From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 4F7673858D39; Wed, 25 Aug 2021 14:05:05 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 4F7673858D39 From: "segher at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug c/102062] powerpc suboptimal unrolling simple array sum Date: Wed, 25 Aug 2021 14:05:05 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: c X-Bugzilla-Version: 11.2.0 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: segher 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: Message-ID: In-Reply-To: References: 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 List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 25 Aug 2021 14:05:05 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102062 --- Comment #6 from Segher Boessenkool --- (In reply to Nicholas Piggin from comment #0) > I may be unaware of a constraint of C standard here, but maintaining the = two > base addresses seems pointless, This is an ordering problem. The unroller works (late) in RTL, it cannot do a good job of induction variable opts. > so is beginning the first at offset -4. This is actually useful: it makes it possible to use update-form insns much more often. It isn't optimised away later when it turns out not to help -- see ordering again. > The bigger problem is keeping a single sum. That is the variable expansion thing.=