Regression on trunk: missed optimization for dead code, work as expected on clang-18

[ZY546]

Reduced code:
https://godbolt.org/z/chrT7v9vo

int m;
void func(short a, short b) {
    short f = 1;
    if(
    (f ? ((a ? b : 0) ? 1 : 0) : 0)
    -
    (f ? ((a ? b : 0) ? 1 : 0) : 0)
    ){ 
        m=1;
    }
}

Clang-trunk:

func(short, short):                              # @func(short, short)
        test    si, si
        setne   al
        sete    cl
        test    di, di
        setne   dl
        sete    sil
        and     dl, al
        or      sil, cl
        cmp     dl, sil
        jne     .LBB0_2
        mov     dword ptr [rip + m], 1
.LBB0_2:                                # %if.end
        ret

Expected code (Clang-18.1.0):

func(short, short):                              # @func(short, short)
        ret

[svs-quic]

Bisected to #85193
cc: @dtcxzyw

[Backl1ght]

The condition of if-statement is simplified to ((a NE 0) AND (b NE 0)) XOR ((a EQ 0) OR (b EQ 0)), and can not be simplified further https://godbolt.org/z/91Ex6dM5h . What make this more interesting is that we can simplify ((a EQ 0) AND (b EQ 0)) XOR ((a NE 0) OR (b NE 0)) to true https://alive2.llvm.org/ce/z/tSeGb6 .

The cause is that we will convert (a EQ 0) AND (b EQ 0) to (a OR b) EQ 0 and (a NE 0) OR (b NE 0) to (a OR b) NE 0, and then finally simplified ((a OR b) EQ 0) XOR ((a OR b) NE 0) to true. But we won't do anything to (a NE 0) AND (b NE 0) and (a EQ 0) OR (b EQ 0).