[FFmpeg-devel] [PATCH] ff_h[yc]scale_fast_mmext always clobbers %rbx
Carl Eugen Hoyos
cehoyos at ag.or.at
Wed May 6 22:08:41 CEST 2015
Nick Lewycky <nlewycky <at> google.com> writes:
> On 6 May 2015 at 11:58, Carl Eugen Hoyos:
> > Nick Lewycky <nlewycky <at> google.com> writes:
> > > This occurs when building ffmpeg with clang
> > > -fsanitize=address -O1 -fPIE.
> > What is the usecase for -O1?
> It's very important for asan. ASan instruments
> every memory access (outside inline asm, for now)
> and if we don't run the optimizer then every local
> variable is a stack allocation with loads and
> stores, and all those loads and stores get
> instrumented leading to both crazy slowdown and
> binary size increase.
What I meant was (and I believe I wasn't clear):
What is the usecase for -O1 as opposed to default
Or in other words: Is the issue with clang also
reproducible with -O2 and -O3?
> > Did you check performance with and without
> > your patch?
I believe such a performance test is a precondition
for an asm patch (but I am not the maintainer).
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