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 EFF84384A40A; Wed, 27 Jan 2021 08:54:11 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org EFF84384A40A
From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/98845] [8/9/10/11 Regression] ICE: SSA
 corruption (Unable to coalesce ssa_names 2 and 23 which are marked as MUST
 COALESCE.) since r6-528-g465770e43996a132
Date: Wed, 27 Jan 2021 08:54:11 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: tree-optimization
X-Bugzilla-Version: 11.0
X-Bugzilla-Keywords: ice-on-valid-code
X-Bugzilla-Severity: normal
X-Bugzilla-Who: rguenth at gcc dot gnu.org
X-Bugzilla-Status: ASSIGNED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P2
X-Bugzilla-Assigned-To: rguenth at gcc dot gnu.org
X-Bugzilla-Target-Milestone: 8.5
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-98845-4-rzDth1bSvw@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-98845-4@http.gcc.gnu.org/bugzilla/>
References: <bug-98845-4@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: Wed, 27 Jan 2021 08:54:12 -0000

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D98845

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
+find_duplicates: <bb 6> duplicate of <bb 20>
+Removing basic block 20

@@ -170,7 +180,7 @@
   <bb 17> [local count: 3614577]:
   goto <bb 13>; [100.00%]

-  <bb 6> [local count: 7016531]:
+  <bb 6> [local count: 8742389]:
   p_218_24 =3D p_217_23(D)(ab);
   p_217_32 =3D p_217_23(D)(ab);
   goto <bb 13>; [100.00%]
@@ -213,12 +223,10 @@
   if (p_218_8 !=3D 0)
     goto <bb 19>; [83.51%]
   else
-    goto <bb 20>; [16.49%]
-
-  <bb 20> [local count: 1725858]:
+    goto <bb 6>; [16.49%]

   <bb 13> [local count: 12356965]:
-  # _9 =3D PHI <1(17), 0(20), 0(6)>
+  # _9 =3D PHI <1(17), 0(6)>
   return _9;

but that makes _23(D) live on the path from bb 12 to bb 13.  The issue here
is that _23 and _32 are unused but their RHS is still accounted for during
LIVE problem solving but they are ignored during VN and by tail-merging
which just looks at BB side-effects.

So the testcase is really an artifact of -fno-tree-dce.

One could argue that tail merging should treat a use of abnormals as
side-effect but I think that won't play well with its structure.=