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[GTO] Avoid newly exposing prototypes when supertype fields are removed - #9278
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When GlobalTypeOptimization removes all fields from a non-empty supertype descriptor, a subtype descriptor whose unread supertype fields are also removed can shift a subsequent externref field to index 0. Check whether the supertype retained any kept fields after removal (!superHasKeptFields) rather than checking whether the unoptimized supertype had empty fields (!super->getStruct().fields.empty()) when deciding whether to insert an i8 placeholder at index 0 for exposedNoProtoDescs.
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This pull request fixes an issue in GlobalTypeOptimization where a type with a supertype whose fields were all removed during optimization was not correctly identified as having no kept fields. This caused it to miss adding a placeholder at index 0 to prevent prototype exposure. The fix introduces a superHasKeptFields flag to track if any fields from the supertype are actually kept, and updates the condition to use this flag. A corresponding test case has been added to verify the behavior. I have no feedback to provide.
kripken
approved these changes
Oct 19, 2026
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When GlobalTypeOptimization removes all fields from a non-empty supertype descriptor, a subtype descriptor whose unread supertype fields are also removed can shift a subsequent externref field to index 0. Check whether the supertype retained any kept fields after removal (!superHasKeptFields) rather than checking whether the unoptimized supertype had empty fields (!super->getStruct().fields.empty()) when deciding whether to insert an i8 placeholder at index 0 for exposedNoProtoDescs.