Re: Defend against -ffast-math in meson builds

Hi,

On Wed, Mar 11, 2026 at 02:03:28PM -0400, Tom Lane wrote:
> Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com> 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