Optimize ~~(expr) in optimized code.

src/mips/lithium-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 1278 matching lines @@
     LOperand* right = UseFixed(instr->right(), a0);
     LArithmeticT* result = new(zone()) LArithmeticT(instr->op(), left, right);
     return MarkAsCall(DefineFixed(result, v0), instr);
   }
 }
 
 
 LInstruction* LChunkBuilder::DoBitNot(HBitNot* instr) {
   ASSERT(instr->value()->representation().IsInteger32());
   ASSERT(instr->representation().IsInteger32());
+  if (instr->HasNoUses()) return NULL;
   LOperand* value = UseRegisterAtStart(instr->value());
   return DefineAsRegister(new(zone()) LBitNotI(value));
 }
 
 
 LInstruction* LChunkBuilder::DoDiv(HDiv* instr) {
   if (instr->representation().IsDouble()) {
     return DoArithmeticD(Token::DIV, instr);
   } else if (instr->representation().IsInteger32()) {
     // TODO(1042) The fixed register allocation
@@ skipping 1026 matching lines @@
 
 
 LInstruction* LChunkBuilder::DoLoadFieldByIndex(HLoadFieldByIndex* instr) {
   LOperand* object = UseRegister(instr->object());
   LOperand* index = UseRegister(instr->index());
   return DefineAsRegister(new(zone()) LLoadFieldByIndex(object, index));
 }
 
 
 } }  // namespace v8::internal