[Bug tree-optimization/92924] [10 regression] reproducible indirect call profile merging causes 80% slowdown in Firefox pref-reftest-singletons id-getter microbenchmarks

[hubicka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92924

--- Comment #17 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
I further hacked the script to record only values that are useful, where useful
means with greater count then all / TOPN_VALUES / 2.  I use same test in GCC
itself (that was bug in original luxou's patch that it required count to be at
least 50% so we did more then two speculations only when the number of targets
was precisely 2 and probability precisely 50%).

I also added special case for those calls which have only one target.

Now I get:
== Stats for all ==
stats for indirect_call:
  total: 160441 freq: 833372200
  not executed at all: 134836
  invalid: 0 (0.00%) freq:0 (0.00%)
  only one target: 20036 (12.49%) freq:108329394 (13.00%)
  tracked values:
    0 values:      111 times (0.07%) freq:    14162014 (1.70%)
    1 values:     2963 times (1.85%) freq:   594520090 (71.34%)
    2 values:     2284 times (1.42%) freq:   111578254 (13.39%)
    3 values:      185 times (0.12%) freq:     2525320 (0.30%)
    4 values:       26 times (0.02%) freq:     2257128 (0.27%)

stats for topn:
  total: 6620 freq: 16471134
  not executed at all: 6236
  invalid: 0 (0.00%) freq:0 (0.00%)
  only one target: 196 (2.96%) freq:3535103 (21.46%)
  tracked values:
    0 values:       39 times (0.59%) freq:     5340350 (32.42%)
    1 values:       84 times (1.27%) freq:     6006897 (36.47%)
    2 values:       59 times (0.89%) freq:     1547519 (9.40%)
    3 values:        6 times (0.09%) freq:       41265 (0.25%)
    4 values:        0 times (0.00%) freq:           0 (0.00%)

== Stats for mainline ==
stats for indirect_call:
  total: 160441 freq: 865715132
  not executed at all: 134862
  invalid: 156 (0.10%) freq:64839775 (7.49%)
  only one target: 1255 (0.78%) freq:604290 (0.07%)
  tracked values:
    0 values:    14939 times (9.31%) freq:   356592480 (41.19%)
    1 values:     8535 times (5.32%) freq:   377193150 (43.57%)
    2 values:      660 times (0.41%) freq:    66082791 (7.63%)
    3 values:       15 times (0.01%) freq:      133242 (0.02%)
    4 values:       19 times (0.01%) freq:      269404 (0.03%)

stats for topn:
  total: 6620 freq: 16793729
  not executed at all: 6235
  invalid: 10 (0.15%) freq:1307937 (7.79%)
  only one target: 10 (0.15%) freq:1300 (0.01%)
  tracked values:
    0 values:      182 times (2.75%) freq:     9195915 (54.76%)
    1 values:      156 times (2.36%) freq:     6111713 (36.39%)
    2 values:       26 times (0.39%) freq:      173054 (1.03%)
    3 values:        1 times (0.02%) freq:        3810 (0.02%)
    4 values:        0 times (0.00%) freq:           0 (0.00%)

So with 4 targets we seem to be able to track 98.3% of trained branhces while
with reproducible merging this drops to 45%

I will send you the hacked script