[Bug tree-optimization/106293] [13 Regression] 456.hmmer at -Ofast -march=native regressed by 19% on zen2 and zen3 in July 2022

["yann at ywg dot ch" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106293

Yann Girsberger <yann at ywg dot ch> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |yann at ywg dot ch

--- Comment #6 from Yann Girsberger <yann at ywg dot ch> ---
I found a DCE Regression in trunk that bisects to the same commit as in the
original report.
It seems to be present in -Ofast and -O2.
Let me know if this should be a new report. 

cat case.c #14
int a;
static long b = 4073709551612, d;
short c;
void foo();
static char e(int **f) {
  **f = 0;
  if (a) {
    unsigned long *g = &b;
    unsigned long **h = &g;
    for (; d;) {
      foo();
      for (; c;) {
        unsigned long ***i = &h;
      }
    }
  }
  return 1;
}
int main() {
  int *j = &a;
  e(&j);
  if (b <= 0)
    foo();
}

`gcc-cb93c5f8008b95743b741d6f1842f9be50c6985c (trunk) -O2` can not eliminate
`foo` but `gcc-releases/gcc-12.2.0 -O2` can.

`gcc-cb93c5f8008b95743b741d6f1842f9be50c6985c (trunk) -O2 -S -o /dev/stdout
case.c`
--------- OUTPUT ---------
main:
.LFB1:
        .cfi_startproc
        cmpq    $0, b(%rip)
        movl    $0, a(%rip)
        jle     .L8
        xorl    %eax, %eax
        ret
.L8:
        pushq   %rax
        .cfi_def_cfa_offset 16
        xorl    %eax, %eax
        call    foo
        xorl    %eax, %eax
        popq    %rdx
        .cfi_def_cfa_offset 8
        ret
---------- END OUTPUT ---------


`gcc-releases/gcc-12.2.0 -O2 -S -o /dev/stdout case.c`
--------- OUTPUT ---------
main:
.LFB1:
        .cfi_startproc
        movl    $0, a(%rip)
        xorl    %eax, %eax
        ret
---------- END OUTPUT ---------


Bisects to:
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=d2a898666609452ef79a14feae1cadc3538e4b45