https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79649
--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> --- typedef __SIZE_TYPE__ size_t; struct A { int a; char b[1024]; }; extern struct A __seg_gs a; void f1 (size_t n) { for (size_t i = 0; i < n; ++i) a.b[i] = 0; } certainly compiles fine with my patch.