From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 8C6D7385842B; Sat, 4 Dec 2021 07:15:26 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 8C6D7385842B From: "pinskia at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug rtl-optimization/103550] 2 more instructions generated by gcc than clang Date: Sat, 04 Dec 2021 07:15:26 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: rtl-optimization X-Bugzilla-Version: 12.0 X-Bugzilla-Keywords: missed-optimization, ra X-Bugzilla-Severity: enhancement 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: 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: Sat, 04 Dec 2021 07:15:26 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D103550 --- Comment #5 from Andrew Pinski --- (In reply to cqwrteur from comment #4) > (In reply to Andrew Pinski from comment #2) > > Looks like it is a register allocation/scheduling issue. The extra > > instructions are mov. >=20 > Are there good algos that can allocate registers optimal? note the move instructions might be "free" on most modern x86 machine, it j= ust takes up icache space and decode time. having so little registers and having a 2 operand instruction set makes register allocation a hard problem really. Yes LLVM might get it right in t= his testcase but there are others where GCC might do a better job.=