# MLIR -- Canonicalizers and Declarative Rewrite Patterns

DevFeed: [MLIR -- Canonicalizers and Declarative Rewrite Patterns](<https://devfeed.tech/articles/mlir-canonicalizers-and-declarative-rewrite-patterns-40477.md>)

Original publisher: [Read original article](<https://www.jeremykun.com/2023/09/20/mlir-canonicalizers-and-declarative-rewrite-patterns/>)

Published: 2023-09-20T08:00:00Z

Content type: tutorial

Language: en

Sources: [Jeremy Kun](<https://devfeed.tech/sources/jeremy-kun.md>)

Topics: [Code](<https://devfeed.tech/topics/code.md>), [C++](<https://devfeed.tech/topics/c-plus-plus.md>), [Development](<https://devfeed.tech/topics/development.md>)

Tags: [c-plus-plus](<https://devfeed.tech/tags/c-plus-plus.md>), [canonicalization](<https://devfeed.tech/tags/canonicalization.md>), [compilers](<https://devfeed.tech/tags/compilers.md>), [complex-numbers](<https://devfeed.tech/tags/complex-numbers.md>), [declarative](<https://devfeed.tech/tags/declarative.md>), [deprecated](<https://devfeed.tech/tags/deprecated.md>), [maintenance](<https://devfeed.tech/tags/maintenance.md>), [mathematics](<https://devfeed.tech/tags/mathematics.md>), [mlir](<https://devfeed.tech/tags/mlir.md>), [polynomials](<https://devfeed.tech/tags/polynomials.md>), [primer](<https://devfeed.tech/tags/primer.md>), [programming](<https://devfeed.tech/tags/programming.md>), [rewrite](<https://devfeed.tech/tags/rewrite.md>), [tablegen](<https://devfeed.tech/tags/tablegen.md>), [test](<https://devfeed.tech/tags/test.md>)

## AI overview

This tutorial explains how to implement general canonicalization patterns in MLIR. It covers both C++ canonicalizers and declarative rewrite rules in TableGen, including an identity-based polynomial rewrite and its testing considerations.

## Source excerpt

Table of Contents In a previous article we defined folding functions, and used them to enable some canonicalization and the sccp constant propagation pass for the poly dialect. This time we'll see how to add more general canonicalization patterns. The code for this article is in this pull request, and as usual the commits are organized to be read in order. Why is Canonicalization Needed? MLIR provides folding as a mechanism to simplify an IR, which can result in simpler, more efficient ops (e.