Horton

Re: refactor architecture-specific popcount code

Nathan Bossart <nathandbossart@gmail.com>

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From: Nathan Bossart <nathandbossart@gmail.com>
To: Heikki Linnakangas <hlinnaka@iki.fi>
Cc: John Naylor <johncnaylorls@gmail.com>, pgsql-hackers@postgresql.org
Date: 2026-01-15T19:07:18Z
Lists: pgsql-hackers

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Here is a new patch set.  Notably, I've added a 0004 that does the
following:

* Removes TRY_POPCNT_X86_64.  We now assume that the required CPUID
intrinsics are available, as we have long done in some of the CRC-32C code.

* Moves the MSVC check for HAVE_X86_64_POPCNTQ to configuration-time.  This
way, we set it for all relevant platforms in one place.

* Moves the #defines for USE_SSE2 and USE_NEON to c.h so that they can be
used elsewhere without simd.h.  Consequently, we can remove POPCNT_AARCH64.

* Moves the #includes for pg_bitutils.h to below the system headers in
pg_popcount_{aarch64,x86}.c (since we no longer depend on macros defined in
pg_bitutils.h).

-- 
nathan

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