[Bug tree-optimization/122364] New: Missed reduction chain vectorization

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122364

            Bug ID: 122364
           Summary: Missed reduction chain vectorization
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

int q[32];

unsigned __attribute__((noipa))
foo ()
{
  unsigned res = 0;
  for (int i = 0; i < 8; ++i)
    res += q[4*i] + q[4*i+1] + q[4*i+2] + q[4*i+3];
  return res;
}


is still not discovered as reduction chain which is because of the
unsigned conversion getting in the way of vect_slp_linearize_chain.
Recursively skipping sign conversions on leafs might work around this
and more complicated examples (short of simply pattern matching this
very case).