[8u] RFR(s): 8154210: Zero: Better byte behaviour

[Severin Gehwolf]

Hi,

Could somebody please review and approve this fix for JDK8u Zero? The
April CPU patches for OpenJDK broke this (bug 8132051). Please see the
bug for details.

The fixes are:
- Fix the jump table which is used for Zero release builds, since
  JDK-8132051 introduced a new bytecode _fast_zputfield.
- Make sure that results, which are a subword of a stack slot
  (possibly narrowed) are always at the lowest address.

The fix was originally written by Andrew Haley.

Bug: https://bugs.openjdk.java.net/browse/JDK-8154210
webrev: http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8154210/webrev.01/

Once the April CPU patches hit JDK 9 trees we need to make sure this
gets properly forward-ported. Unfortunately this hasn't happened yet
(or maybe it didn't reach jdk9/hs yet).

Thoughts?

Thanks,
Severin