[llvm] [NVPTX] Handle unreachable default in llvm::SwitchIns. (PR #72641)

[Artem Belevich via llvm-commits]

Artem-B wrote:

Can you elaborate on the actual impact the `exit` does have on performance?

While exit does result in code with more branches on PTX level, SASS looks largely identical with the difference that unreachable code does call exit. https://godbolt.org/z/s8f5nc8cs

I'm concerned that special-casing unreachable in switch we may make it possible that we re-open a possibility that we'll re-introduce the original issue where we break structured CFG for ptxas if the switch ends up being replicated within more complicated CFG.


https://github.com/llvm/llvm-project/pull/72641