hans added inline comments.

================
Comment at: lib/Headers/x86intrin.h:49
+static __inline__ unsigned int __attribute__((__always_inline__, __nodebug__))
+__tzcnt_u32(unsigned int __X) { return __X ? __builtin_ctz(__X) : 32; }
+#ifdef __x86_64__
----------------
I'm worried about the conditional here. IIRC, ffmpeg uses TZCNT just as a 
faster encoding for BSF, but now we're putting a conditional in the way, so 
this will be slower actually. On the other hand, the alternative is weird too 
:-/


https://reviews.llvm.org/D26335



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