Greedy: Make trySplitAroundHintReg try to match hints with subreg copies (#160294)

This is essentially the same patch as
116ca9522e89f1e4e02676b5bbe505e80c4d4933;
when trying to match a physreg hint, try to find a compatible physreg if
there is
a subregister copy. This has the slight difference of using getSubReg on
the hint
instead of getMatchingSuperReg (the other use should also use getSubReg
instead,
it's faster).

At the moment this turns out to have very little effect. The adjacent
code needs
better handling of subregisters, so continue adding this piecemeal. The
X86 test
shows a net reduction in real instructions, plus a few new kills.

0 files changed, 0 insertions, 0 deletions