[llvm] [TableGen] Add `!instances` operator to get defined records (PR #129680)

[Rahul Joshi via llvm-commits]

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@@ -1192,6 +1193,41 @@ class ExistsOpInit final : public TypedInit, public FoldingSetNode {
   std::string getAsString() const override;
 };
 
+/// !instances<type>([regex]) - Produces a list of records whose type is `type`.
+/// If `regex` is provided, only records whose name matches the regular
+/// expression `regex` will be included.
+class InstancesOpInit final : public TypedInit, public FoldingSetNode {
+private:
+  const RecTy *Type;
+  const Init *Regex;
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jurahul wrote:

Can this be a `StringInit` here? That way you avoid an error check and prevent creating an illegal InstancesOpInit instance.

https://github.com/llvm/llvm-project/pull/129680