[9] RFR(S): 8179678: ArrayCopy with same src and dst can cause incorrect execution or compiler crash

[Roland Westrelin]

> Call nodes have complicated graph of following control
> projections. You don't check for them. Why?  I think that was the
> reason that we scan memory edges instead of control when searching for
> calls.

Catch and CatchProj?

The logic I changed handles an array copy, once it is expanded, whose
destination is a non escaping array.

Escape analysis only considers the destination of "validated" array
copies as non escaping:

PointsToNode::EscapeState es = PointsToNode::ArgEscape;
if (call->is_ArrayCopy()) {
  ArrayCopyNode* ac = call->as_ArrayCopy();
  if (ac->is_clonebasic() ||
      ac->is_arraycopy_validated() ||
      ac->is_copyof_validated() ||
      ac->is_copyofrange_validated()) {
    es = PointsToNode::NoEscape;
  }
}

An array copy is "validated" when LibraryCallKit::inline_arraycopy()
inserted guards to validate that this arraycopy is a "good" arraycopy.

In PhaseMacroExpand::generate_arraycopy() the stub calls that are
inserted are all connected through a single ProjNode to the result
Region except:

1- the slow arraycopy call which has Catch and CatchProj nodes. But with
validated arraycopies, there shouldn't be a slow arraycopy alone but at
least one stub call on one of the control path.

2- a checkcast arraycopy for which the return of the call needs to be
checked: checkcast arraycopy are explicitly skipped for validated
arraycopies.

3- if the copy size is null, PhaseMacroExpand::generate_arraycopy()
would generate no call but that special case should be handled by
ArrayCopyNode::Ideal.

4- A generic arraycopy (if C2 can't tell whether inputs to arraycopy are
arrays).

I found that 4 can happen eventhough given the arraycopy is validated,
it could be avoided. So here is a new webrev which sets src_elem =
dest_elem in PhaseMacroExpand::expand_arraycopy_node() when dest_elem is
known and the arraycopy is validated.

http://cr.openjdk.java.net/~roland/8179678/webrev.03/

Roland.