8361144: Strenghten the Ideal Verification in PhaseIterGVN::verify_Ideal_for by comparing the hash of a node before and after Ideal

[benoitmaillard]

This PR adds a node hash comparison after calling Ideal in PhaseIterGVN::verify_Ideal_for to introduce an additional layer of verification for missed optimizations. Previously, we relied on the return value of Ideal, which is expected to be nullptr if no transformation was done.

By also checking the node's hash before and after Ideal, we could catch inconsistencies in the implementation or unintended modifications to the graph. Both of these may indicate missed or incomplete optimizations.

Testing

• GitHub Actions
• tier1-3, plus some internal testing

Thank you for reviewing!

---

Progress

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Issue

• JDK-8361144: Strenghten the Ideal Verification in PhaseIterGVN::verify_Ideal_for by comparing the hash of a node before and after Ideal (Enhancement - P4)

Reviewers

• Galder Zamarreño (@galderz - Author)

Contributors

• Emanuel Peter <epeter@openjdk.org>

Reviewing

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Update a local copy of the PR:
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[mlbridge]

Webrevs

• 02: Full - Incremental (75f81296)
• 01: Full - Incremental (28851936)
• 00: Full (e06b4d53)

[galderz]

Have you considered adding a test for this? Is that feasible?

[dafedafe]

Thanks @benoitmaillard! Definitely an additional check worth doing. I left a couple of inline comments.

[benoitmaillard]

Have you considered adding a test for this? Is that feasible?

@galderz I have considered doing it, but there is no known case that triggers the condition. This change was suggested by @eme64 when discussing the related JDK-8359602.

[benoitmaillard]

/contributor add @eme64

[openjdk]

@benoitmaillard
Contributor Emanuel Peter <epeter@openjdk.org> successfully added.