Retrofitting Symbolic Holes to LLVM IR

Symbolic holes are one of the fundamental building blocks of solver-aided and interactive programming. Unknown values can be soundly integrated into programs, and automated tools such as SAT solvers can be used to prove properties of programs containing them. However, supporting symbolic holes in a programming language is challenging; specifying interactions of holes with the type system and execution semantics requires careful design. This paper motivates and introduces the implementation of symbolic holes with unknown type to LLVM IR, a strongly-typed compiler intermediate language. We describe how such holes can be implemented safely by abstracting unsound and type-unsafe details behind a new primitive IR manipulation. Our implementation co-operates well with existing features such as type and dependency checking. Finally, we highlight potentially fruitful areas for investigation using our implementation.