From x86inc:
> On AMD cpus <=K10, an ordinary ret is slow if it immediately follows either
> a branch or a branch target. So switch to a 2-byte form of ret in that case.
> We can automatically detect "follows a branch", but not a branch target.
> (SSSE3 is a sufficient condition to know that your cpu doesn't have this problem.)
x86inc can automatically determine whether to use REP_RET rather than
REP in most of these cases, so impact is minimal. Additionally, a few
REP_RETs were used unnecessary, despite the return being nowhere near a
branch.
The only CPUs affected were AMD K10s, made between 2007 and 2011, 16
years ago and 12 years ago, respectively.
In the future, everyone involved with x86inc should consider dropping
REP_RETs altogether.
x64 always has MMX, MMXEXT, SSE and SSE2 and this means
that some functions for MMX, MMXEXT and 3dnow are always
overridden by other functions (unless one e.g. explicitly
disables SSE2) for x64. So given that the only systems that
benefit from these functions are truely ancient 32bit x86s
they are removed.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
The attribution was removed by libav while moving the code to libavutil
The original code is from
commit eb4825b5d4
Author: Loren Merritt <lorenm@u.washington.edu>
Date: Thu Aug 10 19:06:25 2006 +0000
sse and 3dnow implementations of float->int conversion and mdct windowing.
15% faster vorbis.
and
commit 069720565c
Author: Loren Merritt <lorenm@u.washington.edu>
Date: Fri Aug 11 18:19:37 2006 +0000
vorbis simd tweaks
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Lynne
Andreas Rheinhardt
James Almer
Ronald S. Bultje
Carl Eugen Hoyos
Michael Niedermayer
Justin Ruggles