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QC Li / iOS Dev
Reduce iOS app size
By analyzing source code
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By Analyzing source code…
Internal Modules
Analyzed
3
Binary size
Reduced
44%
For LINE app
Saved
2.1MB
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Agenda › App Size
› Link Map
› Find Redundant Code
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App Size
Overview
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› 📦 The space an app takes on the disk
of user’s cellphone.
› ⏳ It takes longer time to download or
update an app with bigger binary size.
App Size
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App
…
🗄 Database
📐 Storyboard / UI file
📚 Translation Text
🖼 Image 📃 Code
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More code, larger binary size
📃 📦
📦
📦📦
📃
📃📃
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When app size getting bigger…
› Redundant code increases in app
› More features ➡ Bigger size
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How to find redundant code?
› Like losing weight
› We should have a scale first.
› Can compare the weight change before and after.
› May need to analyze body composition.
› By removing redundant code, it can reduce app size.
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Link Map
Using link map as scale to analyze iOS app size
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Link Map
› An intermediate file generated by
compiler.
› Recorded the memory layout of
an app by combining binary from
other object file.
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By default Xcode doesn’t
generate link map but it is
easy to turn this build
option on.
Generate it!
Turn this on
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Link Map Format
› Path and Arch
› Object files
› Sections
› Symbols
› Dead Stripped Symbols
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Object Files
› Each object files (.o) is
generated from source
code by compiler.
› There is an ID number for
each object file in link
map.
Filename
ID
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› Memory layout
› Address
› Size
› Summarize all sizes will
get total size of the app.
Sections
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› Memory layout details
› Address
› Size
› File — Object file
› Name
Symbols
Symbol
Object
file ID
Size
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› Unique name for
compiler usage.
› Help to address
corresponding code.
› Use tool to get meaning.
Mangling
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What we learned from Link Map
› Compare the size between components.
› Observe the size change before and after.
› Knowing the size of each component.
› Down to source file level.
› Combining object file list and symbol list from Link Map file.
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Find Redundant Code
By using SourceKit to analyze source code
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Redundant Code Sample 1
Compiler warns about non-used variable
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Redundant Code Sample 2
Non-used interface (var or function)
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Redundant Code Sample 3
Referenced but not really in use
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Redundant Code
› Unreferenced declarations
› How to find those unreferenced declaration?
› Variables or functions that are not in use
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Find Unreferenced Declaration
› Use “Find Call Hierarchy” in IDE.
› Compiler have those information.
› We could analyze compiler
intermediate steps
› Is there a systematic, lightweight
way?
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SourceKit
› Open source by Apple
› Swift language tool
› IDE supports
› Indexing
› Syntax highlight
› Code completion
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sourcekitd
› SourceKitService
› XPC
› Xcode send request
› sourcekitd response
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SourceKit C API
› SourceKit provides a set of APIs that
you can write your program to call
SourceKit.
› There are some 3rd open source
softwares help you communicate with
SourceKit, such as SourceKitten.
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Use SourceKit for parsing
📃
📋
💻 🔬
Source Code
Parsed Result
SourceKit Parsing Program
XPC
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Example Source Code
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Example Parsing Result
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Find Declarations
There is a public declaration of structure called MilkTea
Declaration
Name
Type
Accessibility
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Find References
Inside MilkTea, there is a public declaration of variable sugar which is a SugarAmount
Reference to
another type
Type Name
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Build Dependency
MilkTea
SugarAmount
IceAmount
Double
sugar
volume
ice
init()
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Build Dependency (Simplified)
MilkTea
SugarAmount
IceAmount
Double
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Build Dependency Graph
Module A
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Build Dependency Graph across Modules
Module A
Module B
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Traverse Dependency Graph
Module A
Module B
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Find Unreached Nodes
Module A
Module B
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Unreferenced Declaration
› They are not in use because they are not reached
› We could consider to remove them from source code
› Unreached nodes are unreferenced declaration
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Practice in LINE
Internal Modules
Applied on
3
Binary size
Reduced
44%
For LINE app
Saved
2.1MB
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Recap
› To find out redundant code, we can use language tool such as SourceKit to
analyze source code and build dependency graph.
› Remove redundant code reduces app binary size.
› Link Map helps us have a better understanding of binary size for each
components and source files.
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Thank you