Implement eval-at-once in evaluator.

- Add evaluator_traits with HasEvalTo flag, which is true if evaluator
  has evalTo() function.
- Add AllAtOnce traversal, which calls evalTo() in evaluator.
- If source evaluator in copy_using_evaluator has HasEvalTo set, then
  use AllAtOnce traversal.

Eigen/src/Core/AssignEvaluator.h

@@ -38,7 +38,6 @@ namespace internal {
 ***************************************************************************/
 
 // copy_using_evaluator_traits is based on assign_traits
-// (actually, it's identical)
 
 template <typename Derived, typename OtherDerived>
 struct copy_using_evaluator_traits
@@ -48,7 +47,8 @@ public:
     DstIsAligned = Derived::Flags & AlignedBit,
     DstHasDirectAccess = Derived::Flags & DirectAccessBit,
     SrcIsAligned = OtherDerived::Flags & AlignedBit,
-    JointAlignment = bool(DstIsAligned) && bool(SrcIsAligned) ? Aligned : Unaligned
+    JointAlignment = bool(DstIsAligned) && bool(SrcIsAligned) ? Aligned : Unaligned,
+    SrcEvalBeforeAssign = (evaluator_traits<OtherDerived>::HasEvalTo == 1)
   };
 
 private:
@@ -83,7 +83,8 @@ private:
 
 public:
   enum {
-    Traversal = int(MayInnerVectorize)  ? int(InnerVectorizedTraversal)
+    Traversal = int(SrcEvalBeforeAssign) ? int(AllAtOnceTraversal) 
+              : int(MayInnerVectorize)   ? int(InnerVectorizedTraversal)
               : int(MayLinearVectorize)  ? int(LinearVectorizedTraversal)
               : int(MaySliceVectorize)   ? int(SliceVectorizedTraversal)
               : int(MayLinearize)        ? int(LinearTraversal)
@@ -599,6 +600,26 @@ struct copy_using_evaluator_impl<DstXprType, SrcXprType, SliceVectorizedTraversa
   }
 };
 
+/****************************
+*** All-at-once traversal ***
+****************************/
+
+template<typename DstXprType, typename SrcXprType>
+struct copy_using_evaluator_impl<DstXprType, SrcXprType, AllAtOnceTraversal, NoUnrolling>
+{
+  inline static void run(DstXprType &dst, const SrcXprType &src)
+  {
+    typedef typename evaluator<DstXprType>::type DstEvaluatorType;
+    typedef typename evaluator<SrcXprType>::type SrcEvaluatorType;
+    typedef typename DstXprType::Index Index;
+
+    DstEvaluatorType dstEvaluator(dst);
+    SrcEvaluatorType srcEvaluator(src);
+
+    srcEvaluator.evalTo(dstEvaluator);
+  }
+};
+
 /***************************************************************************
 * Part 4 : Entry points
 ***************************************************************************/

Eigen/src/Core/CoreEvaluators.h

@@ -32,6 +32,18 @@ namespace Eigen {
 
 namespace internal {
 
+// evaluator_traits<T> contains traits for evaluator_impl<T> 
+
+template<typename T>
+struct evaluator_traits
+{
+  // 1 if evaluator_impl<T>::evalTo() exists
+  // 0 if evaluator_impl<T> allows coefficient-based access
+  static const int HasEvalTo = 0;
+};
+
+// evaluator<T>::type is type of evaluator for T
+
 template<typename T>
 struct evaluator_impl {};
 

Eigen/src/Core/util/Constants.h

@@ -242,7 +242,9 @@ enum {
     * scalar loops to handle the unaligned boundaries */
   SliceVectorizedTraversal,
   /** \internal Special case to properly handle incompatible scalar types or other defecting cases*/
-  InvalidTraversal
+  InvalidTraversal,
+  /** \internal Evaluate all entries at once */
+  AllAtOnceTraversal
 };
 
 /** \internal \ingroup enums