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From: "rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/106902] [11/12/13/14 Regression] Program compiled with
 -O3 -mfma produces different result
Date: Thu, 18 May 2023 16:52:08 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106902

--- Comment #27 from rguenther at suse dot de <rguenther at suse dot de> ---
> Am 18.05.2023 um 10:31 schrieb amonakov at gcc dot gnu.org <gcc-bugzilla@=
gcc.gnu.org>:
>=20
> =EF=BB=BFhttps://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106902
>=20
> --- Comment #25 from Alexander Monakov <amonakov at gcc dot gnu.org> ---
> (In reply to Richard Biener from comment #24)
>> As of the patch it looks good, I wonder if we want to check for OPTIMIZE=
_BOTH
>> though since at least when no extra negations are required the contracti=
on
>> should also be a win when optimizing for size?
>=20
> Makes sense, I'll change that (current target hooks always return true for
> fma).
>=20
>> Also I wondered about the PROP_gimple_any check - do we get into the
>> gimplification langhook after lowering?  I see we are not resetting the
>> langhook after lowering (only in free-lang-data, but that only runs with
>> LTO).
>=20
> Yes, that surprised me. I caught it when analyzing ICE on slp-50.c testca=
se.
>=20
>> We probably at least should gate the langhook invocation in the gimplifi=
er
>> with what you added in the patch or specify whether the gimplifier is
>> invoked from the middle-end via the gimplifier context.
>=20
> Perhaps. I'll add a comment that we want to handle -ffp-contract=3Don str=
ictly
> during initial gimplification, to hash this out further on gcc-patches, if
> necessary.=20=20
>=20
>> If we go for c-family only the genericize entry could be another place to
>> handle this.
>=20
> That seems less convenient to me. Is IFN_FMA representable as a tree?

Yes, that=E2=80=99s possible.  Let=E2=80=99s see if others have an opinion =
on the ml.

>> Did you run into any of NON_LVALUE / C_MAYBE_CONST wrappings of the
>> multiplication btw?
>=20
> No, I'm not familiar with those, so I didn't try to construct correspondi=
ng
> testcases.
>=20
> --=20
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