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Subject: [Bug rtl-optimization/102840] [12 Regression]
 gcc.target/i386/pr22076.c by r12-4475
Date: Tue, 19 Oct 2021 15:36:03 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102840

--- Comment #2 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Roger Sayle from comment #1)
> I believe this test case is poorly written, and not correctly testing the
> original issue in PR target/22076 which concerned suboptimal moving of
> arguments via memory (fixed by prohibiting reload using mmx registers).
>=20
> Prior to my patch, with -m32 -O2 -fomit-frame-pointer -mmmx -mno-sse2, GCC
> generated:
>=20
> test:   movq    .LC1, %mm0
>         paddb   .LC0, %mm0
>         movq    %mm0, x
>         ret
>=20
> .x:     .zero 8
> .LC0:   .byte   1
>         .byte   2
>         .byte   3
>         .byte   4
>         .byte   5
>         .byte   6
>         .byte   7
>         .byte   8
> .LC1:   .byte   11
>         .byte   22
>         .byte   33
>         .byte   44
>         .byte   55
>         .byte   66
>         .byte   77
>         .byte   88
>=20
> which indeed doesn't use movl, and requires two movq.
>=20
> After my patch, we now generate the much more efficient (dare I say optim=
al):
> test:   movl    $807671820, %eax
>         movl    $1616136252, %edx
>         movl    %eax, x
>         movl    %edx, x+4
>         ret
>=20
> which has evaluated the _mm_add_pi8 at compile-time, and effectively mems=
ets
> x to the correct value in the minimum possible number of cycles.  In fact,
> failing to evaluate this at compile-time is a regression since v4.1
> (according to godbolt)

If your analysis is correct, why does -m64 stay the same?=