📖2015 LLVM Developers’ Meeting: Joseph Groff & Chris Lattner “Swift's High-Level IR: A Case Study..."
- url
- https://www.youtube.com/watch?v=Ntj8ab-5cvE
- slides
https://llvm.org/devmtg/2015-10/slides/GroffLattner-SILHighLevelIR.pdf
- even though C/C++ are pretty low-level languages, the gap between C/C++ and LLVM IR is still great
- LLVM IR is too low-level for language analysis (uninitialized, unreachable, etc), so clang developed a side pipeline
- design of SIL
- very similar to LLVM IR
- high-level type system (including generics)
- $Swift.Int is just a structure
struct Int { var value: Builtin.Int64 } - constants are instructions
- attached source location
- no value/constant divide
- phi nodes → basic block arguments (jump with arguments)
- more uniform IR
- more natural
- (maps nicely to CPS’s continuation call)
- builtin can reference LLVM instructions directly
- SIL passes
- raw SIL + canonical SIL
- there are some mandatory optimizations that always guaranteed run
- Lowering
- SILGen handles operational lowering
- IRGen handles type lowering & concretization of the target
- SIL is a big investment: lowering, pass manager, inliner, testing infrastructure, etc. (lots of duplication)