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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/113441] [14 Regression] Fail to fold the last
 element with multiple loop
Date: Tue, 23 Jan 2024 12:52:44 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113441

--- Comment #19 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #18)
> (In reply to Tamar Christina from comment #17)
> > Ok, bisected to
> >=20
> > g:2efe3a7de0107618397264017fb045f237764cc7 is the first bad commit
> > commit 2efe3a7de0107618397264017fb045f237764cc7
> > Author: Hao Liu <hliu@os.amperecomputing.com>
> > Date:   Wed Dec 6 14:52:19 2023 +0800
> >=20
> >     tree-optimization/112774: extend the SCEV CHREC tree with a nonwrap=
ping
> > flag
> >=20
> > Before this commit we were unable to analyse the stride of the access.
> > After this niters seems to estimate the loop trip count at 4 and after =
that
> > the logs diverge enormously.
>=20
> Hum, but that's backward and would match to what I said in comment#2 - we
> should get better code with that.
>=20
> Juzhe - when you revert the above ontop of trunk does the generated code
> look better for Risc-V?

It doesn't revert but you can do

diff --git a/gcc/tree-scalar-evolution.cc b/gcc/tree-scalar-evolution.cc
index 25e3130e2f1..7870c8d76fb 100644
--- a/gcc/tree-scalar-evolution.cc
+++ b/gcc/tree-scalar-evolution.cc
@@ -2054,7 +2054,7 @@ analyze_scalar_evolution (class loop *loop, tree var)

 void record_nonwrapping_chrec (tree chrec)
 {
-  CHREC_NOWRAP(chrec) =3D 1;
+  CHREC_NOWRAP(chrec) =3D 0;

   if (dump_file && (dump_flags & TDF_SCEV))
     {=