diff --git a/mlir/lib/Dialect/GPU/IR/GPUDialect.cpp b/mlir/lib/Dialect/GPU/IR/GPUDialect.cpp
--- a/mlir/lib/Dialect/GPU/IR/GPUDialect.cpp
+++ b/mlir/lib/Dialect/GPU/IR/GPUDialect.cpp
@@ -172,6 +172,8 @@
   case SparseHandleKind::SpMat:
     return "sparse.spmat_handle";
   }
+  llvm_unreachable("unknown sparse handle kind");
+  return "";
 }
 
 Type GPUDialect::parseType(DialectAsmParser &parser) const {