Crankshaft: Recognize (i >>> 0) === i for integer32 inputs and replace

src/x64/lithium-codegen-x64.cc

 // Copyright 2013 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 1480 matching lines @@
         if (shift_count != 0) {
           __ rorl(ToRegister(left), Immediate(shift_count));
         }
         break;
       case Token::SAR:
         if (shift_count != 0) {
           __ sarl(ToRegister(left), Immediate(shift_count));
         }
         break;
       case Token::SHR:
-        if (shift_count == 0 && instr->can_deopt()) {
+        if (shift_count != 0) {
+          __ shrl(ToRegister(left), Immediate(shift_count));
+        } else if (instr->can_deopt()) {
           __ testl(ToRegister(left), ToRegister(left));
           DeoptimizeIf(negative, instr->environment());
         } else {
-          __ shrl(ToRegister(left), Immediate(shift_count));
+          // Even if the shift is zero, we have to zero out the high bits with
+          // a movl for negative inputs.
+          __ movl(ToRegister(left), ToRegister(left));
         }
         break;
       case Token::SHL:
         if (shift_count != 0) {
           __ shll(ToRegister(left), Immediate(shift_count));
         }
         break;
       default:
         UNREACHABLE();
         break;
@@ skipping 4170 matching lines @@
                                FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64