[llvm-branch-commits] Add SimplifyTypeTests pass. (PR #141327)

[Peter Collingbourne via llvm-branch-commits]

https://github.com/pcc created https://github.com/llvm/llvm-project/pull/141327

This pass figures out whether inlining has exposed a constant address to
a lowered type test, and remove the test if so and the address is known
to pass the test. Unfortunately this pass ends up needing to reverse
engineer what LowerTypeTests did; this is currently inherent to the design
of ThinLTO importing where LowerTypeTests needs to run at the start.

TODO: Add tests.