* LU unit test: finally test fixed sizes

* ReturnByValue: after all don't eval to temporary for generic MatrixBase impl

Eigen/src/Core/ReturnByValue.h

@@ -65,22 +65,8 @@ template<typename Derived>
 template<typename OtherDerived>
 Derived& MatrixBase<Derived>::operator=(const ReturnByValue<OtherDerived>& other)
 {
-  // Here we evaluate to a temporary matrix tmp, which we then copy. The main purpose
-  // of this is to limit the number of instantiations of the template method evalTo<Destination>():
-  // we only instantiate for PlainMatrixType.
-  // Notice that this behaviour is specific to this operator in MatrixBase. The corresponding operator in class Matrix
-  // does not evaluate into a temporary first.
-  // TODO find a way to avoid evaluating into a temporary in the cases that matter. At least Block<> matters
-  // for the implementation of blocked algorithms.
-  // Should we:
-  //  - try a trick like for the products, where the destination is abstracted as an array with stride?
-  //  - or just add an operator in class Block, so we get a separate instantiation there (bad) but at least not more
-  //    than that, and at least that's easy to make work?
-  //  - or, since here we're talking about a compromise between code size and performance, let the user choose?
-  //    Not obvious: many users will never find out about this feature, and it's hard to find a good API.
-  PlainMatrixType tmp;
-  other.evalTo(tmp);
-  return derived() = tmp;
+  other.evalTo(derived());
+  return derived();
 }
 
 #endif // EIGEN_RETURNBYVALUE_H