From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugs-return-351877-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org>
Received: (qmail 23815 invoked by alias); 30 Mar 2011 12:16:10 -0000
Received: (qmail 23802 invoked by uid 22791); 30 Mar 2011 12:16:06 -0000
X-SWARE-Spam-Status: No, hits=-2.9 required=5.0	tests=ALL_TRUSTED,AWL,BAYES_00
X-Spam-Check-By: sourceware.org
Received: from localhost (HELO gcc.gnu.org) (127.0.0.1)    by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Wed, 30 Mar 2011 12:16:02 +0000
From: "burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug fortran/48363] New: Recursion not converted into a loop
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
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: burnus 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-Changed-Fields:
Message-ID: <bug-48363-4@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
Date: Wed, 30 Mar 2011 12:40:00 -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
X-SW-Source: 2011-03/txt/msg03190.txt.bz2

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48363

           Summary: Recursion not converted into a loop
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: burnus@gcc.gnu.org


For the following Fortran program, the recursion could be replaced by a loop.
That's what happening for the related C program, but for the Fortran program
the recursion remains. (Tried with -O3.)

(I guess the I/O statement (_gfortran_st_write* and _gfortran_transfer_*_write)
confuse the ME, but I do not see why that should prevent the loop
transformation. Hints how to modify the FE to help the ME are welcome, too.)

! Fortran version
call x (1)
contains
  recursive subroutine x (i)
    use iso_fortran_env
    integer, value :: i
    if (mod (i, 1000000) == 0) write (error_unit,'(a,i0)')'i=', i
    call x (i+1)
  end subroutine x
end


/* C version */
#include <stdio.h>
static void
x (int i) {
  if (!(i % 1000000))
    fprintf(stderr, "i=%d\n", i);
  x(i + 1);
}
int main () {
  x (1);
}