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From: Bertrand Drouvot <[email protected]>
To: Tom Lane <[email protected]>
Cc: Peter Eisentraut <[email protected]>
Cc: Andres Freund <[email protected]>
Cc: [email protected]
Subject: Re: Defend against -ffast-math in meson builds
Date: Wed, 11 Mar 2026 18:29:47 +0000
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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	<[email protected]>
	<[email protected]>
	<abGPko4lPv/[email protected]>
	<[email protected]>
	<[email protected]>
	<[email protected]>

Hi,

On Wed, Mar 11, 2026 at 02:03:28PM -0400, Tom Lane wrote:
> Bertrand Drouvot <[email protected]> writes:
> > But still, I'm not sure the code-level guard is enough for meson. I think we
> > need to put a guard in meson.build for the "oddity" described in [1]:
> 
> > it compiles fine with CFLAGS="-ffast-math" CC="gcc" meson setup meson_build but
> > produces issues during the regression tests.
> 
> > I just had a closer look and it looks like that the reason is that it's being
> > added at link time:
> 
> > $ cat meson_build/build.ninja | grep LINK_ARGS | grep -c "ffast-math"
> > 254
> 
> Oy.  Surely that is a meson bug?  AFAICS most of the effects of
> -ffast-math should occur at compile time.  Perhaps it also results
> in linking a different version of libm, but that's not everything.
> So just transposing it into link flags is not okay.

What I can see is that with CFLAGS="-ffast-math", I get:

$ objdump -t meson_build/src/backend/postgres | grep crtfast
0000000000000000 l    df *ABS*  0000000000000000              crtfastmath.c

but it's empty without it.

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com

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