[llvm] [ARM] Create DeadRegisterPass for ARM (PR #155530)

[Craig Topper via llvm-commits]

topperc wrote:

> X86 backend has cmp and subs nodes. How do you deal with that? I tried reading the code but couldn't follow

Mostly X86ISD::CMP is only used for compares with 0 and X86ISD::SUB is used everywhere else, but it looks like there are several place that forgot that. I fixed some 5.5 years ago e195ff98f6cc2f868d5f8c19d2ab93cfb3a2cb65

https://github.com/llvm/llvm-project/pull/155530