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      1 //== Environment.cpp - Map from Stmt* to Locations/Values -------*- C++ -*--==//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 //  This file defined the Environment and EnvironmentManager classes.
     11 //
     12 //===----------------------------------------------------------------------===//
     13 
     14 #include "clang/AST/ExprCXX.h"
     15 #include "clang/AST/ExprObjC.h"
     16 #include "clang/Analysis/AnalysisContext.h"
     17 #include "clang/Analysis/CFG.h"
     18 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
     19 #include "llvm/Support/raw_ostream.h"
     20 
     21 using namespace clang;
     22 using namespace ento;
     23 
     24 static const Expr *ignoreTransparentExprs(const Expr *E) {
     25   E = E->IgnoreParens();
     26 
     27   switch (E->getStmtClass()) {
     28   case Stmt::OpaqueValueExprClass:
     29     E = cast<OpaqueValueExpr>(E)->getSourceExpr();
     30     break;
     31   case Stmt::ExprWithCleanupsClass:
     32     E = cast<ExprWithCleanups>(E)->getSubExpr();
     33     break;
     34   case Stmt::CXXBindTemporaryExprClass:
     35     E = cast<CXXBindTemporaryExpr>(E)->getSubExpr();
     36     break;
     37   case Stmt::SubstNonTypeTemplateParmExprClass:
     38     E = cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement();
     39     break;
     40   default:
     41     // This is the base case: we can't look through more than we already have.
     42     return E;
     43   }
     44 
     45   return ignoreTransparentExprs(E);
     46 }
     47 
     48 static const Stmt *ignoreTransparentExprs(const Stmt *S) {
     49   if (const Expr *E = dyn_cast<Expr>(S))
     50     return ignoreTransparentExprs(E);
     51   return S;
     52 }
     53 
     54 EnvironmentEntry::EnvironmentEntry(const Stmt *S, const LocationContext *L)
     55   : std::pair<const Stmt *,
     56               const StackFrameContext *>(ignoreTransparentExprs(S),
     57                                          L ? L->getCurrentStackFrame()
     58                                            : nullptr) {}
     59 
     60 SVal Environment::lookupExpr(const EnvironmentEntry &E) const {
     61   const SVal* X = ExprBindings.lookup(E);
     62   if (X) {
     63     SVal V = *X;
     64     return V;
     65   }
     66   return UnknownVal();
     67 }
     68 
     69 SVal Environment::getSVal(const EnvironmentEntry &Entry,
     70                           SValBuilder& svalBuilder) const {
     71   const Stmt *S = Entry.getStmt();
     72   const LocationContext *LCtx = Entry.getLocationContext();
     73 
     74   switch (S->getStmtClass()) {
     75   case Stmt::CXXBindTemporaryExprClass:
     76   case Stmt::ExprWithCleanupsClass:
     77   case Stmt::GenericSelectionExprClass:
     78   case Stmt::OpaqueValueExprClass:
     79   case Stmt::ParenExprClass:
     80   case Stmt::SubstNonTypeTemplateParmExprClass:
     81     llvm_unreachable("Should have been handled by ignoreTransparentExprs");
     82 
     83   case Stmt::AddrLabelExprClass:
     84   case Stmt::CharacterLiteralClass:
     85   case Stmt::CXXBoolLiteralExprClass:
     86   case Stmt::CXXScalarValueInitExprClass:
     87   case Stmt::ImplicitValueInitExprClass:
     88   case Stmt::IntegerLiteralClass:
     89   case Stmt::ObjCBoolLiteralExprClass:
     90   case Stmt::CXXNullPtrLiteralExprClass:
     91   case Stmt::ObjCStringLiteralClass:
     92   case Stmt::StringLiteralClass:
     93     // Known constants; defer to SValBuilder.
     94     return svalBuilder.getConstantVal(cast<Expr>(S)).getValue();
     95 
     96   case Stmt::ReturnStmtClass: {
     97     const ReturnStmt *RS = cast<ReturnStmt>(S);
     98     if (const Expr *RE = RS->getRetValue())
     99       return getSVal(EnvironmentEntry(RE, LCtx), svalBuilder);
    100     return UndefinedVal();
    101   }
    102 
    103   // Handle all other Stmt* using a lookup.
