-----Original Message-----
From: Richard Biener [mailto:richard.guent...@gmail.com]
Sent: Friday, August 21, 2015 2:03 PM
To: Ajit Kumar Agarwal
Cc: Jeff Law; GCC Patches; gcc@gcc.gnu.org; Vinod Kathail; Shail Aditya Gupta;
Vidhumouli Hunsigida; Nagaraju Mekala
Subject: Re: [RFC]: Vectorization cost benefit changes.
On Fri, Aug 21, 2015 at 7:18 AM, Ajit Kumar Agarwal
<ajit.kumar.agar...@xilinx.com> wrote:
> All:
>
> I have done the vectorization cost changes as given below. I have considered
> only the cost associated with the inner instead of outside.
> The consideration of inside scalar and vector cost is done as the inner cost
> are the most cost effective than the outside cost.
>>I think you are confused about what the variables cost are associated to.
>>You are changing a place that computes also the cost for
>>non-outer-loop->>vectorization so your patch is clearly not applicable.
>>vec_outside_cost is the cost of setting up invariants for example.
>>All costs apply to the "outer" loop - if there is a nested loop inside that
>>loop its costs are folded into the "outer" loop cost already at this stage.
>>So I think your analysis is simply wrong and thus your patch.
>>You need to find another place to fix inner loop cost.
Thanks for your valuable suggestions and feedback. I will certainly look into
it.
Thanks & Regards
Ajit
Richard.
> min_profitable_iters = ((scalar_single_iter_cost
> - vec_inside_cost) *vf);
>
> The Scalar_single_iter_cost consider the hardcoded value 50 which is
> used for most of the targets and the scalar cost is multiplied With
> 50. This scalar cost is subtracted with vector cost and as the scalar cost is
> increased the chances of vectorization is more with same Vectorization factor
> and more loops will be vectorized.
>
> I have not changed the iteration count which is hardcoded with 50 and
> I will do the changes to replace the 50 with the static Estimates of
> iteration count if you agree upon the below changes.
>
> I have ran the SPEC cpu 2000 benchmarks with the below changes for
> i386 targets and the significant gains are achieved with respect To INT and
> FP benchmarks.
>
> Here is the data.
>
> Ratio of vectorization cost changes(FP benchmarks) vs Ratio of without
> vectorization cost changes( FP benchmarks) = 4640.102 vs 4583.379.
> Ratio of vectorization cost changes (INT benchmarks ) vs Ratio of
> without vectorization cost changes( INT benchmarks0 = 3812.883 vs
> 3778.558
>
> Please give your feedback on the below changes for vectorization cost benefit.
>
> diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c index
> 422b883..35d538f 100644
> --- a/gcc/tree-vect-loop.c
> +++ b/gcc/tree-vect-loop.c
> @@ -2987,11 +2987,8 @@ vect_estimate_min_profitable_iters (loop_vec_info
> loop_vinfo,
> min_profitable_iters = 1;
> else
> {
> - min_profitable_iters = ((vec_outside_cost - scalar_outside_cost) *
> vf
> - - vec_inside_cost * peel_iters_prologue
> - - vec_inside_cost * peel_iters_epilogue)
> - / ((scalar_single_iter_cost * vf)
> - - vec_inside_cost);
> + min_profitable_iters = ((scalar_single_iter_cost
> + - vec_inside_cost) *vf);
>
> if ((scalar_single_iter_cost * vf * min_profitable_iters)
> <= (((int) vec_inside_cost * min_profitable_iters)
>
> Thanks & Regards
> Ajit
