Thanks a lot Tobias,
yes, I could have looked harder :-)
This isn't by any chance documented on the developer website of gcc somewhere?
It would be sad, if that knowledge is not publicy available for the future.
Thanks again for the explanation and keep up the good work.
Regards,
Andre
On Mon, 29 Jul 2024 09:29:28 +0200
Tobias Burnus <bur...@net-b.de> wrote:
> Hi Andre,
>
> Andre Vehreschild wrote:
> > I am wondering why the testcase has no `!{ dg-do ... }` line. What will
> > dejagnu do then? Sorry for the may be stupid question, but I never
> > encountered a testcase without a dg-do line. It was the minimum for me.
>
> Well, then you need look harder ;-)
>
> In gcc/testsuite/, the default is '{ dg-do compile }', i.e. you can
> specify or leave out that line without any additional effect. Having it
> might be a tad clearer, albeit makes the test a tad longer.
>
> But if you want to 'run' or 'link', you need to specify the dg-do line.
> There are several files which don't have the "dg-do compile" line, also
> under gcc/testsuite/gfortran.dg
>
> In case of libgomp, it is becomes interesting: the default is running
> the code, i.e. you need a 'compile' or 'link' when it shouldn't be run.
>
> However, at least for Fortran (libgomp.{oacc-}fortran), there is a
> difference between specifying nothing and specifying 'dg-do run': In
> case of the default, it is compiled and run. But if you specify 'dg-do
> run', it is compiled multiple times with different optimization options
> and then run.
>
> (Actually, also under gcc/testsuite/gfortran.dg, you get multiple
> compilations + runs with 'dg-do run'. If you use dg-additional-options,
> you can also add options. I think with dg-options, you set it to a
> single run [not confirmed].)
>
> The downside of compiling + running it multiple times is a longer test
> time without any real benefit. However, especially with Fortran,
> compiling with different optimization levels did expose issues in the
> past, both in the Fortran front end and in the middle end. — Thus, there
> some benefit of using it.
>
> In any case, there more complex the code is that front-end + middle-end
> code have to process, the more useful is "dg-do run". The more work is
> done by the run-time library, be it libgfortran or libgomp, the less
> useful it becomes as the heavy lifting is done in the run-time library.
> — As libgomp progressing already takes quite some time (albeit it can
> now run in parallel), there are some who prefer few 'dg-do run' and
> others who prefer if all Fortran testcases there use 'dg-do run' …
>
> I hope it helps,
>
> Tobias
>
--
Andre Vehreschild * Email: vehre ad gmx dot de
