Allow smi comparisons to have constant operands.

runtime/vm/flow_graph_compiler_x64.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_X64.
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/flow_graph_compiler.h"
 
 #include "lib/error.h"
@@ skipping 1215 matching lines @@
     if (destination.IsXmmRegister()) {
       __ movsd(destination.xmm_reg(), ToStackSlotAddress(source));
     } else {
       ASSERT(destination.IsDoubleStackSlot());
       __ movsd(XMM0, ToStackSlotAddress(source));
       __ movsd(ToStackSlotAddress(destination), XMM0);
     }
   } else {
     ASSERT(source.IsConstant());
     if (destination.IsRegister()) {
-      __ LoadObject(destination.reg(), source.constant());
+      const Object& constant = source.constant();
+      if (constant.IsSmi() && (Smi::Cast(constant).Value() == 0)) {
+        __ xorq(destination.reg(), destination.reg());
+      } else {
+        __ LoadObject(destination.reg(), constant);
+      }
     } else {
       ASSERT(destination.IsStackSlot());
       StoreObject(ToStackSlotAddress(destination), source.constant());
     }
   }
 
   move->Eliminate();
 }
 
 
@@ skipping 65 matching lines @@
 void ParallelMoveResolver::Exchange(const Address& mem1, const Address& mem2) {
   __ Exchange(mem1, mem2);
 }
 
 
 #undef __
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64