Landing: 475e9efffaf8
Project / Subsystem
gcc / i386
Date
2026-08-11
Author
Hongyu Wang
Commit
475e9efffaf8de781d7e17b687faf1807e104b01
Source
github
Perf win
No
Breaking
No
All attributes
- project
- gcc
- subsystem
- i386
- patch_id
- —
- commit_hash
- 475e9efffaf8de781d7e17b687faf1807e104b01
- source_type
- github
- headline
- i386: Disallow APX EGPR in FMA4/XOP instructions
- tldr
- Disallows use of extended general-purpose registers (EGPRs) in FMA4/XOP instructions on i386 to prevent unencodable instructions.
- author
- Hongyu Wang
- outcome
- committed
- performance_win
- false
- breaking_change
- false
- series_id
- —
- series_parts
- []
- tags
-
- • i386
- • optimization
- • encoding
- discussion_id_link
- —
- bugzilla_pr
- —
- date
- 2026-08-11T00:00:00.000Z
This commit prevents the use of APX EGPRs with FMA4 and XOP instructions on i386. These instructions are VEX-only and cannot be promoted to EVEX form. The change modifies instruction patterns to use a ‘jm’ constraint instead of ‘m’ and adds the ‘gpr16’ attribute to the address, thereby avoiding EGPR usage in specific scenarios and resolving an unencodable instruction issue.