From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 13203 invoked by alias); 22 Oct 2013 11:32:41 -0000 Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-bugs-owner@gcc.gnu.org Received: (qmail 13172 invoked by uid 48); 22 Oct 2013 11:32:38 -0000 From: "glisse at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/58806] New attribute for functions that access memory only through their arguments Date: Tue, 22 Oct 2013 11:32:00 -0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: tree-optimization X-Bugzilla-Version: 4.9.0 X-Bugzilla-Keywords: X-Bugzilla-Severity: enhancement X-Bugzilla-Who: glisse at gcc dot gnu.org X-Bugzilla-Status: UNCONFIRMED X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-SW-Source: 2013-10/txt/msg01596.txt.bz2 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58806 --- Comment #3 from Marc Glisse --- (In reply to Richard Biener from comment #2) > You cannot find the PR because it's already implemented via the "fn spec" > attribute (conveniently not user-accessible because bike-shedding about > whether separate attributes are required). The documentation resides > in gimple.c:gimple_call_arg_flags, Thanks, I knew of the EAF_* flags (none look that promising for my particular use), but not of this "fn spec" attribute. > and I _think_ it doesn't quite provide > what you want as it was designed to help the context and flow-insensitive > points-to analysis which doesn't benefit from "this call does not clobber > or read from escaped memory". But what it provides is "the argument to > this function does not escape" which is important. I locally changed the name to fn_spec so I could try it. Nothing helps for comment #0. The combination EAF_NOCLOBBER | EAF_NOESCAPE (aka 'r') is enough to optimize comment #1. However, EAF_NOCLOBBER is exactly the opposite of what I want since the whole point of g is to write to its argument, and I don't see why EAF_NOESCAPE should be necessary since there is no other call afterwards. So I guess more flags (ECF_* since they wouldn't apply to a specific argument) would be good. I tried the attributes nothrow,nonnull,leaf on comment #0 because that's what gcc puts on memcpy and gcc knows that memcpy(data,...) doesn't change *p, but that didn't work, I should look at where exactly the difference between memcpy and init plays a role.