RyuJIT

RyuJIT is the just-in-time compiler used by the Microsoft .NET runtime, including CoreCLR, to translate Common Intermediate Language (CIL/IL) into native machine code at runtime. Implemented in C++, it is architecture‑aware and emits code for x86, x64, ARM32, and ARM64 targets. RyuJIT is the standard JIT for .NET Core and later .NET releases, replacing the older JIT used in legacy .NET Framework implementations for modern runtimes on Windows, Linux, and macOS.

It supports tiered compilation, starting with quick, less-optimized code to reduce startup time, followed by recompilation of hot methods with more aggressive optimizations. The compiler uses a modern SSA-based intermediate representation, and it performs inlining, register allocation, and various optimization passes. It also includes SIMD support through hardware intrinsics to improve throughput on vectorizable workloads.

RyuJIT is developed as part of the dotnet/runtime open-source project and is released under the project's open-source license. As the default JIT in current .NET releases, it continues to receive ongoing improvements from Microsoft and the wider community, including platform- and architecture-specific enhancements, performance optimizations, and better cross-platform support.

Overall, RyuJIT aims to deliver balanced startup performance and steady high throughput across diverse workloads, with ongoing work focusing on faster compilation, better code quality, and expanded hardware support.