In
computing
Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and the development of both computer hardware, hardware and softw ...
, copy-and-patch compilation is a simple
compiler
In computing, a compiler is a computer program that Translator (computing), translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primaril ...
technique intended for
just-in-time compilation
In computing, just-in-time (JIT) compilation (also dynamic translation or run-time compilations) is compilation (of computer code) during execution of a program (at run time) rather than before execution. This may consist of source code transl ...
(JIT compilation) that uses
pattern matching
In computer science, pattern matching is the act of checking a given sequence of tokens for the presence of the constituents of some pattern. In contrast to pattern recognition, the match usually must be exact: "either it will or will not be a ...
to match pre-generated templates to parts of an
abstract syntax tree
An abstract syntax tree (AST) is a data structure used in computer science to represent the structure of a program or code snippet. It is a tree representation of the abstract syntactic structure of text (often source code) written in a formal ...
(AST) or
bytecode
Bytecode (also called portable code or p-code) is a form of instruction set designed for efficient execution by a software interpreter. Unlike human-readable source code, bytecodes are compact numeric codes, constants, and references (normal ...
stream, and emit corresponding pre-written
machine code
In computer programming, machine code is computer code consisting of machine language instructions, which are used to control a computer's central processing unit (CPU). For conventional binary computers, machine code is the binaryOn nonb ...
fragments that are then
patched to insert
memory address
In computing, a memory address is a reference to a specific memory location in memory used by both software and hardware. These addresses are fixed-length sequences of digits, typically displayed and handled as unsigned integers. This numeric ...
es,
register addresses, constants and other parameters to produce executable code. Code not matched by templates can be either be interpreted in the normal way, or code created to directly call
interpreter
Interpreting is translation from a spoken or signed language into another language, usually in real time to facilitate live communication. It is distinguished from the translation of a written text, which can be more deliberative and make use o ...
code.
Compilation
While copy-and-patch is a "quick-and-dirty" approach to compilation that is orders of magnitude faster than more rigorous techniques, it often yields code that can in many cases approach the performance of partially optimized code produced by those techniques.
Copy-and-patch was first described by Fredrik Kjolstad and Haoran Xu in a 2021 paper.
, Xu was working on an implementation for
Lua that generates templates automatically, based on high-level language descriptions of the interpreter primitives.
, a bytecode-based copy-and-patch implementation was used for the
Python 3.13 JIT compiler.
See also
*
Compile and go system
*
Tracing just-in-time compilation
References
{{reflist
Compiler construction