LLVM’s ORC JIT [1] is a powerful framework for just-in-time compilation of LLVM IR. However, when applied to large codebases, ORC often exhibits a surprisingly high front-load ratio: we have to parse all IR modules before execution even reaches main(). This diminishes the benefits of JITing and contributes to phenomena as the “time to first plot” latency in Julia, one of ORC’s large-scale users [2].

The llvm-autojit plugin [3] is a new experimental compiler extension for automatic just-in-time compilation with ORC. The project reached a proof-of-concept state, where basic C, C++ and Rust programs build and run successfully. It integrates easily with build systems like CMake, make and cargo, making it practical to apply to real-world projects.

In this talk, we will examine the front-loading issue in ORC and explain how llvm-autojit mitigates it. Attendees will learn about pass plugins, LLVM IR code transformations, callgraphs and runtime libraries. And they will see how to experiment with ORC-based JITing in their own projects.

[1] https://llvm.org/docs/ORCv2.html [2] https://discourse.julialang.org/t/time-to-first-plot-clarification/58534 [3] https://github.com/weliveindetail/llvm-autojit