RFR: 8302670: use-after-free related to PhaseIterGVN interaction with Unique_Node_List and Node_Stack [v10]

[Kim Barrett]

On Tue, 16 May 2023 16:12:56 GMT, Justin King <jcking at openjdk.org> wrote:

>> Emanuel Peter has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Second batch of suggestions from @chhagedorn
>
> src/hotspot/share/libadt/dict.hpp line 65:
> 
>> 63: 
>> 64:   // Allow move constructor for && (eg. capture return of function)
>> 65:   Dict(Dict&&) = default;
> 
> Nit: You might consider invalidating the other dict being moved from, to catch accidental use-after-move. Could be punted to a future change.

The only way to get use-after-move is with an explicit `std::move` or equivalent.

But shouldn't there also be a move-assign operator?  I think at some point the standard mandates
some amount of the Rule of Five (previously the Rule of Three), and some violations are already
deprecated in C++14 (and gcc warns about them).

OTOH, I think the rationale of needing a move constructor to permit returning noncopyable objects from functions is eliminated by C++17's guaranteed copy elision.  So it might be that these move constructors are only needed until we upgrade the language standard we use.  (I hope that will be soon-ish, but it's not imminent.)

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PR Review Comment: https://git.openjdk.org/jdk/pull/13833#discussion_r1197640395