Internalize strings in-place

src/arm/codegen-arm.cc

Index: src/arm/codegen-arm.cc
diff --git a/src/arm/codegen-arm.cc b/src/arm/codegen-arm.cc
index 06e92168b6f7c1a2e6966d0e8af408de9ef936a9..934875220ca02b657e0701ca4457e53eec7a6807 100644
--- a/src/arm/codegen-arm.cc
+++ b/src/arm/codegen-arm.cc
@@ -322,6 +322,9 @@ 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.
   __ ldr(result, FieldMemOperand(string, HeapObject::kMapOffset));
   __ ldrb(result, FieldMemOperand(result, Map::kInstanceTypeOffset));
@@ -332,17 +335,24 @@ void StringCharLoadGenerator::Generate(MacroAssembler* masm,
   __ b(eq, &check_sequential);
 
   // Dispatch on the indirect string shape: slice or cons.
-  Label cons_string;
-  __ tst(result, Operand(kSlicedNotConsMask));
+  Label cons_string, thin_string;
+  __ and_(result, result, Operand(kStringRepresentationMask));
+  __ cmp(result, Operand(kConsStringTag));
   __ b(eq, &cons_string);
+  __ cmp(result, Operand(kThinStringTag));
+  __ b(eq, &thin_string);
 
   // Handle slices.
-  Label indirect_string_loaded;
   __ ldr(result, FieldMemOperand(string, SlicedString::kOffsetOffset));
   __ ldr(string, FieldMemOperand(string, SlicedString::kParentOffset));
   __ add(index, index, Operand::SmiUntag(result));
   __ jmp(&indirect_string_loaded);
 
+  // Handle thin strings.
+  __ bind(&thin_string);
+  __ ldr(string, FieldMemOperand(string, ThinString::kActualOffset));
+  __ jmp(&indirect_string_loaded);
+
   // 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
@@ -354,10 +364,7 @@ void StringCharLoadGenerator::Generate(MacroAssembler* masm,
   __ b(ne, call_runtime);
   // Get the first of the two strings and load its instance type.
   __ ldr(string, FieldMemOperand(string, ConsString::kFirstOffset));
-
-  __ bind(&indirect_string_loaded);
-  __ ldr(result, FieldMemOperand(string, HeapObject::kMapOffset));
-  __ ldrb(result, FieldMemOperand(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