Dynamic compilation

Program execution
General concepts
Code Translation Compiler Compile time Optimizing compiler Intermediate representation (IR) Execution Runtime system Runtime Executable Interpreter Virtual machine
Types of code
Source code Object code Bytecode Machine code Microcode
Compilation strategies
Ahead-of-time (AOT) Just-in-time (JIT) Tracing just-in-time Compile and go system Precompilation Transcompilation Recompilation
Notable runtimes
Android Runtime (ART) BEAM (Erlang) Common Language Runtime (CLR) and Mono CPython and PyPy crt0 (C target-specific initializer) Java virtual machine (JVM) LuaJIT Objective-C and Swift's V8 and Node.js Zend Engine (PHP)
Notable compilers & toolchains
GNU Compiler Collection (GCC) LLVM and Clang MSVC
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Dynamic compilation is a process used by some programming language implementations to gain performance during program execution. Although the technique originated in Smalltalk,^[1] the best-known language that uses this technique is Java. Since the machine code emitted by a dynamic compiler is constructed and optimized at program runtime, the use of dynamic compilation enables optimizations for efficiency not available to statically-compiled programs (i.e. those compiled by a so-called "batch compiler", as written below) except through code duplication or metaprogramming.

Runtime environments using dynamic compilation typically have programs run slowly for the first few minutes, and then after that, most of the compilation and recompilation is done and it runs quickly. Due to this initial performance lag, dynamic compilation is undesirable in certain cases. In most implementations of dynamic compilation, some optimizations that could be done at the initial compile time are delayed until further compilation at run-time, causing further unnecessary slowdowns. Just-in-time compilation is a form of dynamic compilation.