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/ASTLambda.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,
                                    bool &IsArray) {
    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;
        IsArray = true;
      } else if (Type->isAnyComplexType()) {
        const ComplexType *CT = Type->castAs<ComplexType>();
        Type = CT->getElementType();
        ArraySize = 2;
        MostDerivedLength = I + 1;
        IsArray = true;
      } else if (const FieldDecl *FD = getAsField(Path[I])) {
        Type = FD->getType();
        ArraySize = 0;
        MostDerivedLength = I + 1;
        IsArray = false;
      } else {
        // Path[I] describes a base class.
        ArraySize = 0;
        IsArray = false;
      }
    }
    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.
    unsigned Invalid : 1;

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

    /// Indicator of whether the most-derived object is an array element.
    unsigned MostDerivedIsArrayElement : 1;

    /// The length of the path to the most-derived object of which this is a
    /// subobject.
    unsigned MostDerivedPathLength : 29;

    /// The size of the array of which the most-derived object is an element.
    /// This will always be 0 if the most-derived object is not an array
    /// element. 0 is not an indicator of whether or not the most-derived object
    /// is an array, however, because 0-length arrays are allowed.
    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),
          MostDerivedIsArrayElement(false), MostDerivedPathLength(0),
          MostDerivedArraySize(0), MostDerivedType(T) {}

    SubobjectDesignator(ASTContext &Ctx, const APValue &V)
        : Invalid(!V.isLValue() || !V.hasLValuePath()), IsOnePastTheEnd(false),
          MostDerivedIsArrayElement(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()) {
          bool IsArray = false;
          MostDerivedPathLength =
              findMostDerivedSubobject(Ctx, getType(V.getLValueBase()),
                                       V.getLValuePath(), MostDerivedArraySize,
                                       MostDerivedType, IsArray);
          MostDerivedIsArrayElement = IsArray;
        }
      }
    }

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

    /// Determine whether this is a one-past-the-end pointer.
    bool isOnePastTheEnd() const {
      assert(!Invalid);
      if (IsOnePastTheEnd)
        return true;
      if (MostDerivedIsArrayElement &&
          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();
      MostDerivedIsArrayElement = true;
      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();
        MostDerivedIsArrayElement = false;
        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;
      MostDerivedIsArrayElement = true;
      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() &&
          MostDerivedIsArrayElement) {
        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;

    /// \brief Have we emitted a diagnostic explaining why we couldn't constant
    /// fold (not just why it's not strictly a constant expression)?
    bool HasFoldFailureDiagnostic;

    /// \brief Whether or not we're currently speculatively evaluating.
    bool IsSpeculativelyEvaluating;

    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,

      /// Evaluate as a constant expression. Continue evaluating if we find a
      /// MemberExpr with a base that can't be evaluated.
      EM_DesignatorFold,
    } 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),
        HasFoldFailureDiagnostic(false), IsSpeculativelyEvaluating(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.
        FFDiag(Loc, diag::note_constexpr_call_limit_exceeded);
        return false;
      }
      if (CallStackDepth <= getLangOpts().ConstexprCallDepth)
        return true;
      FFDiag(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) {
        FFDiag(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);

  private:
    OptionalDiagnostic Diag(SourceLocation Loc, diag::kind DiagId,
                            unsigned ExtraNotes, bool IsCCEDiag) {

      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 (!HasFoldFailureDiagnostic)
              break;
            // We've already failed to fold something. Keep that diagnostic.
          case EM_ConstantExpression:
          case EM_PotentialConstantExpression:
          case EM_ConstantExpressionUnevaluated:
          case EM_PotentialConstantExpressionUnevaluated:
          case EM_DesignatorFold:
            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;
        HasFoldFailureDiagnostic = !IsCCEDiag;
        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();
    }
  public:
    // Diagnose that the evaluation could not be folded (FF => FoldFailure)
    OptionalDiagnostic
    FFDiag(SourceLocation Loc,
          diag::kind DiagId = diag::note_invalid_subexpr_in_const_expr,
          unsigned ExtraNotes = 0) {
      return Diag(Loc, DiagId, ExtraNotes, false);
    }

