http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54966
--- Comment #10 from vincenzo Innocente <vincenzo.innocente at cern dot ch> 2012-11-09 11:33:37 UTC --- I've repeated the tests again on a different machine and the result are the same gcc version 4.8.0 20121108 (experimental) [trunk revision 193333] (GCC) at O3 lto degrades the performances in two cases, improves in another… at O2 lto just degrades performance for two cases (different than O3) and does not improve for the others with Ofast the differences are even more dramatic [innocent@vinavx0 bugs48]$ c++ -Ofast smatrix.ii -march=native -flto ; taskset -c 2 ./a.out size 5. v1: time in cycles 14255.6 size 5. v2: time in cycles 3699.28 size 5. v3: time in cycles 3715.55 size 6. v1: time in cycles 9179.85 size 6. v2: time in cycles 1906.91 size 6. v3: time in cycles 1812.73 [innocent@vinavx0 bugs48]$ c++ -Ofast smatrix.ii -march=native ; taskset -c 2 ./a.out size 5. v1: time in cycles 13933.9 size 5. v2: time in cycles 2125.56 size 5. v3: time in cycles 1028.43 size 6. v1: time in cycles 28168 size 6. v2: time in cycles 3528.72 size 6. v3: time in cycles 2533.5 c++ -O3 smatrix.ii -march=native; taskset -c 2 ./a.out size 5. v1: time in cycles 13896.1 size 5. v2: time in cycles 2107.25 size 5. v3: time in cycles 1647.42 size 6. v1: time in cycles 31095.6 size 6. v2: time in cycles 3862.43 size 6. v3: time in cycles 3510.14 c++ -O3 smatrix.ii -march=native -flto; ./a.out size 5. v1: time in cycles 16183.5 size 5. v2: time in cycles 3696.15 size 5. v3: time in cycles 3698.27 size 6. v1: time in cycles 36323.5 size 6. v2: time in cycles 2799.47 size 6. v3: time in cycles 2705.73 [innocent@vinavx0 bugs48]$ taskset -c 2 ./a.out size 5. v1: time in cycles 16150.1 size 5. v2: time in cycles 3718.54 size 5. v3: time in cycles 3784.38 size 6. v1: time in cycles 36326.3 size 6. v2: time in cycles 2785.33 size 6. v3: time in cycles 2714.69 c++ -O2 smatrix.ii -march=native -flto ; taskset -c 2 ./a.out size 5. v1: time in cycles 13809.2 size 5. v2: time in cycles 3999.39 size 5. v3: time in cycles 4186.2 size 6. v1: time in cycles 35057.3 size 6. v2: time in cycles 4657.59 size 6. v3: time in cycles 4766.62 c++ -O2 smatrix.ii -march=native; taskset -c 2 ./a.out size 5. v1: time in cycles 11300.6 size 5. v2: time in cycles 2877.27 size 5. v3: time in cycles 2947.01 size 6. v1: time in cycles 30520 size 6. v2: time in cycles 4623.54 size 6. v3: time in cycles 5287.95
