[llvm] [InstCombine] Fold `mul (sext bool X), Y` into `select X, -Y, 0` (PR #84792)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

Looks fine to me.

Codegen looks a bit worse, at least for 8-bit: https://alive2.llvm.org/ce/z/5D7Ban Do you think an undo transform in the backend would be worthwhile?

https://github.com/llvm/llvm-project/pull/84792