[Bug target/107456] std::atomic::fetch_xxx generate LOCK CMPXCHG instead of simpler LOCK instructions

[marko.makela at mariadb dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107456

--- Comment #2 from Marko Mäkelä <marko.makela at mariadb dot com> ---
Sorry for the noise. I posted a variant of the program to
https://github.com/llvm/llvm-project/issues/58685 and g++-12 is already
emitting the optimal code. Example:

#include <atomic>
bool lock_add_sete(std::atomic<uint32_t> &a, uint32_t b)
{
  return 0 == b + a.fetch_add(b);
}

   0:   f0 01 37                lock add %esi,(%rdi)
   3:   0f 94 c0                sete   %al
   6:   c3                      ret