probinson 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__
----------------
hans wrote:
> 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
> :-/
I thought there was a peephole to notice a guard like this and do the right
thing? In which case having the guard is fine.
https://reviews.llvm.org/D26335
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