Actually WONNX also transforms to an IR first (early versions did not and simply translated the graph 1:1 to GPU shader invocations in topographically sorted order of the graph). In WONNX the IR nodes are (initially) simply (copy-on-write references to) the ONNX nodes. This IR is then optimized in various ways, including the fusion of ONNX ops (e.g. Conv+ReLU->ConvReLU). The newly inserted node still embeds an ONNX node structure to describe it but uses an internal operator.
