diff --git a/mlir/tools/mlir-tblgen/RewriterGen.cpp b/mlir/tools/mlir-tblgen/RewriterGen.cpp
--- a/mlir/tools/mlir-tblgen/RewriterGen.cpp
+++ b/mlir/tools/mlir-tblgen/RewriterGen.cpp
@@ -369,6 +369,11 @@
 
     // If a constraint is specified, we need to generate C++ statements to
     // check the constraint.
+    // Only check the constraint of an optional attribute if it has value.
+    if (attr.isOptional()) {
+      os.indent(indent) << "if (tblgen_attr) {\n";
+      indent += 2;
+    }
     emitMatchCheck(
         depth,
         tgfmt(matcher.getConditionTemplate(), &fmtCtx.withSelf("tblgen_attr")),
@@ -376,6 +381,10 @@
                 "{2}\"",
                 op.getOperationName(), namedAttr->name,
                 matcher.getAsConstraint().getDescription()));
+    if (attr.isOptional()) {
+      os.indent(indent) << "}\n";
+      indent -= 2;
+    }
   }
 
   // Capture the value