[clang] [clang]bytecode] Add degenerate pointers (PR #160086)

[Shafik Yaghmour via cfe-commits]

================
@@ -252,14 +264,19 @@ class Pointer {
 
   /// Checks if the pointer is null.
   bool isZero() const {
-    if (isBlockPointer())
+    switch (StorageKind) {
+    case Storage::Int:
+      return Int.Value == 0 && Offset == 0;
+    case Storage::Block:
       return BS.Pointee == nullptr;
-    if (isFunctionPointer())
-      return Fn.isZero();
-    if (isTypeidPointer())
+    case Storage::Fn:
+      return asFunctionPointer().isZero();
+    case Storage::Typeid:
       return false;
-    assert(isIntegralPointer());
-    return Int.Value == 0 && Offset == 0;
+    case Storage::Degen:
+      return DP.Pointee == nullptr;
----------------
shafik wrote:

How do we end up w/ a degenerate pointer that is `nullptr`? Is this testable?

https://github.com/llvm/llvm-project/pull/160086