https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123444
Jeffrey A. Law <law at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
Last reconfirmed| |2026-01-07
CC| |contact at victordn dot me,
| |rdapp at gcc dot gnu.org
--- Comment #1 from Jeffrey A. Law <law at gcc dot gnu.org> ---
Bisects to:
commit ca8d97f8cb8d282c190183e9c297d5e0490bab4e
Author: Victor Do Nascimento <[email protected]>
Date: Thu May 8 15:28:05 2025 +0100
vect: Relax known iteration number constraint
At present we reject uncounted loops outright when doing initial loop
analysis in `vect_analyze_loop_form'.
We have the following gating condition that causes rejection of a
given loop:
if (integer_zerop (info->assumptions)
|| !info->number_of_iterations
|| chrec_contains_undetermined (info->number_of_iterations))
We can do away with this check altogether, but not without problems,
allowing many malformed loops through which ought to be rejected as
early as possible.
We observe that a common thread running through these malformed loops
is the absence of any scalar evolution between iterations.
We have therefore adjusted the analysis replacing the checks on
`niters' for a test for the presence of scalar evolution in the loop,
which can be detected via the presence of phi nodes in the loop.
gcc/ChangeLog:
* tree-vect-loop.cc (vect_analyze_loop_form): Relax niters
condition.
