[clang] [Clang] Consider preferred_type in bitfield warnings (#116760) (PR #116785)

[Oliver Hunt via cfe-commits]

================
@@ -10488,7 +10488,14 @@ static bool AnalyzeBitFieldAssignment(Sema &S, FieldDecl *Bitfield, Expr *Init,
     // The RHS is not constant.  If the RHS has an enum type, make sure the
     // bitfield is wide enough to hold all the values of the enum without
     // truncation.
-    if (const auto *EnumTy = OriginalInit->getType()->getAs<EnumType>()) {
+    const auto *EnumTy = OriginalInit->getType()->getAs<EnumType>();
+    const PreferredTypeAttr *PTAttr = nullptr;
+    if (!EnumTy) {
+      PTAttr = Bitfield->getAttr<PreferredTypeAttr>();
+      if (PTAttr)
+        EnumTy = PTAttr->getType()->getAs<EnumType>();
+    }
+    if (EnumTy) {
----------------
ojhunt wrote:

Nope, as we're conditionally setting EnumTy in the if(!EnumTy) branch (i.e. EnumTy may not be null afterwards)

https://github.com/llvm/llvm-project/pull/116785