PyTorch/XLA 1.7 release

Summary

Cloud TPUs now support the PyTorch 1.7 release, via PyTorch/XLA integration. The release has daily automated testing for the supported models: Torchvision ResNet, FairSeq Transformer and RoBERTa, HuggingFace GLUE and LM, and Facebook Research DLRM.

New Features

• TriangularSolve (#2498) (example)
• New ops supported by PyTorch/XLA:
  • round (#2457)
  • baddbmm_out (#2451)
  • var_out (#2495)
  • asinh, acosh, atanh (#2501)
• Documentation on adding more supported ops: (#2458)

Bug Fixes

• exponential_() returning 0 (#2562)
• cross_entropy on inf input (#2553)