MIPS: Improvement of “MIPS: Fixed crashes exposed though fuzzing.” (r17886).

src/mips/macro-assembler-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 5064 matching lines @@
   AdduAndCheckForOverflow(index, index, index, scratch);
   BranchOnOverflow(&index_tag_bad, scratch);
   Branch(&index_tag_ok);
   bind(&index_tag_bad);
   Throw(kIndexIsTooLarge);
   bind(&index_tag_ok);
 
   lw(at, FieldMemOperand(string, String::kLengthOffset));
   ThrowIf(ge, kIndexIsTooLarge, index, Operand(at));
 
-  li(at, Operand(Smi::FromInt(0)));
-  ThrowIf(lt, kIndexIsNegative, index, Operand(at));
+  ASSERT(Smi::FromInt(0) == 0);
+  ThrowIf(lt, kIndexIsNegative, index, Operand(zero_reg));
 
   SmiUntag(index, index);
 }
 
 
 void MacroAssembler::PrepareCallCFunction(int num_reg_arguments,
                                           int num_double_arguments,
                                           Register scratch) {
   int frame_alignment = ActivationFrameAlignment();
 
@@ skipping 652 matching lines @@
        opcode == BGTZL);
   opcode = (cond == eq) ? BEQ : BNE;
   instr = (instr & ~kOpcodeMask) | opcode;
   masm_.emit(instr);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_MIPS