Landing: e91f79891fc6

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Project / Subsystem

gcc / risc-v

Date

2026-09-13

Author

Michiel Derhaeg

Commit

e91f79891fc657d48310f82da0da61eb4a0587ed

Source

github

Perf win

Yes

Breaking

No

View on GitHub →

All attributes

project: gcc
subsystem: risc-v
patch_id: —
commit_hash: e91f79891fc657d48310f82da0da61eb4a0587ed
source_type: github
headline: RISC-V RV32 uses CLMULR for reversed CRC32, improving performance.
tldr: Optimizes reversed CRC32 calculation on RISC-V RV32 by using the CLMULR instruction, avoiding a slower table-based fallback.
author: Michiel Derhaeg
outcome: committed
performance_win: true
breaking_change: false
series_id: —
series_parts: []
tags: • risc-v
• optimization
• compiler
• crc32
discussion_id_link: —
bugzilla_pr: —
url: https://github.com/gcc-mirror/gcc/commit/e91f79891fc657d48310f82da0da61eb4a0587ed
date: 2026-09-13T00:00:00.000Z

This commit enhances the CRC32 calculation for the RISC-V 32-bit architecture (rv32) by utilizing the CLMULR instruction. Previously, calculating a reflected polynomial for 32-bit CRC required an operand that was 33 bits wide, exceeding register capacity and forcing a fallback to a less efficient table-based method. By leveraging the CLMULR instruction’s property to produce specific bits of a carry-less product, the compiler can now use the unshifted 32-bit reflected polynomial, resulting in a performance improvement for CRC32 operations on RV32 systems with the Zbc extension.