[clang] [CIR] Record the source level identity of functions on cir.func (PR #207261)

[Erich Keane via cfe-commits]

================
@@ -1298,6 +1298,48 @@ def CIR_CXXSpecialMemberAttr : AnyAttrOf<[
   CIR_CXXAssignAttr
 ]>;
 
+//===----------------------------------------------------------------------===//
+// FuncInfoAttr
+//===----------------------------------------------------------------------===//
+
+def CIR_FuncInfoAttr : CIR_Attr<"FuncInfo", "func_info"> {
+  let summary = "Holds the source level identity of a function";
+  let description = [{
+    Carries facts about the source declaration a function was emitted from,
+    precomputed during CIRGen while the AST is available. Passes that want
+    to reason about what the source calls read this attribute instead of
+    the AST.
----------------
erichkeane wrote:

The above text is pretty awkward.  We probably shouldn't mention the AST in it either.  Please phrase this as if it is describing the purpose of this attribute in a more general sense.

https://github.com/llvm/llvm-project/pull/207261