Implement LayerNormalization fusion #280
Merged
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This fuses subgraphs like below, excluding the "Add" in the top left corner, into a
LayerNormalization
operator:So far this has been tested with BERT, GPT-2 and Whisper models.
This is a rather complex fusion and as a result, is liable to be brittle. That is, other equivalent ways of expressing the operator will not match. Also it doesn't help with operators which are variations of this such as RMSNorm (used in Llama etc.). In future it would probably make sense to break this up so that the individual sub-steps (centering, variance normalization, shift + scale) are fused separately.
TODO: