Dear experts,
sorry if this is a stupid question, but I was playing with offloading for
the nvptx-none target and found different behavior between e.g. gfortran-10
on OpenSuse and the Nvidia compiler (nvfortran) for the attached code.
With "nvfortran -mp=multicore offload-test.f90" the code prints:
2.000000 2000.000
s1: 1001000.
s2: 1001000.
With "/usr/bin/gfortran-10 -fopenmp -foffload=nvptx-none offload-test.f90":
2.00000000 2000.00000
s1: 1001000.00
s2: 0.00000000
The core difference between the evaluations s1 and s2 is:
s1:
!$omp target data map(a,s)
!$omp target teams reduction(+:s) map(s)
do i = 1, n
s = s + a(i)
end do
!$omp end target teams
!$omp end target data
s2:
!$omp target data map(a,s)
!$omp target teams reduction(+:s)
do i = 1, n
s = s + a(i)
end do
!$omp end target teams
!$omp end target data
I was assuming that the map clause in the reduction should not be necessary,
but the result seems to tell me that either I am wrong (and gfortran is right),
or nvfortran is wrong.
With OpenACC this seems to be different; at least a simple example I tried
with the reduction within an !$acc data ... !$acc end data did not show
unexpected behavior.
Can anybody tell me that I am wrong (and point me to the right place in the
OpenMP standard), or should I open a PR?
Thanks
Harald
program p5
implicit none
integer :: i, n = 1000
real :: s
real, allocatable :: a(:)
allocate (a(n))
do i = 1, n
a(i) = 2*i
end do
print *, a(1),a(n)
call s1 ()
print *, "s1:", s
call s2 ()
print *, "s2:", s
contains
subroutine s1 ()
integer :: i
s = 0.
!$omp target data map(a,s)
!$omp target teams reduction(+:s) map(s)
do i = 1, n
s = s + a(i)
end do
!$omp end target teams
!$omp end target data
end subroutine s1
!----------------
subroutine s2 ()
integer :: i
s = 0.
!$omp target data map(a,s)
!$omp target teams reduction(+:s)
do i = 1, n
s = s + a(i)
end do
!$omp end target teams
!$omp end target data
end subroutine s2
end program
