[Bug tree-optimization/34683] [4.3 Regression] SSA rewriting in the loop unroller causes quadratic behavior

["rguenth at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #40 from rguenth at gcc dot gnu dot org  2008-01-10 15:32 -------
After you fix this, we're back to SCCVN is slow with lots of virtual operands.
For -O2 (which appearantly is the worst case) we now have the following
profile:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total           
 time   seconds   seconds    calls   s/call   s/call  name    
 10.33      3.08     3.08 313563133     0.00     0.00  VN_INFO
  8.85      5.72     2.64      365     0.01     0.04  DFS
  7.17      7.86     2.14 96368081     0.00     0.00  iterative_hash_expr
  5.77      9.58     1.72   472085     0.00     0.00  valueize_vuses
  5.43     11.20     1.62   216407     0.00     0.00  visit_reference_op_store
  4.93     12.67     1.47  2093493     0.00     0.00  ggc_alloc_stat
  3.15     13.61     0.94 17042636     0.00     0.00  set_bb_for_stmt
  2.63     14.40     0.79  2442685     0.00     0.00  add_vars_for_offset
  1.74     14.92     0.52                             operand_build_cmp
  1.54     15.38     0.46   226140     0.00     0.00  shared_vuses_from_stmt
  1.48     15.82     0.44   245792     0.00     0.00  vn_reference_lookup
  1.27     16.20     0.38  5272581     0.00     0.00  mark_all_vars_used_1
  1.24     16.57     0.37 16115332     0.00     0.00  bitmap_set_bit
  1.14     16.91     0.34       58     0.01     0.02  remove_unused_locals
  1.14     17.25     0.34  6878571     0.00     0.00  htab_find_slot_with_hash
  1.04     17.56     0.31  4286747     0.00     0.00  add_virtual_operand
  1.04     17.87     0.31   255362     0.00     0.00  vec_gc_o_reserve_1
...


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34683