Re: [Patch, v2] OpenMP/Fortran: Fix handling of 'declare target' with 'link' clause [PR11555]

[Tobias Burnus <burnus@net-b.de>]

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