On Fri, Mar 29, 2024 at 12:30:14PM -0400, Tom Lane wrote:
> Nathan Bossart <nathandbossart@gmail.com> writes:
>>> I see google web references to the xgetbv instruction as far back as 2009
>>> for Intel 64 bit HW and 2010 for AMD 64bit HW, maybe you could test for
>>> _xgetbv() MSVC built-in. How far back do you need to go?
>
>> Hm. It seems unlikely that a compiler would understand AVX512 intrinsics
>> and not XGETBV then. I guess the other question is whether CPUID
>> indicating AVX512 is enabled implies the availability of XGETBV on the CPU.
>> If that's not safe, we might need to add another CPUID test.
>
> Some quick googling says that (1) XGETBV predates AVX and (2) if you
> are worried about old CPUs, you should check CPUID to verify whether
> XGETBV exists before trying to use it. I did not look for the
> bit-level details on how to do that.
That extra CPUID check should translate to exactly one additional line of
code, so I think I'm inclined to just add it.
--
Nathan Bossart
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