https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94578
Bug ID: 94578
Summary: Incorrect assignment of RESHAPE() result to a Fortran
pointer
Product: gcc
Version: 8.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: howisjw at hotmail dot com
Target Milestone: ---
The other day, I tried to compile a large Fortran code using gcc 8.3.0. In the
code the reshape function is used and the resulting is assigned to a Fortran
pointer. The results are not what I expected to be. I am not sure if it a bug
or if I do something which is not according to the latest Fortran standard. I
created a simple program (see below) to demostrate the problem.
If I use the tmp array, like
tmp = reshape(source=array2d, shape=shape(array1d))
array1d = tmp
it all works. I have the impression that under-the-hood the result of the
reshape function is stored in array1d using a some kind of memory copy. This
works fine if array1d is contiguous in memory. However, if array1d is a Fortran
pointer (my case) do not have to be contiguous in memory.
program bug_reshape
implicit none
type :: value_and_derivatives
real(kind=8) :: x,s,t,st,ss,tt
logical :: up_to_date
end type value_and_derivatives
type :: tsolution
type(value_and_derivatives) :: x, y
end type tsolution
type(tsolution), dimension(3*4), target :: solution
! Locals
integer :: i, j
type(value_and_derivatives), dimension(3,4) :: array2d
type(value_and_derivatives), dimension(:), pointer :: array1d
type(value_and_derivatives), dimension(3*4) :: tmp
array1d => solution%x
do j=1,4
do i=1,3
array2d(i,j) = value_and_derivatives(i*j, i, j, 0.1*i*j, 0.1*i, 0.1*j,
.true.)
end do
end do
array1d = reshape(source=array2d, shape=shape(array1d))
print*,"--- array2d ---"
do j=1,4
do i=1,3
print '(2(i1,1x),6(e15.7,1x),l)',i,j,array2d(i,j)
end do
end do
print*,"--- array1d ---"
do i=1,12
print '(i1,1x,6(e15.7,1x),l)',i,array1d(i)
end do
end program bug_reshape
Jan-Willem
