From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 13326 invoked by alias); 14 Jul 2010 21:30:42 -0000 Received: (qmail 13318 invoked by uid 22791); 14 Jul 2010 21:30:42 -0000 X-SWARE-Spam-Status: No, hits=-1.8 required=5.0 tests=AWL,BAYES_00,T_RP_MATCHES_RCVD X-Spam-Check-By: sourceware.org Received: from mail.codesourcery.com (HELO mail.codesourcery.com) (38.113.113.100) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Wed, 14 Jul 2010 21:30:32 +0000 Received: (qmail 14589 invoked from network); 14 Jul 2010 21:30:30 -0000 Received: from unknown (HELO ?84.152.203.213?) (bernds@127.0.0.2) by mail.codesourcery.com with ESMTPA; 14 Jul 2010 21:30:30 -0000 Message-ID: <4C3E2C62.40808@codesourcery.com> Date: Wed, 14 Jul 2010 21:30:00 -0000 From: Bernd Schmidt User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.10) Gecko/20100625 Thunderbird/3.0.5 MIME-Version: 1.0 To: Jeff Law CC: GCC Patches Subject: Re: Emit more REG_EQUIV notes for function args (PR42235) References: <4C3D9C06.60901@codesourcery.com> <4C3E07EF.1030306@redhat.com> In-Reply-To: <4C3E07EF.1030306@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Mailing-List: contact gcc-patches-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-patches-owner@gcc.gnu.org X-SW-Source: 2010-07/txt/msg01196.txt.bz2 On 07/14/2010 08:54 PM, Jeff Law wrote: > On 07/14/10 05:14, Bernd Schmidt wrote: >> When moving arguments into pseudos, we are being very careful not to >> emit any instructions that could possibly clobber other argument >> registers. Currently, we generate unnecessarily complicated sequences >> of code for simple zero or sign extensions. >> >> With this patch, we check can_extend_p and the necessary predicates to >> see if an extend insn is available for the conversion we have to do. > Right, but what guarantee do we have that the conversion insn doesn't > clobber a function argument register? ISTM that to be safe you > actually have to scan the insns created by gen_extend_insn to ensure > they don't clobber something important. > > I'm not an expert on what ports do these days, but I did work on a port > (mn10200) where conversion "insns" where implemented as special function > calls under the hood. I don't recall if we allowed those special > function calls to have visible side effects, but if they did, they'd > show up as clobbers/uses attached to the normal conversion insn. Of > course the mn102 is dead, but I think it's method for implementing > conversions was valid and if another port were to do something similar > it would likely not interact well with your change. Hmm, ok. That's awful, but I kind of expected someone would say that. Did this really happen for integer zero/sign extend, or only for floating point stuff? If necessary I can try to test for a single insn with single_set and push it to the sequence otherwise. Bernd