Add a mechanism to override the detected cpu features.

src/ia32/assembler-ia32.h

Index: src/ia32/assembler-ia32.h
diff --git a/src/ia32/assembler-ia32.h b/src/ia32/assembler-ia32.h
index 55eff931907b11e66d05c28c1c177fcc85590aa7..5c0928a5a9b6519f9a9f86bc5c318e48ef19b63f 100644
--- a/src/ia32/assembler-ia32.h
+++ b/src/ia32/assembler-ia32.h
@@ -535,6 +535,7 @@ class CpuFeatures : public AllStatic {
   // Check whether a feature is supported by the target CPU.
   static bool IsSupported(CpuFeature f) {
     ASSERT(initialized_);
+    if ((force_feature_ & (static_cast<uint64_t>(1) << f)) != 0) return true;

[Sven Panne, 2013/09/16 13:48:05]

Lift out

   static_cast<uint64_t>(1) << f

into a private helper now that it's all over the place.

     if (f == SSE2 && !FLAG_enable_sse2) return false;
     if (f == SSE3 && !FLAG_enable_sse3) return false;
     if (f == SSE4_1 && !FLAG_enable_sse4_1) return false;
@@ -550,13 +551,23 @@ class CpuFeatures : public AllStatic {
 
   static bool IsSafeForSnapshot(CpuFeature f) {
     return (IsSupported(f) &&
-            (!Serializer::enabled() || !IsFoundByRuntimeProbingOnly(f)));
+            (!Serializer::enabled() || !IsFoundByRuntimeProbingOnly(f))) ||
+           ((force_feature_ & (static_cast<uint64_t>(1) << f)) != 0);
+  }
+
+  static void ForceFeature(CpuFeature f) {

[Sven Panne, 2013/09/16 13:48:05]

I am not sure about the future use cases, perhaps some scoped form might be more
appropriate.

+    force_feature_ = force_feature_ | (static_cast<uint64_t>(1) << f);
+  }
+
+  static void ClearForcedFeatures() {
+    force_feature_ = 0;
   }
 
  private:
 #ifdef DEBUG
   static bool initialized_;
 #endif
+  static uint64_t force_feature_;
   static uint64_t supported_;
   static uint64_t found_by_runtime_probing_only_;