[Bug tree-optimization/123103] missed optimization for redundant conditional

[652023330028 at smail dot nju.edu.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123103

--- Comment #4 from Yi <652023330028 at smail dot nju.edu.cn> ---
(In reply to Andrew Pinski from comment #3)
> You definitely reduced this testcase too much because you introduced
> possible undefined behavior due to the return value being possible not being
> have a value.

Thanks for the feedback.

reduced code:
https://godbolt.org/z/KGW5bfrcn

int t1, t2;
int ab() {
  int e=t1, f=t2;
  if (!e && !f) return 1;
  else{
    if (e)
        return 0;
    if (f)
        return 1;
  }
}

GCC -O3:
ab:
        movl    t2(%rip), %ecx
        movl    t1(%rip), %esi
        orl     %ecx, %esi
        je      .L2
        movl    t1(%rip), %eax
        xorl    %edx, %edx
        testl   %eax, %eax
        jne     .L1
        testl   %ecx, %ecx
        jne     .L2
.L1:
        movl    %edx, %eax
        ret
.L2:
        movl    $1, %edx
        movl    %edx, %eax
        ret


Expected (Clang -O3):
ab:
        xor     eax, eax
        cmp     dword ptr [rip + t1], 0
        sete    al
        ret