Define LLVM_IS_TRIVIALLY_COPYABLE

[rogfer01]

Summary

Some objects have storage specifics which force them to be trivially copyable. Enforcing this requirement at compile time should avoid wasting time debugging du to accidentally breaking it.

As suggested in D48589 llvm::isPodLike almost does something like this. This change extracts the relevant logic so we can skip compiling it if the compiler does not support that trait (yet).

[rogfer01]

Not needed for now.

include/llvm/Support/type_traits.h

 
 #ifndef __has_feature
 #define LLVM_DEFINED_HAS_FEATURE
 #define __has_feature(x) 0
 #endif
 
 namespace llvm {
 
-/// isPodLike - This is a type trait that is used to determine whether a given
-/// type can be copied around with memcpy instead of running ctors etc.
-template <typename T>
-struct isPodLike {
-  // std::is_trivially_copyable is available in libc++ with clang, libstdc++
-  // that comes with GCC 5.
+/// If the compiler is able to implement is_trivially_copyable
+/// define LLVM_IS_TRIVIALLY_COPYABLE, otherwise leave it undefined.
 #if (__has_feature(is_trivially_copyable) && defined(_LIBCPP_VERSION)) ||      \
     (defined(__GNUC__) && __GNUC__ >= 5)
-  // If the compiler supports the is_trivially_copyable trait use it, as it
-  // matches the definition of isPodLike closely.
-  static const bool value = std::is_trivially_copyable<T>::value;
+// std::is_trivially_copyable is available in libc++ with clang, libstdc++
+// that comes with GCC 5.
+#define LLVM_IS_TRIVIALLY_COPYABLE(Ty) std::is_trivially_copyable<Ty>::value
 #elif __has_feature(is_trivially_copyable)
-  // Use the internal name if the compiler supports is_trivially_copyable but we
-  // don't know if the standard library does. This is the case for clang in
-  // conjunction with libstdc++ from GCC 4.x.
-  static const bool value = __is_trivially_copyable(T);
+#define LLVM_IS_TRIVIALLY_COPYABLE(Ty) __is_trivially_copyable(Ty)
+#endif
+
+/// isPodLike - This is a type trait that is used to determine whether a given
+/// type can be copied around with memcpy instead of running ctors etc.
+template <typename T>
+struct isPodLike {
+// If the compiler can implement the is_trivially_copyable trait use it, as it
+// matches the definition of isPodLike closely.
+#if defined(LLVM_IS_TRIVIALLY_COPYABLE)
+  static const bool value = LLVM_IS_TRIVIALLY_COPYABLE(T);
 #else
   // If we don't know anything else, we can (at least) assume that all non-class
   // types are PODs.
   static const bool value = !std::is_class<T>::value;
 #endif
 };
 
 // std::pair's are pod-like if their elements are.