Fix torch.mm export to ONNX (#34661)
Summary:
torch.mm is exported as Gemm operator in ONNX and both have an optional input: out.
out is considered as broadcastable in Gemm and during graph optimization the optional input (out) would get selected. Since out is optional, in case when it is not defined in torch.mm that would result in the following exception:
IndexError: vector::_M_range_check: __n (which is 2) >= this->size() (which is 2)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/34661
Reviewed By: hl475
Differential Revision: D20496398
Pulled By: houseroad
fbshipit-source-id: e677aef0a6aefb1f83a54033153aaabe5c23bc0f
