[Bug tree-optimization/109088] GCC does not always vectorize conditional reduction

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109088

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-03-10
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
            Summary|GCC fail auto-vectorization |GCC does not always
                   |                            |vectorize conditional
                   |                            |reduction

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
GCC does vectorize:
    if (a[i] > b[i]) {
      result += a[i];
    }

Even for variable-length vectors.
Just we don't vectorize when there is an extra conditional operation.

GCC will even vectorize with variable-length vectors:
#include <stdint.h>

uint64_t single_loop_with_if_condition(
        uint64_t * restrict a,
        uint64_t * restrict b,
        uint64_t * restrict c,
        int loop_size) {
  uint64_t result = 0;

  for (int i = 0; i < loop_size; i++) {
    c[i] = a[i] + 1;
    if (a[i] > b[i]) {
      result += c[i];
    }
  }
  return result;
}