swift234

Consistenly use RCIdentity to get the RCRoot of the operand.
We were using a stripCast in some places and getRCIdentityRoot in others.
stripCasts is not identical to getRCIdentityRoot.

In particular, it does not look through struct_extract, tuple_extract,
unchecked_enum_data.

Created a struct and tuple test cases for make sure things are optimized
as they should be.

We have test case for unchecked_enum_data before.