http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57396
Bug ID: 57396
Summary: Wrong code with -fpredictive-commoning in Fortran
double-loop
Product: gcc
Version: 4.9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: bugs at stellardeath dot org
Created attachment 30182
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=30182&action=edit
Small test case
The following example program produces incorrect output when compiled with -O3,
but remains correct with -O3 -fno-predictive-commining:
> cat test.f90
module testmod
implicit none
contains
subroutine foo(n)
integer, intent(in) :: n
real :: r(0:n,-n:n), a(0:n,-n:n), dj
integer :: k, j
! initialize with some dummy values
do j = -n, n
a(:, j) = j
r(:,j) = j + 1
end do
! here be dragons
do k = 0, n
dj = r(k, k - 2) * a(k, k - 2)
r(k,k) = a(k, k - 1) * dj
enddo
print *, r(0,0)
end subroutine
end module
program test
use testmod
implicit none
call foo(5)
end program
> gfortran -O3 test.f90
> ./a.out
-3.00000000
>
> gfortran -O3 -fno-predictive-commoning test.f90
> ./a.out
-2.00000000
>
This only happens with gfortran 4.8, with 4.7.2 it produces the correct output
(-2.0). My specific version is:
> gfortran --version
GNU Fortran (GCC) 4.9.0 20130517 (experimental)
Copyright (C) 2013 Free Software Foundation, Inc.
GNU Fortran comes with NO WARRANTY, to the extent permitted by law.
You may redistribute copies of GNU Fortran
under the terms of the GNU General Public License.
For more information about these matters, see the file named COPYING
