(Non-)offloading diagnostics

[Thomas Schwinge]

Hi!

In light of the -Whsa testsuite patches just posted, I think we first
need to clarify the general policy questions I posted a month ago:

On Tue, 26 Jan 2016 11:46:14 +0100, I wrote:
> On Thu, 10 Dec 2015 18:51:48 +0100, Martin Jambor <mjambor@suse.cz> wrote:
> > On Mon, Dec 07, 2015 at 12:46:45PM +0100, Jakub Jelinek wrote:
> > > On Mon, Dec 07, 2015 at 12:17:58PM +0100, Martin Jambor wrote:
> > > > [...]  There are no failing
> > > > testcases if HSA is not configured.  If it is, there are some, all of
> > > > which fall into one the following categories:
> > > > 
> > > >   1) HSA cannot compile a function for one reason or another (most
> > > >      common cause is inability of HSA to take an address of a function
> > > >      or make an indirect call) and gives a warning, which is regarded
> > > >      as an "excess error" by dejagnu.
> 
> Confirmed:
> 
>     [...]/gcc/testsuite/c-c++-common/gomp/clauses-1.c: In function 'bar._omp_fn.26.hsa.31':
>     cc1: warning: could not emit HSAIL for the function [-Whsa]
>     cc1: note: support for HSA does not implement non-gridified OpenMP parallel constructs.
>     [...]
> 
> ..., and many more.  So, with --enable-offload-targets=[...],hsa we
> regress (PASS -> FAIL; "test for excess errors") such compile tests.
> 
> > > It would be good if there is a -W* switch to turn such warnings off.
> > > Not just for the purposes of dejagnu libgomp testing, but say one
> > > might try to compile a program primarily say for XeonPhi or PTX offloading,
> > > but have HSA enabled to, but care primarily about the former two, etc.
> > 
> > All these warnings are in the -Whsa group and can be suppressed with
> > -Wno-hsa.
> 
> These compile tests are done without any -W* flags; -Whsa is enabled by
> default.

I'm a proponent of enabling as many useful warnings by default, or if not
by default, then with -Wall.  -Whsa is enabled by default, and has thus
set a precedent of doing that.

> How to address this mismatch?  Put -Wno-has into all regressing
> test case files individually?  Run the affected testsuites with -Wno-hsa?
> Not enable -Whsa by default (but I agree it's useful to users)?
> (Instead, enable with -Wall, which any sane user should be specifying?)

Even if a bit tedious, my preference actually is to add to the test cases
an (expected) dg-warning everywhere where such a non-offloading warning
currently triggers, because that's what users will be seeing (with -Whsa
enabled by default), and because that will make it obvious (PASS -> FAIL
for the warning check) when that warning disappears (say, because the
compiler can now offload the respective construct, yay).

> A very similar problem also exists for nvptx offloading (Nathan CCed),
> where we emit similar warnings (enabled by default).  As nvptx offloading
> happens during link-time (not compile-time, as with hsa offloading),
> these don't affect GCC's compile tests, but need to be worked around in
> libgomp test cases.


Grüße
 Thomas