[Bug tree-optimization/94828] New: Failure to merge merge-able loops

[gabravier at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94828

            Bug ID: 94828
           Summary: Failure to merge merge-able loops
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabravier at gmail dot com
  Target Milestone: ---

void f(int *__restrict a, int *__restrict b, size_t sz)
{
    for (int i = 0; i < sz; ++i)
        a[i] += b[i];

    for (int i = 0; i < sz; ++i)
        a[i] += b[i];
}

These two loops could be merged into a single one doing two additions per
iteration. ICC does this transformation, GCC does not.

Also, I'd like to note that from the GCC output, only the first loop is
vectorized, and not the second one.

See https://godbolt.org/z/DfGpSi