[SYCL] Add [const]reverse_iterator to accessors (#7991)

Add `reverse_iterator` and `const_reverse_iterator` to `accessor`,
`host_accessor` and `local_accessor`, and corresponding tests.

Author: maarquitos14

sycl/include/sycl/accessor.hpp

@@ -1219,6 +1219,8 @@ class __SYCL_EBO __SYCL_SPECIAL_CLASS __SYCL_TYPE(accessor) accessor :
   using iterator = typename detail::accessor_iterator<value_type, Dimensions>;
   using const_iterator =
       typename detail::accessor_iterator<const value_type, Dimensions>;
+  using reverse_iterator = std::reverse_iterator<iterator>;
+  using const_reverse_iterator = std::reverse_iterator<const_iterator>;
   using difference_type =
       typename std::iterator_traits<iterator>::difference_type;
 
@@ -2129,6 +2131,16 @@ class __SYCL_EBO __SYCL_SPECIAL_CLASS __SYCL_TYPE(accessor) accessor :
         get_offset());
   }
 
+  reverse_iterator rbegin() const noexcept { return reverse_iterator(end()); }
+  reverse_iterator rend() const noexcept { return reverse_iterator(begin()); }
+
+  const_reverse_iterator crbegin() const noexcept {
+    return const_reverse_iterator(cend());
+  }
+  const_reverse_iterator crend() const noexcept {
+    return const_reverse_iterator(cbegin());
+  }
+
 private:
 #ifdef __SYCL_DEVICE_ONLY__
   size_t getTotalOffset() const {

sycl/test/basic_tests/accessor/iterator-member-types.cpp

@@ -1,9 +1,8 @@
 // RUN: %clangxx -fsycl -fsyntax-only %s
 //
-// Purpose of this test is to check that [accessor|host_accessor]::iterator and
-// ::const_iterator are aliased to the correct type.
-// FIXME: extend this test to also check ::reverse_iterator and
-// ::const_reverse_iterator
+// Purpose of this test is to check that [accessor|host_accessor]::iterator,
+// ::const_iterator, ::reverse_iterator and ::const_reverse_iterator are aliased
+// to the correct type.
 #include <sycl/sycl.hpp>
 
 #include <type_traits>
@@ -21,6 +20,16 @@ void check_accessor() {
       std::is_same_v<sycl::detail::accessor_iterator<
                          const typename AccessorT::value_type, Dimensions>,
                      typename AccessorT::const_iterator>);
+
+  static_assert(
+      std::is_same_v<std::reverse_iterator<sycl::detail::accessor_iterator<
+                         typename AccessorT::value_type, Dimensions>>,
+                     typename AccessorT::reverse_iterator>);
+
+  static_assert(
+      std::is_same_v<std::reverse_iterator<sycl::detail::accessor_iterator<
+                         const typename AccessorT::value_type, Dimensions>>,
+                     typename AccessorT::const_reverse_iterator>);
 }
 
 template <typename DataT, int Dimensions, sycl::access_mode AccessMode>
@@ -34,6 +43,16 @@ void check_host_accessor() {
       std::is_same_v<sycl::detail::accessor_iterator<
                          const typename AccessorT::value_type, Dimensions>,
                      typename AccessorT::const_iterator>);
+
+  static_assert(
+      std::is_same_v<std::reverse_iterator<sycl::detail::accessor_iterator<
+                         typename AccessorT::value_type, Dimensions>>,
+                     typename AccessorT::reverse_iterator>);
+
+  static_assert(
+      std::is_same_v<std::reverse_iterator<sycl::detail::accessor_iterator<
+                         const typename AccessorT::value_type, Dimensions>>,
+                     typename AccessorT::const_reverse_iterator>);
 }
 
