[SYCL] Fix C++14/C++20 compatibility issues (#6410)

* Show that stdcpp_compat.cpp test misses some warnings
* Fix -std=C++XX incompatibilities
* Clarify comment pointing that it's a workaround for clang
...and not something mandated by the C++20.

Author: aelovikov-intel

sycl/include/CL/sycl/id.hpp

@@ -118,6 +118,11 @@ template <int dimensions = 1> class id : public detail::array<dimensions> {
 // OP is: ==, !=
 #ifndef __SYCL_DISABLE_ID_TO_INT_CONV__
   using detail::array<dimensions>::operator==;
+  // Needed for clang in C++20 mode as the above operator== would be ambigious
+  // between regular/reversed call for "Id == Id" case.
+  bool operator==(const id<dimensions> &rhs) const {
+    return this->detail::array<dimensions>::operator==(rhs);
+  }
 #if __cpp_impl_three_way_comparison < 201907
   using detail::array<dimensions>::operator!=;
 #endif

sycl/include/sycl/ext/oneapi/device_global/properties.hpp

@@ -45,6 +45,7 @@ struct implement_in_csr_key {
       property_value<implement_in_csr_key, sycl::detail::bool_constant<Enable>>;
 };
 
+#if __cplusplus >= 201703L // inline variables
 inline constexpr device_image_scope_key::value_t device_image_scope;
 
 template <host_access_enum Access>
@@ -68,6 +69,7 @@ template <bool Enable>
 inline constexpr implement_in_csr_key::value_t<Enable> implement_in_csr;
 inline constexpr implement_in_csr_key::value_t<true> implement_in_csr_on;
 inline constexpr implement_in_csr_key::value_t<false> implement_in_csr_off;
+#endif // __cplusplus >= 201703L
 
 template <> struct is_property_key<device_image_scope_key> : std::true_type {};
 template <> struct is_property_key<host_access_key> : std::true_type {};

sycl/include/sycl/ext/oneapi/experimental/cuda/barrier.hpp

@@ -14,7 +14,11 @@
 #include <cstddef>
 
 __SYCL_INLINE_NAMESPACE(cl) {
-namespace sycl::ext::oneapi::experimental::cuda {
+namespace sycl {
+namespace ext {
+namespace oneapi {
+namespace experimental {
+namespace cuda {
 
 class barrier {
   int64_t state;
@@ -141,6 +145,9 @@ class barrier {
   static constexpr uint64_t max() { return (1 << 20) - 1; }
 #pragma pop_macro("max")
 };
-
-} // namespace sycl::ext::oneapi::experimental::cuda
+} // namespace cuda
+} // namespace experimental
+} // namespace oneapi
+} // namespace ext
+} // namespace sycl
 } // __SYCL_INLINE_NAMESPACE(cl)

sycl/include/sycl/ext/oneapi/matrix/matrix-jit.hpp

@@ -17,7 +17,8 @@ __SYCL_INLINE_NAMESPACE(cl) {
 namespace sycl {
 namespace ext {
 namespace oneapi {
-namespace experimental::matrix {
+namespace experimental {
+namespace matrix {
 
 enum class matrix_layout { row_major, col_major, packed_a, packed_b };
 
@@ -171,6 +172,7 @@ joint_matrix_store(Group sg,
 #endif // __SYCL_DEVICE_ONLY__
 }
 
+#if __cplusplus >= 201703L // if constexpr
 template <typename Group, typename T1, typename T2, typename T3, size_t M,
           size_t K, size_t N, matrix_layout LayoutA, matrix_layout LayoutB,
           matrix_layout LayoutC>
@@ -202,6 +204,7 @@ joint_matrix_mad(Group sg, joint_matrix<T1, M, K, LayoutA, Group> &mA,
                       PI_ERROR_INVALID_DEVICE);
 #endif // __SYCL_DEVICE_ONLY__
 }
+#endif // __cplusplus >= 201703L
 
 template <typename Group, typename T, size_t NumRows, size_t NumCols,
           matrix_layout Layout, typename T2>
@@ -624,7 +627,8 @@ class wi_data {
   }
 };
 
-} // namespace experimental::matrix
+} // namespace matrix
+} // namespace experimental
 } // namespace oneapi
 } // namespace ext
 } // namespace sycl

sycl/include/sycl/ext/oneapi/matrix/static-query.hpp

@@ -26,7 +26,8 @@ __SYCL_INLINE_NAMESPACE(cl) {
 namespace sycl {
 namespace ext {
 namespace oneapi {
-namespace experimental::matrix {
+namespace experimental {
+namespace matrix {
 
 enum class tpu {
   dpas,
@@ -416,7 +417,8 @@ struct tpu_params<
   scope_t scope = scope_t::sub_group;
 };
 #endif
-} // namespace experimental::matrix
+} // namespace matrix
+} // namespace experimental
 } // namespace oneapi
 } // namespace ext
 } // namespace sycl

sycl/include/sycl/ext/oneapi/properties/property_value.hpp

@@ -48,6 +48,7 @@ struct property_value
   using key_t = PropertyT;
 };
 
