[clang] [InstCombine] Add combines/simplifications for `llvm.ptrmask` (PR #67166)

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goldsteinn wrote:

> > > We should update LangRef and require that the integer arg has the size of the pointer index type
> > 
> > 
> > As in disallow say `ptrmask.p0.i32` on typical systems with 64-bit pointer index? (So a lot of the current usages). Or something else?
> 
> Yes, exactly. I've started working on a patch at #69343, but it's not quite done yet.

Okay, Ill wait on LangRef update to get this in.
Do you want me to take up the langref patch or do you want to finish it up?
I'm happy to (would like to a bit in fact), although its in a few areas I'm not really familiar with (Verifier)
so will probably be slower going that what you can get done.

https://github.com/llvm/llvm-project/pull/67166