[llvm] [NVPTX] Only run LowerUnreachable when necessary (PR #109868)

[Artem Belevich via llvm-commits]

Artem-B wrote:

> this pass is only necessary when targeting Pascal or earlier via ptxas from CUDA 11.4 or earlier. This PR updates NVPTXTargetMachine.cpp to reflect that.

I'm confused. The comment you quoted in the description only says 

> I do still encounter
miscompilations with Julia's unreachable-heavy code when targeting these
older GPUs using an older ptxas version (specifically, from CUDA 11.4 or
below). 

The way I read it, it says that 11.4 and older ptxas with older GPUs may have more bugs that are not fixed by this patch, but I do not think it implies that the newer versions of ptxas or the newer GPUs do not need this pass.

What am I missing?

https://github.com/llvm/llvm-project/pull/109868