[Bug tree-optimization/116528] New: Not vectoring TSVC s318 loop

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116528

            Bug ID: 116528
           Summary: Not vectoring TSVC s318 loop
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: kugan at gcc dot gnu.org
  Target Milestone: ---

See:

typedef float real_t;
extern __attribute__((aligned(64))) real_t a[32000];


real_t not_woring(struct args_t *func_args) {
  int k, index;
  int inc = 1;
  real_t max, chksum;
    k = 0;
    index = 0;
    max = (a[0]);
    k += inc;
    for (int i = 1; i < 32000; i++) {
      if (a[k] > max) {
          index = i;
          max = (a[k]);
      }
      k += inc;
    }
  return max + index + 1;
}

Also in https://godbolt.org/z/ra4h6ndKz

ifcvt dump is:

  <bb 3> [local count: 1063004408]:
  # k_16 = PHI <k_12(7), 1(15)>
  # index_17 = PHI <index_5(7), 0(15)>
  # max_19 = PHI <_29(7), max_10(15)>
  # ivtmp_15 = PHI <ivtmp_14(7), 31999(15)>
  _1 = a[k_16];
  _13 = _1 > max_19;
  index_5 = _13 ? k_16 : index_17;
  _29 = MAX_EXPR <_1, max_19>;
  k_12 = k_16 + 1;
  ivtmp_14 = ivtmp_15 - 1;
  if (ivtmp_14 != 0)
    goto <bb 7>; [98.99%]
  else
    goto <bb 6>; [1.01%]

  <bb 7> [local count: 1052266995]:
  goto <bb 3>; [100.00%]

  <bb 16> [local count: 10737416]:

Here PHI # max_19 = PHI <_29(7), max_10(15)> has two uses 
  _29 = MAX_EXPR <_1, max_19>;
and 
 _13 = _1 > max_19;

As a result, this is not a vect_is_simple_reduction. How can we support this?