Ruby Executes JIT Code: The Hidden Mechanics Behind the Magic
2 days ago
- #JIT
- #Performance
- #Ruby
- Ruby's JIT compilers (YJIT and ZJIT) compile methods into machine code for faster execution while keeping the original bytecode for de-optimization.
- JIT-compiled code lives alongside bytecode in the Instruction Sequence (ISEQ) data structure, with a pointer (`jit_entry`) to the native code when compiled.
- Ruby decides to compile methods based on call thresholds: profiling starts at 25 calls, and compilation occurs at 30 calls.
- De-optimization happens when JIT assumptions (e.g., method always called with integers) fail, reverting execution to the interpreter.
- TracePoint activation forces Ruby to discard JIT code and interpret bytecode to ensure correct event triggering.
- Ruby doesn't compile all methods to avoid wasting resources on rarely used code and to allow for better optimization through profiling.