Re: [PATCH] Merging Cilk Plus into Trunk (Patch 1 of approximately 22)

[Gabriel Dos Reis <gdr at integrable-solutions dot net>]

On Wed, Sep 5, 2012 at 5:09 PM, Iyer, Balaji V <balaji.v.iyer@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