[mlir] Make classof substitution in interface use an instance

The substitution supported by `extraClassOf` is currently limited to only the base instance, i.e. `Operation*`, `Type` or `Attribute`, which limits the kind of checks you can perform in the `classof` implementation.

Since prior to the user code, the interface concept is fetched, we can use it to construct an instance of the interface, allowing use of its methods in the `classof` check.

Since an instance of the interface allows access to the base class methods through the `->` operator, I've gone ahead and replaced the substitution of `$_op/$_type/$_attr` with an interface instance. This is also consistent with `extraSharedClassDeclaration` and other methods created in the interface class which do the same.

Author: zero9178

mlir/include/mlir/IR/Interfaces.td

@@ -114,7 +114,7 @@ class Interface<string name, list<Interface> baseInterfacesArg = []> {
   // be used to better enable "optional" interfaces, where an entity only
   // implements the interface if some dynamic characteristic holds.
   // `$_attr`/`$_op`/`$_type` may be used to refer to an instance of the
-  // entity being checked.
+  // interface instance being checked.
   code extraClassOf = "";
 
   // An optional set of base interfaces that this interface

mlir/test/mlir-tblgen/op-interface.td

@@ -11,9 +11,11 @@ def ExtraClassOfInterface : OpInterface<"ExtraClassOfInterface"> {
 
 // DECL: class ExtraClassOfInterface
 // DECL:   static bool classof(::mlir::Operation * base) {
-// DECL-NEXT:     if (!getInterfaceFor(base))
+// DECL-NEXT:     auto* concept = getInterfaceFor(base);
+// DECL-NEXT:     if (!concept)
 // DECL-NEXT:       return false;
-// DECL-NEXT:     return base->someOtherMethod();
+// DECL-NEXT:     ExtraClassOfInterface odsInterfaceInstance(base, concept);
+// DECL-NEXT:     return odsInterfaceInstance->someOtherMethod();
 // DECL-NEXT:   }
 
 def ExtraShardDeclsInterface : OpInterface<"ExtraShardDeclsInterface"> {

mlir/tools/mlir-tblgen/OpInterfacesGen.cpp

@@ -582,10 +582,12 @@ void InterfaceGenerator::emitInterfaceDecl(const Interface &interface) {
   // Emit classof code if necessary.
   if (std::optional<StringRef> extraClassOf = interface.getExtraClassOf()) {
     auto extraClassOfFmt = tblgen::FmtContext();
-    extraClassOfFmt.addSubst(substVar, "base");
+    extraClassOfFmt.addSubst(substVar, "odsInterfaceInstance");
     os << "  static bool classof(" << valueType << " base) {\n"
-       << "    if (!getInterfaceFor(base))\n"
+       << "    auto* concept = getInterfaceFor(base);\n"
+       << "    if (!concept)\n"
           "      return false;\n"
+          "    " << interfaceName << " odsInterfaceInstance(base, concept);\n"
        << "    " << tblgen::tgfmt(extraClassOf->trim(), &extraClassOfFmt)
        << "\n  }\n";
   }