[Archetype builder] Never use the representative as the archetype anchor #6684
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…hor. The "representative" potential archetype chosen by the archetype builder is essentially chosen at random, because this is a union-find data structure. Therefore, it should never be used as the "archetype anchor", which is the canonical representative of an equivalence class that affects both semantics and ABI. Decouple the computation of the archetype anchor from the representative, and verify that the chosen archetype anchor no worse than all other choices.
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@swift-ci please smoke test and merge |
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Note: this is the same as the previous PR. The CI failure we'd seen was caused by something else. |
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The "representative" potential archetype chosen by the archetype
builder is essentially chosen at random, because this is a union-find
data structure. Therefore, it should never be used as the "archetype
anchor", which is the canonical representative of an equivalence class
that affects both semantics and ABI.
Decouple the computation of the archetype anchor from the
representative, and verify that the chosen archetype anchor no worse
than all other choices.
Replace this paragraph with a description of your changes and rationale. Provide links to external references/discussions if appropriate.
Resolves SR-NNNN.