📝Swift Intermediate Language (SIL)

SIL is a Swift Intermediate Language, an intermediate representation of Swift that sits between AST and LLVM IR.

It is very similar to LLVM IR but is higher level and Swift-specific. It preserves more source language information (types).

Notable features:

• High-level type system (including generics)
• Constants are instructions. No Value/Constant divide. There is a place to attach source information to literals, etc.
• No phi nodes. Instead, basic blocks receive arguments.
• SIL does not know about objects’ layout—this is handled by LLVM IR lowering.

Resources

• 2015 LLVM Developers’ Meeting: Joseph Groff & Chris Lattner “Swift’s High-Level IR: A Case Study…”
• swift/SIL.rst at main · apple/swift · GitHub—documentation