Goodbye, MMX Usage inside Qt possibly removed soon

lists.qt-project.org

20 pointsguruz6 comments

Uh, none of that makes any sense.

You don't have to stop using MMX to use AVX, although you might benefit from using equivalent SSE2 instructions when available (might as well, who doesn't have an SSE2 processor now, you have to go pre-P4 for that), and that gets a tiny little mention near the end.

I think he's saying that the MMX versions of these functions actually perform worse than what the compiler could produce from the plain C code, because the compiler would be able to use SSE2 for all floating-point math. Hence, these elaborately hand-optimized code paths are actually "pessimizations".

... for new hardware.

If you still target Pentium 2 boxes, this is bad news for you :)

I don't think he's saying that you need to stop using MMX to use AVX. I think he's saying that MMX is old and SSE is much better, especially on x86-64 where you're guaranteed to have at least SSE2.

Then hes trying to make his point confusingly and over-verbosely.

For some strange reason, when I see MMX, I am reminded of Sega's old "with blast processing" commercials.

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