Re: [gentoo-user] Re: Multilib ABI specific CPU use flags?

[Jonathan Yong]

On 10/9/20 5:44 AM, Walter Dnes wrote:

On Fri, Oct 09, 2020 at 12:26:17AM +0000, Jonathan Yong wrote

I have a skylake system:
CPU_FLAGS_X86: aes avx avx2 f16c fma3 mmx mmxext pclmul popcnt rdrand
sse sse2 sse3 sse4_1 sse4_2 ssse3

   A heavy-handed 2-part solution
1) remove "avx2" from CPU_FLAGS_X86

This was my initial reaction, then I realized I don't need 32bit OpenCV (for now), since the only package depending on it is 64bit.

2) assuming you have "-march=native" or "-march=skylake" in your CFLAGS
and CXXFLAGS, follow that with "-march=no-avx2".  e.g...
"-march=skylake -march=no-avx2"

   This tells gcc "I don't have avx2, so don't compile any avx2 code".
I think the performance loss will be minimal.

The CMake configure arguments still tell OpenCV to build the AVX2 code unfortunately. So #1 is required regardless.

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