Re: Support 'UNSUPPORTED: [...]: exception handling disabled' for libstdc++ testing (was: Support in the GCC(/C++) test suites for '-fno-exceptions')

[Jonathan Wakely <jwakely@redhat.com>]

[-- Attachment #1: Type: text/plain, Size: 6661 bytes --]

On Wed, 7 Jun 2023 at 08:13, Thomas Schwinge wrote:

> Hi!
>
> On 2023-06-06T20:31:21+0100, Jonathan Wakely <jwakely@redhat.com> wrote:
> > On Tue, 6 Jun 2023 at 20:14, Thomas Schwinge <thomas@codesourcery.com>
> > wrote:
> >> This issue comes up in context of me working on C++ support for GCN and
> >> nvptx target.  Those targets shall default to '-fno-exceptions' -- or,
> >> "in other words", '-fexceptions' is not supported.  (Details omitted
> >> here.)
> >>
> >> It did seem clear to me that with such a configuration it'll be hard to
> >> get clean test results.  Then I found code in
> >> 'gcc/testsuite/lib/gcc-dg.exp:gcc-dg-prune':
> >>
> >>     # If exceptions are disabled, mark tests expecting exceptions to be
> >> enabled
> >>     # as unsupported.
> >>     if { ![check_effective_target_exceptions_enabled] } {
> >>         if [regexp "(^|\n)\[^\n\]*: error: exception handling disabled"
> >> $text] {
> >>             return "::unsupported::exception handling disabled"
> >>         }
> >>
> >> ..., which, in a way, sounds as if the test suite generally is meant to
> >> produce useful results for '-fno-exceptions', nice surprise!
> >>
> >> Running x86_64-pc-linux-gnu (not yet GCN, nvptx) 'make check' with:
> >>
> >>     RUNTESTFLAGS='--target_board=unix/-fno-exceptions\{,-m32\}'
> >>
> >> ..., I find that indeed this does work for a lot of test cases, where we
> >> then get (random example):
> >>
> >>      PASS: g++.dg/coroutines/pr99710.C  (test for errors, line 23)
> >>     -PASS: g++.dg/coroutines/pr99710.C (test for excess errors)
> >>     +UNSUPPORTED: g++.dg/coroutines/pr99710.C: exception handling
> disabled
> >>
> >> ..., due to:
> >>
> >>      [...]/g++.dg/coroutines/pr99710.C: In function 'task my_coro()':
> >>     +[...]/g++.dg/coroutines/pr99710.C:18:10: error: exception handling
> >> disabled, use '-fexceptions' to enable
> >>      [...]/g++.dg/coroutines/pr99710.C:23:7: error: await expressions
> are
> >> not permitted in handlers
> >>      compiler exited with status 1
> >>
> >> But, we're nowhere near clean test results: PASS -> FAIL as well as
> >> XFAIL -> XPASS regressions, due to 'error: exception handling disabled'
> >> precluding other diagnostics seems to be one major issue.
> >>
> >> Is there interest in me producing the obvious (?) changes to those test
> >> cases, such that compiler g++ as well as target library libstdc++ test
> >> results are reasonably clean?  (If you think that's all "wasted effort",
> >> then I suppose I'll just locally ignore any FAILs/XPASSes/UNRESOLVEDs
> >> that appear in combination with
> >> 'UNSUPPORTED: [...]: exception handling disabled'.)
> >
> > I would welcome that for libstdc++.
>
> Assuming no issues found in testing, OK to push the attached
> "Support 'UNSUPPORTED: [...]: exception handling disabled' for libstdc++
> testing"?
> (Thanks, Jozef!)
>

Yes please.


