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

[Nikita Popov via cfe-commits]

nikic 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 https://github.com/llvm/llvm-project/pull/69343, but it's not quite done yet.

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