Derive synthetic type bounds for expressions

Currently synthesizes Smi as the lower bound for numeric operations (except for +, which might result in a string). That would need to change in places where we want to track constants as type feedback. Does not do anything about variables yet. R=jkummerow@chromium.org BUG= Review URL: https://codereview.chromium.org/17842004 git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15422 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
2013-07-01 13:59:18 +00:00 · 2013-07-01 13:59:18 +00:00 · fd484c9df9
commit fd484c9df9
parent 493d1f1c21
2 changed files with 210 additions and 121 deletions
--- a/src/typing.cc
+++ b/src/typing.cc
@ -45,13 +45,13 @@ AstTyper::AstTyper(CompilationInfo* info)
 }


-#define CHECK_ALIVE(call)                     \
+#define RECURSE(call)                         \
  do {                                        \
+    ASSERT(!visitor->HasStackOverflow());     \
    call;                                     \
    if (visitor->HasStackOverflow()) return;  \
  } while (false)

-
 void AstTyper::Run(CompilationInfo* info) {
  AstTyper* visitor = new(info->zone()) AstTyper(info);
  Scope* scope = info->scope();
@ -59,52 +59,48 @@ void AstTyper::Run(CompilationInfo* info) {
  // Handle implicit declaration of the function name in named function
  // expressions before other declarations.
  if (scope->is_function_scope() && scope->function() != NULL) {
-    CHECK_ALIVE(visitor->VisitVariableDeclaration(scope->function()));
+    RECURSE(visitor->VisitVariableDeclaration(scope->function()));
  }
-  CHECK_ALIVE(visitor->VisitDeclarations(scope->declarations()));
-  CHECK_ALIVE(visitor->VisitStatements(info->function()->body()));
+  RECURSE(visitor->VisitDeclarations(scope->declarations()));
+  RECURSE(visitor->VisitStatements(info->function()->body()));
 }

+#undef RECURSE

-#undef CHECK_ALIVE
-#define CHECK_ALIVE(call)            \
+#define RECURSE(call)                \
  do {                               \
+    ASSERT(!HasStackOverflow());     \
    call;                            \
    if (HasStackOverflow()) return;  \
  } while (false)


 void AstTyper::VisitStatements(ZoneList<Statement*>* stmts) {
-  ASSERT(!HasStackOverflow());
  for (int i = 0; i < stmts->length(); ++i) {
    Statement* stmt = stmts->at(i);
-    CHECK_ALIVE(Visit(stmt));
+    RECURSE(Visit(stmt));
  }
 }


 void AstTyper::VisitBlock(Block* stmt) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(VisitStatements(stmt->statements()));
+  RECURSE(VisitStatements(stmt->statements()));
 }


 void AstTyper::VisitExpressionStatement(ExpressionStatement* stmt) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(stmt->expression()));
+  RECURSE(Visit(stmt->expression()));
 }


 void AstTyper::VisitEmptyStatement(EmptyStatement* stmt) {
-  ASSERT(!HasStackOverflow());
 }


 void AstTyper::VisitIfStatement(IfStatement* stmt) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(stmt->condition()));
-  CHECK_ALIVE(Visit(stmt->then_statement()));
-  CHECK_ALIVE(Visit(stmt->else_statement()));
+  RECURSE(Visit(stmt->condition()));
+  RECURSE(Visit(stmt->then_statement()));
+  RECURSE(Visit(stmt->else_statement()));

  if (!stmt->condition()->ToBooleanIsTrue() &&
      !stmt->condition()->ToBooleanIsFalse()) {
@ -114,18 +110,15 @@ void AstTyper::VisitIfStatement(IfStatement* stmt) {


 void AstTyper::VisitContinueStatement(ContinueStatement* stmt) {
-  ASSERT(!HasStackOverflow());
 }


 void AstTyper::VisitBreakStatement(BreakStatement* stmt) {
-  ASSERT(!HasStackOverflow());
 }


 void AstTyper::VisitReturnStatement(ReturnStatement* stmt) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(stmt->expression()));
+  RECURSE(Visit(stmt->expression()));

