optimize new dot product

Eigen/src/Core/InnerProduct.h

diff --git a/Eigen/src/Core/InnerProduct.h b/Eigen/src/Core/InnerProduct.h
index c8b1c1d..38689da 100644
--- a/Eigen/src/Core/InnerProduct.h
+++ b/Eigen/src/Core/InnerProduct.h
@@ -132,24 +132,21 @@
   static EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE Scalar run(const Evaluator& eval) {
     const UnsignedIndex size = static_cast<UnsignedIndex>(eval.size());
     if (size < PacketSize) return inner_product_impl<Evaluator, false>::run(eval);
+
     const UnsignedIndex packetEnd = numext::round_down(size, PacketSize);
+    const UnsignedIndex quadEnd = numext::round_down(size, 4 * PacketSize);
     const UnsignedIndex numPackets = size / PacketSize;
+    const UnsignedIndex numRemPackets = (packetEnd - quadEnd) / PacketSize;
 
-    Packet presult0 = eval.template packet<Packet>(0 * PacketSize);
-    Packet presult1 = pzero(Packet());
-    Packet presult2 = pzero(Packet());
-    Packet presult3 = pzero(Packet());
+    Packet presult0, presult1, presult2, presult3;
 
+    presult0 = eval.template packet<Packet>(0 * PacketSize);
     if (numPackets >= 2) presult1 = eval.template packet<Packet>(1 * PacketSize);
     if (numPackets >= 3) presult2 = eval.template packet<Packet>(2 * PacketSize);
     if (numPackets >= 4) {
       presult3 = eval.template packet<Packet>(3 * PacketSize);
 
-      const UnsignedIndex numRemPackets = (numPackets - 4) % 4;
-      const UnsignedIndex quadStart = 4 * PacketSize;
-      const UnsignedIndex quadEnd = (numPackets - numRemPackets) * PacketSize;
-
-      for (UnsignedIndex k = quadStart; k < quadEnd; k += 4 * PacketSize) {
+      for (UnsignedIndex k = 4 * PacketSize; k < quadEnd; k += 4 * PacketSize) {
         presult0 = eval.packet(presult0, k + 0 * PacketSize);
         presult1 = eval.packet(presult1, k + 1 * PacketSize);
         presult2 = eval.packet(presult2, k + 2 * PacketSize);
@@ -159,16 +156,16 @@
       if (numRemPackets >= 1) presult0 = eval.packet(presult0, quadEnd + 0 * PacketSize);
       if (numRemPackets >= 2) presult1 = eval.packet(presult1, quadEnd + 1 * PacketSize);
       if (numRemPackets == 3) presult2 = eval.packet(presult2, quadEnd + 2 * PacketSize);
+
+      presult2 = padd(presult2, presult3);
     }
 
-    Scalar result = predux(padd(padd(presult0, presult1), padd(presult2, presult3)));
+    if (numPackets >= 3) presult1 = padd(presult1, presult2);
+    if (numPackets >= 2) presult0 = padd(presult0, presult1);
 
-    if (size > packetEnd) {
-      Scalar scalarAccum = eval.coeff(packetEnd);
-      for (UnsignedIndex k = packetEnd + 1; k < size; k++) {
-        scalarAccum = eval.coeff(scalarAccum, k);
-      }
-      result += scalarAccum;
+    Scalar result = predux(presult0);
+    for (UnsignedIndex k = packetEnd; k < size; k++) {
+      result = eval.coeff(result, k);
     }
 
     return result;