Update edm::bit_cast

Use std::bit_cast in C++20 mode. Othwerwise, use __builtin_bit_cast if available.

FWCore/Utilities/interface/bit_cast.h

@@ -20,17 +20,39 @@
 
 // system include files
 #include <cstring>
+#include <type_traits>
 
-// user include files
+#if __cplusplus >= 202002L
+
+// in C++20 we can use std::bit_cast
+
+#include <bit>
+
+namespace edm {
+  using std::bit_cast;
+}  // namespace edm
+
+#else
+
+// before C++20 we can use __builtin_bit_cast in recent compilers
 
 namespace edm {
-  //in C++20 we can use std::bit_cast which is constexpr
   template <class To, class From>
+  constexpr
   inline To bit_cast(const From &src) noexcept {
+    static_assert(std::is_trivially_copyable_v<From>);
+    static_assert(std::is_trivially_copyable_v<To>);
     static_assert(sizeof(To) == sizeof(From), "incompatible types");
+#ifdef GCC_PREREQUISITE(11,0,0) || CLANG_PREREQUISITE(9,0,0)
+    return __builtin_bit_cast(To, src);
+#else
     To dst;
     std::memcpy(&dst, &src, sizeof(To));
     return dst;
+#endif
   }
 }  // namespace edm
+
+#endif  // __cplusplus >= 202002L
+
 #endif