[NNC] fix support for FP16 in CudaCodgen (#44209)
Summary:
Fixes a bug where FP16 values could be incorrectly cast to a half type that doesn't have a cast operator by inserting the cuda specific cast to float during handling of the Cast node, not as a wrapper around printing Loads and Stores. Two main changes: the HalfChecker now inserts the casts to float explicitly in the IR, and the PrioritizeLoad mutator now consumes both Loads and a Cast which immediately preceded a load.
Tested with test_jit_fuser_te.py and test_tensorexpr.py, plus C++ tests obv.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44209
Reviewed By: izdeby
Differential Revision: D23575577
Pulled By: nickgg
fbshipit-source-id: 808605aeb2af812758f96f9fdc11b07e08053b46
