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From: Anthonin Bonnefoy <[email protected]>
To: Thomas Munro <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Cc: Matheus Alcantara <[email protected]>
Subject: Re: LLVM 22
Date: Wed, 14 Jan 2026 17:12:45 +0100
Message-ID: <CAO6_XqoH-6HBmrFZrRXQuc+_PvkMYDxXcbLW+fsUfTnUnMi2mA@mail.gmail.com> (raw)
In-Reply-To: <CA+hUKGLJ63fpt_u0OXDR91fbpicDXK01fivzDSBMOtPazEanFQ@mail.gmail.com>
References: <CA+hUKGJTumad75o8Zao-LFseEbt=enbUFCM7LZVV=c8yg2i7dg@mail.gmail.com>
	<CA+hUKGJv+QUOy8yOHe_0VfRGTSrHaCvo0xZG-1JGTqBurcPkOw@mail.gmail.com>
	<CA+hUKGLJ63fpt_u0OXDR91fbpicDXK01fivzDSBMOtPazEanFQ@mail.gmail.com>

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.gma...


Attachments:

  [application/octet-stream] 21_lifetime.s (4.1K, 2-21_lifetime.s)
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  [application/octet-stream] 22_no_poisoned.s (4.0K, 3-22_no_poisoned.s)
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  [application/octet-stream] 22_poisoned.s (4.0K, 4-22_poisoned.s)
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  [application/octet-stream] 21_no_lifetime.s (4.1K, 5-21_no_lifetime.s)
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  Subject: Re: LLVM 22
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