Reapply r9870 "Remove some initialization checks based on source positions.".

Reapply r9870 "Remove some initialization checks based on source positions.".

This reverts r9896 "Revert r9870 due to browser-test failures." See below for
the diff from the previous version for the ia32 platform. The code for other
platforms has been changed accordingly.

TEST=mjsunit/compiler/lazy-const-lookup.js


diff --git a/src/ia32/full-codegen-ia32.cc b/src/ia32/full-codegen-ia32.cc
index 2cbf518..1990f2f 100644
--- a/src/ia32/full-codegen-ia32.cc
+++ b/src/ia32/full-codegen-ia32.cc
@@ -1258,13 +1258,17 @@ void FullCodeGenerator::EmitVariableLoad(VariableProxy* proxy) {
         // binding is initialized:
         //   function() { f(); let x = 1; function f() { x = 2; } }
         //
-        // Check that we always have valid source position.
-        ASSERT(var->initializer_position() != RelocInfo::kNoPosition);
-        ASSERT(proxy->position() != RelocInfo::kNoPosition);
-        bool skip_init_check =
-            var->mode() != CONST &&
-            var->scope()->DeclarationScope() == scope()->DeclarationScope() &&
-            var->initializer_position() < proxy->position();
+        bool skip_init_check;
+        if (var->scope()->DeclarationScope() != scope()->DeclarationScope()) {
+          skip_init_check = false;
+        } else {
+          // Check that we always have valid source position.
+          ASSERT(var->initializer_position() != RelocInfo::kNoPosition);
+          ASSERT(proxy->position() != RelocInfo::kNoPosition);
+          skip_init_check = var->mode() != CONST &&
+              var->initializer_position() < proxy->position();
+        }
+
         if (!skip_init_check) {
           // Let and const need a read barrier.
           Label done;

Committed: http://code.google.com/p/v8/source/detail?r=9915

[Steven, 2011-11-07 17:13:53]

PTAL.

[Jakob Kummerow, 2011-11-07 17:36:26]

LGTM.

As discussed, please run Chromium's browser_tests on this before landing, just
to be sure.