From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49596) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cEghE-0005EJ-6E for qemu-devel@nongnu.org; Wed, 07 Dec 2016 13:12:01 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cEghB-0006YE-1W for qemu-devel@nongnu.org; Wed, 07 Dec 2016 13:12:00 -0500 Received: from mail-ua0-f175.google.com ([209.85.217.175]:35620) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1cEghA-0006Y2-Lv for qemu-devel@nongnu.org; Wed, 07 Dec 2016 13:11:56 -0500 Received: by mail-ua0-f175.google.com with SMTP id 12so423759522uas.2 for ; Wed, 07 Dec 2016 10:11:56 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20161207180727.6286-2-rth@twiddle.net> References: <20161207180727.6286-1-rth@twiddle.net> <20161207180727.6286-2-rth@twiddle.net> From: Peter Maydell Date: Wed, 7 Dec 2016 18:10:35 +0000 Message-ID: Content-Type: text/plain; charset=UTF-8 Subject: Re: [Qemu-devel] [PATCH 1/2] tcg/aarch64: Fix addsub2 for 0+C List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Richard Henderson Cc: QEMU Developers , =?UTF-8?B?QWxleCBCZW5uw6ll?= On 7 December 2016 at 18:07, Richard Henderson wrote: > When al == xzr, we cannot use addi/subi because that encodes xsp. > Force a zero into the temp register for that (rare) case. Incidentally I was slightly surprised that the optimisation pass didn't turn "add2 rlo, rhi, 0, 0, 0, 0" into moves of 0 into rlo and rhi. Constant shifts of xzr in the guest don't seem worth spending much effort on optimising though :-) thanks -- PMM