Revert "Clean up after r16292 (disable optimization for StringWrappers)."

src/x64/full-codegen-x64.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2917 matching lines @@
 }
 
 
 void FullCodeGenerator::EmitIsStringWrapperSafeForDefaultValueOf(
     CallRuntime* expr) {
   ZoneList<Expression*>* args = expr->arguments();
   ASSERT(args->length() == 1);
 
   VisitForAccumulatorValue(args->at(0));
 
-  Label materialize_true, materialize_false, skip_lookup;
+  Label materialize_true, materialize_false;
   Label* if_true = NULL;
   Label* if_false = NULL;
   Label* fall_through = NULL;
   context()->PrepareTest(&materialize_true, &materialize_false,
                          &if_true, &if_false, &fall_through);
 
   __ AssertNotSmi(rax);
 
   // Check whether this map has already been checked to be safe for default
   // valueOf.
   __ movq(rbx, FieldOperand(rax, HeapObject::kMapOffset));
   __ testb(FieldOperand(rbx, Map::kBitField2Offset),
            Immediate(1 << Map::kStringWrapperSafeForDefaultValueOf));
-  __ j(not_zero, &skip_lookup);
+  __ j(not_zero, if_true);
 
   // Check for fast case object. Generate false result for slow case object.
   __ movq(rcx, FieldOperand(rax, JSObject::kPropertiesOffset));
   __ movq(rcx, FieldOperand(rcx, HeapObject::kMapOffset));
   __ CompareRoot(rcx, Heap::kHashTableMapRootIndex);
   __ j(equal, if_false);
 
   // Look for valueOf string in the descriptor array, and indicate false if
   // found. Since we omit an enumeration index check, if it is added via a
   // transition that shares its descriptor array, this is a false positive.
@@ skipping 21 matching lines @@
   __ bind(&loop);
   __ movq(rdx, FieldOperand(rbx, 0));
   __ Cmp(rdx, isolate()->factory()->value_of_string());
   __ j(equal, if_false);
   __ addq(rbx, Immediate(DescriptorArray::kDescriptorSize * kPointerSize));
   __ bind(&entry);
   __ cmpq(rbx, rcx);
   __ j(not_equal, &loop);
 
   __ bind(&done);
-
-  // Set the bit in the map to indicate that there is no local valueOf field.
-  __ or_(FieldOperand(rbx, Map::kBitField2Offset),
-         Immediate(1 << Map::kStringWrapperSafeForDefaultValueOf));
-
   // Reload map as register rbx was used as temporary above.
   __ movq(rbx, FieldOperand(rax, HeapObject::kMapOffset));
 
-  __ bind(&skip_lookup);
-
   // If a valueOf property is not found on the object check that its
   // prototype is the un-modified String prototype. If not result is false.
   __ movq(rcx, FieldOperand(rbx, Map::kPrototypeOffset));
   __ testq(rcx, Immediate(kSmiTagMask));
   __ j(zero, if_false);
   __ movq(rcx, FieldOperand(rcx, HeapObject::kMapOffset));
   __ movq(rdx, Operand(rsi, Context::SlotOffset(Context::GLOBAL_OBJECT_INDEX)));
   __ movq(rdx, FieldOperand(rdx, GlobalObject::kNativeContextOffset));
   __ cmpq(rcx,
           ContextOperand(rdx, Context::STRING_FUNCTION_PROTOTYPE_MAP_INDEX));
+  __ j(not_equal, if_false);
+  __ jmp(if_true);
+
   PrepareForBailoutBeforeSplit(expr, true, if_true, if_false);
-  Split(equal, if_true, if_false, fall_through);
-
   context()->Plug(if_true, if_false);
 }
 
 
 void FullCodeGenerator::EmitIsFunction(CallRuntime* expr) {
   ZoneList<Expression*>* args = expr->arguments();
   ASSERT(args->length() == 1);
 
   VisitForAccumulatorValue(args->at(0));
 
@@ skipping 1855 matching lines @@
   *context_length = 0;
   return previous_;
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64