Avoid allocating unnecessary result locations for some instructions.

runtime/vm/intermediate_language_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/intermediate_language.h"
 
 #include "lib/error.h"
@@ skipping 1037 matching lines @@
   Register result = locs()->out().reg();
   __ LoadObject(result, field());
   __ movq(result, FieldAddress(result, Field::value_offset()));
 }
 
 
 LocationSummary* StoreStaticFieldInstr::MakeLocationSummary() const {
   LocationSummary* locs = new LocationSummary(1, 1, LocationSummary::kNoCall);
   locs->set_in(0, Location::RequiresRegister());
   locs->set_temp(0, Location::RequiresRegister());
-  locs->set_out(Location::SameAsFirstInput());
+  locs->set_out(is_used()
+                ? Location::SameAsFirstInput()
+                : Location::NoLocation());
   return locs;
 }
 
 
 void StoreStaticFieldInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   Register value = locs()->in(0).reg();
   Register temp = locs()->temp(0).reg();
-  ASSERT(locs()->out().reg() == value);
+  ASSERT(!is_used() || (locs()->out().reg() == value));
 
   __ LoadObject(temp, field());
   if (this->value()->NeedsStoreBuffer()) {
     __ StoreIntoObject(temp, FieldAddress(temp, Field::value_offset()), value);
   } else {
     __ StoreIntoObjectNoBarrier(
         temp, FieldAddress(temp, Field::value_offset()), value);
   }
 }
 
@@ skipping 1235 matching lines @@
     __ j(ABOVE_EQUAL, deopt);
   }
 }
 
 
 }  // namespace dart
 
 #undef __
 
 #endif  // defined TARGET_ARCH_X64