This small example exposes an error with the executable code for a MATMUL reference when one of its actual arguments is a multirank coindexed object. The example compares the result of that MATMUL with the value computed by first assigning the coindexed object to a local array and passing it instead. The error occurs for both ifort 2021.9 and ifx 2023.1
Judging from the output, I suspect that in the first case MATMUL is being handed the transpose
of the matrix by mistake (e.g., by mistaking the column-major data for row-major)
$ ifort -coarray -coarray-num-images=2 bug.f90
$ ./a.out
error on image 1
c1= 2.000000 4.000000 6.000000 8.000000
c2= 4.000000 2.000000 8.000000 6.000000
real :: a(2,2), b(2,2)[*], c1(2,2), c2(2,2), tmp(2,2)
a = reshape([0,1,1,0], shape=[2,2])
b = this_image()*reshape([1,2,3,4], shape=[2,2])
sync all
if (this_image() < num_images()) then
c1 = matmul(a, b(:,:)[this_image()+1]) ! EXCHANGES ROWS OF B
tmp = b(:,:)[this_image()+1]
c2 = matmul(a, tmp)
if (any(c1 /= c2)) then
print *, 'error on image', this_image()
print *, 'c1=', c1
print *, 'c2=', c2
error stop
end if
end if
end
