Landing: 875a6c6192a6

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Project / Subsystem

gcc / match.pd

Date

2026-04-09

Author

Daniel Barboza

Commit

875a6c6192a68f75ad213f2a1b3804e7724073e7

Source

github

Perf win

Yes

Breaking

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All attributes

project: gcc
subsystem: match.pd
patch_id: —
commit_hash: 875a6c6192a68f75ad213f2a1b3804e7724073e7
source_type: github
headline: match.pd: Canonicalize right shift comparisons.
tldr: Canonicalizes right shift comparisons with constants into left shifts.
author: Daniel Barboza
outcome: committed
performance_win: true
breaking_change: false
series_id: —
series_parts: []
tags: • optimization
• pattern matching
• RISC-V
• x86
• aarch64
discussion_id_link: —
bugzilla_pr: —
url: https://github.com/gcc-mirror/gcc/commit/875a6c6192a68f75ad213f2a1b3804e7724073e7
date: 2026-04-09T00:00:00.000Z

The match.pd pattern matching system now canonicalizes right shift non-equality comparisons involving constants. Expressions like (A >> CST1) CMP CST2 are transformed into equivalent comparisons involving left-shifted constants (A CMP (CST2 << CST1)), potentially simplifying the comparison to a single operation. This optimization aims to improve pattern matching and subsequent code generation by reducing complex shift-and-compare sequences.