Normalize loops with non-zero start. (#43179)
Summary:
This diff normalizes for-loops that have non 0 loop starts to always start from 0. Given a for-loop, this normalization changes the loop start to be 0 and adjusts the loop end and all accesses to the index variable within the loop body appropriately.
This diff also adds tests for several cases of normalization and also tests normalization in conjunction with `splitwithTail` transformation.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43179
Reviewed By: nickgg
Differential Revision: D23220534
Pulled By: navahgar
fbshipit-source-id: 64be0c72e4dbc76906084f7089dea81ae07d6020