    OptionalDiagnostic FFDiag(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, /*IsCCEDiag*/false);
      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.
    OptionalDiagnostic CCEDiag(SourceLocation 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, true);
    }
    OptionalDiagnostic CCEDiag(const Expr *E, diag::kind DiagId
                                 = diag::note_invalid_subexpr_in_const_expr,
                               unsigned ExtraNotes = 0) {
      return CCEDiag(E->getExprLoc(), 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:
      case EM_DesignatorFold:
        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 after encountering undefined behavior?
    bool keepEvaluatingAfterUndefinedBehavior() {
      switch (EvalMode) {
      case EM_EvaluateForOverflow:
      case EM_IgnoreSideEffects:
      case EM_ConstantFold:
      case EM_DesignatorFold:
        return true;

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

    /// Note that we hit something that was technically undefined behavior, but
    /// that we can evaluate past it (such as signed overflow or floating-point
    /// division by zero.)
    bool noteUndefinedBehavior() {
      EvalStatus.HasUndefinedBehavior = true;
      return keepEvaluatingAfterUndefinedBehavior();
    }

    /// 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:
      case EM_DesignatorFold:
        return false;
      }
      llvm_unreachable("Missed EvalMode case");
    }

    /// Notes that we failed to evaluate an expression that other expressions
    /// directly depend on, and determine if we should keep evaluating. This
    /// should only be called if we actually intend to keep evaluating.
    ///
    /// Call noteSideEffect() instead if we may be able to ignore the value that
    /// we failed to evaluate, e.g. if we failed to evaluate Foo() in:
    ///
    /// (Foo(), 1)      // use noteSideEffect
    /// (Foo() || true) // use noteSideEffect
    /// Foo() + 1       // use noteFailure
    LLVM_ATTRIBUTE_UNUSED_RESULT bool noteFailure() {
      // Failure when evaluating some expression often means there is some
      // subexpression whose evaluation was skipped. Therefore, (because we
      // don't track whether we skipped an expression when unwinding after an
      // evaluation failure) every evaluation failure that bubbles up from a
      // subexpression implies that a side-effect has potentially happened. We
      // skip setting the HasSideEffects flag to true until we decide to
      // continue evaluating after that point, which happens here.
      bool KeepGoing = keepEvaluatingAfterFailure();
      EvalStatus.HasSideEffects |= KeepGoing;
      return KeepGoing;
    }

    bool allowInvalidBaseExpr() const {
      return EvalMode == EM_DesignatorFold;
    }
  };

  /// 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 treat the current evaluation as the correct pointer
  /// offset fold for the current EvalMode
  struct FoldOffsetRAII {
    EvalInfo &Info;
    EvalInfo::EvaluationMode OldMode;
    explicit FoldOffsetRAII(EvalInfo &Info, bool Subobject)
        : Info(Info), OldMode(Info.EvalMode) {
      if (!Info.checkingPotentialConstantExpression())
        Info.EvalMode = Subobject ? EvalInfo::EM_DesignatorFold
                                  : EvalInfo::EM_ConstantFold;
    }

    ~FoldOffsetRAII() { Info.EvalMode = OldMode; }
  };

  /// RAII object used to optionally suppress diagnostics and side-effects from
  /// a speculative evaluation.
  class SpeculativeEvaluationRAII {
    /// Pair of EvalInfo, and a bit that stores whether or not we were
    /// speculatively evaluating when we created this RAII.
    llvm::PointerIntPair<EvalInfo *, 1, bool> InfoAndOldSpecEval;
    Expr::EvalStatus Old;

    void moveFromAndCancel(SpeculativeEvaluationRAII &&Other) {
      InfoAndOldSpecEval = Other.InfoAndOldSpecEval;
      Old = Other.Old;
      Other.InfoAndOldSpecEval.setPointer(nullptr);
    }

    void maybeRestoreState() {
      EvalInfo *Info = InfoAndOldSpecEval.getPointer();
      if (!Info)
        return;

      Info->EvalStatus = Old;
      Info->IsSpeculativelyEvaluating = InfoAndOldSpecEval.getInt();
    }

  public:
    SpeculativeEvaluationRAII() = default;

    SpeculativeEvaluationRAII(
        EvalInfo &Info, SmallVectorImpl<PartialDiagnosticAt> *NewDiag = nullptr)
        : InfoAndOldSpecEval(&Info, Info.IsSpeculativelyEvaluating),
          Old(Info.EvalStatus) {
      Info.EvalStatus.Diag = NewDiag;
      Info.IsSpeculativelyEvaluating = true;
    }

    SpeculativeEvaluationRAII(const SpeculativeEvaluationRAII &Other) = delete;
    SpeculativeEvaluationRAII(SpeculativeEvaluationRAII &&Other) {
      moveFromAndCancel(std::move(Other));
    }

