From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C4D67C2D0F4 for ; Wed, 8 Apr 2020 18:12:59 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A0C5B20768 for ; Wed, 8 Apr 2020 18:12:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A0C5B20768 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 48yC7D2T3BzDr74 for ; Thu, 9 Apr 2020 04:12:56 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=permerror (SPF Permanent Error: Unknown mechanism found: ip:192.40.192.88/32) smtp.mailfrom=kernel.crashing.org (client-ip=63.228.1.57; helo=gate.crashing.org; envelope-from=segher@kernel.crashing.org; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) by lists.ozlabs.org (Postfix) with ESMTP id 48yC5L5K2czDr3r for ; Thu, 9 Apr 2020 04:11:17 +1000 (AEST) Received: from gate.crashing.org (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id 038IB2N5014718; Wed, 8 Apr 2020 13:11:02 -0500 Received: (from segher@localhost) by gate.crashing.org (8.14.1/8.14.1/Submit) id 038IB1lA014717; Wed, 8 Apr 2020 13:11:01 -0500 X-Authentication-Warning: gate.crashing.org: segher set sender to segher@kernel.crashing.org using -f Date: Wed, 8 Apr 2020 13:11:01 -0500 From: Segher Boessenkool To: Christophe Leroy Subject: Re: [PATCH v5 18/21] powerpc64: Add prefixed instructions to instruction data type Message-ID: <20200408181101.GG26902@gate.crashing.org> References: <20200406080936.7180-1-jniethe5@gmail.com> <20200406080936.7180-19-jniethe5@gmail.com> <7182352.hY56U9iWWN@townsend> <4a8cf8b1-63e7-0b68-dede-48454bf5a4a7@c-s.fr> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4a8cf8b1-63e7-0b68-dede-48454bf5a4a7@c-s.fr> User-Agent: Mutt/1.4.2.3i X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Alistair Popple , npiggin@gmail.com, bala24@linux.ibm.com, Jordan Niethe , linuxppc-dev@lists.ozlabs.org, dja@axtens.net Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Mon, Apr 06, 2020 at 12:25:27PM +0200, Christophe Leroy wrote: > > if (ppc_inst_prefixed(x) != ppc_inst_prefixed(y)) > > return false; > > else if (ppc_inst_prefixed(x)) > > return !memcmp(&x, &y, sizeof(struct ppc_inst)); > > Are we sure memcmp() is a good candidate for the comparison ? Can we do > simpler ? Especially, I understood a prefixed instruction is a 64 bits > properly aligned instruction, can we do a simple u64 compare ? Or is GCC > intelligent enough to do that without calling memcmp() function which is > heavy ? A prefixed insn is *not* 8-byte aligned, it is 4-byte aligned, fwiw. memcmp() isn't as heavy as you fear, not with a non-ancient GCC at least. But this could be written in a nicer way, sure :-) Segher