On Wed, Sep 5, 2012 at 5:09 PM, Iyer, Balaji V <balaji.v.i...@intel.com> wrote:
> Hello Everyone,
> Attached, please find the 1st of ~22 patches that implements Cilk
> Plus. This patch will implement Elemental Functions into the C compiler.
> Please check it in to the trunk if it looks OK.
>
> Below, I will give you a small example about what elemental function
> is and how it can be useful. Details about elemental function can be found in
> the following link
> (http://software.intel.com/en-us/articles/elemental-functions-writing-data-parallel-code-in-cc-using-intel-cilk-plus)
>
> Let's say we have two for loops like this:
>
> int my_func (int x, int y);
>
> For (ii = 0; ii < 10000; ii++)
> X[ii] = my_func (Y[ii], Z[ii]);
>
> For (jj = 1; jj < 10000; jj++) {
> A[jj] = my_func (B[ii], A[jj-1]) + A[jj-1];
>
>
> Assume that my_func's body is not visible during this compilation (e.g it is
> in some library).
>
> If a vectorized version for my_func is available, then the first for loop can
> be vectorized. However, even if such a version of my_func is available, the
> 2nd for loop cannot be vectorized. It would be beneficial if there is a
> vectorized version and a scalar version of my_func. This is where an
> elemental function comes to play. If we annotate *both* the function
> declaration and the function with the following attribute, the compiler will
> create a vector and scalar version of the function.
>
> __attribute__((vector)) my_func (int x, int y);
>
> __attribute__((vector)) my_func (int x, int y)
> {
> ... /* Body of the function. */
> }
1. You should consider a different name for the attribute.
2. Considering this example, won't you get the same behaviour
if my_func was declared with "pure" attribute? If not, why?
-- Gaby
