Hello Marc,
Please see my response below.
Thanks for looking at my patch!
Sincerely,
Balaji V. Iyer.
>-----Original Message-----
>From: Marc Glisse [mailto:marc.gli...@inria.fr]
>Sent: Thursday, September 06, 2012 2:06 AM
>To: Gabriel Dos Reis
>Cc: Iyer, Balaji V; gcc-patches@gcc.gnu.org; Aldy Hernandez
>(al...@redhat.com); Jeff Law; r...@redhat.com
>Subject: Re: [PATCH] Merging Cilk Plus into Trunk (Patch 1 of approximately 22)
>
>On Wed, 5 Sep 2012, Gabriel Dos Reis wrote:
>
>> On Wed, Sep 5, 2012 at 5:09 PM, Iyer, Balaji V <balaji.v.i...@intel.com>
>> wrote:
>>> 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]);
>
>I assume X, Y and Z are __restrict pointers (or something the compiler can
>detect
>doesn't alias).
Yes, the compiler must detect that.
>
>> 2. Considering this example, won't you get the same behaviour
>> if my_func was declared with "pure" attribute? If not, why?
>
>AFAIU, my_func is defined in a separate library and because of the attribute on
>the definition, it will actually export overloads:
>int myfunc(int,int);
>v2si myfunc(v2si,v2si);
>v4si myfunc(v4si,v4si);
>etc (where does it stop? seems problematic if the library is compiled for
>sse4 and I then compile and link an avx program)
The user can provide at most 1 vector length and the compiler will map it to
appropriate vector value. If the user omits the vectorlength clause then the
compiler picks a vectorlength based on the architecture's vector units and the
data width. So, it will stop at 2 (1 scalar and 1 vector) :-).
>
>(hopefully with implementations more clever than breaking the vectors into
>pieces and calling the basic myfunc on each)
>
>The attribute on the declaration then lets gcc's vectorizer know it can call
>those
>overloads.
>
>With suitable pure/const attribute you could unroll the loop a bit and reorder
>the
>calls to myfunc, but without myfunc's body, you couldn't do as much.
>
>Note that this is my guess from reading the example and completely ignoring the
>patch, it could be miles from the truth, and it needs better explanation (the
>doc
>patch is coming later in the series IIRC).
>
>--
>Marc Glisse
