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

[Joseph Huber via llvm-commits]

jhuber6 wrote:

We ideally want similar functionality to what https://github.com/llvm/llvm-project/pull/134016 is doing. Basically late resolve features by eliminating potentially invalid code. The previous version did the simple DCE which was good enough to eliminate trivial uses, but we definitely need something more complicated for it to be completely robust. We do this at O0 because otherwise it's useless as a means to guard potentially invalid code for that target.

In either case this is a bit of a hack because a lot of target specific features require `+ptx73` or whatever, which would then need to be made a function level attribute and then propagated somehow.

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