[llvm] [VPlan] Add support for in-loop AnyOf reductions (PR #131830)

[Luke Lau via llvm-commits]

lukel97 wrote:

> > > The in-loop reductions may be completely not profitable
> > 
> > 
> > Yes, this is only profitable for EVL tail folding due to the vp.merge. The plan is to eventually use the TargetTransformInfo::preferInLoopReduction hook to only enable this for AnyOf reductions with EVL tail folding.
> 
> I mean, the in-loop reduction may be (significantly!!!)less profitable than vp.merge.

The in-loop reduction should be a single vcpop.m which I think should be cheap on most microarchitectures? On the spacemit-x60 it's 2 cycles: https://camel-cdr.github.io/rvv-bench-results/bpi_f3/index.html

This is versus at least a regular comparison linear in EMUL + 4 mask instructions

https://github.com/llvm/llvm-project/pull/131830