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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BFDB4C433F5 for ; Wed, 5 Jan 2022 09:22:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238842AbiAEJWe (ORCPT ); Wed, 5 Jan 2022 04:22:34 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56700 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232036AbiAEJWd (ORCPT ); Wed, 5 Jan 2022 04:22:33 -0500 Received: from mail-pl1-x636.google.com (mail-pl1-x636.google.com [IPv6:2607:f8b0:4864:20::636]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C9C0EC061761 for ; Wed, 5 Jan 2022 01:22:32 -0800 (PST) Received: by mail-pl1-x636.google.com with SMTP id s15so1513276plg.12 for ; Wed, 05 Jan 2022 01:22:32 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=x4xfp6CvEJH53YpVF7NoIR4W7WJmaRDYx9TOiF5fZvk=; b=pzntNYzQoq7fieH9S6EzCJAKxBPFIgpNJ6vOhcmRgOw6o54+5T8cCDHf0wP+fDKizr CuQnfY+er2z+Ta6vGVeRhQhQeSVQdjNQKFeGsxg/yAH+mowM0mUvmZ/5BZFGL2QqkM2u g0fLSQaqsn1Tly4S0rBbcIL4Nyk3Hw4iNEM1Drst3NMIcLwUvnVsYUhqm9GBhkLYzCO/ A5CQUEQ7sh5jm5Pp/+MdUXdm9lM0XVdjzDfpvU4D3gI8Tgky4FI2YUgyTarElH39q5mN vOKaCUq5PyOVQqUvF8S9hsj7M4GoATJW4yZx/yBdvZYBZ29kVt+w4iTwxTsfnCoq0jHF 3ANA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=x4xfp6CvEJH53YpVF7NoIR4W7WJmaRDYx9TOiF5fZvk=; b=KbtlaGnDpNyp77lmc0vr2IzOolbRH5Y5BTSZWw5sozaUEVMac4LFF4bqwgajaVsCMC EBjgF/0As9YJCr8kDkUCkd/uhs6yz7i/1fJm2njgNr8yYkXpltiC/IkZtqDSjgZWmmdZ oIi6056Nmo+3xwM25FWw9HUb/bAOqneT0Jd2SGFA/Ip/mWfjxyVrngcwNDyYiScKx+Kc tN0PdgKB02QDRMJnTRV9z1nH3joX+ueRYx6m+8mvvtYFWtNwre7VM5XJRqo0NfqRp6QK aN1bPQtEwCX6PPWO0MVfDZCzpwGY8B63jqiZaoqB8QiRUMrOi1lTcQvUDEFKW6LnAPlR NnCA== X-Gm-Message-State: AOAM531pvasT2KqZIyuhcBVJgNaj+7IctQDoA3CbvrS3VhJ5CSNj1Z+Z 7OZe5eL3dYYK+A8qpi9ZOqQ= X-Google-Smtp-Source: ABdhPJyZu377ZIk3x3tbCz5avW/A16Fs8irkz0vIcQcbm3TLVlFE5VsqWxhTKnK7vuB311NTd2LYGA== X-Received: by 2002:a17:903:22ca:b0:149:b1e2:a8ca with SMTP id y10-20020a17090322ca00b00149b1e2a8camr18896555plg.46.1641374552415; Wed, 05 Jan 2022 01:22:32 -0800 (PST) Received: from localhost.localdomain ([193.203.214.57]) by smtp.gmail.com with ESMTPSA id a3sm46936261pfv.47.2022.01.05.01.22.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 05 Jan 2022 01:22:32 -0800 (PST) From: cgel.zte@gmail.com X-Google-Original-From: chi.minghao@zte.com.cn To: gregkh@linuxfoundation.org Cc: arnd@arndb.de, cgel.zte@gmail.com, chi.minghao@zte.com.cn, fkassabri@habana.ai, linux-kernel@vger.kernel.org, obitton@habana.ai, ogabbay@kernel.org, osharabi@habana.ai, ynudelman@habana.ai, zealci@zte.com.cn Subject: Re: [PATCH misc-next] drivers/misc: remove redundant rc variable Date: Wed, 5 Jan 2022 09:22:29 +0000 Message-Id: <20220105092229.617027-1-chi.minghao@zte.com.cn> X-Mailer: git-send-email 2.25.1 In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I found that there are indeed some optimizations after removing the redundancy. For example: int foo(int a, int b) { int ret; ret = a>b ? a: b; return ret; } int main() { int val; val = foo(7,2); return 0; } and int foo(int a, int b) { return a>b ? a: b; } int main() { int val; val = foo(7,2); return 0; } The corresponding disassembly code is as follows： 1129: f3 0f 1e fa endbr64 112d: 55 push %rbp 112e: 48 89 e5 mov %rsp,%rbp 1131: 89 7d fc mov %edi,-0x4(%rbp) 1134: 89 75 f8 mov %esi,-0x8(%rbp) 1137: 8b 45 fc mov -0x4(%rbp),%eax 113a: 39 45 f8 cmp %eax,-0x8(%rbp) 113d: 0f 4d 45 f8 cmovge -0x8(%rbp),%eax 1141: 5d pop %rbp 1142: c3 retq and 1129: f3 0f 1e fa endbr64 112d: 55 push %rbp 112e: 48 89 e5 mov %rsp,%rbp 1131: 89 7d ec mov %edi,-0x14(%rbp) 1134: 89 75 e8 mov %esi,-0x18(%rbp) 1137: 8b 45 ec mov -0x14(%rbp),%eax 113a: 39 45 e8 cmp %eax,-0x18(%rbp) 113d: 0f 4d 45 e8 cmovge -0x18(%rbp),%eax 1141: 89 45 fc mov %eax,-0x4(%rbp) 1144: 8b 45 fc mov -0x4(%rbp),%eax 1147: 5d pop %rbp 1148: c3 retq After removing the redundancy, the compiler does have some optimizations