[Bug target/110013] [i386] vector_size(8) on 32-bit ABI emits broken MMX

[husseydevin at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110013

--- Comment #2 from Devin Hussey <husseydevin at gmail dot com> ---
Scratch that. There is a somewhat easy way to fix this following psABI AND
using MMX with SSE.

Upon calling a function, we can have the following sequence

func:
    movdq2q  mm0, xmm0
    movq     mm1, [esp + n]
    call     mmx_func
    movq2dq  xmm0, mm0
    emms

Then, this prologue:

mmx_func:
    movq2dq   xmm0, mm0
    movq2dq   xmm1, mm1
    emms
    ...
    movdq2q   mm0, xmm0
    ret