[Bug rtl-optimization/70710] New: [5/6/7 Regression] Compile time hog w/ -O -g -fpeel-loops

["asolokha at gmx dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70710

            Bug ID: 70710
           Summary: [5/6/7 Regression] Compile time hog w/ -O -g
                    -fpeel-loops
           Product: gcc
           Version: 5.3.0
            Status: UNCONFIRMED
          Keywords: compile-time-hog
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: asolokha at gmx dot com
  Target Milestone: ---

gcc 5.3.0 and later takes infinite time to compile the following reduced
snippet w/ -O[123] (or -Ofast) -g -fpeel-loops on x86_64-pc-linux-gnu:

long int mh = 0;
int du = 0;

void
vg (void)
{
  int qe;
  char u1;

  for (qe = 0; qe < 16; ++qe)
    {
      mh &= du;
      du &= mh;
      u1 = du;
    }
  mh = 0;
}

Several top calls brought up by perf:

  48.52%  cc1                      [.] nonzero_bits1
  17.45%  cc1                      [.] cached_nonzero_bits
  14.68%  cc1                      [.] reg_nonzero_bits_for_combine
   1.29%  cc1                      [.] bitmap_bit_p
   1.12%  cc1                      [.] target_default_pointer_address_modes_p
   0.85%  cc1                      [.] val_signbit_known_set_p
   0.27%  cc1                      [.] rtx_equal_p
   0.26%  cc1                      [.] commutative_operand_precedence
   0.22%  cc1                      [.] simplify_binary_operation_1
   0.18%  cc1                      [.] simplify_replace_fn_rtx
   0.15%  cc1                      [.] volatile_insn_p
   0.12%  cc1                      [.] simplify_binary_operation
   0.12%  cc1                      [.] avoid_constant_pool_reference
   0.11%  cc1                      [.] ggc_internal_alloc
   0.10%  cc1                      [.] simplify_const_binary_operation
   0.07%  cc1                      [.] simplify_associative_operation
   0.06%  cc1                      [.] validate_subreg
   0.05%  cc1                      [.] swap_commutative_operands_p
   0.05%  cc1                      [.] copy_rtx
   0.04%  cc1                      [.] simplify_gen_binary
   0.02%  cc1                      [.] simplify_subreg

The original code had stuck for about 14 hours in compilation before I noticed
that.