2014-06-17 21:26 GMT+02:00 Jeff Law <l...@redhat.com>: > On 06/13/14 10:59, Kai Tietz wrote: >> >> 2014-06-13 17:58 GMT+02:00 Jeff Law <l...@redhat.com>: >>> >>> On 06/13/14 09:56, Richard Henderson wrote: >>>> >>>> >>>> On 06/13/2014 08:36 AM, Jeff Law wrote: >>>>> >>>>> >>>>> So you may have answered this already, but why can't this be a combiner >>>>> pattern? >>>> >>>> >>>> >>>> Until pass_duplicate_computed_gotos, we (intentionally) have a single >>>> indirect >>>> branch in the entire function. This vastly reduces the size of the CFG. >>> >>> >>> Ah, the factoring bits. Should have known. >>> >>> >>>> >>>> Peep2 is currently running before d_c_g, so currently Kai can't solve >>>> this >>>> problem in peep2. >>>> >>>> I don't think peep2 should run after sched2, but I'll bet we can reorder >>>> things >>>> a bit so that d_c_g runs before peep2. >>> >>> >>> Yea, seems worth a try. >>> >>> jeff >>> >> >> Well, I tested to put the second sched2 pass before the sched2 pass. >> That works in general. There are just some opportunties which weren't >> caught then. I attached a sample, which demonstrates that pretty >> well. I noticed that I had to put that pass behind reload blocks was >> necessary for better hit-rate of the peephole optimization. > > So can you tell us why this sample code misses opportunities? Otherwise we > have to dig into it ourselves to tease out that information. > > I think we're zeroing in on a path to move d_c_g before peep2, but I'd like > to have a clearer understanding of why we'd still be missing opportunities. > If we can avoid running peep2 twice, that'd be good. > > jeff
Hi Jeff, I just did retest my testcase with recent source. I can't reproduce this missed optimization before sched2 pass anymore. I moved second peephole2 pass just before split_before_sched2 and everything got caught. To remove first peephole2 pass seems to cause weaker code for impossible pushes, etc Nevertheless it might be a point to make this new peephole instead a define_split? I admit that this operation isn't a split, nevertheless we would avoid a second peephole pass. Kai
