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 1DD013844079; Fri,  3 Jul 2020 17:38:14 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 1DD013844079
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
 s=default; t=1593797894;
 bh=KVRtTx2Bolg36FPHP5vDWbNEm9svuidmtuwcdBuARa8=;
 h=From:To:Subject:Date:From;
 b=wTEfAFedxGk3UvDpo5YopS9JfAZBEc0zhLyCHM/wKllaUDjUUnMo461hRW/u9/mqR
 KDYW9Eew/cmm3bKoanBdFG4h2dBeGPuW2tchYtnqBSJSLw8aTBZ08mY5jCfR+eUmSR
 gO+BCHtFqvFmb4ooIPv/G4y05ll1RyD1AsLujsZY=
From: "imachug at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/96050] New: PDP-11: 32-bit MOV from offset(Rn) overrides
 Rn
Date: Fri, 03 Jul 2020 17:38:13 +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: 10.1.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: imachug at gmail dot com
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-96050-4@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: <http://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: <http://gcc.gnu.org/mailman/listinfo/gcc-bugs>,
 <mailto:gcc-bugs-request@gcc.gnu.org?subject=subscribe>
X-List-Received-Date: Fri, 03 Jul 2020 17:38:14 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D96050

            Bug ID: 96050
           Summary: PDP-11: 32-bit MOV from offset(Rn) overrides Rn
           Product: gcc
           Version: 10.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: imachug at gmail dot com
  Target Milestone: ---

Consider the following code:


struct {
        unsigned long a, b;
} structure;

void calc() {
        unsigned long x =3D structure.a;
        unsigned long y =3D structure.b;
        asm volatile(""::"r"(x), "r"(y));
}


("asm volatile" is just to stop GCC from removing x and y completely)

When this source is compiled with "-Os -S", GCC erroneously generates the
following assembly to load structure members to registers:


mov     $_structure,r0
mov     (r0),r2
mov     02(r0),r3
mov     04(r0),r0
mov     06(r0),r1


"mov 04(r0), r0" overrides r0, which the next instruction assumes to contain
the old non-overwritten value.

I think this has to do with disabled early clobbering on movsi insn, but ad=
ding
"&" to lines 529, 536 in pdp11.md (i.e. changing "=3Dr,r,g,g" to "=3D&r,r,g=
,g" in
"[(set (match_operand:SI 0 "nonimmediate_operand" "=3Dr,r,g,g")") didn't fi=
x the
bug for me.


$ ./tools/bin/pdp11-aout-gcc -v
Using built-in specs.
COLLECT_GCC=3D./tools/bin/pdp11-aout-gcc-10.1.0
COLLECT_LTO_WRAPPER=3D/[redacted]/tools/libexec/gcc/pdp11-aout/10.1.0/lto-w=
rapper
Target: pdp11-aout
Configured with: ../configure --prefix /[redacted]/tools --target pdp11-aout
--enable-languages=3Dc --with-gnu-as --with-gnu-ld --without-headers
--disable-libssp
Thread model: single
Supported LTO compression algorithms: zlib
gcc version 10.1.0 (GCC)=20

$ uname -a
Linux [redacted] 5.3.0-59-generic #53-Ubuntu SMP Wed Jun 3 15:52:15 UTC 2020
x86_64 x86_64 x86_64 GNU/Linux=