Landing: c0fd049ae753
Project / Subsystem
gcc / i386
Date
2026-05-18
Author
Jakub Jelinek
Commit
c0fd049ae75349dc273de868fd3b3e8935115418
Source
github
Perf win
Yes
Breaking
No
All attributes
- project
- gcc
- subsystem
- i386
- patch_id
- —
- commit_hash
- c0fd049ae75349dc273de868fd3b3e8935115418
- source_type
- github
- headline
- i386: Implement bitreverse<mode>2 optab for GFNI
- tldr
- GCC now uses the GFNI instruction set to accelerate bit reversal operations on x86 when compiling with `-mgfni` and `-msse2`.
- author
- Jakub Jelinek
- outcome
- committed
- performance_win
- true
- breaking_change
- false
- series_id
- —
- series_parts
- []
- tags
-
- • i386
- • gfni
- • optimization
- • bit manipulation
- discussion_id_link
- —
- bugzilla_pr
- —
- date
- 2026-05-18T00:00:00.000Z
This commit enables the use of the GFNI instruction set for bit reversal operations on x86 when compiling with -mgfni and -msse2. It implements the bitreverse<mode>2 optab by using the gf2p8affineqb instruction with a special constant that reverses bits in each byte. For modes wider than QImode, a byteswap is also performed. This improves the performance of __builtin_bitreverse when targeting modern x86 processors.