[llvm] [ADT] Specialize ValueIsPresent for PointerUnion (PR #121847)

[Sergei Barannikov via llvm-commits]

================
@@ -614,12 +610,11 @@ template <typename T> struct ValueIsPresent<std::optional<T>> {
   static inline decltype(auto) unwrapValue(std::optional<T> &t) { return *t; }
 };
 
-// If something is "nullable" then we just compare it to nullptr to see if it
-// exists.
+// Specialization for types convertible to bool.
 template <typename T>
-struct ValueIsPresent<T, std::enable_if_t<IsNullable<T>>> {
+struct ValueIsPresent<T, std::enable_if_t<std::is_constructible_v<bool, T>>> {
----------------
s-barannikov wrote:

I thought about it, but figured that checking whether the type is convertible to bool exactly answers the question "does an object have a value". This may not be desired for non-class types (e.g. `int`) but those shouldn't really be used in this context.


https://github.com/llvm/llvm-project/pull/121847