-----Original Message----- From: Richard Biener [mailto:richard.guent...@gmail.com] Sent: Monday, August 03, 2015 2:59 PM To: Ajit Kumar Agarwal Cc: Jeff Law; gcc@gcc.gnu.org; Vinod Kathail; Shail Aditya Gupta; Vidhumouli Hunsigida; Nagaraju Mekala Subject: Re: vectorization cost macro TARGET_VECTORIZE_ADD_STMT_COST
On Sun, Aug 2, 2015 at 4:13 PM, Ajit Kumar Agarwal <ajit.kumar.agar...@xilinx.com> wrote: > All: > > The definition of the following macro that determine the statement cost that > adds to vectorization cost. > > #define TARGET_VECTORIZE_ADD_STMT_COST. > > In the implementation of the above macro the following is done for many > vectorization supported architectures like i386, ARM. > > if (where == vect_body && stmt_info && stmt_in_inner_loop_p (stmt_info)) > count *= 50; /* FIXME. */ > > I have the following questions. > > 1. Why the multiplication factor of 50 is choosen? >>It's a wild guess. See >>tree-vect-loop.c:vect_get_single_scalar_iteration_cost. > 2. The comment mentions that the inner loop relative to the loop being > vectorized is added more weight. If more weight is added to the inner > loop for the loop being vectorized, the chances of vectorizing the inner loop > decreases. Why the inner loop cost is increased with relative to the loop > being vectorized? >>In fact adding more weight to the inner loop increases the chance of >>vectorizing it (if vectorizing the inner loop is profitable). >>Both scalar and vector cost get biased by a factor of 50 (we assume 50 >>iterations of the inner loop for one iteration of the outer loop), so a >>non-profitable >>vectorization in the outer loop can be offsetted by >>profitable inner loop vectorization. >>Yes, '50' can be improved if we actually know the iteration count of the >>inner loop or if we have profile-feedback. Thanks for the valuable information and suggestions. Thanks & Regards Ajit Richard. > Thanks & Regards > Ajit
