Merge bleeding edge into the GC branch up to 7948. The asserts

tools/gcmole/gcmole.cc

Index: tools/gcmole/gcmole.cc
===================================================================
--- tools/gcmole/gcmole.cc	(revision 7948)
+++ tools/gcmole/gcmole.cc	(working copy)
@@ -69,6 +69,47 @@
 }
 
 
+struct Resolver {
+  explicit Resolver(clang::ASTContext& ctx)
+      : ctx_(ctx), decl_ctx_(ctx.getTranslationUnitDecl()) {
+  }
+
+  Resolver(clang::ASTContext& ctx, clang::DeclContext* decl_ctx)
+      : ctx_(ctx), decl_ctx_(decl_ctx) {
+  }
+
+  clang::DeclarationName ResolveName(const char* n) {
+    clang::IdentifierInfo* ident = &ctx_.Idents.get(n);
+    return ctx_.DeclarationNames.getIdentifier(ident);
+  }
+
+  Resolver ResolveNamespace(const char* n) {
+    return Resolver(ctx_, Resolve<clang::NamespaceDecl>(n));
+  }
+
+  template<typename T>
+  T* Resolve(const char* n) {
+    if (decl_ctx_ == NULL) return NULL;
+
+    clang::DeclContext::lookup_result result =
+        decl_ctx_->lookup(ResolveName(n));
+
+    clang::DeclContext::lookup_iterator end = result.second;
+    for (clang::DeclContext::lookup_iterator i = result.first;
+         i != end;
+         i++) {
+      if (isa<T>(*i)) return cast<T>(*i);
+    }
+
+    return NULL;
+  }
+
+ private:
+  clang::ASTContext& ctx_;
+  clang::DeclContext* decl_ctx_;
+};
+
+
 class CalleesPrinter : public clang::RecursiveASTVisitor<CalleesPrinter> {
  public:
   explicit CalleesPrinter(clang::MangleContext* ctx) : ctx_(ctx) {
@@ -140,12 +181,14 @@
   Callgraph callgraph_;
 };
 
+
 class FunctionDeclarationFinder
     : public clang::ASTConsumer,
       public clang::RecursiveASTVisitor<FunctionDeclarationFinder> {
  public:
   explicit FunctionDeclarationFinder(clang::Diagnostic& d,
-                                     clang::SourceManager& sm)
+                                     clang::SourceManager& sm,
+                                     const std::vector<std::string>& args)
       : d_(d), sm_(sm) { }
 
   virtual void HandleTranslationUnit(clang::ASTContext &ctx) {
@@ -202,102 +245,809 @@
 }
 
 
-static bool IsHandleType(const clang::DeclarationName& handleDeclName,
-                         const clang::QualType& qtype) {
-  const clang::Type* canonical_type =
-      qtype.getTypePtr()->getCanonicalTypeUnqualified().getTypePtr();
+static const int kNoEffect = 0;
+static const int kCausesGC = 1;
+static const int kRawDef = 2;
+static const int kRawUse = 4;
+static const int kAllEffects = kCausesGC | kRawDef | kRawUse;
 
-  if (const clang::TemplateSpecializationType* type =
-          canonical_type->getAs<clang::TemplateSpecializationType>()) {
-    if (clang::TemplateDecl* decl =
-            type->getTemplateName().getAsTemplateDecl()) {
-      if (decl->getTemplatedDecl()->getDeclName() == handleDeclName) {
-        return true;
-      }
+class Environment;
+
+class ExprEffect {
+ public:
+  bool hasGC() { return (effect_ & kCausesGC) != 0; }
+  void setGC() { effect_ |= kCausesGC; }
+
+  bool hasRawDef() { return (effect_ & kRawDef) != 0; }
+  void setRawDef() { effect_ |= kRawDef; }
+
+  bool hasRawUse() { return (effect_ & kRawUse) != 0; }
+  void setRawUse() { effect_ |= kRawUse; }
+
+  static ExprEffect None() { return ExprEffect(kNoEffect, NULL); }
+  static ExprEffect NoneWithEnv(Environment* env) {
+    return ExprEffect(kNoEffect, env);
+  }
+  static ExprEffect RawUse() { return ExprEffect(kRawUse, NULL); }
+
+  static ExprEffect Merge(ExprEffect a, ExprEffect b);
+  static ExprEffect MergeSeq(ExprEffect a, ExprEffect b);
+  ExprEffect Define(const std::string& name);
+
+  Environment* env() {
+    return reinterpret_cast<Environment*>(effect_ & ~kAllEffects);
+  }
+
+ private:
+  ExprEffect(int effect, Environment* env)
+      : effect_((effect & kAllEffects) |
+                reinterpret_cast<intptr_t>(env)) { }
+
+  intptr_t effect_;
+};
+
+
+const std::string BAD_EXPR_MSG("Possible problem with evaluation order.");
+const std::string DEAD_VAR_MSG("Possibly dead variable.");
+
+
+class Environment {
+ public:
+  Environment() { }
+
+  static Environment Unreachable() {
+    Environment env;
+    env.live_.set();
+    return env;
+  }
+
+  static Environment Merge(const Environment& l,
+                           const Environment& r) {
+    return Environment(l, r);
+  }
+
+  Environment ApplyEffect(ExprEffect effect) const {
+    Environment out = effect.hasGC() ? Environment() : Environment(*this);
+    if (effect.env() != NULL) out.live_ |= effect.env()->live_;
+    return out;
+  }
+
+  typedef std::map<std::string, int> SymbolTable;
+
+  bool IsAlive(const std::string& name) const {
+    SymbolTable::iterator code = symbol_table_.find(name);
+    if (code == symbol_table_.end()) return false;
+    return live_[code->second];
+  }
+
+  bool Equal(const Environment& env) {
+    return live_ == env.live_;
+  }
+
+  Environment Define(const std::string& name) const {
+    return Environment(*this, SymbolToCode(name));
+  }
+
+  void MDefine(const std::string& name) {
+    live_.set(SymbolToCode(name));
+  }
+
+  static int SymbolToCode(const std::string& name) {
+    SymbolTable::iterator code = symbol_table_.find(name);
+
+    if (code == symbol_table_.end()) {
+      int new_code = symbol_table_.size();
+      symbol_table_.insert(std::make_pair(name, new_code));
+      return new_code;
     }
-  } else if (const clang::RecordType* type =
-                 canonical_type->getAs<clang::RecordType>()) {
-    if (const clang::ClassTemplateSpecializationDecl* t =
-        dyn_cast<clang::ClassTemplateSpecializationDecl>(type->getDecl())) {
-      if (t->getSpecializedTemplate()->getDeclName() == handleDeclName) {
-        return true;
+
+    return code->second;
+  }
+
+  static void ClearSymbolTable() {
+    std::vector<Environment*>::iterator end = envs_.end();
+    for (std::vector<Environment*>::iterator i = envs_.begin();
+         i != end;
+         ++i) {
+      delete *i;
+    }
+    envs_.clear();
+    symbol_table_.clear();
+  }
+
+  void Print() const {
+    bool comma = false;
+    std::cout << "{";
+    SymbolTable::iterator end = symbol_table_.end();
+    for (SymbolTable::iterator i = symbol_table_.begin();
+         i != end;
+         ++i) {
+      if (live_[i->second]) {
+        if (comma) std::cout << ", ";
+        std::cout << i->first;
+        comma = true;
       }
     }
+    std::cout << "}";
   }
 
