From: Richard Biener <rguenther@suse.de>
To: gcc-patches@gcc.gnu.org
Subject: [PATCH] tree-optimization/113080 - missing final value replacement
Date: Tue, 19 Dec 2023 13:31:13 +0100 (CET) [thread overview]
Message-ID: <20231219123113.s3rSPYN0QZ6MrW301i22sa3O2WTNJeqUTj_uWxucOXU@z> (raw)
When performing final value replacement we guard against exponential
(temporary) code growth due to unsharing of trees (SCEV heavily
relies on tree sharing). The following relaxes this a tiny bit
to cover some more optimizations and puts in comments as to what
the real fix would be.
Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.
PR tree-optimization/113080
* tree-scalar-evolution.cc (expression_expensive_p): Allow
a tiny bit of growth due to expansion of shared trees.
(final_value_replacement_loop): Add comment.
* gcc.dg/tree-ssa/sccp-3.c: New testcase.
---
gcc/testsuite/gcc.dg/tree-ssa/sccp-3.c | 20 ++++++++++++++++++++
gcc/tree-scalar-evolution.cc | 11 ++++++++++-
2 files changed, 30 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/sccp-3.c
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/sccp-3.c b/gcc/testsuite/gcc.dg/tree-ssa/sccp-3.c
new file mode 100644
index 00000000000..b8c67427f16
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/sccp-3.c
@@ -0,0 +1,20 @@
+/* PR/113080 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-optimized" } */
+
+int a,b,n;
+int w;
+void fun1(int t)
+{
+ for(int i=0;i<100;i++)
+ {
+ a+=w;
+ b-=w;
+ t+=a+b;
+ }
+ n=t;
+}
+
+/* We should apply final value replacement to all reductions and
+ elide the loop. */
+/* { dg-final { scan-tree-dump-times "<bb" 1 "optimized" } } */
diff --git a/gcc/tree-scalar-evolution.cc b/gcc/tree-scalar-evolution.cc
index 94250b143b3..d743402d1c8 100644
--- a/gcc/tree-scalar-evolution.cc
+++ b/gcc/tree-scalar-evolution.cc
@@ -3529,7 +3529,12 @@ expression_expensive_p (tree expr, bool *cond_overflow_p)
uint64_t expanded_size = 0;
*cond_overflow_p = false;
return (expression_expensive_p (expr, cond_overflow_p, cache, expanded_size)
- || expanded_size > cache.elements ());
+ /* ??? Both the explicit unsharing and gimplification of expr will
+ expand shared trees to multiple copies.
+ Guard against exponential growth by counting the visits and
+ comparing againt the number of original nodes. Allow a tiny
+ bit of duplication to catch some additional optimizations. */
+ || expanded_size > (cache.elements () + 1));
}
/* Match.pd function to match bitwise inductive expression.
@@ -3867,6 +3872,10 @@ final_value_replacement_loop (class loop *loop)
fprintf (dump_file, "\n");
}
any = true;
+ /* ??? Here we'd like to have a unshare_expr that would assign
+ shared sub-trees to new temporary variables either gimplified
+ to a GIMPLE sequence or to a statement list (keeping this a
+ GENERIC interface). */
def = unshare_expr (def);
remove_phi_node (&psi, false);
--
2.35.3
reply other threads:[~2023-12-19 12:32 UTC|newest]
Thread overview: [no followups] expand[flat|nested] mbox.gz Atom feed
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20231219123113.s3rSPYN0QZ6MrW301i22sa3O2WTNJeqUTj_uWxucOXU@z \
--to=rguenther@suse.de \
--cc=gcc-patches@gcc.gnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).