On Tue, Apr 25, 2023 at 1:05 AM Jeff Law <jeffreya...@gmail.com> wrote > > > > > On 4/24/23 02:06, Richard Biener via Gcc-patches wrote: > > On Fri, Apr 21, 2023 at 11:01 PM Philipp Tomsich > > <philipp.toms...@vrull.eu> wrote: > >> > >> Any guidance on the next steps for this patch? > > > > I think we want to perform this transform later, in particular when > > the test is a loop exit test we do not want to do it as it prevents > > coalescing of the IV on the backedge at out-of-SSA time. > > > > That means doing the transform in folding and/or before inlining > > (the test could become a loop exit test) would be a no-go. In fact > > for SSA coalescing we'd want the reverse transform in some cases, see > > PRs 86270 and 70359. > > > > If we can reliably undo for the loop case I suppose we can do the > > canonicalization to compare against zero. In any case please split > > up the patch (note > I've also > > hoped we could eventually get rid of that part of > > tree-ssa-forwprop.cc > in favor > > of match.pd patterns since it uses GENERIC folding :/). > > > Do we have enough information to do this at expansion time? That would > avoid introducing the target dependencies to drive this in gimple.
I think so, but there isn't any convenient place to do this I think. I suppose there's no hope to catch it during RTL opts? > Jeff
