[Bug tree-optimization/59190] atomic ops on a non-escaped variable don't need atomicity

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59190

--- Comment #1 from Marc Glisse <glisse at gcc dot gnu.org> ---
A first step could be to teach alias analysis about BUILT_IN_ATOMIC_*,
currently it thinks i escapes in __atomic_add_fetch_4 (&i._M_i, 1, 5).
Unrelated, but maybe those builtins could also get the nonnull attribute?