    104   default:
    105     return lookupExpr(EnvironmentEntry(S, LCtx));
    106   }
    107 }
    108 
    109 Environment EnvironmentManager::bindExpr(Environment Env,
    110                                          const EnvironmentEntry &E,
    111                                          SVal V,
    112                                          bool Invalidate) {
    113   if (V.isUnknown()) {
    114     if (Invalidate)
    115       return Environment(F.remove(Env.ExprBindings, E));
    116     else
    117       return Env;
    118   }
    119   return Environment(F.add(Env.ExprBindings, E, V));
    120 }
    121 
    122 namespace {
    123 class MarkLiveCallback : public SymbolVisitor {
    124   SymbolReaper &SymReaper;
    125 public:
    126   MarkLiveCallback(SymbolReaper &symreaper) : SymReaper(symreaper) {}
    127   bool VisitSymbol(SymbolRef sym) override {
    128     SymReaper.markLive(sym);
    129     return true;
    130   }
    131   bool VisitMemRegion(const MemRegion *R) override {
    132     SymReaper.markLive(R);
    133     return true;
    134   }
    135 };
    136 } // end anonymous namespace
    137 
    138 // removeDeadBindings:
    139 //  - Remove subexpression bindings.
    140 //  - Remove dead block expression bindings.
    141 //  - Keep live block expression bindings:
    142 //   - Mark their reachable symbols live in SymbolReaper,
    143 //     see ScanReachableSymbols.
    144 //   - Mark the region in DRoots if the binding is a loc::MemRegionVal.
    145 Environment
    146 EnvironmentManager::removeDeadBindings(Environment Env,
    147                                        SymbolReaper &SymReaper,
    148                                        ProgramStateRef ST) {
    149 
    150   // We construct a new Environment object entirely, as this is cheaper than
    151   // individually removing all the subexpression bindings (which will greatly
    152   // outnumber block-level expression bindings).
    153   Environment NewEnv = getInitialEnvironment();
    154 
    155   MarkLiveCallback CB(SymReaper);
    156   ScanReachableSymbols RSScaner(ST, CB);
    157 
    158   llvm::ImmutableMapRef<EnvironmentEntry,SVal>
    159     EBMapRef(NewEnv.ExprBindings.getRootWithoutRetain(),
    160              F.getTreeFactory());
    161 
    162   // Iterate over the block-expr bindings.
    163   for (Environment::iterator I = Env.begin(), E = Env.end();
    164        I != E; ++I) {
    165 
    166     const EnvironmentEntry &BlkExpr = I.getKey();
    167     const SVal &X = I.getData();
    168 
    169     if (SymReaper.isLive(BlkExpr.getStmt(), BlkExpr.getLocationContext())) {
    170       // Copy the binding to the new map.
    171       EBMapRef = EBMapRef.add(BlkExpr, X);
    172 
    173       // If the block expr's value is a memory region, then mark that region.
    174       if (Optional<loc::MemRegionVal> R = X.getAs<loc::MemRegionVal>())
    175         SymReaper.markLive(R->getRegion());
    176 
    177       // Mark all symbols in the block expr's value live.
    178       RSScaner.scan(X);
    179       continue;
    180     } else {
    181       SymExpr::symbol_iterator SI = X.symbol_begin(), SE = X.symbol_end();
    182       for (; SI != SE; ++SI)
    183         SymReaper.maybeDead(*SI);
    184     }
    185   }
    186 
    187   NewEnv.ExprBindings = EBMapRef.asImmutableMap();
    188   return NewEnv;
    189 }
    190 
    191 void Environment::print(raw_ostream &Out, const char *NL,
    192                         const char *Sep) const {
    193   bool isFirst = true;
    194 
    195   for (Environment::iterator I = begin(), E = end(); I != E; ++I) {
    196     const EnvironmentEntry &En = I.getKey();
    197 
    198     if (isFirst) {
    199       Out << NL << NL
    200           << "Expressions:"
    201           << NL;
    202       isFirst = false;
    203     } else {
    204       Out << NL;
    205     }
    206 
    207     const Stmt *S = En.getStmt();
    208     assert(S != nullptr && "Expected non-null Stmt");
    209 
    210     Out << " (" << (const void*) En.getLocationContext() << ','
    211       << (const void*) S << ") ";
    212     LangOptions LO; // FIXME.
    213     S->printPretty(Out, nullptr, PrintingPolicy(LO));
    214     Out << " : " << I.getData();
    215   }
    216 }
    217