Re: Vectorizing HIRLAM 2: One out of the "unhandled data-ref" garbage bin :-)

[Andrew Pinski <pinskia at physics dot uc dot edu>]

On Oct 21, 2005, at 9:19 AM, Toon Moene wrote:

> L.S.,
>
> This code:
>
>       SUBROUTINE S(A, B, N)
>       DIMENSION A(N), B(N)
>       READ*,Z,B
>       DO I = 1, N
>          A(I) = Z * B(I)
>       ENDDO
>       PRINT*,A
>       END
>
> when compiled thusly:

The problem here is not really related to the vectorizer but the
tree aliasing code.  The loop looks like this at -O2 in the tree dumps:
  # z_49 = PHI <z_86(1), z_124(3)>;
  # i_1 = PHI <1(1), i_48(3)>;
<L8>:;
  D.982_41 = i_1 + -1;
  #   VUSE <z_49>;
  D.983_43 = (*b_20)[D.982_41];
  #   VUSE <z_49>;
  z.4_45 = z;
  D.985_46 = D.983_43 * z.4_45;
  #   z_124 = V_MAY_DEF <z_49>;
  (*a_36)[D.982_41] = D.985_46;
  i_48 = i_1 + 1;
  if (i_1 == D.972_25) goto <L4>; else goto <L13>;

Notice how the statement which does "A(I) =" has a V_MAY_DEF of z.  If 
we
recorded it correctly,  A and B would aliasing nothing as they are 
arguments
passed in.

-- Pinski