On Fri, Dec 05, 2014 at 03:36:01PM -0700, Jeff Law wrote: > >So combine tries to combine 6+7+8; the RTL it comes up with is a parallel > >of the memory decrement (without cc clobber, but that is fine), and setting > >r88 to the mem minus one. There is no such pattern in the target, and > >combine cannot break the parallel into two sets (because the first modifies > >the mem used by the second), so 6+7+8 doesn't combine. > > > >Adding a bridge pattern in the target would work; or you can enhance > >combine > >so it can break up this parallel correctly. > I think myself or someone suggested a bridge pattern in the past, but I > can't find it, perhaps it was one of the other threads WRT limitations > of the combiner. > > Zhenqiang, can you look at what happens if you provide a pattern for > 6+7+8 (probably via a define_and_split)?
I tried this out yesterday. There are a few options (a bridge pattern for 6+7+8, or one for 7+8). I went with 6+7+8. So the code combine is asked to optimise is 6 A = M 7 T = A + B 8 M = T 9 C = cmp T, 0 and the bridge pattern I added is M = M + B :: T = M + B (I made it to split to M = M + B ; T = M which is probably not optimal, but irrelevant for the rest here). So combine happily combines 6+7+8 to the bridge pattern. But then it forgets to make a link from 9. I suppose it just doesn't know how to make a link to a parallel (it wouldn't ever be useful before my recent patches). Investigating... Segher
