add a check for loop state variables

Signed-off-by: Chun-Wei Chen <jacky82226@gmail.com>

onnx/defs/controlflow/defs.cc

@@ -277,9 +277,18 @@ void ClearShape(TypeProto& input_type) {
 
 void LoopInferenceFunction(InferenceContext& ctx) {
   auto num_inputs = ctx.getNumInputs();
+  auto num_outputs = ctx.getNumOutputs();
   assert(num_inputs >= 2);
   auto num_loop_state_vars = num_inputs - 2; // skip 'M' and 'cond'
 
+  if (num_loop_state_vars > num_outputs) {
+    fail_type_inference(
+        "The number of loop state variables for input is larger than the number of outputs. ",
+        num_loop_state_vars,
+        " > ",
+        num_outputs);
+  }
+
   std::vector<const TypeProto*> subgraph_input_types;
   subgraph_input_types.reserve(num_inputs);
 
@@ -328,8 +337,6 @@ void LoopInferenceFunction(InferenceContext& ctx) {
 
   // if empty(), assume inferencing was skipped
   if (!subgraph_output_types.empty()) {
-    auto num_outputs = ctx.getNumOutputs();
-
     // subgraph outputs the condition value first but that is only used
     // internally and not returned by Loop.
     if (subgraph_output_types.size() != num_outputs + 1) {