Started to model the cost of divisions more accurately.

Eigen/src/Core/NumTraits.h

@@ -60,6 +60,23 @@ template<typename T> struct GenericNumTraits
     MulCost = 1
   };
 
+  // Division is messy but important, because it is expensive and throughput
+  // varies significantly. The following numbers are based on min division
+  // throughput on Haswell.
+  template<bool Vectorized>
+  struct Div {
+    enum {
+#ifdef EIGEN_VECTORIZE_AVX
+      AVX = true,
+#else
+      AVX = false,
+#endif
+      Cost = IsInteger ? (sizeof(T) == 8 ? (IsSigned ? 24 : 21) : (IsSigned ? 8 : 9)):
+          Vectorized ? (sizeof(T) == 8 ? (AVX ? 16 : 8) : (AVX ? 14 : 7)) : 8
+    };
+  };
+
+
   typedef T Real;
   typedef typename internal::conditional<
                      IsInteger,