Editing Just-in-time compilation (section)

{{short description|Dynamically compiling bytecode to machine code during runtime}}
{{Program execution}}
In [[computing]], '''just-in-time''' ('''JIT''') '''compilation''' (also '''dynamic translation''' or '''run-time compilations''')<ref name="Michigan" /> is [[compiler|compilation]] (of [[Source code|computer code]]) during execution of a program (at [[run time (program lifecycle phase)|run time]]) rather than before execution.{{sfn|Aycock|2003}} This may consist of [[source code translation]] but is more commonly [[bytecode]] translation to [[machine code]], which is then executed directly. A system implementing a JIT compiler typically continuously analyses the code being executed and identifies parts of the code where the speedup gained from compilation or recompilation would outweigh the overhead of compiling that code.

JIT compilation is a combination of the two traditional approaches to translation to machine code&mdash;[[Ahead-of-time compilation|ahead-of-time compilation (AOT)]], and [[Interpreter (computing)|interpretation]]&mdash;and combines some advantages and drawbacks of both.{{sfn|Aycock|2003}} Roughly, JIT compilation combines the speed of compiled code with the flexibility of interpretation, with the overhead of an interpreter and the additional overhead of compiling and [[Linker (computing)|linking]] (not just interpreting). JIT compilation is a form of [[dynamic compilation]], and allows [[adaptive optimization]] such as [[dynamic recompilation]] and [[microarchitecture]]-specific speedups.{{refn|group=nb|Ahead-of-Time compilers can target specific microarchitectures as well, but the difference between AOT and JIT in that matter is one of portability. A JIT can render code tailored to the currently running CPU at runtime, whereas an AOT, in lieu of optimizing for a generalized subset of uarches, must know the target CPU in advance: such code may not only be not performant on other CPU types but may be outright unstable.}}<ref name="Notario" /> Interpretation and JIT compilation are particularly suited for [[dynamic programming language]]s, as the runtime system can handle [[Late binding|late-bound]] data types and enforce security guarantees.