MinMax Reducer with tagged operator doesn't compile

[crtrott]

Reproducer:

#include<Kokkos_Core.hpp>

struct TagMin {};

typedef Kokkos::Experimental::MinMax<double>::value_type value_type;

struct functor {
  Kokkos::View<double*> a;

  functor(Kokkos::View<double*> a_):a(a_) {}

  KOKKOS_INLINE_FUNCTION
  void operator() (const TagMin, const int& i, value_type& val) const {
    if(a(i) < val.min_val) val.min_val = a(i);
    if(a(i) > val.max_val) val.max_val = a(i);
  }
};

int main(int argc, char* argv[]) {
  Kokkos::initialize(argc,argv);

  Kokkos::View<double*> a("A", 100);
  Kokkos::deep_copy(a,5.0);
  a(5) = 3.0;
  a(7) = 6.0;

  value_type result;
  Kokkos::parallel_reduce(Kokkos::RangePolicy<TagMin>(0,100), functor(a), Kokkos::Experimental::MinMax<double>(result));

  printf("Result: %lf %lf\n",result.min_val,result.max_val);

  Kokkos::finalize();
}

Error message:

g++ -I./ -I/home/crtrott/Kokkos/kokkos/core/src -I/home/crtrott/Kokkos/kokkos/containers/src -I/home/crtrott/Kokkos/kokkos/algorithms/src  --std=c++11 -mavx -fopenmp -O3 -g  -c main.cpp
In file included from /home/crtrott/Kokkos/kokkos/core/src/Kokkos_Parallel.hpp:63:0,
                 from /home/crtrott/Kokkos/kokkos/core/src/Kokkos_OpenMP.hpp:61,
                 from /home/crtrott/Kokkos/kokkos/core/src/Kokkos_Core.hpp:57,
                 from main.cpp:1:
/home/crtrott/Kokkos/kokkos/core/src/impl/Kokkos_FunctorAdapter.hpp: In instantiation of ‘static void Kokkos::Impl::FunctorValueJoin<FunctorType, ArgTag, T&, Enable>::join(const FunctorType&, volatile void*, const volatile void*) [with FunctorType = Kokkos::Experimental::MinMax<double>; ArgTag = TagMin; T = Kokkos::Experimental::MinMaxScalar<double>; Enable = void]’:
/home/crtrott/Kokkos/kokkos/core/src/OpenMP/Kokkos_OpenMP_Parallel.hpp:391:24:   required from ‘void Kokkos::Impl::ParallelReduce<FunctorType, Kokkos::RangePolicy<Traits ...>, ReducerType, Kokkos::OpenMP>::execute() const [with FunctorType = functor; ReducerType = Kokkos::Experimental::MinMax<double>; Traits = {TagMin}]’
/home/crtrott/Kokkos/kokkos/core/src/Kokkos_Parallel_Reduce.hpp:895:11:   required from ‘static void Kokkos::Impl::ParallelReduceAdaptor<PolicyType, FunctorType, ReturnType>::execute(const string&, const PolicyType&, const FunctorType&, ReturnType&) [with PolicyType = Kokkos::RangePolicy<TagMin>; FunctorType = functor; ReturnType = Kokkos::Experimental::MinMax<double>; std::__cxx11::string = std::__cxx11::basic_string<char>]’
/home/crtrott/Kokkos/kokkos/core/src/Kokkos_Parallel_Reduce.hpp:1258:74:   required from ‘void Kokkos::parallel_reduce(const PolicyType&, const FunctorType&, const ReturnType&, typename Kokkos::Impl::enable_if<Kokkos::is_execution_policy<PolicyType>::value>::type*) [with PolicyType = Kokkos::RangePolicy<TagMin>; FunctorType = functor; ReturnType = Kokkos::Experimental::MinMax<double>; typename Kokkos::Impl::enable_if<Kokkos::is_execution_policy<PolicyType>::value>::type = void]’
main.cpp:28:119:   required from here
/home/crtrott/Kokkos/kokkos/core/src/impl/Kokkos_FunctorAdapter.hpp:641:27: error: no match for ‘operator+=’ (operand types are ‘volatile Kokkos::Experimental::MinMaxScalar<double>’ and ‘const volatile Kokkos::Experimental::MinMaxScalar<double>’)
       *((volatile T*)lhs) += *((const volatile T*)rhs);
                           ^
make: *** [main.o] Error 1

Works after taking away tag.

[tjfulle]

@crtrott, on my laptop using gcc 6.4 and clang 4.0, and the current version of Kokkos snapshot in to Trilinos, the reproducer compiles and runs, but I get an error in the answer as described in #1250.

[tjfulle]

To add to my previous comment, when I made the reproducer, I used the installed version of Kokkos in Trilinos and the Trilinos makefile to define compiler/compiler flags. In the failing sparta builds, I believe sparta is using the Kokkos makefile directly. Not sure that extra info helps?

[crtrott]

Did you compile for OpenMP in your Trilinos version? This particular bug seems to be restricted to OpenMP. The "Incorrect Answer" bug actually effects every backend including Serial. If I were just to fix the compilation issue, this reproducer would run into the other bug and give the wrong answer.

[tjfulle]

I’ll check that. I just used the default execution space in Kokkos. I thought I used OpenMP, but maybe not?

[crtrott]

No it is not. Only if you enable OpenMP globally for Trilinos. I also have added a unit test which catches this issues.