On Mon, Nov 29, 2021 at 4:24 PM Aldy Hernandez <al...@redhat.com> wrote:
>
> On Mon, Nov 29, 2021 at 3:48 PM Richard Biener
> <richard.guent...@gmail.com> wrote:
> >
> > On Mon, Nov 29, 2021 at 3:39 PM Jeff Law <jeffreya...@gmail.com> wrote:
> > >
> > >
> > >
> > > On 11/29/2021 7:00 AM, Aldy Hernandez via Gcc-patches wrote:
> > > > As discussed in the PR. The code makes no difference, so whatever test
> > > > we added this special case for has been fixed or is being papered over.
> > > > I think we should fix any fall out upstream.
> > > >
> > > > [Unless Andrew can remember why we added this and it still applies.]
> > > >
> > > > Tested on x86-64 Linux.
> > > >
> > > > OK for trunk?
> > > >
> > > > PR 103451
> > > >
> > > > gcc/ChangeLog:
> > > >
> > > > * range-op.cc (operator_div::wi_fold): Remove
> > > > can_throw_non_call_exceptions special case.
> > > >
> > > > gcc/testsuite/ChangeLog:
> > > >
> > > > * gcc.dg/pr103451.c: New test.
> > > I'll defer to Andrew, but it seems wrong to me. The whole point is to
> > > set the result to varying so that we don't know the result and never
> > > remove the division which is critical for -fnon-call-exceptions.
> >
> > But that has nothing to do with computing the value range for
> > the result which is only accessible when the stmt does _not_ throw ...
> >
> > That is, if we compute non-VARYING here and because of that
> > remove the stmt then _that's_ the place to fix (IMO)
>
> Ughh, I think you're both right.
>
> We should fix this upstream AND we should test for the presence of the
> division by 0 in the optimized dump.
>
> Of course doing both opens a can of worms. The division by zero can
> be cleaned up by (at least) DCE, DSE, and the code sinking passes.
> I've fixed all 3 in the attached (untested) patch. Dunno what y'all
> want to do at this point.
I think you need to add -fno-delete-dead-exceptions to the testcase.
The sinking
bug looks real, but just
&& (cfun->can_delete_dead_exceptions
|| !stmt_could_throw_p (cfun, stmt))
is needed there. That change is OK.
Thanks,
Richard.
>
> Aldy
