Re: [PATCH 2/2] arm: lib: xor-neon: disable clang vectorization

From: Adrian Ratiu <adrian.ratiu@collabora.com>
To: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc: linux-arm-kernel@lists.infradead.org,
	Nathan Chancellor <natechancellor@gmail.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Arnd Bergmann <arnd@arndb.de>,
	clang-built-linux@googlegroups.com, linux-kernel@vger.kernel.org,
	kernel@collabora.com
Subject: Re: [PATCH 2/2] arm: lib: xor-neon: disable clang vectorization
Date: Sat, 07 Nov 2020 20:12:39 +0200	[thread overview]
Message-ID: <87r1p5ujc8.fsf@collabora.com> (raw)
In-Reply-To: <20201107102203.GV1551@shell.armlinux.org.uk>

On Sat, 07 Nov 2020, Russell King - ARM Linux admin 
<linux@armlinux.org.uk> wrote:
> On Fri, Nov 06, 2020 at 07:14:36AM +0200, Adrian Ratiu wrote: 
>> diff --git a/arch/arm/lib/xor-neon.c b/arch/arm/lib/xor-neon.c 
>> index e1e76186ec23..84c91c48dfa2 100644 --- 
>> a/arch/arm/lib/xor-neon.c +++ b/arch/arm/lib/xor-neon.c @@ 
>> -18,6 +18,10 @@ MODULE_LICENSE("GPL"); 
>>   * Pull in the reference implementations while instructing GCC 
>>   (through * -ftree-vectorize) to attempt to exploit implicit 
>>   parallelism and emit * NEON instructions. 
>> + 
> 
> Please tidy this up before submission; we normally continue the 
> "*" for blank lines in comment blocks. Thanks. 

Indeed, thank you. I will fix it if I don't replace this patch 
entirely with something similar to what Nick suggested.

Perhaps adding a checkpatch test for this is a good idea?

Adrian

>
>> + * On Clang the loop vectorizer is enabled by default, but due to a bug
>> + * (https://bugs.llvm.org/show_bug.cgi?id=40976) vectorization is broke
>> + * so xor-neon is disabled in favor of the default reg implementations.
>>   */
>>  #ifdef CONFIG_CC_IS_GCC
>>  #pragma GCC optimize "tree-vectorize"
>> -- 
>> 2.29.0
>> 
>> 
>
> -- 
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!