[9] RFR(S): 8156760: VM crashes if -XX:-ReduceInitialCardMarks is set

[yumin qi]

Hi, Tobias

src/share/vm/opto/graphKit.cpp:

4210   // If we are writing a NULL then we need no post barrier
4211   if (val != NULL && val->is_Con() && val->bottom_type() ==
TypePtr::NULL_PTR) {

val is valid now so val != NULL can be removed I think.

I'm not a Reviewer


Thanks

Yumin



On Mon, May 23, 2016 at 3:29 AM, Tobias Hartmann <tobias.hartmann at oracle.com
> wrote:

> Hi Roland,
>
> thanks for the review! Please see comments below.
>
> On 23.05.2016 11:34, Roland Westrelin wrote:
> >
> > Hi Tobias,
> >
> >> Problem 3: C2 crashes with SIGSEGV in
> >> ArrayCopyNode::prepare_array_copy() because we expect an array
> >> clone/copy and dereference 'src_type->isa_aryptr()' but actually have
> >> a non-array Object.clone() [3]. This is because with
> >> !ReduceInitialCardMarks, ArrayCopyNode::try_clone_instance() does not
> >> capture the Object.clone() intrinsic because we emit card marking
> >> code (we bail out in 'ArrayCopyNode::finish_transform()'). We
> >> continue assuming that the array copy is a non-instance copy. I added
> >> an additional check to bail out in this case.
> >
> > One problem I noticed in this code is that
> > ArrayCopyNode::try_clone_instance() returns NULL to mean both this is
> > not a basic clone:
> >
> >   if (!is_clonebasic()) {
> >     return NULL;
> >   }
> >
> > and the clone failed:
> >
> >   if (!finish_transform(phase, can_reshape, ctl, mem)) {
> >     return NULL;
> >   }
> >
> > ArrayCopyNode::finish_transform() would fail with
> > !ReduceInitialCardMarks. The way I fixed this locally is to return
> > NodeSentinel when the clone fails so the caller can distinguish not a
> > clone from a failure. And then ArrayCopyNode::finish_transform():
> >
> >   Node* mem = try_clone_instance(phase, can_reshape, count);
> >   if (mem != NULL) {
> >     return mem == NodeSentinel ? NULL: mem;
> >   }
> >
> > Does that solve the same problem you're seeing?
>
> Yes, that's a better solution and solves the problem as well.
>
> Here is the updated webrev:
> http://cr.openjdk.java.net/~thartmann/8156760/webrev.01/
>
> Thanks,
> Tobias
>
> >
> > Roland.
> >
>