Environment.cpp

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//===- Environment.cpp - Map from Stmt* to Locations/Values ---------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
//  This file defined the Environment and EnvironmentManager classes.
//
//===----------------------------------------------------------------------===//

#include "clang/StaticAnalyzer/Core/PathSensitive/Environment.h"
#include "clang/AST/Expr.h"
#include "clang/AST/ExprCXX.h"
#include "clang/AST/PrettyPrinter.h"
#include "clang/AST/Stmt.h"
#include "clang/Analysis/AnalysisDeclContext.h"
#include "clang/Basic/LLVM.h"
#include "clang/Basic/LangOptions.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/SValBuilder.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/SVals.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/SymExpr.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/SymbolManager.h"
#include "llvm/ADT/ImmutableMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>

using namespace clang;
using namespace ento;

static const Expr *ignoreTransparentExprs(const Expr *E) {
  E = E->IgnoreParens();

  switch (E->getStmtClass()) {
  case Stmt::OpaqueValueExprClass:
    E = cast<OpaqueValueExpr>(E)->getSourceExpr();
    break;
  case Stmt::ExprWithCleanupsClass:
    E = cast<ExprWithCleanups>(E)->getSubExpr();
    break;
  case Stmt::ConstantExprClass:
    E = cast<ConstantExpr>(E)->getSubExpr();
    break;
  case Stmt::CXXBindTemporaryExprClass:
    E = cast<CXXBindTemporaryExpr>(E)->getSubExpr();
    break;
  case Stmt::SubstNonTypeTemplateParmExprClass:
    E = cast<SubstNonTypeTemplateParmExpr>(E)->getReplacement();
    break;
  default:
    // This is the base case: we can't look through more than we already have.
    return E;
  }

  return ignoreTransparentExprs(E);
}

static const Stmt *ignoreTransparentExprs(const Stmt *S) {
  if (const auto *E = dyn_cast<Expr>(S))
    return ignoreTransparentExprs(E);
  return S;
}

EnvironmentEntry::EnvironmentEntry(const Stmt *S, const LocationContext *L)
    : std::pair<const Stmt *,
                const StackFrameContext *>(ignoreTransparentExprs(S),
                                           L ? L->getStackFrame()
                                             : nullptr) {}

SVal Environment::lookupExpr(const EnvironmentEntry &E) const {
  const SVal* X = ExprBindings.lookup(E);
  if (X) {
    SVal V = *X;
    return V;
  }
  return UnknownVal();
}

SVal Environment::getSVal(const EnvironmentEntry &Entry,
                          SValBuilder& svalBuilder) const {
  const Stmt *S = Entry.getStmt();
  const LocationContext *LCtx = Entry.getLocationContext();

  switch (S->getStmtClass()) {
  case Stmt::CXXBindTemporaryExprClass:
  case Stmt::ExprWithCleanupsClass:
  case Stmt::GenericSelectionExprClass:
  case Stmt::OpaqueValueExprClass:
  case Stmt::ConstantExprClass:
  case Stmt::ParenExprClass:
  case Stmt::SubstNonTypeTemplateParmExprClass:
    llvm_unreachable("Should have been handled by ignoreTransparentExprs");

  case Stmt::AddrLabelExprClass:
  case Stmt::CharacterLiteralClass:
  case Stmt::CXXBoolLiteralExprClass:
  case Stmt::CXXScalarValueInitExprClass:
  case Stmt::ImplicitValueInitExprClass:
  case Stmt::IntegerLiteralClass:
  case Stmt::ObjCBoolLiteralExprClass:
  case Stmt::CXXNullPtrLiteralExprClass:
  case Stmt::ObjCStringLiteralClass:
  case Stmt::StringLiteralClass:
  case Stmt::TypeTraitExprClass:
    // Known constants; defer to SValBuilder.
    return svalBuilder.getConstantVal(cast<Expr>(S)).getValue();

  case Stmt::ReturnStmtClass: {
    const auto *RS = cast<ReturnStmt>(S);
    if (const Expr *RE = RS->getRetValue())
      return getSVal(EnvironmentEntry(RE, LCtx), svalBuilder);
    return UndefinedVal();
  }

