Deep Compression of Pre-trained Transformer Models

Pre-trained transformer models have achieved remarkable success in natural language processing (NLP) and have recently become competitive alternatives to Convolution Neural Networks (CNN) and Recurrent Neural Networks (RNN) in vision and speech tasks, respectively. Due to their excellent computational efficiency and scalability, transformer models can be trained on exceedingly large amounts of data at the expense of tremendous growth in model size. As high performance, large-scale, and pre-trained transformer models become increasingly available for users to download and fine-tune for customized downstream tasks, their deployment becomes challenging due to the vast amount of operations and large memory footprint. To address this challenge, we introduce methods to deeply compress pre-trained transformer models across three major application domains: NLP, speech, and vision. Specifically, we quantize transformer backbones down to 4-bit and further achieve 50% fine-grained structural sparsity on pre-trained BERT, Wav2vec2.0, and Vision Transformer (ViT) models to demonstrate 16x compression while maintaining model accuracy. This is achieved by identifying critical initialization strategies for quantization- and sparsity- aware fine-tuning as well as developing novel techniques such as quantizers with a zero-preserving format and scheduled dropout. These hardware-friendly techniques need only to be applied in the fine-tuning phase for downstream tasks, which renders them especially suitable for acceleration and deployment of pre-trained transformer models.