advice on gfortran options for a port

[Gerald Pfeifer]

On Mon, 16 Nov 2015, Anton Shterenlikht wrote:
> However, what is the best way to allow building
> with the default compiler with no graphite optimisation
> options, and optinally with gcc6 with graphite, with
> the above optimisations?

The general ports infrastructure does not easily support this.

If you build locally, you could build gcc6-devel accordingly
and add an option to the other port(s).

> Finally, the info page for gcc6 has:
> 
>        -ftree-loop-linear
>        -floop-interchange
>        -floop-strip-mine
>        -floop-block
>        -floop-unroll-and-jam
>            Perform loop nest optimizations.  Same as -floop-nest-optimize.  To
>            use this code transformation, GCC has to be configured with
>            --with-isl to enable the Graphite loop transformation
>            infrastructure.
> 
> This is not very clear.
> Does it mean that all 5 mentioned options are equivalent to the
> single option -floop-nest-optimize?

This is a good question.  Best check with gcc-help at gcc.gnu.org and
copy Tobias Grosser <grosser at fim.uni-passau.de> and Sebastian Pop           
<sebpop at gmail.com> as two of the Graphite maintainers.

> So is there a more detailed description of each of these options?

I believe there used to be one in gcc5-devel.  Interesting that this
got lost in the newer version.

Gerald