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clarify list drop specialization state

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Brendan Hansknecht 2024-07-16 13:14:39 -07:00
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11
crates/compiler/mono/src/drop_specialization.rs
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@ -1088,7 +1088,16 @@ fn specialize_list<'a, 'i>(
}};
}
// TODO: Investigate if there is still any utility in List drop specialization.
// TODO: Maybe re-enable drop specialization for lists.
// It won't be as useful now, but it can still apply to lists that we know aren't seamless slices.
// It also could technically apply to seamless slices if we know everything about their underlying allocation.
// To fix this would require adding the restrictions on application above and properly implementing DecRef for the new list.
// DecRef would be easy to implement, but currently the new list has Dec/DecRef both as the same.
// Extra context starts here: https://roc.zulipchat.com/#narrow/stream/316715-contributing/topic/Implement.20RocRefcounted.20for.20RocResult/near/451651633
// With most important message here: https://roc.zulipchat.com/#narrow/stream/316715-contributing/topic/Implement.20RocRefcounted.20for.20RocResult/near/451692266
//
// If we don't re-enable this, we should fully remove the list wiring and trackind at some point.
//
// Fundamentally, an allocation for a list holds onto exactly one reference to all elements in the allocation.
// So even if there are 100 references to the list, the list will hold only 1 reference to each element.
// On top of that, the list now holds onto a reference to dead elements.