8155790: aarch64: debug VM fails to start after 8155617

[Edward Nevill]

Hi,

Please review the following webrev

http://cr.openjdk.java.net/~enevill/8155790/

JIRA: https://bugs.openjdk.java.net/browse/JDK-8155790


This fixes an issue where the debug build fails to start after 8155617 with the error

# Internal Error (/scratch/rwestrel/hs-comp/hotspot/src/share/vm/runtime/stubRoutines.cpp:344), pid=16911, tid=16912 
# assert(s.body[i] == 32) failed: what? 

The problem is that I failed to observe that the base register must point immediately after the end of the block being zeroed on exit from the zero loop.

In addition the base register can sometimes be byte aligned due to vectorisation and this was not handled.

The above webrev fixes this. I have tested a debug build with jtreg hotspot and langtools.

OK to push?

Ed.