From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) by sourceware.org (Postfix) with ESMTP id 4A5373854815 for ; Tue, 26 Jan 2021 17:55:40 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 4A5373854815 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: sourceware.org; spf=fail smtp.mailfrom=segher@kernel.crashing.org Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 10QHsSsg000501; Tue, 26 Jan 2021 11:54:33 -0600 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 10QHsRMK000500; Tue, 26 Jan 2021 11:54:27 -0600 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Tue, 26 Jan 2021 11:54:27 -0600 From: Segher Boessenkool To: Richard Biener Cc: Richard Sandiford , Bill Schmidt , GCC Patches Subject: Re: [PATCH 1/4] unroll: Add middle-end unroll factor estimation Message-ID: <20210126175427.GF30983@gate.crashing.org> References: <763e39c6-b3b3-f1ce-484b-e864d28d9fb4@linux.ibm.com> <20210121214526.GK30983@gate.crashing.org> <20210122213705.GP30983@gate.crashing.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.3i X-Spam-Status: No, score=-7.1 required=5.0 tests=BAYES_00, JMQ_SPF_NEUTRAL, KAM_DMARC_STATUS, TXREP, T_SPF_HELO_PERMERROR, T_SPF_PERMERROR autolearn=no autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 26 Jan 2021 17:55:41 -0000 Hi! On Tue, Jan 26, 2021 at 11:47:53AM +0100, Richard Biener wrote: > Anyway, I think the GIMPLE -> RTL transition currently is a too > big step Much agreed. I also think that the expand pass itself needs a lot of work to bring it into this century: it does much too much work, in a circuitous way that makes debugging it hard, etc. > and we should eventually try to lower GIMPLE That should help the above problem, too: break expand into stages, get rid of all the premature optimisations (and implement those elsewhere where needed!), and get a much better debuggable end result (that is also a lot less code). > and IV > selection should happen on a lower form where we for example > can do the 1st level scheduling on I don't think that helps, but maybe :-) > or at least have a better idea > on resource allocation This is the holy grail. Wait, I should decorate that: O_o !!! >>> This is the holy grail. <<< !!! O_o > and latencies in dependence cycles since > that's what really matters for unrolling. I don't think latencies matter much for such decisions. If the compiler depends too much on actual machine latencies, makes "too sharp" decisions, the code will run lousy on a slightly different (say, newer) machine. But certainly there needs to be *some* idea of how parallel some code can run, yes. Segher