Landing: 5dc4ab23e0d0
Project / Subsystem
gcc / expand_mult
Date
2026-09-20
Author
Stefan Schulze Frielinghaus
Commit
5dc4ab23e0d01a1fd20c1365bdb2de039d831ff9
Source
github
Perf win
Yes
Breaking
No
All attributes
- project
- gcc
- subsystem
- expand_mult
- patch_id
- —
- commit_hash
- 5dc4ab23e0d01a1fd20c1365bdb2de039d831ff9
- source_type
- github
- headline
- expand_mult: Look through vector mode for constant multipliers
- tldr
- GCC's `expand_mult` now correctly determines shift amounts for vector constants by examining the scalar operand's mode.
- author
- Stefan Schulze Frielinghaus
- outcome
- committed
- performance_win
- true
- breaking_change
- false
- series_id
- —
- series_parts
- []
- tags
-
- • gcc
- • optimization
- • vectorization
- discussion_id_link
- —
- bugzilla_pr
- —
- date
- 2026-09-20T00:00:00.000Z
GCC’s expand_mult function has been improved to correctly handle constant vector multipliers. When the scalar operand is a CONST_WIDE_INT, the function now looks through the vector mode to determine the scalar mode for calculating the shift amount. This ensures accurate code generation for vector operations, as highlighted by a new test case for a bug that previously miscalculated shift amounts.