[SYCL] Return trivial default constructor to half type (#4631)

Return trivial default constructor to half type. Without
default constructor it is impossible to create union with
half type. Changed implementation of marray and
half_vec constructors for optimizing them to use half
with trivial default constructor. Update files accordingly
to returned half trivial default constructor.
This patch corrects #4518

Signed-off-by: mdimakov maxim.dimakov@intel.com

Author: maximdimakov

sycl/include/CL/sycl/bit_cast.hpp

@@ -8,7 +8,6 @@
 
 #pragma once
 
-#include <cstdint>
 #include <type_traits>
 
 #if __cpp_lib_bit_cast
@@ -21,21 +20,6 @@ namespace sycl {
 // forward decl
 namespace detail {
 inline void memcpy(void *Dst, const void *Src, std::size_t Size);
-
-namespace half_impl {
-class half;
-}
-using half = cl::sycl::detail::half_impl::half;
-
-template <typename T>
-#ifdef __SYCL_DEVICE_ONLY__
-using lowering_half_type =
-    typename std::conditional<std::is_same<T, half>::value, _Float16, T>::type;
-#else
-using lowering_half_type =
-    typename std::conditional<std::is_same<T, half>::value, std::uint16_t,
-                              T>::type;
-#endif
 }
 
 template <typename To, typename From>
@@ -57,8 +41,7 @@ constexpr
 #if __has_builtin(__builtin_bit_cast)
   return __builtin_bit_cast(To, from);
 #else  // __has_builtin(__builtin_bit_cast)
-  static_assert(std::is_trivially_default_constructible<
-                    typename sycl::detail::lowering_half_type<To>>::value,
+  static_assert(std::is_trivially_default_constructible<To>::value,
                 "To must be trivially default constructible");
   To to;
   sycl::detail::memcpy(&to, &from, sizeof(To));

sycl/include/CL/sycl/half_type.hpp

@@ -37,11 +37,6 @@ __SYCL_INLINE_NAMESPACE(cl) {
 namespace sycl {
 namespace detail {
 
-// bitselect builtin uses union with half specialization, but half has no
-// trivial constructor. This struct allow to use host half class instead of main
-// half class in the bitselect builtin.
-template <typename T> struct builtins_helper;
-
 inline __SYCL_CONSTEXPR_HALF uint16_t float2Half(const float &Val) {
   const uint32_t Bits = sycl::bit_cast<uint32_t>(Val);
 
@@ -194,7 +189,7 @@ class __SYCL_EXPORT half {
 // The main host half class
 class __SYCL_EXPORT half_v2 {
 public:
-  __SYCL_CONSTEXPR_HALF half_v2() : Buf(float2Half(0.0f)) {}
+  half_v2() = default;
   constexpr half_v2(const half_v2 &) = default;
   constexpr half_v2(half_v2 &&) = default;
 
@@ -260,8 +255,6 @@ class __SYCL_EXPORT half_v2 {
   // Initialize underlying data
   constexpr explicit half_v2(uint16_t x) : Buf(x) {}
 
-  template <typename T> friend struct cl::sycl::detail::builtins_helper;
-
 private:
   uint16_t Buf;
 };
@@ -308,9 +301,11 @@ template <int NumElements> struct half_vec {
   alignas(detail::vector_alignment<StorageT, NumElements>::value)
       StorageT s[NumElements];
 
-  __SYCL_CONSTEXPR_HALF half_vec() {
-    for (int i = 0; i < NumElements; i++)
+  __SYCL_CONSTEXPR_HALF half_vec() : s{0.0f} { initialize_data(); }
+  constexpr void initialize_data() {
+    for (size_t i = 0; i < NumElements; ++i) {
       s[i] = StorageT(0.0f);
+    }
   }
 };
 
@@ -323,7 +318,7 @@ template <int NumElements> struct half_vec {
 
 class half {
 public:
-  __SYCL_CONSTEXPR_HALF half() : Data(0.0f){};
+  half() = default;
   constexpr half(const half &) = default;
   constexpr half(half &&) = default;
 
