https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79570
--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> --- Seems before r197942 sel_remove_insn with only_disconnect true actually kept BLOCK_FOR_INSN on the (temporarily) removed insn. But sel_bb_head would certainly not return that temporarily removed insn, so what the patch does preserves what we used to do before in that case.
