http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52370
--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Until we get more fine-grained warning control, I believe the only way to fix this is make sure TREE_NO_WARNING is set on Fortran optional argument related variables (not just the data pointer (b.0 here), but I think the others too (bounds, size, ...).