[stdlib] Speed up bridged Dictionary instances #17742
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Dictionary’s native storage classes and _SwiftDeferredNSDictionary override -[NSDictionary getObjects:andKeys:] instead of its safer replacement, -[NSDictionary getObjects:andKeys:count:]. Overriding the correct method will considerably speed up some Cocoa operations on bridged dictionaries. rdar://problem/39285882
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@swift-ci please test |
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I don't think we have benchmarks for bridged dictionaries yet, but just in case: @swift-ci please benchmark |
jtbandes
reviewed
Jul 4, 2018
stdlib/public/core/Dictionary.swift
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| // The user is expected to provide a storage of the correct size | ||
| if let unmanagedKeys = _UnmanagedAnyObjectArray(keys) { | ||
| if let unmanagedObjects = _UnmanagedAnyObjectArray(objects) { | ||
| // keys nonnull, objects nonnull | ||
| for (offset: i, element: (key: key, value: val)) in full.enumerated() { | ||
| unmanagedObjects[i] = _bridgeAnythingToObjectiveC(val) | ||
| unmanagedKeys[i] = _bridgeAnythingToObjectiveC(key) | ||
| guard i < count else { break } |
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Sorry for the drive-by comment, but shouldn’t this be checked before assigning at position i? (Same applies below)
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Gah, of course! Serves me right for not adding proper tests. Thanks!
Build comment file:Optimized (O)Regression (1)
Improvement (8)
No Changes (446)
Unoptimized (Onone)Regression (12)
Improvement (9)
No Changes (434)
Hardware Overview |
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I added new microbenchmarks to help us track performance. Copying elements in bulk out of an Improvement (1)
No Changes (2)
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@swift-ci test |
stdlib/public/core/Dictionary.swift
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| @@ -2961,6 +2975,7 @@ final internal class _SwiftDeferredNSDictionary<Key: Hashable, Value> | |||
| // keys null, objects nonnull | |||
| for position in 0..<bucketCount { | |||
| if bridgedBuffer.isInitializedEntry(at: position) { | |||
| guard i < count else { break } | |||
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you could eke out a one less loop iteration by checking this after you increment i -- and adding an early out above for count == 0
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Good point! It can often be more than one iteration, too, since the loop skips over empty buckets.
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…ementations This breaks out of the loop immediately when the last slot has been filled in the output buffer, skipping a final sequence of iterations over empty buckets.
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@swift-ci test and merge |
This was referenced Jul 10, 2018
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Dictionary’s native storage classes and_SwiftDeferredNSDictionaryoverride-[NSDictionary getObjects:andKeys:]instead of its safer replacement,-[NSDictionary getObjects:andKeys:count:].Overriding the correct method will considerably speed up some Cocoa operations on bridged dictionaries.
rdar://problem/39285882