Improve Deserialization Performance #734
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We only needed this because of quadratic hashing costs that were corrected in swiftlang#655. As it stands, computing this hash up front is pessimizing deserialization of source file dependency graphs.
There's no need to completely empty out this scratch buffer especially since we can use it to amortize the cost of reallocation of the backing buffer for the array here.
Blobs are now decoded as ArraySlices, so we need to switch to the stdlib entrypoint. This has the added upside of being *much* more performant than String.init(data:encoding:) which not only cost a copy to create the Data, but also could not take advantage of stdlib's fast paths for UTF8 buffers as inputs.
artemcm
approved these changes
Jun 29, 2021
davidungar
approved these changes
Jun 29, 2021
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Consume the new non-owning bitstream deserialization in swiftlang/swift-tools-support-core#236 to provide a 3-5x boost to deserialization performance for source and module dependency graph files. Also, undo a cached hash optimization that was only really necessary because of the quadratic COW issue resolved in #654. Otherwise, the hash was being eagerly computed during deserialization which forced an extra half-second of wall time.