On 11/9/2017 8:58 AM, James Darnley wrote:
> ---
> I've changed this patch slightly because I discovered that it would cause an
> illegal instruction exception on much older processors (probably all without
> AVX). I was running xgetbv() almost uncontitionally. Now it is a little more
> like what is the in x264 patch.
>
> libavutil/x86/cpu.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/libavutil/x86/cpu.c b/libavutil/x86/cpu.c
> index f33088c8c7..589fdef7da 100644
> --- a/libavutil/x86/cpu.c
> +++ b/libavutil/x86/cpu.c
> @@ -97,6 +97,7 @@ int ff_get_cpu_flags_x86(void)
> int max_std_level, max_ext_level, std_caps = 0, ext_caps = 0;
> int family = 0, model = 0;
> union { int i[3]; char c[12]; } vendor;
> + int xcr0_lo = 0, xcr0_hi = 0;
>
> if (!cpuid_test())
> return 0; /* CPUID not supported */
> @@ -132,8 +133,8 @@ int ff_get_cpu_flags_x86(void)
> /* Check OXSAVE and AVX bits */
> if ((ecx & 0x18000000) == 0x18000000) {
> /* Check for OS support */
> - xgetbv(0, eax, edx);
> - if ((eax & 0x6) == 0x6) {
> + xgetbv(0, xcr0_lo, xcr0_hi);
> + if ((xcr0_lo & 0x6) == 0x6) {
> rval |= AV_CPU_FLAG_AVX;
> if (ecx & 0x00001000)
> rval |= AV_CPU_FLAG_FMA3;
> @@ -154,6 +155,13 @@ int ff_get_cpu_flags_x86(void)
> if (ebx & 0x00000100)
> rval |= AV_CPU_FLAG_BMI2;
> }
> +#if HAVE_AVX512 /* F, CD, BW, DQ, VL */
Nit: Maybe move this chunk inside the HAVE_AVX2 block, at the end of it,
right above the BMI checks.
> + if ((xcr0_lo & 0xe6) == 0xe6) {
Nit: The proper check here i think would be
if ((xcr0_lo & 0xe0) == 0xe0) {
if ((rval & AV_CPU_FLAG_AVX) && (ebx & 0xd0030000) == 0xd0030000)
rval |= AV_CPU_FLAG_AVX512;
}
But it's functionally the same.
> + if ((ebx & 0xd0030000) == 0xd0030000)
> + rval |= AV_CPU_FLAG_AVX512;
> +
> + }
> +#endif
> }
>
> cpuid(0x80000000, max_ext_level, ebx, ecx, edx);
>
LGTM either way.
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