https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79412
--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Seems the C FE on such redeclarations doesn't merge the decls (correct), but overwrites the type in pop_scope: 1345 I_SYMBOL_BINDING (b->id) = b->shadowed; 1346 if (b->shadowed && b->shadowed->u.type) 1347 TREE_TYPE (b->shadowed->decl) = b->shadowed->u.type; so we end up gimplifying POSTINCREMENT_EXPR of a VAR_DECL with array type, no wonder we ICE on that.
