[RISCV] Use vcompress in deinterleave2 intrinsic lowering (#118325)

This is analogous to febbf91 which added shuffle lowering using
vcompress; we can do the same thing in the deinterleave2 lowering path
which is used for scalable vectors.

Note that we can further improve this for high lmul usage by adjusting
how we materialize the mask (whose result is at most m1 with a known bit
pattern). I am deliberately staging the work so that the changes to
reduce register pressure are more easily evaluated on their own merit.

0 files changed, 0 insertions, 0 deletions