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

[Sergei Barannikov via llvm-commits]

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@@ -614,12 +614,11 @@ 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.
+// If something is "nullable" then we just cast it to bool to see if it exists.
 template <typename T>
 struct ValueIsPresent<T, std::enable_if_t<IsNullable<T>>> {
   using UnwrappedType = T;
-  static inline bool isPresent(const T &t) { return t != T(nullptr); }
+  static inline bool isPresent(const T &t) { return static_cast<bool>(t); }
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s-barannikov wrote:

It appears `is_convertible` only handles implicit conversions, i.e. it returns false for types with `explicit operator bool()`. I used `is_constructible` with swapped arguments instead.



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