[Bug target/115961] [15 Regression] wrong code on llvm-18.1.8 since r15-1936-g80e446e829d818

[slyfox at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115961

--- Comment #1 from Sergei Trofimovich <slyfox at gcc dot gnu.org> ---
Forgot to post minimized example:

// $ cat a.cc
struct e { unsigned pre : 12; unsigned a : 4; };

static unsigned min_u(unsigned a, unsigned b) { return (b < a) ? b : a; }

__attribute__((noipa))
void bug(e * v, unsigned def, unsigned use) {
    e & defE = *v;
    defE.a = min_u(use + 1, 0xf);
}

__attribute__((noipa, optimize(0)))
int main(void) {
    e v = { 0xded, 3 };

    bug(&v, 32, 33);
    if (v.a != 0xf) __builtin_trap();
}