[Bug debug/55585] compile time hog at -O1 -fboundscheck -g

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55585

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> 2012-12-04 11:00:39 UTC ---
(In reply to comment #4)
> Interestingly, the magic switch is -fstrict-aliasing... 20x speedup. for a
> Fortran code quite a surprise.
> 
> > time gfortran -c -O1 -fbounds-check -g -fstrict-aliasing slow.f90 
> real    0m11.483s
> 
> I think for Fortran -fstrict-aliasing could well be the default at -O1, but
> maybe there is an underlying reason why this flag is needed ?

Well, it probably enables CSE that removes some of the bounds-checking calls.
Not sure why exactly without investigating.

GFortran could enable strict-aliasing unconditionally if it likes (even
at -O0).