[Bug target/98442] [X86] suboptimal for memset with CLEAR_BY_PIECES

["hjl.tools at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98442

--- 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:
> 
> https://gitlab.com/x86-gcc/gcc/-/tree/users/hjl/pieces/master
> 
> 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= 0; i != 64; i++)
     Tab[i] = 0;
}
[hjl@gnu-cfl-1 gcc]$ ./xgcc -B./ -march=skylake -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]$ 

This requires middle-end changes.