* Make ReturnByValue have the EvalBeforeAssigningBit and explicitly

enforce this mechanism (otherwise ReturnByValue bypasses it).
 (use .noalias() to get the old behavior.)
* Remove a hack in Inverse, futile optimization for 2x2 expressions.

Eigen/src/Core/NoAlias.h

@@ -45,12 +45,18 @@ class NoAlias
   public:
     NoAlias(ExpressionType& expression) : m_expression(expression) {}
 
-    /** Behaves like MatrixBase::lazyAssign(other)
-      * \sa MatrixBase::lazyAssign() */
+    /* \sa MatrixBase::lazyAssign() */
     template<typename OtherDerived>
     EIGEN_STRONG_INLINE ExpressionType& operator=(const StorageBase<OtherDerived>& other)
     { return m_expression.lazyAssign(other.derived()); }
 
+    template<typename OtherDerived>
+    EIGEN_STRONG_INLINE ExpressionType& operator=(const ReturnByValue<OtherDerived>& other)
+    {
+      other.evalTo(m_expression);
+      return m_expression;
+    }
+
     /** \sa MatrixBase::operator+= */
     template<typename OtherDerived>
     EIGEN_STRONG_INLINE ExpressionType& operator+=(const StorageBase<OtherDerived>& other)

Eigen/src/Core/ReturnByValue.h

@@ -36,9 +36,9 @@ struct ei_traits<ReturnByValue<Derived> >
   enum {
     // We're disabling the DirectAccess because e.g. the constructor of
     // the Block-with-DirectAccess expression requires to have a coeffRef method.
-    // Also, we don't want to have to implement the stride stuff.
+    // FIXME this should be fixed so we can have DirectAccessBit here.
     Flags = (ei_traits<typename ei_traits<Derived>::ReturnType>::Flags
-             | EvalBeforeNestingBit) & ~DirectAccessBit
+             | EvalBeforeNestingBit | EvalBeforeAssigningBit) & ~DirectAccessBit
   };
 };
 
@@ -83,8 +83,11 @@ template<typename Derived>
 template<typename OtherDerived>
 Derived& DenseBase<Derived>::operator=(const ReturnByValue<OtherDerived>& other)
 {
-  other.evalTo(derived());
-  return derived();
+  // since we're by-passing the mechanisms in Assign.h, we implement here the EvalBeforeAssigningBit.
+  // override by using .noalias(), see corresponding operator= in NoAlias.
+  typename Derived::PlainObject result(rows(), cols());
+  other.evalTo(result);
+  return (derived() = result);
 }
 
 #endif // EIGEN_RETURNBYVALUE_H