[PATCH] msvcrt: Import memmove from musl

[Fabian Maurer]

Hello Piotr,

it would probably also be useful to benchmark the different glibc
implementations. Because for games, 10% more speed would be nice. I doubt a C
implementation can compete with an AVX based one.

> You patch is only affecting a subset of memmove calls. It also slows down
some cases a lot (around 1.5-2 times).

You mean the cases were we could use memcpy?

> I've also tested full implementation from musl (that uses their memcpy
implementation in some cases). It performs much better. It's much slower than
native if buffers overlap (around 3 times slower).

musl is slower in a lot of cases. I'm attaching a cheap test program. You can
compile it normally with "gcc" or you can link musl static with "musl-gcc".
That should compare the best glibc implementation vs the best musl
implementation. Correct me if I'm wrong though.

Regards,
Fabian Maurer
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