What is automatic mixed precision? How is it implemented? What does it have to do with mode dispatch keys, fallthrough kernels? What are AMP policies? How is its cast caching implemented? How does torchvision also support AMP? What's up with Intel's CPU autocast implementation?

Further reading.

• Autocast implementation lives at https://github.com/pytorch/pytorch/blob/master/aten/src/ATen/autocast_mode.cpp
• How to add autocast implementations to custom operators that are out of tree https://pytorch.org/tutorials/advanced/dispatcher.html#autocast
• CPU autocasting PR https://github.com/pytorch/pytorch/pull/57386