[Bug tree-optimization/110760] New: slp introduces new wrapped arithmetic

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110760

            Bug ID: 110760
           Summary: slp introduces new wrapped arithmetic
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kristerw at gcc dot gnu.org
  Target Milestone: ---

Consider the following function from gcc.dg/vect/bb-slp-layout-5.c:

int a[4], b[4], c[4];

void f1()
{
  a[0] = b[3] - c[3];
  a[1] = b[2] + c[2];
  a[2] = b[1] - c[1];
  a[3] = b[0] + c[0];
}

This is vectorized by slp2:
  vector(4) int vect__1.5;
  vector(4) int vect__2.8;
  vector(4) int vect__12.10;
  vector(4) int vect__3.9;
  vector(4) int _22;
  vect__1.5_18 = MEM <vector(4) int> [(int *)&b];
  vect__2.8_19 = MEM <vector(4) int> [(int *)&c];
  vect__12.10_21 = vect__1.5_18 + vect__2.8_19;
  vect__3.9_20 = vect__1.5_18 - vect__2.8_19;
  _22 = VEC_PERM_EXPR <vect__3.9_20, vect__12.10_21, { 3, 6, 1, 4 }>;
  MEM <vector(4) int> [(int *)&a] = _22;

But this introduces new calculations in the temporary vectors of the unused
elements:
  b[0] - c[0];
  b[1] + c[1];
  b[2] - c[2];
  b[3] + c[3];
and these calculations may wrap for input where the original program did not
wrap.