtin_clzs: {
    APSInt Val;
    if (!EvaluateInteger(E->getArg(0), Val, Info))
      return false;
    if (!Val)
      return Error(E);

    return Success(Val.countLeadingZeros(), E);
  }

  case Builtin::BI__builtin_constant_p:
    return Success(EvaluateBuiltinConstantP(Info.Ctx, E->getArg(0)), E);

  case Builtin::BI__builtin_ctz:
  case Builtin::BI__builtin_ctzl:
  case Builtin::BI__builtin_ctzll:
  case Builtin::BI__builtin_ctzs: {
    APSInt Val;
    if (!EvaluateInteger(E->getArg(0), Val, Info))
      return false;
    if (!Val)
      return Error(E);

    return Success(Val.countTrailingZeros(), E);
  }

  case Builtin::BI__builtin_eh_return_data_regno: {
    int Operand = E->getArg(0)->EvaluateKnownConstInt(Info.Ctx).getZExtValue();
    Operand = Info.Ctx.getTargetInfo().getEHDataRegisterNumber(Operand);
    return Success(Operand, E);
  }

  case Builtin::BI__builtin_expect:
    return Visit(E->getArg(0));

  case Builtin::BI__builtin_ffs:
  case Builtin::BI__builtin_ffsl:
  case Builtin::BI__builtin_ffsll: {
    APSInt Val;
    if (!EvaluateInteger(E->getArg(0), Val, Info))
      return false;

    unsigned N = Val.countTrailingZeros();
    return Success(N == Val.getBitWidth() ? 0 : N + 1, E);
  }

  case Builtin::BI__builtin_fpclassify: {
    APFloat Val(0.0);
    if (!EvaluateFloat(E->getArg(5), Val, Info))
      return false;
    unsigned Arg;
    switch (Val.getCategory()) {
    case APFloat::fcNaN: Arg = 0; break;
    case APFloat::fcInfinity: Arg = 1; break;
    case APFloat::fcNormal: Arg = Val.isDenormal() ? 3 : 2; break;
    case APFloat::fcZero: Arg = 4; break;
    }
    return Visit(E->getArg(Arg));
  }

  case Builtin::BI__builtin_isinf_sign: {
    APFloat Val(0.0);
    return EvaluateFloat(E->getArg(0), Val, Info) &&
           Success(Val.isInfinity() ? (Val.isNegative() ? -1 : 1) : 0, E);
  }

  case Builtin::BI__builtin_isinf: {
    APFloat Val(0.0);
    return EvaluateFloat(E->getArg(0), Val, Info) &&
           Success(Val.isInfinity() ? 1 : 0, E);
  }

  case Builtin::BI__builtin_isfinite: {
    APFloat Val(0.0);
    return EvaluateFloat(E->getArg(0), Val, Info) &&
           Success(Val.isFinite() ? 1 : 0, E);
  }

  case Builtin::BI__builtin_isnan: {
    APFloat Val(0.0);
    return EvaluateFloat(E->getArg(0), Val, Info) &&
           Success(Val.isNaN() ? 1 : 0, E);
  }

  case Builtin::BI__builtin_isnormal: {
    APFloat Val(0.0);
    return EvaluateFloat(E->getArg(0), Val, Info) &&
           Success(Val.isNormal() ? 1 : 0, E);
  }

  case Builtin::BI__builtin_parity:
  case Builtin::BI__builtin_parityl:
  case Builtin::BI__builtin_parityll: {
    APSInt Val;
    if (!EvaluateInteger(E->getArg(0), Val, Info))
      return false;

    return Success(Val.countPopulation() % 2, E);
  }

  case Builtin::BI__builtin_popcount:
  case Builtin::BI__builtin_popcountl:
  case Builtin::BI__builtin_popcountll: {
    APSInt Val;
    if (!EvaluateInteger(E->getArg(0), Val, Info))
      return false;

    return Success(Val.countPopulation(), E);
  }

  case Builtin::BIstrlen:
    // A call to strlen is not a constant expression.
    if (Info.getLangOpts().CPlusPlus11)
      Info.CCEDiag(E, diag::note_constexpr_invalid_function)
        << /*isConstexpr*/0 << /*isConstructor*/0 << "'strlen'";
    else
      Info.CCEDiag(E, diag::note_invalid_subexpr_in_const_expr);
    // Fall through.
  case Builtin::BI__builtin_strlen: {
    // As an extension, we support __builtin_strlen() as a constant expression,
    // and support folding strlen() to a constant.
    LValue String;
    if (!EvaluatePointer(E->getArg(0), String, Info))
      return false;

