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