Array Vs pointer and loop parameter optimization

Hi,

I have an optimization question regarding the following code, that does a 'findloc',  It appears that for ifort the do loop parameter change the optimization, and passing an pointer instead of the array lead to better optimization too.  For ifort, the loop parameters degrades the performances, and not in gfortran. Both gives better performances with a pointer than an array with the target attribute, but removing the target attribute gfortran gives the same results as the pointer and still no effect of the loop parameters, where ifort is unaffected by the target attributes.  I don't know if there is an optimization issue here, but I'd appreciate a discussion on this.  The results are obtained with -O3 -xHost.

Thanks.

Time      |   array, 1:size     |  array st:end:step         | pointer 1:size       | pt st:end:step  |
  ifort   |      12.56          |        20.52               |   4.26               |     18.36       |
gfortran  |       20.34         |        20.56               |          13.7        |     13.7        |


Without the target on the array :

Time      |   array, 1:size  |  array st:end:step |
  ifort   |      12.64          |        20.59               |
gfortran  |       13.74         |        13.74               |

program foo
implicit none
integer,dimension(:),allocatable,target :: array
integer :: i,val,k,tmp(1:2)
integer,dimension(:),pointer :: pt_marker
double precision :: t0,t1
allocate(array(20000000))
do i=1,20000000
  array(i)=i
end do
tmp=[1,20000000]
pt_marker=>array(tmp(1):tmp(2))
call cpu_time(t0)
do i=1,100000
  val=9*i
  call t(pt_marker,val,k,.false.)
end do
call cpu_time(t1)
print *,'time pt',t1-t0
call cpu_time(t0)
do i=1,100000
  val=9*i
  call t(array,val,k,.false.)
end do
call cpu_time(t1)
print *,'time array',t1-t0
print *,val,k
deallocate(array)
contains
subroutine t(array,value,j,bac2) ! result(j)
integer(kind=4),dimension(:) :: array
logical,optional :: bac2
logical :: bac
integer(kind=4) :: i,value,j,st,en,step
bac=.false.
if(present(bac2)) bac=bac2
if(bac) then
        en=1
        st=size(array,1)
        step=-1
else
        st=1
        en=size(array,1)
        step=1
end if
do i=st,en,step !1,size(array,1)
!do i=1,size(array,1)
  if(array(i) .eq. value) then
        j=i
        exit
  end if
end do
end subroutine


end program