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 [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id 17621384F022 for ; Wed, 7 Sep 2022 01:44:49 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 17621384F022 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=1662515088; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=sTBvqPc3wk28L8iRNb7QaWNe9nIKAieR2TRwtrwuh5g=; b=AAKRGT596DK5ualPn3N0zvpeXrLozxBR9JFQeSNQvMnVGRjGouawZ94EknA+tCUg+JiAGk Cb4+nwtShgs65ZCL5I1fq0aY46/Y89snkHNQKY2wKmeEMplqnEf+1n/vVcHe9vhnjSup0U C0ScZdF1ScKAwmBbStxBh7LAMp248e0= Received: from mail-qk1-f200.google.com (mail-qk1-f200.google.com [209.85.222.200]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_128_GCM_SHA256) id us-mta-96-rv17ok1vMQ6PB66E9HKBJA-1; Tue, 06 Sep 2022 21:44:47 -0400 X-MC-Unique: rv17ok1vMQ6PB66E9HKBJA-1 Received: by mail-qk1-f200.google.com with SMTP id bk21-20020a05620a1a1500b006be9f844c59so10713840qkb.9 for ; Tue, 06 Sep 2022 18:44:47 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date; bh=sTBvqPc3wk28L8iRNb7QaWNe9nIKAieR2TRwtrwuh5g=; b=LhaobAVQKQrOSmIof+mc9h+UGyzIl29+7HDOtpasiVXhUwDNiejjoQBs/Nz0euKg56 /FBt4E15NgwmyTrfxQqD7ANmjcdektKgmxe6cER9ltnFhwf48hMtXnzEo6YuzXepnesl Oi0psi7/R+BQJBqYCamMGA+r0i8YS3AmbNeKPUzm7yCP9AJ3OO2gKi50bY3bkj1mQCPX VTcQMlIF4+8OwbEO3Nj2Nz1e+iH789R6kM7f+i5AH03KAZV1eY3O49nstmD/K86pZmpK sToC7RC5F8OmLOmaVak7/UsagxRMQ9Y60QshchALoyp4e6zdgbTz/i4Lx4lQLBpdfBWR vgaw== X-Gm-Message-State: ACgBeo1kqPuCiGzwVpWGd2jgdhvGerkaprD5DuD+JD7sTYRtKfxyrycv h9vZRssZm7VkdZ87mBx+yZ8KNY78J6BU/xrlP1AT5vBsl+Vg0CrOIyUxoABMADfZbcT1s28zHpG pfpME/qBwCj8h+kU= X-Received: by 2002:a05:622a:1305:b0:344:9050:79dc with SMTP id v5-20020a05622a130500b00344905079dcmr1326438qtk.335.1662515087032; Tue, 06 Sep 2022 18:44:47 -0700 (PDT) X-Google-Smtp-Source: AA6agR6+1eVMPW6m2wBy2DmEhissp1hDb59+pqzXLN/DFicAxolwI0PY27KEksaMTl86FieQOs07RA== X-Received: by 2002:a05:622a:1305:b0:344:9050:79dc with SMTP id v5-20020a05622a130500b00344905079dcmr1326424qtk.335.1662515086751; Tue, 06 Sep 2022 18:44:46 -0700 (PDT) Received: from barrymore.redhat.com (130-44-159-43.s15913.c3-0.arl-cbr1.sbo-arl.ma.cable.rcncustomer.com. [130.44.159.43]) by smtp.gmail.com with ESMTPSA id n76-20020a37404f000000b006baed2827f2sm12217666qka.44.2022.09.06.18.44.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 06 Sep 2022 18:44:46 -0700 (PDT) From: Jason Merrill To: gcc-patches@gcc.gnu.org Cc: libstdc++@gcc.gnu.org Subject: [PATCH RFA] libstdc++: small dynamic_cast optimization Date: Tue, 6 Sep 2022 21:44:44 -0400 Message-Id: <20220907014444.1469136-1-jason@redhat.com> X-Mailer: git-send-email 2.31.1 MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="US-ASCII"; x-default=true X-Spam-Status: No, score=-12.8 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_NONE,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 List-Id: An email discussion of optimizing EH led me to wonder why we weren't doing this already. Not that this change affects EH at all. Tested x86_64-pc-linux-gnu. Does this seem worthwhile? libstdc++-v3/ChangeLog: * libsupc++/dyncast.cc (__dynamic_cast): Avoid virtual function call in simple success case. --- libstdc++-v3/libsupc++/dyncast.cc | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/libstdc++-v3/libsupc++/dyncast.cc b/libstdc++-v3/libsupc++/dyncast.cc index 853c911a4cf..616e4c05766 100644 --- a/libstdc++-v3/libsupc++/dyncast.cc +++ b/libstdc++-v3/libsupc++/dyncast.cc @@ -71,6 +71,12 @@ __dynamic_cast (const void *src_ptr, // object started from if (whole_prefix->whole_type != whole_type) return NULL; + // Avoid virtual function call in the simple success case. + if (src2dst >= 0 + && src2dst == -prefix->whole_object + && *whole_type == *dst_type) + return const_cast (whole_ptr); + whole_type->__do_dyncast (src2dst, __class_type_info::__contained_public, dst_type, whole_ptr, src_type, src_ptr, result); if (!result.dst_ptr) base-commit: 0a2fba3697411c07a8330abfe7460ce62bce5e7f -- 2.31.1