Enable optimization of arraycopy as loads/stores with Shenandoah

[Roman Kennke]

Am Donnerstag, den 08.12.2016, 17:41 +0100 schrieb Roland Westrelin:
> > Ok. And what happens when ReduceInitialCardMarks is false? Because
> > this
> > might be what we need.
> 
> For instance clone:
> 
>     post_barrier(control(),
>                  memory(raw_adr_type),
>                  alloc_obj,
>                  no_particular_field,
>                  raw_adr_idx,
>                  no_particular_value,
>                  T_OBJECT,
>                  false);
> 
> void GraphKit::post_barrier(Node* ctl,
>                             Node* store,
>                             Node* obj,
>                             Node* adr,
>                             uint  adr_idx,
>                             Node* val,
>                             BasicType bt,
>                             bool use_precise) {
>   BarrierSet* bs = Universe::heap()->barrier_set();
>   set_control(ctl);
>   switch (bs->kind()) {
>     case BarrierSet::G1SATBCTLogging:
>       g1_write_barrier_post(store, obj, adr, adr_idx, val, bt,
> use_precise);
>       break;
> 
>     case BarrierSet::CardTableForRS:
>     case BarrierSet::CardTableExtension:
>       write_barrier_post(store, obj, adr, adr_idx, val, use_precise);
>       break;
> 
>     case BarrierSet::ModRef:
>     case BarrierSet::ShenandoahBarrierSet:
>       break;
> 
>     default      :
>       ShouldNotReachHere();
> 
>   }
> }
> 
> For array clone, if I follow the logic correctly
> arrayof_oop_disjoint_arraycopy stub.
> 
> The shenandoah clone barrier is a no-op unless
> ShenandoahBarrierSet::need_update_refs_barrier() is true. If it's
> false
> often enough, then it seems a reasonable trade off to do the bulk
> copy
> and have an extra call.

Ok. I know I went through this a while ago, but needed a refresher ;-)

Thanks, Roman