Make sure that top bits are zero when storing untagged 32 bit values

src/x64/lithium-gap-resolver-x64.cc

 // Copyright 2011 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 186 matching lines @@
       Register dst = cgen_->ToRegister(destination);
       if (cgen_->IsInteger32Constant(constant_source)) {
         __ movl(dst, Immediate(cgen_->ToInteger32(constant_source)));
       } else {
         __ LoadObject(dst, cgen_->ToHandle(constant_source));
       }
     } else {
       ASSERT(destination->IsStackSlot());
       Operand dst = cgen_->ToOperand(destination);
       if (cgen_->IsInteger32Constant(constant_source)) {
-        // Allow top 32 bits of an untagged Integer32 to be arbitrary.
-        __ movl(dst, Immediate(cgen_->ToInteger32(constant_source)));
+        // Zero top 32 bits of a 64 bit spill slot that holds a 32 bit untagged
+        // value.
+        __ movq(dst, Immediate(cgen_->ToInteger32(constant_source)));
       } else {
         __ LoadObject(kScratchRegister, cgen_->ToHandle(constant_source));
         __ movq(dst, kScratchRegister);
       }
     }
 
   } else if (source->IsDoubleRegister()) {
     XMMRegister src = cgen_->ToDoubleRegister(source);
     if (destination->IsDoubleRegister()) {
       __ movaps(cgen_->ToDoubleRegister(destination), src);
@@ skipping 93 matching lines @@
       moves_[i].set_source(source);
     }
   }
 }
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64