[Bug rtl-optimization/67206] Redundant spills in simple copy loop for 32-bit x86 target

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67206

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
The memmove issue is because of

(compute_affine_dependence
  stmt_a: _16 = *_15;
  stmt_b: *_12 = _16;
) -> dependence analysis failed

      /* Now check that if there is a dependence this dependence is
         of a suitable form for memmove.  */
      vec<loop_p> loops = vNULL;
      ddr_p ddr;
      loops.safe_push (loop);
      ddr = initialize_data_dependence_relation (single_load, single_store,
                                                 loops);
      compute_affine_dependence (ddr, loop);
      if (DDR_ARE_DEPENDENT (ddr) == chrec_dont_know)
        {
          free_dependence_relation (ddr);
          loops.release ();
          return;
        }

note that we don't use dependence analysis only to decide memcpy vs. memmove
(we use general alias analysis for that) but it is used to guard against
a[i+1] = a[i] which is not a memmove.  The loop in the example could be of
that form if out == in + 1.