[Bug tree-optimization/126417] New: Incorrect floating-point re-association

"kristerw at gcc dot gnu.org via Gcc-bugs" <[email protected]> Sun, 26 Jul 2026 11:28:05 +0000

Newsgroups	gmane.comp.gcc.bugs
Message-ID	<[email protected]/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126417

            Bug ID: 126417
           Summary: Incorrect floating-point re-association
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kristerw at gcc dot gnu.org
            Blocks: 118443
  Target Milestone: ---

The following function is miscompiled for x86_64 with -O2:

float
g(float *v)
{
  return v[0]+v[1]+v[2]+v[3];
}

The slp2 pass vectorizes the code, changing the calculation order to:
  (v[0] + v[2]) + (v[1] + v[3])
This is not permitted unless -fassociative-math is enabled.


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118443
[Bug 118443] [Meta bug] Bugs triggered by and blocking more smtgcc testing