Internalize strings in-place

src/x64/codegen-x64.cc

Index: src/x64/codegen-x64.cc
diff --git a/src/x64/codegen-x64.cc b/src/x64/codegen-x64.cc
index 2432d7ed4f40460756f6ca90cdfebf0fb3e1e90a..9d2ef78e41c6167f3d49919b7cf11aa45ae6e925 100644
--- a/src/x64/codegen-x64.cc
+++ b/src/x64/codegen-x64.cc
@@ -67,6 +67,9 @@ void StringCharLoadGenerator::Generate(MacroAssembler* masm,
                                        Register index,
                                        Register result,
                                        Label* call_runtime) {
+  Label indirect_string_loaded;
+  __ bind(&indirect_string_loaded);
+
   // Fetch the instance type of the receiver into result register.
   __ movp(result, FieldOperand(string, HeapObject::kMapOffset));
   __ movzxbl(result, FieldOperand(result, Map::kInstanceTypeOffset));
@@ -77,16 +80,23 @@ void StringCharLoadGenerator::Generate(MacroAssembler* masm,
   __ j(zero, &check_sequential, Label::kNear);
 
   // Dispatch on the indirect string shape: slice or cons.
-  Label cons_string;
-  __ testb(result, Immediate(kSlicedNotConsMask));
-  __ j(zero, &cons_string, Label::kNear);
+  Label cons_string, thin_string;
+  __ andl(result, Immediate(kStringRepresentationMask));
+  __ cmpl(result, Immediate(kConsStringTag));
+  __ j(equal, &cons_string, Label::kNear);
+  __ cmpl(result, Immediate(kThinStringTag));
+  __ j(equal, &thin_string, Label::kNear);
 
   // Handle slices.
-  Label indirect_string_loaded;
   __ SmiToInteger32(result, FieldOperand(string, SlicedString::kOffsetOffset));
   __ addp(index, result);
   __ movp(string, FieldOperand(string, SlicedString::kParentOffset));
-  __ jmp(&indirect_string_loaded, Label::kNear);
+  __ jmp(&indirect_string_loaded);
+
+  // Handle thin strings.
+  __ bind(&thin_string);
+  __ movp(string, FieldOperand(string, ThinString::kActualOffset));
+  __ jmp(&indirect_string_loaded);
 
   // Handle cons strings.
   // Check whether the right hand side is the empty string (i.e. if
@@ -98,10 +108,7 @@ void StringCharLoadGenerator::Generate(MacroAssembler* masm,
                  Heap::kempty_stringRootIndex);
   __ j(not_equal, call_runtime);
   __ movp(string, FieldOperand(string, ConsString::kFirstOffset));
-
-  __ bind(&indirect_string_loaded);
-  __ movp(result, FieldOperand(string, HeapObject::kMapOffset));
-  __ movzxbl(result, FieldOperand(result, Map::kInstanceTypeOffset));
+  __ jmp(&indirect_string_loaded);
 
   // Distinguish sequential and external strings. Only these two string
   // representations can reach here (slices and flat cons strings have been