In [[computer programming]], '''[[loop-invariant code]]''' consists of statements or expressions (in an [[imperative programming|imperative]] [[programming language]]) whichthat can be moved outside the body of a loop without affecting the semantics of the program. '''Loop-invariant code motion''' (also called '''hoisting''' or '''scalar promotion''') is a [[compiler optimization]] whichthat performs this movement automatically.
==Example==
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For example, if all reaching definitions for the operands of some simple expression are outside of the loop, the expression can be moved out of the loop.
Recent work usingby Moyen, Rubiano and [[Thomas Seiller|Seiller]] uses data-flow dependence analysis <ref>{{cite journalbook |last1=Moyen |first1=Jean-Yves |last2=Rubiano |first2=Thomas |last3=Seiller |first3=Thomas |titlechapter=Loop Quasi-Invariant Chunk Detection |journaltitle=Automated Technology for Verification and Analysis |series=Lecture Notes in Computer Science |date=2017 |volume=10482 |pages=91–108 |doi=10.1007/978-3-319-68167-2_7|isbn=978-3-319-68166-5 }}</ref> allows to detect not only invariant commands but larger code fragments such as an inner loop. The analysis also detects quasi-invariants of arbitrary degrees, that is commands or code fragments that become invariant after a fixed number of iterations of the loop body. This technique was later used by Aubert, Rubiano, Rusch, and [[Thomas Seiller|Seiller]] to automatically parallelise loops.<ref>{{cite book |last1=Aubert |first1=Clément |last2=Rubiano |first2=Thomas
|last3=Rusch |first3=Neea |last4=Seiller |first4=Thomas |chapter= Distributing and Parallelizing Non-canonical Loops |title= Verification, Model Checking, and Abstract Interpretation |series=Lecture Notes in Computer Science |date=2023 |volume=13881 |pages=91–108 |doi=10.1007/978-3-031-24950-1_1 }}</ref>
