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..19a459bf9b7d80f5a093bebe3e2abdf0e0cec75e 100644
--- a/src/x64/codegen-x64.cc
+++ b/src/x64/codegen-x64.cc
@@ -77,9 +77,12 @@ 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;
@@ -88,6 +91,11 @@ void StringCharLoadGenerator::Generate(MacroAssembler* masm,
   __ movp(string, FieldOperand(string, SlicedString::kParentOffset));
   __ jmp(&indirect_string_loaded, Label::kNear);
 
+  // Handle thin strings.
+  __ bind(&thin_string);
+  __ movp(string, FieldOperand(string, ThinString::kActualOffset));
+  __ jmp(&indirect_string_loaded, Label::kNear);
+
   // Handle cons strings.
   // Check whether the right hand side is the empty string (i.e. if
   // this is really a flat string in a cons string). If that is not