[mlir] Introduce OptionalAttrWithDefault

[jpienaar]

Summary

Currently DefaultValuedAttr is confusingly cactually default valued &
optional but that was an artifact of development and longstanding TODO
to address. Add new attribute that matches this behavior for cases where
that is actually the desired behavior before addressing TODO.

[rriddle]

Typo in the description: cactually

Also, if I'm reading it right, this is an incremental step to fixing DefaultValuedAttr>

mlir/include/mlir/IR/OpBase.td

972

Would DefaultValuedOptionalAttr be more inline with how we name other things?

[jpienaar]

Rename to DefaultValuedOptionalAttr

mlir/include/mlir/IR/OpBase.td

class DefaultValuedAttr<Attr attr, string val> :
   let convertFromStorage = attr.convertFromStorage;
   let constBuilderCall = attr.constBuilderCall;
   let defaultValue = val;
   let valueType = attr.valueType;
 
   let baseAttr = attr;
 }
 
+// Decorates an optional attribute to have an (unvalidated) default value
+// return by ODS generated accessors if not present.
+class DefaultValuedOptionalAttr<Attr attr, string val> :
+    Attr<attr.predicate, attr.summary> {
+  // Construct this attribute with the input attribute and change only
+  // the default value.
+  // Note: this has to be kept up to date with Attr above.
+  let storageType = attr.storageType;
+  let returnType = attr.returnType;
+  let convertFromStorage = attr.convertFromStorage;
+  let constBuilderCall = attr.constBuilderCall;
+  let defaultValue = val;
+  let valueType = attr.valueType;
+  let isOptional = 1;
+
+  let baseAttr = attr;
+}
+
 // Decorates an attribute as optional. The return type of the generated
 // attribute accessor method will be Optional<>.
 class OptionalAttr<Attr attr> : Attr<attr.predicate, attr.summary> {
   // Rewrite the attribute to be optional.
   // Note: this has to be kept up to date with Attr above.
   let storageType = attr.storageType;
   let returnType = "::llvm::Optional<" # attr.returnType #">";
   let convertFromStorage = "$_self ? " # returnType # "(" #

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

 def Test2_Dialect : Dialect {
   let name = "test2";
   let cppNamespace = "foobar2";
   let emitAccessorPrefix = kEmitAccessorPrefix_Prefixed;
 }
 def AgetOp : Op<Test2_Dialect, "a_get_op", []> {
   let arguments = (ins
       SomeAttr:$aAttr,
-      DefaultValuedAttr<SomeAttr, "4.2">:$bAttr,
+      DefaultValuedOptionalAttr<SomeAttr, "4.2">:$bAttr,
       OptionalAttr<SomeAttr>:$cAttr
   );
 }
 
 // DECL-LABEL: AgetOp declarations
 
 // Test attribute name methods
 // ---

 
 // DEF:      void AgetOp::build(
 // DEF:        odsState.addAttribute(getAAttrAttrName(odsState.name), aAttr);
 // DEF:        odsState.addAttribute(getBAttrAttrName(odsState.name), bAttr);
 // DEF:        if (cAttr) {
 // DEF-NEXT:     odsState.addAttribute(getCAttrAttrName(odsState.name), cAttr);
 
 // DEF:      void AgetOp::build(
-// DEF:        some-return-type aAttr, some-return-type bAttr, /*optional*/some-attr-kind cAttr
+// DEF:        some-return-type aAttr, /*optional*/some-return-type bAttr, /*optional*/some-attr-kind cAttr
 // DEF:        odsState.addAttribute(getAAttrAttrName(odsState.name), some-const-builder-call(odsBuilder, aAttr));
 
 // DEF:      void AgetOp::build(
 // DEF:        ::llvm::ArrayRef<::mlir::NamedAttribute> attributes
 // DEF:      odsState.addAttributes(attributes);
 
 def SomeTypeAttr : TypeAttrBase<"SomeType", "some type attribute">;