diff --git a/mlir/include/mlir/Dialect/SPIRV/IR/SPIRVMiscOps.td b/mlir/include/mlir/Dialect/SPIRV/IR/SPIRVMiscOps.td
--- a/mlir/include/mlir/Dialect/SPIRV/IR/SPIRVMiscOps.td
+++ b/mlir/include/mlir/Dialect/SPIRV/IR/SPIRVMiscOps.td
@@ -56,7 +56,7 @@
 
 // -----
 
-def SPV_UndefOp : SPV_Op<"Undef", []> {
+def SPV_UndefOp : SPV_Op<"Undef", [NoSideEffect]> {
   let summary = "Make an intermediate object whose value is undefined.";
 
   let description = [{