[Bug tree-optimization/87746] [9 Regression] ICE in vect_update_misalignment_for_peel, at tree-vect-data-refs.c:1035

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87746

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
Ick.  if-conversion leaves us with quite a mess:

  <bb 3> [local count: 955630224]:
  # i_20 = PHI <i_17(10), 0(21)>
  _1 = replacements[i_20].subreg_loc;
  _2 = (long int) y_13(D);
  _3 = (struct rtx_def * *) _2;
  _ifc__42 = replacements[i_20].subreg_loc;
  _ifc__43 = _3;
  _ifc__44 = _1 == x_12(D) ? _ifc__43 : _ifc__42;
  replacements[i_20].subreg_loc = _ifc__44;
  _4 = replacements[i_20].where;
  _22 = _1 == x_12(D);
  _9 = ~_22;
  _18 = _4 == x_12(D);
  _19 = _9 & _18;
  _5 = (long int) y_13(D);
  _6 = (struct rtx_def * *) _5;
  _ifc__45 = replacements[i_20].where;
  _ifc__46 = _6;
  _ifc__47 = _19 ? _ifc__46 : _ifc__45;
  replacements[i_20].where = _ifc__47;
  _ifc__48 = replacements[i_20].subreg_loc;
  _ifc__49 = 0B;
  _ifc__50 = _19 ? _ifc__49 : _ifc__48;
  replacements[i_20].subreg_loc = _ifc__50;
  i_17 = i_20 + 1;
  if (n_replacements_11(D) > i_17)
    goto <bb 10>; [89.00%]
  else
    goto <bb 8>; [11.00%]

throwing VN on if-converted loops improves this to the following also avoiding
the ICE:

  <bb 3> [local count: 955630224]:
  # i_20 = PHI <i_17(10), 0(21)>
  _1 = replacements[i_20].subreg_loc;
  _2 = (long int) y_13(D);
  _3 = (struct rtx_def * *) _2;
  _ifc__44 = _1 != x_12(D) ? _1 : _3;
  replacements[i_20].subreg_loc = _ifc__44;
  _4 = replacements[i_20].where;
  _22 = _1 == x_12(D);
  _9 = ~_22;
  _18 = _4 == x_12(D);
  _19 = _9 & _18;
  _ifc__47 = _19 ? _3 : _4;
  replacements[i_20].where = _ifc__47;
  _ifc__50 = _19 ? 0B : _ifc__44;
  replacements[i_20].subreg_loc = _ifc__50;
  i_17 = i_20 + 1;
  if (n_replacements_11(D) > i_17)
    goto <bb 10>; [89.00%]
  else
    goto <bb 8>; [11.00%]

The dead store is of course still confusing us.  My old store-commoning
patch would maybe help here.  Or a region-based DSE.  Or somehow
integrating basic DSE with VN.

Anyhow the ICE is still odd.