Ensure that BoxInt32 input is correctly preserved on the slow-path.

runtime/vm/flow_graph_compiler_x64.cc

 // Copyright (c) 2013, 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 "vm/ast_printer.h"
@@ skipping 1424 matching lines @@
     __ popq(left);
   } else {
     __ cmpl(left, right);
   }
 }
 
 
 // This function must be in sync with FlowGraphCompiler::RecordSafepoint and
 // FlowGraphCompiler::SlowPathEnvironmentFor.
 void FlowGraphCompiler::SaveLiveRegisters(LocationSummary* locs) {
+#if defined(DEBUG)
+  locs->CheckWritableInputs();
+#endif
+
   // TODO(vegorov): avoid saving non-volatile registers.
   __ PushRegisters(locs->live_registers()->cpu_registers(),
                    locs->live_registers()->fpu_registers());
 }
 
 
 void FlowGraphCompiler::RestoreLiveRegisters(LocationSummary* locs) {
   __ PopRegisters(locs->live_registers()->cpu_registers(),
                   locs->live_registers()->fpu_registers());
 }
@@ skipping 267 matching lines @@
   __ movups(reg, Address(RSP, 0));
   __ AddImmediate(RSP, Immediate(kFpuRegisterSize), PP);
 }
 
 
 #undef __
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64