[NFC] Give NullablePtr some PointerLikeTypeTraits

Allows it to be used in PointerIntPair and PointerUnion.

Author: beccadax

include/swift/Basic/NullablePtr.h

@@ -20,6 +20,7 @@
 #include <cassert>
 #include <cstddef>
 #include <type_traits>
+#include "llvm/Support/PointerLikeTypeTraits.h"
 
 namespace swift {
 /// NullablePtr pointer wrapper - NullablePtr is used for APIs where a
@@ -81,4 +82,19 @@ class NullablePtr {
 
 } // end namespace swift
 
+namespace llvm {
+template <typename T> struct PointerLikeTypeTraits;
+template <typename T> struct PointerLikeTypeTraits<swift::NullablePtr<T>> {
+public:
+  static inline void *getAsVoidPointer(swift::NullablePtr<T> ptr) {
+    return static_cast<void *>(ptr.getPtrOrNull());
+  }
+  static inline swift::NullablePtr<T> getFromVoidPointer(void *ptr) {
+    return swift::NullablePtr<T>(static_cast<T*>(ptr));
+  }
+  enum { NumLowBitsAvailable = PointerLikeTypeTraits<T *>::NumLowBitsAvailable };
+};
+
+}
+
 #endif // SWIFT_BASIC_NULLABLEPTR_H