From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34747) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WQIN7-0007WA-Gb for qemu-devel@nongnu.org; Wed, 19 Mar 2014 11:25:45 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WQIMz-0000BJ-31 for qemu-devel@nongnu.org; Wed, 19 Mar 2014 11:25:37 -0400 Received: from mail-qa0-x232.google.com ([2607:f8b0:400d:c00::232]:45393) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WQIMy-0000BB-J6 for qemu-devel@nongnu.org; Wed, 19 Mar 2014 11:25:28 -0400 Received: by mail-qa0-f50.google.com with SMTP id o15so8619064qap.23 for ; Wed, 19 Mar 2014 08:25:28 -0700 (PDT) Sender: Richard Henderson Message-ID: <5329B6E3.5030002@twiddle.net> Date: Wed, 19 Mar 2014 08:25:23 -0700 From: Richard Henderson MIME-Version: 1.0 References: <1395178235-29056-1-git-send-email-rth@twiddle.net> <1395178235-29056-4-git-send-email-rth@twiddle.net> <53293783.3050509@weilnetz.de> In-Reply-To: <53293783.3050509@weilnetz.de> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v2 3/4] tcg: Mask shift counts to avoid undefined behavior List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Weil , qemu-devel@nongnu.org Cc: peter.maydell@linaro.org On 03/18/2014 11:21 PM, Stefan Weil wrote: > Are there test cases which fail with the old code? Only when running under analysis tools looking for technical violations of the standard. Under normal circumstances it would never crash since, as with the native backends, the underlying cpu is going to treat this some rational way. But I sincerely doubt that we could measure any performance loss in TCI. The single extra arithmetic operation should be swallowed by the loop back to interpret the next opcode. r~