http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14741
--- Comment #19 from Sebastian Pop <spop at gcc dot gnu.org> --- Default: tile_size = 32 gfortran -ffast-math -O3 -floop-nest-optimize t.f90 -v ./a.out 176.42500000000001 10.239999999999826 and then with a trivial patch that replaces that default constant 32 with the param that we already have in -floop-block we can see that there is not much impact of the tile size: gfortran -ffast-math -O3 -floop-nest-optimize t.f90 --param loop-block-tile-size=51 ./a.out 173.49000000000001 10.239999999999826 gfortran -ffast-math -O3 -floop-nest-optimize t.f90 --param loop-block-tile-size=10 ./a.out 175.32499999999999 10.239999999999826 gfortran -ffast-math -O3 -floop-nest-optimize t.f90 --param loop-block-tile-size=20 ./a.out 173.91000000000000 10.239999999999826 gfortran -ffast-math -O3 -floop-nest-optimize t.f90 --param loop-block-tile-size=30 ./a.out 177.07499999999999 10.239999999999826 gfortran -ffast-math -O3 -floop-nest-optimize t.f90 --param loop-block-tile-size=40 ./a.out 173.77500000000001 10.239999999999826 gfortran -ffast-math -O3 -floop-nest-optimize t.f90 --param loop-block-tile-size=50 ./a.out 176.96500000000000 10.239999999999826 gfortran -ffast-math -O3 -floop-nest-optimize t.f90 --param loop-block-tile-size=60 ./a.out 176.78999999999999 10.239999999999826 gfortran -ffast-math -O3 -floop-nest-optimize t.f90 --param loop-block-tile-size=70 ./a.out 176.12500000000000 10.239999999999826 gfortran -ffast-math -O3 -floop-nest-optimize t.f90 --param loop-block-tile-size=80 ./a.out 175.55000000000001 10.239999999999826 gfortran -ffast-math -O3 -floop-nest-optimize t.f90 --param loop-block-tile-size=90 ./a.out 184.63500000000002 10.239999999999826 gfortran -ffast-math -O3 -floop-nest-optimize t.f90 --param loop-block-tile-size=100 ./a.out 187.30500000000001 10.239999999999826 gfortran -ffast-math -O3 -floop-nest-optimize t.f90 --param loop-block-tile-size=110 ./a.out 187.99000000000001 10.239999999999826 gfortran -ffast-math -O3 -floop-nest-optimize t.f90 --param loop-block-tile-size=120 ./a.out 188.13999999999999 10.239999999999826