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Re: [Qemu-trivial] [Qemu-devel] [PATCH] Update the avx2 configure test t

From: Richard Henderson
Subject: Re: [Qemu-trivial] [Qemu-devel] [PATCH] Update the avx2 configure test to be compatible with clang
Date: Thu, 8 Aug 2019 22:22:03 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0

On 8/8/19 9:19 PM, Rebecca Cran wrote:
> clang doesn't support the GCC pragma to enable AVX2, but instead
> requires the command line option -mavx2. Since GCC also supports that,
> remove the pragma lines and add the -mavx2 option when building the
> test.

No, this means we're not testing what we need:

We need to compile exactly one function using avx2.

The other functions should be compiled with sse4 and sse2, respectively, and we
choose between them by testing cpuid bits at startup.  If you supply -mavx2 to
the entire compilation, then the routine that is supposed to use only sse2 will
in fact use avx2, and then the runtime selection is moot.


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