[SYCL][NFC] Unify vec implementation

Unified code related to `vec` alignment to reduce amount of macro-based
branching we have for preview breaking changes mode.

Author: AlexeySachkov

sycl/include/sycl/detail/vector_traits.hpp

@@ -9,6 +9,7 @@
 #pragma once
 
 #include <algorithm>   // for std::min and vs2017 win
+#include <limits>      // for numeric_limits
 #include <type_traits> // for integral_constant, conditional_t, remove_cv_t
 
 namespace sycl {
@@ -17,9 +18,36 @@ namespace detail {
 
 // 4.10.2.6 Memory layout and alignment
 #ifdef __INTEL_PREVIEW_BREAKING_CHANGES
-// due to MSVC the maximum alignment for sycl::vec is 64 and this proposed
-// change is being brought to the spec committee.
+// SYCL 2020 vec alignment requirements have been relaxed in
+// KhronosGroup/SYCL-Docs#448. New specification wording only guarantees 64-byte
+// alignment of vec class and we leverage this here to avoid dealing with MSVC
+// limitations (see below).
 constexpr size_t MaxVecAlignment = 64;
+#else
+// This version is preserved to maintain API/ABI compatibility with older
+// releases.
+// FIXME: drop this branch once API/ABI break is allowed
+
+#if defined(_WIN32) && (_MSC_VER)
+// MSVC Compiler doesn't allow using of function arguments with alignment
+// requirements. MSVC Compiler Error C2719: 'parameter': formal parameter with
+// __declspec(align('#')) won't be aligned. The align __declspec modifier
+// is not permitted on function parameters. Function parameter alignment
+// is controlled by the calling convention used.
+// For more information, see Calling Conventions
+// (https://docs.microsoft.com/en-us/cpp/cpp/calling-conventions).
+// For information on calling conventions for x64 processors, see
+// Calling Convention
+// (https://docs.microsoft.com/en-us/cpp/build/x64-calling-convention).
+constexpr size_t MaxVecAlignment = 64;
+#else
+// To match ABI of previos releases, we don't impose any restrictions on vec
+// alignment on Linux
+constexpr size_t MaxVecAlignment = std::numeric_limits<size_t>::max();
+#endif
+
+#endif // __INTEL_PREVIEW_BREAKING_CHANGES
+
 template <typename T, size_t N>
 struct vector_alignment_impl
     : std::conditional_t<
@@ -29,12 +57,6 @@ struct vector_alignment_impl
           std::integral_constant<size_t,
                                  (std::min)(sizeof(T) * N, MaxVecAlignment)>> {
 };
-#else
-template <typename T, size_t N>
-struct vector_alignment_impl
-    : std::conditional_t<N == 3, std::integral_constant<int, sizeof(T) * 4>,
-                         std::integral_constant<int, sizeof(T) * N>> {};
-#endif
 
 template <typename T, size_t N>
 struct vector_alignment

sycl/include/sycl/types.hpp

@@ -272,30 +272,6 @@ template <typename T> using vec_data = detail::vec_helper<T>;
 template <typename T>
 using vec_data_t = typename detail::vec_helper<T>::RetType;
 
-#if !defined(__INTEL_PREVIEW_BREAKING_CHANGES)
-
-#if defined(_WIN32) && (_MSC_VER)
-// MSVC Compiler doesn't allow using of function arguments with alignment
-// requirements. MSVC Compiler Error C2719: 'parameter': formal parameter with
-// __declspec(align('#')) won't be aligned. The align __declspec modifier
-// is not permitted on function parameters. Function parameter alignment
-// is controlled by the calling convention used.
-// For more information, see Calling Conventions
-// (https://docs.microsoft.com/en-us/cpp/cpp/calling-conventions).
-// For information on calling conventions for x64 processors, see
-// Calling Convention
-// (https://docs.microsoft.com/en-us/cpp/build/x64-calling-convention).
-#pragma message("Alignment of class vec is not in accordance with SYCL \
-specification requirements, a limitation of the MSVC compiler(Error C2719).\
-Requested alignment applied, limited at 64.")
-#define __SYCL_ALIGNED_VAR(type, x, var)                                       \
-  type __declspec(align((x < 64) ? x : 64)) var
-#else
-#define __SYCL_ALIGNED_VAR(type, x, var) alignas(x) type var
-#endif
-
-#endif //! defined(__INTEL_PREVIEW_BREAKING_CHANGES)
-
 /// Provides a cross-patform vector class template that works efficiently on
 /// SYCL devices as well as in host C++ code.
 ///
@@ -1458,31 +1434,12 @@ template <typename Type, int NumElements> class vec {
     return (NumElements == 1) ? getValue(Index, 0) : getValue(Index, 0.f);
   }
 
-#if defined(__INTEL_PREVIEW_BREAKING_CHANGES)
-
   // fields
 
-  // Alignment is the same as size, to a maximum size of 64.
-  // detail::vector_alignment will return that value.
+  // Alignment is the same as size, to a maximum size of 64 (with some
+  // exceptions, see detail::vector_alignment).
   alignas(detail::vector_alignment<DataT, NumElements>::value) DataType m_Data;
 
-#endif // defined(__INTEL_PREVIEW_BREAKING_CHANGES)
-
-#if !defined(__INTEL_PREVIEW_BREAKING_CHANGES)
-
-  // fields
-
-  // Used "__SYCL_ALIGNED_VAR" instead "alignas" to handle MSVC compiler.
-  // For MSVC compiler max alignment is 64, e.g. vec<double, 16> required
-  // alignment of 128 and MSVC compiler cann't align a parameter with requested
-  // alignment of 128. For alignment request larger than 64, 64-alignment
-  // is applied
-  __SYCL_ALIGNED_VAR(DataType,
-                     (detail::vector_alignment<DataT, NumElements>::value),
-                     m_Data);
-
-#endif // !defined(__INTEL_PREVIEW_BREAKING_CHANGES)
-
   // friends
   template <typename T1, typename T2, typename T3, template <typename> class T4,
             int... T5>
@@ -2554,7 +2511,3 @@ struct CheckDeviceCopyable<
 
 } // namespace _V1
 } // namespace sycl
-
-#if !defined(__INTEL_PREVIEW_BREAKING_CHANGES)
-#undef __SYCL_ALIGNED_VAR
-#endif // !defined(__INTEL_PREVIEW_BREAKING_CHANGES)