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 999C53858C5F; Wed, 13 Sep 2023 08:35:08 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 999C53858C5F
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1694594108;
	bh=Os6HU647LTpNZOAGhruF5xdzn2/3+LSipOfZFXwX3v0=;
	h=From:To:Subject:Date:In-Reply-To:References:From;
	b=tKrtltBTcK0J7PjDO/DU9DjHM+tkPhPoNAZpyCLFUJaIpquE7uI0BYbHjDfYfxS1u
	 0KBtbS9HfDgZeMCXZuDW0IUndYV44i/xaapIeXhl3Sww4oTsYlDO6RuJ6O19TjOv9A
	 /OVx5SdKlw4H/plS2fsGnYKXiIrczn9vAzdzZsXs=
From: "juzhe.zhong at rivai dot ai" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/110751] RISC-V: Suport undefined value that allows
 VSETVL PASS use TA/MA
Date: Wed, 13 Sep 2023 08:34:58 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Version: 14.0
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: juzhe.zhong at rivai dot ai
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-110751-4-QMUN1i82Oc@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-110751-4@http.gcc.gnu.org/bugzilla/>
References: <bug-110751-4@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=3D110751

--- Comment #32 from JuzheZhong <juzhe.zhong at rivai dot ai> ---
(In reply to Richard Biener from comment #31)
> On GIMPLE an "undefined" operand representation would be the default
> definition of an SSA name with the appropriate type.  That's a somewhat
> "heavy" representation and it also doesn't fit the target hook return val=
ue
> nicely,
> but we could handle a NULL_TREE return value from the target hook in the
> way to create such SSA name.

Thanks Richi.

How does this special "SSA" represent in RTX or How could I recognize this =
is
a "undefine" value in "expand" stage ?

I wondering whether my approach (passing a scalar 0) to the ELSE value whic=
h is
easily recognized in RTL backend ("expand stage") is suitable ?=20

Since you could see there will be one more move instruction inside the loop
which hurt vector performance a lot, I want to find a quick way to fix it f=
or
now.=