Revert D26676150: Simplify index expressions constructed in loop flattening - #51173
Test Plan: revert-hammer
Differential Revision:
D26676150 (https://github.com/pytorch/pytorch/commit/1f01899e4a2c04063fd8305ee304f063c04edc78)
Original commit changeset: e202e0c8610e
fbshipit-source-id: 9611dda6897b67e16e44c731994bc9e5fccab0b9
