From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by sourceware.org (Postfix) with ESMTPS id 4ACB73858D28 for ; Thu, 26 Jan 2023 14:58:49 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 4ACB73858D28 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=redhat.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1674745128; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:mime-version:mime-version: content-type:content-type:in-reply-to:in-reply-to: references:references; bh=1fIL0CUDOCeifX9FYPTmLQhTuCcrIA3aD8TZdCmvYto=; b=LRd/9UGNSxEQr0m4oWtdgv4Yvb2cEW7BnVTm4nYH/q84MmjS4NgiGInMk7/zwayPEjQvvd B57BMMphqpIR79hXzymX6QHRW6OHYo+ErheTZUufpTtjvJYqLdes13kQFXdnG0NgUDqU7+ ZKUeHRQknas8MiUQBBpx5rHeugX95dY= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-407-R1C42WQhNj2f5NXrc9lDzw-1; Thu, 26 Jan 2023 09:58:46 -0500 X-MC-Unique: R1C42WQhNj2f5NXrc9lDzw-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 436CB2A59553; Thu, 26 Jan 2023 14:58:46 +0000 (UTC) Received: from tucnak.zalov.cz (unknown [10.39.192.223]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 05387492C14; Thu, 26 Jan 2023 14:58:45 +0000 (UTC) Received: from tucnak.zalov.cz (localhost [127.0.0.1]) by tucnak.zalov.cz (8.17.1/8.17.1) with ESMTPS id 30QEwglp1155864 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Thu, 26 Jan 2023 15:58:43 +0100 Received: (from jakub@localhost) by tucnak.zalov.cz (8.17.1/8.17.1/Submit) id 30QEwgMG1154209; Thu, 26 Jan 2023 15:58:42 +0100 Date: Thu, 26 Jan 2023 15:58:41 +0100 From: Jakub Jelinek To: Patrick Palka , Andrew Pinski , gcc-patches@gcc.gnu.org, jason@redhat.com Subject: Re: [PATCH] constexprify some tree variables Message-ID: Reply-To: Jakub Jelinek References: <1668794731-9349-1-git-send-email-apinski@marvell.com> MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Spam-Status: No, score=-3.8 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On Thu, Jan 26, 2023 at 03:51:07PM +0100, Jakub Jelinek via Gcc-patches wrote: > On Thu, Jan 26, 2023 at 09:45:35AM -0500, Patrick Palka via Gcc-patches wrote: > > > -extern const unsigned char tree_code_length[]; > > > + > > > +#define DEFTREECODE(SYM, NAME, TYPE, LENGTH) LENGTH, > > > +#define END_OF_BASE_TREE_CODES 0, > > > +constexpr unsigned char tree_code_length[] = { > > > +#include "all-tree.def" > > > +}; > > > + > > > +#undef DEFTREECODE > > > +#undef END_OF_BASE_TREE_CODES > > > > IIUC defining these globals as non-inline constexpr gives them internal > > linkage, and so each TU contains its own unique copy of these globals. > > This bloats cc1plus by a tiny bit and is technically an ODR violation > > because some inline functions such as tree_class_check also ODR-use > > these variables and so each defn of tree_class_check will refer to a > > "different" tree_code_class. Since inline variables are a C++17 > > feature, I guess we could fix this by defining the globals the old way > > before C++17 and as inline constexpr otherwise? > > Agreed, just use > __cpp_inline_variables >= 201606L > to select between the old and new ways. And I'd argue with the tiny bit. In my x86_64-linux cc1plus from today, I see 193 _ZL16tree_code_length vars, 374 bytes each, and 324 _ZL14tree_code_type vars, 1496 bytes each. So, that means waste of 555016 .rodata bytes, plus being highly non-cache friendly. Jakub