What is a JIT compiler?

Traditionally, there are two methods for executing programming languages: compiler and interpreter. The compiler initially converts the complete code into machine code and then executes it. In contrast, the interpreter executes the code by compiling it line by line.

Just-In-Time (JIT) compilation is a method to compile the code at runtime. It is also called dynamic translation. As a result, the code execution is sped up. A JIT compiler dynamically converts the code sections into machine code during runtime. It finds the patterns in the program execution, observes the frequently executed code sections, and optimizes them to gain efficiency. A JIT compiler maintains a balance between the compiler’s performance and the interpreter’s flexibility by using this dynamic compilation method.

How does a JIT compiler work

There are three main steps in the working of a JIT compiler: analysis, optimization, and code generation.

1. Analysis: The JIT compiler observes the code execution and finds the frequency and behavior of various code sections. It also collects the runtime data and identifies the frequent and important parts of the code for optimization.

2. Optimization: After the code sections are identified in the analysis step, the JIT compiler applies different optimization tricks and techniques. The optimization may include inliningInlining is a process in which the function calls are replaced with the actual function code to eliminate the overhead of the function calls., loop unrollingLoop unrolling is a loop transformation technique used to enhance the performance of the loop. In this technique, the loop body is expanded to have the code of multiple iterations to reduce the loop maintenance and branching instructions., optimizing memory access patterns, eliminating redundant operations, etc. The optimization steps are performed according to the available architecture.

3. Code generation: The optimal code is generated and executed once the optimization steps are performed. The JIT compiler converts the optimized code into machine code for the underlying hardware architecture. This code is executed, which provides significant performance over other compiled or interpreted executions.

Advantages of a JIT compiler

There are multiple advantages of a JIT compiler. Some of them are as follows:

• Performance improvement
• Flexibility
• Adaptive optimization
• Platform independency
• Reduce memory footprint

Examples of JIT compilers

There are several JIT compilers available. Some of them are listed below:

• PyPy and PyPy3: It is a JIT compiler for Python and Python3 programming languages.
• V8 JavaScript engine: It is a high-performance JavaScript engine developed by Google for its Chrome browser.
• RyuJIT: Common language runtime (CLR)includes the JIT compiler called RyuJIT compiler. It was previously known as the .NET JIT compiler.
• HotSpot JVM:: This is a Java runtime environment with a JIT compiler.
• GraalVM: It is a multilanguage virtual machine that supports JIT compilation for multiple languages, such as Java, Python, Ruby, JavaScript, etc.
• LuaJIT: It’s a JIT compiler for the Lua programming language.
• Rubinius: It’s a JIT compiler for the Ruby programming language.