    SpeculativeEvaluationRAII &operator=(SpeculativeEvaluationRAII &&Other) {
      maybeRestoreState();
      moveFromAndCancel(std::move(Other));
      return *this;
    }

    ~SpeculativeEvaluationRAII() { maybeRestoreState(); }
  };

  /// 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() && MostDerivedIsArrayElement)
    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;
    }

    // Use a different note for an inheriting constructor, because from the
    // user's perspective it's not really a function at all.
    if (auto *CD = dyn_cast_or_null<CXXConstructorDecl>(Frame->Callee)) {
      if (CD->isInheritingConstructor()) {
        addDiag(Frame->CallLoc, diag::note_constexpr_inherited_ctor_call_here)
          << CD->getParent();
        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 InvalidBase : 1;
    unsigned CallIndex : 31;
    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();
      InvalidBase = false;
      CallIndex = V.getLValueCallIndex();
      Designator = SubobjectDesignator(Ctx, V);
    }

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

    void setInvalid(APValue::LValueBase B, unsigned I = 0) {
      set(B, I, true);
    }

    // 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) {
      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);
static bool EvaluateAsRValue(EvalInfo &Info, const Expr *E, APValue &Result);

//===----------------------------------------------------------------------===//
// 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.FFDiag(Loc, diag::note_constexpr_non_global, 1)
        << IsReferenceType << !Designator.Entries.empty()
        << !!VD << VD;
      NoteLValueLocation(Info, Base);
    } else {
      Info.FFDiag(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.Invalid && Designator.isOnePastTheEnd()) {
    const ValueDecl *VD = Base.dyn_cast<const ValueDecl*>();
    Info.FFDiag(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().CPlusPlus14 && This &&
      Info.EvaluatingDecl == This->getLValueBase())
    return true;

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

  // We allow _Atomic(T) to be initialized from anything that T can be
  // initialized from.
  if (const AtomicType *AT = Type->getAs<AtomicType>())
    Type = AT->getValueType();

  // 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;
}

static 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 isZeroSized(const LValue &Value) {
  const ValueDecl *Decl = GetLValueBaseDecl(Value);
  if (Decl && isa<VarDecl>(Decl)) {
    QualType Ty = Decl->getType();
    if (Ty->isArrayType())
      return Ty->isIncompleteType() ||
             Decl->getASTContext().getTypeSize(Ty) == 0;
  }
  return false;
}

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 bool HandleOverflow(EvalInfo &Info, const Expr *E,
                           const T &SrcValue, QualType DestType) {
  Info.CCEDiag(E, diag::note_constexpr_overflow)
    << SrcValue << DestType;
  return Info.noteUndefinedBehavior();
}

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)
    return 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)
    return HandleOverflow(Info, E, Value, DestType);
  return true;
}

static APSInt HandleIntToIntCast(EvalInfo &Info, const Expr *E,
                                 QualType DestType, QualType SrcType,
                                 const 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)
    return 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.FFDiag(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.FFDiag(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.FFDiag(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 bool CheckedIntArithmetic(EvalInfo &Info, const Expr *E,
                                 const APSInt &LHS, const APSInt &RHS,
                                 unsigned BitWidth, Operation Op,
                                 APSInt &Result) {
  if (LHS.isUnsigned()) {
    Result = Op(LHS, RHS);
    return true;
  }

  APSInt Value(Op(LHS.extend(BitWidth), RHS.extend(BitWidth)), false);
  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
      return HandleOverflow(Info, E, Value, E->getType());
  }
  return true;
}

/// 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.FFDiag(E);
    return false;
  case BO_Mul:
    return CheckedIntArithmetic(Info, E, LHS, RHS, LHS.getBitWidth() * 2,
                                std::multiplies<APSInt>(), Result);
  case BO_Add:
    return CheckedIntArithmetic(Info, E, LHS, RHS, LHS.getBitWidth() + 1,
                                std::plus<APSInt>(), Result);
  case BO_Sub:
    return CheckedIntArithmetic(Info, E, LHS, RHS, LHS.getBitWidth() + 1,
                                std::minus<APSInt>(), Result);
  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.FFDiag(E, diag::note_expr_divide_by_zero);
      return false;
    }
    Result = (Opcode == BO_Rem ? LHS % RHS : LHS / RHS);
    // Check for overflow case: INT_MIN / -1 or INT_MIN % -1. APSInt supports
    // this operation and gives the two's complement result.
    if (RHS.isNegative() && RHS.isAllOnesValue() &&
        LHS.isSigned() && LHS.isMinSignedValue())
      return HandleOverflow(Info, E, -LHS.extend(LHS.getBitWidth() + 1),
                            E->getType());
    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.FFDiag(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 Info.noteUndefinedBehavior();
  }
  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->isDependentType()) {
    Info.FFDiag(Loc);
    return false;
  }

