diff --git a/mlir/include/mlir/Dialect/SparseTensor/IR/SparseTensorOps.td b/mlir/include/mlir/Dialect/SparseTensor/IR/SparseTensorOps.td
--- a/mlir/include/mlir/Dialect/SparseTensor/IR/SparseTensorOps.td
+++ b/mlir/include/mlir/Dialect/SparseTensor/IR/SparseTensorOps.td
@@ -460,9 +460,6 @@
   let assemblyFormat = "(`stable` $stable^)? $n"
                        "`,`$xs (`jointly` $ys^)? attr-dict"
                        "`:` type($xs) (`jointly` type($ys)^)?";
-  let builders = [
-        OpBuilder<(ins "Value":$n, "ValueRange":$xs, "ValueRange":$ys)>
-  ];
   let hasVerifier = 1;
 }
 
diff --git a/mlir/include/mlir/IR/OpBase.td b/mlir/include/mlir/IR/OpBase.td
--- a/mlir/include/mlir/IR/OpBase.td
+++ b/mlir/include/mlir/IR/OpBase.td
@@ -1246,9 +1246,10 @@
 // "true" if the attribute is present and "false" otherwise.
 def UnitAttr : Attr<CPred<"$_self.isa<::mlir::UnitAttr>()">, "unit attribute"> {
   let storageType = [{ ::mlir::UnitAttr }];
-  let constBuilderCall = "$_builder.getUnitAttr()";
+  let constBuilderCall = "(($0) ? $_builder.getUnitAttr() : nullptr)";
   let convertFromStorage = "$_self != nullptr";
   let returnType = "bool";
+  let defaultValue = "false";
   let valueType = NoneType;
   let isOptional = 1;
 }
@@ -1575,7 +1576,7 @@
 class ConstF32Attr<string val> : ConstantAttr<F32Attr, val>;
 def ConstBoolAttrFalse : ConstantAttr<BoolAttr, "false">;
 def ConstBoolAttrTrue : ConstantAttr<BoolAttr, "true">;
-def ConstUnitAttr : ConstantAttr<UnitAttr, "unit">;
+def ConstUnitAttr : ConstantAttr<UnitAttr, "true">;
 
 // Constant string-based attribute. Wraps the desired string in escaped quotes.
 class ConstantStrAttr<Attr attribute, string val>
diff --git a/mlir/lib/Dialect/SparseTensor/IR/SparseTensorDialect.cpp b/mlir/lib/Dialect/SparseTensor/IR/SparseTensorDialect.cpp
--- a/mlir/lib/Dialect/SparseTensor/IR/SparseTensorDialect.cpp
+++ b/mlir/lib/Dialect/SparseTensor/IR/SparseTensorDialect.cpp
@@ -706,11 +706,6 @@
   return success();
 }
 
-void SortOp::build(OpBuilder &odsBuilder, OperationState &odsState, Value n,
-                   ValueRange xs, ValueRange ys) {
-  build(odsBuilder, odsState, n, xs, ys, /*stable=*/false);
-}
-
 LogicalResult SortOp::verify() {
   if (getXs().empty())
     return emitError("need at least one xs buffer.");
diff --git a/mlir/test/mlir-tblgen/op-attribute.td b/mlir/test/mlir-tblgen/op-attribute.td
--- a/mlir/test/mlir-tblgen/op-attribute.td
+++ b/mlir/test/mlir-tblgen/op-attribute.td
@@ -488,6 +488,11 @@
 // DEF-NEXT:   (*this)->removeAttr(getAttrAttrName());
 
 // DEF: build(::mlir::OpBuilder &odsBuilder, ::mlir::OperationState &odsState, /*optional*/::mlir::UnitAttr attr)
+// DEF: build(::mlir::OpBuilder &odsBuilder, ::mlir::OperationState &odsState, /*optional*/bool attr)
+
+// DECL-LABEL: UnitAttrOp declarations
+// DECL-NOT: declarations
+// DECL: build(::mlir::OpBuilder &odsBuilder, ::mlir::OperationState &odsState, /*optional*/bool attr = false)
 
 
 // Test elementAttr field of TypedArrayAttr.
diff --git a/mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp b/mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp
--- a/mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp
+++ b/mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp
@@ -1635,9 +1635,9 @@
 }
 
 void OpEmitter::genPopulateDefaultAttributes() {
-  // All done if no attributes have default values.
+  // All done if no attributes, except optional ones, have default values.
   if (llvm::all_of(op.getAttributes(), [](const NamedAttribute &named) {
-        return !named.attr.hasDefaultValue();
+        return !named.attr.hasDefaultValue() || named.attr.isOptional();
       }))
     return;
 
@@ -1667,8 +1667,8 @@
     fctx.withBuilder(odsBuilder);
     std::string defaultValue = std::string(
         tgfmt(attr.getConstBuilderTemplate(), &fctx, attr.getDefaultValue()));
-    body.indent() << formatv(" attributes.append(attrNames[{0}], {1});\n",
-                             index, defaultValue);
+    body.indent() << formatv("attributes.append(attrNames[{0}], {1});\n", index,
+                             defaultValue);
     body.unindent() << "}\n";
   }
 }
@@ -2143,12 +2143,16 @@
     if (attr.isDerivedAttr() || inferredAttributes.contains(namedAttr.name))
       continue;
 
-    // TODO(jpienaar): The wrapping of optional is different for default or not,
-    // so don't unwrap for default ones that would fail below.
-    bool emitNotNullCheck = (attr.isOptional() && !attr.hasDefaultValue()) ||
-                            (attr.hasDefaultValue() && !isRawValueAttr);
+    // TODO: The wrapping of optional is different for default or not, so don't
+    // unwrap for default ones that would fail below.
+    bool emitNotNullCheck =
+        (attr.isOptional() && !attr.hasDefaultValue()) ||
+        (attr.hasDefaultValue() && !isRawValueAttr) ||
+        // TODO: UnitAttr is optional, not wrapped, but needs to be guarded as
+        // the constant materialization is only for true case.
+        (isRawValueAttr && attr.getAttrDefName() == "UnitAttr");
     if (emitNotNullCheck)
-      body << formatv("  if ({0}) ", namedAttr.name) << "{\n";
+      body.indent() << formatv("if ({0}) ", namedAttr.name) << "{\n";
 
     if (isRawValueAttr && canUseUnwrappedRawValue(attr)) {
       // If this is a raw value, then we need to wrap it in an Attribute
@@ -2175,7 +2179,7 @@
                       namedAttr.name);
     }
     if (emitNotNullCheck)
-      body << "  }\n";
+      body.unindent() << "  }\n";
   }
 
   // Create the correct number of regions.
@@ -2966,7 +2970,7 @@
       // call. This should be set instead.
       std::string defaultValue = std::string(
           tgfmt(attr.getConstBuilderTemplate(), &fctx, attr.getDefaultValue()));
-      body << "  if (!attr)\n    attr = " << defaultValue << ";\n";
+      body << "if (!attr)\n  attr = " << defaultValue << ";\n";
     }
     body << "return attr;\n";
   };