[TensorExpr] When lanes differ, insert Broadcast instead of Cast (#45179)
Summary:
We need to check if dtypes differ in scalar type or lanes to decide between
Cast and Broadcast.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/45179
Test Plan: test_tensorexpr --gtest_filter=TensorExprTest.SimplifyBroadcastTermExpander
Reviewed By: bwasti
Differential Revision: D23873316
Pulled By: asuhan
fbshipit-source-id: ca141be67e10c2b6c5f2ff9c11e42dcfc62ac620