  // TODO(rossberg): we only need this for inlining into test contexts...
  stmt->expression()->RecordToBooleanTypeFeedback(oracle());
@ -133,22 +126,20 @@ void AstTyper::VisitReturnStatement(ReturnStatement* stmt) {


 void AstTyper::VisitWithStatement(WithStatement* stmt) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(stmt->expression());
-  CHECK_ALIVE(stmt->statement());
+  RECURSE(stmt->expression());
+  RECURSE(stmt->statement());
 }


 void AstTyper::VisitSwitchStatement(SwitchStatement* stmt) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(stmt->tag()));
+  RECURSE(Visit(stmt->tag()));
  ZoneList<CaseClause*>* clauses = stmt->cases();
  SwitchStatement::SwitchType switch_type = stmt->switch_type();
  for (int i = 0; i < clauses->length(); ++i) {
    CaseClause* clause = clauses->at(i);
    if (!clause->is_default()) {
      Expression* label = clause->label();
-      CHECK_ALIVE(Visit(label));
+      RECURSE(Visit(label));

      SwitchStatement::SwitchType label_switch_type =
          label->IsSmiLiteral() ? SwitchStatement::SMI_SWITCH :
@ -159,7 +150,7 @@ void AstTyper::VisitSwitchStatement(SwitchStatement* stmt) {
      else if (switch_type != label_switch_type)
        switch_type = SwitchStatement::GENERIC_SWITCH;
    }
-    CHECK_ALIVE(VisitStatements(clause->statements()));
+    RECURSE(VisitStatements(clause->statements()));
  }
  if (switch_type == SwitchStatement::UNKNOWN_SWITCH)
    switch_type = SwitchStatement::GENERIC_SWITCH;
@ -177,9 +168,8 @@ void AstTyper::VisitSwitchStatement(SwitchStatement* stmt) {


 void AstTyper::VisitDoWhileStatement(DoWhileStatement* stmt) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(stmt->body()));
-  CHECK_ALIVE(Visit(stmt->cond()));
+  RECURSE(Visit(stmt->body()));
+  RECURSE(Visit(stmt->cond()));

  if (!stmt->cond()->ToBooleanIsTrue()) {
    stmt->cond()->RecordToBooleanTypeFeedback(oracle());
@ -188,9 +178,8 @@ void AstTyper::VisitDoWhileStatement(DoWhileStatement* stmt) {


 void AstTyper::VisitWhileStatement(WhileStatement* stmt) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(stmt->cond()));
-  CHECK_ALIVE(Visit(stmt->body()));
+  RECURSE(Visit(stmt->cond()));
+  RECURSE(Visit(stmt->body()));

  if (!stmt->cond()->ToBooleanIsTrue()) {
    stmt->cond()->RecordToBooleanTypeFeedback(oracle());
@ -199,171 +188,185 @@ void AstTyper::VisitWhileStatement(WhileStatement* stmt) {


 void AstTyper::VisitForStatement(ForStatement* stmt) {
-  ASSERT(!HasStackOverflow());
  if (stmt->init() != NULL) {
-    CHECK_ALIVE(Visit(stmt->init()));
+    RECURSE(Visit(stmt->init()));
  }
  if (stmt->cond() != NULL) {
-    CHECK_ALIVE(Visit(stmt->cond()));
+    RECURSE(Visit(stmt->cond()));

    stmt->cond()->RecordToBooleanTypeFeedback(oracle());
  }
-  CHECK_ALIVE(Visit(stmt->body()));
+  RECURSE(Visit(stmt->body()));
  if (stmt->next() != NULL) {
-    CHECK_ALIVE(Visit(stmt->next()));
+    RECURSE(Visit(stmt->next()));
  }
 }


 void AstTyper::VisitForInStatement(ForInStatement* stmt) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(stmt->enumerable()));
-  CHECK_ALIVE(Visit(stmt->body()));
+  RECURSE(Visit(stmt->enumerable()));
+  RECURSE(Visit(stmt->body()));

