[clang] [StaticAnalyzer] Migrate away from PointerUnion::{is,get} (NFC) (PR #118421)

[Balazs Benics via cfe-commits]

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@@ -205,10 +205,10 @@ const NamedDecl *nonloc::PointerToMember::getDecl() const {
     return nullptr;
 
   const NamedDecl *ND = nullptr;
-  if (PTMD.is<const NamedDecl *>())
-    ND = PTMD.get<const NamedDecl *>();
+  if (isa<const NamedDecl *>(PTMD))
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steakhal wrote:

I think we should use dyn_cast here.

https://github.com/llvm/llvm-project/pull/118421