[Bug tree-optimization/83277] New: [8 Regression] [graphite] Wrong code w/ -O2 -floop-nest-optimize

asolokha at gmx dot com gcc-bugzilla@gcc.gnu.org
Mon Dec 4 17:34:00 GMT 2017


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83277

            Bug ID: 83277
           Summary: [8 Regression] [graphite] Wrong code w/ -O2
                    -floop-nest-optimize
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: asolokha at gmx dot com
  Target Milestone: ---

gcc-8.0.0-alpha20171126 snapshot (r255155), as well as gcc-8.0.0-alpha20171203
snapshot (r255368) w/ r255382 applied on top of it, produce wrong code w/ -O2
-floop-nest-optimize for the following snippet:

int rk, si = 0;
int jr[2];

int
wv (signed char n8)
{
  const int tw = 8;
  int xq[tw];
  int bj, pu = 0;

  for (bj = 0; bj < tw; ++bj)
    xq[bj] = 0;

  bj = 0;
  while (bj < 1)
    {
      int gs = n8 ^ 128;

      if (gs != 0)
        {
          int u7[3];

          while (bj < 2)
            {
              u7[bj] = 0;
              ++bj;
            }

          jr[0] = u7[0];
          rk = xq[0];
          pu = n8;

          if (si != 0)
            return si;
        }
    }

  return pu;
}

int
main (void)
{
  signed char ax = 1;

  return wv (ax) != ax;
}

% gcc-8.0.0-alpha20171203 -O2 -o good lu41pybr.c && ./good
% echo $?
0

% gcc-8.0.0-alpha20171203 -O2 -floop-nest-optimize -o bad lu41pybr.c && ./bad
zsh: exit 1     ./bad
% echo $?
1


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