  stmt->RecordTypeFeedback(oracle());
 }


 void AstTyper::VisitForOfStatement(ForOfStatement* stmt) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(stmt->iterable()));
-  CHECK_ALIVE(Visit(stmt->body()));
+  RECURSE(Visit(stmt->iterable()));
+  RECURSE(Visit(stmt->body()));
 }


 void AstTyper::VisitTryCatchStatement(TryCatchStatement* stmt) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(stmt->try_block()));
-  CHECK_ALIVE(Visit(stmt->catch_block()));
+  RECURSE(Visit(stmt->try_block()));
+  RECURSE(Visit(stmt->catch_block()));
 }


 void AstTyper::VisitTryFinallyStatement(TryFinallyStatement* stmt) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(stmt->try_block()));
-  CHECK_ALIVE(Visit(stmt->finally_block()));
+  RECURSE(Visit(stmt->try_block()));
+  RECURSE(Visit(stmt->finally_block()));
 }


 void AstTyper::VisitDebuggerStatement(DebuggerStatement* stmt) {
-  ASSERT(!HasStackOverflow());
 }


 void AstTyper::VisitFunctionLiteral(FunctionLiteral* expr) {
-  ASSERT(!HasStackOverflow());
 }


 void AstTyper::VisitSharedFunctionInfoLiteral(SharedFunctionInfoLiteral* expr) {
-  ASSERT(!HasStackOverflow());
 }


 void AstTyper::VisitConditional(Conditional* expr) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(expr->condition()));
-  CHECK_ALIVE(Visit(expr->then_expression()));
-  CHECK_ALIVE(Visit(expr->else_expression()));
+  RECURSE(Visit(expr->condition()));
+  RECURSE(Visit(expr->then_expression()));
+  RECURSE(Visit(expr->else_expression()));

  expr->condition()->RecordToBooleanTypeFeedback(oracle());
+
+  MergeLowerType(expr, Type::Intersect(
+      expr->then_expression()->lower_type(),
+      expr->else_expression()->lower_type()));
+  MergeUpperType(expr, Type::Union(
+      expr->then_expression()->upper_type(),
+      expr->else_expression()->upper_type()));
 }


 void AstTyper::VisitVariableProxy(VariableProxy* expr) {
-  ASSERT(!HasStackOverflow());
+  // TODO(rossberg): typing of variables
 }


 void AstTyper::VisitLiteral(Literal* expr) {
-  ASSERT(!HasStackOverflow());
+  Type* type = Type::Constant(expr->value(), isolate_);
+  MergeLowerType(expr, type);
+  MergeUpperType(expr, type);
 }


 void AstTyper::VisitRegExpLiteral(RegExpLiteral* expr) {
-  ASSERT(!HasStackOverflow());
+  MergeLowerType(expr, Type::RegExp());
+  MergeUpperType(expr, Type::RegExp());
 }


 void AstTyper::VisitObjectLiteral(ObjectLiteral* expr) {
-  ASSERT(!HasStackOverflow());
  ZoneList<ObjectLiteral::Property*>* properties = expr->properties();
  for (int i = 0; i < properties->length(); ++i) {
    ObjectLiteral::Property* prop = properties->at(i);
-    CHECK_ALIVE(Visit(prop->value()));
+    RECURSE(Visit(prop->value()));

    if ((prop->kind() == ObjectLiteral::Property::MATERIALIZED_LITERAL &&
        !CompileTimeValue::IsCompileTimeValue(prop->value())) ||
        prop->kind() == ObjectLiteral::Property::COMPUTED) {
-      if (prop->key()->value()->IsInternalizedString() && prop->emit_store())
+      if (prop->key()->value()->IsInternalizedString() && prop->emit_store()) {
        prop->RecordTypeFeedback(oracle());
+      }
    }
  }
+
+  MergeLowerType(expr, Type::Object());
+  MergeUpperType(expr, Type::Object());
 }


 void AstTyper::VisitArrayLiteral(ArrayLiteral* expr) {
-  ASSERT(!HasStackOverflow());
  ZoneList<Expression*>* values = expr->values();
  for (int i = 0; i < values->length(); ++i) {
    Expression* value = values->at(i);
-    CHECK_ALIVE(Visit(value));
+    RECURSE(Visit(value));
  }
+
+  MergeLowerType(expr, Type::Array());
+  MergeUpperType(expr, Type::Array());
 }


 void AstTyper::VisitAssignment(Assignment* expr) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(expr->target()));
-  CHECK_ALIVE(Visit(expr->value()));
-
  // TODO(rossberg): Can we clean this up?
  if (expr->is_compound()) {
-    CHECK_ALIVE(Visit(expr->binary_operation()));
+    RECURSE(Visit(expr->binary_operation()));

