[llvm] [SimplifyCFG] Replace unreachable switch lookup table holes with poison (PR #94990)

[via llvm-commits]

================
@@ -6322,6 +6333,9 @@ SwitchLookupTable::SwitchLookupTable(
       if (!ConstVal) {
         // This is an undef. We could deal with it, but undefs in lookup tables
         // are very seldom. It's probably not worth the additional complexity.
+        // TODO: In switches with holes and an unreachable default branch, this
----------------
DianQK wrote:

It's fine with me, but I hope you can restore the unhandled cases to their previous values in this PR.

https://github.com/llvm/llvm-project/pull/94990