  if (!Type->isConstantSizeType()) {
    // sizeof(vla) is not a constantexpr: C99 6.5.3.4p2.
    // FIXME: Better diagnostic.
    Info.FFDiag(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.FFDiag(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);
    if (!Result) {
      // Assume variables referenced within a lambda's call operator that were
      // not declared within the call operator are captures and during checking
      // of a potential constant expression, assume they are unknown constant
      // expressions.
      assert(isLambdaCallOperator(Frame->Callee) &&
             (VD->getDeclContext() != Frame->Callee || VD->isInitCapture()) &&
             "missing value for local variable");
      if (Info.checkingPotentialConstantExpression())
        return false;
      // FIXME: implement capture evaluation during constant expr evaluation.
      Info.FFDiag(E->getLocStart(),
           diag::note_unimplemented_constexpr_lambda_feature_ast)
          << "captures not currently allowed";
      return false;
    }
    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.FFDiag(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.FFDiag(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.FFDiag(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 ObjCEncodeExpr, MakeStringConstant
  if (auto PE = dyn_cast<PredefinedExpr>(Lit))
    Lit = PE->getFunctionName();
  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);
}

/// Determine whether a type would actually be read by an lvalue-to-rvalue
/// conversion. If it's of class type, we may assume that the copy operation
/// is trivial. Note that this is never true for a union type with fields
/// (because the copy always "reads" the active member) and always true for
/// a non-class type.
static bool isReadByLvalueToRvalueConversion(QualType T) {
  CXXRecordDecl *RD = T->getBaseElementTypeUnsafe()->getAsCXXRecordDecl();
  if (!RD || (RD->isUnion() && !RD->field_empty()))
    return true;
  if (RD->isEmpty())
    return false;

  for (auto *Field : RD->fields())
    if (isReadByLvalueToRvalueConversion(Field->getType()))
      return true;

  for (auto &BaseSpec : RD->bases())
    if (isReadByLvalueToRvalueConversion(BaseSpec.getType()))
      return true;

  return false;
}

/// Diagnose an attempt to read from any unreadable field within the specified
/// type, which might be a class type.
static bool diagnoseUnreadableFields(EvalInfo &Info, const Expr *E,
                                     QualType T) {
  CXXRecordDecl *RD = T->getBaseElementTypeUnsafe()->getAsCXXRecordDecl();
  if (!RD)
    return false;

  if (!RD->hasMutableFields())
    return false;

  for (auto *Field : RD->fields()) {
    // If we're actually going to read this field in some way, then it can't
    // be mutable. If we're in a union, then assigning to a mutable field
    // (even an empty one) can change the active member, so that's not OK.
    // FIXME: Add core issue number for the union case.
    if (Field->isMutable() &&
        (RD->isUnion() || isReadByLvalueToRvalueConversion(Field->getType()))) {
      Info.FFDiag(E, diag::note_constexpr_ltor_mutable, 1) << Field;
      Info.Note(Field->getLocation(), diag::note_declared_at);
      return true;
    }

    if (diagnoseUnreadableFields(Info, E, Field->getType()))
      return true;
  }

  for (auto &BaseSpec : RD->bases())
    if (diagnoseUnreadableFields(Info, E, BaseSpec.getType()))
      return true;

  // All mutable fields were empty, and thus not actually read.
  return false;
}

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

namespace {
/// 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");
  }

  explicit operator bool() const { return Value; }
};
} // end anonymous namespace

/// 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.FFDiag(E, diag::note_constexpr_access_past_end)
        << handler.AccessKind;
    else
      Info.FFDiag(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.FFDiag(E, diag::note_constexpr_access_uninit) << handler.AccessKind;
      return handler.failed();
    }

    if (I == N) {
      // If we are reading an object of class type, there may still be more
      // things we need to check: if there are any mutable subobjects, we
      // cannot perform this read. (This only happens when performing a trivial
      // copy or assignment.)
      if (ObjType->isRecordType() && handler.AccessKind == AK_Read &&
          diagnoseUnreadableFields(Info, E, ObjType))
        return handler.failed();

