Landing: ded7c4e85122
Project / Subsystem
gcc / libstdc++
Date
2026-09-22
Author
Tamar Christina
Commit
ded7c4e851228c008304bad10d6b0aedc9deef3b
Source
github
Perf win
Yes
Breaking
No
All attributes
- project
- gcc
- subsystem
- libstdc++
- patch_id
- —
- commit_hash
- ded7c4e851228c008304bad10d6b0aedc9deef3b
- source_type
- github
- headline
- libstdc++: Reject impossible regex DFS starts early
- tldr
- Added a pre-check to libstdc++'s regex engine to quickly reject impossible match starting positions.
- author
- Tamar Christina
- outcome
- committed
- performance_win
- true
- breaking_change
- false
- series_id
- —
- series_parts
- []
- tags
-
- • libstdc++
- • regex
- • optimization
- • performance
- discussion_id_link
- —
- bugzilla_pr
- —
- date
- 2026-09-22T00:00:00.000Z
This commit introduces a pre-check to the DFS regex executor that examines the first character of a potential match. It rejects starting positions where no match is possible without building the full DFS state, which can be expensive. This optimization significantly speeds up regex searches, particularly for patterns like IPv4 addresses where many positions cannot possibly start a valid match.