-  return false;
+  static Environment* Allocate(const Environment& env) {
+    Environment* allocated_env = new Environment(env);
+    envs_.push_back(allocated_env);
+    return allocated_env;
+  }
+
+ private:
+  Environment(const Environment& l, const Environment& r)
+      : live_(l.live_ & r.live_) {
+  }
+
+  Environment(const Environment& l, int code)
+      : live_(l.live_) {
+    live_.set(code);
+  }
+
+  static SymbolTable symbol_table_;
+  static std::vector<Environment* > envs_;
+
+  static const int kMaxNumberOfLocals = 256;
+  std::bitset<kMaxNumberOfLocals> live_;
+
+  friend class ExprEffect;
+  friend class CallProps;
+};
+
+
+class CallProps {
+ public:
+  CallProps() : env_(NULL) { }
+
+  void SetEffect(int arg, ExprEffect in) {
+    if (in.hasGC()) gc_.set(arg);
+    if (in.hasRawDef()) raw_def_.set(arg);
+    if (in.hasRawUse()) raw_use_.set(arg);
+    if (in.env() != NULL) {
+      if (env_ == NULL) env_ = in.env();
+      env_->live_ |= in.env()->live_;
+    }
+  }
+
+  ExprEffect ComputeCumulativeEffect(bool result_is_raw) {
+    ExprEffect out = ExprEffect::NoneWithEnv(env_);
+    if (gc_.any()) out.setGC();
+    if (raw_use_.any()) out.setRawUse();
+    if (result_is_raw) out.setRawDef();
+    return out;
+  }
+
+  bool IsSafe() {
+    if (!gc_.any()) return true;
+    std::bitset<kMaxNumberOfArguments> raw = (raw_def_ | raw_use_);
+    if (!raw.any()) return true;
+    return gc_.count() == 1 && !((raw ^ gc_).any());
+  }
+
+ private:
+  static const int kMaxNumberOfArguments = 64;
+  std::bitset<kMaxNumberOfArguments> raw_def_;
+  std::bitset<kMaxNumberOfArguments> raw_use_;
+  std::bitset<kMaxNumberOfArguments> gc_;
+  Environment* env_;
+};
+
+
+Environment::SymbolTable Environment::symbol_table_;
+std::vector<Environment* > Environment::envs_;
+
+
+ExprEffect ExprEffect::Merge(ExprEffect a, ExprEffect b) {
+  Environment* a_env = a.env();
+  Environment* b_env = b.env();
+  Environment* out = NULL;
+  if (a_env != NULL && b_env != NULL) {
+    out = Environment::Allocate(*a_env);
+    out->live_ &= b_env->live_;
+  }
+  return ExprEffect(a.effect_ | b.effect_, out);
 }
 
 
-class ExpressionClassifier :
-    public clang::RecursiveASTVisitor<ExpressionClassifier> {
+ExprEffect ExprEffect::MergeSeq(ExprEffect a, ExprEffect b) {
+  Environment* a_env = b.hasGC() ? NULL : a.env();
+  Environment* b_env = b.env();
+  Environment* out = (b_env == NULL) ? a_env : b_env;
+  if (a_env != NULL && b_env != NULL) {
+    out = Environment::Allocate(*b_env);
+    out->live_ |= a_env->live_;
+  }
+  return ExprEffect(a.effect_ | b.effect_, out);
+}
+
+
+ExprEffect ExprEffect::Define(const std::string& name) {
+  Environment* e = env();
+  if (e == NULL) {
+    e = Environment::Allocate(Environment());
+  }
+  e->MDefine(name);
+  return ExprEffect(effect_, e);
+}
+
+
+static std::string THIS ("this");
+
+
+class FunctionAnalyzer {
  public:
-  ExpressionClassifier(clang::DeclarationName handleDeclName,
-                       clang::MangleContext* ctx,
-                       clang::CXXRecordDecl* objectDecl)
-      : handleDeclName_(handleDeclName),
-        ctx_(ctx),
-        objectDecl_(objectDecl) {
+  FunctionAnalyzer(clang::MangleContext* ctx,
+                   clang::DeclarationName handle_decl_name,
+                   clang::CXXRecordDecl* object_decl,
+                   clang::CXXRecordDecl* smi_decl,
+                   clang::Diagnostic& d,
+                   clang::SourceManager& sm,
+                   bool dead_vars_analysis)
+      : ctx_(ctx),
+        handle_decl_name_(handle_decl_name),
+        object_decl_(object_decl),
+        smi_decl_(smi_decl),
+        d_(d),
+        sm_(sm),
+        block_(NULL),
+        dead_vars_analysis_(dead_vars_analysis) {
   }
 
