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 9C8893858CDB; Sat, 13 Aug 2022 17:31:54 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 9C8893858CDB
From: "sebastien.michelland@ens-lyon.fr" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/106609] New: [SH] miscompilation of loop involving noreturn
 call
Date: Sat, 13 Aug 2022 17:31:54 +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: 12.1.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: sebastien.michelland@ens-lyon.fr
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
 attachments.created
Message-ID: <bug-106609-4@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
X-BeenThere: gcc-bugs@gcc.gnu.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Gcc-bugs mailing list <gcc-bugs.gcc.gnu.org>
List-Unsubscribe: <https://gcc.gnu.org/mailman/options/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=unsubscribe>
List-Archive: <https://gcc.gnu.org/pipermail/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-request@gcc.gnu.org?subject=help>
List-Subscribe: <https://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Sat, 13 Aug 2022 17:31:54 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106609

            Bug ID: 106609
           Summary: [SH] miscompilation of loop involving noreturn call
           Product: gcc
           Version: 12.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sebastien.michelland@ens-lyon.fr
  Target Milestone: ---

Created attachment 53452
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D53452&action=3Dedit
Minimal test case

GCC 12.1.0 generates incorrect code for loops that call into noreturn funct=
ions
starting at -O1. For example,

__attribute__((noreturn)) void g(void);
void f(int *values)
{
    for(int i =3D 0; i < 8; i++)
        if(values[i] !=3D 0) g();
}

gets compiled into

        sts.l   pr,@-r15
        mov     #8,r1
.L3:    bt.s    .L2
        dt      r1
        mov.l   .L5,r1 # _g
        jsr     @r1
        nop
.L2:    bf      .L3
        lds.l   @r15+,pr
        rts=20=20=20=20=20
        nop

which has the obvious issue of not reading its input, and also using the T =
bit
through bt.s before doing any test.

I suppose this is an overly aggressive loop/CFG optimization, but I was not
able to trim it down as unfolding -O1 into the list of optimizations provid=
ed
by -Q --help=3Doptimizers produced a completely different program. The bug =
still
occurs with -fno-aggressive-loop-optimizations at least.

With -funroll-all-loops, instead of 8 mov.l/tst/bf I just get 8 bf which
suggests that the test is wrongly eliminated causing the load to become dea=
d.

Found in:
  GCC 12.1.0
  Commit 4991e2092 of today's master
Not found in:
  GCC 11.1.0
Configured with:
  ../gcc-12.1.0/configure --prefix=3D$PREFIX --target=3Dsh3eb-elf
--enable-languages=3Dc --without-headers
Reproduction instructions:
  $PREFIX/bin/sh3eb-elf-gcc -S noreturn-loop-bug.c -o - -O1=