The document discusses SIL (Swift Intermediate Language), which is the intermediate representation used by the Swift compiler. It provides an overview of SIL and how the Swift compiler uses it, demonstrates converting Swift code to SIL, and shows how optimizations are performed from raw SIL to canonical SIL. Examples are given of memory optimizations and how flag settings can control optimizations. In summary, learning SIL provides insights into how the Swift compiler works and is worthwhile for optimization.

2. Hi, I'm Yusuke
@kitasuke
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

3. Why SIL?
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

4. Why SIL?
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

5. Why SIL?
→ Better idea of Swift type system !
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

6. Why SIL?
→ Better idea of Swift type system !
→ Optimizations magic "✨
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

7. Why SIL?
→ Better idea of Swift type system !
→ Optimizations magic "✨
→ For fun and profit $
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

8. SIL
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

9. Swift
Intermediate
LanguageSIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

10. SIL is a language specific
Intermediate
Representation
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

11. Swift
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

12. Swift Compiler
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

13. Swift Compiler
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

14. Swift Compiler
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

15. raw SIL
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

16. canonical SIL
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

17. Objective-C
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

18. Clang
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

19. Clang
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

20. SIL
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

21. How SIL works?
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

22. sample.swift
func number() -> Int {
let x: Int
x = 1
return x
}
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

23. Emit SIL
$swiftc -emit-sil sample.swift > sample.sil
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

24. sample.sil
sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int {
bb0:
%0 = alloc_stack $Int, let, name "x"
%1 = integer_literal $Builtin.Int64, 1
%2 = struct $Int (%1 : $Builtin.Int64)
store %2 to %0 : $*Int
dealloc_stack %0 : $*Int
return %2 : $Int
}
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

25. sample.sil
sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int {
bb0:
%0 = alloc_stack $Int, let, name "x"
%1 = integer_literal $Builtin.Int64, 1
%2 = struct $Int (%1 : $Builtin.Int64)
store %2 to %0 : $*Int
dealloc_stack %0 : $*Int
return %2 : $Int
}
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

26. sample.sil
sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int {
bb0:
%0 = alloc_stack $Int, let, name "x"
%1 = integer_literal $Builtin.Int64, 1
%2 = struct $Int (%1 : $Builtin.Int64)
store %2 to %0 : $*Int
dealloc_stack %0 : $*Int
return %2 : $Int
}
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

27. sample.sil
sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int {
bb0:
%0 = alloc_stack $Int, let, name "x"
%1 = integer_literal $Builtin.Int64, 1
%2 = struct $Int (%1 : $Builtin.Int64)
store %2 to %0 : $*Int
dealloc_stack %0 : $*Int
return %2 : $Int
}
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

28. sample.sil
sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int {
bb0:
%0 = alloc_stack $Int, let, name "x"
%1 = integer_literal $Builtin.Int64, 1
%2 = struct $Int (%1 : $Builtin.Int64)
store %2 to %0 : $*Int
dealloc_stack %0 : $*Int
return %2 : $Int
}
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

29. sample.sil
sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int {
bb0:
%0 = alloc_stack $Int, let, name "x"
%1 = integer_literal $Builtin.Int64, 1
%2 = struct $Int (%1 : $Builtin.Int64)
store %2 to %0 : $*Int
dealloc_stack %0 : $*Int
return %2 : $Int
}
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

30. sample.sil
sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int {
bb0:
%0 = alloc_stack $Int, let, name "x"
%1 = integer_literal $Builtin.Int64, 1
%2 = struct $Int (%1 : $Builtin.Int64)
store %2 to %0 : $*Int
dealloc_stack %0 : $*Int
return %2 : $Int
}
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

31. sample.sil
sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int {
bb0:
%0 = alloc_stack $Int, let, name "x"
%1 = integer_literal $Builtin.Int64, 1
%2 = struct $Int (%1 : $Builtin.Int64)
store %2 to %0 : $*Int
dealloc_stack %0 : $*Int
return %2 : $Int
}
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

32. sample.sil
sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int {
bb0:
%0 = alloc_stack $Int, let, name "x"
%1 = integer_literal $Builtin.Int64, 1
%2 = struct $Int (%1 : $Builtin.Int64)
store %2 to %0 : $*Int
dealloc_stack %0 : $*Int
return %2 : $Int
}
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

33. Emit SIL with optimizations
$swiftc -emit-sil -O sample.swift > sample.sil
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

34. sample.sil with optimizations
sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int {
bb0:
%0 = integer_literal $Builtin.Int64, 1
%1 = struct $Int (%0 : $Builtin.Int64)
return %1 : $Int
}
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

35. sample.sil with optimizations
sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int {
bb0:
%0 = integer_literal $Builtin.Int64, 1
%1 = struct $Int (%0 : $Builtin.Int64)
return %1 : $Int
}
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

36. sample.sil with optimizations
sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int {
bb0:
%0 = integer_literal $Builtin.Int64, 1
%1 = struct $Int (%0 : $Builtin.Int64)
return %1 : $Int
}
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

37. sample.sil with optimizations
sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int {
bb0:
%0 = integer_literal $Builtin.Int64, 1
%1 = struct $Int (%0 : $Builtin.Int64)
return %1 : $Int
}
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

38. sample.sil with optimizations
sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int {
bb0:
%0 = integer_literal $Builtin.Int64, 1
%1 = struct $Int (%0 : $Builtin.Int64)
return %1 : $Int
}
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

39. sample.sil with optimizations
sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int {
bb0:
%0 = integer_literal $Builtin.Int64, 1
%1 = struct $Int (%0 : $Builtin.Int64)
return %1 : $Int
}
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

40. Diff
sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int {
bb0:
%0 = alloc_stack $Int, let, name "x"
%1 = integer_literal $Builtin.Int64, 1
%2 = struct $Int (%1 : $Builtin.Int64)
store %2 to %0 : $*Int
dealloc_stack %0 : $*Int
return %2 : $Int
}
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

41. sample.swift
func number() -> Int {
let x: Int
x = 1
return x
}
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

42. sample.swift with optimizations
func number() -> Int {
return 1
}
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

43. Mem2Reg
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

44. Register Promotion of
Stack Allocations
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

45. Optimizations !✨
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

46. Optimization flags
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

47. Optimization flags
→ -Onone
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

48. Optimization flags
→ -Onone
→ -O
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

49. Optimization flags
→ -Onone
→ -O
→ -Ounchecked
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

50. Optimization flags
→ -Onone
→ -O
→ -Ounchecked
→ -Osize
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

51. Tips for debug
→ -Xllvm -sil-print-all
→ -Xllvm -sil-print-only-functions
→ -Xllvm -sil-print-before/after/around
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

52. Summary
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

53. Summary
→ Optimize, optimize and optimize !
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

54. Summary
→ Optimize, optimize and optimize !
→ Better idea of how Swift Compiler works "
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

55. Summary
→ Optimize, optimize and optimize !
→ Better idea of how Swift Compiler works "
→ Definitely worth learning #
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

56. References
→ Swift type in SIL
→ swift/docs/SIL.rst
→ Debugging the Swift Compiler
→ Swift's High-Level IR: A Case Study of
Complementing LLVM IR with Language-Specific
Optimization
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018

57. Thank you!
SIL for First Time Learners, Yusuke Kita (@kitasuke), /dev/world/2018