@@ -395,7 +390,6 @@ class half {
   }
 
   template <typename Key> friend struct std::hash;
-  template <typename T> friend struct cl::sycl::detail::builtins_helper;
 
 private:
   StorageT Data;

sycl/include/CL/sycl/marray.hpp

@@ -48,13 +48,17 @@ template <typename Type, std::size_t NumElements> class marray {
   using EnableIfSuitableTypes = typename std::enable_if<
       conjunction<TypeChecker<ArgTN, DataT>...>::value>::type;
 
+  constexpr void initialize_data(const Type &Arg) {
+    for (size_t i = 0; i < NumElements; ++i) {
+      MData[i] = Arg;
+    }
+  }
+
 public:
   constexpr marray() : MData{} {}
 
-  explicit constexpr marray(const Type &Arg) {
-    for (std::size_t I = 0; I < NumElements; ++I) {
-      MData[I] = Arg;
-    }
+  explicit constexpr marray(const Type &Arg) : MData{Arg} {
+    initialize_data(Arg);
   }
 
   template <

sycl/source/detail/builtins_relational.cpp

@@ -18,21 +18,6 @@ namespace s = cl::sycl;
 namespace d = s::detail;
 
 __SYCL_INLINE_NAMESPACE(cl) {
-namespace sycl {
-namespace detail {
-
-// The declaration of this struct is in the CL/sycl/half_type.hpp
-template <typename T> struct builtins_helper {
-  using RetType = T;
-  static constexpr RetType get(T value) { return value; }
-};
-
-template <> struct builtins_helper<s::cl_half> {
-  using RetType = uint16_t;
-  static constexpr RetType get(s::cl_half value) { return value.Data.Buf; }
-};
-} // namespace detail
-} // namespace sycl
 namespace __host_std {
 namespace {
 
@@ -118,20 +103,19 @@ template <> union databitset<s::cl_double> {
 template <> union databitset<s::cl_half> {
   static_assert(sizeof(s::cl_short) == sizeof(s::cl_half),
                 "size of cl_half is not equal to 16 bits(cl_short).");
-  uint16_t f;
+  s::cl_half f;
   s::cl_short i;
 };
 
 template <typename T>
 typename sycl::detail::enable_if_t<d::is_sgenfloat<T>::value,
                                    T> inline __bitselect(T a, T b, T c) {
-  d::builtins_helper<T> helper;
   databitset<T> ba;
-  ba.f = helper.get(a);
+  ba.f = a;
   databitset<T> bb;
-  bb.f = helper.get(b);
+  bb.f = b;
   databitset<T> bc;
-  bc.f = helper.get(c);
+  bc.f = c;
   databitset<T> br;
   br.f = 0;
   br.i = ((ba.i & ~bc.i) | (bb.i & bc.i));

sycl/test/abi/sycl_symbols_windows.dump

@@ -341,7 +341,6 @@
 ??0half_v2@host_half_impl@detail@sycl@cl@@QEAA@AEBM@Z
 ??0half_v2@host_half_impl@detail@sycl@cl@@QEAA@AEBV01234@@Z
 ??0half_v2@host_half_impl@detail@sycl@cl@@QEAA@G@Z
-??0half_v2@host_half_impl@detail@sycl@cl@@QEAA@XZ
 ??0handler@sycl@cl@@AEAA@V?$shared_ptr@Vqueue_impl@detail@sycl@cl@@@std@@_N@Z
 ??0host_selector@sycl@cl@@QEAA@$$QEAV012@@Z
 ??0host_selector@sycl@cl@@QEAA@AEBV012@@Z

sycl/test/basic_tests/types.cpp

@@ -90,7 +90,7 @@ template <> inline void checkSizeForFloatingPoint<s::half, sizeof(int16_t)>() {
 }
 
 int main() {
-  // Test for half constexpr default constructors
+  // Test for creating constexpr expressions
   constexpr sycl::specialization_id<sycl::vec<sycl::half, 2>> id(1.0);
   constexpr sycl::marray<sycl::half, 2> MH(3);
   // Check the size and alignment of the SYCL vectors.

sycl/test/regression/half_union.cpp

@@ -0,0 +1,14 @@
+// RUN: %clangxx -fsycl %s -o %t.out
+// RUN: %RUN_ON_HOST %t.out
+
+#include <CL/sycl.hpp>
+
+typedef union _u16_to_half {
+  unsigned short u;
+  cl::sycl::half h;
+} u16_to_sycl_half;
+
+int main() {
+  u16_to_sycl_half unh;
+  return 0;
+}