Refactors CPU feature detection.

runtime/vm/cpu_x64.h

Index: runtime/vm/cpu_x64.h
===================================================================
--- runtime/vm/cpu_x64.h	(revision 0)
+++ runtime/vm/cpu_x64.h	(revision 0)
@@ -0,0 +1,61 @@
+// 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.
+
+#ifndef VM_CPU_X64_H_
+#define VM_CPU_X64_H_
+
+#include "vm/allocation.h"
+#include "vm/flags.h"
+
+namespace dart {
+
+DECLARE_FLAG(bool, use_sse41);
+
+class HostCPUFeatures : public AllStatic {
+ public:
+  static void InitOnce();
+  static char* hardware() {
+    DEBUG_ASSERT(initialized_);
+    return hardware_;
+  }
+  static bool sse2_supported() {
+    DEBUG_ASSERT(initialized_);
+    return sse2_supported_;
+  }
+  static bool sse4_1_supported() {
+    DEBUG_ASSERT(initialized_);
+    return sse4_1_supported_ && FLAG_use_sse41;
+  }
+
+ private:
+  static const uint64_t kSSE2BitMask = static_cast<uint64_t>(1) << 26;
+  static const uint64_t kSSE4_1BitMask = static_cast<uint64_t>(1) << 51;
+  static char* hardware_;
+  static bool sse2_supported_;
+  static bool sse4_1_supported_;
+#if defined(DEBUG)
+  static bool initialized_;
+#endif
+};
+
+class TargetCPUFeatures : public AllStatic {
+ public:
+  static void InitOnce() { HostCPUFeatures::InitOnce(); }
+  static char* hardware() {
+    return HostCPUFeatures::hardware();
+  }
+  static bool sse2_supported() {
+    return HostCPUFeatures::sse2_supported();
+  }
+  static bool sse4_1_supported() {
+    return HostCPUFeatures::sse4_1_supported();
+  }
+  static bool double_truncate_round_supported() {
+    return false;
+  }
+};
+
+}  // namespace dart
+
+#endif  // VM_CPU_X64_H_