+#if __cplusplus >= 201703L // pack fold expressions
 template <typename PropertyT, typename... A, typename... B>
 constexpr std::enable_if_t<detail::IsCompileTimeProperty<PropertyT>::value,
                            bool>
@@ -63,6 +64,7 @@ operator!=(const property_value<PropertyT, A...> &,
            const property_value<PropertyT, B...> &) {
   return (!std::is_same<A, B>::value || ...);
 }
+#endif // __cplusplus >= 201703L
 
 template <typename V, typename = void> struct is_property_value {
   static constexpr bool value =

sycl/include/sycl/ext/oneapi/reduction.hpp

@@ -226,7 +226,7 @@ template <class Reducer> class combiner {
   }
 
   template <class _T, access::address_space Space, class BinaryOperation>
-  static inline constexpr bool BasicCheck =
+  static constexpr bool BasicCheck =
       std::is_same<typename remove_AS<_T>::type, T>::value &&
       (Space == access::address_space::global_space ||
        Space == access::address_space::local_space);
@@ -2089,6 +2089,7 @@ void reduCGFuncImplArrayHelper(nd_item<Dims> NDIt, LocalAccT LocalReds,
   }
 }
 
+#if __cplusplus >= 201703L // pack fold expressions
 template <bool Pow2WG, bool IsOneWG, typename... Reductions, int Dims,
           typename... LocalAccT, typename... OutAccT, typename... ReducerT,
           typename... Ts, typename... BOPsT, size_t... Is>
@@ -2169,6 +2170,7 @@ void reduCGFuncImpl(handler &CGH, KernelType KernelFunc,
         BOPsTuple, InitToIdentityProps, ArrayIs);
   });
 }
+#endif // __cplusplus >= 201703L
 
 template <typename KernelName, typename KernelType, int Dims,
           typename... Reductions, size_t... Is>
@@ -2391,6 +2393,9 @@ void reduAuxCGFuncImplArrayHelper(nd_item<Dims> NDIt, size_t LID, size_t GID,
   }
 }
 
+// Pack fold expressions are used either in the function itself or down its
+// callstack.
+#if __cplusplus >= 201703L
 template <bool UniformPow2WG, bool IsOneWG, typename... Reductions, int Dims,
           typename... LocalAccT, typename... InAccT, typename... OutAccT,
           typename... Ts, typename... BOPsT, size_t... Is>
@@ -2466,6 +2471,7 @@ void reduAuxCGFuncImpl(handler &CGH, size_t NWorkItems, size_t NWorkGroups,
         OutAccsTuple, IdentitiesTuple, BOPsTuple, InitToIdentityProps, ArrayIs);
   });
 }
+#endif // __cplusplus >= 201703L
 
 template <typename KernelName, typename KernelType, typename... Reductions,
           size_t... Is>

sycl/test/basic_tests/stdcpp_compat.cpp

@@ -1,9 +1,9 @@
 // RUN: %clangxx -std=c++14 -fsycl -Wall -pedantic -Wno-c99-extensions -Wno-deprecated -fsyntax-only -Xclang -verify=expected,cxx14 %s -c -o %t.out
 // RUN: %clangxx -std=c++14 -fsycl -Wall -pedantic -Wno-c99-extensions -Wno-deprecated -fsyntax-only -Xclang -verify %s -c -o %t.out -DSYCL_DISABLE_CPP_VERSION_CHECK_WARNING=1
-// RUN: %clangxx -std=c++14 -fsycl --no-system-header-prefix=CL/sycl -Wall -pedantic -Wno-c99-extensions -Wno-deprecated -fsyntax-only -Xclang -verify=cxx14,warning_extension,expected %s -c -o %t.out
-// RUN: %clangxx -std=c++17 -fsycl --no-system-header-prefix=CL/sycl -Wall -pedantic -Wno-c99-extensions -Wno-deprecated -fsyntax-only -Xclang -verify %s -c -o %t.out
-// RUN: %clangxx -std=c++20 -fsycl --no-system-header-prefix=CL/sycl -Wall -pedantic -Wno-c99-extensions -Wno-deprecated -fsyntax-only -Xclang -verify %s -c -o %t.out
-// RUN: %clangxx            -fsycl --no-system-header-prefix=CL/sycl -Wall -pedantic -Wno-c99-extensions -Wno-deprecated -fsyntax-only -Xclang -verify %s -c -o %t.out
+// RUN: %clangxx -std=c++14 -fsycl --no-system-header-prefix=CL/sycl --no-system-header-prefix=sycl -Wall -pedantic -Wno-c99-extensions -Wno-deprecated -fsyntax-only -Xclang -verify=cxx14,warning_extension,expected %s -c -o %t.out
+// RUN: %clangxx -std=c++17 -fsycl --no-system-header-prefix=CL/sycl --no-system-header-prefix=sycl -Wall -pedantic -Wno-c99-extensions -Wno-deprecated -fsyntax-only -Xclang -verify %s -c -o %t.out
+// RUN: %clangxx -std=c++20 -fsycl --no-system-header-prefix=CL/sycl --no-system-header-prefix=sycl -Wall -pedantic -Wno-c99-extensions -Wno-deprecated -fsyntax-only -Xclang -verify %s -c -o %t.out
+// RUN: %clangxx            -fsycl --no-system-header-prefix=CL/sycl --no-system-header-prefix=sycl -Wall -pedantic -Wno-c99-extensions -Wno-deprecated -fsyntax-only -Xclang -verify %s -c -o %t.out
 
 // The test checks SYCL headers C++ compiance and that a warning is emitted
 // when compiling in < C++17 mode.