Why the attn mask is not used in forward function?

[HanielF]

Compared with left_product function, attention mask is not used in forward() function.
How to use the attention mask in the forward method?

[Doraemonzzz]

When use forward() function, there is no direct way to use attention mask since we haven't compute attention matrix. If you need use attention mask, we suggest you use left_product, however, this will get loss in efficiency.