Fix bug with mint unboxing on non-SSE 4.1 machines.

runtime/vm/assembler_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"
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/assembler.h"
 #include "vm/heap.h"
 #include "vm/memory_region.h"
@@ skipping 15 matching lines @@
 #endif
 
 bool CPUFeatures::sse3_supported() {
   DEBUG_ASSERT(initialized_);
   return sse3_supported_;
 }
 
 
 bool CPUFeatures::sse4_1_supported() {
   DEBUG_ASSERT(initialized_);
-  return sse4_1_supported_;
+  return sse4_1_supported_ && FLAG_use_sse41;
 }
 
 
 #define __ assembler.
 
 void CPUFeatures::InitOnce() {
   Assembler assembler;
   __ pushq(RBP);
   __ pushq(RBX);
   __ movq(RBP, RSP);
@@ skipping 2025 matching lines @@
 
 const char* Assembler::XmmRegisterName(XmmRegister reg) {
   ASSERT((0 <= reg) && (reg < kNumberOfXmmRegisters));
   return xmm_reg_names[reg];
 }
 
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64