 struct user_defined_t {

sycl/unittests/accessor/AccessorIterator.cpp

@@ -176,6 +176,7 @@ class AccessorIteratorTest : public ::testing::Test {
 // FIXME: consider turning this into parameterized test to check various
 // accessor types
 TEST_F(AccessorIteratorTest, IteratorTraits) {
+
   using IteratorT = sycl::accessor<int>::iterator;
   ASSERT_TRUE(
       (std::is_same_v<sycl::accessor<int>::difference_type,
@@ -194,6 +195,7 @@ TEST_F(AccessorIteratorTest, IteratorTraits) {
 // Based on requirements listed at
 // https://en.cppreference.com/w/cpp/named_req/RandomAccessIterator
 TEST_F(AccessorIteratorTest, LegacyRandomAccessIteratorRequirements) {
+
   using IteratorT = sycl::accessor<int>::iterator;
   IteratorT It;
   auto &RefToIt = It;
@@ -435,10 +437,8 @@ TEST_F(AccessorIteratorTest, PartialCopyWithOffset3D) {
       sycl::range<3>{7, 7, 7}, sycl::range<3>{3, 3, 3}, sycl::id<3>{2, 2, 2}));
   ASSERT_NO_FATAL_FAILURE(checkPartialCopyThroughIterator(
       sycl::range<3>{8, 8, 8}, sycl::range<3>{4, 4, 4}, sycl::id<3>{4, 4, 4}));
-  // FIXME: figure out why the test below fails
-  // ASSERT_NO_FATAL_FAILURE(checkPartialCopyThroughIterator(
-  //     sycl::range<3>{7, 7, 7}, sycl::range<3>{3, 3, 3}, sycl::id<3>{4, 4,
-  //     4}));
+  ASSERT_NO_FATAL_FAILURE(checkPartialCopyThroughIterator(
+      sycl::range<3>{7, 7, 7}, sycl::range<3>{3, 3, 3}, sycl::id<3>{4, 4, 4}));
   ASSERT_NO_FATAL_FAILURE(checkPartialCopyThroughIterator(
       sycl::range<3>{7, 7, 7}, sycl::range<3>{3, 4, 5}, sycl::id<3>{3, 2, 1}));
   ASSERT_NO_FATAL_FAILURE(checkPartialCopyThroughIterator(
@@ -525,3 +525,49 @@ TEST_F(AccessorIteratorTest, PartialWriteWithOffset3D) {
   ASSERT_NO_FATAL_FAILURE(checkWriteThroughIterator(
       sycl::range<3>{3, 6, 4}, sycl::range<3>{1, 3, 2}, sycl::id<3>{1, 3, 2}));
 }
+
+TEST_F(AccessorIteratorTest, IteratorEquivalentIncrements) {
+  std::vector<int> reference(6);
+  std::iota(reference.begin(), reference.end(), 0);
+  sycl::buffer<int> buffer(reference.data(), sycl::range<1>{reference.size()});
+  auto accessor = buffer.template get_access<sycl::access_mode::read_write>();
+  auto a = accessor.begin();
+  auto b = accessor.begin();
+  a++;
+  ++b;
+  ASSERT_TRUE(a == b);
+}
+
+TEST_F(AccessorIteratorTest, IteratorEquivalentDecrements) {
+  std::vector<int> reference(6);
+  std::iota(reference.begin(), reference.end(), 0);
+  sycl::buffer<int> buffer(reference.data(), sycl::range<1>{reference.size()});
+  auto accessor = buffer.template get_access<sycl::access_mode::read_write>();
+  auto a = accessor.begin();
+  auto b = accessor.begin();
+  a--;
+  --b;
+  ASSERT_TRUE(a == b);
+}
+
+TEST_F(AccessorIteratorTest, IteratorSubscriptOperator) {
+  std::vector<int> reference(6);
+  std::iota(reference.begin(), reference.end(), 0);
+  sycl::buffer<int> buffer(reference.data(), sycl::range<1>{reference.size()});
+  auto accessor = buffer.template get_access<sycl::access_mode::read_write>();
+  auto a = accessor.begin();
+  auto b = accessor.begin();
+  ASSERT_TRUE(a[3] == *(3 + b));
+}
+
+TEST_F(AccessorIteratorTest, IteratorInequalitiesOperators) {
+  std::vector<int> reference(6);
+  std::iota(reference.begin(), reference.end(), 0);
+  sycl::buffer<int> buffer(reference.data(), sycl::range<1>{reference.size()});
+  auto accessor = buffer.template get_access<sycl::access_mode::read_write>();
+  auto a = accessor.begin();
+  auto b = accessor.begin();
+  ASSERT_FALSE(a > b);
+  ASSERT_TRUE(a <= b);
+  ASSERT_TRUE(a >= b);
+}