On 17.06.21 23:57, Sandra Loosemore wrote:

> On 6/17/21 1:40 PM, Jakub Jelinek wrote:
>> Could we introduce a different option which wouldn't imply enabling that
>> target:
>> -foffload-options=<target triplet list>=option

I think that works – in particular, if we do not document all
the legacy stuff but just how it should be used.

That includes not mentioning that disable and default can
be used in a list and that those can also take arguments.

> I don't feel qualified to comment on the details of the behavior, but
> separating the options and making them more orthogonal to one another
> would certainly make things easier to document.  :-)

I fully concur.

Probably not fully polished, but I have attached a version for discussion.

> One other thing I'd like to see in the docs is how to ask GCC what
> offload targets it is configured to support by default.  This could be
> put in a paragraph that also includes the language about how you need
> to have the compilers for those offload targets installed too.

"gcc -v 2>&1 |grep OFFLOAD_TARGET_NAMES"  shows them.

Note that with the flags under discussion, you can modify
the output, e.g.
* "gcc -v -foffload=disable" removes it
* "gcc -v -foffload=nvptx-none" either gives an error (not supported) or
   just shows that single target.

  * * *

Installing:
Building oneself: "make install" – and everything is there

With a distributions, you need to find the name of the .rpm/.deb
package for the target your are interested in and then run
apt-get / yum / zypper / ...

Hence, when you normally build GCC as a user, for all configured offload
targets, their lto1 should be there - and if lto-wrapper cannot find it,
it aborts with a fatal error.
For distribution compilers, it usually just means that the optional
package is not installed – the missing lto1 should/is then just ignored,
That's the reason why GCC's configure script now has a flag
--enable-offload-defaulted to toggle between supporting optional packages
(distro use) and always errors (normal use).

If you want to know how to build it, have a lot of fun with incomplete
documentation and a look at https://gcc.gnu.org/wiki/Offloading or
at the SUSE/Debian/Red Hat build scripts or g-t-s – and expect that
you won't finish soon ...

Tobias

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