is causal hints for transformer (#106143)
Summary:
make is_causal hint flags available for the top level transformer module.
It's debatable whether this is useful -- at present we autodetect causal masks for src and tgt masks in transformer encoder and decoder, respectively. is_causal flags available woul enable users to short-cut this check by asserting whether they mask is causal, or not.
I am putting this diff up for discussion, not as a solution. Not doing anything may be the right solution, unless there is strong (data-driven) user demand. -- it appears the consensus is to move ahead with this, as per discussions below.
@cpuhrsch @mikaylagawarecki @jbschlosser @janEbert
Test Plan: sandcastle
Differential Revision: D47373260
Pull Request resolved: https://github.com/pytorch/pytorch/pull/106143
Approved by: https://github.com/mikaylagawarecki
