[SimplifyCFG] Allow some switch optimizations early in the pipeline (#158242)

While we do not want to form actual lookup tables early, we do want to
perform some optimizations, as they may enable inlining of the much
simpler form.

Builds on https://github.com/llvm/llvm-project/pull/156477, which
originally included this change as well. This PR makes two changes on
top of it:

* Do not perform the optimization early if it requires adding a mask
check. These make the resulting IR less analyzable.
* Add a new SimplifyCFG option that controls switch-to-arithmetic
conversion separately from switch-to-lookup conversion. Enable the new
flag at the end of the function simplification pipeline. This means that
we attempt the arithmetic conversion before inlining, but avoid it in
the early pipeline, where it may lose information.

0 files changed, 0 insertions, 0 deletions