[llvm] [PreISelIntrinsicLowering] Look through ptrtoint for a constant (e.g. global ptr) when trying to produce memset_pattern16 (PR #129220)

[Alex Bradbury via llvm-commits]

asb wrote:

> I'm not sure I understand why we need to do this. That is, shouldn't LIR be passing the pattern directly as an argument to experimental.memset.pattern and leave it to intrinsic lowering to create the global, instead of creating the global itself?

You're absolutely right, the process of LoopIdiomRecognize creating a global value and loading that is unnecessary and should have been removed for the ptr case as it had been for int and fp. I've updated #126736 to reflect this and reworked this patch to just look through a ptrtoint for a constant arg.

This continues along the path of leaving memset.pattern as taking an integer type for now, and potentially allowing overloads of other types in future work.

https://github.com/llvm/llvm-project/pull/129220