[llvm] Eliminating li of 0 into arg registers of unused arguments (PR #122741)

[Hubert Tong via llvm-commits]

hubert-reinterpretcast wrote:

Reproducing @diggerlin's response to https://github.com/llvm/llvm-project/pull/122741#issuecomment-2634489475:

> > > This PR as-is is not about introducing poison to the DAG (that's the how, not the what). The actual operative change is the handling of poison for the width extensions.
> > 
> > These should not be mixed in. Introducing poison should be separate from any of this other stuff
> 
> do you means we should have two separate patches? one for  introducing poison to the DAG, other patch for handling of poison for the width extensions?

https://github.com/llvm/llvm-project/pull/122741