Avoid allocating unnecessary result locations for some instructions.

runtime/vm/intermediate_language.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/intermediate_language.h"
 
 #include "vm/bit_vector.h"
 #include "vm/dart_entry.h"
 #include "vm/flow_graph_allocator.h"
 #include "vm/flow_graph_builder.h"
@@ skipping 1516 matching lines @@
   // Chain the new context in context_value to its parent in CTX.
   __ StoreIntoObject(context_value,
                      FieldAddress(context_value, Context::parent_offset()),
                      CTX);
   // Set new context as current context.
   __ MoveRegister(CTX, context_value);
 }
 
 
 LocationSummary* StoreVMFieldInstr::MakeLocationSummary() const {
-  return LocationSummary::Make(2,
-                               Location::SameAsFirstInput(),
-                               LocationSummary::kNoCall);
+  return LocationSummary::Make(
+      2,
+      is_used() ? Location::SameAsFirstInput() : Location::NoLocation(),
+      LocationSummary::kNoCall);
 }
 
 
 void StoreVMFieldInstr::EmitNativeCode(FlowGraphCompiler* compiler) {
   Register value_reg = locs()->in(0).reg();
   Register dest_reg = locs()->in(1).reg();
-  ASSERT(value_reg == locs()->out().reg());
+  ASSERT(!is_used() || (value_reg == locs()->out().reg()));
 
   if (value()->NeedsStoreBuffer()) {
     __ StoreIntoObject(dest_reg, FieldAddress(dest_reg, offset_in_bytes()),
                        value_reg);
   } else {
     __ StoreIntoObjectNoBarrier(
         dest_reg, FieldAddress(dest_reg, offset_in_bytes()), value_reg);
   }
 }
 
@@ skipping 78 matching lines @@
     value->set_use_index(i);
     value->AddToEnvUseList();
   }
   instr->set_env(copy);
 }
 
 
 #undef __
 
 }  // namespace dart