[Bug tree-optimization/105833] New: Dead Code Elimination Regression at -O2 (trunk vs. 12.1.0)

[theodort at inf dot ethz.ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105833

            Bug ID: 105833
           Summary: Dead Code Elimination Regression at -O2 (trunk vs.
                    12.1.0)
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: theodort at inf dot ethz.ch
  Target Milestone: ---

cat case.c #4
void foo();

static int b;
static int **c;
static int ***d = &c;
static int ****e = &d;

static char(a)(char g, int h) { return h >= 2 ? g : g << h; }

int main() {
  **e == 0;
  b = b ? 4 : 0;
  if (!a(*e != 0, b))
    foo();
}

`gcc-1982fe2692b6c3b7f969ffc4edac59f9d4359e91 (trunk) -O2` can not eliminate
`foo` but `gcc-releases/gcc-12.1.0 -O2` can.

`gcc-1982fe2692b6c3b7f969ffc4edac59f9d4359e91 (trunk) -O2 -S -o /dev/stdout
case.c`
--------- OUTPUT ---------
main:
.LFB1:
        .cfi_startproc
        movl    b(%rip), %ecx
        xorl    %eax, %eax
        testl   %ecx, %ecx
        setne   %al
        sall    $2, %eax
        cmpq    $0, d(%rip)
        movl    %eax, b(%rip)
        je      .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-12.1.0 -O2 -S -o /dev/stdout case.c`
--------- OUTPUT ---------
main:
.LFB1:
        .cfi_startproc
        movl    b(%rip), %edx
        xorl    %eax, %eax
        testl   %edx, %edx
        setne   %al
        sall    $2, %eax
        movl    %eax, b(%rip)
        xorl    %eax, %eax
        ret
---------- END OUTPUT ---------


Bisects to:
https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=b7501739f3b14ac7749aace93f636d021fd607f7