[llvm] Add Dead Block Elimination to NVVMReflect (PR #144171)

[Yonah Goldberg via llvm-commits]

YonahGoldberg wrote:

@Artem-B The problem is that Codegen Prepare, which is the pass in llc that ultimately cleans up the dead code introduced by reflect elimination, doesn't get run in llc -O0. So in many cases with llc -O0 you will leave behind a ptx instruction that is illegal for the subtarget.

To ensure that this cleanup always happens, regardless of the optimization pipeline, it's better to have it done in the NVVMReflect pass.

https://github.com/llvm/llvm-project/pull/144171