-  bool IsBadExpression(clang::Expr* expr) {
-    has_derefs_ = has_gc_ = false;
-    TraverseStmt(expr);
-    return has_derefs_ && has_gc_;
+
+  // --------------------------------------------------------------------------
+  // Expressions
+  // --------------------------------------------------------------------------
+
+  ExprEffect VisitExpr(clang::Expr* expr, const Environment& env) {
+#define VISIT(type) do {                                                \
+      clang::type* concrete_expr = dyn_cast_or_null<clang::type>(expr); \
+      if (concrete_expr != NULL) {                                      \
+        return Visit##type (concrete_expr, env);                        \
+      }                                                                 \
+    } while(0);
+
+    VISIT(AbstractConditionalOperator);
+    VISIT(AddrLabelExpr);
+    VISIT(ArraySubscriptExpr);
+    VISIT(BinaryOperator);
+    VISIT(BinaryTypeTraitExpr);
+    VISIT(BlockDeclRefExpr);
+    VISIT(BlockExpr);
+    VISIT(CallExpr);
+    VISIT(CastExpr);
+    VISIT(CharacterLiteral);
+    VISIT(ChooseExpr);
+    VISIT(CompoundLiteralExpr);
+    VISIT(CXXBindTemporaryExpr);
+    VISIT(CXXBoolLiteralExpr);
+    VISIT(CXXConstructExpr);
+    VISIT(CXXDefaultArgExpr);
+    VISIT(CXXDeleteExpr);
+    VISIT(CXXDependentScopeMemberExpr);
+    VISIT(CXXNewExpr);
+    VISIT(CXXNoexceptExpr);
+    VISIT(CXXNullPtrLiteralExpr);
+    VISIT(CXXPseudoDestructorExpr);
+    VISIT(CXXScalarValueInitExpr);
+    VISIT(CXXThisExpr);
+    VISIT(CXXThrowExpr);
+    VISIT(CXXTypeidExpr);
+    VISIT(CXXUnresolvedConstructExpr);
+    VISIT(CXXUuidofExpr);
+    VISIT(DeclRefExpr);
+    VISIT(DependentScopeDeclRefExpr);
+    VISIT(DesignatedInitExpr);
+    VISIT(ExprWithCleanups);
+    VISIT(ExtVectorElementExpr);
+    VISIT(FloatingLiteral);
+    VISIT(GNUNullExpr);
+    VISIT(ImaginaryLiteral);
+    VISIT(ImplicitValueInitExpr);
+    VISIT(InitListExpr);
+    VISIT(IntegerLiteral);
+    VISIT(MemberExpr);
+    VISIT(OffsetOfExpr);
+    VISIT(OpaqueValueExpr);
+    VISIT(OverloadExpr);
+    VISIT(PackExpansionExpr);
+    VISIT(ParenExpr);
+    VISIT(ParenListExpr);
+    VISIT(PredefinedExpr);
+    VISIT(ShuffleVectorExpr);
+    VISIT(SizeOfPackExpr);
+    VISIT(StmtExpr);
+    VISIT(StringLiteral);
+    VISIT(SubstNonTypeTemplateParmPackExpr);
+    VISIT(UnaryExprOrTypeTraitExpr);
+    VISIT(UnaryOperator);
+    VISIT(UnaryTypeTraitExpr);
+    VISIT(VAArgExpr);
+#undef VISIT
+
+    return ExprEffect::None();
   }
 
-  bool IsBadCallSite(clang::Expr* expr) {
-    if (isa<clang::CallExpr>(expr)) {
-      clang::CallExpr* call = cast<clang::CallExpr>(expr);
+#define DECL_VISIT_EXPR(type)                                           \
+  ExprEffect Visit##type (clang::type* expr, const Environment& env)
 
-      MarkGCSuspectAsArgument(call);
-      MarkHandleDereferenceAsArgument(call);
+#define IGNORE_EXPR(type)                                               \
+  ExprEffect Visit##type (clang::type* expr, const Environment& env) {  \
+    return ExprEffect::None();                                          \
+  }
 
