[Bug tree-optimization/121631] New: Signed overflow introduced by vectorizer

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121631

            Bug ID: 121631
           Summary: Signed overflow introduced by vectorizer
           Product: gcc
           Version: 16.0
            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: ---

PR111494 did not fix all cases where the vectorizer introduces new signed
overflow when calculating a sum. One example that still fails is the function
below, when compiled for x86_64 with -O3. The final reduction in the vectorized
code is performed using signed integer scalar addition:
  _16 = BIT_FIELD_REF <vect_sum2_14.12_17, 32, 0>;
  _9 = BIT_FIELD_REF <vect_sum2_14.12_17, 32, 32>;
  _8 = BIT_FIELD_REF <vect_sum2_14.12_17, 32, 64>;
  _7 = BIT_FIELD_REF <vect_sum2_14.12_17, 32, 96>;
  _37 = _16 + _8;
  _38 = _9 + _7;
  res1 = _37;
  res2 = _38;



struct mystr
{
  int f1;
  int f2;
};

struct mystr a[16];
struct mystr b[16];
int res1, res2;

void
foo (void)
{
  int i;
  int sum1 = 0;
  int sum2 = 0;

  for (i = 0; i < 16; i++)
  {
    sum1 += a[i].f1 + b[i].f1;
    sum2 += a[i].f2 + b[i].f2;
  }

  res1 = sum1;
  res2 = sum2;
}