Re: Improve CRC32C performance on SSE4.2

On Mon, Jun 23, 2025 at 11:10:45AM -0400, Tom Lane wrote:
> Nathan Bossart <nathandbossart@gmail.com> writes:
>> On Mon, Jun 23, 2025 at 10:51:21AM -0400, Tom Lane wrote:
>>> This has broken the build completely on my RHEL8 x86_64 box,
>>> with gcc 8.5.0:
> 
>> Unfortunately, this will probably require more than replacing
>> _mm512_castsi512_si128 with _mm512_zextsi512_si128 because the latter
>> doesn't exist.
> 
> I was imagining just including _mm512_zextsi128_si512() in the
> code being tested during configure, so that we fall back to
> the non-AVX-512 code if the compiler is too old to have it.
> I don't really feel a need to work harder than that.

Sorry, my note wasn't clear.  Right now, the configure test uses
_mm512_castsi512_si128(), so we can't just do a simple s/cast/zext.  We'll
need to make a slightly bigger modification to the test to make sure the
zext intrinsics are understood.  I agree that we needn't work any harder
than that.

-- 
nathan