    // Fast path: if it's a string literal, search the string value.
    if (const StringLiteral *S = dyn_cast_or_null<StringLiteral>(
            String.getLValueBase().dyn_cast<const Expr *>())) {
      // The string literal may have embedded null characters. Find the first
      // one and truncate there.
      StringRef Str = S->getBytes();
      int64_t Off = String.Offset.getQuantity();
      if (Off >= 0 && (uint64_t)Off <= (uint64_t)Str.size() &&
          S->getCharByteWidth() == 1) {
        Str = Str.substr(Off);

        StringRef::size_type Pos = Str.find(0);
        if (Pos != StringRef::npos)
          Str = Str.substr(0, Pos);

        return Success(Str.size(), E);
      }

      // Fall through to slow path to issue appropriate diagnostic.
    }

    // Slow path: scan the bytes of the string looking for the terminating 0.
    QualType CharTy = E->getArg(0)->getType()->getPointeeType();
    for (uint64_t Strlen = 0; /**/; ++Strlen) {
      APValue Char;
      if (!handleLValueToRValueConversion(Info, E, CharTy, String, Char) ||
          !Char.isInt())
        return false;
      if (!Char.getInt())
        return Success(Strlen, E);
      if (!HandleLValueArrayAdjustment(Info, E, String, CharTy, 1))
        return false;
    }
  }

  case Builtin::BI__atomic_always_lock_free:
  case Builtin::BI__atomic_is_lock_free:
  case Builtin::BI__c11_atomic_is_lock_free: {
    APSInt SizeVal;
    if (!EvaluateInteger(E->getArg(0), SizeVal, Info))
      return false;

    // For __atomic_is_lock_free(sizeof(_Atomic(T))), if the size is a power
    // of two less than the maximum inline atomic width, we know it is
    // lock-free.  If the size isn't a power of two, or greater than the
    // maximum alignment where we promote atomics, we know it is not lock-free
    // (at least not in the sense of atomic_is_lock_free).  Otherwise,
    // the answer can only be determined at runtime; for example, 16-byte
    // atomics have lock-free implementations on some, but not all,
    // x86-64 processors.

    // Check power-of-two.
    CharUnits Size = CharUnits::fromQuantity(SizeVal.getZExtValue());
    if (Size.isPowerOfTwo()) {
      // Check against inlining width.
      unsigned InlineWidthBits =
          Info.Ctx.getTargetInfo().getMaxAtomicInlineWidth();
      if (Size <= Info.Ctx.toCharUnitsFromBits(InlineWidthBits)) {
        if (BuiltinOp == Builtin::BI__c11_atomic_is_lock_free ||
            Size == CharUnits::One() ||
            E->getArg(1)->isNullPointerConstant(Info.Ctx,
                                                Expr::NPC_NeverValueDependent))
          // OK, we will inline appropriately-aligned operations of this size,
          // and _Atomic(T) is appropriately-aligned.
          return Success(1, E);

        QualType PointeeType = E->getArg(1)->IgnoreImpCasts()->getType()->
          castAs<PointerType>()->getPointeeType();
        if (!PointeeType->isIncompleteType() &&
            Info.Ctx.getTypeAlignInChars(PointeeType) >= Size) {
          // OK, we will inline operations on this object.
          return Success(1, E);
        }
      }
    }

    return BuiltinOp == Builtin::BI__atomic_always_lock_free ?
        Success(0, E) : Error(E);
  }
  }
}

static bool HasSameBase(const LValue &A, const LValue &B) {
  if (!A.getLValueBase())
    return !B.getLValueBase();
  if (!B.getLValueBase())
    return false;

