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

[Matt Arsenault via llvm-commits]

arsenm wrote:

> If this becomes more than "I still think ...", can we move this one floor up to discourse for awareness? E.g., we have to update LegalizerHelper to not produce the G_INSERT/G_EXTRACT family anymore. Put a deprecated comment in GenericOpcodes.td. Put a comment in https://llvm.org/docs/GlobalISel/GenericOpcode.html. And more ...


I was working on that last time I had time to look at globalisel, probably 3 years ago at this point. For the G_INSERT_VECTOR_ELT/G_EXTRACT_VECTOR_ELT case, it's easy to just directly handle the constant operand case 

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