From fa44566305be78f5b415f07e363b5707568b6b42 Mon Sep 17 00:00:00 2001
From: Gael Guennebaud <g.gael@free.fr>
Date: Mon, 20 Jul 2009 10:35:47 +0200
Subject: [PATCH] bugfix for a = a * b; when a has to be resized (transplanted
 from a551107ccea8fe027d2672cb82f6b70e741bb996 )

---
 Eigen/src/Core/Matrix.h | 21 +++++++++++++++++++--
 test/product_large.cpp  |  6 ++++++
 2 files changed, 25 insertions(+), 2 deletions(-)

diff --git a/Eigen/src/Core/Matrix.h b/Eigen/src/Core/Matrix.h
index 45b218af1..6b674c1a3 100644
--- a/Eigen/src/Core/Matrix.h
+++ b/Eigen/src/Core/Matrix.h
@@ -493,6 +493,9 @@ class Matrix
       else resize(other.rows(), other.cols());
     }
 
+    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),
@@ -507,8 +510,8 @@ class Matrix
     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
@@ -536,6 +539,20 @@ class Matrix
     }
 };
 
+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
diff --git a/test/product_large.cpp b/test/product_large.cpp
index 1c33578be..637e02b2a 100644
--- a/test/product_large.cpp
+++ b/test/product_large.cpp
@@ -42,4 +42,10 @@ void test_product_large()
     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());
+  }
 }