From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 8D4493858403; Mon, 1 Aug 2022 12:12:15 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 8D4493858403 From: "rsaxvc at gmail dot com" To: gcc-bugs@gcc.gnu.org Subject: [Bug target/106484] Failure to optimize uint64_t/constant division on ARM32 Date: Mon, 01 Aug 2022 12:12:15 +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: 12.1.0 X-Bugzilla-Keywords: missed-optimization X-Bugzilla-Severity: enhancement X-Bugzilla-Who: rsaxvc at gmail dot com 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: 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 X-BeenThere: gcc-bugs@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-bugs mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 01 Aug 2022 12:12:15 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D106484 --- Comment #3 from rsaxvc at gmail dot com --- > 32-bit division by constant relies on a 32x32->64 bit multiply. I believe only the upper half of the bits are required for the product to represent the integer component of the quotient. This makes parameter passi= ng much easier in the uint64_t/constant case. > We don't have an instruction for that on arm nor does gcc support 128-bit= integer types on a 32-bit compiler. I ran into that as well. The attached uint64_t umulh( uint64_t a, uint64_t = b ) implements a 64x64->64MSBsOf128BitProduct using only 32x32->64 bit multiplication, 64-bit addition, and register-aligned shifting.=