http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54146
--- Comment #22 from Steven Bosscher <steven at gcc dot gnu.org> 2012-08-06 19:36:35 UTC --- IRA/reload spends a rather significant amount of time here: FOR_EACH_BB_REVERSE (bb) { bitmap_iterator bi; rtx insn; CLEAR_REG_SET (live_relevant_regs); --> memset (live_subregs_used, 0, max_regno * sizeof (int)); This is running with max_regno=O(1e6) and n_basic_blocks=O(1e5) ...