Landing: eaca0fdd031b
Project / Subsystem
gcc / doc
Date
2026-08-05
Author
Kyrylo Tkachov
Commit
eaca0fdd031bbed1d2ff7dd86c3adfecef1c51cc
Source
github
Perf win
No
Breaking
No
All attributes
- project
- gcc
- subsystem
- doc
- patch_id
- —
- commit_hash
- eaca0fdd031bbed1d2ff7dd86c3adfecef1c51cc
- source_type
- github
- headline
- Documentation clarifies lane freedom for widen sum reductions
- tldr
- Documentation now accurately describes the lane freedom in widening sum reduction patterns, ensuring correct implementation by ports.
- author
- Kyrylo Tkachov
- outcome
- committed
- performance_win
- false
- breaking_change
- false
- series_id
- —
- series_parts
- []
- tags
-
- • documentation
- • vectorization
- discussion_id_link
- —
- bugzilla_pr
- —
- date
- 2026-08-05T00:00:00.000Z
The documentation for reduc_widen_ssum and reduc_widen_usum patterns has been updated to clarify that the assignment of input elements to accumulator elements is unconstrained. This change ensures that ports understand they can regroup input elements, for example, using pairwise widening adds. It also emphasizes that intermediate sums must not overflow and reserves widen_[us]sum names for lane-preserving patterns. The WIDEN_SUM_EXPR in tree.def now also reflects this documentation.