    Expression* target = expr->target();
    Property* prop = target->AsProperty();
    if (prop != NULL) {
      prop->RecordTypeFeedback(oracle(), zone());
-      if (!prop->key()->IsPropertyName())  // i.e., keyed
+      if (!prop->key()->IsPropertyName()) {  // i.e., keyed
        expr->RecordTypeFeedback(oracle(), zone());
+      }
    }
-    return;
+  } else {
+    RECURSE(Visit(expr->target()));
+    RECURSE(Visit(expr->value()));
+
+    if (expr->target()->AsProperty()) {
+      expr->RecordTypeFeedback(oracle(), zone());
+    }
+
+    MergeLowerType(expr, expr->value()->lower_type());
+    MergeUpperType(expr, expr->value()->upper_type());
  }
-  if (expr->target()->AsProperty())
-    expr->RecordTypeFeedback(oracle(), zone());
+  // TODO(rossberg): handle target variables
 }


 void AstTyper::VisitYield(Yield* expr) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(expr->generator_object()));
-  CHECK_ALIVE(Visit(expr->expression()));
+  RECURSE(Visit(expr->generator_object()));
+  RECURSE(Visit(expr->expression()));
+
+  // We don't know anything about the type.
 }


 void AstTyper::VisitThrow(Throw* expr) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(expr->exception()));
+  RECURSE(Visit(expr->exception()));
+
+  // Lower type is None already.
+  MergeUpperType(expr, Type::None());
 }


 void AstTyper::VisitProperty(Property* expr) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(expr->obj()));
-  CHECK_ALIVE(Visit(expr->key()));
+  RECURSE(Visit(expr->obj()));
+  RECURSE(Visit(expr->key()));

  expr->RecordTypeFeedback(oracle(), zone());
+
+  // We don't know anything about the type.
 }


 void AstTyper::VisitCall(Call* expr) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(expr->expression()));
+  RECURSE(Visit(expr->expression()));
  ZoneList<Expression*>* args = expr->arguments();
  for (int i = 0; i < args->length(); ++i) {
    Expression* arg = args->at(i);
-    CHECK_ALIVE(Visit(arg));
+    RECURSE(Visit(arg));
  }

  Expression* callee = expr->expression();
@ -374,35 +377,38 @@ void AstTyper::VisitCall(Call* expr) {
  } else {
    expr->RecordTypeFeedback(oracle(), CALL_AS_FUNCTION);
  }
+
+  // We don't know anything about the type.
 }


 void AstTyper::VisitCallNew(CallNew* expr) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(expr->expression()));
+  RECURSE(Visit(expr->expression()));
  ZoneList<Expression*>* args = expr->arguments();
  for (int i = 0; i < args->length(); ++i) {
    Expression* arg = args->at(i);
-    CHECK_ALIVE(Visit(arg));
+    RECURSE(Visit(arg));
  }

  expr->RecordTypeFeedback(oracle());
+
+  // We don't know anything about the type.
 }


 void AstTyper::VisitCallRuntime(CallRuntime* expr) {
-  ASSERT(!HasStackOverflow());
  ZoneList<Expression*>* args = expr->arguments();
  for (int i = 0; i < args->length(); ++i) {
    Expression* arg = args->at(i);
-    CHECK_ALIVE(Visit(arg));
+    RECURSE(Visit(arg));
  }
+
+  // We don't know anything about the type.
 }


 void AstTyper::VisitUnaryOperation(UnaryOperation* expr) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(expr->expression()));
+  RECURSE(Visit(expr->expression()));

