improve aliasing detection for inverse and add unit test

2 files changed, 17 insertions, 2 deletions

diff --git a/Eigen/src/LU/Inverse.h b/Eigen/src/LU/Inverse.h
index e1276c6a3..5ccc59a32 100644
--- a/Eigen/src/LU/Inverse.h
+++ b/Eigen/src/LU/Inverse.h
@@ -295,8 +295,10 @@ struct ei_inverse_impl : public ReturnByValue<ei_inverse_impl<MatrixType> >
 
   template<typename Dest> inline void evalTo(Dest& dst) const
   {
-    // FIXME this is a naive aliasing check that could be improved. It only catches x = x.inverse();
-    ei_assert(&dst != (Dest*)(&m_matrix) && "Aliasing problem detected in inverse(), you need to do inverse().eval() here.");
+    const int Size = EIGEN_ENUM_MIN(MatrixType::ColsAtCompileTime,Dest::ColsAtCompileTime);
+    ei_assert(( (Size<=1) || (Size>4) || (ei_extract_data(m_matrix)!=ei_extract_data(dst)))
+              && "Aliasing problem detected in inverse(), you need to do inverse().eval() here.");
+
     ei_compute_inverse<MatrixTypeNestedCleaned, Dest>::run(m_matrix, dst);
   }
 };
diff --git a/test/inverse.cpp b/test/inverse.cpp
index 1e567ad14..4d9297eb4 100644
--- a/test/inverse.cpp
+++ b/test/inverse.cpp
@@ -82,6 +82,19 @@ template<typename MatrixType> void inverse(const MatrixType& m)
   m3.computeInverseWithCheck(m4, invertible);
   VERIFY( rows==1 ? invertible : !invertible );
 #endif
+
+  // check in-place inversion
+  if(MatrixType::RowsAtCompileTime>=2 && MatrixType::RowsAtCompileTime<=4)
+  {
+    // in-place is forbidden
+    VERIFY_RAISES_ASSERT(m1 = m1.inverse());
+  }
+  else
+  {
+    m2 = m1.inverse();
+    m1 = m1.inverse();
+    VERIFY_IS_APPROX(m1,m2);
+  }
 }
 
 void test_inverse()