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..10dc83bb6e8769885f67a97dc32fef7534d16d60 100644
--- a/src/arm64/codegen-arm64.cc
+++ b/src/arm64/codegen-arm64.cc
@@ -108,8 +108,12 @@ 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;
@@ -119,6 +123,11 @@ void StringCharLoadGenerator::Generate(MacroAssembler* masm,
   __ 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