Re: Popcount optimization using AVX512

Hi,

On 2024-11-06 20:26:47 -0600, Nathan Bossart wrote:
> From d0fb7e0e375f7b76d4df90910c21e9448dd3b380 Mon Sep 17 00:00:00 2001
> From: Nathan Bossart <nathan(at)postgresql(dot)org>
> Date: Wed, 16 Oct 2024 15:57:55 -0500
> Subject: [PATCH v3 1/1] use __attribute__((target(...))) for AVX-512 stuff

One thing that'd I'd like to see this being used is to elide the indirection
when the current target platform *already* supports the necessary
intrinsics. Adding a bunch of indirection for short & common operations is
decidedly not great. It doesn't have to be part of the same commit, but it
seems like it's worth doing as part of the same series, as I think it'll lead
to rather different looking configure checks.

> diff --git a/src/include/c.h b/src/include/c.h
> index 55dec71a6d..6f5ca25542 100644
> --- a/src/include/c.h
> +++ b/src/include/c.h
> @@ -174,6 +174,16 @@
> #define pg_attribute_nonnull(...)
> #endif
>
> +/*
> + * pg_attribute_target allows specifying different target options that the
> + * function should be compiled with (e.g., for using special CPU instructions).
> + */
> +#if __has_attribute (target)
> +#define pg_attribute_target(...) __attribute__((target(__VA_ARGS__)))
> +#else
> +#define pg_attribute_target(...)
> +#endif

Think it'd be good to mention that there still needs to be configure check to
verify that specific target attribute is understood by the compiler.

Greetings,

Andres Freund