  // Handle all other Stmt* using a lookup.
  default:
    return lookupExpr(EnvironmentEntry(S, LCtx));
  }
}

Environment EnvironmentManager::bindExpr(Environment Env,
                                         const EnvironmentEntry &E,
                                         SVal V,
                                         bool Invalidate) {
  if (V.isUnknown()) {
    if (Invalidate)
      return Environment(F.remove(Env.ExprBindings, E));
    else
      return Env;
  }
  return Environment(F.add(Env.ExprBindings, E, V));
}

namespace {

class MarkLiveCallback final : public SymbolVisitor {
  SymbolReaper &SymReaper;

public:
  MarkLiveCallback(SymbolReaper &symreaper) : SymReaper(symreaper) {}

  bool VisitSymbol(SymbolRef sym) override {
    SymReaper.markLive(sym);
    return true;
  }

  bool VisitMemRegion(const MemRegion *R) override {
    SymReaper.markLive(R);
    return true;
  }
};

} // namespace

// removeDeadBindings:
//  - Remove subexpression bindings.
//  - Remove dead block expression bindings.
//  - Keep live block expression bindings:
//   - Mark their reachable symbols live in SymbolReaper,
//     see ScanReachableSymbols.
//   - Mark the region in DRoots if the binding is a loc::MemRegionVal.
Environment
EnvironmentManager::removeDeadBindings(Environment Env,
                                       SymbolReaper &SymReaper,
                                       ProgramStateRef ST) {
  // We construct a new Environment object entirely, as this is cheaper than
  // individually removing all the subexpression bindings (which will greatly
  // outnumber block-level expression bindings).
  Environment NewEnv = getInitialEnvironment();

  MarkLiveCallback CB(SymReaper);
  ScanReachableSymbols RSScaner(ST, CB);

  llvm::ImmutableMapRef<EnvironmentEntry, SVal>
    EBMapRef(NewEnv.ExprBindings.getRootWithoutRetain(),
             F.getTreeFactory());

  // Iterate over the block-expr bindings.
  for (Environment::iterator I = Env.begin(), E = Env.end();
       I != E; ++I) {
    const EnvironmentEntry &BlkExpr = I.getKey();
    const SVal &X = I.getData();

    if (SymReaper.isLive(BlkExpr.getStmt(), BlkExpr.getLocationContext())) {
      // Copy the binding to the new map.
      EBMapRef = EBMapRef.add(BlkExpr, X);

      // Mark all symbols in the block expr's value live.
      RSScaner.scan(X);
    }
  }

  NewEnv.ExprBindings = EBMapRef.asImmutableMap();
  return NewEnv;
}

void Environment::print(raw_ostream &Out, const char *NL,
                        const char *Sep,
                        const ASTContext &Context,
                        const LocationContext *WithLC) const {
  if (ExprBindings.isEmpty())
    return;

  if (!WithLC) {
    // Find the freshest location context.
    llvm::SmallPtrSet<const LocationContext *, 16> FoundContexts;
    for (auto I : *this) {
      const LocationContext *LC = I.first.getLocationContext();
      if (FoundContexts.count(LC) == 0) {
        // This context is fresher than all other contexts so far.
        WithLC = LC;
        for (const LocationContext *LCI = LC; LCI; LCI = LCI->getParent())
          FoundContexts.insert(LCI);
      }
    }
  }

  assert(WithLC);

  PrintingPolicy PP = Context.getPrintingPolicy();

  Out << NL << "Expressions by stack frame:" << NL;
  WithLC->dumpStack(Out, "", NL, Sep, [&](const LocationContext *LC) {
    for (auto I : ExprBindings) {
      if (I.first.getLocationContext() != LC)
        continue;

      const Stmt *S = I.first.getStmt();
      assert(S != nullptr && "Expected non-null Stmt");

      Out << "(LC" << LC->getID() << ", S" << S->getID(Context) << ") ";
      S->printPretty(Out, /*Helper=*/nullptr, PP);
      Out << " : " << I.second << NL;
    }
  });
}