[Bug target/38306] [4.4/4.5/4.6 Regression] 15% slowdown w.r.t. 4.3 of computational kernel on some architectures

[Joost.VandeVondele at pci dot uzh.ch]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38306

--- Comment #23 from Joost VandeVondele <Joost.VandeVondele at pci dot uzh.ch> 2011-02-21 12:53:30 UTC ---
(In reply to comment #22)
> What is the performance with 4.3 -O2?  

4.3:
> gfortran -O2 -march=native -funroll-loops -ffast-math test.f90 ; ./a.out
Time for evaluation [s]:                        4.373

4.6:
>  gfortran -O2 -march=native -funroll-loops -ffast-math test.f90 ; ./a.out
Time for evaluation [s]:                        4.347

so, same performance. 

Given that vectorization only happens at -O3, it is an important optimization
level for numerical codes. Nevertheless, I would propose to remove the
regression tag, and instead refocus the bug on the what current trunk does at
-O3 vs -O2 -ftree-vectorize as noted in comment #21

> gfortran -O2 -march=native -funroll-loops  -ffast-math  -ftree-vectorize test.f90 ; ./a.out
Time for evaluation [s]:                        2.694

> gfortran -O3 -march=native -funroll-loops  -ffast-math  -ftree-vectorize test.f90 ; ./a.out
Time for evaluation [s]:                        4.536