Avoid converting array holding existentials #3006
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Motivation: When converting an Array that holds existentials, it is necessary for Swift to allocate a new Array and copy the elements into it, so that it can fix up their existential boxes. We forced this to happen with taking a `[ChannelHandler]` to `[ChannelHandler & Sendable]`, without rewriting the other functions. The result of that was that the other functions needed to convert the channel handler types, causing extra allocations in this path. Modifications: Propagate the constraint down to the point where we iterate the Array. Result: Allocations reduced.
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Of course, this change just moved the cost into the SyncOperations instead. So they now need to have totally separate codepaths to avoid reprojecting the array. |
That should be same type at runtime as Sendable is just a marker protocol. @Lukasa did you opened a swiftlang issue? |
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I didn't, but I don't think the fact that it's the same type at runtime is quite true. |
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Motivation:
When converting an Array that holds existentials, it is necessary for Swift to allocate a new Array and copy the elements into it, so that it can fix up their existential boxes. We forced this to happen with taking a
[ChannelHandler]to[ChannelHandler & Sendable], without rewriting the other functions.The result of that was that the other functions needed to convert the channel handler types, causing extra allocations in this path.
Modifications:
Propagate the constraint down to the point where we iterate the Array.
Result:
Allocations reduced.