[FFmpeg-devel] [PATCH] skip no-op loop iterations in ff_flac_compute_autocorr

[Bobby Bingham]

On Wed, 08 Apr 2009 17:42:55 -0400
Justin Ruggles <justin.ruggles at gmail.com> wrote:

> Bobby Bingham wrote:
> > Attached patch skips a bunch of iterations which are no-ops because
> > data1[-lag...-1] are all zero.
> 
> looks ok. do the ASM versions do the same?

No, the SSE2 version does not do this, but if I'm reading this right,
changing it to do the same doesn't actually help ...

This is on an Athlon 64 X2, in case it matters.  I'm attaching the
(rather trivial) patch in case it is useful on some other processor.

Before:
2918550 dezicycles in flac_compute_autocorr_sse2, 1 runs, 0 skips
2522720 dezicycles in flac_compute_autocorr_sse2, 2 runs, 0 skips
2319855 dezicycles in flac_compute_autocorr_sse2, 4 runs, 0 skips
2220241 dezicycles in flac_compute_autocorr_sse2, 8 runs, 0 skips
2169318 dezicycles in flac_compute_autocorr_sse2, 16 runs, 0 skips
2152224 dezicycles in flac_compute_autocorr_sse2, 32 runs, 0 skips
2138448 dezicycles in flac_compute_autocorr_sse2, 64 runs, 0 skips
2133790 dezicycles in flac_compute_autocorr_sse2, 128 runs, 0 skips
2132774 dezicycles in flac_compute_autocorr_sse2, 256 runs, 0 skips
2148665 dezicycles in flac_compute_autocorr_sse2, 512 runs, 0 skips
2136874 dezicycles in flac_compute_autocorr_sse2, 1024 runs, 0 skips
2132130 dezicycles in flac_compute_autocorr_sse2, 2048 runs, 0 skips
2139767 dezicycles in flac_compute_autocorr_sse2, 4096 runs, 0 skips
2146832 dezicycles in flac_compute_autocorr_sse2, 8191 runs, 1 skips
2147972 dezicycles in flac_compute_autocorr_sse2, 16382 runs, 2 skips

After:
2888910 dezicycles in flac_compute_autocorr_sse2, 1 runs, 0 skips
2516665 dezicycles in flac_compute_autocorr_sse2, 2 runs, 0 skips
2321807 dezicycles in flac_compute_autocorr_sse2, 4 runs, 0 skips
2223960 dezicycles in flac_compute_autocorr_sse2, 8 runs, 0 skips
2419460 dezicycles in flac_compute_autocorr_sse2, 16 runs, 0 skips
2275824 dezicycles in flac_compute_autocorr_sse2, 32 runs, 0 skips
2205534 dezicycles in flac_compute_autocorr_sse2, 64 runs, 0 skips
2169755 dezicycles in flac_compute_autocorr_sse2, 128 runs, 0 skips
2153054 dezicycles in flac_compute_autocorr_sse2, 256 runs, 0 skips
2143111 dezicycles in flac_compute_autocorr_sse2, 512 runs, 0 skips
2137918 dezicycles in flac_compute_autocorr_sse2, 1024 runs, 0 skips
2138707 dezicycles in flac_compute_autocorr_sse2, 2048 runs, 0 skips
2144707 dezicycles in flac_compute_autocorr_sse2, 4096 runs, 0 skips
2147715 dezicycles in flac_compute_autocorr_sse2, 8192 runs, 0 skips
2148168 dezicycles in flac_compute_autocorr_sse2, 16384 runs, 0 skips
-- 
Bobby Bingham
Never trust atoms.  Or anything made of atoms.
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