[Bug middle-end/110228] [13/14 Regression] llvm-16 miscompiled due to an maybe uninitialized and optimizations saying that the uninitialized has a nonzero bits of 1.

["pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110228

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[14 Regression] llvm-16     |[13/14 Regression] llvm-16
                   |miscompiled due to an maybe |miscompiled due to an maybe
                   |uninitialized and           |uninitialized and
                   |optimizations saying that   |optimizations saying that
                   |the uninitialized has a     |the uninitialized has a
                   |nonzero bits of 1.          |nonzero bits of 1.
   Target Milestone|14.0                        |13.2

--- Comment #16 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
here is a (x86_64 as it requires the inline-asm to force an undefined value
inside LookupFlags but LookupFlags is not used until the next iteration)
program which we have been miscompiling -O2 since r13-4459-g6508d5e5a1a8:
```
unsigned a[4] = {1,1,1,1};

unsigned tt1 = 0;
__attribute__((noipa))
static void bug(unsigned & p, unsigned *t, int n, int t2) {

    for(int i = 0; i < n; i++) {
        bool LookupFlags ;
        unsigned v = t[i];
        unsigned tt = tt1;
      if (v == 0)
        LookupFlags = 0;
     else if (v == 1)
        LookupFlags = 1;
     if (LookupFlags) {
        tt|=3u;
        LookupFlags = 0;
     }
     asm("movq $-1, %q1":"+a"(LookupFlags));
       p = tt;
    }
}


int main() {
    unsigned r = 42;
    bug(r,a, sizeof(a)/sizeof(a[0]), 1);
    __builtin_printf("%u\n", r);
    if (r != 3) __builtin_abort();
}
```

Yes it is a bit odd but that was the only way I could get the code added in
r13-4459-g6508d5e5a1a8 to be invoked and even have LookupFlags|=v==1 happening
and get what could get undefined behavior in the loop.