dash::copy copies the wrong values in global to local

[bertwesarg]

Extending the example in #653 gives now the wrong values in the target matrix:

#include <iostream>

#include <libdash.h>

int
main(int ac, char *av[])
{
    using TeamSpecT = dash::TeamSpec<2>;
    using MatrixT = dash::NArray<double, 2>;
    using PatternT = typename MatrixT::pattern_type;
    using SizeSpecT = dash::SizeSpec<2>;
    using DistSpecT = dash::DistributionSpec<2>;

    dash::init(&ac, &av);

    auto size_spec = SizeSpecT(16, 16);
    auto dist_spec = DistSpecT(dash::BLOCKED, dash::BLOCKED);

    auto& team_all = dash::Team::All();
    TeamSpecT team_all_spec(team_all.size(), 1);
    team_all_spec.balance_extents();
    MatrixT grid_more(size_spec, dist_spec, team_all, team_all_spec);
    dash::fill(grid_more.begin(), grid_more.end(), (double)team_all.myid());
    team_all.barrier();

    if (team_all.myid() == 0) {
        auto gextents = grid_more.extents();
        for (    uint32_t y = 0; y < gextents[0]; ++y) {
            std::cout << "[" << y << "] := {";
            for (uint32_t x = 0; x < gextents[1]; ++x)
                std::cout << " " << (double)grid_more[y][x];
            std::cout << "}\n";
        }
    }

    dash::Team& team_fewer= team_all.split(4);
    team_all.barrier();
    if (!team_fewer.is_null() && 0 == team_fewer.position()) {
        TeamSpecT team_fewer_spec(team_fewer.size(), 1);
        team_fewer_spec.balance_extents();

        MatrixT grid_fewer(size_spec, dist_spec, team_fewer, team_fewer_spec);
        dash::fill(grid_fewer.begin(), grid_fewer.end(), -1.0);

        auto lextents= grid_fewer.pattern().local_extents();

        for (uint32_t y = 0; y < lextents[0]; ++y) {
            auto gcorner_fewer = grid_fewer.pattern().global({y, 0});
            auto gbegin = grid_more.begin() + grid_more.pattern().global_at(gcorner_fewer);

            auto loffset = grid_fewer.pattern().local_at({y, 0});
            dash::copy(gbegin, gbegin + lextents[1],
                       grid_fewer.lbegin() + loffset);
        }
        team_fewer.barrier();

        if (team_fewer.myid() == 0) {
            auto gextents = grid_fewer.extents();
            for (    uint32_t y = 0; y < gextents[0]; ++y) {
                std::cout << "[" << y << "] := {";
                for (uint32_t x = 0; x < gextents[1]; ++x)
                    std::cout << " " << (double)grid_fewer[y][x];
                std::cout << "}\n";
            }
        }

        team_fewer.barrier();
    }
    team_all.barrier();

    dash::finalize();

    return 0;
}

The source matrix looks like this:

[0] := { 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1}
[1] := { 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1}
[2] := { 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1}
[3] := { 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1}
[4] := { 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1}
[5] := { 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1}
[6] := { 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1}
[7] := { 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1}
[8] := { 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3}
[9] := { 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3}
[10] := { 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3}
[11] := { 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3}
[12] := { 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3}
[13] := { 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3}
[14] := { 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3}
[15] := { 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3}

But the result matrix looks like this:

[0] := { 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1}
[1] := { 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1}
[2] := { 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1}
[3] := { 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1}
[4] := { 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1}
[5] := { 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1}
[6] := { 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1}
[7] := { 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1}
[8] := { 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2}
[9] := { 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2}
[10] := { 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2}
[11] := { 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2}
[12] := { 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2}
[13] := { 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2}
[14] := { 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2}
[15] := { 2 2 2 2 2 2 2 2 3 3 3 3 3 3 3 3}

[devreal]

Analysis: The current implementation of dash::copy (dash::copy_impl) does not observe the iteration space of the iterator but instead uses the local iteration space(s), starting from the first unit in the range passed to copy. That of course is not how dash::copy should operate.

Working on a fix.