specialize for Size==0 in order to catch user bugs and not clutter

the compiler output with an infinite recursion. Also add a #define switch
for loop unrolling.

src/Core/CopyHelper.h

@@ -40,6 +40,17 @@ template<int UnrollCount, int Rows> struct CopyHelperUnroller
   }
 };
 
+// prevent buggy user code from causing an infinite recursion
+template<int UnrollCount> struct CopyHelperUnroller<UnrollCount, 0>
+{
+  template <typename Derived1, typename Derived2>
+  static void run(Derived1 &dst, const Derived2 &src)
+  {
+    EIGEN_UNUSED(dst);
+    EIGEN_UNUSED(src);
+  }
+};
+
 template<int Rows> struct CopyHelperUnroller<1, Rows>
 {
   template <typename Derived1, typename Derived2>
@@ -63,7 +74,7 @@ template<typename Scalar, typename Derived>
 template<typename OtherDerived>
 void MatrixBase<Scalar, Derived>::_copy_helper(const MatrixBase<Scalar, OtherDerived>& other)
 {
-  if(SizeAtCompileTime != Dynamic && SizeAtCompileTime <= 25)
+  if(EIGEN_UNROLLED_LOOPS && SizeAtCompileTime != Dynamic && SizeAtCompileTime <= 25)
     CopyHelperUnroller<SizeAtCompileTime, RowsAtCompileTime>::run(*this, other);
   else
     for(int i = 0; i < rows(); i++)

src/Core/Dot.h

@@ -32,7 +32,7 @@ struct DotUnroller
   static void run(const Derived1 &v1, const Derived2& v2, typename Derived1::Scalar &dot)
   {
     DotUnroller<Index-1, Size, Derived1, Derived2>::run(v1, v2, dot);
-    dot += v1[Index] * conj(v2[Index]);
+    dot += v1.read(Index) * conj(v2.read(Index));
   }
 };
 
@@ -41,7 +41,7 @@ struct DotUnroller<0, Size, Derived1, Derived2>
 {
   static void run(const Derived1 &v1, const Derived2& v2, typename Derived1::Scalar &dot)
   {
-    dot = v1[0] * conj(v2[0]);
+    dot = v1.read(0) * conj(v2.read(0));
   }
 };
 
@@ -56,20 +56,32 @@ struct DotUnroller<Index, Dynamic, Derived1, Derived2>
   }
 };
 
+// prevent buggy user code from causing an infinite recursion
+template<int Index, typename Derived1, typename Derived2>
+struct DotUnroller<Index, 0, Derived1, Derived2>
+{
+  static void run(const Derived1 &v1, const Derived2& v2, typename Derived1::Scalar &dot)
+  {
+    EIGEN_UNUSED(v1);
+    EIGEN_UNUSED(v2);
+    EIGEN_UNUSED(dot);
+  }
+};
+
 template<typename Scalar, typename Derived>
 template<typename OtherDerived>
 Scalar MatrixBase<Scalar, Derived>::dot(const OtherDerived& other) const
 {
   assert(IsVector && OtherDerived::IsVector && size() == other.size());
   Scalar res;
-  if(SizeAtCompileTime != Dynamic && SizeAtCompileTime <= 16)
+  if(EIGEN_UNROLLED_LOOPS && SizeAtCompileTime != Dynamic && SizeAtCompileTime <= 16)
     DotUnroller<SizeAtCompileTime-1, SizeAtCompileTime, Derived, OtherDerived>
       ::run(*static_cast<const Derived*>(this), other, res);
   else
   {
-    res = (*this)[0] * conj(other[0]);
+    res = (*this).read(0) * conj(other.read(0));
     for(int i = 1; i < size(); i++)
-      res += (*this)[i]* conj(other[i]);
+      res += (*this).read(i)* conj(other.read(i));
   }
   return res;
 }

src/Core/Product.h

@@ -61,6 +61,21 @@ struct ProductUnroller<Index, Dynamic, Lhs, Rhs>
   }
 };
 
