[FFmpeg-devel] [flamefest-start] A little something on MMX/SSE intrinsics

Måns Rullgård mans
Wed Feb 27 22:33:09 CET 2008

Michael Niedermayer <michaelni at gmx.at> writes:

> On Wed, Feb 27, 2008 at 03:29:56PM -0500, Alexander Strange wrote:
>> I don't think anyone can get Altivec asm to work better than
>> intrinsics on more than one CPU - PPC is really, really
>> scheduling-sensitive, especially the G5 and Cell.
> Until i see benchmarks id guess gcc+intrinsics will be slower than
> unsheduled naively written asm()

That depends on the CPU.  Some CPUs are quite particular about
instruction scheduling.

>> I guess you can always try, though, but don't do anything to
>> discourage people who know altivec from adding more. There's still a
>> lot missing from H.264.
> Code is either well written or should be rejected.
> Intrinsics != well written.

That's where you're wrong.  Code using intrinsics can be well-written.
The problem is not the code, but the compiler.

I agree that if the most commonly used compilers can't compile
intrinsics properly, plain assembler should be used.  I have no idea
whether this is the case for Altivec, and neither do you.

M?ns Rullg?rd
mans at mansr.com

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