# Why Do Peephole Optimizations Work?

DevFeed: [Why Do Peephole Optimizations Work?](<https://devfeed.tech/articles/why-do-peephole-optimizations-work-39750.md>)

Original publisher: [Read original article](<https://blog.regehr.org/archives/2485>)

Author: regehr

Published: 2023-11-01T16:23:20Z

Content type: article

Language: en

Sources: [Embedded in Academia](<https://devfeed.tech/sources/embedded-in-academia.md>)

Topics: [Optimization](<https://devfeed.tech/topics/optimization.md>), [compilers](<https://devfeed.tech/topics/compilers.md>), [LLVM](<https://devfeed.tech/topics/llvm.md>), [Code](<https://devfeed.tech/topics/code.md>)

Tags: [code](<https://devfeed.tech/tags/code.md>), [compilers](<https://devfeed.tech/tags/compilers.md>), [execution](<https://devfeed.tech/tags/execution.md>), [llvm](<https://devfeed.tech/tags/llvm.md>), [optimization](<https://devfeed.tech/tags/optimization.md>), [reduce](<https://devfeed.tech/tags/reduce.md>), [uncategorized](<https://devfeed.tech/tags/uncategorized.md>)

## AI overview

The article explains why peephole optimizations work in modern compilers. It contrasts local instruction rewrites with transformations over SSA-based intermediate representations and discusses correctness in terms of observable behavior and refinement.

## Source excerpt

In its original form, a peephole optimization applied to a collection of instructions located close together in a program. For example, in a register transfer language we might find this sequence of instructions: r0 = xor r8, -1 r1 = xor r9, -1 r0 = and r0, r1 Here, assuming the two's complement representation, -1 [...]