DBC: Handle constants correctly in the optimizing backend

runtime/vm/intermediate_language_dbc.cc

 // Copyright (c) 2016, 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_DBC.
 #if defined(TARGET_ARCH_DBC)
 
 #include "vm/intermediate_language.h"
 
 #include "vm/cpu.h"
@@ skipping 321 matching lines @@
   if (compiler->is_optimizing()) {
     __ LoadClassId(locs()->out(0).reg(), locs()->in(0).reg());
   } else {
     __ LoadClassIdTOS();
   }
 }
 
 
 EMIT_NATIVE_CODE(Constant, 0, Location::RequiresRegister()) {
   if (compiler->is_optimizing()) {
-    __ LoadConstant(locs()->out(0).reg(), value());
+    if (locs()->out(0).IsRegister()) {
+      __ LoadConstant(locs()->out(0).reg(), value());
+    }
   } else {
     __ PushConstant(value());
   }
 }
 
 
 EMIT_NATIVE_CODE(UnboxedConstant, 0, Location::RequiresRegister()) {
   // The register allocator drops constant definitions that have no uses.
   if (locs()->out(0).IsInvalid()) {
     return;
@@ skipping 1611 matching lines @@
   __ IfULe(length, index);
   compiler->EmitDeopt(deopt_id(),
                       ICData::kDeoptCheckArrayBound,
                       (generalized_ ? ICData::kGeneralized : 0) |
                       (licm_hoisted_ ? ICData::kHoisted : 0));
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_DBC