Horton

Re: refactor architecture-specific popcount code

John Naylor <johncnaylorls@gmail.com>

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From: John Naylor <johncnaylorls@gmail.com>
To: Nathan Bossart <nathandbossart@gmail.com>
Cc: Greg Burd <greg@burd.me>, Heikki Linnakangas <hlinnaka@iki.fi>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2026-02-11T07:10:37Z
Lists: pgsql-hackers

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On Wed, Feb 11, 2026 at 1:45 AM Nathan Bossart <nathandbossart@gmail.com> wrote:
>
> On Sat, Feb 07, 2026 at 03:54:31PM +0700, John Naylor wrote:
> > Okay, this is looking good. I have just one more suggestion: For 0002,
> > just copy the word-wise functions verbatim. That way, it's a pure
> > refactoring commit and the exception doesn't need explaining. With
> > that, I'd say go ahead and commit 0001/2.
>
> Seems reasonable.  Here is an updated patch set.  I've also swapped 0003
> and 0004.

0002: I just noticed another thing that could be done in a separate
follow-up patch:

@@ -220,17 +170,6 @@ pg_popcount_masked_portable(const char *buf, int
bytes, bits8 mask)
  * actual external functions.  The compiler should be able to inline the
  * portable versions here.
  */
-int
-pg_popcount32(uint32 word)
-{
-   return pg_popcount32_portable(word);
-}

The last sentence doesn't seem to be true anymore for the functions
that remain here:

(Needed to add "#undef HAVE_X86_64_POPCNTQ" in a few places to demonstrate)
objdump --no-show-raw-insn --no-addresses -drwC -M intel
/path/to/postgres | grep -C 5 pg_popcount_portable

<pg_popcount_optimized>:
        jmp    <pg_popcount_portable>

I don't think we need to worry about this, but the attached looks
nicer to me. There might be a disadvantage of using macros here, but
I'm not sure what it would be.

-- 
John Naylor
Amazon Web Services

Commits

  1. Make use of pg_popcount() in more places.

  2. Remove uses of popcount builtins.

  3. Remove some unnecessary optimizations in popcount code.

  4. Remove specialized word-length popcount implementations.

  5. Move x86-64-specific popcount code to pg_popcount_x86.c.

  6. Refactor some SIMD and popcount macros.

  7. Rename "fast" and "slow" popcount functions.

  8. Rename pg_popcount_avx512.c to pg_popcount_x86.c.

  9. Remove trailing zero words from Bitmapsets

  10. Don't use _BitScanForward64/_BitScanReverse64 on 32-bit MSVC builds