[SYCL] Add default constructor to sycl::local_accessor. (#7815)

Adding default constructor to sycl::local_accessor to comply with spec.

Author: maarquitos14

sycl/include/sycl/accessor.hpp

@@ -2405,6 +2405,12 @@ class __SYCL_SPECIAL_CLASS local_accessor_base :
   ConcreteASPtrType MData;
 
 #else
+public:
+  local_accessor_base()
+      : detail::LocalAccessorBaseHost{/*Size*/ sycl::range<3>{0, 0, 0},
+                                      /*Dims*/ 0, /*ElemSize*/ sizeof(DataT)} {}
+
+protected:
   local_accessor_base(const detail::LocalAccessorImplPtr &Impl)
       : detail::LocalAccessorBaseHost{Impl} {}
 
@@ -2681,7 +2687,7 @@ class __SYCL_EBO __SYCL_SPECIAL_CLASS __SYCL_TYPE(local_accessor) local_accessor
   size_t byte_size() const noexcept { return this->size() * sizeof(DataT); }
 
   size_t max_size() const noexcept {
-    return (std::numeric_limits<difference_type>::max)();
+    return empty() ? 0 : (std::numeric_limits<difference_type>::max)();
   }
 
   bool empty() const noexcept { return this->size() == 0; }

sycl/unittests/accessor/CMakeLists.txt

@@ -1,3 +1,4 @@
 add_sycl_unittest(AccessorTests OBJECT
   AccessorIterator.cpp
+  LocalAccessorDefaultCtor.cpp
 )

sycl/unittests/accessor/LocalAccessorDefaultCtor.cpp

@@ -0,0 +1,44 @@
+#include <gtest/gtest.h>
+#include <sycl/sycl.hpp>
+
+#include <vector>
+
+using namespace sycl;
+using AccT = sycl::local_accessor<int, 1>;
+
+TEST(LocalAccessorDefaultCtorTest, LocalAcessorDefaultCtorIsEmpty) {
+  bool empty;
+
+  AccT acc;
+  empty = acc.empty();
+
+  EXPECT_TRUE(empty == true);
+}
+
+TEST(LocalAccessorDefaultCtorTest, LocalAcessorDefaultCtorSizeQueries) {
+  AccT acc;
+  size_t byte_size;
+  size_t size;
+  size_t max_size;
+
+  byte_size = acc.byte_size();
+  size = acc.size();
+  max_size = acc.max_size();
+
+  EXPECT_TRUE(byte_size == 0);
+  EXPECT_TRUE(size == 0);
+  EXPECT_TRUE(max_size == 0);
+}
+
+TEST(LocalAccessorDefaultCtorTest, LocalAcessorDefaultCtorPtrQueries) {
+  AccT acc;
+
+  // The return values of get_pointer() and get_multi_ptr() are
+  // unspecified. Just check they can run without any issue.
+  auto ptr = acc.get_pointer();
+  (void)ptr;
+  // TODO: uncomment check with get_multi_ptr() when SYCL 2020 multi_ptr feature
+  // will be merged
+  // auto multi_ptr = acc.get_multi_ptr();
+  // (void)multi_ptr;
+}