From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [c++std-parallel-1632] Re: Compilers and RCU readers: Once more unto the breach! Date: Wed, 20 May 2015 11:16:47 -0700 Message-ID: <20150520181647.GU6776@linux.vnet.ibm.com> References: <20150520005510.GA23559@linux.vnet.ibm.com> <20150520024148.GD6776@linux.vnet.ibm.com> <20150520114745.GC11498@arm.com> <20150520121522.GH6776@linux.vnet.ibm.com> <20150520154617.GE11498@arm.com> <555CAE4B.4050202@redhat.com> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from e37.co.us.ibm.com ([32.97.110.158]:43831 "EHLO e37.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754396AbbETSQw (ORCPT ); Wed, 20 May 2015 14:16:52 -0400 Received: from /spool/local by e37.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 20 May 2015 12:16:52 -0600 Content-Disposition: inline In-Reply-To: <555CAE4B.4050202@redhat.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: c++std-parallel@accu.org Cc: Will Deacon , Linus Torvalds , Linux Kernel Mailing List , "linux-arch@vger.kernel.org" , "gcc@gcc.gnu.org" , p796231 , "mark.batty@cl.cam.ac.uk" , Peter Zijlstra , Ramana Radhakrishnan , David Howells , Andrew Morton , Ingo Molnar , "michaelw@ca.ibm.com" On Wed, May 20, 2015 at 04:54:51PM +0100, Andrew Haley wrote: > On 05/20/2015 04:46 PM, Will Deacon wrote: > > I'm not sure... you'd require the compiler to perform static analysis of > > loops to determine the state of the machine when they exit (if they exit!) > > in order to show whether or not a dependency is carried to subsequent > > operations. If it can't prove otherwise, it would have to assume that a > > dependency *is* carried, and it's not clear to me how it would use this > > information to restrict any subsequent dependency removing optimisations. > > It'd just convert consume to acquire. It should not need to, actually. Thanx, Paul