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/Matrix.h

@@ -577,7 +577,7 @@ class Matrix
     template<typename OtherDerived>
     EIGEN_STRONG_INLINE Matrix& _set(const MatrixBase<OtherDerived>& other)
     {
-      _set_selector(other.derived(), typename ei_meta_if<static_cast<bool>(int(OtherDerived::Flags) & EvalBeforeAssigningBit), ei_meta_true, ei_meta_false>::ret());
+      _set_selector(other.derived(), typename ei_meta_if<static_cast<bool>(int(OtherDerived::Flags) & MayAliasBit), ei_meta_true, ei_meta_false>::ret());
       return *this;
     }