[Bug tree-optimization/127310] [17 Regression] Segfault during vectorisation of mixed-sign dot-product since r17-3693

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127310

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Ah, so the issue is

  if (vect_is_emulated_mixed_dot_prod (slp_node))
...
      /* Three dot-products and a subtraction.  */
      ncopies_for_cost *= 4;

I have a patch.