| From: | David Rowley <dgrowleyml(at)gmail(dot)com> |
|---|---|
| To: | Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> |
| Cc: | John Naylor <john(dot)naylor(at)enterprisedb(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Amit Khandekar <amitdkhan(dot)pg(at)gmail(dot)com> |
| Subject: | Re: call popcount32/64 directly on non-x86 platforms |
| Date: | 2021-08-12 13:33:06 |
| Message-ID: | CAApHDvqNoBg0_yEW8fQQCMH0p=-TEZR1f-ZDJphKcifrKPmYsg@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Fri, 13 Aug 2021 at 01:28, David Rowley <dgrowleyml(at)gmail(dot)com> wrote:
>
> On Fri, 13 Aug 2021 at 01:11, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> wrote:
> > So when on MSVC, you don't have to check CPUID for support?
>
> That still needs to be checked in MSVC and as far as I can see it is
> being properly checked.
Something there that might cause confusion is we do a configure check
to see if popcntq works and define HAVE_X86_64_POPCNTQ if it does.
I'm still a bit confused at why we bother doing that. Surely it just
means that if the build machine does not have popcntq that we'll
always use pg_popcount64_slow, regardless if the machine that's
actually running the code has popcntq.
Maybe you saw that there's no such equivalent test when we set
HAVE_X86_64_POPCNTQ for MSVC on x86_64. The reason for that is that
we do the run-time test using cpuid.
David
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