+// prevent buggy user code from causing an infinite recursion
+template<int Index, typename Lhs, typename Rhs>
+struct ProductUnroller<Index, 0, Lhs, Rhs>
+{
+  static void run(int row, int col, const Lhs& lhs, const Rhs& rhs,
+                  typename Lhs::Scalar &res)
+  {
+    EIGEN_UNUSED(row);
+    EIGEN_UNUSED(col);
+    EIGEN_UNUSED(lhs);
+    EIGEN_UNUSED(rhs);
+    EIGEN_UNUSED(res);
+  }
+};
+
 template<typename Lhs, typename Rhs> class Product
   : public MatrixBase<typename Lhs::Scalar, Product<Lhs, Rhs> >
 {
@@ -93,14 +108,15 @@ template<typename Lhs, typename Rhs> class Product
     Scalar _read(int row, int col) const
     {
       Scalar res;
-      if(Lhs::ColsAtCompileTime != Dynamic && Lhs::ColsAtCompileTime <= 16)
+      if(EIGEN_UNROLLED_LOOPS
+      && Lhs::ColsAtCompileTime != Dynamic && Lhs::ColsAtCompileTime <= 16)
         ProductUnroller<Lhs::ColsAtCompileTime-1, Lhs::ColsAtCompileTime, LhsRef, RhsRef>
           ::run(row, col, m_lhs, m_rhs, res);
       else
       {
-        res = m_lhs(row, 0) * m_rhs(0, col);
+        res = m_lhs.read(row, 0) * m_rhs.read(0, col);
         for(int i = 1; i < m_lhs.cols(); i++)
-          res += m_lhs(row, i) * m_rhs(i, col);
+          res += m_lhs.read(row, i) * m_rhs.read(i, col);
       }
       return res;
     }
@@ -112,7 +128,7 @@ template<typename Lhs, typename Rhs> class Product
 
 template<typename Scalar, typename Derived>
 template<typename OtherDerived>
-Product<Derived, OtherDerived>
+const Product<Derived, OtherDerived>
 MatrixBase<Scalar, Derived>::lazyProduct(const MatrixBase<Scalar, OtherDerived> &other) const
 {
   return Product<Derived, OtherDerived>(ref(), other.ref());

src/Core/Trace.h

@@ -31,7 +31,7 @@ template<int Index, int Rows, typename Derived> struct TraceUnroller
   static void run(const Derived &mat, typename Derived::Scalar &trace)
   {
     TraceUnroller<Index-1, Rows, Derived>::run(mat, trace);
-    trace += mat(Index, Index);
+    trace += mat.read(Index, Index);
   }
 };
 
@@ -39,7 +39,7 @@ template<int Rows, typename Derived> struct TraceUnroller<0, Rows, Derived>
 {
   static void run(const Derived &mat, typename Derived::Scalar &trace)
   {
-    trace = mat(0, 0);
+    trace = mat.read(0, 0);
   }
 };
 
@@ -52,12 +52,22 @@ template<int Index, typename Derived> struct TraceUnroller<Index, Dynamic, Deriv
   }
 };
 
+// prevent buggy user code from causing an infinite recursion
+template<int Index, typename Derived> struct TraceUnroller<Index, 0, Derived>
+{
+  static void run(const Derived &mat, typename Derived::Scalar &trace)
+  {
+    EIGEN_UNUSED(mat);
+    EIGEN_UNUSED(trace);
+  }
+};
+
 template<typename Scalar, typename Derived>
 Scalar MatrixBase<Scalar, Derived>::trace() const
 {
   assert(rows() == cols());
   Scalar res;
-  if(RowsAtCompileTime != Dynamic && RowsAtCompileTime <= 16)
+  if(EIGEN_UNROLLED_LOOPS && RowsAtCompileTime != Dynamic && RowsAtCompileTime <= 16)
     TraceUnroller<RowsAtCompileTime-1, RowsAtCompileTime, Derived>
       ::run(*static_cast<const Derived*>(this), res);
   else