Slow Swift

Exploring Swift runtime performance. Singapore 2017. http://iOSConf.sg

Video: https://www.youtube.com/watch?v=G88qaR9R0v0

Transcript

1. 2017
   Slow Swift
   

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2. Marcin Krzyżanowski
   @krzyzanowskim
   PDFViewer.io
   pspdfkit.com
   github.com/krzyzanowskim
   CryptoSwift
   ObjectivePGP
   
   Natalie
   krzyzanowskim.com
   

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4. 1.4x
   

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5. –Waldi Ravens
   “A Objective-
   (red.)
   C program is like a fast dance on a newly
   waxed dance floor by people carrying razors.”
   Why Swift?
   

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6. –Waldi Ravens
   “A Objective-
   (red.)
   C program is like a fast dance on a newly
   waxed dance floor by people carrying razors.”
   Why Swift?
   

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7. Script Swift?
   #!/usr/bin/env xcrun -sdk macosx swift
   print(“iOSConf.sg Rocks!”)
   

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8. Script Swift?
   #!/usr/bin/env xcrun -sdk macosx swift
   print(“iOSConf.sg Rocks!”)
   -Onone
   500x to 1000x slower than default optimized build
   

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9. Compiled Swift
   • Optimized builds
   
   • Build times ;-(
   
   

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10. Compiled Swift
    • Optimized builds
    
    • Build times ;-(
    
    let arr: [Int] = [1] + [2] + [3] + [4] + [5] + [6]
    

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11. Compiled Swift
    • Optimized builds
    
    • Build times ;-(
    
    let arr: [Int] = [1] + [2] + [3] + [4] + [5] + [6]
    Expression is too complex
    to be solved in reasonable time
    

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12. Compiled Swift
    “Speedup AES.encrypt() compilation time from 68230.37ms to 678.34ms”
    

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13. Source → Binary
    as seen…
    

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14. Compilation
    SWIFT_OPTIMIZATION_LEVEL
    -Onone
    -O
    -O -whole-module-optimization
    

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15. Compilation
    SWIFT_OPTIMIZATION_LEVEL
    -Onone
    -O
    -O -whole-module-optimization
    

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16. Compilation
    SWIFT_DISABLE_SAFETY_CHECKS
    Disable runtime safety checks when optimizing.
    

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17. Compilation
    SWIFT_ENFORCE_EXCLUSIVE_ACCESS
    full
    compile-time
    none
    (SE-0176)
    

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18. Compilation
    GCC_GENERATE_DEBUGGING_SYMBOLS
    The shortcuts taken by optimized code may occasionally produce
    surprising results: some variables you declared may not exist at all
    

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19. Source Optimization
    • &+ and &- and &* but + and - and *
    • discarding any overflow (~~SWIFT_DISABLE_SAFETY_CHECKS)
    
    • init(truncatingIfNeeded:)
    
    • init(truncatingBitPattern:) no longer public ;-)
    
    • private init(_truncatingBits:) uses Builtin.truncOrBitCast
    

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20. Source Optimization
    In-Out Parameters
    –Swift Programming Language
    “An inout parameter has a value that is passed in to the
    function, is modified by the function, and is passed back out
    of the function to replace the original value.”
    func core(block: inout Array)
    

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21. Source Optimization
    • Can be optimized to pass-by-value
    
    • Pointers are useful for performance
    In-Out Parameters
    

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22. Source Optimization
    Obvious
    • struct over class
    
    • final class
    
    • private final class
    

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23. Source Optimization
    non-Obvious
    2.7s
    

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24. Source Optimization
    non-Obvious
    

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25. Source Optimization
    non-Obvious
    1.2s
    2.7s
    

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26. Source Optimization
    • for-loop over map
    • for-loop over reduce
    • transformation over the dictionary with reduce may end up with O(n2)
    

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27. Source Optimization
    0.9s
    

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28. Source Optimization
    0.8s
    

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29. Source Optimization
    Inlining
    

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30. Source Optimization
    Inlining
    • Automatic inlining (SIL, LLVM)
    

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31. Source Optimization
    Inlining
    • Automatic inlining (SIL, LLVM)
    • Inline all the things with @inline(__always)
    

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32. Source Optimization
    Inlining
    • Automatic inlining (SIL, LLVM)
    • Inline all the things with @inline(__always)
    • Force inlining with @_transparent
    

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33. Source Optimization
    Inlining
    • Automatic inlining (SIL, LLVM)
    • Inline all the things with @inline(__always)
    • Force inlining with @_transparent
    • Public interface @_inlineable
    

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34. Source Optimization
    Inlining
    • Automatic inlining (SIL, LLVM)
    • Inline all the things with @inline(__always)
    • Force inlining with @_transparent
    • Public interface @_inlineable
    • Be careful with ABI and public API
    

