Integrated: 8260653: Unreachable nodes keep speculative types alive

[Nils Eliasson]

On Wed, 17 Feb 2021 10:27:08 GMT, Nils Eliasson <neliasso at openjdk.org> wrote:

> The RunThese test fails because after first igvn.optimize() (directly after parsing) there are unreachable nodes cycles left. Later when remove_speculative_types() is called - only reachable nodes will have their speculative type removed. At the end of remove_speculative_types() there is an assert that all speculative types have been removed that will fail.
> 
> This problem will not cause crashes in production - it is only a sanity test.
> 
> I suggest adding a call to PhaseRemoveUseless before remove_speculative_types. This will cost a few extra cycles but it is the only way we can guarantee that no unreachable nodes are left.
> 
> When debugging this I experimented with adding a call to verify_graph_edges to check for dead code at the same spot. This triggers failures in a lot of test. The conclusion is that it is very common that we have dead node cycles - but they very rarely keep speculative types alive.
> 
> A big thank you to Dean Long how created the reproducer for this bug.
> 
> Please review.

This pull request has now been integrated.

Changeset: 3a21e1df
Author:    Nils Eliasson <neliasso at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/3a21e1df
Stats:     6 lines in 1 file changed: 5 ins; 0 del; 1 mod

8260653: Unreachable nodes keep speculative types alive

Reviewed-by: vlivanov, thartmann

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PR: https://git.openjdk.java.net/jdk/pull/2606