[Bug tree-optimization/40073] Vector short/char shifts generate sub-optimal code

["alalaw01 at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=40073

alalaw01 at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |alalaw01 at gcc dot gnu.org
            Version|4.5.0                       |6.0

--- Comment #6 from alalaw01 at gcc dot gnu.org ---
Same problem on AArch64 (at -O3). We've decided the shift is to be done on
integers, widening the arguments and then truncating, before we hit the
vectorizer:

  int i;
  short unsigned int _4;
  int _5;
  int _8;
  short unsigned int _9;
  int pretmp_18;
  unsigned int ivtmp_21;
  unsigned int ivtmp_22;

  <bb 2>:
  pretmp_18 = (int) j_6(D);

  <bb 3>:
  # i_14 = PHI <i_11(4), 0(2)>
  # ivtmp_22 = PHI <ivtmp_21(4), 1024(2)>
  _4 = b[i_14];
  _5 = (int) _4;
  _8 = _5 << pretmp_18;
  _9 = (short unsigned int) _8;
  a[i_14] = _9;
  i_11 = i_14 + 1;
  ivtmp_21 = ivtmp_22 - 1;
  if (ivtmp_21 == 0)