In some cases pre can create loop carried dependencies spanning multiple iterations aka scalar replacement. This deficiency can be illustrated with attached test-case. After pre for stmt

            DO I = 0,I2
               T1 = 0.5D0 * (U1(I,J,K)    + U1(I+1,J,K))

pre creates loop carried dependence:

  <bb 172>:
...
  pretmp_690 = MEM[(real(kind=8)[0:] *)pretmp_675][pretmp_689];
...
  <bb 107>:
  # i_1 = PHI <0(172), i_437(175)>
  # prephitmp_691 = PHI <pretmp_690(172), _440(175)>


Note that in this particular test-case we have arrays with unknown stride1. If we have arrays with stride1 == 1 such transformation does not happen as for the following simple test-case which is successfully vectorized:

	subroutine bar(a,b,c,d,n, m)
	integer n, m
	real*8 a(n,*), b(n,*), c(n,*), d(n,*)
	do j=1,m
	do i=1,m
	x1 = 0.5 * (a(i,j) + a(i+1,j))
	x2 = 0.5 * (b(i,j) + b(i+1,j))
	x3 = 0.5 * (c(i,j) + c(i+1,j))
	d(i,j) = (x1 + x2 + x3) / 3.0
	enddo
	enddo
	end