[RISCV] Don't move source if passthru already dominates in vmv.v.v peephole (#105792)

Currently we move the source down to where vmv.v.v to make sure that the
new passthru dominates, but we do this even if it already does.

This adds a simple local dominance check (taken from
X86FastPreTileConfig.cpp) and avoids doing the move if it can.

It also modifies the move to only move it to just past the passthru
definition, and not all the way down to the vmv.v.v.

This allows folding to succeed in some edge cases, which prevents
regressions in an upcoming patch.

0 files changed, 0 insertions, 0 deletions