http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55135
--- Comment #15 from Richard Biener <rguenth at gcc dot gnu.org> 2013-03-01 10:44:10 UTC --- (In reply to comment #10) > Created attachment 29557 [details] > Collected hacks to make the test case compile in reasonable time with -O0 > > Patch does 2 things: > > - Queue up to-be-removed EH regions, instead of removing them one-by-one. > Removing them one at a time results in walking the list of EH regions > repeatedly, thus taking O(# of EH regions ** 2) time. This (properly cleaned up) looks reasonable to me. > - Rewrite init_subregs_of_mode and subroutines to first collect the > invalid mode change subregs in sbitmaps, and then converting the final > sbitmap to a bitmap. This trades memory for time: the bitmap lookups are > also potentially O(# of registers ** 2) and this test case has more than > one million registers, many of them with invalid mode changes (to be fixed > up by IRA/LRA). Hmm - this is because we hit the O(n) complexity we have on our bitmap implementation? Can't we improve init_subregs_of_mode by first collecting all mode changes we see for a pseudo (eventually using DF info?) and then do the processing in some more optimal order? Trading memory O(number of pseudos) with a large constant factor sounds like something waiting for trouble for other testcases ... > Peak memory at -O0 is <4GB. Compile time on a "Quad-Core AMD Opteron(tm) > Processor 8354" at 2200MHz is 240s, half of it still taken up by IRA+LRA. > > At -O1 the einline pass is consuming almost all compile time again. > -> Honza: Can we please have a proper permanent fix for this recurring > problem? What's there now just Does Not Work!
