[clang] [CIR] Add CIR vtable attribute (PR #154415)

[Henrich Lauko via cfe-commits]

================
@@ -496,6 +496,46 @@ def CIR_GlobalViewAttr : CIR_Attr<"GlobalView", "global_view", [
   }];
 }
 
+//===----------------------------------------------------------------------===//
+// VTableAttr
+//===----------------------------------------------------------------------===//
+
+def VTableAttr : CIR_Attr<"VTable", "vtable", [TypedAttrInterface]> {
+  let summary = "Represents a C++ vtable";
+  let description = [{
+    Wraps a #cir.const_record containing vtable data.
+
+    Example:
+    ```
+    cir.global linkonce_odr @_ZTV1B = #cir.vtable<<
+        {#cir.const_array<[#cir.null : !cir.ptr<i8>,
+         #cir.global_view<@_ZTI1B> : !cir.ptr<i8>,
+         #cir.global_view<@_ZN1BD1Ev> : !cir.ptr<i8>,
+         #cir.global_view<@_ZN1BD0Ev> : !cir.ptr<i8>,
+         #cir.global_view<@_ZNK1A5quackEv> : !cir.ptr<i8>]>
+         : !cir.array<!cir.ptr<i8> x 5>}>>
+      : !cir.record<"", !cir.array<!cir.ptr<i8> x 5>>
+    ```
+  }];
+
+  // `vtable_data` is a const record with one element, containing an array of
+  // vtable information.
+  let parameters = (ins AttributeSelfTypeParameter<"">:$type,
+                        "mlir::ArrayAttr":$vtable_data);
----------------
xlauko wrote:

```suggestion
  let parameters = (ins 
    AttributeSelfTypeParameter<"">:$type,
    "mlir::ArrayAttr":$vtable_data
  );
```

https://github.com/llvm/llvm-project/pull/154415