Re: [PATCH] Remove can_throw_non_call_exceptions special case from operator_div::wi_fold.

[Aldy Hernandez <aldyh@redhat.com>]

Will adjust, re-test and commit.

Thanks.
Aldy

On Tue, Nov 30, 2021 at 10:00 AM Richard Biener
<richard.guenther@gmail.com> wrote:
>
> On Tue, Nov 30, 2021 at 9:51 AM Aldy Hernandez <aldyh@redhat.com> wrote:
> >
> > On Tue, Nov 30, 2021 at 8:37 AM Richard Biener
> > <richard.guenther@gmail.com> wrote:
> > >
> > > On Mon, Nov 29, 2021 at 4:24 PM Aldy Hernandez <aldyh@redhat.com> wrote:
> > > >
> > > > On Mon, Nov 29, 2021 at 3:48 PM Richard Biener
> > > > <richard.guenther@gmail.com> wrote:
> > > > >
> > > > > On Mon, Nov 29, 2021 at 3:39 PM Jeff Law <jeffreyalaw@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.
> >
> > Did you mean the entire patch (as attached) is OK, or just the sink part?
>
> The DCE and DSE parts are wrong and not needed.  The remaining pieces
> are OK.
>
> Thanks,
> Richard.
>
> > Thanks.
> > Aldy
>