[llvm] [AArch64][SVE] Detect MOV (imm, pred, zeroing/merging) (PR #116032)

[Paul Walker via llvm-commits]

paulwalker-arm wrote:

Thanks for the clarification. I just wasn't sure if the example was a real reproducer or just a means to demonstrate the problem.  Given this is ACLE related, let's park the decision to replace `DUP_MERGE_PASSTHRU` for now and stick with adding the new patterns.

The missed optimisation of the all active case isn't too surprising given there's already an unpredicated builtin that should be used instead.  That said, I see no harm in updating `instCombineSVEDup` to replace such instances with a vector splat.

https://github.com/llvm/llvm-project/pull/116032