[Bug ipa/65076] [5 Regression] 16% tramp3d-v4.cpp compile time regression

["hubicka at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65076

--- Comment #52 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
$ time /aux/hubicka/trunk-install/bin/g++ -Ofast -fpermissive --param
large-function-insns=1 tramp3d-v4.ii -w ;  ./a.out -n 3

real    0m34.232s
user    0m33.729s
sys     0m0.532s
i = 1    t = 0.00209225  dt = 0.00209225 (0.0175509s/it)
i = 2    t = 0.00410537  dt = 0.00201312 (0.164169s/it)
i = 3    t = 0.00603889  dt = 0.00193352 (0.167095s/it)

$ time /aux/hubicka/trunk-install/bin/g++ -Ofast -fpermissive --param
large-function-insns=10 tramp3d-v4.ii -w ;  ./a.out -n 3

real    0m34.226s
user    0m33.749s
sys     0m0.506s
i = 1    t = 0.00209225  dt = 0.00209225 (0.0187211s/it)
i = 2    t = 0.00410537  dt = 0.00201312 (0.177041s/it)
i = 3    t = 0.00603889  dt = 0.00193352 (0.181561s/it)
$ time /aux/hubicka/trunk-install/bin/g++ -Ofast -fpermissive --param
large-function-insns=100 tramp3d-v4.ii -w ;  ./a.out -n 3

real    0m34.012s
user    0m33.455s
sys     0m0.586s
i = 1    t = 0.00209225  dt = 0.00209225 (0.0175891s/it)
i = 2    t = 0.00410537  dt = 0.00201312 (0.172188s/it)
i = 3    t = 0.00603889  dt = 0.00193352 (0.175776s/it)
$ time /aux/hubicka/trunk-install/bin/g++ -Ofast -fpermissive --param
large-function-insns=500 tramp3d-v4.ii -w ;  ./a.out -n 3

real    0m35.720s
user    0m35.252s
sys     0m0.498s
i = 1    t = 0.00209225  dt = 0.00209225 (0.0190959s/it)
i = 2    t = 0.00410537  dt = 0.00201312 (0.147543s/it)
i = 3    t = 0.00603889  dt = 0.00193352 (0.151731s/it)

$ time /aux/hubicka/trunk-install/bin/g++ -Ofast -fpermissive --param
large-function-insns=2700 tramp3d-v4.ii -w ;  ./a.out -n 3

real    0m36.697s
user    0m36.192s
sys     0m0.536s

$ time /aux/hubicka/trunk-install/bin/g++ -Ofast -fpermissive --param
large-function-insns=1000 tramp3d-v4.ii -w ;  ./a.out -n 3

real    0m36.369s
user    0m35.900s
sys     0m0.500s
i = 1    t = 0.00209225  dt = 0.00209225 (0.00889301s/it)
i = 2    t = 0.00410537  dt = 0.00201312 (0.137394s/it)
i = 3    t = 0.00603889  dt = 0.00193352 (0.14172s/it)
$ time /aux/hubicka/trunk-install/bin/g++ -Ofast -fpermissive --param
large-function-insns=2700 tramp3d-v4.ii -w ;  ./a.out -n 3

real    0m36.730s
user    0m36.216s
sys     0m0.546s
i = 1    t = 0.00209225  dt = 0.00209225 (0.00888801s/it)
i = 2    t = 0.00410537  dt = 0.00201312 (0.134414s/it)
i = 3    t = 0.00603889  dt = 0.00193352 (0.137397s/it)


$ time /aux/hubicka/trunk-install/bin/g++ -Ofast -fpermissive --param
large-function-insns=10000 tramp3d-v4.ii -w ;  ./a.out -n 3

real    0m37.722s
user    0m37.215s
sys     0m0.539s
i = 1    t = 0.00209225  dt = 0.00209225 (0.00893092s/it)
i = 2    t = 0.00410537  dt = 0.00201312 (0.171207s/it)
i = 3    t = 0.00603889  dt = 0.00193352 (0.17444s/it)
$ time /aux/hubicka/trunk-install/bin/g++ -Ofast -fpermissive --param
large-function-insns=100000 tramp3d-v4.ii -w ;  ./a.out -n 3

real    0m37.675s
user    0m37.147s
sys     0m0.559s
i = 1    t = 0.00209225  dt = 0.00209225 (0.00888085s/it)
i = 2    t = 0.00410537  dt = 0.00201312 (0.169823s/it)
i = 3    t = 0.00603889  dt = 0.00193352 (0.173361s/it)


So there seems to be 8% compile time performance drop somewhere in between 100
and 1000 of large-function-insns and the current default 2700 seems to sit in
sweet spot of the performance (bellow 500 or above 10000 starts dropping).

The text segment size is 589645 for 10000, 587750 for 2700, 591666 for 1000,
576922 for 500

GCC 4.9 seems happy with growth of 100 and drops a bit at growth of 30. It also
delivers smaller binary at those growth settings (489406 bytes).

So it seems to suggest that noticeable part of the remaining regression may be
due to new heuristics prefferring large functions. I will experiment with
re-adding the combined function size into the denomiator. But my first
experiments does not look amazing.