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 13961384475E; Tue, 25 Jun 2024 09:41:19 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 13961384475E
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1719308480;
	bh=o5SxFxXceCALHSuGAfNfhGW3tNn6e8EoRPdeNSwVX8w=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=CQBUwZU3SK1ix/9v6KpAkvOqTWEhrHX89Zgw1auq6i5NwmQVtkfck0DxEpk3nHzOX
	 vPT8sPKHYfGoBfHlKaVnTHA2zL3kpCESFQqXTGTmXXjNuxNk/tE/zUsPCk1qg2c7cl
	 N88nz3TK4Uy7bp1ajsQs6Vlf9DarGG3V+Fz7Ts2c=
From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/115629] Inefficient if-convert of masked
 conditionals
Date: Tue, 25 Jun 2024 09:41:17 +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: 15.0
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: enhancement
X-Bugzilla-Who: rguenth at gcc dot gnu.org
X-Bugzilla-Status: NEW
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_status cf_reconfirmed_on everconfirmed
Message-ID: <bug-115629-4-oiG0CFfGpJ@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-115629-4@http.gcc.gnu.org/bugzilla/>
References: <bug-115629-4@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=3D115629

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2024-06-25
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
I think the transform is profitable for scalar for all cases as well.

Now, if-conversion records BB predicates and uses those to predicate
stmts/PHIs, I'm not sure how to go optimize it on that level.

It's more a CFG transform of a if (A) x; else { if (B) x; else y; } to
if (A || B) x; else y;  with the downside that in this case evaluating
'B' has side-effects (memory dereference which can trap).

Due to the trapping this needs to be somehow done in if-conversion
where you also need to determine that x =3D=3D x' (both copies of x
evaluate to the same code).  Some scalar GIMPLE opt could have
de-duplicated the BB with 'x' (tail-merging to the rescue?  it considers
the cands but somehow doesn't merge - I think the PHI node isn't
supported).=