Request for reviews (S): 7190310: Inlining WeakReference.get(), and hoisting $referent may lead to non-terminating loops

[Roland Westrelin]

Hi Vladimir,

> I updated webrev:
> 
> http://cr.openjdk.java.net/~kvn/7190310/webrev.01
> 
> During testing I found several problem with code for unsafe.getObject() intrinsic code in both: C1 and C2. I moved some checks in C1 from G1UnsafeGetObjSATBBarrierStub stub into shared code and also added static klass analysis to avoid generation of G1/membar code if klass is not Reference or Object. In C2 I hit bad graph problem because If node's projections in insert_pre_barrier() were not put on IGVN worklist.
> 
> I added jtreg tests (thanks to John Cuthbertson for unsafe test which I extended).
> 
> Tested with CTW and Kitchensink with C1, C2, tiered.

The c1 side doesn't look right to me. 

insert_mem_bar(Op_MemBarCPUOrder) is not the same as __ membar_acquire(). __ membar_acquire() actually emits instructions on some platforms. Also, optimizations in c1 are performed at the HIR level. So adding the barrier at the LIR won't prevent any further optimization.

Can this problem actually happen with c1?

Roland.