linux-kernel - [PATCH 0/2] arm: lib: xor-neon: Remove warn & disble neon vect

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Message-Id: <20201106051436.2384842-1-adrian.ratiu@collabora.com>
Date:   Fri,  6 Nov 2020 07:14:34 +0200
From:   Adrian Ratiu <adrian.ratiu@...labora.com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Arnd Bergmann <arnd@...db.de>,
        clang-built-linux@...glegroups.com,
        Russell King <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org, kernel@...labora.com
Subject: [PATCH 0/2] arm: lib: xor-neon: Remove warn & disble neon vect

Dear all,

This is my attempt to close the loop on a relatively old discussion
[1] caused by a compiler bug [2]. In a nutshell, the Clang build issues
a bogus warning about GCC while it silently botches the neon auto-loop
vectorization. :)

Many thanks to all who have investigated this issue before me. Arnd
posted a workaround for xor.h [3], but I very much like his first
suggestion of disabling the broken feature until the compiler is fixed.

Tested on latest linux next-20201105 using bcm2835 & versatile configs
and Clang 10.0.1

P.S: While testing aarch64/imx8m I also noticed vectorization is broke
there as well, but that deserves its own patch because it's a separate
xor-neon implementation (if this approach is deemed sensible).

[1] https://patchwork.kernel.org/project/linux-arm-kernel/patch/20190528235742.105510-1-natechancellor@gmail.com/
[2] https://bugs.llvm.org/show_bug.cgi?id=40976
[3] https://bugs.llvm.org/show_bug.cgi?id=40976#c6

Kind regards,
Adrian

Adrian Ratiu (1):
  arm: lib: xor-neon: disable clang vectorization

Nathan Chancellor (1):
  arm: lib: xor-neon: remove unnecessary GCC < 4.6 warning

 arch/arm/include/asm/xor.h |  3 ++-
 arch/arm/lib/Makefile      |  3 +++
 arch/arm/lib/xor-neon.c    | 13 +++++--------
 3 files changed, 10 insertions(+), 9 deletions(-)

-- 
2.29.0