RFR (11): [backport] 8221766: Load-reference barriers for Shenandoah

[Roman Kennke]

>>> http://cr.openjdk.java.net/~rkennke/backport-jdk11-JDK-8221766/webrev.01/
> 
> graphKit.cpp
> 
> You pulled an unrelated change:
> 
> 3892   store_to_memory(ctrl, basic_plus_adr(str, coder_offset),
> 3893                   value, T_BYTE, coder_field_idx, MemNode::unordered);

It reverts the part back to original jdk11 upstream because we no longer
need to insert into the control flow there. Is that not ok?

See:
https://builds.shipilev.net/patch-openjdk-shenandoah-jdk11/src/hotspot/share/opto/cfgnode.cpp.udiff.html

> cfgnode.hpp
> 
> That change doesn't seem needed

Are you sure? We do have a corresponding call to step_over_gc_barrier()
in jdk/jdk too.

http://hg.openjdk.java.net/jdk/jdk/file/ce8bab2c4185/src/hotspot/share/opto/cfgnode.cpp#l1451

Roman