RFR(M): 8130847: Cloned object's fields observed as null after C2 escape analysis

[Roland Westrelin]

> The next change puzzles me:
> 
> -         if (!call->may_modify(tinst, phase)) {
> +         if (call->may_modify(tinst, phase)) {
> -           mem = call->in(TypeFunc::Memory);
> +           assert(call->is_ArrayCopy(), "ArrayCopy is the only call node that doesn't make allocation escape");
> 
> Why only ArrayCopy? I think it is most of calls. What set of tests you ran?
> 
> Methods naming is confusing. membar_for_arraycopy() does not check for membar but for calls which can modify. handle_arraycopy() could be make_arraycopy_load().

What about:

static bool may_modify(const TypeOopPtr *t_oop, MemBarNode* mb, PhaseTransform *phase);

instead of membar_for_arraycopy()

So ArrayCopyNode would have:

virtual bool may_modify(const TypeOopPtr *t_oop, PhaseTransform *phase);

and

static bool may_modify(const TypeOopPtr *t_oop, MemBarNode* mb, PhaseTransform *phase);

that do the same thing except the static method also looks for a graph pattern starting from a MemBar.

Roland.

> 
> Add explicit check:
> && strcmp(_name, "unsafe_arraycopy") != 0)
> 
> Thanks,
> Vladimir
> 
> On 7/28/15 7:05 AM, Roland Westrelin wrote:
>> http://cr.openjdk.java.net/~roland/8130847/webrev.00/
>> 
>> When an allocation which is the destination of an ArrayCopyNode is eliminated, field’s values recorded at a safepoint (to reallocate the object) do not take the ArrayCopyNode into account at all and the effect or the ArrayCopyNode is lost on a deoptimization. This fix records values from the source of the ArrayCopyNode, emitting new loads if necessary.
>> 
>> I also use the opportunity to pin the loads generated in LoadNode::can_see_arraycopy_value() because they depend on all checks that validate the array copy and not only on the check that immediately dominates.
>> 
>> Roland.
>>