Huge compile time & run time performance regression 3.3 -> HEAD

[Richard Guenther]

On Sun, 18 May 2003, Richard Guenther wrote:

> Hi!
>
> As 3.3 is now out, I start comparing 3.3 to HEAD wrt compile time
> performance and performance of the resulting code. As always these
> comparisons are for a POOMA based scientific application.
>
> I experience a 100% compile time regression (673.50s -> 1284.48s) and
> a 12% runtime performance regression (150s -> 171s) when comparing
> gcc3.3 to HEAD.
>
> Time reports follow, the most prominent regressions are expand, global CSE
> (>300%!), loop analysis and branch prediction.

Top of a profile of gcc3.4 is

Flat profile:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total
 time   seconds   seconds    calls   s/call   s/call  name
  7.47     79.18    79.18      906     0.09     0.09  compute_store_table
  6.92    152.54    73.36 262785751     0.00     0.00  expr_equiv_p
  6.76    224.21    71.67   170098     0.00     0.00  fixup_var_refs_insns
  5.58    283.38    59.17    12865     0.00     0.00  loop_regs_scan
  4.39    329.97    46.59   364279     0.00     0.00  compute_transp
  4.10    373.46    43.49 308470718     0.00     0.00
splay_tree_splay_helper
  3.27    408.15    34.69 201411415     0.00     0.00  fixup_var_refs_1
  3.02    440.22    32.07 192083288     0.00     0.00  true_dependence
  2.88    470.76    30.54 232168274     0.00     0.00
mems_in_disjoint_alias_sets_p
  2.39    496.11    25.35    10203     0.00     0.00  loop_regs_update
  2.36    521.17    25.06      686     0.04     0.04  build_store_vectors
  2.00    542.36    21.19  3266323     0.00     0.00
invalid_mode_change_p
  1.95    563.04    20.68   374046     0.00     0.00  alloc_page
  1.86    582.79    19.75 180849685     0.00     0.00  find_loads
  1.47    598.39    15.60   214475     0.00     0.00  ldst_entry
  1.28    611.95    13.56  4111368     0.00     0.00
gt_ggc_mx_lang_tree_node
  1.04    622.99    11.04 201411428     0.00     0.00  fixup_var_refs_insn
  1.03    633.94    10.95      906     0.01     0.01  store_motion
  1.03    644.86    10.92    18177     0.00     0.00  fixup_var_refs
  1.01    655.57    10.71 1468353297     0.00     0.00
splay_tree_compare_ints
  1.00    666.14    10.57 15850095     0.00     0.00  walk_tree

full profile can be fetched from

http:://www.tat.physik.uni-tuebingen.de/~rguenth/gcc/profile_34.gz

Richard.