Horton

Re: LLVM 22

Anthonin Bonnefoy <anthonin.bonnefoy@datadoghq.com>

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From: Anthonin Bonnefoy <anthonin.bonnefoy@datadoghq.com>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Matheus Alcantara <matheusssilv97@gmail.com>
Date: 2026-01-14T16:12:45Z
Lists: pgsql-hackers

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Hi,

I've tried to generate multiple bitcode for a simple 'select aid % 2
FROM pgbench_accounts limit 10;' query. To keep bitcode simple, I've
modified the passes to use "default<O0>,mem2reg,inline" when we have
JIT inline without optimization (as described in [0]). I've tried the
following
- LLVM21: With lifetime
- LLVM21: Without lifetime
- LLVM22: With Poison
- LLVM22: Without Poison

In the 4 scenarios, the generated bc were the same with the exact same
instructions. Removing the lifetime end or the poison value doesn't
seem to change anything at this level of optimisation.

I'm not sure how to interpret this. Maybe the test is incorrect and a
different function needs to be called to possibly trigger the issue?
Or the poison/lifetime is only useful when going through the O3
optimisation pass?

[0]: https://www.postgresql.org/message-id/CAO6_XqrNjJnbn15ctPv7o4yEAT9fWa-dK15RSyun6QNw9YDtKg%40mail.gmail.com

Commits

  1. jit: No backport::SectionMemoryManager for LLVM 22.

  2. jit: Stop emitting lifetime.end for LLVM 22.