none (none.delete@this.none.com) on November 18, 2020 8:18 am wrote:
> Dummond D. Slow (mental.delete@this.protozoa.us) on November 18, 2020 7:17 am wrote:
> [...]
> > You know I am not completely sure about this as I can't check, but I heard that SPEC uses x264's
> > code WITHOUT SIMD assembly compiled (whether disabling ASM intentionally or not compiling with yasm
> > or whatever, no idea). If that is true it probably grossly changes character of the workload because
> > compiler autovectorization tends to fails on vectorizing multimedia integer algorithms. Normally,
> > x264 spends like 55% (figure given by devs 8-9 years back) in hand-tuned x86 SIMD.
>
> You're correct: no assembly (or intrinsics) are in any SPEC test; portability is paramount.
> So yes, that's not a good representation for the publicly available x264. But then it could
> be argued that you should use HW IP for that anyway, and so that part of SPEC is not very
> interesting; but it has quite a high IPC which makes it interesting to study.

x264 in SPEC is not there to help you decide which PC to buy for ripping DVD content!
It is there as an exemplar of certain styles of code: various generic compression techniques (so lots of bit by bit manipulation) and various image analysis techniques (so searches over images and image comparisons at various frequency granularities).