From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id B31203846405; Tue, 16 Feb 2021 22:54:26 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org B31203846405 From: "segher at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/99068] Missed PowerPC lhau optimization Date: Tue, 16 Feb 2021 22:54:25 +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: 10.2.0 X-Bugzilla-Keywords: missed-optimization X-Bugzilla-Severity: enhancement X-Bugzilla-Who: segher at gcc dot gnu.org X-Bugzilla-Status: RESOLVED X-Bugzilla-Resolution: INVALID 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: Tue, 16 Feb 2021 22:54:26 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99068 --- Comment #8 from Segher Boessenkool --- Using update form instructions constrains register allocation and schedulin= g. It is *not* always a good idea. That is one of the reasons why we currently use update form instructions on= ly when insns just happen to land close (in the same basic block). See auto_inc_dec.c . We also do some work to make it more likely that loops will use these constructs. We don't go out of our way to use update form insns at the cost of everything else. You will see them more often if you use -Os or -O1.=