RequirementMachine: Minimization understands 'relations' among layout requirements #40732
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It's used to store more than just the rule ID. However, add a getRuleID() method that also asserts that Kind is ApplyRewriteRule for readability.
… requirements A superclass requirement 'T : C' implies a layout requirement 'T : AnyObject' (if the class is @objc) or 'T : _NativeObject' (if the class is not @objc). In the latter case, there might already be a 'T : AnyObject' requirement, in which case the type parameter 'T' is subject to two layout requirements: T : AnyObject T : _NativeObject The second requirement implies the first however. To encode this in the world of rewrite loops, we the notion of a 'relation' between property symbols, and a 'Relation' rewrite step. Here, the relation is that _NativeObject < AnyObject. Once this relation is recorded, the Relation rewrite step will transform T.[layout: _NativeObject].[layout: AnyObject] into T.[layout: _NativeObject] and vice versa. This rewrite step allows us to construct a rewrite loop which makes the first rewrite rule redundant via the second.
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@swift-ci Please test source compatibility |
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A superclass requirement 'T : C' implies a layout requirement 'T : AnyObject' (if the class is @objc) or 'T : _NativeObject'
(if the class is not @objc).
In the latter case, there might already be a 'T : AnyObject' requirement, in which case the type parameter 'T' is subject to two layout requirements:
The second requirement implies the first however. To encode this in the world of rewrite loops, we the notion of a 'relation'
between property symbols, and a 'Relation' rewrite step.
Here, the relation is that _NativeObject < AnyObject. Once this relation is recorded, the Relation rewrite step will transform
into
and vice versa.
This rewrite step allows us to construct a rewrite loop which makes the first rewrite rule redundant via the second.