RFR: Fix and rewrite update-refs barrier selector

[Roman Kennke]

Good. Sorry for breaking it. Thanks for fixing!

On Wed, Jan 24, 2018 at 6:03 PM, Aleksey Shipilev <shade at redhat.com> wrote:

> On 01/24/2018 05:31 PM, Aleksey Shipilev wrote:
> > After Traversal GC commit, normal cycle on Compiler.compiler fails
> within:
> >
> > V  [libjvm.so+0x153c713]  oop ShenandoahHeap::evac_update_oop_ref<unsigned
> int>(unsigned int*,
> > bool&)+0x333
> > V  [libjvm.so+0x1539082]  ShenandoahBarrierSet::write_ref_array(HeapWord*,
> unsigned long)+0x852
> > V  [libjvm.so+0x133be02]  void ObjArrayKlass::do_copy<unsigned
> int>(arrayOop, unsigned int*,
> > arrayOop, unsigned int*, int, Thread*)+0x142
> > V  [libjvm.so+0x133932b]  ObjArrayKlass::copy_array(arrayOop, int,
> arrayOop, int, int, Thread*)+0x72b
> > V  [libjvm.so+0xf23325]  JVM_ArrayCopy+0x1e5
> >
> > The troubling bit is why do we even get here:
> >
> >   inline void do_oop_work(T* p) {
> >     oop o;
> >     if (STOREVAL_WRITE_BARRIER) {
> >       bool evac;
> >       o = _heap->evac_update_oop_ref(p, evac); <--- ????
> >       if ((ALWAYS_ENQUEUE || evac) && !oopDesc::is_null(o)) {
> >         ShenandoahBarrierSet::enqueue(o);
> >       }
> >     } else {
> >       o = _heap->maybe_update_oop_ref(p);
> >     }
> >     if (UPDATE_MATRIX && !oopDesc::is_null(o)) {
> >       _heap->connection_matrix()->set_connected(p, o);
> >     }
> >   }
> >
> > It happens because the condition in selector is wrong:
> >   http://cr.openjdk.java.net/~shade/shenandoah/traversal-
> regr-1/webrev.01/
>
> Actually, let's rewrite the damn fragile thing:
>   http://cr.openjdk.java.net/~shade/shenandoah/traversal-regr-1/webrev.02/
>
> -Aleksey
>
>
>