Change the specialization for nullable types to cast to bool

Author: s-barannikov

llvm/include/llvm/ADT/PointerUnion.h

@@ -259,17 +259,6 @@ struct CastInfo<To, const PointerUnion<PTs...>>
                                           CastInfo<To, PointerUnion<PTs...>>> {
 };
 
-// The default implementation of isPresent() for nullable types returns true
-// if the active member is not the first one, even if its value is nullptr.
-// Override the default behavior to return false for all possible null values.
-template <typename... PTs>
-struct ValueIsPresent<PointerUnion<PTs...>,
-                      std::enable_if_t<IsNullable<PointerUnion<PTs...>>>> {
-  using Union = PointerUnion<PTs...>;
-  static bool isPresent(const Union &V) { return static_cast<bool>(V); }
-  static Union &unwrapValue(Union &V) { return V; }
-};
-
 // Teach SmallPtrSet that PointerUnion is "basically a pointer", that has
 // # low bits available = min(PT1bits,PT2bits)-1.
 template <typename ...PTs>

llvm/include/llvm/Support/Casting.h

@@ -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); }
   static inline decltype(auto) unwrapValue(T &t) { return t; }
 };