Use temporary variable for StoreIndexed that returns a value.

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 "lib/error.h"
 #include "vm/flow_graph_compiler.h"
 #include "vm/locations.h"
@@ skipping 358 matching lines @@
   compiler->GenerateCall(token_index(),
                          try_index(),
                          &StubCode::CallNativeCFunctionLabel(),
                          PcDescriptors::kOther);
   __ popq(RAX);
 }
 
 
 LocationSummary* StoreIndexedComp::MakeLocationSummary() const {
   const intptr_t kNumInputs = 3;
-  return MakeSimpleLocationSummary(kNumInputs, Location::RequiresRegister());
+  return MakeSimpleLocationSummary(kNumInputs, Location::NoLocation());
 }
 
 
 void StoreIndexedComp::EmitNativeCode(FlowGraphCompiler* compiler) {
   Register receiver = locs()->in(0).reg();
   Register index = locs()->in(1).reg();
   Register value = locs()->in(2).reg();
-  Register result = locs()->out().reg();
 
-  // Call operator []= but preserve the third argument value under the
-  // arguments as the result of the computation.
   const String& function_name =
       String::ZoneHandle(String::NewSymbol(Token::Str(Token::kASSIGN_INDEX)));
 
-  // Insert a copy of the value (third argument) under the arguments.
-  // TODO(fschneider): Avoid preserving the value if the result is not used.
-  __ pushq(value);
   __ pushq(receiver);
   __ pushq(index);
   __ pushq(value);
+  const intptr_t kNumArguments = 3;
+  const intptr_t kNumArgsChecked = 1;  // Type-feedback.
   compiler->EmitInstanceCall(cid(),
                              token_index(),
                              try_index(),
                              function_name,
-                             3,
-                             Array::ZoneHandle(),
-                             1);
-  __ popq(result);
+                             kNumArguments,
+                             Array::ZoneHandle(),  // No optional arguments.
+                             kNumArgsChecked);
 }
 
 
 LocationSummary* InstanceSetterComp::MakeLocationSummary() const {
   const intptr_t kNumInputs = 2;
   return MakeSimpleLocationSummary(kNumInputs, Location::RequiresRegister());
   return NULL;
 }
 
 
@@ skipping 650 matching lines @@
   if (locs()->out().reg() != RAX) {
     __ movq(locs()->out().reg(), RAX);
   }
 }
 
 }  // namespace dart
 
 #undef __
 
 #endif  // defined TARGET_ARCH_X64