From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1NY0MA-0006lc-D5 for qemu-devel@nongnu.org; Thu, 21 Jan 2010 11:58:06 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1NY0M9-0006l5-3T for qemu-devel@nongnu.org; Thu, 21 Jan 2010 11:58:05 -0500 Received: from [199.232.76.173] (port=50116 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1NY0M8-0006kx-RB for qemu-devel@nongnu.org; Thu, 21 Jan 2010 11:58:04 -0500 Received: from are.twiddle.net ([75.149.56.221]:59994) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1NY0M7-0000pd-Tv for qemu-devel@nongnu.org; Thu, 21 Jan 2010 11:58:04 -0500 Message-ID: <4B58877C.5060408@twiddle.net> Date: Thu, 21 Jan 2010 08:57:32 -0800 From: Richard Henderson MIME-Version: 1.0 Subject: Re: [Qemu-devel] possible qemu miscompilation by latest gcc References: <4B57F0EB.1050905@cs.utah.edu> In-Reply-To: <4B57F0EB.1050905@cs.utah.edu> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: John Regehr Cc: qemu-devel@nongnu.org On 01/20/2010 10:15 PM, John Regehr wrote: > Hi folks- > > Just wanted to let you know that perhaps the function > helper_neon_rshl_s8() is being miscompiled by the latest gcc. > > I'm using qemu 0.12.2 and gcc rev 156103, which is a pre-version of gcc > 4.5. This is on an x86 machine running Ubuntu 9.10. > > At -O2 or higher this is the resulting object code: > > 00002060 : > 2060: 31 c0 xor %eax,%eax > 2062: c3 ret > > If this is not the intended result, then either the function has a > latent bug or else the compiler is doing something bad. Confirmed. The compiler is at fault. http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42833 r~