I’ve written a very simple PopART program using the C++ interface, but every time I try to compile it to run on an IPU device I get the following error:
terminate called after throwing an instance of ‘popart::error’
what(): Could not find loss tensor ‘L1:0’ in main graph tensors
I’m defining the loss in my program like so:
auto loss = builder->aiGraphcoreOpset1().l1loss({outputs[0]}, 0.1f, popart::ReductionType::Sum, “l1LossVal”);
Is there something wrong with my loss definition that’s resulting in it being pruned out of the graph? I’ve followed the same structure as one of the Graphcore examples here.
This error usually happens when the model protobuf you pass to the TrainingSession or InferenceSession objects doesn’t contain the loss tensor. A common reason for this is when you call builder->getModelProto() before you add the loss tensor to the graph. To ensure your loss tensor is part of the protobuf your calls should be in the following order:
...
auto loss = builder->aiGraphcoreOpset1().l1loss(...);
auto proto = builder->getModelProto();
auto session = popart::TrainingSession::createFromOnnxModel(...);
...
The key point is that the getModelProto() call should be the last call from the builder interface before setting up the PopART session.