From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 7242 invoked by alias); 29 Mar 2006 01:03:57 -0000 Received: (qmail 7224 invoked by uid 48); 29 Mar 2006 01:03:55 -0000 Date: Wed, 29 Mar 2006 01:03:00 -0000 Message-ID: <20060329010355.7223.qmail@sourceware.org> X-Bugzilla-Reason: CC References: Subject: [Bug middle-end/26900] Number of iterations not know for simple loop In-Reply-To: Reply-To: gcc-bugzilla@gcc.gnu.org To: gcc-bugs@gcc.gnu.org From: "rakdver at gcc dot gnu dot org" Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Archive: List-Post: List-Help: Sender: gcc-bugs-owner@gcc.gnu.org X-SW-Source: 2006-03/txt/msg02811.txt.bz2 List-Id: ------- Comment #4 from rakdver at gcc dot gnu dot org 2006-03-29 01:03 ------- (In reply to comment #1) > Note that we in principle know the number of iterations - just we cannot prove > the loop runs at least once in number of iterations analysis. Of course we > know this because we did loop header copying on the loop and no other pass > interfered with this. Maybe we should remember the BB of the loop header copy > so we can verify > later that it still dominates the loop header. I do not see much difference wrto the current system (where we simply check all blocks that dominate the loop header); checking just the one known to be the copy of the original header would be a bit more efficient, but it might also cause us to miss some opportunities to learn something about the bounds of the loop from the other conditions. I do not think remembering what the copied loop header is affects the need to deal with symbolic range simplification in any way. I think I can however improve the # of iterations analysis to be less demanding to fold, though. -- rakdver at gcc dot gnu dot org changed: What |Removed |Added ---------------------------------------------------------------------------- AssignedTo|unassigned at gcc dot gnu |rakdver at gcc dot gnu dot |dot org |org Status|UNCONFIRMED |ASSIGNED Ever Confirmed|0 |1 Last reconfirmed|0000-00-00 00:00:00 |2006-03-29 01:03:55 date| | http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26900