-      return derefs_.any() &&
-          ((gc_.count() > 1) || (gc_.any() && (gc_ ^ derefs_).any()));
+  IGNORE_EXPR(AddrLabelExpr);
+  IGNORE_EXPR(BinaryTypeTraitExpr);
+  IGNORE_EXPR(BlockExpr);
+  IGNORE_EXPR(CharacterLiteral);
+  IGNORE_EXPR(ChooseExpr);
+  IGNORE_EXPR(CompoundLiteralExpr);
+  IGNORE_EXPR(CXXBoolLiteralExpr);
+  IGNORE_EXPR(CXXDependentScopeMemberExpr);
+  IGNORE_EXPR(CXXNullPtrLiteralExpr);
+  IGNORE_EXPR(CXXPseudoDestructorExpr);
+  IGNORE_EXPR(CXXScalarValueInitExpr);
+  IGNORE_EXPR(CXXNoexceptExpr);
+  IGNORE_EXPR(CXXTypeidExpr);
+  IGNORE_EXPR(CXXUnresolvedConstructExpr);
+  IGNORE_EXPR(CXXUuidofExpr);
+  IGNORE_EXPR(DependentScopeDeclRefExpr);
+  IGNORE_EXPR(DesignatedInitExpr);
+  IGNORE_EXPR(ExtVectorElementExpr);
+  IGNORE_EXPR(FloatingLiteral);
+  IGNORE_EXPR(ImaginaryLiteral);
+  IGNORE_EXPR(IntegerLiteral);
+  IGNORE_EXPR(OffsetOfExpr);
+  IGNORE_EXPR(ImplicitValueInitExpr);
+  IGNORE_EXPR(PackExpansionExpr);
+  IGNORE_EXPR(PredefinedExpr);
+  IGNORE_EXPR(ShuffleVectorExpr);
+  IGNORE_EXPR(SizeOfPackExpr);
+  IGNORE_EXPR(StmtExpr);
+  IGNORE_EXPR(StringLiteral);
+  IGNORE_EXPR(SubstNonTypeTemplateParmPackExpr);
+  IGNORE_EXPR(UnaryExprOrTypeTraitExpr);
+  IGNORE_EXPR(UnaryTypeTraitExpr);
+  IGNORE_EXPR(VAArgExpr);
+  IGNORE_EXPR(GNUNullExpr);
+  IGNORE_EXPR(OverloadExpr);
+
+  DECL_VISIT_EXPR(CXXThisExpr) {
+    return Use(expr, expr->getType(), THIS, env);
+  }
+
+  DECL_VISIT_EXPR(AbstractConditionalOperator) {
+    Environment after_cond = env.ApplyEffect(VisitExpr(expr->getCond(), env));
+    return ExprEffect::Merge(VisitExpr(expr->getTrueExpr(), after_cond),
+                             VisitExpr(expr->getFalseExpr(), after_cond));
+  }
+
+  DECL_VISIT_EXPR(ArraySubscriptExpr) {
+    clang::Expr* exprs[2] = {expr->getBase(), expr->getIdx()};
+    return Par(expr, 2, exprs, env);
+  }
+
+  bool IsRawPointerVar(clang::Expr* expr, std::string* var_name) {
+    if (isa<clang::BlockDeclRefExpr>(expr)) {
+      *var_name = cast<clang::BlockDeclRefExpr>(expr)->getDecl()->
+          getNameAsString();
+      return true;
+    } else if (isa<clang::DeclRefExpr>(expr)) {
+      *var_name = cast<clang::DeclRefExpr>(expr)->getDecl()->getNameAsString();
+      return true;
     }
     return false;
   }
 
-  virtual bool VisitExpr(clang::Expr* expr) {
-    has_derefs_ = has_derefs_ || IsRawPointerType(expr);
-    return !has_gc_ || !has_derefs_;
+  DECL_VISIT_EXPR(BinaryOperator) {
+    clang::Expr* lhs = expr->getLHS();
+    clang::Expr* rhs = expr->getRHS();
+    clang::Expr* exprs[2] = {lhs, rhs};
+
+    switch (expr->getOpcode()) {
+      case clang::BO_Comma:
+        return Seq(expr, 2, exprs, env);
+
+      case clang::BO_LAnd:
+      case clang::BO_LOr:
+        return ExprEffect::Merge(VisitExpr(lhs, env), VisitExpr(rhs, env));
+
+      case clang::BO_Assign: {
+        std::string var_name;
+        if (IsRawPointerVar(lhs, &var_name)) {
+          return VisitExpr(rhs, env).Define(var_name);
+        }
+        return Par(expr, 2, exprs, env);
+      }
+
+      default:
+        return Par(expr, 2, exprs, env);
+    }
   }
 
-  virtual bool VisitCallExpr(clang::CallExpr* expr) {
-    has_gc_ = has_gc_ || CanCauseGC(expr);
-    return !has_gc_ || !has_derefs_;
+  DECL_VISIT_EXPR(CXXBindTemporaryExpr) {
+    return VisitExpr(expr->getSubExpr(), env);
   }
- private:
-  void MarkHandleDereferenceAsArgument(clang::CallExpr* call) {
-    derefs_.reset();
 
-    if (clang::CXXMemberCallExpr* memcall =
-            dyn_cast<clang::CXXMemberCallExpr>(call)) {
-      if (ManipulatesRawPointers(memcall->getImplicitObjectArgument())) {
-        derefs_.set(0);
+  DECL_VISIT_EXPR(CXXConstructExpr) {
+    return VisitArguments<>(expr, env);
+  }
+
+  DECL_VISIT_EXPR(CXXDefaultArgExpr) {
+    return VisitExpr(expr->getExpr(), env);
+  }
+
+  DECL_VISIT_EXPR(CXXDeleteExpr) {
+    return VisitExpr(expr->getArgument(), env);
+  }
+
+  DECL_VISIT_EXPR(CXXNewExpr) {
+    return Par(expr,
+               expr->getNumConstructorArgs(),
+               expr->getConstructorArgs(),
+               env);
+  }
+
+  DECL_VISIT_EXPR(ExprWithCleanups) {
+    return VisitExpr(expr->getSubExpr(), env);
+  }
+
+  DECL_VISIT_EXPR(CXXThrowExpr) {
+    return VisitExpr(expr->getSubExpr(), env);
+  }
+
+  DECL_VISIT_EXPR(InitListExpr) {
+    return Seq(expr, expr->getNumInits(), expr->getInits(), env);
+  }
+
+  DECL_VISIT_EXPR(MemberExpr) {
+    return VisitExpr(expr->getBase(), env);
+  }
+
+  DECL_VISIT_EXPR(OpaqueValueExpr) {
+    return VisitExpr(expr->getSourceExpr(), env);
+  }
+
+  DECL_VISIT_EXPR(ParenExpr) {
+    return VisitExpr(expr->getSubExpr(), env);
+  }
+
+  DECL_VISIT_EXPR(ParenListExpr) {
+    return Par(expr, expr->getNumExprs(), expr->getExprs(), env);
+  }
+
+  DECL_VISIT_EXPR(UnaryOperator) {
+    // TODO We are treating all expressions that look like &raw_pointer_var
+    //      as definitions of raw_pointer_var. This should be changed to
+    //      recognize less generic pattern:
+    //
+    //         if (maybe_object->ToObject(&obj)) return maybe_object;
+    //
+    if (expr->getOpcode() == clang::UO_AddrOf) {
+      std::string var_name;
+      if (IsRawPointerVar(expr->getSubExpr(), &var_name)) {
+        return ExprEffect::None().Define(var_name);
       }
     }
+    return VisitExpr(expr->getSubExpr(), env);
+  }
 