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35. Memory
    

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36. Memory
    

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37. Memory
    • What if…. raw chunk of memory (Unmanaged)
    
    • allocate buffer
    
    • deallocate buffer
    
    • no ARC, no COW, nothing
    

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38. Memory
    

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39. Array()
    turns out to be nearly 10% slower compared to
    
    UnsafeMutablePointer.allocate(capacity:)
    Memory
    

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40. Memory
    Stack
    free space
    Heap
    Static data
    Literals
    Instructions 0x000000
    0xFFFFFF
    

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41. Memory
    Stack
    free space
    Heap
    Static data
    Literals
    Instructions
    • Stack allocation - fast (%rsp)
    

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42. Memory
    Stack
    free space
    Heap
    Static data
    Literals
    Instructions
    • Stack allocation - fast (%rsp)
    • Heap allocation - slow (slower) (syscalls)
    

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43. Memory
    Stack
    free space
    Heap
    Static data
    Literals
    Instructions
    • Stack allocation - fast (%rsp)
    • Heap allocation - slow (slower) (syscalls)
    • Preallocation
    

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44. Memory
    Stack
    free space
    Heap
    Static data
    Literals
    Instructions
    • Stack allocation - fast (%rsp)
    • Heap allocation - slow (slower) (syscalls)
    • Preallocation
    • array.reserveCapacity(1024)
    

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45. Quiz
    

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46. Allocation
    Stack
    free space
    Heap
    Static data
    Literals
    Instructions
    

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47. Allocation
    Stack
    free space
    Heap
    Static data
    Literals
    Instructions
    (lldb) register read rsp
    rsp = 0x00007fff5fbff630
    (lldb) frame variable -L
    0x00007fff5fbff658: ([Int]) array = 3 values {
    0x00007fa5391de610: [0] = 0
    0x00007fa53e6bf3f0: [1] = -1
    0x00007fa53e6a91d0: [2] = 1
    }
    

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48. Allocation
    Stack
    free space
    Heap
    Static data
    Literals
    Instructions
    

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49. Allocation
    Stack
    free space
    Heap
    Static data
    Literals
    Instructions
    (lldb) register read rsp
    rsp = 0x000070000ec06c00
    (lldb) fr variable -L
    0x000070000ec06c18: (@lvalue [Int]) array = 0x0000000100d002b0: {
    0x0000000100d002b0: &array = 2 values {
    0x00007fd7df41ae10: [0] = 0
    0x00007fd7df485c90: [1] = -1
    0x00007fd7df4829b0: [2] = 1
    }
    

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50. Allocation
    Stack
    free space
    Heap
    Static data
    Literals
    Instructions
    

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51. Allocation
    Stack
    free space
    Heap
    Static data
    Literals
    Instructions
    (lldb) register read rsp
    rsp = 0x000070000ec06c00
    (lldb) fr variable -L
    0x00007fff5fbff680: (@lvalue MyStruct) s = 0x0000000100f06820: {
    0x0000000100f06820: &s = {
    0x0000000100f06820: value = "test"
    }
    }
    

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52. Generics
    

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53. –who knows
    “Generic code enables you to write flexible, reusable
    functions and types that can work with any type, subject to
    requirements that you define.”
    

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55. Generics
    

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56. Generics
    0.20s
    

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57. Generics
    

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58. Generics
    0.06s
    0.20s
    

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59. Generics
    

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60. Generics
    

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61. Generics
    

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62. Generics & Optimization
    • Automatic specialization
    

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63. Generics & Optimization
    • Automatic specialization
    • in the same module
    

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64. Generics & Optimization
    • Automatic specialization
    • in the same module
    • otherwise use @_specialize(exported: true, where T == Int)
    

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65. Generics & Optimization
    • Automatic specialization
    • in the same module
    • otherwise use @_specialize(exported: true, where T == Int)
    • Whole Module Optimization won’t help
    

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66. Generics & Optimization
    • Automatic specialization
    • in the same module
    • otherwise use @_specialize(exported: true, where T == Int)
    • Whole Module Optimization won’t help
    • Sometimes it won’t optimize for the same module
    

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67. Generics & Optimization
    • Automatic specialization
    • in the same module
    • otherwise use @_specialize(exported: true, where T == Int)
    • Whole Module Optimization won’t help
    • Sometimes it won’t optimize for the same module
    • Avoid generics in public API
    

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68. Let's Recap…
    

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69. Let's Recap…
    Debug
    is
    slow
    

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70. Pre-allocate
    memory
    Let's Recap…
    

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71. Let's Recap…
    Stack
    vs
    Heap
    

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72. Let's Recap…Copy
    is
    bad
    

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73. Let's Recap…
    Use carefully
    

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74. Let's Recap…
    Less Swift is
    faster Swift
    

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75. @krzyzanowskim
    krzyzanowskim.com
    Thank you!
    

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