[llvm] [SelectionDAG] Add a flag to sort DAGs before showing them in debug prints (PR #149732)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

> > Or we could focus efforts on finally ensuring the DAG is topologically sorted to begin with: #83422
> 
> True, aside from the problems raised in the said issue, I remember compilation time is/was also a concern?
> 
> But in any case, I feel like this patch can provide a quick and easy solution for improving developers' life, at least in a short term.

Agreed, I'm just rather annoyed at the lack on interest in helping with something that should have been done a decade ago.....

FTR a topological sorted dag should reduce backend compile time: https://llvm-compile-time-tracker.com/?config=Overview&stat=instructions%3Au&remote=RKSimon

https://github.com/llvm/llvm-project/pull/149732