From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 31389 invoked by alias); 25 Oct 2014 01:41:08 -0000 Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-bugs-owner@gcc.gnu.org Received: (qmail 31274 invoked by uid 48); 25 Oct 2014 01:40:52 -0000 From: "pinskia at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug target/61915] [AArch64] High amounts of GP to FP register moves using LRA on AArch64 Date: Sat, 25 Oct 2014 06:46:00 -0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: target X-Bugzilla-Version: 5.0 X-Bugzilla-Keywords: missed-optimization X-Bugzilla-Severity: normal X-Bugzilla-Who: pinskia at gcc dot gnu.org X-Bugzilla-Status: NEW X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: ramana 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: 7bit X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-SW-Source: 2014-10/txt/msg01985.txt.bz2 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61915 --- Comment #17 from Andrew Pinski --- (In reply to Wilco from comment #16) > (In reply to Andrew Pinski from comment #13) > > (In reply to Wilco from comment #9) > > > I committed a workaround > > > (http://gcc.gnu.org/ml/gcc-patches/2014-09/msg00362.html) by increasing the > > > int<->fp move cost. Can you try this and check the issue has indeed gone? > > > You need -mcpu=cortex-a57. > > > > Note when I submitted ThunderX support I used a base of 2 instead of a base > > of 1 due to 2 being the default and all values are relative to that. This > > is mentioned in https://gcc.gnu.org/onlinedocs/gccint/Costs.html . In fact > > a value of 2 means reload will not look at the constraints of a move > > instruction. > > > > So I think the cortex* cpus should also re-base these values based on 2 > > being gpr-to-gpr value. > > You mean only use multiples of 2? That's interesting as I've not seen that > done elsewhere. Are these costs in any way related to real issue and latency > cycles? Most targets have complex tables with all the exact latencies for > every little uarch detail, but from what I've seen in the allocator these > costs have almost no meaning. Not always multiple of 2 though in the case of ThunderX they are multiple of twos. The costs are not really directly related to the latency cost but it is relative to one another. So I could have used 2, 3, 4 (meaning latency of 1, 2, 3) instead. I used the factor of 2 instead of 1 for ThunderX because 2 + 3 != 4 but rather 5. > > So did you find that setting the FP move cost so low actually works alright > on ThunderX? I'd like to figure out a setting for the generic target that > works out well across all AArch64 implementations. Yes it seems to at least on the things we have benchmarked but we have not done much big benchmarks like SPEC yet.