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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() : 0) {}
     58 
     59 SVal Environment::lookupExpr(const EnvironmentEntry &E) const {
     60   const SVal* X = ExprBindings.lookup(E);
     61   if (X) {
     62     SVal V = *X;
     63     return V;
     64   }
     65   return UnknownVal();
     66 }
     67 
     68 SVal Environment::getSVal(const EnvironmentEntry &Entry,
     69                           SValBuilder& svalBuilder) const {
     70   const Stmt *S = Entry.getStmt();
     71   const LocationContext *LCtx = Entry.getLocationContext();
     72 
     73   switch (S->getStmtClass()) {
     74   case Stmt::CXXBindTemporaryExprClass:
     75   case Stmt::ExprWithCleanupsClass:
     76   case Stmt::GenericSelectionExprClass:
     77   case Stmt::OpaqueValueExprClass:
     78   case Stmt::ParenExprClass:
     79   case Stmt::SubstNonTypeTemplateParmExprClass:
     80     llvm_unreachable("Should have been handled by ignoreTransparentExprs");
     81 
     82   case Stmt::AddrLabelExprClass:
     83   case Stmt::CharacterLiteralClass:
     84   case Stmt::CXXBoolLiteralExprClass:
     85   case Stmt::CXXScalarValueInitExprClass:
     86   case Stmt::ImplicitValueInitExprClass:
     87   case Stmt::IntegerLiteralClass:
     88   case Stmt::ObjCBoolLiteralExprClass:
     89   case Stmt::CXXNullPtrLiteralExprClass:
     90   case Stmt::ObjCStringLiteralClass:
     91   case Stmt::StringLiteralClass:
     92     // Known constants; defer to SValBuilder.
     93     return svalBuilder.getConstantVal(cast<Expr>(S)).getValue();
     94 
     95   case Stmt::ReturnStmtClass: {
     96     const ReturnStmt *RS = cast<ReturnStmt>(S);
     97     if (const Expr *RE = RS->getRetValue())
     98       return getSVal(EnvironmentEntry(RE, LCtx), svalBuilder);
     99     return UndefinedVal();
    100   }
    101 
    102   // Handle all other Stmt* using a lookup.
    103   default:
    104     return lookupExpr(EnvironmentEntry(S, LCtx));
    105   }
    106 }
    107 
    108 Environment EnvironmentManager::bindExpr(Environment Env,
    109                                          const EnvironmentEntry &E,
    110                                          SVal V,
    111                                          bool Invalidate) {
    112   if (V.isUnknown()) {
    113     if (Invalidate)
    114       return Environment(F.remove(Env.ExprBindings, E));
    115     else
    116       return Env;
    117   }
    118   return Environment(F.add(Env.ExprBindings, E, V));
    119 }
    120 
    121 namespace {
    122 class MarkLiveCallback : public SymbolVisitor {
    123   SymbolReaper &SymReaper;
    124 public:
    125   MarkLiveCallback(SymbolReaper &symreaper) : SymReaper(symreaper) {}
    126   bool VisitSymbol(SymbolRef sym) {
    127     SymReaper.markLive(sym);
    128     return true;
    129   }
    130   bool VisitMemRegion(const MemRegion *R) {
    131     SymReaper.markLive(R);
    132     return true;
    133   }
    134 };
    135 } // end anonymous namespace
    136 
    137 // removeDeadBindings:
    138 //  - Remove subexpression bindings.
    139 //  - Remove dead block expression bindings.
    140 //  - Keep live block expression bindings:
    141 //   - Mark their reachable symbols live in SymbolReaper,
    142 //     see ScanReachableSymbols.
    143 //   - Mark the region in DRoots if the binding is a loc::MemRegionVal.
    144 Environment
    145 EnvironmentManager::removeDeadBindings(Environment Env,
    146                                        SymbolReaper &SymReaper,
    147                                        ProgramStateRef ST) {
    148 
    149   // We construct a new Environment object entirely, as this is cheaper than
    150   // individually removing all the subexpression bindings (which will greatly
    151   // outnumber block-level expression bindings).
    152   Environment NewEnv = getInitialEnvironment();
    153 
    154   MarkLiveCallback CB(SymReaper);
    155   ScanReachableSymbols RSScaner(ST, CB);
    156 
    157   llvm::ImmutableMapRef<EnvironmentEntry,SVal>
    158     EBMapRef(NewEnv.ExprBindings.getRootWithoutRetain(),
    159              F.getTreeFactory());
    160 
    161   // Iterate over the block-expr bindings.
    162   for (Environment::iterator I = Env.begin(), E = Env.end();
    163        I != E; ++I) {
    164 
    165     const EnvironmentEntry &BlkExpr = I.getKey();
    166     const SVal &X = I.getData();
    167 
    168     if (SymReaper.isLive(BlkExpr.getStmt(), BlkExpr.getLocationContext())) {
    169       // Copy the binding to the new map.
    170       EBMapRef = EBMapRef.add(BlkExpr, X);
    171 
    172       // If the block expr's value is a memory region, then mark that region.
    173       if (Optional<loc::MemRegionVal> R = X.getAs<loc::MemRegionVal>())
    174         SymReaper.markLive(R->getRegion());
    175 
    176       // Mark all symbols in the block expr's value live.
    177       RSScaner.scan(X);
    178       continue;
    179     } else {
    180       SymExpr::symbol_iterator SI = X.symbol_begin(), SE = X.symbol_end();
    181       for (; SI != SE; ++SI)
    182         SymReaper.maybeDead(*SI);
    183     }
    184   }
    185 
    186   NewEnv.ExprBindings = EBMapRef.asImmutableMap();
    187   return NewEnv;
    188 }
    189 
    190 void Environment::print(raw_ostream &Out, const char *NL,
    191                         const char *Sep) const {
    192   bool isFirst = true;
    193 
    194   for (Environment::iterator I = begin(), E = end(); I != E; ++I) {
    195     const EnvironmentEntry &En = I.getKey();
    196 
    197     if (isFirst) {
    198       Out << NL << NL
    199           << "Expressions:"
    200           << NL;
    201       isFirst = false;
    202     } else {
    203       Out << NL;
    204     }
    205 
    206     const Stmt *S = En.getStmt();
    207 
    208     Out << " (" << (const void*) En.getLocationContext() << ','
    209       << (const void*) S << ") ";
    210     LangOptions LO; // FIXME.
    211     S->printPretty(Out, 0, PrintingPolicy(LO));
    212     Out << " : " << I.getData();
    213   }
    214 }
    215