[FIRRTL] Update LowerClasses to handle AnyRef and AnyRef cast. (#6117)

The FIRRTL AnyRef type is converted to an OM Any type, and FIRRTL
AnyRef casts are converted to OM Any casts. This is a straightforward
conversion of the same concepts into the OM dialect.

lib/Dialect/FIRRTL/Transforms/LowerClasses.cpp

@@ -860,6 +860,17 @@ struct WireOpConversion : public OpConversionPattern<WireOp> {
   }
 };
 
+struct AnyCastOpConversion : public OpConversionPattern<ObjectAnyRefCastOp> {
+  using OpConversionPattern::OpConversionPattern;
+
+  LogicalResult
+  matchAndRewrite(ObjectAnyRefCastOp op, OpAdaptor adaptor,
+                  ConversionPatternRewriter &rewriter) const override {
+    rewriter.replaceOpWithNewOp<AnyCastOp>(op, adaptor.getInput());
+    return success();
+  }
+};
+
 struct ObjectSubfieldOpConversion
     : public OpConversionPattern<firrtl::ObjectSubfieldOp> {
   using OpConversionPattern::OpConversionPattern;
@@ -1088,6 +1099,12 @@ static void populateTypeConverter(TypeConverter &converter) {
     return om::ClassType::get(type.getContext(), type.getNameAttr());
   });
 
+  // Convert FIRRTL AnyRef type to OM Any type.
+  converter.addConversion([](om::AnyType type) { return type; });
+  converter.addConversion([](firrtl::AnyRefType type) {
+    return om::AnyType::get(type.getContext());
+  });
+
   // Convert FIRRTL List type to OM List type.
   auto convertListType = [&converter](auto type) -> std::optional<mlir::Type> {
     auto elementType = converter.convertType(type.getElementType());
@@ -1162,6 +1179,7 @@ static void populateRewritePatterns(
   patterns.add<PathOpConversion>(converter, patterns.getContext(),
                                  pathInfoTable);
   patterns.add<WireOpConversion>(converter, patterns.getContext());
+  patterns.add<AnyCastOpConversion>(converter, patterns.getContext());
   patterns.add<ObjectSubfieldOpConversion>(converter, patterns.getContext(),
                                            classTypeTable);
   patterns.add<ClassFieldOpConversion>(converter, patterns.getContext());

test/Dialect/FIRRTL/lower-classes.mlir

@@ -322,3 +322,17 @@ firrtl.circuit "ModuleInstances" {
   // CHECK:   %[[F1:.+]] = om.object.field %[[O1]], [@outputProp]
   // CHECK:   om.class.field @outputProp, %[[F1]]
 }
+
+// CHECK-LABEL: firrtl.circuit "AnyCast"
+firrtl.circuit "AnyCast" {
+  firrtl.class private @Foo() {}
+
+  firrtl.module @AnyCast(out %foo: !firrtl.anyref) {
+    // CHECK: %[[OBJ:.+]] = om.object @Foo
+    %fooObject = firrtl.object @Foo()
+    // CHECK: %[[CAST:.+]] = om.any_cast %[[OBJ]]
+    %0 = firrtl.object.anyref_cast %fooObject : !firrtl.class<@Foo()>
+    // CHECK: om.class.field @foo, %[[CAST]]
+    firrtl.propassign %foo, %0 : !firrtl.anyref
+  }
+}