[Bug tree-optimization/108358] New: Dead Code Elimination Regression at -Os (trunk vs. 12.2.0)

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108358

            Bug ID: 108358
           Summary: Dead Code Elimination Regression at -Os (trunk vs.
                    12.2.0)
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: yann at ywg dot ch
  Target Milestone: ---

Created attachment 54233
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54233&action=edit
presented code as file

cat case.c #25
struct a {
  int b;
  int c;
  short d;
  int e;
  int f;
};
struct g {
  struct a f;
  struct a h;
};
int i;
void foo();
void bar31_(void);
int main() {
  struct g j, l = {2, 1, 6, 1, 1, 7, 5, 1, 0, 1};
  for (; i; ++i)
    bar31_();
  j = l;
  struct g m = j;
  struct g k = m;
  if (k.h.b)
    ;
  else
    foo();
}

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

`gcc-cb93c5f8008b95743b741d6f1842f9be50c6985c (trunk) -Os -S -o /dev/stdout
case.c`
--------- OUTPUT ---------
main:
.LFB0:
        .cfi_startproc
        pushq   %rbx
        .cfi_def_cfa_offset 16
        .cfi_offset 3, -16
        movl    $.LC0, %esi
        movl    $10, %ecx
        subq    $80, %rsp
        .cfi_def_cfa_offset 96
        leaq    40(%rsp), %rdi
        leaq    40(%rsp), %rbx
        rep movsl
.L2:
        cmpl    $0, i(%rip)
        je      .L7
        call    bar31_
        incl    i(%rip)
        jmp     .L2
.L7:
        movq    %rsp, %rdi
        movl    $10, %ecx
        movq    %rbx, %rsi
        rep movsl
        cmpl    $0, 20(%rsp)
        jne     .L4
        xorl    %eax, %eax
        call    foo
.L4:
        addq    $80, %rsp
        .cfi_def_cfa_offset 16
        xorl    %eax, %eax
        popq    %rbx
        .cfi_def_cfa_offset 8
        ret
---------- END OUTPUT ---------


`gcc-releases/gcc-12.2.0 -Os -S -o /dev/stdout case.c`
--------- OUTPUT ---------
main:
.LFB0:
        .cfi_startproc
        cmpl    $0, i(%rip)
        jne     .L7
        xorl    %eax, %eax
        ret
.L7:
        pushq   %rax
        .cfi_def_cfa_offset 16
.L3:
        call    bar31_
        incl    i(%rip)
        cmpl    $0, i(%rip)
        jne     .L3
        xorl    %eax, %eax
        popq    %rdx
        .cfi_def_cfa_offset 8
        ret
---------- END OUTPUT ---------


Bisects to:
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=f6c168f8c06047bfaa3005e570126831b8855dcc