[BUILD] Fix Warnings and Enable Warnings as Errors (#794)

lib/Analysis/Utility.cpp

@@ -28,11 +28,10 @@ bool maybeSharedAllocationOp(Operation *op) {
 }
 
 std::string getValueOperandName(Value value, AsmState &state) {
-  auto *op = value.getDefiningOp();
   std::string opName;
   llvm::raw_string_ostream ss(opName);
   value.printAsOperand(ss, state);
-  return std::move(opName);
+  return opName;
 }
 
 } // namespace mlir