Re: [PATCH] ARM: xor-neon: Replace __GNUC__ checks with CONFIG_CC_IS_GCC

[Nathan Chancellor <natechancellor@gmail.com>]

On Fri, May 31, 2019 at 01:06:13PM -0700, Nick Desaulniers wrote:
> On Fri, May 31, 2019 at 12:21 PM Arnd Bergmann <arnd@arndb.de> wrote:
> > clang, I would suggest dropping your patch then, and instead adding
> 
> I disagree.  The minimum version of gcc required to build the kernel
> is 4.6, so the comment about older versions of gcc is irrelevant and
> should be removed.
> 
> Nathan's -Rpass warnings are warning that vectorization was not
> calculated to be profitable **for 1 of the 4 functions** by LLVM.
> Surely we wouldn't disable NEON opts for XOR because 1 of 4 was not
> vectorized?

Well I kept it short but clang warns that all of the loops are not
profitable.

However, the config option for xor-neon.c is CONFIG_XOR_BLOCKS, which
also controls the arm64 implementation. We wouldn't want to disable it
for clang altogether if it works on arm64 fine.

If it turns out to be broken for both, I suppose I would be okay with
disabling CONFIG_XOR_BLOCKS for clang but it should be done in a
separate patch as this one should be applied regardless of clang working
or not (because this warning will appear again when clang is fixed).

Cheers,
Nathan