Request for reviews (M): 6957939: Reduce registers usage by DecodeN/EncodeP

[Vladimir Kozlov]

http://cr.openjdk.java.net/~kvn/6957939/webrev

Fixed 6957939: Reduce registers usage by DecodeN/EncodeP

DecodeN/EncodeP usually produce result in the different
from input register because types difference (32bit narrow
oop vs 64bit oop).

Try to reuse input regiser for result if DecodeN/EncodeP is
the only user by recording bias for input and ouput lrgs.
It is done after copy bias for spill copies was recorded
so they will get priority since only one copy bias could
be recorded.

Tested with CTW, GCBasher with +VerifyOops.