[llvm] [MachineLICM] Give opportunity to analyze physregs for invariance. (PR #84779)

[Stanislav Mekhanoshin via llvm-commits]

rampitec wrote:

> > This looks reasonable, but isn't it the same as `isIgnorableUse`? Or do you need this because you want hoisting but still want to prevent rematerialization?
> 
> Yes, the latter. We've added the implicit def/use of these registers to prevent rematerialization from occurring.

Is it the same as adding code to ignore $vg to the `isIgnorableUse` instead and then override `isTriviallyReMaterializable` to check for $vg imp-use and return false?

https://github.com/llvm/llvm-project/pull/84779