Change TraitRef subtyping checks to equality #29960
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Trait references are always invariant, so all uses of subtyping between them are equivalent to using equality. Moreover, the overlap check was previously performed twice per impl pair, once in each direction. It is now performed only once, and internally uses the equality check. On glium, a crate that spends some time in coherence, this change sped up coherence checking by a few percent (not very significant).
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Performance numbers please. |
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@bors r+ |
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📌 Commit 612d001 has been approved by |
While measurements are always nice, I don't see any reason to gate on them (and I know @aturon has a lot on his plate right now). There is nor reason to think that this change will make the compiler slower. (Keep in mind that trait references are always invariant, so doing |
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⌛ Testing commit 612d001 with merge 2a0ce4a... |
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…sakis Trait references are always invariant, so all uses of subtyping between them are equivalent to using equality. Moreover, the overlap check was previously performed twice per impl pair, once in each direction. It is now performed only once, and internally uses the equality check. On glium, a crate that spends some time in coherence, this change sped up coherence checking by a few percent (not very significant). r? @nikomatsakis
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Trait references are always invariant, so all uses of subtyping between
them are equivalent to using equality.
Moreover, the overlap check was previously performed twice per impl
pair, once in each direction. It is now performed only once, and
internally uses the equality check.
On glium, a crate that spends some time in coherence, this change sped
up coherence checking by a few percent (not very significant).
r? @nikomatsakis