Track used output tensors explicitly.

Kludge - see comments in this commit for explanation.

src/graph.cc

@@ -270,7 +270,6 @@ bool Graph::tryResolveNode(onnx::NodeProto &node)
 		const_cast<Tensor*>(i)->consumers.push_back(n);
 	}
 
-	n->onnx_node = &node;
 	n->isResolved = false;
 	n->op_name = new_node;
 	n->onnx_name = node.name();
@@ -289,6 +288,28 @@ bool Graph::tryResolveNode(onnx::NodeProto &node)
 	if( node.attribute_size() != 0 )
 		n->parseAttributes( node );
 
+	// create output nodes for the tensor.
+	// this is a kludge around a chicken & egg problem caused by bad design in
+	// onnx2c:
+	// we don't want to save a copy of the onnx::NodeProto in the onnx2c::node object
+	// (since who knows how protobuf keeps its internals).
+	// So create a list of that tells if outputs are used or not *before* resolving
+	// the node.
+	std::vector<bool> output_used;
+	for(int nn = 0; nn<node.output_size(); nn++)
+	{
+		// ONNX spec:
+		// "There are two ways to leave an optional input or output unspecified:
+		// the first, available only for trailing inputs and outputs, is to simply
+		// not provide that input; the second method is to use an empty string in
+		// place of an input or output name."
+		if( node.output(nn) == "" )
+			output_used.push_back(false);
+		else
+			output_used.push_back(true);
+	}
+	n->set_output_used(output_used);
+
 	// Configure Node internals, and populate its outputs vector.
 	n->resolve();
 

src/node.cc

@@ -7,20 +7,11 @@
 using namespace toC;
 
 int64_t Node::onnx_ir_version;
-bool Node::is_output_N_used(unsigned N)
+bool Node::is_output_N_used(unsigned N) const
 {
-	// ONNX spec:
-	// "There are two ways to leave an optional input or output unspecified:
-	// the first, available only for trailing inputs and outputs, is to simply
-	// not provide that input; the second method is to use an empty string in
-	// place of an input or output name."
-
-	if( (int)N >= onnx_node->output_size() )
-		return false;
-
-	if( onnx_node->output(N) == "" )
+	if( N >= output_used.size() )
 		return false;
-
+	return output_used[N];
 	return true;
 }
 

src/node.h

@@ -19,7 +19,6 @@ typedef std::tuple<const Tensor *, std::string> function_parameter;
 class Node {
 	public:
 	bool isResolved;       // has this node been visited in current compilation step.
-	const onnx::NodeProto *onnx_node;
 	std::string onnx_name; //ONNX name of the individual node
 	std::string op_name;   //ONNX name of node type
 	static int64_t onnx_ir_version;
@@ -28,12 +27,19 @@ class Node {
 	// NB: this is deprecated. Whenever a node is updated,
 	// any reference to this variable should be removed.
 	// instead of outputs.push_back(), use register_output()
+	// Eventually this variable should be made protected
 	std::vector<Tensor *> outputs;
 private:
 	std::vector<function_parameter> input_params;
 	std::vector<function_parameter> output_params;
+	// truth table telling if the Nth output is used or not.
+	// This might not be as long as the number of outputs in the Node operand's specification
+	// (i.e .when trailing outputs are not used)
+	std::vector<bool> output_used;
 
 public:
+	void set_output_used(std::vector<bool>val){output_used = val; }
+
 	// when output is removed, get the vector of tensors from output_params.
 	std::vector<Tensor *> get_outputs(void) const {return outputs;}
 
@@ -47,7 +53,7 @@ class Node {
 
 
 	/* Print the C implmementation of the operator */
-	virtual void print(std::ostream &destination) const = 0; 
+	virtual void print(std::ostream &destination) const = 0;
 
 	/* Print comma-separated list of function parameters.
 	 * Unused optional tensors skipped. e.g.:
@@ -77,8 +83,8 @@ class Node {
 
 	/* Check if an optional output is used in the network.
 	 * N is Nth output specified in the Operator.md specification for this node.
-	 * Start counting N from 0. */
-	bool is_output_N_used(unsigned N);
+	 * Start counting N from 0, including the non-optional outputs. */
+	bool is_output_N_used(unsigned N) const;
 
 	/* Not all node types have attributes. Override where needed */
 	virtual void parseAttributes( onnx::NodeProto &node )
@@ -87,7 +93,7 @@ class Node {
 	}
 
 	/* TODO: these should be part of class Tensor... */
-	/* Check input constraints, as used in 
+	/* Check input constraints, as used in
 	 * https://github.com/onnx/onnx/blob/master/docs/Operators.md
 	 */
 	/* (u)int32, (u)int64, float16/32/64, bfloat*/