From 5f796398d05621b61553128e3cb43a6859f2cf9c Mon Sep 17 00:00:00 2001
From: Alexey Sachkov <alexey.sachkov@intel.com>
Date: Fri, 20 Jan 2023 08:10:57 -0500
Subject: [PATCH 1/2] [SYCL] Make half default constructor constexpr

Unfortunately, it seem to be impossible to have a trivial default
constexpr constructor until we enable C++23 mode. Therefore, this patch
made a few other adjustments to account for non-trivial default
constructor of `half` class.
---
 sycl/include/sycl/bit_cast.hpp                       | 4 ++--
 sycl/include/sycl/half_type.hpp                      | 9 +++++----
 sycl/source/detail/builtins_relational.cpp           | 1 +
 sycl/test/basic_tests/half-constexpr-constructor.cpp | 9 +++++++++
 sycl/test/regression/half_union.cpp                  | 2 +-
 5 files changed, 18 insertions(+), 7 deletions(-)
 create mode 100644 sycl/test/basic_tests/half-constexpr-constructor.cpp

diff --git a/sycl/include/sycl/bit_cast.hpp b/sycl/include/sycl/bit_cast.hpp
index 342281b1a5785..f945ce6cfa9f6 100644
--- a/sycl/include/sycl/bit_cast.hpp
+++ b/sycl/include/sycl/bit_cast.hpp
@@ -41,8 +41,8 @@ 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<To>::value,
-                "To must be trivially default constructible");
+  static_assert(std::is_default_constructible<To>::value,
+                "To must be default constructible");
   To to;
   sycl::detail::memcpy(&to, &from, sizeof(To));
   return to;
diff --git a/sycl/include/sycl/half_type.hpp b/sycl/include/sycl/half_type.hpp
index ace7be7352c6c..ec7a51104f7db 100644
--- a/sycl/include/sycl/half_type.hpp
+++ b/sycl/include/sycl/half_type.hpp
@@ -137,7 +137,8 @@ namespace host_half_impl {
 // The main host half class
 class __SYCL_EXPORT half {
 public:
-  half() = default;
+  constexpr half() {}
+
   constexpr half(const half &) = default;
   constexpr half(half &&) = default;
 
@@ -206,7 +207,7 @@ class __SYCL_EXPORT half {
   friend class sycl::ext::intel::esimd::detail::WrapperElementTypeProxy;
 
 private:
-  uint16_t Buf;
+  uint16_t Buf = {};
 };
 
 } // namespace host_half_impl
@@ -272,7 +273,7 @@ class half {
 class [[__sycl_detail__::__uses_aspects__(aspect::fp16)]] half {
 #endif
 public:
-  half() = default;
+  constexpr half() {}
   constexpr half(const half &) = default;
   constexpr half(half &&) = default;
 
@@ -548,7 +549,7 @@ class [[__sycl_detail__::__uses_aspects__(aspect::fp16)]] half {
   friend class sycl::ext::intel::esimd::detail::WrapperElementTypeProxy;
 
 private:
-  StorageT Data;
+  StorageT Data = {};
 };
 } // namespace half_impl
 
diff --git a/sycl/source/detail/builtins_relational.cpp b/sycl/source/detail/builtins_relational.cpp
index 8d64e1379733f..31bcd4b28271e 100644
--- a/sycl/source/detail/builtins_relational.cpp
+++ b/sycl/source/detail/builtins_relational.cpp
@@ -116,6 +116,7 @@ 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).");
+  databitset(): i(0) {}
   s::cl_half f;
   s::cl_short i;
 };
diff --git a/sycl/test/basic_tests/half-constexpr-constructor.cpp b/sycl/test/basic_tests/half-constexpr-constructor.cpp
new file mode 100644
index 0000000000000..6b0e640a7ba3b
--- /dev/null
+++ b/sycl/test/basic_tests/half-constexpr-constructor.cpp
@@ -0,0 +1,9 @@
+// RUN: %clangxx -fsycl -fsyntax-only %s
+
+#include <sycl/sycl.hpp>
+
+int main() {
+  constexpr sycl::half h;
+
+  return 0;
+}
diff --git a/sycl/test/regression/half_union.cpp b/sycl/test/regression/half_union.cpp
index 1b67f8cb76c39..8683bbb2af25a 100644
--- a/sycl/test/regression/half_union.cpp
+++ b/sycl/test/regression/half_union.cpp
@@ -5,7 +5,7 @@
 
 typedef union _u16_to_half {
   unsigned short u;
-  sycl::half h;
+  sycl::half h = 0.0;
 } u16_to_sycl_half;
 
 int main() {

From cf8afc297995303a5a85570a5d1b325d50477f8c Mon Sep 17 00:00:00 2001
From: Alexey Sachkov <alexey.sachkov@intel.com>
Date: Fri, 20 Jan 2023 08:25:47 -0500
Subject: [PATCH 2/2] Mark half constructor as default

---
 sycl/include/sycl/half_type.hpp | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/sycl/include/sycl/half_type.hpp b/sycl/include/sycl/half_type.hpp
index ec7a51104f7db..16c47c4ca77f3 100644
--- a/sycl/include/sycl/half_type.hpp
+++ b/sycl/include/sycl/half_type.hpp
@@ -137,7 +137,7 @@ namespace host_half_impl {
 // The main host half class
 class __SYCL_EXPORT half {
 public:
-  constexpr half() {}
+  constexpr half() = default;
 
   constexpr half(const half &) = default;
   constexpr half(half &&) = default;
@@ -273,7 +273,7 @@ class half {
 class [[__sycl_detail__::__uses_aspects__(aspect::fp16)]] half {
 #endif
 public:
-  constexpr half() {}
+  constexpr half() = default;
   constexpr half(const half &) = default;
   constexpr half(half &&) = default;