IsRowMajor is an enum value defined in DenseBase. However, in the template specialization of GeneralProduct<Lhs,Rhs,OuterProduct>, derived from ProductBase<--MatrixBase<--DenseBase, another struct is defined with the same name IsRowMajor. This causes a compilation error in Assign_MKL.h, line 51 when MKL is enabled:
Eigen/Eigen/src/Core/Assign_MKL.h:51:50: error: dependent-name ‘Src:: IsRowMajor’ is parsed as a non-type, but instantiation yields a type
StorageOrdersAgree = (int(Dst::IsRowMajor) == int(Src::IsRowMajor)),
Changing the struct's name seems to fix the problem.
Thank you for the report.