[Bug target/91502] suboptimal atomic_fetch_sub and atomic_fetch_add

[nruslan_devel at yahoo dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91502

--- Comment #1 from Ruslan Nikolaev <nruslan_devel at yahoo dot com> ---
btw, the same problem for

#include <stdatomic.h>

int func(_Atomic(long) *a)
{
        return (atomic_fetch_sub(a, 1) <= 0);
}

In the previous case clang/llvm was just like gcc, i.e., unable to optimize; in
this case clang/llvm was able to produce better code, but gcc still cannot.