[clang] [compiler-rt] [ubsan] Improve scoped enum diagnostic printer (PR #216460)

[Yanzuo Liu via cfe-commits]

================
@@ -3959,6 +3959,14 @@ llvm::Constant *CodeGenFunction::EmitCheckTypeDescriptor(QualType T) {
   uint16_t TypeInfo = 0;
   bool IsBitInt = false;
 
+  // isIntegerType() never holds for scoped enums, and getAs<BitIntType> can't
+  // see through the EnumType node to a __BitInt underlying type even for
+  // unscoped enums.
+  QualType BackupT = T;
+  if (const EnumType *ET = T->getAs<EnumType>())
+    if (ET->getDecl()->isComplete())
----------------
zwuis wrote:

> But "incomplete" can be a little weird with enums. For example:
> 
> ```
> enum class E : bool;
> int f(E* x) { return (int)*x; }
> ```
> 
> The type isn't incomplete, but the enum decl is.

For this enum, `TagDecl::isCompleteDefinition` returns `false` because the enum doesn't have 'body' (`{}`); `EnumDecl::isComplete` returns `true`.

https://github.com/llvm/llvm-project/pull/216460