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

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index c182dd0ce5800d8db1247fcdf9d4490c0881e6ca..c24512ecae390cc9d0821aa06d2e110f2207ecad 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -2935,7 +2935,7 @@ void FullCodeGenerator::EmitIsStringWrapperSafeForDefaultValueOf(
 
   VisitForAccumulatorValue(args->at(0));
 
-  Label materialize_true, materialize_false;
+  Label materialize_true, materialize_false, skip_lookup;
   Label* if_true = NULL;
   Label* if_false = NULL;
   Label* fall_through = NULL;
@@ -2949,7 +2949,7 @@ void FullCodeGenerator::EmitIsStringWrapperSafeForDefaultValueOf(
   __ movq(rbx, FieldOperand(rax, HeapObject::kMapOffset));
   __ testb(FieldOperand(rbx, Map::kBitField2Offset),
            Immediate(1 << Map::kStringWrapperSafeForDefaultValueOf));
-  __ j(not_zero, if_true);
+  __ j(not_zero, &skip_lookup);
 
   // Check for fast case object. Generate false result for slow case object.
   __ movq(rcx, FieldOperand(rax, JSObject::kPropertiesOffset));
@@ -2967,7 +2967,7 @@ void FullCodeGenerator::EmitIsStringWrapperSafeForDefaultValueOf(
   __ cmpq(rcx, Immediate(0));
   __ j(equal, &done);
 
-  __ LoadInstanceDescriptors(rbx, rbx);
+  __ LoadInstanceDescriptors(rbx, r8);
   // rbx: descriptor array.
   // rcx: valid entries in the descriptor array.
   // Calculate the end of the descriptor array.
@@ -2975,24 +2975,28 @@ void FullCodeGenerator::EmitIsStringWrapperSafeForDefaultValueOf(
   SmiIndex index = masm_->SmiToIndex(rdx, rcx, kPointerSizeLog2);
   __ lea(rcx,
          Operand(
-             rbx, index.reg, index.scale, DescriptorArray::kFirstOffset));
+             r8, index.reg, index.scale, DescriptorArray::kFirstOffset));
   // Calculate location of the first key name.
-  __ addq(rbx, Immediate(DescriptorArray::kFirstOffset));
+  __ addq(r8, Immediate(DescriptorArray::kFirstOffset));
   // Loop through all the keys in the descriptor array. If one of these is the
   // internalized string "valueOf" the result is false.
   __ jmp(&entry);
   __ bind(&loop);
-  __ movq(rdx, FieldOperand(rbx, 0));
+  __ movq(rdx, FieldOperand(r8, 0));
   __ Cmp(rdx, isolate()->factory()->value_of_string());
   __ j(equal, if_false);
-  __ addq(rbx, Immediate(DescriptorArray::kDescriptorSize * kPointerSize));
+  __ addq(r8, Immediate(DescriptorArray::kDescriptorSize * kPointerSize));
   __ bind(&entry);
-  __ cmpq(rbx, rcx);
+  __ cmpq(r8, rcx);
   __ j(not_equal, &loop);
 
   __ bind(&done);
-  // Reload map as register rbx was used as temporary above.
-  __ movq(rbx, FieldOperand(rax, HeapObject::kMapOffset));
+
+  // Set the bit in the map to indicate that there is no local valueOf field.
+  __ or_(FieldOperand(rbx, Map::kBitField2Offset),
+         Immediate(1 << Map::kStringWrapperSafeForDefaultValueOf));
+
+  __ 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.
@@ -3004,10 +3008,9 @@ void FullCodeGenerator::EmitIsStringWrapperSafeForDefaultValueOf(
   __ 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);
 }