https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83638
--- Comment #4 from dave.anglin at bell dot net --- On 2018-03-26 2:23 PM, mikulas at artax dot karlin.mff.cuni.cz wrote: > If the userspace wants to optimize different code paths for lockless atomics > and for locked atomics, atomic_is_lock_free should return false, to indicate > that the atomic operation is as costly as taking a lock. At the moment, there's not really any way to specify this in the backend. I believe the function returns true in your examples because the call to can_compare_and_swap_p() in fold_builtin_atomic_always_lock_free() passes true for the allow_libcall argument. /* Check if a compare_and_swap pattern exists for the mode which represents the required size. The pattern is not allowed to fail, so the existence of the pattern indicates support is present. Also require that an atomic load exists for the required size. */ if (can_compare_and_swap_p (mode, true) && can_atomic_load_p (mode)) return boolean_true_node; else return boolean_false_node;
