Integrated: 8361700: Missed optimization in PhaseIterGVN for mask and shift patterns due to missing notification in PhaseIterGVN::add_users_of_use_to_worklist

[Benoît Maillard]

On Wed, 16 Jul 2025 12:42:32 GMT, Benoît Maillard <bmaillard at openjdk.org> wrote:

> This PR addresses a missed optimization in `PhaseIterGVN` due to the lack of change notification to indirect users within `PhaseIterGVN::add_users_of_use_to_worklist`. 
> 
> The affected optimization is the transformation of `(x & mask) >> shift` into `(x >> shift) & (mask >> shift)`, where `mask` is a constant. This transformation is handled in `RShiftNode::IdealIL` for both `RShiftI` and `RShiftL` nodes. 
> 
> The dependency of this optimization extends beyond a direct input: from the viewpoint of a shift node, it relies on changes to the inputs of its inputs (i.e., an `AndI`/`AndL` input node to the shift). Therefore, when the `And` node changes, the corresponding shift node must be notified to allow the optimization to take place. 
> 
> Currently, `PhaseIterGVN::add_users_of_use_to_worklist` contains specific logic to handle similar dependencies for other cases, but this specific scenario is not addressed. The proposed fix adds the necessary logic in `add_users_of_use_to_worklist` to ensure proper notification for this optimization pattern. 
> 
> ### Testing
> - [x] [GitHub Actions](https://github.com/benoitmaillard/jdk/actions?query=branch%3AJDK-8361700)
> - [x] tier1-3, plus some internal testing
> - [x] Added test from the fuzzer
> 
> Thank you for reviewing!

This pull request has now been integrated.

Changeset: 62a58062
Author:    Benoît Maillard <bmaillard at openjdk.org>
Committer: Tobias Hartmann <thartmann at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/62a58062e5f3d0a723608d98d2412ea779f73897
Stats:     69 lines in 2 files changed: 69 ins; 0 del; 0 mod

8361700: Missed optimization in PhaseIterGVN for mask and shift patterns due to missing notification in PhaseIterGVN::add_users_of_use_to_worklist

Reviewed-by: thartmann, mchevalier, mhaessig, jkarthikeyan

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PR: https://git.openjdk.org/jdk/pull/26347