From aab747021be5ed1a1e9667243d884eb72003599d Mon Sep 17 00:00:00 2001
From: Jonas Harsch <jonas_harsch@web.de>
Date: Fri, 2 Jul 2021 20:33:52 +0000
Subject: Don't crash when attempting to shuffle an empty tensor.

---
 .../Eigen/CXX11/src/Tensor/TensorShuffling.h       |  6 ++-
 unsupported/test/cxx11_tensor_shuffling.cpp        | 55 ++++++++++++++++++++++
 2 files changed, 59 insertions(+), 2 deletions(-)

diff --git a/unsupported/Eigen/CXX11/src/Tensor/TensorShuffling.h b/unsupported/Eigen/CXX11/src/Tensor/TensorShuffling.h
index 0999815d7..e5e5efdee 100644
--- a/unsupported/Eigen/CXX11/src/Tensor/TensorShuffling.h
+++ b/unsupported/Eigen/CXX11/src/Tensor/TensorShuffling.h
@@ -142,7 +142,8 @@ struct TensorEvaluator<const TensorShufflingOp<Shuffle, ArgType>, Device>
         m_unshuffledInputStrides[i] =
             m_unshuffledInputStrides[i - 1] * input_dims[i - 1];
         m_outputStrides[i] = m_outputStrides[i - 1] * m_dimensions[i - 1];
-        m_fastOutputStrides[i] = internal::TensorIntDivisor<Index>(m_outputStrides[i]);
+        m_fastOutputStrides[i] = internal::TensorIntDivisor<Index>(
+                  m_outputStrides[i] > 0 ? m_outputStrides[i] : Index(1));
       }
     } else {
       m_unshuffledInputStrides[NumDims - 1] = 1;
@@ -151,7 +152,8 @@ struct TensorEvaluator<const TensorShufflingOp<Shuffle, ArgType>, Device>
         m_unshuffledInputStrides[i] =
             m_unshuffledInputStrides[i + 1] * input_dims[i + 1];
         m_outputStrides[i] = m_outputStrides[i + 1] * m_dimensions[i + 1];
-        m_fastOutputStrides[i] = internal::TensorIntDivisor<Index>(m_outputStrides[i]);
+        m_fastOutputStrides[i] = internal::TensorIntDivisor<Index>(
+                  m_outputStrides[i] > 0 ? m_outputStrides[i] : Index(1));
       }
     }
 
diff --git a/unsupported/test/cxx11_tensor_shuffling.cpp b/unsupported/test/cxx11_tensor_shuffling.cpp
index 2ec85d2d4..89a64c021 100644
--- a/unsupported/test/cxx11_tensor_shuffling.cpp
+++ b/unsupported/test/cxx11_tensor_shuffling.cpp
@@ -215,6 +215,59 @@ static void test_shuffle_unshuffle()
 }
 
 
+template <int DataLayout>
+static void test_empty_shuffling()
+{
+  Tensor<float, 4, DataLayout> tensor(2,3,0,7);
+  tensor.setRandom();
+  array<ptrdiff_t, 4> shuffles;
+  shuffles[0] = 0;
+  shuffles[1] = 1;
+  shuffles[2] = 2;
+  shuffles[3] = 3;
+
+  Tensor<float, 4, DataLayout> no_shuffle;
+  no_shuffle = tensor.shuffle(shuffles);
+
+  VERIFY_IS_EQUAL(no_shuffle.dimension(0), 2);
+  VERIFY_IS_EQUAL(no_shuffle.dimension(1), 3);
+  VERIFY_IS_EQUAL(no_shuffle.dimension(2), 0);
+  VERIFY_IS_EQUAL(no_shuffle.dimension(3), 7);
+
+  for (int i = 0; i < 2; ++i) {
+    for (int j = 0; j < 3; ++j) {
+      for (int k = 0; k < 0; ++k) {
+        for (int l = 0; l < 7; ++l) {
+          VERIFY_IS_EQUAL(tensor(i,j,k,l), no_shuffle(i,j,k,l));
+        }
+      }
+    }
+  }
+
+  shuffles[0] = 2;
+  shuffles[1] = 3;
+  shuffles[2] = 1;
+  shuffles[3] = 0;
+  Tensor<float, 4, DataLayout> shuffle;
+  shuffle = tensor.shuffle(shuffles);
+
+  VERIFY_IS_EQUAL(shuffle.dimension(0), 0);
+  VERIFY_IS_EQUAL(shuffle.dimension(1), 7);
+  VERIFY_IS_EQUAL(shuffle.dimension(2), 3);
+  VERIFY_IS_EQUAL(shuffle.dimension(3), 2);
+
+  for (int i = 0; i < 2; ++i) {
+    for (int j = 0; j < 3; ++j) {
+      for (int k = 0; k < 0; ++k) {
+        for (int l = 0; l < 7; ++l) {
+          VERIFY_IS_EQUAL(tensor(i,j,k,l), shuffle(k,l,j,i));
+        }
+      }
+    }
+  }
+}
+
+
 EIGEN_DECLARE_TEST(cxx11_tensor_shuffling)
 {
   CALL_SUBTEST(test_simple_shuffling<ColMajor>());
@@ -225,4 +278,6 @@ EIGEN_DECLARE_TEST(cxx11_tensor_shuffling)
   CALL_SUBTEST(test_shuffling_as_value<RowMajor>());
   CALL_SUBTEST(test_shuffle_unshuffle<ColMajor>());
   CALL_SUBTEST(test_shuffle_unshuffle<RowMajor>());
+  CALL_SUBTEST(test_empty_shuffling<ColMajor>());
+  CALL_SUBTEST(test_empty_shuffling<RowMajor>());
 }
-- 
cgit v1.2.3