Revert "[SYCL] vec abi unification and trivially copyable (intel#9492)"

This reverts commit 531aabf.

Author: cperkinsintel

sycl/include/sycl/detail/vector_traits.hpp

@@ -16,20 +16,12 @@ inline namespace _V1 {
 namespace detail {
 
 // 4.10.2.6 Memory layout and alignment
-// due to MSVC the maximum alignment for sycl::vec is 64 and this proposed
-// change is being brought to the spec committee.
-constexpr size_t MaxVecAlignment = 64;
-template <typename T, size_t N>
+template <typename T, int N>
 struct vector_alignment_impl
-    : std::conditional_t<
-          N == 3,
-          std::integral_constant<size_t,
-                                 (std::min)(sizeof(T) * 4, MaxVecAlignment)>,
-          std::integral_constant<size_t,
-                                 (std::min)(sizeof(T) * N, MaxVecAlignment)>> {
-};
+    : std::conditional_t<N == 3, std::integral_constant<int, sizeof(T) * 4>,
+                         std::integral_constant<int, sizeof(T) * N>> {};
 
-template <typename T, size_t N>
+template <typename T, int N>
 struct vector_alignment
     : vector_alignment_impl<std::remove_cv_t<std::remove_reference_t<T>>, N> {};
 } // namespace detail

sycl/include/sycl/half_type.hpp

@@ -259,12 +259,28 @@ using BIsRepresentationT = half;
 // for vec because they are actually defined as an integer type under the
 // hood. As a result half values will be converted to the integer and passed
 // as a kernel argument which is expected to be floating point number.
+template <int NumElements> struct half_vec {
+  alignas(
+      vector_alignment<StorageT, NumElements>::value) StorageT s[NumElements];
 
-using Vec2StorageT = std::array<StorageT, 2>;
-using Vec3StorageT = std::array<StorageT, 3>;
-using Vec4StorageT = std::array<StorageT, 4>;
-using Vec8StorageT = std::array<StorageT, 8>;
-using Vec16StorageT = std::array<StorageT, 16>;
+  __SYCL_CONSTEXPR_HALF half_vec() : s{0.0f} { initialize_data(); }
+  template <typename... Ts,
+            typename = std::enable_if_t<(sizeof...(Ts) == NumElements) &&
+                                        (std::is_same_v<half, Ts> && ...)>>
+  __SYCL_CONSTEXPR_HALF half_vec(const Ts &...hs) : s{hs...} {}
+
+  constexpr void initialize_data() {
+    for (size_t i = 0; i < NumElements; ++i) {
+      s[i] = StorageT(0.0f);
+    }
+  }
+};
+
+using Vec2StorageT = half_vec<2>;
+using Vec3StorageT = half_vec<3>;
+using Vec4StorageT = half_vec<4>;
+using Vec8StorageT = half_vec<8>;
+using Vec16StorageT = half_vec<16>;
 #endif
 
 #ifndef __SYCL_DEVICE_ONLY__