Internalize strings in-place

src/arm64/codegen-arm64.cc

Index: src/arm64/codegen-arm64.cc
diff --git a/src/arm64/codegen-arm64.cc b/src/arm64/codegen-arm64.cc
index e6ddcfadb8dadfb221c93b293f9c7430fb4edfe2..4fb9a2d93901e783fde2b38db8b87366ab374e52 100644
--- a/src/arm64/codegen-arm64.cc
+++ b/src/arm64/codegen-arm64.cc
@@ -99,6 +99,9 @@ void StringCharLoadGenerator::Generate(MacroAssembler* masm,
                                        Register result,
                                        Label* call_runtime) {
   DCHECK(string.Is64Bits() && index.Is32Bits() && result.Is64Bits());
+  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));
@@ -108,17 +111,25 @@ void StringCharLoadGenerator::Generate(MacroAssembler* masm,
   __ TestAndBranchIfAllClear(result, kIsIndirectStringMask, &check_sequential);
 
   // Dispatch on the indirect string shape: slice or cons.
-  Label cons_string;
-  __ TestAndBranchIfAllClear(result, kSlicedNotConsMask, &cons_string);
+  Label cons_string, thin_string;
+  __ And(result, result, kStringRepresentationMask);
+  __ Cmp(result, kConsStringTag);
+  __ B(eq, &cons_string);
+  __ Cmp(result, kThinStringTag);
+  __ B(eq, &thin_string);
 
   // Handle slices.
-  Label indirect_string_loaded;
   __ Ldr(result.W(),
          UntagSmiFieldMemOperand(string, SlicedString::kOffsetOffset));
   __ Ldr(string, FieldMemOperand(string, SlicedString::kParentOffset));
   __ Add(index, index, result.W());
   __ B(&indirect_string_loaded);
 
+  // Handle thin strings.
+  __ Bind(&thin_string);
+  __ Ldr(string, FieldMemOperand(string, ThinString::kActualOffset));
+  __ B(&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
@@ -129,10 +140,7 @@ void StringCharLoadGenerator::Generate(MacroAssembler* masm,
   __ JumpIfNotRoot(result, Heap::kempty_stringRootIndex, 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));
+  __ B(&indirect_string_loaded);
 
   // Distinguish sequential and external strings. Only these two string
   // representations can reach here (slices and flat cons strings have been