[Bug tree-optimization/84552] New: [8 Regression] Compile time hog w/ -O2 -floop-nest-optimize -fno-tree-copy-prop -fno-tree-fre -fno-tree-loop-ivcanon

[asolokha at gmx dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84552

            Bug ID: 84552
           Summary: [8 Regression] Compile time hog w/ -O2
                    -floop-nest-optimize -fno-tree-copy-prop -fno-tree-fre
                    -fno-tree-loop-ivcanon
           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: ---

gcc-8.0.0-alpha20180218 snapshot (r257797) takes indefinite time to compile the
following snippet w/ -O2 -floop-nest-optimize -fno-tree-copy-prop -fno-tree-fre
-fno-tree-loop-ivcanon:

int cx;

int
e6 (int pj, int xe)
{
  for (cx = 0; cx < 2; ++cx)
    while (xe < 1)
      {
        for (cx = 0; cx < 2; ++cx)
          pj *= 2;

        if (cx != 0)
          goto o3;

        ++xe;
      }

 o3:
  return pj;
}

% timeout 5 gcc-8.0.0-alpha20180218 -O2 -floop-nest-optimize
-fno-tree-copy-prop -fno-tree-fre -fno-tree-loop-ivcanon -c v8gjilr7.c
zsh: exit 124   timeout 5 gcc-8.0.0-alpha20180218 -O2 -floop-nest-optimize
-fno-tree-copy-pro

Two outstanding entries captured by perf top:

  61.24%  cc1       [.] degenerate_phi_result
  38.49%  cc1       [.] follow_copies_to_constant