Revert of Internalize strings in-place

src/arm64/codegen-arm64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/arm64/codegen-arm64.h"
 
 #if V8_TARGET_ARCH_ARM64
 
 #include "src/arm64/simulator-arm64.h"
 #include "src/codegen.h"
@@ skipping 90 matching lines @@
   DCHECK(string.Is64Bits() && index.Is32Bits() && result.Is64Bits());
   // Fetch the instance type of the receiver into result register.
   __ Ldr(result, FieldMemOperand(string, HeapObject::kMapOffset));
   __ Ldrb(result, FieldMemOperand(result, Map::kInstanceTypeOffset));
 
   // We need special handling for indirect strings.
   Label check_sequential;
   __ TestAndBranchIfAllClear(result, kIsIndirectStringMask, &check_sequential);
 
   // Dispatch on the indirect string shape: slice or cons.
-  Label cons_string, thin_string;
-  __ And(result, result, kStringRepresentationMask);
-  __ Cmp(result, kConsStringTag);
-  __ B(eq, &cons_string);
-  __ Cmp(result, kThinStringTag);
-  __ B(eq, &thin_string);
+  Label cons_string;
+  __ TestAndBranchIfAllClear(result, kSlicedNotConsMask, &cons_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
   // the case we would rather go to the runtime system now to flatten
   // the string.
   __ Bind(&cons_string);
   __ Ldr(result, FieldMemOperand(string, ConsString::kSecondOffset));
   __ 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));
@@ skipping 43 matching lines @@
   __ Ldrb(result, MemOperand(string, index, SXTW));
   __ Bind(&done);
 }
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM64