From d75b34db33833f966f082b348746be91d47d067c Mon Sep 17 00:00:00 2001
From: "olivf@chromium.org"
 <olivf@chromium.org@ce2b1a6d-e550-0410-aec6-3dcde31c8c00>
Date: Wed, 17 Jul 2013 14:10:38 +0000
Subject: [PATCH] There is no undefined Literal.

BUG=
R=rossberg@chromium.org

Review URL: https://codereview.chromium.org/18429005

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15724 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
---
 src/ast.cc          | 22 +++++++++++++++-------
 src/ast.h           |  6 +++---
 src/full-codegen.cc |  2 +-
 src/hydrogen.cc     |  2 +-
 4 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/src/ast.cc b/src/ast.cc
index 964f5bc..f34c7bb 100644
--- a/src/ast.cc
+++ b/src/ast.cc
@@ -71,8 +71,14 @@ bool Expression::IsNullLiteral() {
 }
 
 
-bool Expression::IsUndefinedLiteral() {
-  return AsLiteral() != NULL && AsLiteral()->value()->IsUndefined();
+bool Expression::IsUndefinedLiteral(Isolate* isolate) {
+  VariableProxy* var_proxy = AsVariableProxy();
+  if (var_proxy == NULL) return false;
+  Variable* var = var_proxy->var();
+  // The global identifier "undefined" is immutable. Everything
+  // else could be reassigned.
+  return var != NULL && var->location() == Variable::UNALLOCATED &&
+         var_proxy->name()->Equals(isolate->heap()->undefined_string());
 }
 
 
@@ -385,12 +391,13 @@ static bool IsVoidOfLiteral(Expression* expr) {
 static bool MatchLiteralCompareUndefined(Expression* left,
                                          Token::Value op,
                                          Expression* right,
-                                         Expression** expr) {
+                                         Expression** expr,
+                                         Isolate* isolate) {
   if (IsVoidOfLiteral(left) && Token::IsEqualityOp(op)) {
     *expr = right;
     return true;
   }
-  if (left->IsUndefinedLiteral() && Token::IsEqualityOp(op)) {
+  if (left->IsUndefinedLiteral(isolate) && Token::IsEqualityOp(op)) {
     *expr = right;
     return true;
   }
@@ -398,9 +405,10 @@ static bool MatchLiteralCompareUndefined(Expression* left,
 }
 
 
-bool CompareOperation::IsLiteralCompareUndefined(Expression** expr) {
-  return MatchLiteralCompareUndefined(left_, op_, right_, expr) ||
-      MatchLiteralCompareUndefined(right_, op_, left_, expr);
+bool CompareOperation::IsLiteralCompareUndefined(
+    Expression** expr, Isolate* isolate) {
+  return MatchLiteralCompareUndefined(left_, op_, right_, expr, isolate) ||
+      MatchLiteralCompareUndefined(right_, op_, left_, expr, isolate);
 }
 
 
diff --git a/src/ast.h b/src/ast.h
index 78b7843..f14156f 100644
--- a/src/ast.h
+++ b/src/ast.h
@@ -353,8 +353,8 @@ class Expression: public AstNode {
   // True iff the expression is the null literal.
   bool IsNullLiteral();
 
-  // True iff the expression is the undefined literal.
-  bool IsUndefinedLiteral();
+  // True if we can prove that the expression is the undefined literal.
+  bool IsUndefinedLiteral(Isolate* isolate);
 
   // Expression type bounds
   Bounds bounds() { return bounds_; }
@@ -1994,7 +1994,7 @@ class CompareOperation: public Expression {
 
   // Match special cases.
   bool IsLiteralCompareTypeof(Expression** expr, Handle<String>* check);
-  bool IsLiteralCompareUndefined(Expression** expr);
+  bool IsLiteralCompareUndefined(Expression** expr, Isolate* isolate);
   bool IsLiteralCompareNull(Expression** expr);
 
  protected:
diff --git a/src/full-codegen.cc b/src/full-codegen.cc
index 82d4f7c..76d3fff 100644
--- a/src/full-codegen.cc
+++ b/src/full-codegen.cc
@@ -1605,7 +1605,7 @@ bool FullCodeGenerator::TryLiteralCompare(CompareOperation* expr) {
     return true;
   }
 
-  if (expr->IsLiteralCompareUndefined(&sub_expr)) {
+  if (expr->IsLiteralCompareUndefined(&sub_expr, isolate())) {
     EmitLiteralCompareNil(expr, sub_expr, kUndefinedValue);
     return true;
   }
diff --git a/src/hydrogen.cc b/src/hydrogen.cc
index 7d120b7..154027f 100644
--- a/src/hydrogen.cc
+++ b/src/hydrogen.cc
@@ -8164,7 +8164,7 @@ void HOptimizedGraphBuilder::VisitCompareOperation(CompareOperation* expr) {
   if (expr->IsLiteralCompareTypeof(&sub_expr, &check)) {
     return HandleLiteralCompareTypeof(expr, sub_expr, check);
   }
-  if (expr->IsLiteralCompareUndefined(&sub_expr)) {
+  if (expr->IsLiteralCompareUndefined(&sub_expr, isolate())) {
     return HandleLiteralCompareNil(expr, sub_expr, kUndefinedValue);
   }
   if (expr->IsLiteralCompareNull(&sub_expr)) {
-- 
2.7.4