[RISCV] Rematerialize vid.v (#97520)

This adds initial support for rematerializing vector instructions,
starting with vid.v since it's simple and has the least number of
operands. It has one passthru operand which we need to check is
undefined. It also has an AVL operand, but it's fine to rematerialize
with it because it's scalar and register allocation is split between
vector and scalar.
    
RISCVInsertVSETVLI can still happen before vector regalloc if
-riscv-vsetvl-after-rvv-regalloc is false, so this makes sure that we
only rematerialize after regalloc by checking for the implicit uses that
are added.

0 files changed, 0 insertions, 0 deletions