Hi, Thomas
Actually, yes, AIX does allow dereference of a NULL pointer.
Thanks, David
On Fri, Nov 27, 2020 at 9:15 AM Thomas Schwinge <tho...@codesourcery.com> wrote:
>
> Hi David!
>
> On 2020-11-24T15:29:17-0500, David Edelsohn via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> > On Tue, Nov 24, 2020 at 5:19 AM Thomas Schwinge <tho...@codesourcery.com>
> > wrote:
> >> On 2020-11-21T10:50:10-0500, David Edelsohn <dje....@gmail.com> wrote:
> >> > I see
> >> >
> >> > "during GIMPLE pass: omplower"
> >> >
> >> > message for kernels-decompose-ice-2.c. kernels-decompose-ice-1.c
> >> > explicitly prunes that output, but kernels-decompose-ice-2.c does not.
> >> > Is there a reason that the second testcase does not prune that output
> >> > or can we add it?
> >>
> >> So, the expectation (as verified by my x86_64-pc-linux-gnu and
> >> powerpc64le-unknown-linux-gnu testing) is that
> >> 'c-c++-common/goacc/kernels-decompose-ice-1.c' (currently) runs into an
> >> ICE "during GIMPLE pass: omplower", and
> >> 'c-c++-common/goacc/kernels-decompose-ice-2.c' (currently) runs into an
> >> ICE "during GIMPLE pass: omp_oacc_kernels_decompose".
> >>
> >> Now, you're reporting that for the latter testcase you're instead also
> >> seeing an ICE "during GIMPLE pass: omplower". Can you please show the
> >> full ICE report/backtrace, so that we verify that it's not yet another
> >> separate issue?
>
> On gcc119 ('uname -a': "AIX power8-aix 2 7 00F9C1964C00"), I've now also
> reproduced the issue.
>
> >> Maybe the AIX system configuration (ABI?)
> >> mandates/causes some slight difference in how front ends set attributes
> >> such as 'TREE_ADDRESSABLE' on DECLs, which 'omp_oacc_kernels_decompose'
> >> (currently) is sensitive to (hence the ICEs).
>
> That's not the case; the input into 'omp_oacc_kernels_decompose' seems to
> be exactly the same as on other systems.
>
> > The error messages reported on AIX are:
> >
> > Executing on host: /tmp/GCC/gcc/xgcc -B/tmp/GCC/gcc/
> > /nasfarm/edelsohn/src/src/gcc/testsuite/c-c++-common/goacc/kernels-decompose-ice-2.c
> > -fdiagnostics-plain-output -fopenacc -fopenacc-kernels=decompose -S
> > -o kernels-decompose-ice-2.s (timeout = 300)
> > spawn -ignore SIGHUP /tmp/GCC/gcc/xgcc -B/tmp/GCC/gcc/
> > /nasfarm/edelsohn/src/src/gcc/testsuite/c-c++-common/goacc/kernels-decompose-ice-2.c
> > -fdiagnostics-plain-output -fopenacc -fopenacc-kernels=decompose -S -o
> > kernels-decompose-ice-2.s
> > during GIMPLE pass: omplower
> > /nasfarm/edelsohn/src/src/gcc/testsuite/c-c++-common/goacc/kernels-decompose-ice-2.c:
> > In function 'main':
> > /nasfarm/edelsohn/src/src/gcc/testsuite/c-c++-common/goacc/kernels-decompose-ice-2.c:13:9:
> > internal compiler error: in lower_omp_target, at omp-low.c:12216
>
> That's indeed the location of the 'gcc_assert' responsible for the
> 'omplower' ICE, which currently is expected, if we don't run into the
> 'omp_oacc_kernels_decompose' ICE first. It's still strange however, why
> we're seeing this "for AIX" (not better classified) only: I suppose it
> isn't a feature "of AIX" that it can dereference a 'NULL' pointer ;-) --
> which is what seems to be happening here:
>
> 742 gimple_seq inner_sequence = gimple_bind_body
> (inner_bind);
> (gdb) next
> 743 gcc_assert (gimple_code (inner_sequence) != GIMPLE_BIND
> (gdb) print inner_sequence
> $1 = (gimple_seq) 0x0
> (gdb) next
> 745 gimple_seq_add_seq (&new_body, inner_sequence);
>
> So we have 'inner_sequence == NULL', and yet the 'next' didn't trigger a
> SIGSEGV in:
>
> static inline enum gimple_code
> gimple_code (const gimple *g)
> {
> return g->code;
> }
>
> Strange, isn't it?
>
>
> However: this issue should now (indirectly) be fixed via "In
> 'gcc/omp-oacc-kernels-decompose.cc:flatten_binds', don't choke on empty
> GIMPLE sequence" that I've just pushed to master branch in commit
> 4b5726fda653d11f882fb9a112e4cffa12f7ed61.
>
>
> > during GIMPLE pass: omplower
> > /nasfarm/edelsohn/src/src/gcc/testsuite/c-c++-common/goacc/kernels-decompose-ice-2.c:
> > In function 'main':
> > /nasfarm/edelsohn/src/src/gcc/testsuite/c-c++-common/goacc/kernels-decompose-ice-2.c:13:9:
> > internal compiler error: in lower_omp_target, at omp-low.c:12216
> > ranges offset out of range
>
> That last line actually comes from here:
>
> libbacktrace/dwarf.c: error_callback (data, "ranges offset out of
> range", 0);
>
>
> Grüße
> Thomas
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