https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81766
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> --- find_bb_boundaries doesn't seem to expect existing NOTE_INSN_BASIC_BLOCK, so calling it on existing blocks exposes un-optimalities in case labels are valid after NOTE_INSN_BASIC_BLOCK.
