From a4c8701e9aa0ac14ffb626692a22995bda2026fb Mon Sep 17 00:00:00 2001
From: Gael Guennebaud <g.gael@free.fr>
Date: Mon, 5 Dec 2016 15:08:09 +0100
Subject: [PATCH] bug #1356: fix calls to evaluator::coeffRef(0,0) to get the
 address of the destination by adding a dstDataPtr() member to the kernel.
 This fixes undefined behavior if dst is empty (nullptr). (grafted from
 0db6d5b3f434ae2e0c2e8b78402e062e67e86339 )

---
 Eigen/src/Core/AssignEvaluator.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/Eigen/src/Core/AssignEvaluator.h b/Eigen/src/Core/AssignEvaluator.h
index 0d0189657..14400d246 100644
--- a/Eigen/src/Core/AssignEvaluator.h
+++ b/Eigen/src/Core/AssignEvaluator.h
@@ -407,7 +407,7 @@ struct dense_assignment_loop<Kernel, LinearVectorizedTraversal, NoUnrolling>
                                                             : int(Kernel::AssignmentTraits::DstAlignment),
       srcAlignment = Kernel::AssignmentTraits::JointAlignment
     };
-    const Index alignedStart = dstIsAligned ? 0 : internal::first_aligned<requestedAlignment>(&kernel.dstEvaluator().coeffRef(0), size);
+    const Index alignedStart = dstIsAligned ? 0 : internal::first_aligned<requestedAlignment>(kernel.dstDataPtr(), size);
     const Index alignedEnd = alignedStart + ((size-alignedStart)/packetSize)*packetSize;
 
     unaligned_dense_assignment_loop<dstIsAligned!=0>::run(kernel, 0, alignedStart);
@@ -527,7 +527,7 @@ struct dense_assignment_loop<Kernel, SliceVectorizedTraversal, NoUnrolling>
       dstAlignment = alignable ? int(requestedAlignment)
                                : int(Kernel::AssignmentTraits::DstAlignment)
     };
-    const Scalar *dst_ptr = &kernel.dstEvaluator().coeffRef(0,0);
+    const Scalar *dst_ptr = kernel.dstDataPtr();
     if((!bool(dstIsAligned)) && (UIntPtr(dst_ptr) % sizeof(Scalar))>0)
     {
       // the pointer is not aligend-on scalar, so alignment is not possible
@@ -683,6 +683,11 @@ public:
       : int(DstEvaluatorType::Flags)&RowMajorBit ? inner
       : outer;
   }
+
+  EIGEN_DEVICE_FUNC const Scalar* dstDataPtr() const
+  {
+    return m_dstExpr.data();
+  }
   
 protected:
   DstEvaluatorType& m_dst;