RFR: 8302670: use-after-free related to PhaseIterGVN interaction with Unique_Node_List and Node_Stack [v2]

[Emanuel Peter]

On Wed, 10 May 2023 11:15:53 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

>> Emanuel Peter has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   update copyright years
>
> src/hotspot/share/libadt/vectset.hpp line 57:
> 
>> 55:   VectorSet(Arena* arena);
>> 56: 
>> 57:   // Allow move constructor for && (eg. capture return of function)
> 
> It's not completely clear yet to me why this is required and how it correlates with `NONCOPYABLE` but I leave this to the experts :)

I took this from @jcking . From what I understand:
`NONCOPYABLE` disables the copy constructor (`&`) and move operator. Somehow, this also disables the move constructor (`&&`). Re-enabling that one allows things like returning local containers, and capturing them via that move constructor.

Unique_Node_List some_function() {
  Unique_Node_List local_worklist;
  // do stuff
  return local_worklist;
}

void other_function() {
  Unique_Node_List capture_worklist = some_function();
  // capture_worklist has its scope widened to this function
}

But if someone has a more detailed explanation, I'm glad to hear it ;)

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PR Review Comment: https://git.openjdk.org/jdk/pull/13833#discussion_r1189856118