Unsafe.getObject() doesn't get loop hoisted in C2

[Aaron Grunthal]

While trying to optimize the JRuby runtime I've run into a field that's 
declared volatile but would benefit from non-volatile accesses for some 
important read operations.

I've tried to use Unsafe.getObject to achieve identical semantics to a 
non-volatile field access, but it seems like hotspot C2 cannot perform 
loop invariant code motion on getObject. I.e. it's losing one of the 
major performance benefits of non-volatile accesses since the volatile 
read itself is not that expensive, at least on x86.

My alternative is to declare the field as non-volatile and use Unsafe 
for volatile/atomic access in all other places, but this is something I 
would like to avoid as it seems more brittle than using getObject only 
in a few places (like CHM does for example).

The question is whether this is intentional or something that should be 
fixed?

- Aaron

test + disassembly : https://gist.github.com/4420897#file-test-java
compilable test: https://gist.github.com/4426366
Originally reported in concurrency-interest:
http://cs.oswego.edu/pipermail/concurrency-interest/2013-January/010520.html