[Bug tree-optimization/116338] GCC is not vectoring TSVC s255 while clang can

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116338

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
The issue is the recurrence

  <bb 2> [local count: 10737416]:
  x_10 = b[31999];
  y_11 = b[31998];

  <bb 3> [local count: 1063004408]:
  # x_18 = PHI <_1(5), x_10(2)>
  # y_19 = PHI <x_18(5), y_11(2)>
  _1 = b[i_20];
..

  <bb 5> [local count: 1052266995]:
  goto <bb 3>; [100.00%]

we handle some cases via vect_phi_first_order_recurrence_p, somebody needs
to dig in why this one isn't (or can't be) handled with that mechanism.