[Bug tree-optimization/84111] New: [8 Regression] Compile time hog w/ -O2

[asolokha at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84111

            Bug ID: 84111
           Summary: [8 Regression] Compile time hog w/ -O2
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Keywords: compile-time-hog
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: asolokha at gmx dot com
  Target Milestone: ---
            Target: x86_64-*-*

gcc-8.0.0-alpha20180121 snapshot (r256935) takes indefinite time to compile the
following snippet w/ -O2:

void
zo (int oy, int l3, int qc)
{
  int cg = 0;
  int *h8 = &oy;

  while (cg < 1)
    {
      int re;

      re = l3;
      *h8 = oy;

 el:
      for (cg = 0; cg < 36; ++cg)
        {
          *h8 = 0;
          if (oy != 0)
            l3 = 0;

          while (re < 1)
            {
            }
        }
    }

  if (qc < 33)
    {
      h8 = 0;
      ++l3;
      ++qc;

      if ((oy / *h8) != 0)
        goto el;
    }
}

% timeout 5 gcc-8.0.0-alpha20180128 -O2 -c utfcfeh4.c
zsh: exit 124   timeout 5 gcc-8.0.0-alpha20180128 -O2 -c utfcfeh4.c

Two outstanding entries captured by perf top:

  64.16%  cc1  [.] degenerate_phi_result
  24.43%  cc1  [.] follow_copies_to_constant