RFR: 8282590: C2: assert(addp->is_AddP() && addp->outcnt() > 0) failed: Don't process dead nodes [v8]

[Christian Hagedorn]

On Thu, 17 Mar 2022 10:55:09 GMT, Emanuel Peter <duke at openjdk.java.net> wrote:

>> Problem:
>> Sometimes nodes are generated, and then not properly added to any other node, nor added to the worklist, so that it could be deleted. In some cases, a node can thus survive after IGVN and enter into `ConnectionGraph::compute_escape`, where no dead nodes are expected (except constants).
>> 
>> In `ArrayCopyNode::prepare_array_copy`:
>> In one, I now add the new ConvI2LNode to the worklist if we are aborting.
>> In the other case, I could safely reorder the code, such new ConvI2LNode would only be generated once we know we are not going to abort.
>> 
>> In `SubTypeCheckNode::Ideal`:
>> Replaced `set_req` with `set_req_X`, such that the input-node that is replaced (which is now potentially a dead node) is put on the worklist.
>> 
>> In `ArrayCopyNode::Ideal`:
>> If we decide to `return NULL` we also need to add the potentially dead forward / backward memory nodes to the worklist, they may turn out to be dead.
>> 
>> Added a regression test: the test + flag combination that first reproduced this issue.
>> 
>> All Tests, including this new regression test are passing. Tests rerun after small refactorings.
>
> Emanuel Peter has updated the pull request incrementally with one additional commit since the last revision:
> 
>   remove condition that is always true

Looks good!

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Marked as reviewed by chagedorn (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/7728