  if (A.getLValueBase().getOpaqueValue() !=
      B.getLValueBase().getOpaqueValue()) {
    const Decl *ADecl = GetLValueBaseDecl(A);
    if (!ADecl)
      return false;
    const Decl *BDecl = GetLValueBaseDecl(B);
    if (!BDecl || ADecl->getCanonicalDecl() != BDecl->getCanonicalDecl())
      return false;
  }

  return IsGlobalLValue(A.getLValueBase()) ||
         A.getLValueCallIndex() == B.getLValueCallIndex();
}

namespace {

/// \brief Data recursive integer evaluator of certain binary operators.
///
/// We use a data recursive algorithm for binary operators so that we are able
/// to handle extreme cases of chained binary operators without causing stack
/// overflow.
class DataRecursiveIntBinOpEvaluator {
  struct EvalResult {
    APValue Val;
    bool Failed;

    EvalResult() : Failed(false) { }

    void swap(EvalResult &RHS) {
      Val.swap(RHS.Val);
      Failed = RHS.Failed;
      RHS.Failed = false;
    }
  };

  struct Job {
    const Expr *E;
    EvalResult LHSResult; // meaningful only for binary operator expression.
    enum { AnyExprKind, BinOpKind, BinOpVisitedLHSKind } Kind;

    Job() : StoredInfo(nullptr) {}
    void startSpeculativeEval(EvalInfo &Info) {
      OldEvalStatus = Info.EvalStatus;
      Info.EvalStatus.Diag = nullptr;
      StoredInfo = &Info;
    }
    ~Job() {
      if (StoredInfo) {
        StoredInfo->EvalStatus = OldEvalStatus;
      }
    }
  private:
    EvalInfo *StoredInfo; // non-null if status changed.
    Expr::EvalStatus OldEvalStatus;
  };

  SmallVector<Job, 16> Queue;

  IntExprEvaluator &IntEval;
  EvalInfo &Info;
  APValue &FinalResult;

public:
  DataRecursiveIntBinOpEvaluator(IntExprEvaluator &IntEval, APValue &Result)
    : IntEval(IntEval), Info(IntEval.getEvalInfo()), FinalResult(Result) { }

  /// \brief True if \param E is a binary operator that we are going to handle
  /// data recursively.
  /// We handle binary operators that are comma, logical, or that have operands
  /// with integral or enumeration type.
  static bool shouldEnqueue(const BinaryOperator *E) {
    return E->getOpcode() == BO_Comma ||
           E->isLogicalOp() ||
           (E->getLHS()->getType()->isIntegralOrEnumerationType() &&
            E->getRHS()->getType()->isIntegralOrEnumerationType());
  }

  bool Traverse(const BinaryOperator *E) {
    enqueue(E);
    EvalResult PrevResult;
    while (!Queue.empty())
      process(PrevResult);

    if (PrevResult.Failed) return false;

    FinalResult.swap(PrevResult.Val);
    return true;
  }

private:
  bool Success(uint64_t Value, const Expr *E, APValue &Result) {
    return IntEval.Success(Value, E, Result);
  }
  bool Success(const APSInt &Value, const Expr *E, APValue &Result) {
    return IntEval.Success(Value, E, Result);
  }
  bool Error(const Expr *E) {
    return IntEval.Error(E);
  }
  bool Error(const Expr *E, diag::kind D) {
    return IntEval.Error(E, D);
  }

  OptionalDiagnostic CCEDiag(const Expr *E, diag::kind D) {
    return Info.CCEDiag(E, D);
  }

  // \brief Returns true if visiting the RHS is necessary, false otherwise.
  bool VisitBinOpLHSOnly(EvalResult &LHSResult, const BinaryOperator *E,
                         bool &SuppressRHSDiags);

  bool VisitBinOp(const EvalResult &LHSResult, const EvalResult &RHSResult,
                  const BinaryOperator *E, APValue &Result);

  void EvaluateExpr(const Expr *E, EvalResult &Result) {
    Result.Failed = !Evaluate(Result.Val, Info, E);
    if (Result.Failed)
      Result.Val = APValue();
  }

  void process(EvalResult &Result);

  void enqueue(const Expr *E) {
    E = E->IgnoreParens();
    Queue.resize(Queue.size()+1);
    Queue.back().E = E;
    Queue.back().Kind = Job::AnyExprKind;
  }