  // Collect type feedback.
  Handle<Type> op_type = oracle()->UnaryType(expr->UnaryOperationFeedbackId());
@ -411,25 +417,55 @@ void AstTyper::VisitUnaryOperation(UnaryOperation* expr) {
    // TODO(rossberg): only do in test or value context.
    expr->expression()->RecordToBooleanTypeFeedback(oracle());
  }
+
+  switch (expr->op()) {
+    case Token::NOT:
+    case Token::DELETE:
+      MergeLowerType(expr, Type::Boolean());
+      MergeUpperType(expr, Type::Boolean());
+      break;
+    case Token::VOID:
+      MergeLowerType(expr, Type::Undefined());
+      MergeUpperType(expr, Type::Undefined());
+      break;
+    case Token::ADD:
+    case Token::SUB: {
+      MergeLowerType(expr, Type::Smi());
+      Type* upper = *expr->expression()->upper_type();
+      MergeUpperType(expr, upper->Is(Type::Number()) ? upper : Type::Number());
+      break;
+    }
+    case Token::BIT_NOT:
+      MergeLowerType(expr, Type::Smi());
+      MergeUpperType(expr, Type::Signed32());
+      break;
+    case Token::TYPEOF:
+      MergeLowerType(expr, Type::InternalizedString());
+      MergeUpperType(expr, Type::InternalizedString());
+      break;
+    default:
+      UNREACHABLE();
+  }
 }


 void AstTyper::VisitCountOperation(CountOperation* expr) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(expr->expression()));
+  RECURSE(Visit(expr->expression()));

  expr->RecordTypeFeedback(oracle(), zone());
  Property* prop = expr->expression()->AsProperty();
  if (prop != NULL) {
    prop->RecordTypeFeedback(oracle(), zone());
  }
+
+  MergeLowerType(expr, Type::Smi());
+  MergeUpperType(expr, Type::Number());
 }


 void AstTyper::VisitBinaryOperation(BinaryOperation* expr) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(expr->left()));
-  CHECK_ALIVE(Visit(expr->right()));
+  RECURSE(Visit(expr->left()));
+  RECURSE(Visit(expr->right()));

  // Collect type feedback.
  Handle<Type> type, left_type, right_type;
@ -443,13 +479,69 @@ void AstTyper::VisitBinaryOperation(BinaryOperation* expr) {
  if (expr->op() == Token::OR || expr->op() == Token::AND) {
    expr->left()->RecordToBooleanTypeFeedback(oracle());
  }
+
+  switch (expr->op()) {
+    case Token::COMMA:
+      MergeLowerType(expr, expr->right()->lower_type());
+      MergeUpperType(expr, expr->right()->upper_type());
+      break;
+    case Token::OR:
+    case Token::AND:
+      MergeLowerType(expr, Type::Intersect(
+          expr->left()->lower_type(), expr->right()->lower_type()));
+      MergeUpperType(expr, Type::Union(
+          expr->left()->upper_type(), expr->right()->upper_type()));
+      break;
+    case Token::BIT_OR:
+    case Token::BIT_AND: {
+      MergeLowerType(expr, Type::Smi());
+      Type* upper =
+          Type::Union(expr->left()->upper_type(), expr->right()->upper_type());
+      MergeUpperType(expr,
+          upper->Is(Type::Signed32()) ? upper : Type::Signed32());
+      break;
+    }
+    case Token::BIT_XOR:
+    case Token::SHL:
+    case Token::SAR:
+      MergeLowerType(expr, Type::Smi());
+      MergeUpperType(expr, Type::Signed32());
+      break;
+    case Token::SHR:
+      MergeLowerType(expr, Type::Smi());
+      MergeUpperType(expr, Type::Unsigned32());
+      break;
+    case Token::ADD: {
+      Handle<Type> l = expr->left()->lower_type();
+      Handle<Type> r = expr->right()->lower_type();
+      MergeLowerType(expr,
+          l->Is(Type::Number()) && r->Is(Type::Number()) ? Type::Smi() :
+          l->Is(Type::String()) || r->Is(Type::String()) ? Type::String() :
+              Type::None());
+      l = expr->left()->upper_type();
+      r = expr->right()->upper_type();
+      MergeUpperType(expr,
+          l->Is(Type::Number()) && r->Is(Type::Number()) ? Type::Number() :
+          l->Is(Type::String()) || r->Is(Type::String()) ? Type::String() :
+              Type::NumberOrString());
+      break;
+    }
+    case Token::SUB:
+    case Token::MUL:
+    case Token::DIV:
+    case Token::MOD:
+      MergeLowerType(expr, Type::Smi());
+      MergeUpperType(expr, Type::Number());
+      break;
+    default:
+      UNREACHABLE();
+  }
 }


