Re: rep movsb vs. simpler instructions for memcpy/memmove

On Thu, 13 Mar 2025 13:40:09 +0000, Stefan Monnier wrote:

So __memmove_ssse3 is no longer that big ("only" 3901 bytes); it's
still the biggest implementation, but many others are quite a bit
bigger than the 0x113=275 bytes of my ssememmove.

Imagine that:: almost a page for memmove entry points.
My 66000 has MM memmove as an instruction (4-bytes) always
optimal, no checking required.

>
What is different about MM compared to `rep movsb`

MM does not modify the pointers. MM keeps its current index,
thus the compiler can use the Rf pointer multiple times.

                                                   that you can
confidently state that it will always be optimal?

Compared to the explosion in memmove() subroutine, yes.
Compared to a device living on My 66000 interconnect, maybe.
Compared to executing instructions on a core, yes.

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        Stefan