From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-return-141750-listarch-gcc=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 28213 invoked by alias); 3 Nov 2007 15:27:33 -0000
Received: (qmail 28205 invoked by uid 22791); 3 Nov 2007 15:27:32 -0000
X-Spam-Check-By: sourceware.org
Received: from nikam-dmz.ms.mff.cuni.cz (HELO nikam.ms.mff.cuni.cz) (195.113.20.16)     by sourceware.org (qpsmtpd/0.31) with ESMTP; Sat, 03 Nov 2007 15:27:30 +0000
Received: by nikam.ms.mff.cuni.cz (Postfix, from userid 29025) 	id 1F15B5BA2B; Sat,  3 Nov 2007 16:27:28 +0100 (CET)
Date: Sat, 03 Nov 2007 15:27:00 -0000
From: Zdenek Dvorak <rakdver@kam.mff.cuni.cz>
To: Kenneth Zadeck <zadeck@naturalbridge.com>
Cc: gcc@gcc.gnu.org
Subject: Re: Tree-SSA and POST_INC address mode inompatible in GCC4?
Message-ID: <20071103152728.GA14818@kam.mff.cuni.cz>
References: <2E073B3ABB3F664DBA1D1C4D5FB47EF405C97B92@NT-IRVA-0752.brcm.ad.broadcom.com> <87fxzna11s.fsf@numenor.site> <20071103142504.GA5043@kam.mff.cuni.cz> <472C8B27.6080303@naturalbridge.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <472C8B27.6080303@naturalbridge.com>
User-Agent: Mutt/1.5.9i
Mailing-List: contact gcc-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc/>
List-Post: <mailto:gcc@gcc.gnu.org>
List-Help: <http://gcc.gnu.org/ml/>
Sender: gcc-owner@gcc.gnu.org
X-SW-Source: 2007-11/txt/msg00080.txt.bz2

Hi,

> >> I believe that this is something new and is most likely fallout from
> >> diego's reworking of the tree to rtl converter.
> >>
> >> To fix this will require a round of copy propagation, most likely in
> >> concert with some induction variable detection, since the most
> >> profitable place for this will be in loops.  
> >>
> >> I wonder if any of this effects the rtl level induction variable
> >> discovery?
> >>     
> >
> > it should not (iv analysis is able to deal with this kind of ivs).
> >
> does the iv analysis canonize them in a way that we should perhaps
> consider moving the auto-inc detection after the iv analysis?

no, iv analysis does not change the program; also, since the code in
this particular example is not in any loop, iv analysis is somewhat
irrelevant for it.

Btw.  I would have actually expected this code to be folded to

 *a_3(D) = D.1543_2;
  a_4 = a_3(D) + 1;
  b_5 = b_1(D) + 1;
  D.1543_6 = *b_5;
  *a_4 = D.1543_6;
  a_7 = a_3 + 2;
  b_8 = b_1 + 2;
  D.1543_9 = *b_8;
  *a_7 = D.1543_9;
  a_10 = a_3 + 3;
  b_11 = b_1 + 3;
  D.1543_12 = *b_11;
  *a_10 = D.1543_12;
  a_13 = a_3 + 4;
  b_14 = b_1 + 4;
  D.1543_15 = *b_14;
  *a_13 = D.1543_15;

etc.; I am fairly sure we used to do this.

Zdenek