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From: "hjl.tools at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/110273] [12/13/14 Regression] i686-w64-mingw32 with
 -mavx512f generates AVX instructions without stack alignment
Date: Sat, 27 Jan 2024 19:01:08 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110273

--- Comment #14 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Zeb Figura from comment #13)
> (In reply to Sam James from comment #11)
> > (In reply to Jens-Hanno Schwalm from comment #10)
> > > Hi, i think we found a very-similar issue in darktable code, you migh=
t look
> > > at
> > >=20
> > > https://github.com/darktable-org/darktable/pull/15742
> > >=20
> >=20
> > If you're hitting this on another target than i686-w64-mingw32, please =
file
> > a new bug. We can always mark it as a dupe if it turns out to be, altho=
ugh I
> > suspect it isn't here.
>=20
> FWIW, I think the relevant part of i686-w64-ming32 is actually just
> STACK_REALIGN_DEFAULT. I can reproduce the same lack of alignment with
> "-mstackrealign -mavx512 -O2" with i386-linux-gnu, whereas "-mstackrealign
> -mavx2 -O2" does align the stack. [-O2 is necessary here otherwise gcc wi=
ll
> just use vmovdqu and not bother aligning the stack. No idea what the more
> targeted optimization is.]
>=20

For the attached testcase here, GCC 13.2 generates:

[hjl@gnu-cfl-3 tmp]$ gcc -S -mstackrealign -mavx512f -O2 -m32 x.c
[hjl@gnu-cfl-3 tmp]$ head -20 x.s
        .file   "x.c"
        .text
        .p2align 4
        .globl  ddraw7_GetCaps
        .type   ddraw7_GetCaps, @function
ddraw7_GetCaps:
.LFB0:
        .cfi_startproc
        leal    4(%esp), %ecx
        .cfi_def_cfa 1, 0
        andl    $-16, %esp  <<<<< Stack realignment.
        vpxor   %xmm0, %xmm0, %xmm0
        xorl    %eax, %eax
        pushl   -4(%ecx)
        pushl   %ebp
        movl    %esp, %ebp
        .cfi_escape 0x10,0x5,0x2,0x75,0
        pushl   %edi
        pushl   %ecx
        .cfi_escape 0xf,0x3,0x75,0x78,0x6
[hjl@gnu-cfl-3 tmp]$=20

It works for me.  Please file a separate bug if-mstackrealign -mavx512f -O2
doesn't work for you on Linux.=