Re: Optimizing PostgreSQL with LLVM's PGO+LTO

From: Andres Freund <andres(at)anarazel(dot)de>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: João Paulo Labegalini de Carvalho <jaopaulolc(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Optimizing PostgreSQL with LLVM's PGO+LTO
Date: 2023-01-27 23:08:50
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On 2023-01-27 15:06:37 -0500, Tom Lane wrote:
> There are a lot of places where we're implicitly relying on
> cross-compilation-unit optimizations NOT happening, because the code isn't
> adequately decorated with memory barriers and the like.

We have a fallback compiler barrier implementation doing that, but it
shouldn't be used on any halfway reasonable compiler. Cross-compilation-unit
calls don't provide a memory barrier - I assume you're thinking about a
compiler barrier?

I'm sure we have a few places that aren't that careful, but I would hope it's
not a large number. Are you thinking of specific "patterns" we've repeated all
over, or just a few cases you recall?


Andres Freund

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