RFR(M): 8231561: [lworld] C2 generates inefficient code for acmp

[Roland Westrelin]

> http://cr.openjdk.java.net/~thartmann/8231561/webrev.00/

Don't use need to also change the cmp() implementation so it takes the
_clear_prop_bits into account? Otherwise you would risk replacing a
LoadKlass with _clear_prop_bits = true with one with _clear_prop_bits =
false which could cause a crash. I suppose replacing one with
_clear_prop_bits = false with one with _clear_prop_bits = true is ok
though but too complicated to handle.

Roland.