[FFmpeg-devel] [RFC] Disable gcc auto-vectorisation

[Ramiro Polla]

2009/7/13 M?ns Rullg?rd <mans at mansr.com>:
> Since gcc 4.3, the auto-vectoriser (-ftree-vectorize) has been enabled
> at -O3 optimisation level. ?This vectoriser is, mildly put, useless.
> When it doesn't produce outright broken code, it is a gamble whether
> the result is any faster whatsoever, and we have seen cases where it
> introduced a significant slowdown.
>
> My proposal is to disable this misfeature by adding
> -fno-tree-vectorize to the compiler flags when using gcc.
>
> Does anyone have a good reason for not doing this?

That's mostly what led me to write the x86 asm for mlpdec =)
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39821

I'm sure other dsp functions would benefit too.