[Bug tree-optimization/110539] New: [14 Regression] Dead Code Elimination Regression at since r14-338-g1dd154f6407

["theodort at inf dot ethz.ch" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110539

            Bug ID: 110539
           Summary: [14 Regression] Dead Code Elimination Regression at
                    since r14-338-g1dd154f6407
           Product: gcc
           Version: 14.0
            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: ---

https://godbolt.org/z/h9vrrj5je

Given the following code:

void foo(void);
static int a, c = 1;
static short b;
static int *d = &c, *e = &a;
static int **f = &d;
void __assert_fail() __attribute__((__noreturn__));
static void g(short h) {
    if (*d)
        ;
    else {
        if (e) __assert_fail();
        if (a) {
            __builtin_unreachable();
        } else
            __assert_fail();
    }
    if ((((0, 0) || h) == h) + b) *f = 0;
}
int main() {
    int i = 0 != 10 & a;
    g(i);
    *e = 9;
    e = 0;
    if (d == 0)
        ;
    else
        foo();
    ;
}

gcc-trunk -O2 does not eliminate the call to foo:

main:
        subq    $8, %rsp
        movq    d(%rip), %rax
        movq    e(%rip), %rdx
        movl    (%rax), %edi
        testl   %edi, %edi
        jne     .L2
        xorl    %eax, %eax
        call    __assert_fail
.L2:
        xorl    %ecx, %ecx
        xorl    %esi, %esi
        movq    %rcx, d(%rip)
        cmpq    $0, d(%rip)
        movl    $9, (%rdx)
        movq    %rsi, e(%rip)
        je      .L3
        call    foo
.L3:
        xorl    %eax, %eax
        popq    %rdx
        ret

gcc-13.1.0 -O2 eliminates the call to foo:

main:
        movq    d(%rip), %rax
        movq    e(%rip), %rdx
        movl    (%rax), %esi
        testl   %esi, %esi
        jne     .L2
        pushq   %rcx
        xorl    %eax, %eax
        call    __assert_fail
.L2:
        xorl    %eax, %eax
        movq    %rax, d(%rip)
        xorl    %eax, %eax
        movl    $9, (%rdx)
        xorl    %edx, %edx
        movq    %rdx, e(%rip)
        ret

Bisects to r14-338-g1dd154f6407