SIL for the first time
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The document introduces the Swift Intermediate Language (SIL), a high-level intermediate representation (IR) designed to optimize the Swift programming language. It covers the stages of SIL, its structure, and details various guaranteed and general optimization passes within the Swift compiler. The document also includes examples of SIL code and emphasizes its importance for Swift developers in understanding compiler functionality and optimizations.
SIL for the first time
- 1. SIL for the first time Yusuke Kita @kitasuke
- 2. SIL
- 4. Why SIL?
- 5. Better understanding of how optimizations work
- 6. What is SIL?
- 7. SIL is an SSA-form IR with high-level semantic information designed to implement the Swift programming language
- 10. Where all the magic happens !
- 11. How it works?
- 12. Swift Compiler
- 13. Swift Compiler • Front end
- 14. Swift Compiler • Front end • Middle end
- 15. Swift Compiler • Front end • Middle end • Back end
- 16. Swift Compiler • Front end • Middle end • Back end
- 17. Parsing ➡ AST
- 18. Semantic analysis ➡ type checked AST
- 19. SIL generation ➡ raw SIL
- 20. SIL guaranteed transformations ➡ canonical SIL
- 21. Swift Compiler • Front end • Middle end • Back end
- 22. LLVM IR Generation ➡ LLVM IR
- 23. Swift Compiler • Front end • Middle end • Back end
- 24. LLVM ➡ .o
- 25. Recap
- 26. Swift Compiler
- 28. How SIL works?
- 29. SIL Stage
- 30. SIL Stage • Raw SIL
- 31. SIL Stage • Raw SIL • Canonical SIL
- 32. Raw SIL • May not have a fully-constructed SSA graph • May contain dataflow errors • Should not be used for native code generation or distribution
- 33. Canonical SIL • Dataflow errors must be eliminated • Certain instructions must be canonicalized to simpler forms. • Performance optimization and native code generation are derived from this form • A module can be distributed containing SIL in this (or later) forms.
- 34. Optimizations
- 35. Optimizations • Guaranteed Optimization Passes and Diagnostic Passes
- 36. Optimizations • Guaranteed Optimization Passes and Diagnostic Passes • General Optimization Passes (not running at -Onone)
- 37. Guaranteed Optimization Passes and Diagnostic Passes • Mandatory inlining • Memory promotion • Constant propagation • Return analysis • Critical edge splitting
- 38. General Optimization Passes • Generic Specialization • Witness and VTable Devirtualization • Performance Inlining • Reference Counting Optimizations • Memory Promotion/Optimizations • High-level domain specific optimizations
- 39. Lots of optimizations happening here !
- 40. SIL Gen
- 41. SIL Gen • Raw SIL $swiftc -emit-silgen sample.swift
- 42. SIL Gen • Raw SIL $swiftc -emit-silgen sample.swift • Canonical SIL $swiftc -emit-sil sample.swift
- 43. How .sil file looks like?
- 44. sample.swift func number() -> Int { let x: Int x = 1 return x }
- 45. sample.sil sil_stage canonical import Builtin import Swift import SwiftShims // main ... // number() sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int { bb0: %0 = alloc_stack $Int, let, name "x" // users: %3, %4 %1 = integer_literal $Builtin.Int64, 1 // user: %2 %2 = struct $Int (%1 : $Builtin.Int64) // users: %5, %3 store %2 to %0 : $*Int // id: %3 dealloc_stack %0 : $*Int // id: %4 return %2 : $Int // id: %5 } // end sil function '_T06sample6numberSiyF' // Int.init(_builtinIntegerLiteral:) ...
- 46. Let's take a look from the top on down
- 47. SIL Stage sil_stage canonical SIL files declare the processing stage of the included SIL with one of the declarations sil_stage raw or sil_stage canonical at top level.
- 48. Import import Builtin import Swift import SwiftShims SIL is reliant on Swift's type system and declarations. In a .sil file, there are no implicit imports. The swift and/or Builtin standard modules must be imported explicitly if used.
- 49. Legal SIL Types • A loadable legal SIL type, $T • The address of a legal SIL type, $*T
- 50. Linkage sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int hidden definitions are unique and visible only within the current Swift module. In LLVM IR, they will be emitted with external linkage and hidden visibility.
- 51. Name Mangling sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int The name @_T06sample6numberSiyF is the mangled name of the number Swift function.
- 52. Calling Convention How Swift functions are emitted in SIL • @convention(swift) • @convention(method) • @convention(witness_method) • @convention(c) • @convention(objc_method)
- 53. Type Lowering sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int A formal type is the type of a value in Swift, such as an expression result.Type lowering is the process of turning a formal type into its lowered type. The lowered type of a declaration will usually be thin.
- 54. Basic Blocks bb0: In SIL, basic blocks take arguments, which are used as an alternative to LLVM's phi nodes.
- 55. alloc_stack %0 = alloc_stack $Int, let, name "x" Allocates uninitialized memory that is sufficiently aligned on the stack to contain a value of type Int.
- 56. integer_literal %1 = integer_literal $Builtin.Int64, 1 Creates an integer literal value. The result will be of type Builtin.Int64, which must be a builtin integer type. The literal value is specified using Swift’s integer literal syntax.
- 57. struct %2 = struct $Int (%1 : $Builtin.Int64) Creates a value of a loadable struct type by aggregating multiple loadable values.
- 58. store store %2 to %0 : $*Int Stores the value %2 to memory at address %0. The type of %0 is *Int and the type of %2 is Int.
- 59. dealloc_stack dealloc_stack %0 : $*Int Deallocates memory previously allocated by alloc_stack. The allocated value in memory must be uninitialized or destroyed prior to being deallocated.
- 60. return return %2 : $Int Exits the current function and returns control to the calling function.
- 61. sample.sil sil_stage canonical import Builtin import Swift import SwiftShims // main ... // number() sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int { bb0: %0 = alloc_stack $Int, let, name "x" // users: %3, %4 %1 = integer_literal $Builtin.Int64, 1 // user: %2 %2 = struct $Int (%1 : $Builtin.Int64) // users: %5, %3 store %2 to %0 : $*Int // id: %3 dealloc_stack %0 : $*Int // id: %4 return %2 : $Int // id: %5 } // end sil function '_T06sample6numberSiyF' // Int.init(_builtinIntegerLiteral:) ...
- 62. SIL with optimizations swiftc -emit-sil sample.swift -O Compile with optimizations
- 63. sample.swift func number() -> Int { let x: Int x = 1 return x }
- 64. sil_stage canonical import Builtin import Swift import SwiftShims // main ... // number() sil hidden @_T06sample6numberSiyF : $@convention(thin) () -> Int { bb0: %0 = integer_literal $Builtin.Int64, 1 // user: %1 %1 = struct $Int (%0 : $Builtin.Int64) // user: %2 return %1 : $Int // id: %2 } // end sil function '_T06sample6numberSiyF'
- 65. Summary • Not so difficult than expected • Good to know how Swift Compiler works as Swift developer • Especially Swift optimizations
- 66. References • swift/docs/SIL.rst • Swiftコンパイラのアーキテクチャ • Swiftコンパイラの構造と基盤テクニック
- 67. Thank you