[re-un-revert] Replace per-save-point array snapshots with an undo trail - #889
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Creating a save point previously copied the four mutable register arrays (ints, positions, values, and storedCaptures) to enable restoration during backtracking. This led to a large amount of reference counting traffic and copy-on-write of the original register arrays whenever they were updated. This change moves the restoration data from using full copies of each array in every save point, to tracking a log of the changes to each array in the processor itself and only storing the current state of the logs in each save point. This allows `SavePoint` to be a trivial type (almost) and removes all the copy-on-write traffic. Backtracking now uses the tracking logs to unwind the registers to the specific previous state. This change also includes a minor refactor, moving the `storedCaptures` array to the `Registers` struct, alongside the other mutable registers.
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=== swift ================================================ Add UndoableArray.swift to Runtime CMakeLists (Issue/PR 92749) For coordination with swiftlang/swift-experimental-string-processing#889. === swift-experimental-string-processing ================= [re-un-revert] Replace per-save-point array snapshots with an undo trail (Issue/PR 889) Creating a save point previously copied the four mutable register arrays (ints, positions, values, and storedCaptures) to enable restoration during backtracking. This led to a large amount of reference counting traffic and copy-on-write of the original register arrays whenever they were updated. This change moves the restoration data from using full copies of each array in every save point, to tracking a log of the changes to each array in the processor itself and only storing the current state of the logs in each save point. This allows `SavePoint` to be a trivial type (almost) and removes all the copy-on-write traffic. Backtracking now uses the tracking logs to unwind the registers to the specific previous state. This change also includes a minor refactor, moving the `storedCaptures` array to the `Registers` struct, alongside the other mutable registers.
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Third and final* attempt to land the work originally in #870…