https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113772
--- Comment #5 from Iain Sandoe <iains at gcc dot gnu.org> ---
(In reply to Iain Buclaw from comment #4)
> Looking at gcc/builtins.cc, I have a bad feeling that the only compile-time
> values one can get out of this built-in are "true" and "defer to run-time"
>
> ---
> /* Return a one or zero if it can be determined that object ARG1 of size ARG
> is lock free on this architecture. */
>
> static tree
> fold_builtin_atomic_is_lock_free (tree arg0, tree arg1)
> {
> if (!flag_inline_atomics)
> return NULL_TREE;
>
> /* If it isn't always lock free, don't generate a result. */
> if (fold_builtin_atomic_always_lock_free (arg0, arg1) == boolean_true_node)
> return boolean_true_node;
>
> return NULL_TREE;
> }
> ---
>
> The upstream contributor who tested this on x86 likely didn't get this
> because it's all lock-free.
indeed x86_64 and i686 both build fine .. but "it's all lock-free" is not
entirely true - x86-64 is only lock free up to 16bytes, so it might be a bug
waiting to happen there too.
