Hi all,

looking for some feedback on this, one thing I would like to draw attention to is the fact that this pattern requires 2 separate dependent reductions in the epilogue.
The accumulator vector for the maximum/minimum elements can be reduced to a scalar result trivially with a min/max, but getting the index from accumulator 
vector of indices is more complex and requires using the position of the maximum/minimum scalar result value within the accumulator vector to create a mask.

The given solution works but it's slightly messy. vect_create_epilogue_for_reduction creates the epilogue for one vectorized scalar stmt at a time. This modification makes one
invocation create the epilogue for both related stmts and marks the other as 'done'. Alternate suggestions are welcome.

Joel

[vect] Support min/max + index pattern

Add the capability to vect-loop to support the following pattern.

for (int i = 0; i < n; i ++)
{
    if (data[i] < best)
    {
        best = data[i];
        best_i = i;
    }
}

gcc/ChangeLog:

	* tree-vect-loop.c (vect_reassociating_reduction_simple_p): New                                                                                          
	function.                                                                                                                                                        
	(vect_recog_minmax_index_pattern): New function.                                                                                                             
	(vect_is_simple_reduction): Add multi_use_reduction case.                                                                                                    
	(vect_create_epilog_for_reduction): Add minmax+index epilogue handling.