On x64 use 32bit idiv when possible instead of 64bit one.

runtime/vm/assembler_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"
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/assembler.h"
 #include "vm/heap.h"
 #include "vm/memory_region.h"
@@ skipping 347 matching lines @@
     EmitUint8(0xC7);
     EmitOperand(0, operand);
     EmitImmediate(imm);
   } else {
     movq(TMP, imm);
     movq(dst, TMP);
   }
 }
 
 
-void Assembler::movsxl(Register dst, const Address& src) {
+void Assembler::movsxd(Register dst, Register src) {
+  AssemblerBuffer::EnsureCapacity ensured(&buffer_);
+  Operand operand(src);
+  EmitOperandREX(dst, operand, REX_W);
+  EmitUint8(0x63);
+  EmitOperand(dst & 7, operand);
+}
+
+
+void Assembler::movsxd(Register dst, const Address& src) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   EmitOperandREX(dst, src, REX_W);
   EmitUint8(0x63);
   EmitOperand(dst & 7, src);
 }
 
 
 void Assembler::leaq(Register dst, const Address& src) {
   AssemblerBuffer::EnsureCapacity ensured(&buffer_);
   EmitOperandREX(dst, src, REX_W);
@@ skipping 2115 matching lines @@
 
 const char* Assembler::FpuRegisterName(FpuRegister reg) {
   ASSERT((0 <= reg) && (reg < kNumberOfXmmRegisters));
   return xmm_reg_names[reg];
 }
 
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64