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=-23.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS, USER_IN_DEF_DKIM_WL autolearn=unavailable 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 A4D80C433E6 for ; Tue, 19 Jan 2021 22:06:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6CB1E23104 for ; Tue, 19 Jan 2021 22:06:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729137AbhASWGK (ORCPT ); Tue, 19 Jan 2021 17:06:10 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38306 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728843AbhASWFP (ORCPT ); Tue, 19 Jan 2021 17:05:15 -0500 Received: from mail-pf1-x429.google.com (mail-pf1-x429.google.com [IPv6:2607:f8b0:4864:20::429]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8150AC061573 for ; Tue, 19 Jan 2021 14:04:31 -0800 (PST) Received: by mail-pf1-x429.google.com with SMTP id q20so13167176pfu.8 for ; Tue, 19 Jan 2021 14:04:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=km0tLx3Hb+77Yn2mV9SD+nXc5uKHViN4cP4UCVTdwFw=; b=bXveCDmegZK7Dg+MXhIQShuMS/xuSf2+iMzkzJ0qHV+xN+Dx9mkmfYHphHG4EjeZUt zbWJkvBpPcdwuJiNzcO5yUclwgDQCZpN2krmP3NpehzelE0mh86ww/qLOKKtyvsv3HX6 PqAq9TwxWw9V2hjDpD9zIoji3k57xE4sef5OeKbS6glCur+L1rEo7cpLOPz7vVwNPUVR 0Cp0XZWOTksA6gq5QkyvTtIQrNSKpD4TJcNsqSJS2bsmzPUvGPW3NGCIMbPqE2XBdv+a R/tYfV9EBfYVSlKg2DAoDKhnuGBthnOyhZ/xfP5p0RkER+/J2fgciCT6Ybzu9SomngCC huLQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=km0tLx3Hb+77Yn2mV9SD+nXc5uKHViN4cP4UCVTdwFw=; b=IOVCiUrdiKBL3BJjt4Tp2HrwOFn4CaB63ZM0NeyaFtDwiT3Wtc4p+y+lTrSFigyMF3 +zBgdf44NiPbeJ2ChPd2ZcmeRl6ASE0qJxo1n/Td+b6R1RP7sq9vYc6aocWp0Ovqe+Ch 21fIHA6VjCZcFUE5e7OtgV2dLxan13W37tXW8zDJ0nw8zfs3JrfBgSlTF5B4CYlg3KSo yHpMuw6HMnRAbui08M7i6pLbewqBsLC9P+X8ZQ4FQsGHk1Vj7+rwGO3g8GG94ZBPGLjK ec5ve1q4HRGN7ZuVcowjhzjEyvPrpzIzaP15IkHCEMLRCFQmVu6r5yVbVSQwo5VJd2oQ WtQw== X-Gm-Message-State: AOAM531mOsZc8ZMz0l0Oi7lsWLKT6EVpMWKYnQNrvszdKQCwgY8mM2bX H+Qr/G34o/fE3WP6L6hJOFWJi9XWb7qym+hFmmsZRw== X-Google-Smtp-Source: ABdhPJzQwwcAkLru8Gxy5lZvCPBvEUijRCb6QEO1IugJWKnfsfADLbiM9n7r2/b4i8Mk5i/6XE2X3Q45DiFU8KTywp4= X-Received: by 2002:a63:1142:: with SMTP id 2mr6367757pgr.263.1611093870873; Tue, 19 Jan 2021 14:04:30 -0800 (PST) MIME-Version: 1.0 References: <20210119131724.308884-1-adrian.ratiu@collabora.com> <20210119131724.308884-2-adrian.ratiu@collabora.com> In-Reply-To: From: Nick Desaulniers Date: Tue, 19 Jan 2021 14:04:19 -0800 Message-ID: Subject: Re: [PATCH v4 1/2] arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning To: Arnd Bergmann Cc: Adrian Ratiu , Arnd Bergmann , Linux ARM , Nathan Chancellor , Russell King , Ard Biesheuvel , Arvind Sankar , clang-built-linux , Collabora Kernel ML , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 19, 2021 at 1:35 PM Arnd Bergmann wrote: > > On Tue, Jan 19, 2021 at 10:18 PM 'Nick Desaulniers' via Clang Built > Linux wrote: > > > > On Tue, Jan 19, 2021 at 5:17 AM Adrian Ratiu wrote: > > > diff --git a/arch/arm/lib/xor-neon.c b/arch/arm/lib/xor-neon.c > > > index b99dd8e1c93f..f9f3601cc2d1 100644 > > > --- a/arch/arm/lib/xor-neon.c > > > +++ b/arch/arm/lib/xor-neon.c > > > @@ -14,20 +14,22 @@ MODULE_LICENSE("GPL"); > > > #error You should compile this file with '-march=armv7-a -mfloat-abi=softfp -mfpu=neon' > > > #endif > > > > > > +/* > > > + * TODO: Even though -ftree-vectorize is enabled by default in Clang, the > > > + * compiler does not produce vectorized code due to its cost model. > > > + * See: https://github.com/ClangBuiltLinux/linux/issues/503 > > > + */ > > > +#ifdef CONFIG_CC_IS_CLANG > > > +#warning Clang does not vectorize code in this file. > > > +#endif > > > > Arnd, remind me again why it's a bug that the compiler's cost model > > says it's faster to not produce a vectorized version of these loops? > > I stand by my previous comment: https://bugs.llvm.org/show_bug.cgi?id=40976#c8 > > The point is that without vectorizing the code, there is no point in building > both the default xor code and a "neon" version that has to save/restore > the neon registers but doesn't actually use them. > > Arnd Thoughts? Also, Nathan brings up my previous point about restrict. This would benefit both GCC and Clang as they would not produce 2 "versions" of the loop; one vectorized if the std::distance between x & y >= 8, one scalar otherwise. But the callers would have to ensure no overlap otherwise UB. diff --git a/include/asm-generic/xor.h b/include/asm-generic/xor.h index b62a2a56a4d4..7db16adc7d89 100644 --- a/include/asm-generic/xor.h +++ b/include/asm-generic/xor.h @@ -7,12 +7,21 @@ #include +/* Overrule LLVM's cost model in order to always produce a vectorized loop + * version. + */ +#if defined(__clang__) && defined(CONFIG_ARM) +#define FORCE_VECTORIZE _Pragma("clang loop vectorize(enable)") +#else +#define CLANG_FORCE_VECTORIZE +#endif + static void xor_8regs_2(unsigned long bytes, unsigned long *p1, unsigned long *p2) { long lines = bytes / (sizeof (long)) / 8; - do { + FORCE_VECTORIZE do { p1[0] ^= p2[0]; p1[1] ^= p2[1]; p1[2] ^= p2[2]; @@ -32,7 +41,7 @@ xor_8regs_3(unsigned long bytes, unsigned long *p1, unsigned long *p2, { long lines = bytes / (sizeof (long)) / 8; - do { + FORCE_VECTORIZE do { p1[0] ^= p2[0] ^ p3[0]; p1[1] ^= p2[1] ^ p3[1]; p1[2] ^= p2[2] ^ p3[2]; @@ -53,7 +62,7 @@ xor_8regs_4(unsigned long bytes, unsigned long *p1, unsigned long *p2, { long lines = bytes / (sizeof (long)) / 8; - do { + FORCE_VECTORIZE do { p1[0] ^= p2[0] ^ p3[0] ^ p4[0]; p1[1] ^= p2[1] ^ p3[1] ^ p4[1]; p1[2] ^= p2[2] ^ p3[2] ^ p4[2]; @@ -75,7 +84,7 @@ xor_8regs_5(unsigned long bytes, unsigned long *p1, unsigned long *p2, { long lines = bytes / (sizeof (long)) / 8; - do { + FORCE_VECTORIZE do { p1[0] ^= p2[0] ^ p3[0] ^ p4[0] ^ p5[0]; p1[1] ^= p2[1] ^ p3[1] ^ p4[1] ^ p5[1]; p1[2] ^= p2[2] ^ p3[2] ^ p4[2] ^ p5[2]; -- Thanks, ~Nick Desaulniers