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From: "theodort at inf dot ethz.ch" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/110080] [13/14 Regression] Missed Dead Code
 Elimination at -Os when using __builtin_unreachable since
 r13-6945-g429a7a88438
Date: Thu, 01 Jun 2023 14:02:32 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110080

--- Comment #1 from Theodoros Theodoridis <theodort at inf dot ethz.ch> ---
Oops, the first code snippet is wrong in the original post:=20

void foo(void);
static unsigned char a =3D 131;
static int *b;
static int **c =3D &b;
static void d(int e, unsigned f) {
    int *g;
    if (!e){ // <------------------------ if (!e) is correct
        for (; a; ++a)
            for (e =3D 0; 0;)
                ;
        g =3D &e;
        int **h =3D &g;
        if (**h) {
            foo();
        }
    }
    *c =3D &e;
}
int main() { d(4 & a, a); }

this is also the correct assembly for gcc trunk/13.1/12.3 at -Os:

main:
        movb    a(%rip), %al
        testb   $4, %al
        jne     .L5
        xorl    %edx, %edx
.L2:
        testb   %al, %al
        je      .L12
        incl    %eax
        movb    $1, %dl
        jmp     .L2
.L12:
        testb   %dl, %dl
        je      .L5
        movb    $0, a(%rip)
.L5:
        leaq    -4(%rsp), %rax
        movq    %rax, b(%rip)
        xorl    %eax, %eax
        ret
a:
        .byte   -125


the code with the _builtin_unreachable and the rest are correct=