results: a list of futures.
    body_fn: its input are [predicate_promise, arg0_future, arg0_promise, arg1_future, arg1_promise, ..., invariant_args] and has no returned results.
  }];

  let arguments = (ins TFTensorType:$cond,
                       Variadic<TFTensorType>:$arguments,
                       FlatSymbolRefAttr:$body_fn,
                       I32Attr:$invariant_size);

			t.tag = bytesEncoder(appendTagAndLength(t.scratch[:0], tagAndLength{ClassUniversal, tag, bodyLen, isCompound}))

			tt := new(taggedEncoder)

			tt.body = t

			tt.tag = bytesEncoder(appendTagAndLength(tt.scratch[:0], tagAndLength{
				class:      class,
				tag:        *params.tag,
				length:     bodyLen + t.tag.Len(),
				isCompound: true,
			}))

			return tt, nil
		}

}

LogicalResult FindOwningWhileOp(func::FuncOp body_func, ModuleOp module,
                                TF::WhileOp* while_op) {
  // Given a while loop body function 'body_func', find the tf.While Op that
  // uses it.
  auto uses_optional = body_func.getSymbolUses(module);
  if (!uses_optional.has_value()) {
    body_func.emitOpError() << "no use of while loop body";
    return LogicalResult::failure();

}

func h12requestContentLength(t *testing.T, bodyfn func() io.Reader, wantLen int64) {
	h12Compare{
		Handler: func(w ResponseWriter, r *Request) {
			w.Header().Set("Got-Length", fmt.Sprint(r.ContentLength))
			fmt.Fprintf(w, "Req.ContentLength=%v", r.ContentLength)
		},
		ReqFunc: func(c *Client, url string) (*Response, error) {
			return c.Post(url, "text/plain", bodyfn())
		},