+  DECL_VISIT_EXPR(CastExpr) {
+    return VisitExpr(expr->getSubExpr(), env);
+  }
+
+  DECL_VISIT_EXPR(DeclRefExpr) {
+    return Use(expr, expr->getDecl(), env);
+  }
+
+  DECL_VISIT_EXPR(BlockDeclRefExpr) {
+    return Use(expr, expr->getDecl(), env);
+  }
+
+  ExprEffect Par(clang::Expr* parent,
+                 int n,
+                 clang::Expr** exprs,
+                 const Environment& env) {
+    CallProps props;
+
+    for (int i = 0; i < n; ++i) {
+      props.SetEffect(i, VisitExpr(exprs[i], env));
+    }
+
+    if (!props.IsSafe()) ReportUnsafe(parent, BAD_EXPR_MSG);
+
+    return props.ComputeCumulativeEffect(IsRawPointerType(parent->getType()));
+  }
+
+  ExprEffect Seq(clang::Stmt* parent,
+                 int n,
+                 clang::Expr** exprs,
+                 const Environment& env) {
+    ExprEffect out = ExprEffect::None();
+    Environment out_env = env;
+    for (int i = 0; i < n; ++i) {
+      out = ExprEffect::MergeSeq(out, VisitExpr(exprs[i], out_env));
+      out_env = out_env.ApplyEffect(out);
+    }
+    return out;
+  }
+
+  ExprEffect Use(const clang::Expr* parent,
+                 const clang::QualType& var_type,
+                 const std::string& var_name,
+                 const Environment& env) {
+    if (IsRawPointerType(var_type)) {
+      if (!env.IsAlive(var_name) && dead_vars_analysis_) {
+        ReportUnsafe(parent, DEAD_VAR_MSG);
+      }
+      return ExprEffect::RawUse();
+    }
+    return ExprEffect::None();
+  }
+
+  ExprEffect Use(const clang::Expr* parent,
+                 const clang::ValueDecl* var,
+                 const Environment& env) {
+    return Use(parent, var->getType(), var->getNameAsString(), env);
+  }
+
+
+  template<typename ExprType>
+  ExprEffect VisitArguments(ExprType* call, const Environment& env) {
+    CallProps props;
+    VisitArguments<>(call, &props, env);
+    if (!props.IsSafe()) ReportUnsafe(call, BAD_EXPR_MSG);
+    return props.ComputeCumulativeEffect(IsRawPointerType(call->getType()));
+  }
+
+  template<typename ExprType>
+  void VisitArguments(ExprType* call,
+                      CallProps* props,
+                      const Environment& env) {
     for (unsigned arg = 0; arg < call->getNumArgs(); arg++) {
-      if (ManipulatesRawPointers(call->getArg(arg))) derefs_.set(arg + 1);
+      props->SetEffect(arg + 1, VisitExpr(call->getArg(arg), env));
     }
   }
 
-  void MarkGCSuspectAsArgument(clang::CallExpr* call) {
-    gc_.reset();
 
+  ExprEffect VisitCallExpr(clang::CallExpr* call,
+                           const Environment& env) {
+    CallProps props;
+
     clang::CXXMemberCallExpr* memcall =
         dyn_cast_or_null<clang::CXXMemberCallExpr>(call);
-    if (memcall != NULL && CanCauseGC(memcall->getImplicitObjectArgument())) {
-      gc_.set(0);
+    if (memcall != NULL) {
+      clang::Expr* receiver = memcall->getImplicitObjectArgument();
+      props.SetEffect(0, VisitExpr(receiver, env));
     }
 
-    for (unsigned arg = 0; arg < call->getNumArgs(); arg++) {
-      if (CanCauseGC(call->getArg(arg))) gc_.set(arg + 1);
+    VisitArguments<>(call, &props, env);
+
+    if (!props.IsSafe()) ReportUnsafe(call, BAD_EXPR_MSG);
+
+    ExprEffect out =
+        props.ComputeCumulativeEffect(IsRawPointerType(call->getType()));
+
+    clang::FunctionDecl* callee = call->getDirectCallee();
+    if ((callee != NULL) && KnownToCauseGC(ctx_, callee)) {
+      out.setGC();
     }
+
+    return out;
   }
 
