"JIT Compiler From the Ground Up" [AtA]

While Java programs are deployed as bytecode, performance-relevant code will be compiled, at run time, to machine code whose performance rivals that of any other platform. In the HotSpot JVM, this is the job of the just-in-time compilers C1 and C2 and between speculation and traps, inlining and constant folding, escape analysis and scalar replacement (and many more), they apply a number of heuristics, analyses, and transformations to achieve that. This requires expertise, careful research, thorough testing, and regular reevaluations of old assumptions. In this "Ask the Architects" episode of the Inside Java Podcast, recorded during JavaOne 2026, Nicolai Parlog talks to Roberto Lozano, compiler engineer at the Java Platform Group at Oracle. In our show "Ask the Architects", we talk to experts in OpenJDK about their work on the Java language, API, and runtime.