RE: Question about omp-low.c

["Iyer, Balaji V" <balaji dot v dot iyer at intel dot com>]

> -----Original Message-----
> From: Jakub Jelinek [mailto:jakub@redhat.com]
> Sent: Wednesday, December 18, 2013 1:58 AM
> To: Iyer, Balaji V
> Cc: Jason Merrill (jason@redhat.com); 'gcc@gcc.gnu.org'
> Subject: Re: Question about omp-low.c
> 
> On Wed, Dec 18, 2013 at 04:46:40AM +0000, Iyer, Balaji V wrote:
> > 	I have a question regarding the parallel for implementation. I am
> implementing _Cilk_for based on the routines in omp-low.c and I would like
> to create a child function but would like to move the items that
> gimplify_omp_for inserts in for_pre_body in the top-level function. I need to
> do this because in _Cilk_for, we insert the body of the function into a child
> function and then we call a builtin CilkPlus function called
> __cilkrts_cilk_for_64 and pass in the child function's name, data pointer,
> loop-count and grain.
> >
> > 	The loop count computation gets to be an issue in C++ when we use
> iterator.
> >
> > For example, if we have something like this:
> > Vector <int> array;
> > For (vector<int>::iterator iter =  array.begin(); iter != array.end
> > (); iter++)
> 
> OpenMP also supports C++ iterators, so I don't see why you don't follow
> that.
> The iterators are lowered already by the C++ FE, what the middle-end sees is
> an integral iterator.  Just look at one of the several
> libgomp/testsuite/libgomp.c++/for-* testcases.
> 

I think we are talking two different things or I am not understanding you. I am using OMP's iterator handling mechanism, but the question I have is about the pre-body. It is pre-gimplifying the condition and the initial value and storing it in pre_body. The prebody is then pushed into the child function. I want the pre-body to be pushed into main function. Is it possible for me to do that?


> By following what we do for OpenMP here, I'd hope you can get rid of the
> loop_count you've added to the gimple structure, what is grain, is that
> specific to each of the collapsed trees, or does Cilk+ support only collapse(1),
> and if so or if it is global for the _Cilk_for and not for each iterator, just add a
> clause for it instead.
> 
Grain is a value that user specifies that is passed directly to the runtime that tells it how to divide the work (different from step-size, please see cilk_for_grain.c in my patch). It is very Cilk runtime specific. Loop-count I need it because I need it to pass into the cilk runtime function call (along with grain) to tell the loop count. I calculate this value way ahead before the gimplification of the condition, intial value and the step-size. Now, if I can some-how find a way to make GCC move the pre-body to the parent function instead of the child function, I can try to eliminate this field from the structure.

> 	Jakub