diff --git a/mlir/lib/Transforms/Utils/SideEffectUtils.cpp b/mlir/lib/Transforms/Utils/SideEffectUtils.cpp
--- a/mlir/lib/Transforms/Utils/SideEffectUtils.cpp
+++ b/mlir/lib/Transforms/Utils/SideEffectUtils.cpp
@@ -55,4 +55,6 @@
   case Speculation::NotSpeculatable:
     return false;
   }
+
+  llvm_unreachable("Unhandled enum in mlir::isSpeculatable!");
 }