Landing: b3ade4e315e5
Project / Subsystem
gcc / match.pd
Date
2026-06-12
Author
Kael Andrew Alonzo Franco
Commit
b3ade4e315e5bab56eced1e22eceabbf1a8f15c4
Source
github
Perf win
Yes
Breaking
No
All attributes
- project
- gcc
- subsystem
- match.pd
- patch_id
- —
- commit_hash
- b3ade4e315e5bab56eced1e22eceabbf1a8f15c4
- source_type
- github
- headline
- Optimize bitwise operations for signed integers to -1
- tldr
- GCC now simplifies `(~a) >> a` to `-1` for signed integer `a`, reducing unnecessary computations during compilation.
- author
- Kael Andrew Alonzo Franco
- outcome
- committed
- performance_win
- true
- breaking_change
- false
- series_id
- —
- series_parts
- []
- tags
-
- • optimization
- • bitwise
- • tree-ssa
- discussion_id_link
- —
- bugzilla_pr
- —
- date
- 2026-06-12T00:00:00.000Z
This commit introduces an optimization in match.pd where the expression (~a) >> a simplifies to -1 when a is a signed integer. This transformation is based on the mathematical equivalence ~(a>>a) for right shifts of complement operations. By recognizing this pattern and directly substituting -1, the compiler eliminates redundant bitwise operations, resulting in more efficient code generation.