>
> > I do sometimes run the libstdc++ tests
> > with "unusual" options, like -fno-exceptions and -fno-rtti (e.g. today
> I've
> > been fixing FAILs that only happen with -fexcess-precision=standard). I
> > just manually ignore the tests that fail for -fno-exceptions, but it
> would
> > be great if they were automatically skipped as UNSUPPORTED.
> >
> > We already have a handful of tests that use #if __cpp_exceptions to make
> > those parts conditional on exception support. We also have exactly one
> test
> > that is currently UNSUPPORTED when -fno-exceptions is used:
> > testsuite/18_support/nested_exception/rethrow_if_nested-term.cc:// {
> > dg-skip-if "" { *-*-* } { "-fno-exceptions" } }
>
> ACK -- that'll only work for explicit '-fno-exceptions', but not for
> implicit (say, via 'CC1PLUS_SPEC'), right?


That's right.



> So, indeed:
>
> > That could be changed to use an effective target keyword instead.
>
> I'll look into that later.
>
> > To add an effective-target to the libstdc++ testsuite would be as simple
> as:
> >
> > --- a/libstdc++-v3/testsuite/lib/libstdc++.exp
> > +++ b/libstdc++-v3/testsuite/lib/libstdc++.exp
> > @@ -1421,6 +1421,14 @@ proc check_effective_target_tzdb { } {
> >     }]
> > }
> >
> > +# Return 1 if exception handling is enabled.
> > +proc check_effective_target_exceptions_enabled { } {
> > +    return [check_v3_target_prop_cached et_eh {
> > +       set cond "defined __cpp_exceptions"
> > +       return [v3_check_preprocessor_condition eh $cond]
> > +    }]
> > +}
> > +
>
> Well, we don't even need to do that, because:
>
> > However, you probably want to add it to the main testsuite instead, which
> > would be a little more involved (the v3_check_preprocessor_condition proc
> > is specific to libstdc++).
>
> ..., this has already been done in Subversion r279246
> (Git commit a9046e9853024206bec092dd63e21e152cb5cbca)
> "[MSP430] -Add fno-exceptions multilib" (thanks, Jozef!):
>

Nice.


>
>     --- gcc/testsuite/lib/target-supports.exp
>     +++ gcc/testsuite/lib/target-supports.exp
>     @@ -8990,6 +8990,24 @@ proc check_effective_target_exceptions {} {
>          return 1
>      }
>
>     +# Used to check if the testing configuration supports exceptions.
>     +# Returns 0 if exceptions are unsupported or disabled (e.g. by passing
>     +# -fno-exceptions). Returns 1 if exceptions are enabled.
>     +proc check_effective_target_exceptions_enabled {} {
>     +    return [check_cached_effective_target exceptions_enabled {
>     +   if { [check_effective_target_exceptions] } {
>     +       return [check_no_compiler_messages exceptions_enabled assembly
> {
>     +           void foo (void)
>     +           {
>     +               throw 1;
>     +           }
>     +       }]
>     +   } else {
>     +       # If exceptions aren't supported, then they're not enabled.
>     +       return 0
>     +   }
>     +    }]
>     +}
>
>      proc check_effective_target_tiny {} {
>          return [check_cached_effective_target tiny {
>
> ..., and it even already has one usage in libstdc++, per your
> commit 4c27c6584d0c15926f57ac40f931e238cf0b3110
> "libstdc++: Make testsuite usable with -fno-exceptions":
>
>     --- libstdc++-v3/testsuite/23_containers/vector/bool/72847.cc
>     +++ libstdc++-v3/testsuite/23_containers/vector/bool/72847.cc
>     @@ -15,7 +15,7 @@
>      // with this library; see the file COPYING3.  If not see
>      // <http://www.gnu.org/licenses/>.
>
>     -// { dg-skip-if "" { *-*-* } { "-fno-exceptions" } }
>     +// { dg-require-effective-target exceptions_enabled }
>
>      #include <vector>
>      #include <ext/throw_allocator.h>
>
> ;-)
>
>
Ha! I forgot all about that.

I'll change the rethrow_if_nested-term.cc test to the the effective target
instead of dg-skip-if.