Improve Deserialization Performance for Bitstream Files #236
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These conveniences allowed a custom collector to escape the data in a bitstream container. But we don't really need them - the user can write their own visitor if need be. And these escaped elements are forcing copies in the visitor interface.
Now that we no longer have any entrypoints that can escape this data, switch to a non-owning view of bitstream data. This saves a significant amount of copying overhead when deserializing many/large bitstream files and allows callers to decide for themselves what format they wish to reinterpret the data as.
Creating a buffer of elements then reinterpreting them as unicode scalars involves extra allocations and copies of the underlying data. Instead, create a scratch buffer for an array of bytes and write directly into that.
CodaFi
requested review from
abertelrud,
aciidgh,
friedbunny,
neonichu and
tomerd
as code owners
This improves the performance of appending strings to the bitstream writer somewhat by giving us some room to work with.
neonichu
approved these changes
Jun 29, 2021
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@swift-ci test |
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@swift-ci test |
abertelrud
approved these changes
Jun 30, 2021
An unfortunate stopgap that restores the existing beahvior of passing around owned data.
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Switch to a non-owning intermediate representation to allow the caller to perform the necessary copies when it reinterprets the raw data we provide to them in the visitor. This meant removing the remaining entry points that could possibly allow unowned data to escape - so the initializers on
Bitstreamthat ran theCollectingVisitorhave been struck - as well as the existing deprecated APIs here that we no longer need.The combo of all of the changes here improves the performance of dependency graph deserialization in the Swift driver by 3-5x which translates to a 3-5 second wall time improvement for large projects (> 1000 files).