[Bug fortran/46331] New: Compilation time long with simple function in array constructor

["jvdelisle at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46331

           Summary: Compilation time long with simple function in array
                    constructor
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: jvdelisle@gcc.gnu.org


program foo
    implicit none

    Integer :: i
    Integer, Parameter :: N = 10**4
    Real, Dimension(N) :: xs

    ! Random points
    xs = (/ (rand(0), i=1,N) /)
    print *, xs
end program

The time spent in the FE is not bad, but the resulting translation is horrible
and it wreaks havoc with the middle end and down the road.

I think we should not expand this constructor at all, especially since 'i' is
not used in the function expression. However, rand(0) needs to be called once
for each element.  That means it needs to be translated into:

do i-1,N
  xs = rand(0)
end do

In otherwords, I think another special case in gfc_trans_assignment.  There are
other special cases already there.