diff --git a/mlir/docs/OpDefinitions.md b/mlir/docs/OpDefinitions.md
--- a/mlir/docs/OpDefinitions.md
+++ b/mlir/docs/OpDefinitions.md
@@ -733,7 +733,7 @@
 An example of an operation with an optional group is `std.return`, which has a
 variadic number of operands.
 
-```
+```tablegen
 def ReturnOp : ... {
   let arguments = (ins Variadic<AnyType>:$operands);
 
@@ -743,6 +743,36 @@
 }
 ```
 
+##### Unit Attributes
+
+In MLIR, the [`unit` Attribute](LangRef.md#unit-attribute) is special in that it
+only has one possible value, i.e. it derives meaning from its existence. When a
+unit attribute is used to anchor an optional group and is not the first element
+of the group, the presence of the unit attribute can be directly correlated with
+the presence of the optional group itself. As such, in these situations the unit
+attribute will not be printed or present in the output and will be automatically
+inferred when parsing by the presence of the optional group itself.
+
+For example, the following operation:
+
+```tablegen
+def FooOp : ... {
+  let arguments = (ins UnitAttr:$is_read_only);
+
+  let assemblyFormat = "attr-dict (`is_read_only` $is_read_only^)?";
+}
+```
+
+would be formatted as such:
+
+```mlir
+// When the unit attribute is present:
+foo.op is_read_only
+
+// When the unit attribute is not present:
+foo.op
+```
+
 #### Requirements
 
 The format specification has a certain set of requirements that must be adhered
diff --git a/mlir/test/lib/Dialect/Test/TestOps.td b/mlir/test/lib/Dialect/Test/TestOps.td
--- a/mlir/test/lib/Dialect/Test/TestOps.td
+++ b/mlir/test/lib/Dialect/Test/TestOps.td
@@ -1391,6 +1391,17 @@
   let assemblyFormat = "$operands attr-dict `:` type($result)";
 }
 
+def FormatOptionalUnitAttr : TEST_Op<"format_optional_unit_attribute"> {
+  let arguments = (ins UnitAttr:$is_optional);
+  let assemblyFormat = "(`is_optional` $is_optional^)? attr-dict";
+}
+
+def FormatOptionalUnitAttrNoElide
+    : TEST_Op<"format_optional_unit_attribute_no_elide"> {
+  let arguments = (ins UnitAttr:$is_optional);
+  let assemblyFormat = "($is_optional^)? attr-dict";
+}
+
 //===----------------------------------------------------------------------===//
 // AllTypesMatch type inference
 //===----------------------------------------------------------------------===//
diff --git a/mlir/test/mlir-tblgen/op-format.mlir b/mlir/test/mlir-tblgen/op-format.mlir
--- a/mlir/test/mlir-tblgen/op-format.mlir
+++ b/mlir/test/mlir-tblgen/op-format.mlir
@@ -82,6 +82,20 @@
 
 }) { arg_names = ["i", "j", "k"] } : () -> ()
 
+//===----------------------------------------------------------------------===//
+// Format optional attributes
+//===----------------------------------------------------------------------===//
+
+// CHECK: test.format_optional_unit_attribute is_optional
+test.format_optional_unit_attribute is_optional
+
+// CHECK: test.format_optional_unit_attribute
+// CHECK-NOT: is_optional
+test.format_optional_unit_attribute
+
+// CHECK: test.format_optional_unit_attribute_no_elide unit
+test.format_optional_unit_attribute_no_elide unit
+
 //===----------------------------------------------------------------------===//
 // Format optional operands and results
 //===----------------------------------------------------------------------===//
diff --git a/mlir/tools/mlir-tblgen/OpFormatGen.cpp b/mlir/tools/mlir-tblgen/OpFormatGen.cpp
--- a/mlir/tools/mlir-tblgen/OpFormatGen.cpp
+++ b/mlir/tools/mlir-tblgen/OpFormatGen.cpp
@@ -107,6 +107,11 @@
     Optional<Type> attrType = var->attr.getValueType();
     return attrType ? attrType->getBuilderCall() : llvm::None;
   }
+
+  /// Return if this attribute refers to a UnitAttr.
+  bool isUnitAttr() const {
+    return var->attr.getBaseAttr().getAttrDefName() == "UnitAttr";
+  }
 };
 
 /// This class represents a variable that refers to an operand argument.
@@ -645,9 +650,23 @@
       body << "  if (!" << opVar->getVar()->name << "Operands.empty()) {\n";
     }
 
+    // If the anchor is a unit attribute, we don't need to print it. When
+    // parsing, we will add this attribute if this group is present.
+    Element *elidedAnchorElement = nullptr;
+    auto *anchorAttr = dyn_cast<AttributeVariable>(optional->getAnchor());
+    if (anchorAttr && anchorAttr != firstElement && anchorAttr->isUnitAttr()) {
+      elidedAnchorElement = anchorAttr;
+
+      // Add the anchor unit attribute to the operation state.
+      body << "    result.addAttribute(\"" << anchorAttr->getVar()->name
+           << "\", parser.getBuilder().getUnitAttr());\n";
+    }
+
     // Generate the rest of the elements normally.
-    for (auto &childElement : llvm::drop_begin(elements, 1))
-      genElementParser(&childElement, body, attrTypeCtx);
+    for (Element &childElement : llvm::drop_begin(elements, 1)) {
+      if (&childElement != elidedAnchorElement)
+        genElementParser(&childElement, body, attrTypeCtx);
+    }
     body << "  }\n";
 
     /// Literals.
@@ -1058,10 +1077,23 @@
            << cast<AttributeVariable>(anchor)->getVar()->name << "\")) {\n";
     }
 
+    // If the anchor is a unit attribute, we don't need to print it. When
+    // parsing, we will add this attribute if this group is present.
+    auto elements = optional->getElements();
+    Element *elidedAnchorElement = nullptr;
+    auto *anchorAttr = dyn_cast<AttributeVariable>(anchor);
+    if (anchorAttr && anchorAttr != &*elements.begin() &&
+        anchorAttr->isUnitAttr()) {
+      elidedAnchorElement = anchorAttr;
+    }
+
     // Emit each of the elements.
-    for (Element &childElement : optional->getElements())
-      genElementPrinter(&childElement, body, fmt, op, shouldEmitSpace,
-                        lastWasPunctuation);
+    for (Element &childElement : elements) {
+      if (&childElement != elidedAnchorElement) {
+        genElementPrinter(&childElement, body, fmt, op, shouldEmitSpace,
+                          lastWasPunctuation);
+      }
+    }
     body << "  }\n";
     return;
   }