Needs some guidance in order to let this file compile faster

I wrote a syllable-composing module for an input method. This module consists of only one file.

Tekkon/TekkonSyllableComposer.swift at 06cdbbd2a1c77521e77cdd687bff9d2a9d4f41af · vChewing/Tekkon (

However, in Xcode timeline it looks like it takes pretty much time to compile.

Therefore, I would like to ask here for possible guidance in how to optimize this module for faster compilation.

// More than 20 seconds for compilation on mac mini 2018 (64GB Ram, 6 core) with Xcode 14.

See screenshot here: Needs some guidance in order to let this file compile faster. : swift (

P.S.: I tried to tear this file into certain parts. However, this only boosts the compilation time if I only compile this module only, as it utilizes multiple threads for individual files. If I use this as a swift package in an Xcode project, Xcode only compiles it using one thread per architecture. That's why I decided to duplicate this question from Reddit to here.

Without trying to compile it effectively, my intuition is that these [String: String] static dictionary literals are hard to validate. I have a related case where I had very large dictionaries of [Int: [String]], and it was taking a lot of time to compile. My dictionaries are now externalized as plists, and it builds much faster.
I would try to remove the content of all dictionary to check if it builds much faster. If it does, I would try to find another approach to bring their data into the app. You can try to serialize and lazy load plists, or even json. This is slower at runtime, but you can fallback to literals when shipping.
I would extract these mostly constant dictionaries from the file I'm working on to begin with, as it may already help.

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@tgrapperon is probably right about those large static values taking a lot of time. Before resorting to serialization, maybe try just declaring their types? So instead of

static let arrPhonaToHanyuPinyin = /* … */


static let arrPhonaToHanyuPinyin: [[String]] = /* … */


You can also try to get more fine-grained information about compile times with some compiler flags.

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Thank you for the idea. I just tested it (with module separation into 4 files) but the compile time doesn't change. It costs <5s in multi-core compilation and almost 30s in single-core compilation.

Before using @tgrapperon's approach, I would like to see how slow the speed of compiling such large dictionary literals in Objective-C.

Obj-C will be very fast since it doesn't do much compile-time verification of your values, nor does it do any type inference or generics. It will make you builds more complex though, and you'll have to vend the Obj-C target separately from the Swift one in SPM. Best to fix this in Swift if you can.

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Testing the linked file on an M1 Max MBP benchmarking swiftc file.swift in hyperfine (Xcode 14):

Original file: 1.943s
Give types to the two arrays: 1.507s (23% improvement).
Comment out the contents of two arrays: 1.209s (38% improvement).
Comment out all dictionaries as well: 0.361s (81% improvement).

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Oh. M1 Max CPU is really powerful.
Mine is mac mini 2018 (highest CPU customizable on order).

In a test of just compiling a large array of strings, Instruments says 80+% of the time in swift-frontend is spent in llvm::CSEMIRBuilder::getDominatingInstrForID(llvm::FoldingSetNodeID&, void*&). Next closest is (anonymous namespace)::TwoAddressInstructionPass::removeClobberedSrcRegMap(llvm::MachineInstr*) at 13%.

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