Revert of Internalize strings in-place

src/mips64/codegen-mips64.cc

 // Copyright 2012 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/mips64/codegen-mips64.h"
 
 #if V8_TARGET_ARCH_MIPS64
 
 #include <memory>
 
@@ skipping 604 matching lines @@
   // Fetch the instance type of the receiver into result register.
   __ ld(result, FieldMemOperand(string, HeapObject::kMapOffset));
   __ lbu(result, FieldMemOperand(result, Map::kInstanceTypeOffset));
 
   // We need special handling for indirect strings.
   Label check_sequential;
   __ And(at, result, Operand(kIsIndirectStringMask));
   __ Branch(&check_sequential, eq, at, Operand(zero_reg));
 
   // Dispatch on the indirect string shape: slice or cons.
-  Label cons_string, thin_string;
-  __ And(at, result, Operand(kStringRepresentationMask));
-  __ Branch(&cons_string, eq, at, Operand(kConsStringTag));
-  __ Branch(&thin_string, eq, at, Operand(kThinStringTag));
+  Label cons_string;
+  __ And(at, result, Operand(kSlicedNotConsMask));
+  __ Branch(&cons_string, eq, at, Operand(zero_reg));
 
   // Handle slices.
   Label indirect_string_loaded;
   __ ld(result, FieldMemOperand(string, SlicedString::kOffsetOffset));
   __ ld(string, FieldMemOperand(string, SlicedString::kParentOffset));
   __ dsra32(at, result, 0);
   __ Daddu(index, index, at);
   __ jmp(&indirect_string_loaded);
 
-  // Handle thin strings.
-  __ bind(&thin_string);
-  __ ld(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
   // the case we would rather go to the runtime system now to flatten
   // the string.
   __ bind(&cons_string);
   __ ld(result, FieldMemOperand(string, ConsString::kSecondOffset));
   __ LoadRoot(at, Heap::kempty_stringRootIndex);
   __ Branch(call_runtime, ne, result, Operand(at));
   // Get the first of the two strings and load its instance type.
@@ skipping 122 matching lines @@
   }
 }
 
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_MIPS64