http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56466
--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> 2013-02-27 09:40:09 UTC --- RTL unrolling does excessive manual verify_loop_structure calls. I suppose we can either add an argument to verify_loop_structure to say whether to check only existing loops or remove the checking, or make sure to fixup loops. For sure checking the whole loop tree after processing one innermost loop is excessive: /* Depending on FLAGS, check whether to peel loops completely and do so. */ static void peel_loops_completely (int flags) { struct loop *loop; loop_iterator li; /* Scan the loops, the inner ones first. */ FOR_EACH_LOOP (li, loop, LI_FROM_INNERMOST) { ... if (loop->lpt_decision.decision == LPT_PEEL_COMPLETELY) { report_unroll_peel (loop, locus); peel_loop_completely (loop); #ifdef ENABLE_CHECKING verify_loop_structure (); #endif } } I'd have a changed flag and do a single if (changed) fix_loop_structure (NULL); which also does the verification at the end. Same applies to the loop in the caller.