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Date: Tue, 21 Nov 2017 23:44:23 +1100 (EST)
From: Bruce Evans <brde@optusnet.com.au>
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To: Warner Losh <imp@freebsd.org>
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Subject: Re: svn commit: r326037 - head/share/mk
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On Mon, 20 Nov 2017, Warner Losh wrote:

> Author: imp
> Date: Mon Nov 20 22:41:22 2017
> New Revision: 326037
> URL: https://svnweb.freebsd.org/changeset/base/326037
>
> Log:
>  Add -mno-avx2 for clang as well as -mno-avx. We don't want either of
>  them when asking for no SIMD.

Is this needed.  For SSE, -mno-sse implies -mno-sse[2,3,4,...] so
an multiple set of no-sse* flags are not needed (I have only checked this
for sse2).  Multiple no-sse* flags are also not used.

> Modified: head/share/mk/bsd.cpu.mk
> ==============================================================================
> --- head/share/mk/bsd.cpu.mk	Mon Nov 20 22:27:33 2017	(r326036)
> +++ head/share/mk/bsd.cpu.mk	Mon Nov 20 22:41:22 2017	(r326037)
> @@ -393,7 +393,7 @@ CFLAGS += ${_CPUCFLAGS}
> # (-mfpmath= is not supported)
> #
> .if ${MACHINE_CPUARCH} == "i386" || ${MACHINE_CPUARCH} == "amd64"
> -CFLAGS_NO_SIMD.clang= -mno-avx
> +CFLAGS_NO_SIMD.clang= -mno-avx -mno-avx2
> CFLAGS_NO_SIMD= -mno-mmx -mno-sse

Nearby example of non-use for SSE.

> .endif
> CFLAGS_NO_SIMD += ${CFLAGS_NO_SIMD.${COMPILER_TYPE}}

Testing shows that -mavx2 -mno-avx kills all AVX for clang in an example
that only generates AVX instructions (-mavx2 enabls these as a subset).

Bruce