On Mon, 2008-09-08 at 09:47 -0400, Vladimir Makarov wrote: > Jeff Law wrote: > > H.J. Lu wrote: > >> My understanding is PowerPC is quite sensitive to choice of register > >> as shown in PR 28690. IRA merge may make fixes for PR 28690 > >> ineffective. There are a few small testcases in PR 28690. You can > >> check if those problems in PR 28690 come back due to IRA merge. > >> Also, IRA disables regmove: > >> > >> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37364 > >> > >> I don't know its impact on PowerPC. Can you try > >> > >> --- ./regmove.c.regmove 2008-09-06 10:09:43.000000000 -0700 > >> +++ ./regmove.c 2008-09-06 11:34:24.000000000 -0700 > >> @@ -1117,8 +1117,7 @@ regmove_optimize (rtx f, int nregs) > >> > >> for (pass = 0; pass <= 2; pass++) > >> { > >> - /* We need fewer optimizations for IRA. */ > >> - if ((! flag_regmove || flag_ira) && pass >= > >> flag_expensive_optimizations) > >> + if ((! flag_regmove) && pass >= flag_expensive_optimizations) > >> goto done; > >> > >> if (dump_file) > >> @@ -1167,8 +1166,7 @@ regmove_optimize (rtx f, int nregs) > >> } > >> } > >> > >> - /* All optimizations important for IRA have been done. */ > >> - if (! flag_regmove || flag_ira) > >> + if (! flag_regmove) > >> continue; > >> > >> if (! find_matches (insn, &match)) > >> > >> on the current ira-merge branch. > >> > >> > > I can't express how badly I feel this is the wrong direction to be > > taking. Remove needs to go away and we need to be looking at the > > root failures rather than re-enabling this crap code in regmove.c > > > > I've got a performance regression as well that ties into the disabling > > of regmove, but doing a root cause analysis has made it plainly clear > > that the problem is not regmove, nor IRA, nor the backend port in > > question. For my specific problem the root cause is actually subreg > > lowering. While I could fix my regression by twiddling regmove > > and/or the port itself, neither change is actually solving the > > problem. I would *STRONGLY* suggest you take the time to do a > > root cause analysis or at least avoid installing this bandaid patch. > > > I am agree with Jeff. IRA was designed to replace most of regmove. It > has ability to do what regmove does. Switching on regmove besides > making RA slower only hides what is wrong with IRA. > > Although, it would be interesting to see what regmove can give to IRA. >
Upon further investigation on facerec's regression, it looks like the code generated by the IRA-enabled gcc has many more spills than the one with a disabled IRA, twice or sometimes three times more. I'm trying to reduce the testcase a bit further so it's simpler to analyse. Regards, Luis
