SIL - Intermediate representation language

SIL, aka Swift Intermediate Language, is an intermediate representation language created in 2012.

#1560on PLDB

12Years Old

SIL is an SSA-form IR with high-level semantic information designed to implement the Swift programming language. In contrast to LLVM IR, SIL is a generally target-independent format representation that can be used for code distribution, but it can also express target-specific concepts as well as LLVM can.

Tags: intermediate representation language
Early development of SIL happened in Apple
See also: (2 related languages) CIR, LLVM IR
2 PLDB concepts link to SIL: Rust HIR, Rust MIR

Example from the web:

// SIL is reliant on Swift's type system and declarations, so SIL syntax is an extension of Swift's. A .sil file is a Swift source file with added SIL definitions. The Swift source is parsed only for its declarations; Swift func bodies (except for nested declarations) and top-level code are ignored by the SIL parser. In a .sil file, there are no implicit imports; the swift and/or Builtin standard modules must be imported explicitly if used.
sil_stage canonical

import Swift

// Define types used by the SIL function.

struct Point {
  var x : Double
  var y : Double
}

class Button {
  func onClick()
  func onMouseDown()
  func onMouseUp()
}

// Declare a Swift function. The body is ignored by SIL.
func taxicabNorm(_ a:Point) -> Double {
  return a.x + a.y
}

// Define a SIL function.
// The name @_T5norms11taxicabNormfT1aV5norms5Point_Sd is the mangled name
// of the taxicabNorm Swift function.
sil @_T5norms11taxicabNormfT1aV5norms5Point_Sd : $(Point) -> Double {
bb0(%0 : $Point):
  // func Swift.+(Double, Double) -> Double
  %1 = function_ref @_Tsoi1pfTSdSd_Sd
  %2 = struct_extract %0 : $Point, #Point.x
  %3 = struct_extract %0 : $Point, #Point.y
  %4 = apply %1(%2, %3) : $(Double, Double) -> Double
  return %4 : Double
}

// Define a SIL vtable. This matches dynamically-dispatched method
// identifiers to their implementations for a known static class type.
sil_vtable Button {
  #Button.onClick: @_TC5norms6Button7onClickfS0_FT_T_
  #Button.onMouseDown: @_TC5norms6Button11onMouseDownfS0_FT_T_
  #Button.onMouseUp: @_TC5norms6Button9onMouseUpfS0_FT_T_
}

Example from hello-world:

print Hello World

Language features

Feature	Supported	Example	Token
Print() Debugging	✓		print
Comments	✓	// A comment
Line Comments	✓	// A comment	//
Semantic Indentation	X