+  // --------------------------------------------------------------------------
+  // Statements
+  // --------------------------------------------------------------------------
+
+  Environment VisitStmt(clang::Stmt* stmt, const Environment& env) {
+#define VISIT(type) do {                                                \
+      clang::type* concrete_stmt = dyn_cast_or_null<clang::type>(stmt); \
+      if (concrete_stmt != NULL) {                                      \
+        return Visit##type (concrete_stmt, env);                        \
+      }                                                                 \
+    } while(0);
+
+    if (clang::Expr* expr = dyn_cast_or_null<clang::Expr>(stmt)) {
+      return env.ApplyEffect(VisitExpr(expr, env));
+    }
+
+    VISIT(AsmStmt);
+    VISIT(BreakStmt);
+    VISIT(CompoundStmt);
+    VISIT(ContinueStmt);
+    VISIT(CXXCatchStmt);
+    VISIT(CXXTryStmt);
+    VISIT(DeclStmt);
+    VISIT(DoStmt);
+    VISIT(ForStmt);
+    VISIT(GotoStmt);
+    VISIT(IfStmt);
+    VISIT(IndirectGotoStmt);
+    VISIT(LabelStmt);
+    VISIT(NullStmt);
+    VISIT(ReturnStmt);
+    VISIT(CaseStmt);
+    VISIT(DefaultStmt);
+    VISIT(SwitchStmt);
+    VISIT(WhileStmt);
+#undef VISIT
+
+    return env;
+  }
+
+#define DECL_VISIT_STMT(type)                                           \
+  Environment Visit##type (clang::type* stmt, const Environment& env)
+
+#define IGNORE_STMT(type)                                               \
+  Environment Visit##type (clang::type* stmt, const Environment& env) { \
+    return env;                                                         \
+  }
+
+  IGNORE_STMT(IndirectGotoStmt);
+  IGNORE_STMT(NullStmt);
+  IGNORE_STMT(AsmStmt);
+
+  // We are ignoring control flow for simplicity.
+  IGNORE_STMT(GotoStmt);
+  IGNORE_STMT(LabelStmt);
+
+  // We are ignoring try/catch because V8 does not use them.
+  IGNORE_STMT(CXXCatchStmt);
+  IGNORE_STMT(CXXTryStmt);
+
+  class Block {
+   public:
+    Block(const Environment& in,
+          FunctionAnalyzer* owner)
+        : in_(in),
+          out_(Environment::Unreachable()),
+          changed_(false),
+          owner_(owner) {
+      parent_ = owner_->EnterBlock(this);
+    }
+
+    ~Block() {
+      owner_->LeaveBlock(parent_);
+    }
+
+    void MergeIn(const Environment& env) {
+      Environment old_in = in_;
+      in_ = Environment::Merge(in_, env);
+      changed_ = !old_in.Equal(in_);
+    }
+
+    bool changed() {
+      if (changed_) {
+        changed_ = false;
+        return true;
+      }
+      return false;
+    }
+
+    const Environment& in() {
+      return in_;
+    }
+
+    const Environment& out() {
+      return out_;
+    }
+
+    void MergeOut(const Environment& env) {
+      out_ = Environment::Merge(out_, env);
+    }
+
+    void Seq(clang::Stmt* a, clang::Stmt* b, clang::Stmt* c) {
+      Environment a_out = owner_->VisitStmt(a, in());
+      Environment b_out = owner_->VisitStmt(b, a_out);
+      Environment c_out = owner_->VisitStmt(c, b_out);
+      MergeOut(c_out);
+    }
+
+    void Seq(clang::Stmt* a, clang::Stmt* b) {
+      Environment a_out = owner_->VisitStmt(a, in());
+      Environment b_out = owner_->VisitStmt(b, a_out);
+      MergeOut(b_out);
+    }
+
+    void Loop(clang::Stmt* a, clang::Stmt* b, clang::Stmt* c) {
+      Seq(a, b, c);
+      MergeIn(out());
+    }
+
+    void Loop(clang::Stmt* a, clang::Stmt* b) {
+      Seq(a, b);
+      MergeIn(out());
+    }
+
+
+   private:
+    Environment in_;
+    Environment out_;
+    bool changed_;
+    FunctionAnalyzer* owner_;
+    Block* parent_;
+  };
+
+
+  DECL_VISIT_STMT(BreakStmt) {
+    block_->MergeOut(env);
+    return Environment::Unreachable();
+  }
+
+  DECL_VISIT_STMT(ContinueStmt) {
+    block_->MergeIn(env);
+    return Environment::Unreachable();
+  }
+
+  DECL_VISIT_STMT(CompoundStmt) {
+    Environment out = env;
+    clang::CompoundStmt::body_iterator end = stmt->body_end();
+    for (clang::CompoundStmt::body_iterator s = stmt->body_begin();
+         s != end;
+         ++s) {
+      out = VisitStmt(*s, out);
+    }
+    return out;
+  }
+
+  DECL_VISIT_STMT(WhileStmt) {
+    Block block (env, this);
+    do {
+      block.Loop(stmt->getCond(), stmt->getBody());
+    } while (block.changed());
+    return block.out();
+  }
+
+  DECL_VISIT_STMT(DoStmt) {
+    Block block (env, this);
+    do {
+      block.Loop(stmt->getBody(), stmt->getCond());
+    } while (block.changed());
+    return block.out();
+  }
+
+  DECL_VISIT_STMT(ForStmt) {
+    Block block (VisitStmt(stmt->getInit(), env), this);
+    do {
+      block.Loop(stmt->getCond(),
+                 stmt->getBody(),
+                 stmt->getInc());
+    } while (block.changed());
+    return block.out();
+  }
+
+  DECL_VISIT_STMT(IfStmt) {
+    Environment cond_out = VisitStmt(stmt->getCond(), env);
+    Environment then_out = VisitStmt(stmt->getThen(), cond_out);
+    Environment else_out = VisitStmt(stmt->getElse(), cond_out);
+    return Environment::Merge(then_out, else_out);
+  }
+
+  DECL_VISIT_STMT(SwitchStmt) {
+    Block block (env, this);
+    block.Seq(stmt->getCond(), stmt->getBody());
+    return block.out();
+  }
+
+  DECL_VISIT_STMT(CaseStmt) {
+    Environment in = Environment::Merge(env, block_->in());
+    Environment after_lhs = VisitStmt(stmt->getLHS(), in);
+    return VisitStmt(stmt->getSubStmt(), after_lhs);
+  }
+
+  DECL_VISIT_STMT(DefaultStmt) {
+    Environment in = Environment::Merge(env, block_->in());
+    return VisitStmt(stmt->getSubStmt(), in);
+  }
+
+  DECL_VISIT_STMT(ReturnStmt) {
+    VisitExpr(stmt->getRetValue(), env);
+    return Environment::Unreachable();
+  }
+
   const clang::TagType* ToTagType(const clang::Type* t) {
     if (t == NULL) {
       return NULL;
@@ -311,11 +1061,14 @@
     }
   }
 
