[patch, fortran] Create temporary variables for matmul

[Jerry DeLisle]

On 05/08/2017 11:19 AM, Thomas Koenig wrote:
> Hi Jerry,
> 
>> OK. Could you post some before and after performance results. Intuitively this
>> makes sense to do, but empirically does it pay off.
> 
> Thanks for the reviews!
> 
> Here is a quick&dirty benchmark, with the patch, with
> -finline-matmul-limit=0 used to inhibit matmul inlining
> (to simulate the behavior without).
> 
> $ cat bench.f90
> program main
>   implicit none
>   integer, parameter :: dp = selected_real_kind(15)
>   integer, parameter :: n1 = 10000
>   integer, parameter :: n2 = 1000
>   integer :: i,j,ind
>   real(dp), dimension(3,3*n2) :: a, b
>   real(dp), dimension(3,3) :: c
>   real(dp) :: s
>   s = 0
>   do i=1,n1
>      call random_number(a)
>      call random_number(b)
>      do j=1,n2
>         ind = 3*j-2
>         s = s + sum(matmul(a(:,ind:ind+2),b(:,ind:ind+2)))
>      end do
>   end do
>   print *,s
> end program main
> $ gfortran -Ofast  -finline-matmul-limit=0 bench.f90 && time ./a.out
>    67501526.340284660
> 
> real    0m4,856s
> user    0m4,852s
> sys     0m0,000s
> $ gfortran -Ofast bench.f90 && time ./a.out
>    67502996.159002081
> 
> real    0m2,583s
> user    0m2,580s
> sys     0m0,000s
> 
> Also interesting, a version which actually uses allocatable variables
> as temporaries because we don't to value propagation in the front end:
> 
> program main
>   implicit none
>   integer, parameter :: dp = selected_real_kind(15)
>   integer, parameter :: n1 = 10000
>   integer, parameter :: n2 = 1000
>   integer :: i,j,ind, ind2
>   real(dp), dimension(3,3*n2) :: a, b
>   real(dp), dimension(3,3) :: c
>   real(dp) :: s
>   s = 0
>   do i=1,n1
>      call random_number(a)
>      call random_number(b)
>      do j=1,n2
>         ind = 3*j-2
>         ind2 = ind + 2
>         s = s + sum(matmul(a(:,ind:ind2),b(:,ind:ind2)))
>      end do
>   end do
>   print *,s
> end program main
> $ gfortran -Ofast  -finline-matmul-limit=0 bench2.f90 && time ./a.out
>    67500364.375209823
> 
> real    0m5,480s
> user    0m5,472s
> sys     0m0,000s
> $ gfortran -Ofast bench2.f90 && time ./a.out
>    67498343.869140804
> 
> real    0m3,475s
> user    0m3,476s
> sys     0m0,000s
> 
> Regards
> 
>     Thomas
> 


Very Nice, thanks much.

Jerry