[llvm] [BPF] Use 32-bit move for zero extension when possible (PR #77501)

[via llvm-commits]

eddyz87 wrote:

> Just a nit picking, other part looks good!

Note: there was some discussion in the kernel mailing list ([here](https://lore.kernel.org/bpf/CAADnVQKGkPaCMyesJ=U469AOS5iJ=vmL20B7Ya7HFp8ouC3C5g@mail.gmail.com/)), about enabling 32-bit registers for all CPU versions (but not 32-bit ALU). So I'm not sure now at prospects of this MR, it might accepted as-is, or as a part of a bigger change, idk.

Thank you for taking a look!

https://github.com/llvm/llvm-project/pull/77501