Editing Intermediate representation (section)

{{Short description|Data structure or code used internally by a compiler or virtual machine to represent source code}}
{{redirect|Intermediate form|the use of the term in biology|Transitional fossil}}
{{Use dmy dates|date=March 2020}}
{{Program execution}}

An '''intermediate representation''' ('''IR''') is the [[data structure]] or code used internally by a [[compiler]] or [[virtual machine]] to represent [[source code]]. An IR is designed to be conducive to further processing, such as [[Compiler optimization|optimization]] and [[Program transformation|translation]].<ref name=Walker>{{Cite web| last = Walker| first = David| title = CS320: Compilers: Intermediate Representation | format = Lecture slides | access-date = 2016-02-12 | url = http://www.cs.princeton.edu/courses/archive/spr03/cs320/notes/IR-trans1.pdf}}</ref> A "good" IR must be ''accurate'' – capable of representing the source code without loss of information<ref name=Chow>{{Cite journal| volume = 11| issue = 10| last = Chow| first = Fred| title = The Challenge of Cross-language Interoperability| journal = ACM Queue| access-date = 2016-02-12| date = 2013-11-22| url = https://queue.acm.org/detail.cfm?id=2544374}}</ref> – and ''independent'' of any particular source or target language.<ref name=Walker /> An IR may take one of several forms: an in-memory [[data structure]], or a special [[tuple]]- or [[Stack (abstract data type)|stack]]-based [[bytecode|code]] readable by the program.<ref name=Toal>{{Cite web| last = Toal| first = Ray| title = Intermediate Representations| access-date = 2016-02-12| url = http://cs.lmu.edu/~ray/notes/ir/}}</ref> In the latter case it is also called an ''intermediate language''.

A canonical example is found in most modern compilers. For example, the [[CPython|CPython interpreter]] transforms the linear human-readable text representing a program into an intermediate [[graph (data structure)|graph structure]] that allows [[flow analysis]] and re-arrangement before execution. Use of an intermediate representation such as this allows compiler systems like the [[GNU Compiler Collection]] and [[LLVM]] to be used by many different source languages to [[Code generation (compiler)|generate code]] for many different target [[Instruction set|architectures]].