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From: "hjl.tools at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/98442] [X86] suboptimal for memset with CLEAR_BY_PIECES
Date: Thu, 31 Dec 2020 03:56:50 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98442

--- Comment #3 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to H.J. Lu from comment #2)
> Please take a look at users/hjl/pieces/master branch:
>=20
> https://gitlab.com/x86-gcc/gcc/-/tree/users/hjl/pieces/master
>=20
> You may get some ideas.

I got

[hjl@gnu-cfl-1 gcc]$ cat /tmp/x.c
char Tab[64];
void foo(int n)
{
    for (int i=3D 0; i !=3D 64; i++)
     Tab[i] =3D 0;
}
[hjl@gnu-cfl-1 gcc]$ ./xgcc -B./ -march=3Dskylake -S -O2 /tmp/x.c
[hjl@gnu-cfl-1 gcc]$ cat x.s
        .file   "x.c"
        .text
        .p2align 4
        .globl  foo
        .type   foo, @function
foo:
.LFB0:
        .cfi_startproc
        vpxor   %xmm0, %xmm0, %xmm0
        vmovups %ymm0, Tab(%rip)
        vmovups %ymm0, Tab+32(%rip)
        vzeroupper
        ret
        .cfi_endproc
.LFE0:
        .size   foo, .-foo
        .comm   Tab,64,32
        .ident  "GCC: (GNU) 10.0.0 20190523 (experimental)"
        .section        .note.GNU-stack,"",@progbits
[hjl@gnu-cfl-1 gcc]$=20

This requires middle-end changes.=