mir opt + codegen: handle subtyping fixes #107205 the same issue was caused in multiple places: - mir opts: both copy and destination propagation - codegen: assigning operands to locals (which also propagates values) I changed codegen to always update the type in the operands used for locals which should guard against any new occurrences of this bug going forward. I don't know how to make mir optimizations more resilient here. Hopefully the added tests will be enough to detect any trivially wrong optimizations going forward.