      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.FFDiag(E, diag::note_constexpr_access_past_end)
            << handler.AccessKind;
        else
          Info.FFDiag(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.FFDiag(E, diag::note_constexpr_access_past_end)
            << handler.AccessKind;
        else
          Info.FFDiag(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.FFDiag(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.FFDiag(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.FFDiag(E, diag::note_constexpr_access_volatile_obj, 1)
            << handler.AccessKind << 2 << Field;
          Info.Note(Field->getLocation(), diag::note_declared_at);
        } else {
          Info.FFDiag(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.FFDiag(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.FFDiag(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.MostDerivedIsArrayElement;
  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.
static CompleteObject findCompleteObject(EvalInfo &Info, const Expr *E,
                                         AccessKinds AK, const LValue &LVal,
                                         QualType LValType) {
  if (!LVal.Base) {
    Info.FFDiag(E, diag::note_constexpr_access_null) << AK;
    return CompleteObject();
  }

  CallStackFrame *Frame = nullptr;
  if (LVal.CallIndex) {
    Frame = Info.getCallFrame(LVal.CallIndex);
    if (!Frame) {
      Info.FFDiag(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.FFDiag(E, diag::note_constexpr_access_volatile_type)
        << AK << LValType;
    else
      Info.FFDiag(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.FFDiag(E);
      return CompleteObject();
    }

    // Accesses of volatile-qualified objects are not allowed.
    if (BaseType.isVolatileQualified()) {
      if (Info.getLangOpts().CPlusPlus) {
        Info.FFDiag(E, diag::note_constexpr_access_volatile_obj, 1)
          << AK << 1 << VD;
        Info.Note(VD->getLocation(), diag::note_declared_at);
      } else {
        Info.FFDiag(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().CPlusPlus14 &&
          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.FFDiag(E, diag::note_constexpr_modify_global);
        return CompleteObject();
      } else if (VD->isConstexpr()) {
        // OK, we can read this variable.
      } else if (BaseType->isIntegralOrEnumerationType()) {
        // In OpenCL if a variable is in constant address space it is a const value.
        if (!(BaseType.isConstQualified() ||
              (Info.getLangOpts().OpenCL &&
               BaseType.getAddressSpace() == LangAS::opencl_constant))) {
          if (Info.getLangOpts().CPlusPlus) {
            Info.FFDiag(E, diag::note_constexpr_ltor_non_const_int, 1) << VD;
            Info.Note(VD->getLocation(), diag::note_declared_at);
          } else {
            Info.FFDiag(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.checkingPotentialConstantExpression() &&
            VD->getType().isConstQualified() && !VD->hasDefinition(Info.Ctx)) {
          // The definition of this variable could be constexpr. We can't
          // access it right now, but may be able to in future.
        } else if (Info.getLangOpts().CPlusPlus11) {
          Info.FFDiag(E, diag::note_constexpr_ltor_non_constexpr, 1) << VD;
          Info.Note(VD->getLocation(), diag::note_declared_at);
        } else {
          Info.FFDiag(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.FFDiag(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.FFDiag(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.FFDiag(E, diag::note_constexpr_access_volatile_obj, 1)
          << AK << 0;
        Info.Note(Base->getExprLoc(), diag::note_constexpr_temporary_here);
      } else {
        Info.FFDiag(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.
  //
  // 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().CPlusPlus14 &&
       Info.EvalStatus.HasSideEffects) ||
      (AK != AK_Read && Info.IsSpeculativelyEvaluating))
    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 (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.FFDiag(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) || isa<PredefinedExpr>(Base)) {
      // We represent a string literal array as an lvalue pointing at the
      // corresponding expression, rather than building an array of chars.
      // FIXME: Support 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().CPlusPlus14) {
    Info.FFDiag(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.FFDiag(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.FFDiag(E);
      return false;
    case APValue::LValue:
      return foundPointer(Subobj, SubobjType);
    default:
      // FIXME: can this happen?
      Info.FFDiag(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.FFDiag(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.FFDiag(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().CPlusPlus14) {
    Info.FFDiag(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.FFDiag(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.FFDiag(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.FFDiag(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);
        return 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);
        return 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.FFDiag(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().CPlusPlus14) {
    Info.FFDiag(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.FFDiag(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.FFDiag(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.FFDiag(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.FFDiag(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.noteFailure()) {
      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 {