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

[Tobias Hartmann]

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.
>