 void AstTyper::VisitCompareOperation(CompareOperation* expr) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(expr->left()));
-  CHECK_ALIVE(Visit(expr->right()));
+  RECURSE(Visit(expr->left()));
+  RECURSE(Visit(expr->right()));

  // Collect type feedback.
  Handle<Type> left_type, right_type, combined_type;
@ -458,76 +550,67 @@ void AstTyper::VisitCompareOperation(CompareOperation* expr) {
  MergeLowerType(expr->left(), left_type);
  MergeLowerType(expr->right(), right_type);
  expr->set_combined_type(combined_type);
+
+  MergeLowerType(expr, Type::Boolean());
+  MergeUpperType(expr, Type::Boolean());
 }


 void AstTyper::VisitThisFunction(ThisFunction* expr) {
-  ASSERT(!HasStackOverflow());
 }


 void AstTyper::VisitDeclarations(ZoneList<Declaration*>* decls) {
-  ASSERT(!HasStackOverflow());
  for (int i = 0; i < decls->length(); ++i) {
    Declaration* decl = decls->at(i);
-    CHECK_ALIVE(Visit(decl));
+    RECURSE(Visit(decl));
  }
 }


 void AstTyper::VisitVariableDeclaration(VariableDeclaration* declaration) {
-  ASSERT(!HasStackOverflow());
 }


 void AstTyper::VisitFunctionDeclaration(FunctionDeclaration* declaration) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(declaration->fun()));
+  RECURSE(Visit(declaration->fun()));
 }


 void AstTyper::VisitModuleDeclaration(ModuleDeclaration* declaration) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(declaration->module()));
+  RECURSE(Visit(declaration->module()));
 }


 void AstTyper::VisitImportDeclaration(ImportDeclaration* declaration) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(declaration->module()));
+  RECURSE(Visit(declaration->module()));
 }


 void AstTyper::VisitExportDeclaration(ExportDeclaration* declaration) {
-  ASSERT(!HasStackOverflow());
 }


 void AstTyper::VisitModuleLiteral(ModuleLiteral* module) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(module->body()));
+  RECURSE(Visit(module->body()));
 }


 void AstTyper::VisitModuleVariable(ModuleVariable* module) {
-  ASSERT(!HasStackOverflow());
 }


 void AstTyper::VisitModulePath(ModulePath* module) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(module->module()));
+  RECURSE(Visit(module->module()));
 }


 void AstTyper::VisitModuleUrl(ModuleUrl* module) {
-  ASSERT(!HasStackOverflow());
 }


 void AstTyper::VisitModuleStatement(ModuleStatement* stmt) {
-  ASSERT(!HasStackOverflow());
-  CHECK_ALIVE(Visit(stmt->body()));
+  RECURSE(Visit(stmt->body()));
 }


--- a/src/typing.h
+++ b/src/typing.h
@ -68,6 +68,12 @@ class AstTyper: public AstVisitor {
  void MergeUpperType(Expression* e, Handle<Type> t) {
    e->set_upper_type(handle(Type::Intersect(e->upper_type(), t), isolate_));
  }
+  void MergeLowerType(Expression* e, Type* t) {
+    MergeLowerType(e, handle(t, isolate_));
+  }
+  void MergeUpperType(Expression* e, Type* t) {
+    MergeUpperType(e, handle(t, isolate_));
+  }

  void VisitDeclarations(ZoneList<Declaration*>* declarations);
  void VisitStatements(ZoneList<Statement*>* statements);