Re: [PATCH 6/6] meson: require compiler support for chosen x86-64 instructions

["Daniel P. Berrangé" <berrange@redhat.com>]

On Thu, Jun 20, 2024 at 03:02:54PM +0200, Paolo Bonzini wrote:
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  meson.build | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/meson.build b/meson.build
> index 54e6b09f4fb..c5360fbd299 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -2863,6 +2863,7 @@ have_cpuid_h = cc.links('''
>  config_host_data.set('CONFIG_CPUID_H', have_cpuid_h)
>  
>  config_host_data.set('CONFIG_AVX2_OPT', get_option('avx2') \
> +  .enable_auto_if(get_option('x86_version') >= '3') \
>    .require(have_cpuid_h, error_message: 'cpuid.h not available, cannot enable AVX2') \
>    .require(cc.links('''
>      #include <cpuid.h>
> @@ -2875,6 +2876,7 @@ config_host_data.set('CONFIG_AVX2_OPT', get_option('avx2') \
>    '''), error_message: 'AVX2 not available').allowed())
>  
>  config_host_data.set('CONFIG_AVX512BW_OPT', get_option('avx512bw') \
> +  .enable_auto_if(get_option('x86_version') >= '4') \
>    .require(have_cpuid_h, error_message: 'cpuid.h not available, cannot enable AVX512BW') \
>    .require(cc.links('''
>      #include <cpuid.h>

I'm not sure this makes sense. The CONFIG_AVX* options are used only
to validate whether the toolchain has support for this. The QEMU
code then has a runtime, so it automagically uses AVX2/AVX512
if-and-only-if running on a suitably new CPU.  IOW, we want this
enabled always when the toolchain supports it, regardless of what
x86_version is set.

With regards,
Daniel
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