[clang] [Clang][attr] Add 'cfi_salt' attribute (PR #141846)

[Aaron Ballman via cfe-commits]

================
@@ -7941,6 +7942,32 @@ static bool handleFunctionTypeAttr(TypeProcessingState &state, ParsedAttr &attr,
     return true;
   }
 
+  if (attr.getKind() == ParsedAttr::AT_CFISalt) {
+    if (attr.getNumArgs() == 0)
+      return true;
+
+    // Delay if this is not a function type.
+    StringRef Argument;
+    if (!S.checkStringLiteralArgumentAttr(attr, 0, Argument))
+      return false;
+
+    // Delay if this is not a function type.
+    if (!unwrapped.isFunctionType())
+      return false;
+
+    const auto *FnTy = unwrapped.get()->getAs<FunctionProtoType>();
+    if (!FnTy)
----------------
AaronBallman wrote:

>  I wouldn't expect an attribute that doesn't pass the builtin-TableGen'd stuff to reach this function (like for arg counts/appertainment/etc), so if this IS getting here, it either needs to diagnose here, or figure out WHY we're continuing after failing tablegen.

Type attributes do not have as much automagical hookup with tablegen as declaration attributes; so IIRC all of them have to do manual processing like this. So I do expect to get here (at least, with my psychic debugger), and I think we likely need to diagnose explicitly.

https://github.com/llvm/llvm-project/pull/141846