-  bool IsRawPointerType(clang::Expr* expr) {
-    clang::QualType result = expr->getType();
+  bool IsDerivedFrom(clang::CXXRecordDecl* record,
+                     clang::CXXRecordDecl* base) {
+    return (record == base) || record->isDerivedFrom(base);
+  }
 
+  bool IsRawPointerType(clang::QualType qtype) {
     const clang::PointerType* type =
-        dyn_cast_or_null<clang::PointerType>(expr->getType().getTypePtr());
+        dyn_cast_or_null<clang::PointerType>(qtype.getTypePtrOrNull());
     if (type == NULL) return false;
 
     const clang::TagType* pointee =
@@ -326,146 +1079,154 @@
         dyn_cast_or_null<clang::CXXRecordDecl>(pointee->getDecl());
     if (record == NULL) return false;
 
-    return InV8Namespace(record) &&
-        record->hasDefinition() &&
-        ((record == objectDecl_) || record->isDerivedFrom(objectDecl_));
-  }
+    if (!InV8Namespace(record)) return false;
 
-  bool IsHandleDereference(clang::Expr* expr) {
-    if (expr == NULL) {
-      return false;
-    } else if (isa<clang::UnaryOperator>(expr)) {
-      clang::UnaryOperator* unop = cast<clang::UnaryOperator>(expr);
-      return unop->getOpcode() == clang::UO_Deref &&
-          IsHandleType(handleDeclName_, unop->getSubExpr()->getType());
-    } else if (isa<clang::CXXOperatorCallExpr>(expr)) {
-      clang::CXXOperatorCallExpr* op = cast<clang::CXXOperatorCallExpr>(expr);
-      return (op->getOperator() == clang::OO_Star ||
-              op->getOperator() == clang::OO_Arrow) &&
-          IsHandleType(handleDeclName_, op->getArg(0)->getType());
-    } else {
-      return false;
-    }
-  }
+    if (!record->hasDefinition()) return false;
 
-  bool CanCauseGC(clang::Expr* expr) {
-    if (expr == NULL) return false;
+    record = record->getDefinition();
 
-    has_gc_ = false;
-    has_derefs_ = true;
-    TraverseStmt(expr);
-    return has_gc_;
+    return IsDerivedFrom(record, object_decl_) &&
+        !IsDerivedFrom(record, smi_decl_);
   }
 
-  bool ManipulatesRawPointers(clang::Expr* expr) {
-    if (expr == NULL) return false;
+  Environment VisitDecl(clang::Decl* decl, const Environment& env) {
+    if (clang::VarDecl* var = dyn_cast<clang::VarDecl>(decl)) {
+      Environment out = var->hasInit() ? VisitStmt(var->getInit(), env) : env;
 
-    has_gc_ = true;
-    has_derefs_ = false;
-    TraverseStmt(expr);
-    return has_derefs_;
+      if (IsRawPointerType(var->getType())) {
+        out = out.Define(var->getNameAsString());
+      }
+
+      return out;
+    }
+    // TODO: handle other declarations?
+    return env;
   }
 
-  bool CanCauseGC(const clang::CallExpr* call) {
-    const clang::FunctionDecl* fn = call->getDirectCallee();
-    return (fn != NULL) && KnownToCauseGC(ctx_, fn);
+  DECL_VISIT_STMT(DeclStmt) {
+    Environment out = env;
+    clang::DeclStmt::decl_iterator end = stmt->decl_end();
+    for (clang::DeclStmt::decl_iterator decl = stmt->decl_begin();
+         decl != end;
+         ++decl) {
+      out = VisitDecl(*decl, out);
+    }
+    return out;
   }
 
-  // For generic expression classification.
-  bool has_derefs_;
-  bool has_gc_;
 
-  // For callsite classification.
-  static const int kMaxNumberOfArguments = 64;
-  std::bitset<kMaxNumberOfArguments> derefs_;
-  std::bitset<kMaxNumberOfArguments> gc_;
+  void DefineParameters(const clang::FunctionDecl* f,
+                        Environment* env) {
+    env->MDefine(THIS);
+    clang::FunctionDecl::param_const_iterator end = f->param_end();
+    for (clang::FunctionDecl::param_const_iterator p = f->param_begin();
+         p != end;
+         ++p) {
+      env->MDefine((*p)->getNameAsString());
+    }
+  }
 
-  clang::DeclarationName handleDeclName_;
-  clang::MangleContext* ctx_;
-  clang::CXXRecordDecl* objectDecl_;
-};
 
-const std::string BAD_EXPRESSION_MSG("Possible problem with evaluation order.");
+  void AnalyzeFunction(const clang::FunctionDecl* f) {
+    const clang::FunctionDecl* body = NULL;
+    if (f->hasBody(body)) {
+      Environment env;
+      DefineParameters(body, &env);
+      VisitStmt(body->getBody(), env);
+      Environment::ClearSymbolTable();
+    }
+  }
 
-class ExpressionsFinder : public clang::ASTConsumer,
-                          public clang::RecursiveASTVisitor<ExpressionsFinder> {
- public:
-  explicit ExpressionsFinder(clang::Diagnostic& d, clang::SourceManager& sm)
-      : d_(d), sm_(sm) { }
+  Block* EnterBlock(Block* block) {
+    Block* parent = block_;
+    block_ = block;
+    return parent;
+  }
 
-  struct Resolver {
-    explicit Resolver(clang::ASTContext& ctx)
-        : ctx_(ctx), decl_ctx_(ctx.getTranslationUnitDecl()) {
-    }
+  void LeaveBlock(Block* block) {
+    block_ = block;
+  }
 
-    Resolver(clang::ASTContext& ctx, clang::DeclContext* decl_ctx)
-        : ctx_(ctx), decl_ctx_(decl_ctx) {
-    }
+ private:
+  void ReportUnsafe(const clang::Expr* expr, const std::string& msg) {
+    d_.Report(clang::FullSourceLoc(expr->getExprLoc(), sm_),
+              d_.getCustomDiagID(clang::Diagnostic::Warning, msg));
+  }
 
