[FFmpeg-devel] [PATCH] A rather simple H.264 speed optimization
Mon Jul 28 22:36:01 CEST 2008
On Jul 28, 2008, at 11:53 AM, Jason Garrett-Glaser wrote:
>> What does gcc do with this on 32-bit platforms. I've often seen it
>> some rather horrid things with 64-bit types there.
> h264.c already uses 64-bit write combining in many many places; I'm
> just extending it.
> x264 uses it too, and I have never seen GCC pessimize it. GCC
> pessimizes 64-bit *arithmetic ops*, not copies.
> Dark Shikari
It might be useful to have a COPY64/XCHG64 macro, so we can use 'movq'
or double copies on architectures without 64-bit. There might even be
some opportunities for 128-bit copies, too. This is obviously
incompatible with runtime CPU detection, of course.
gcc should be able to do this on its own, but I haven't seen any
compiler that can and I haven't had time to file a bug about it.
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