[Bug tree-optimization/33113] Failing to represent the stride (with array) of a dataref when it is not a constant

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

------- Comment #1 from rakdver at gcc dot gnu dot org  2007-08-19 20:08 -------
(In reply to comment #0)
> In the following testcase:
> 
> subroutine sub(aa,bb,n,m)
>   implicit none
>   integer, intent(in) :: n,m
>   real, intent(inout) :: aa(n,m)
>   real, intent(in)    :: bb(n,m)
>   integer :: i,j
>  do i = 1,m
>     do j= 2,n
>       aa(i,j)= aa(i,j-1)+bb(i,j-1)
>     enddo
>   enddo
> end subroutine
> end
> 
> The stride of the accesses in the inner-loop is a parameter (m is not a
> compile-time known constant). As a result the data dataref analyzer reports:
> "
> failed: evolution of offset is not affine
> ...
>         base_address:
>         offset from base address:
>         constant offset from base address:
>         step:
>         aligned to:
>         base_object: (*aa_54(D))[0]
>         symbol tag: SMT.25
> "
> 
> Any chance that the dataref analysis can return an (invariant) expression in
> "step", so that further analysis could continue? (for example, the access in
> the outer-loop is consecutive, so if we had an expression to represent the
> inner-loop stride, we could vectorize the outer-loop).

Making us return symbolic stride would not be hard.  The problem is that data
dependence analysis would fail anyway, since we cannot tell whether n is zero.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33113