Re: [PATCH] Fixes to must-tail-call tests

[Jeff Law <law at redhat dot com>]

On 05/27/2016 11:44 AM, David Malcolm wrote:
> On Fri, 2016-05-27 at 13:29 +0100, Thomas Preudhomme wrote:
> > Hi Rainer,
> >
> > On Wednesday 25 May 2016 11:31:12 Rainer Orth wrote:
> > > David Malcolm <dmalcolm@redhat.com> writes:
> > > > The following fixes the known failures of the must-tail-call
> > > > tests.
> > > >
> > > > Tested with --target=
> > > > * aarch64-unknown-linux-gnu
> > > > * ia64-unknown-linux-gnu
> > > > * m68k-unknown-linux-gnu
> > > > * x86_64-pc-linux-gnu
> > >
> > > Even with this patch, there are still failures on sparc-sun
> > > -solaris2.12:
> > >
> > > FAIL: gcc.dg/plugin/must-tail-call-1.c
> > > -fplugin=./must_tail_call_plugin.so
> > > (test for excess errors)
> > >
> > > Excess errors:
> > > /vol/gcc/src/hg/trunk/local/gcc/testsuite/gcc.dg/plugin/must-tail
> > > -call-1.c:1
> > > 2:10: error: cannot tail-call: target is not able to optimize the
> > > call into
> > > a sibling call
> > >
> > > FAIL: gcc.dg/plugin/must-tail-call-2.c
> > > -fplugin=./must_tail_call_plugin.so
> > > (test for excess errors)
> > >
> > > Excess errors:
> > > /vol/gcc/src/hg/trunk/local/gcc/testsuite/gcc.dg/plugin/must-tail
> > > -call-2.c:3
> > > 2:10: error: cannot tail-call: target is not able to optimize the
> > > call into
> > > a sibling call
>
>
> My aim with these tests was to try to cover the various ways in which
> mandatory tail-call optimization can fail.
>
> However, this is very target-dependent, and, as written, the test over
> -specifies the output.
>
> Sorry about this.
>
> I've run the test on all of the configurations in contrib/config
> -list.mk (using the patch kit in
>   https://gcc.gnu.org/ml/gcc-patches/2016-05/msg02100.html )
>
> Collated output can be seen here:
>   https://dmalcolm.fedorapeople.org/gcc/2016-05-27/must-tail-call-logs.txt
> showing all the different error messages across every configuration.
>
> It's not clear to me what the best way forward here is.
> We could simply check for
>    error: cannot tail-call:
> and leave the precise messages we're checking for unspecified.
>
> If we care about checking for the precise messages, one of more
> duplicate copy(s) of the test could be provided, filtering by target to
> specify precise targets, giving more precise output, where this is
> known.
>
> I'm attaching a patch (sans ChangeLog) which strips the precise
> messages in the manner described above.  Retesting on all targets with
> this patch, the only remaining failures are of the form:
>   must-tail-call-1.c:12:10: error: cannot tail-call: machine
> description does not have a sibcall_epilogue instruction pattern
> on targets lacking the pattern.
>
> Thoughts?
I probably should have caught this -- there's all kinds of oddball 
reasons why we might not be able to optimize a tail call, some of which 
are target dependent.

I think trying to give highly precise messages is doomed to long term 
maintenance headaches because they're going to be target dependent.

So I'd go with just stripping the precise messages like you've done.

jeff