[Bug rtl-optimization/69710] performance issue with SP Linpack with Autovectorization

["doug.gilmore at imgtec dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69710

--- Comment #5 from Doug Gilmore <doug.gilmore at imgtec dot com> ---
Thanks for checking on AArch64 Andrew.

BTW, I made my (incorrect) hunch by running a test on gcc113, where
the installed 4.8 compile showed problems for both DP and SP.  (I
assumed that the problem was addressed on DP since we don't see it on
MIPS at DP ToT with the MSA patch applied.)

For Neon after ivopts I see:

  <bb 14>:
  # vectp_dy.20_96 = PHI <vectp_dy.21_94(13), vectp_dy.20_97(21)>
  # ivtmp.22_78 = PHI <0(13), ivtmp.22_77(21)>
  # ivtmp.26_112 = PHI <ivtmp.26_110(13), ivtmp.26_111(21)>
  # ivtmp.31_153 = PHI <ivtmp.31_155(13), ivtmp.31_154(21)>
  vectp_dx.15_88 = (vector(4) float *) ivtmp.26_112;
  _156 = (void *) ivtmp.31_153;
  vect__12.14_85 = MEM[base: _156, offset: 0B];
  ivtmp.31_154 = ivtmp.31_153 + 16;
  vect__15.17_90 = MEM[(float *)vectp_dx.15_88];
  vect__16.18_92 = vect_cst__91 * vect__15.17_90;
  vect__17.19_93 = vect__12.14_85 + vect__16.18_92;
  MEM[base: vectp_dy.20_96, offset: 0B] = vect__17.19_93;
  vectp_dy.20_97 = vectp_dy.20_96 + 16;
  ivtmp.22_77 = ivtmp.22_78 + 1;
  ivtmp.26_111 = ivtmp.26_112 + 16;
  if (ivtmp.22_77 < bnd.9_53)
    goto <bb 21>;
  else
    goto <bb 16>;
...
  <bb 21>:
  goto <bb 14>;

So the problem is indeed exposed on Neon.