From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp-out2.suse.de (smtp-out2.suse.de [IPv6:2001:67c:2178:6::1d]) by sourceware.org (Postfix) with ESMTPS id 71F303858C2D for ; Tue, 16 Aug 2022 12:26:29 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 71F303858C2D Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 08F731FB7C; Tue, 16 Aug 2022 12:26:28 +0000 (UTC) Received: from wotan.suse.de (wotan.suse.de [10.160.0.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 0183C2C149; Tue, 16 Aug 2022 12:26:28 +0000 (UTC) Date: Tue, 16 Aug 2022 12:26:27 +0000 (UTC) From: Richard Biener To: Aldy Hernandez cc: Andrew MacLeod , gcc-patches Subject: Re: [PATCH] Tame path_range_query::compute_imports In-Reply-To: Message-ID: References: <73820.122081107421800679@us-mta-533.us.mimecast.lan> User-Agent: Alpine 2.22 (LSU 394 2020-01-19) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Spam-Status: No, score=-5.0 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, SPF_HELO_NONE, SPF_PASS, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) 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, 16 Aug 2022 12:26:31 -0000 On Tue, 16 Aug 2022, Aldy Hernandez wrote: > On Tue, Aug 16, 2022 at 1:38 PM Richard Biener wrote: > > > > On Tue, 16 Aug 2022, Aldy Hernandez wrote: > > > > > On Mon, Aug 15, 2022 at 11:53 AM Richard Biener wrote: > > > > > > > > The remaining issue I have with the path_range_query is that > > > > we re-use the same instance in the back threader but the > > > > class doesn't provide any way to "restart", aka give m_path > > > > a lifetime. The "start a new path" API seems to essentially > > > > be compute_ranges (), but there's no convenient way to end. > > > > It might be more appropriate to re-instantiate the path_range_query, > > > > though that comes at a cost. Or abstract an actual query, like > > > > adding a > > > > > > Yes, compute_ranges() is the way to start a new path. It resets exit > > > dependencies, the path, relations, etc. I think it would be clearer > > > to name it set_path (or reset_path if we want to share nomenclature > > > with the path_oracle). > > > > > > Instantiating a new path_range_query per path is fine, as long as you > > > allocate the ranger it uses yourself, instead of letting > > > path_range_query allocate it. Instantiating a new ranger does have a > > > cost, and it's best to let path_range_query re-use a ranger from path > > > to path. This is why path_range_query is (class) global in the > > > backwards threader. Andrew mentioned last year making the ranger > > > start-up 0-cost, but it still leaves the internal caching the ranger > > > will do from path to path (well, the stuff outside the current path, > > > cause the stuff inside the path is irrelevant since it'll get > > > recalculated). > > > > > > However, why can't you use compute_ranges (or whatever we rename it to ;-))?? > > > > I've added > > > > auto_bb_flag m_on_path; > > > > to the path query and at set_path time set m_on_path on each BB so > > the m_path->contains () linear walks go away. But I need to clear > > the flag for which I would need something like finish_path (), > > doing it just at the point we deallocate the path query object > > or when we set the next path via compute_ranges doesn't look right > > (and in fact it doesn't work out-of-the-box without adjusting the > > lifetime of the path query object). > > > > So a more incremental thing would be to add such finish_path () > > or to make the whole path query object single-shot, thus remove > > compute_ranges and instead use the CTOR for this. > > > > Probably not too important (for short paths). > > On a high level, I wonder if this matters since we don't allow long > paths for other performance reasons you've already tackled. But OTOH, > I've always been a little uncomfortable with contains_p linear search, > so if you think this makes a difference, go right ahead :). > > I'm fine with either the finish_path() or the single-shot thing you > speak of. Although making path query inmutable makes things cleaner > in the long run. I like it! My guess is that the non-ranger > instantiation penalty would be minimal. I'd even remove the default > (auto-allocated) ranger from path_range_query, to make it obvious that > you need to manage that yourself and avoid folks shooting themselves > in the foot. We currently have path_range_query::path_range_query (bool resolve, gimple_ranger *ranger) : m_cache (new ssa_global_cache), m_has_cache_entry (BITMAP_ALLOC (NULL)), m_resolve (resolve), m_alloced_ranger (!ranger) { if (m_alloced_ranger) m_ranger = new gimple_ranger; else m_ranger = ranger; m_oracle = new path_oracle (m_ranger->oracle ()); if (m_resolve && flag_checking) verify_marked_backedges (cfun); } so at least verify_marked_backedges will explode, I suppose we want to hoist that somehow ... then we allocate the path_oracle - that one does have a reset_path () function at least. It's allocation looks quite harmless, but we should only need it when m_resolve? > Wanna have a go at it? If you'd rather not, I can work on it. If you have cycles go ahead - I'm fiddling with other parts of the threader right now. Richard.