[mlir] Do not print empty property (llvm#93379)

Skip printing property as `<<<NULL ATTRIBUTE>>>` when operation has an
empty property.

Co-authored-by: Biao Wang <biaow@nvidia.com>

Author: bealwang

mlir/lib/IR/Operation.cpp

@@ -801,6 +801,8 @@ ParseResult OpState::genericParseProperties(OpAsmParser &parser,
 /// 'elidedProps'
 void OpState::genericPrintProperties(OpAsmPrinter &p, Attribute properties,
                                      ArrayRef<StringRef> elidedProps) {
+  if (!properties)
+    return;
   auto dictAttr = dyn_cast_or_null<::mlir::DictionaryAttr>(properties);
   if (dictAttr && !elidedProps.empty()) {
     ArrayRef<NamedAttribute> attrs = dictAttr.getValue();

mlir/test/IR/properties.mlir

@@ -38,3 +38,14 @@ test.using_property_ref_in_custom 1 + 4 = 5
 // GENERIC: "test.with_default_valued_properties"()
 // GENERIC-SAME:  <{a = 0 : i32}>
 test.with_default_valued_properties <{a = 0 : i32}>
+
+// CHECK:   test.with_optional_properties
+// CHECK-SAME:  <{b = 0 : i32}>
+// GENERIC: "test.with_optional_properties"()
+// GENERIC-SAME:  <{b = 0 : i32}>
+test.with_optional_properties <{b = 0 : i32}>
+
+// CHECK:   test.with_optional_properties {{$}}
+// GENERIC: "test.with_optional_properties"()
+// GENERIC-SAME:  : () -> ()
+test.with_optional_properties

mlir/test/lib/Dialect/Test/TestOps.td

@@ -3113,6 +3113,11 @@ def TestOpWithDefaultValuedProperties : TEST_Op<"with_default_valued_properties"
   let arguments = (ins DefaultValuedAttr<I32Attr, "0">:$a);
 }
 
+def TestOpWithOptionalProperties : TEST_Op<"with_optional_properties"> {
+  let assemblyFormat = "prop-dict attr-dict";
+  let arguments = (ins OptionalAttr<I32Attr>:$a, OptionalAttr<I32Attr>:$b);
+}
+
 //===----------------------------------------------------------------------===//
 // Test Dataflow
 //===----------------------------------------------------------------------===//