From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id C49323858D28; Thu, 28 Dec 2023 04:30:34 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org C49323858D28 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1703737834; bh=u/vON+nzuR8r1turIJYueslg1jfgR2/PecHcdHoajXY=; h=From:To:Subject:Date:In-Reply-To:References:From; b=mC0mqMAY8PTNMZT6CysxXM5dQqYJoqL4WHCNT4slddZ8wULlvRi4AS2OC6mQGFiS0 dVCPi7N/Q2eOyIhoDqqmSUBpx8KyNpc2wPaMJ7vbDskNh3dIAEUOXF0ZL+T5X87kk9 BOCmxg8sLZIk8zxrMU8g+0dyUTfFm9h94YL9EVOM= From: "tnfchris at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug c/113134] gcc does not version loops with early break conditions that don't have side-effects Date: Thu, 28 Dec 2023 04:30:34 +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: 14.0 X-Bugzilla-Keywords: missed-optimization X-Bugzilla-Severity: normal X-Bugzilla-Who: tnfchris at gcc dot gnu.org X-Bugzilla-Status: NEW 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: In-Reply-To: References: 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: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113134 --- Comment #9 from Tamar Christina --- (In reply to JuzheZhong from comment #8) > Suppose the loop mask is generated by whilelo instruction of ARM SVE. >=20 > Suppose we have 8 elements in a single whole vector. >=20 > mask =3D whilo (0, res) if res =3D 6, then mask =3D 11111000. > data =3D 12345678 >=20 > Then if it is early break. You are reversing both data and mask as follow= s: >=20 > new_mask =3D 00011111 > new_data =3D 87654321 >=20 > Then use the EXTRACT_LAST, we will get value =3D 1 for early break. >=20 > Am I right ? Yeah, the idea being the scalar loop will then run from 1 to 6 to do any si= de effects that we couldn't apply. We went with this approach first because it works for non-masked architectu= res too. In GCC-15 we'll try to implement staying entirely inside a vector loop= by splitting the mask in elements until first active and element from first ac= tive so we can correctly mask the operations.=