-    clang::DeclarationName ResolveName(const char* n) {
-      clang::IdentifierInfo* ident = &ctx_.Idents.get(n);
-      return ctx_.DeclarationNames.getIdentifier(ident);
-    }
 
-    Resolver ResolveNamespace(const char* n) {
-      return Resolver(ctx_, Resolve<clang::NamespaceDecl>(n));
-    }
+  clang::MangleContext* ctx_;
+  clang::DeclarationName handle_decl_name_;
+  clang::CXXRecordDecl* object_decl_;
+  clang::CXXRecordDecl* smi_decl_;
 
-    template<typename T>
-    T* Resolve(const char* n) {
-      if (decl_ctx_ == NULL) return NULL;
+  clang::Diagnostic& d_;
+  clang::SourceManager& sm_;
 
-      clang::DeclContext::lookup_result result =
-          decl_ctx_->lookup(ResolveName(n));
+  Block* block_;
+  bool dead_vars_analysis_;
+};
 
-      for (clang::DeclContext::lookup_iterator i = result.first,
-               e = result.second;
-           i != e;
-           i++) {
-        if (isa<T>(*i)) return cast<T>(*i);
+
+class ProblemsFinder : public clang::ASTConsumer,
+                       public clang::RecursiveASTVisitor<ProblemsFinder> {
+ public:
+  ProblemsFinder(clang::Diagnostic& d,
+                 clang::SourceManager& sm,
+                 const std::vector<std::string>& args)
+      : d_(d), sm_(sm), dead_vars_analysis_(false) {
+    for (unsigned i = 0; i < args.size(); ++i) {
+      if (args[i] == "--dead-vars") {
+        dead_vars_analysis_ = true;
       }
-
-      return NULL;
     }
+  }
 
-   private:
-    clang::ASTContext& ctx_;
-    clang::DeclContext* decl_ctx_;
-  };
-
   virtual void HandleTranslationUnit(clang::ASTContext &ctx) {
     Resolver r(ctx);
 
-    clang::CXXRecordDecl* objectDecl =
+    clang::CXXRecordDecl* object_decl =
         r.ResolveNamespace("v8").ResolveNamespace("internal").
             Resolve<clang::CXXRecordDecl>("Object");
 
-    if (objectDecl != NULL) {
-      expression_classifier_ =
-          new ExpressionClassifier(r.ResolveName("Handle"),
-                                   clang::createItaniumMangleContext(ctx, d_),
-                                   objectDecl);
+    clang::CXXRecordDecl* smi_decl =
+        r.ResolveNamespace("v8").ResolveNamespace("internal").
+            Resolve<clang::CXXRecordDecl>("Smi");
+
+    if (object_decl != NULL) object_decl = object_decl->getDefinition();
+
+    if (smi_decl != NULL) smi_decl = smi_decl->getDefinition();
+
+    if (object_decl != NULL && smi_decl != NULL) {
+      function_analyzer_ =
+          new FunctionAnalyzer(clang::createItaniumMangleContext(ctx, d_),
+                               r.ResolveName("Handle"),
+                               object_decl,
+                               smi_decl,
+                               d_,
+                               sm_,
+                               dead_vars_analysis_);
       TraverseDecl(ctx.getTranslationUnitDecl());
     } else {
-      std::cerr << "Failed to resolve v8::internal::Object" << std::endl;
+      if (object_decl == NULL) {
+        llvm::errs() << "Failed to resolve v8::internal::Object\n";
+      }
+      if (smi_decl == NULL) {
+        llvm::errs() << "Failed to resolve v8::internal::Smi\n";
+      }
     }
   }
 
-  virtual bool VisitExpr(clang::Expr* expr) {
-    if ( expression_classifier_->IsBadCallSite(expr) ) {
-      d_.Report(clang::FullSourceLoc(expr->getExprLoc(), sm_),
-                d_.getCustomDiagID(clang::Diagnostic::Warning,
-                                   BAD_EXPRESSION_MSG));
-    }
-
+  virtual bool VisitFunctionDecl(clang::FunctionDecl* decl) {
+    function_analyzer_->AnalyzeFunction(decl);
     return true;
   }
 
  private:
   clang::Diagnostic& d_;
   clang::SourceManager& sm_;
+  bool dead_vars_analysis_;
 
-  ExpressionClassifier* expression_classifier_;
+  FunctionAnalyzer* function_analyzer_;
 };
 
 
@@ -474,22 +1235,27 @@
  protected:
   clang::ASTConsumer *CreateASTConsumer(clang::CompilerInstance &CI,
                                         llvm::StringRef InFile) {
-    return new ConsumerType(CI.getDiagnostics(), CI.getSourceManager());
+    return new ConsumerType(CI.getDiagnostics(), CI.getSourceManager(), args_);
   }
 
   bool ParseArgs(const clang::CompilerInstance &CI,
                  const std::vector<std::string>& args) {
+    args_ = args;
     return true;
   }
 
-  void PrintHelp(llvm::raw_ostream& ros) { }
+  void PrintHelp(llvm::raw_ostream& ros) {
+  }
+ private:
+  std::vector<std::string> args_;
 };
 
 
 }
 
-static clang::FrontendPluginRegistry::Add<Action<ExpressionsFinder> >
-FindProblems("find-problems", "Find possible problems with evaluations order.");
+static clang::FrontendPluginRegistry::Add<Action<ProblemsFinder> >
+FindProblems("find-problems", "Find GC-unsafe places.");
 
-static clang::FrontendPluginRegistry::Add<Action<FunctionDeclarationFinder> >
+static clang::FrontendPluginRegistry::Add<
+  Action<FunctionDeclarationFinder> >
 DumpCallees("dump-callees", "Dump callees for each function.");