[PATCH] [RFC] __builtin___clear_cache support in LLVM

[JF Bastien]

  I agree this shouldn't be mixed with C11/C++11, what I meant was that I made a similar argument about LLVM needing to support __sync_synchronize for legacy code and Jeffrey/Chandler didn't quite agree with me. The difference here is that __sync_synchronize has an equivalent in fences if the program moves everything to C11/C++11, whereas __clear_cache does not (since generation of code at runtime is still UB).

  I see your point on llvm_unreachable, it sounds good then.

  This change looks good to me since it meets your original intent, I don't know if you want to explore Tim's suggestion further or keep this one as-is for now.

http://llvm-reviews.chandlerc.com/D3084