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 738ED3858D35; Mon, 22 Apr 2024 17:10:32 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 738ED3858D35
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1713805832;
	bh=ES4Oj4OxWaPWypFF1cc+EOiLG/qfHE7hHWMJuh+3nIM=;
	h=From:To:Subject:Date:From;
	b=TN6IDV/ffBTvQzRhrI4gny4/Lx5HeUM5Yxwc0ea6eufAprThXPnk0PUsz3o1WDRLw
	 9QyBQ3dhZLWx1Nr0Vw0XW4Lgs8P/IujvAqC5TctTk8QlA8aph2dGpXUzF+b9oGTilN
	 +5rusw3yhmaKLqxO9spXf1MktyL2YjtwfpOATzSk=
From: "wojciech_mula at poczta dot onet.pl" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/114809] New: [RISC-V RVV] Counting elements might be
 simpler
Date: Mon, 22 Apr 2024 17:10:31 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: wojciech_mula at poczta dot onet.pl
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-114809-4@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=3D114809

            Bug ID: 114809
           Summary: [RISC-V RVV] Counting elements might be simpler
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: wojciech_mula at poczta dot onet.pl
  Target Milestone: ---

Consider this simple procedure

---
#include <cstdint>
#include <cstdlib>

size_t count_chars(const char *src, size_t len, char c) {
    size_t count =3D 0;
    for (size_t i=3D0; i < len; i++) {
        count +=3D src[i] =3D=3D c;
    }

    return count;
}
---

Assembly for it (GCC 14.0, -march=3Drv64gcv -O3):

---
count_chars(char const*, unsigned long, char):
        beq     a1,zero,.L4
        vsetvli a4,zero,e8,mf8,ta,ma
        vmv.v.x v2,a2
        vsetvli zero,zero,e64,m1,ta,ma
        vmv.v.i v1,0
.L3:
        vsetvli a5,a1,e8,mf8,ta,ma
        vle8.v  v0,0(a0)
        sub     a1,a1,a5
        add     a0,a0,a5
        vmseq.vv        v0,v0,v2
        vsetvli zero,zero,e64,m1,tu,mu
        vadd.vi v1,v1,1,v0.t
        bne     a1,zero,.L3
        vsetvli a5,zero,e64,m1,ta,ma
        li      a4,0
        vmv.s.x v2,a4
        vredsum.vs      v1,v1,v2
        vmv.x.s a0,v1
        ret
.L4:
        li      a0,0
        ret
---

The counting procedure might use `vcpop.m` instead of updating vector of
counters (`v1`) and summing them in the end. This would move all mode switc=
hes
outside the loop.

And there's a missing peephole optimization:

        li      a4,0
        vmv.s.x v2,a4

It can be:

        vmv.s.x v2,zero=