From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-420989-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 28124 invoked by alias); 26 Apr 2013 06:52:17 -0000
Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm
Precedence: bulk
List-Id: <gcc-bugs.gcc.gnu.org>
List-Archive: <http://gcc.gnu.org/ml/gcc-bugs/>
List-Post: <mailto:gcc-bugs@gcc.gnu.org>
List-Help: <mailto:gcc-bugs-help@gcc.gnu.org>
Sender: gcc-bugs-owner@gcc.gnu.org
Received: (qmail 28075 invoked by uid 48); 26 Apr 2013 06:52:14 -0000
From: "Joost.VandeVondele at mat dot ethz.ch" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/57071] Optimize  (-1)**k  to 1 - 2 * mod(K, 2)
Date: Fri, 26 Apr 2013 06:52:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: fortran
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: normal
X-Bugzilla-Who: Joost.VandeVondele at mat dot ethz.ch
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Changed-Fields: CC
Message-ID: <bug-57071-4-AsvM6OPV0A@http.gcc.gnu.org/bugzilla/>
In-Reply-To: <bug-57071-4@http.gcc.gnu.org/bugzilla/>
References: <bug-57071-4@http.gcc.gnu.org/bugzilla/>
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
Content-Type: text/plain; charset="UTF-8"
MIME-Version: 1.0
X-SW-Source: 2013-04/txt/msg02134.txt.bz2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57071

Joost VandeVondele <Joost.VandeVondele at mat dot ethz.ch> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |Joost.VandeVondele at mat
                   |                            |dot ethz.ch

--- Comment #2 from Joost VandeVondele <Joost.VandeVondele at mat dot ethz.ch> 2013-04-26 06:52:13 UTC ---
indeed, very common to write this.. however, this is even more common in a loop

DO i=0,N
   y=y+(-1)**i * x**i
ENDDO

so there you really would like to have this converted to some form that uses
...
DO i=..
    tmp_s=-tmp_s  
    tmp_x=tmp_x*x
    y=y+tmp_s*tmp_x
ENDDO

I'm not sure how the different forms behave in this respect.