Landing: 83a74295038a

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Project / Subsystem

gcc / avr

Date

2026-05-21

Author

Georg-Johann Lay

Commit

83a74295038a8319dc547f8ca3f9ca26a0b85187

Source

github

Perf win

Breaking

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project: gcc
subsystem: avr
patch_id: —
commit_hash: 83a74295038a8319dc547f8ca3f9ca26a0b85187
source_type: github
headline: AVR: Overhaul CLZ, CTZ and FFS instructions with hard-reg constraints.
tldr: Improves CLZ, CTZ, and FFS instruction handling for AVR by using hard-reg constraints and code iterators.
author: Georg-Johann Lay
outcome: committed
performance_win: false
breaking_change: false
series_id: —
series_parts: []
tags: • avr
• code generation
• optimization
discussion_id_link: —
bugzilla_pr: —
url: https://github.com/gcc-mirror/gcc/commit/83a74295038a8319dc547f8ca3f9ca26a0b85187
date: 2026-05-21T00:00:00.000Z

This patch overhauls the CLZ, CTZ, and FFS instructions for the AVR architecture. It replaces explicit hard registers with hard-reg constraints to model the register footprint of their libgcc asm implementations. Additionally, the patch introduces code iterators to factor out commonalities, simplifying the code and making it more maintainable. These changes improve the code generation process for these instructions without relying on instruction combining.