As proposed on the list:

- rename EvalBeforeAssignBit to MayAliasBit
- make .lazy() remove the MayAliasBit only, and mark it as deprecated
- add a NoAlias pseudo expression, and MatrixBase::noalias() function
Todo:
- we have to decide whether += and -= assume no aliasing by default ?
- once we agree on the API: update the Sparse module and the unit tests respectively.

Eigen/src/Core/Assign.h

@@ -434,7 +434,7 @@ EIGEN_STRONG_INLINE Derived& MatrixBase<Derived>
 }
 
 template<typename Derived, typename OtherDerived,
-         bool EvalBeforeAssigning = (int(OtherDerived::Flags) & EvalBeforeAssigningBit) != 0,
+         bool EvalBeforeAssigning = (int(OtherDerived::Flags) & MayAliasBit) != 0,
          bool NeedToTranspose = Derived::IsVectorAtCompileTime
                 && OtherDerived::IsVectorAtCompileTime
                 && ((int(Derived::RowsAtCompileTime) == 1 && int(OtherDerived::ColsAtCompileTime) == 1)