[FFmpeg-devel] [PATCH] ff_h[yc]scale_fast_mmext always clobbers %rbx

[Nick Lewycky]

On 6 May 2015 at 11:58, Carl Eugen Hoyos <cehoyos at ag.or.at> wrote:

> 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.

Did you check performance with and without your patch?
>

No.