RFR: 8170100: AArch64: Crash in C1-compiled code accessing References

[Andrew Haley]

In the entry of
TemplateInterpreterGenerator::generate_Reference_get_entry the
sender's SP is saved in r13, a call-clobbered register. We need to
save it in a register which is not call-clobbered when we call
g1_write_barrier_pre().

It would be better to convert all usages of r13 as senderSP to r19,
but this is less risky.  I'll do it in JDK 10.

http://cr.openjdk.java.net/~aph/8170100/

Andrew.