From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id 93BFD3858425; Thu,  9 Nov 2023 12:27:50 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 93BFD3858425
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1699532870;
	bh=nzrf305ZcBvcRIWj+ows7p3FSUwV4IpsO094OsmG4qU=;
	h=From:To:Subject:Date:From;
	b=JuNkZlqebD/5EPqJ6Cu45jksg47c16v1BuH1PYXAeIFJTFsqeFEgLbxmu81dOLo/L
	 aLRVoU8CZDHs3Qh0ouUj80eLBEDHB1W3gFocz7Z1X3YFwY3lAzT/oudbOlO1b42GqW
	 pDIl4IPmPGhIIcDXtZ+r2RziQVSPpz2YmiDCQ1jw=
From: "juzhe.zhong at rivai dot ai" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/112457] New: Possible better vectorization of different
 reduction min/max reduction
Date: Thu, 09 Nov 2023 12:27:50 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: juzhe.zhong at rivai dot ai
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter target_milestone
Message-ID: <bug-112457-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D112457

            Bug ID: 112457
           Summary: Possible better vectorization of different reduction
                    min/max reduction
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: juzhe.zhong at rivai dot ai
  Target Milestone: ---

Hi, Richard.

GCC-14 almost has all features of RVV.

I am planning to participate on improving GCC loop vectorizer in GCC-15.

Fix FAILs of TSVC is one of my plan.

Currently we can vectorize this following case:

int idx =3D 0;
int max =3D 0;
void foo (int n, int * __restrict a){
for (int i =3D 0; i < n; ++i) {
  max =3D max < a[i] ? a[i] : max;
}
}

However, if we change this case it failed:

void foo2 (int n, int * __restrict a){
for (int i =3D 0; i < n; ++i) {
  if (max < a[i]) {
    max =3D a[i];
  } else
    max =3D max;
}
}

Now, I notice another interesting and possible vectorization enhancement wh=
ich
inspired by this patch of LLVM:
https://reviews.llvm.org/D143465

And more advance case is which is case from LLVM patch:
which is vectorization reduction with index:

void foo3 (int n, int * __restrict a){
for (int i =3D 0; i < n; ++i) {
  if (max < a[i]) {
    idx =3D i;
    max =3D a[i];
  }
}
}

I wonder it is a valuable optimization ? If yes, it would be one of my TODO
list.

Thanks.=