[llvm] [DA] Add initial support for monotonicity check (PR #162280)

[Ryotaro Kasuga via llvm-commits]

kasuga-fj wrote:

It's strange to me that `getelementptr` appears twice. I tried replacing it with a single `getelementptr` instruction like `getelementptr inbounds nuw [20 x i8], ptr %A, i64 %indvars.iv, i64 15` and then `nuw`/`nsw` flags were attached as expected.

> I suspect if we start solving this kind of problem in DA, we will eventually reinvent many SCEV wheels in DA.

By limiting the scope to cases where the BTC and the operands of the addrecs are constants, I believe it shouldn’t be very complex. If we want to make (potentially significant) changes to SCEV for the sake of DA to support more complex cases, then I *think* we should first get DA into the default pipeline and demonstrate its usefulness...

https://github.com/llvm/llvm-project/pull/162280