[llvm] [VPlan] Permit licm-sinking recipes with no users (PR #189957)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

> > Would be good if there was a way to test this somehow. Would something like a vectorizable readnone call work?
> 
> I think we'd get proper extensive testing if we review this as part of the invariant-store-sinking -- what do you think?

I went through Intrinsics.td, and tried everything without a return value (as ones with return values would get DCE'd) and without side-effects: they are forbidden by LV -- what am I missing? If we want to show test changes, I don't think there is any way, other than to club this change with https://github.com/llvm/llvm-project/pull/191026.

https://github.com/llvm/llvm-project/pull/189957