Improve error message in IR parser when accessing undefined variable.
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/26771
Test Plan: Imported from OSS
Differential Revision: D17562853
Pulled By: ZolotukhinM
fbshipit-source-id: b4d4bc6001e3ea06f4d1b8691ad2a339a04c16ea
Author
Mikhail Zolotukhin
