On 4/25/23 01:21, Richard Biener wrote:
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?
Combine would be the most natural place in the RTL pipeline, but it'd be
a 2->2 combination which would be rejected.
We could possibly do it as a define_insn_and_split, but the gimple->RTL
interface seems like a better fit to me. If TER has done its job, we
should see a complex enough tree node to do the right thing.
jeff
