[mlir] Automatically add DerivedAttribute op interface

[jpienaar]

Summary

When an operation has derived attributes, add the DerivedAttribute op interface.

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

 
 // Test derived type attr.
 // ---
 def DerivedTypeAttrOp : NS_Op<"derived_type_attr_op", []> {
   let results = (outs AnyTensor:$output);
   DerivedTypeAttr element_dtype = DerivedTypeAttr<"return output().getType();">;
 }
 
-// DECL: bool isDerivedAttribute
+// DECL: class DerivedTypeAttrOp : public Op
+// DECL-SAME: DerivedAttributeOpInterface::Trait
+// DECL: static bool isDerivedAttribute
 // DEF: bool DerivedTypeAttrOp::isDerivedAttribute(StringRef name) {
 // DEF:   if (name == "element_dtype") return true;
 // DEF:   return false;
 // DEF: }
 
 // Test that only default valued attributes at the end of the arguments
 // list get default values in the builder signature
 // ---

mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp

if (attr.isDerivedAttr()) {
       emitAttrWithStorageType(name, attr);
       emitAttrWithReturnType(name, attr);
     }
   }
 
   // Generate helper method to query whether a named attribute is a derived
   // attribute. This enables, for example, avoiding adding an attribute that
   // overlaps with a derived attribute.
-  auto &method =
-      opClass.newMethod("bool", "isDerivedAttribute", "StringRef name");
-  auto &body = method.body();
   auto derivedAttr = make_filter_range(op.getAttributes(),
                                        [](const NamedAttribute &namedAttr) {
                                          return namedAttr.attr.isDerivedAttr();
                                        });
+  if (!derivedAttr.empty()) {
+    opClass.addTrait("DerivedAttributeOpInterface::Trait");
+    auto &method = opClass.newMethod("bool", "isDerivedAttribute",
+                                     "StringRef name", OpMethod::MP_Static);
+    auto &body = method.body();
     for (auto namedAttr : derivedAttr)
       body << "    if (name == \"" << namedAttr.name << "\") return true;\n";
     body << " return false;";
   }
+}
 
 void OpEmitter::genAttrSetters() {
   // Generate raw named setter type. This is a wrapper class that allows setting
   // to the attributes via setters instead of having to use the string interface
   // for better compile time verification.
   auto emitAttrWithStorageType = [&](StringRef name, Attribute attr) {
     auto &method = opClass.newMethod("void", (name + "Attr").str(),
                                      (attr.getStorageType() + " attr").str());