Allow a platform to indicate that some CPU features are always...

src/platform.h

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 229 matching lines @@
                        va_list args);
 
   static char* StrChr(char* str, int c);
   static void StrNCpy(Vector<char> dest, const char* src, size_t n);
 
   // Support for profiler.  Can do nothing, in which case ticks
   // occuring in shared libraries will not be properly accounted
   // for.
   static void LogSharedLibraryAddresses();
 
+  // The return value indicates the CPU features we are sure of because of the
+  // OS.  For example MacOSX doesn't run on any x86 CPUs that don't have SSE2
+  // instructions.
+  // This is a little messy because the interpretation is subject to the cross
+  // of the CPU and the OS.  The bits in the answer correspond to the bit
+  // positions indicated by the members of the CpuFeature enum from globals.h
+  static uint64_t CpuFeaturesImpliedByPlatform();
+
   // Returns the double constant NAN
   static double nan_value();
 
   // Support runtime detection of VFP3 on ARM CPUs.
-  enum CpuFeature { VFP };
   static bool ArmCpuHasFeature(CpuFeature feature);
 
   // Returns the activation frame alignment constraint or zero if
   // the platform doesn't care. Guaranteed to be a power of two.
   static int ActivationFrameAlignment();
 
  private:
   static const int msPerSecond = 1000;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(OS);
@@ skipping 275 matching lines @@
   bool active_;
   PlatformData* data_;  // Platform specific data.
   DISALLOW_IMPLICIT_CONSTRUCTORS(Sampler);
 };
 
 #endif  // ENABLE_LOGGING_AND_PROFILING
 
 } }  // namespace v8::internal
 
 #endif  // V8_PLATFORM_H_