[llvm] [RISCV][GISEL] Legalize G_INSERT and G_EXTRACT for scalable vectors (PR #108220)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> > I still think we should work towards entirely removing G_INSERT and G_EXTRACT
> 
> Can you give me a better idea what you had in mind instead?

Always use total G_MERGE_VALUES / G_UNMERGE_VALUES, G_BUILD_VECTOR, etc. Arbitrary bit offset is impossibly general and hard to work with. It's as constrained as a finally selected instruction, so it's not really that useful for legalization 

https://github.com/llvm/llvm-project/pull/108220