From b0f2b6f297b47585ef007073ec7550fe4cf5bde6 Mon Sep 17 00:00:00 2001
From: Benoit Steiner <benoit.steiner.goog@gmail.com>
Date: Mon, 2 Mar 2015 10:11:40 -0800
Subject: [PATCH] Updated the tensor type casting code as follow: in the case
 where TgtRatio < SrcRatio, disable the vectorization of the source expression
 unless is has direct-access.

---
 unsupported/Eigen/CXX11/src/Tensor/TensorConversion.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/unsupported/Eigen/CXX11/src/Tensor/TensorConversion.h b/unsupported/Eigen/CXX11/src/Tensor/TensorConversion.h
index f594725a8..fb1f1f6ea 100644
--- a/unsupported/Eigen/CXX11/src/Tensor/TensorConversion.h
+++ b/unsupported/Eigen/CXX11/src/Tensor/TensorConversion.h
@@ -93,7 +93,10 @@ struct PacketConverter<TensorEvaluator, SrcPacket, TgtPacket, 1, 2> {
   template<int LoadMode, typename Index>
   EIGEN_DEVICE_FUNC EIGEN_STRONG_INLINE TgtPacket packet(Index index) const {
     const int SrcPacketSize = internal::unpacket_traits<SrcPacket>::size;
-    if (index + SrcPacketSize < m_maxIndex) {
+    // Only call m_impl.packet() when we have direct access to the underlying data. This
+    // ensures that we don't compute the subexpression twice. We may however load some
+    // coefficients twice, but in practice this doesn't negatively impact performance.
+    if (m_impl.data() && (index + SrcPacketSize < m_maxIndex)) {
       // Force unaligned memory loads since we can't ensure alignment anymore
       return internal::pcast<SrcPacket, TgtPacket>(m_impl.template packet<Unaligned>(index));
     } else {