MIPS: Make kAsciiDataHintTag have correct semantics for all both 1 and 2 byte string types.

src/mips/code-stubs-mips.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 6646 matching lines @@
   __ bind(&non_ascii);
   // At least one of the strings is two-byte. Check whether it happens
   // to contain only ASCII characters.
   // t0: first instance type.
   // t1: second instance type.
   // Branch to if _both_ instances have kAsciiDataHintMask set.
   __ And(at, t0, Operand(kAsciiDataHintMask));
   __ and_(at, at, t1);
   __ Branch(&ascii_data, ne, at, Operand(zero_reg));
 
-  __ xor_(t0, t0, t1);
-  STATIC_ASSERT(kOneByteStringTag != 0 && kAsciiDataHintTag != 0);
-  __ And(t0, t0, Operand(kOneByteStringTag | kAsciiDataHintTag));
-  __ Branch(
-         &ascii_data, eq, t0, Operand(kOneByteStringTag | kAsciiDataHintTag));
-
   // Allocate a two byte cons string.
   __ AllocateTwoByteConsString(v0, t2, t0, t1, &call_runtime);
   __ Branch(&allocated);
 
   // We cannot encounter sliced strings or cons strings here since:
   STATIC_ASSERT(SlicedString::kMinLength >= ConsString::kMinLength);
   // Handle creating a flat result from either external or sequential strings.
   // Locate the first characters' locations.
   // a0: first string
   // a1: second string
@@ skipping 1152 matching lines @@
   __ Pop(ra, t1, a1);
   __ Ret();
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_MIPS