From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id 015E13858D1E; Mon, 18 Mar 2024 09:06:25 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 015E13858D1E
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1710752786;
	bh=qh+t0F4OgENy/pgikslPdM5yr+5sHYEV26urKAgVmYo=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=R2z7JGFPPDOaRPn+/J+oG7gMHZv8nCcyvnIwSDUiIISSh+CYoebBejJIK0xXJsGmt
	 h6EmGxZlSXGMVxI5stUHnNhImmjt0N5KH/nmDRWEEH8iU/BEnd/bNGnYe2Ff1Mx+oG
	 4IeIL6msVNHjVDIZ1zMdKz18kzXaNFXBg7l/vFb8=
From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug middle-end/114347] wrong constant folding when casting __bf16
 to int
Date: Mon, 18 Mar 2024 09:06:21 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: middle-end
X-Bugzilla-Version: 13.2.1
X-Bugzilla-Keywords: wrong-code
X-Bugzilla-Severity: normal
X-Bugzilla-Who: jakub at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: 
Message-ID: <bug-114347-4-CFiPr08Xv6@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-114347-4@http.gcc.gnu.org/bugzilla/>
References: <bug-114347-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D114347

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #7)
> (In reply to Jakub Jelinek from comment #6)
> > You can use -fexcess-precision=3D16 if you don't want treating _Float16=
 and
> > __bf16 as having excess precision.  With excess precision, I think the =
above
> > behavior is correct.
> > You'd need (int) (__bf16) 257.0bf16 to get 256 even with excess precisi=
on.
>=20
> Ah, -fexcess-precision=3D16 doesn't seem to be documented though

I've noticed that too.

> (how does
> this influence long double handling then?)

ix86_get_excess_precision has all the details.  x86 has 4 different ways of
excess precision, one is not to use excess precision for anything, another =
only
for __bf16/_Float16 (promote to float), another one is promote everything to
long double and last is unpredictable.
With -fexcess-precision=3Dfast, with -mavx512fp16 we don't promote anything,
without that to float.
With -fexcess-precision=3D16 we don't promote anything.
With -fexcess-precision=3Dstandard and the implicit case, it depends on
-mavx512fp16, -mfpmath=3Dsse, -mfpmath=3D387, -mfpmath=3Dboth etc.=