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 AEA963858C53; Sat, 27 May 2023 18:25:26 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org AEA963858C53
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1685211926;
	bh=QRyAuJmQOu/GWNyCHoiwpKuf6nNpiD/Kcb5hwv2l7+s=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=Ifn0EAOyjxf8GdzBfLKDbs5gCsc47kp21pU/JndOiveHVsUWCmyhqY6fCRH46me3D
	 5mghH+iuc3beYUpmMENaT7g7xVnQcqqRTs/T4gQiD96AHMHxiC4mg1TiAxCHJ85qQq
	 pjFaTmq2gz9+FShcZ6Un3gJpvPTZgZ9SwCutnyw4=
From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: =?UTF-8?B?W0J1ZyBjLzExMDAwN10gSW1wbGVtZW50IHN1cHBvcnQgZm9yIENs?=
 =?UTF-8?B?YW5n4oCZcyBfX2J1aWx0aW5fdW5wcmVkaWN0YWJsZSgp?=
Date: Sat, 27 May 2023 18:25:26 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c
X-Bugzilla-Version: unknown
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: pinskia 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-110007-4-pnVvJlHang@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-110007-4@http.gcc.gnu.org/bugzilla/>
References: <bug-110007-4@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=3D110007

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Richard Yao from comment #3)
> (In reply to Andrew Pinski from comment #2)
> > (In reply to Richard Yao from comment #0)
> > > Having the ability to specify __builtin_unpredictable() as a hint to
> > > encourage the compiler to use cmov would be useful for implementing
> > > algorithms like binary search that have unpredictable branches.
> > > __builtin_expect_with_probability() looks like a possible substitute,=
 but
> > > Clang does not support it and it does not always work as described in
> > > #110001.
> >=20
> > PR 110001 has nothing to do with __builtin_expect_with_probability and
>=20
> I mentioned it briefly in PR 110001, but I guess I should make it explici=
t.
> See line 58 here:
>=20
> https://gcc.godbolt.org/z/ef3Yfchzv
>=20
> That is made into a jump, when all that is necessary is cmov, which is wh=
at
> Clang generates. In the example I had posted in PR 110001, I had not used
> __builtin_expect_with_probability() because it made no difference, but he=
re
> I am using it to show that cmov is not used.



If we look at the -fdump-tree-optimized-lineno dump we see why it was not
turned into a cmov:
  [/app/example.c:58:12 discrim 2] if (a_111 <=3D key_128(D))
    goto <bb 28>; [50.00%]
  else
    goto <bb 23>; [50.00%]

  <bb 23> [local count: 447392427]:
  [/app/example.c:75:40] _268 =3D (long unsigned int) i_82;
  [/app/example.c:75:40] _271 =3D _268 * 4;
  [/app/example.c:75:34] _274 =3D array_89(D) + _271;
  [/app/example.c:5:6] pretmp_277 =3D *_274;
  goto <bb 28>; [100.00%]


There is a load moved inside the conditional.=