Merged more recent changes on main.

Revert diff 334860

Remove unused header

Remove unused header include

Thanks Hussain for this patch!
For now I have a couple of minor comments, I will take a deeper look later.
Also, I don't quite understand yet how VP handles (or plans to handle) specifying alignment parameter. Does it need VPBuilder (not to be confused with VPlan VPBuilder!) for that? Would it make sense to add the Alignment parameter to VP load/store/scatter/gather intrinsics (much like their masked counterparts) for now, unless there is already a way to specify that?

FWIW, we have a similar intrinsic in our downstream compiler for RISC-V. We call it experimental.vector.slideleftfill and is same as flavour 2 of this (except the "offset" need not be an immediate) as suggested by @sdesmalen. We have a separate predicated version (experimental.vector.vp.slideleftfill) too which takes additional arguments for the explicit vector length of the two vectors.

LGTM.

Other than the minor nit, LGTM.

Overall, definitely a good starting point. I just have a couple of minor comments.

Thanks @fpetrogalli for this proposal! I agree with @rogfer01 and @rengolin in that this approach makes a lot of sense.
I have added a few comments inline. Overall looks good.