Revert "Clean up after r16292 (disable optimization for StringWrappers)."

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 5843 matching lines @@
                                             Register scratch3,
                                             Register scratch4,
                                             Label* slow) {
   // First check if the argument is already a string.
   Label not_string, done;
   __ JumpIfSmi(arg, &not_string);
   __ GetObjectType(arg, scratch1, scratch1);
   __ Branch(&done, lt, scratch1, Operand(FIRST_NONSTRING_TYPE));
 
   // Check the number to string cache.
+  Label not_cached;
   __ bind(&not_string);
   // Puts the cached result into scratch1.
   NumberToStringStub::GenerateLookupNumberStringCache(masm,
                                                       arg,
                                                       scratch1,
                                                       scratch2,
                                                       scratch3,
                                                       scratch4,
-                                                      slow);
+                                                      &not_cached);
   __ mov(arg, scratch1);
   __ sw(arg, MemOperand(sp, stack_offset));
+  __ jmp(&done);
+
+  // Check if the argument is a safe string wrapper.
+  __ bind(&not_cached);
+  __ JumpIfSmi(arg, slow);
+  __ GetObjectType(arg, scratch1, scratch2);  // map -> scratch1.
+  __ Branch(slow, ne, scratch2, Operand(JS_VALUE_TYPE));
+  __ lbu(scratch2, FieldMemOperand(scratch1, Map::kBitField2Offset));
+  __ li(scratch4, 1 << Map::kStringWrapperSafeForDefaultValueOf);
+  __ And(scratch2, scratch2, scratch4);
+  __ Branch(slow, ne, scratch2, Operand(scratch4));
+  __ lw(arg, FieldMemOperand(arg, JSValue::kValueOffset));
+  __ sw(arg, MemOperand(sp, stack_offset));
+
   __ bind(&done);
 }
 
 
 void ICCompareStub::GenerateSmis(MacroAssembler* masm) {
   ASSERT(state_ == CompareIC::SMI);
   Label miss;
   __ Or(a2, a1, a0);
   __ JumpIfNotSmi(a2, &miss);
 
@@ skipping 1356 matching lines @@
   __ bind(&fast_elements_case);
   GenerateCase(masm, FAST_ELEMENTS);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_MIPS