bugfix for a = a * b; when a has to be resized

Eigen/src/Core/Matrix.h

diff --git a/Eigen/src/Core/Matrix.h b/Eigen/src/Core/Matrix.h
index 5301f48..32b526e 100644
--- a/Eigen/src/Core/Matrix.h
+++ b/Eigen/src/Core/Matrix.h
@@ -536,6 +536,9 @@
       resizeLike(other);
     }
 
+    template<typename MatrixType, typename OtherDerived, bool EvalBeforeAssigning = (int(OtherDerived::Flags) & EvalBeforeAssigningBit) != 0>
+    struct ei_matrix_set_selector;
+
     /** \internal Copies the value of the expression \a other into \c *this with automatic resizing.
       *
       * *this might be resized to match the dimensions of \a other. If *this was a null matrix (not already initialized),
@@ -550,8 +553,8 @@
     template<typename OtherDerived>
     EIGEN_STRONG_INLINE Matrix& _set(const MatrixBase<OtherDerived>& other)
     {
-      _resize_to_match(other);
-      return Base::operator=(other);
+      ei_matrix_set_selector<Matrix,OtherDerived>::run(*this,other.derived());
+      return *this;
     }
 
     /** \internal Like _set() but additionally makes the assumption that no aliasing effect can happen (which
@@ -600,6 +603,20 @@
     }
 };
 
+template<typename _Scalar, int _Rows, int _Cols, int _Options, int _MaxRows, int _MaxCols>
+template<typename MatrixType, typename OtherDerived>
+struct Matrix<_Scalar, _Rows, _Cols, _Options, _MaxRows, _MaxCols>::ei_matrix_set_selector<MatrixType,OtherDerived,true>
+{
+  static void run(MatrixType& dst, const OtherDerived& src) { dst._set_noalias(src.eval()); }
+};
+
+template<typename _Scalar, int _Rows, int _Cols, int _Options, int _MaxRows, int _MaxCols>
+template<typename MatrixType, typename OtherDerived>
+struct Matrix<_Scalar, _Rows, _Cols, _Options, _MaxRows, _MaxCols>::ei_matrix_set_selector<MatrixType,OtherDerived,false>
+{
+  static void run(MatrixType& dst, const OtherDerived& src) { dst._set_noalias(src); }
+};
+
 /** \defgroup matrixtypedefs Global matrix typedefs
   *
   * \ingroup Core_Module

test/product_large.cpp

diff --git a/test/product_large.cpp b/test/product_large.cpp
index 77ae7b5..9b53e7b 100644
--- a/test/product_large.cpp
+++ b/test/product_large.cpp
@@ -42,4 +42,10 @@
     m = (v+v).asDiagonal() * m;
     VERIFY_IS_APPROX(m, MatrixXf::Constant(N,3,2));
   }
+
+  {
+    // test deferred resizing in Matrix::operator=
+    MatrixXf a = MatrixXf::Random(10,4), b = MatrixXf::Random(4,10), c = a;
+    VERIFY_IS_APPROX((a = a * b), (c * b).eval());
+  }
 }