Landing: b59ff31043ae
Project / Subsystem
gcc / gcc/match.pd
Date
2026-08-07
Author
Kyrylo Tkachov
Commit
b59ff31043ae6b1a5ce8582dd375e2ef9a938d79
Source
github
Perf win
Yes
Breaking
No
All attributes
- project
- gcc
- subsystem
- gcc/match.pd
- patch_id
- —
- commit_hash
- b59ff31043ae6b1a5ce8582dd375e2ef9a938d79
- source_type
- github
- headline
- Fold overflow-free average idiom to fewer operations
- tldr
- GCC now simplifies a common overflow-safe integer average calculation into a more efficient form.
- author
- Kyrylo Tkachov
- outcome
- committed
- performance_win
- true
- breaking_change
- false
- series_id
- —
- series_parts
- []
- tags
-
- • optimization
- • integer
- • aarch64
- discussion_id_link
- —
- bugzilla_pr
- —
- date
- 2026-08-07T00:00:00.000Z
GCC’s pattern matching system (match.pd) has gained a new rule to simplify a common, overflow-free way of calculating the average of two integers. The idiom ((x >> 1) + (y >> 1)) + (x & y & 1) is now transformed into the mathematically equivalent but more efficient (x & y) + ((x ^ y) >> 1). This optimization reduces the number of operations, leading to performance improvements on various architectures, including aarch64, and is also beneficial for vectorization.