Trilinos no longer builds with Scalar=complex<float>

Created by: mhoemmen

@trilinos/tpetra @trilinos/amesos2

I found this out when testing Amesos2. See e.g., #4194 (closed).

Current Behavior

Tpetra and downstream classes do not build with Scalar=complex<float>. I get errors of the form discussed here: https://github.com/kokkos/kokkos/issues/1964 . The case Scalar=Kokkos::complex<double> still works, because it uses a different overload of these Kokkos functions that does not attempt to put the output type in a union with unsigned long long int.

Motivation and Context

Sierra currently enables complex<float> in its Trilinos build. This error also showed up in #4194 (closed), since Amesos2 was incorrectly attempting to build with Scalar=complex<float>, even though it was not enabled in Tpetra.

Possible Solution

I am working on a work-around, namely to overload Kokkos::Impl::atomic_fetch_oper and Kokkos::Impl::atomic_oper_fetch specifically for Kokkos::complex<float>.

Steps to Reproduce

Set the CMake option Trilinos_ENABLE_COMPLEX_FLOAT:BOOL=ON.

Related Issues

• Related to #4194 (closed)