From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 4067 invoked by alias); 19 Oct 2011 00:49:11 -0000 Received: (qmail 4057 invoked by uid 22791); 19 Oct 2011 00:49:09 -0000 X-SWARE-Spam-Status: No, hits=-2.0 required=5.0 tests=AWL,BAYES_00,RP_MATCHES_RCVD,TW_RQ X-Spam-Check-By: sourceware.org Received: from ausxipps301.us.dell.com (HELO ausxipps301.us.dell.com) (143.166.148.223) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Wed, 19 Oct 2011 00:48:55 +0000 X-Loopcount0: from 10.175.216.249 From: To: , CC: Date: Wed, 19 Oct 2011 05:45:00 -0000 Subject: RE: Expanding instructions with condition codes inter-deps Message-ID: <09787EF419216C41A903FD14EE5506DD030CD64EDB@AUSX7MCPC103.AMER.DELL.COM> References: <4E9E0775.3020303@redhat.com> In-Reply-To: <4E9E0775.3020303@redhat.com> Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-IsSubscribed: yes Mailing-List: contact gcc-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-owner@gcc.gnu.org X-SW-Source: 2011-10/txt/msg00304.txt.bz2 >From: gcc-owner@gcc.gnu.org [mailto:gcc-owner@gcc.gnu.org] On Behalf Of Ri= chard Henderson >On 10/17/2011 03:50 AM, Paulo J. Matos wrote: >>... >> (for example, it would be ok to output negqi2, xorqi3 and=20 >> addc_internal since xorqi3 only sets N and Z, not the Carry bit) > >For that you'd have to model all of the flags bits independently. >I don't believe any target has found that level of complexity to be worth = the trouble. Something like that shows up in the pdp11, where "mov" does not touch C. A= nd C matters for multi-word arithmetic, and also for unsigned compares. So= I think a CCmode implementation there would model C separately from the o= ther three flag bits. So not 4 separate elements but two. Right now it's = a cc0 target but I figure on changing that at some point. The reasons Paul= o mentioned are one of the main reasons for that. paul