Re: [PATCH] PR c/104506: Tolerate error_mark_node in useless_type_conversion_p.

[Andrew Pinski <pinskia@gmail.com>]

On Mon, Feb 14, 2022 at 11:33 PM Richard Biener
<richard.guenther@gmail.com> wrote:
>
> On Tue, Feb 15, 2022 at 12:58 AM Andrew Pinski via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > On Mon, Feb 14, 2022 at 4:54 AM Roger Sayle <roger@nextmovesoftware.com> wrote:
> > >
> > >
> > >
> > > This simple fix to the middle-end, resolves PR c/104506, by adding an
> > >
> > > explicit check for error_mark_node to useless_type_conversion_p.  I first
> > >
> > > trying fixing this in the C front-end, but the type is valid at the point
> > >
> > > that the NOP_EXPR is created, so the poisoned type leaks to the middle-end.
> > >
> > > Returning either true or false from useless_type_conversion_p avoids the
> > >
> > > ICE-after-error.  Apologies to Andrew Pinski, I hadn't noticed that he'd
> > >
> > > assigned this PR to himself until after my regression testing had finished.
> > >
> > >
> > >
> > > This patch has been tested on x86_64-pc-linux-gnu with make bootstrap and
> > >
> > > make -k check with no new failures.  Ok for mainline?
> > >
> > >
> > >
> > >
> > >
> > > 2022-02-14  Roger Sayle  <roger@nextmovesoftware.com>
> > >
> > >
> > >
> > > gcc/ChangeLog
> > >
> > > PR c/104506
> > >
> > > * gimple-expr.cc (useless_type_conversion_p): Add a check for
> > >
> > > error_mark_node.
> >
> > I came up with a different patch (attached) which just changes
> > tree_ssa_useless_type_conversion rather than useless_type_conversion_p
> > which I was going to submit but had an issue with my build machine.
> > I did it this way as it was similar to how
> > STRIP_NOPS/tree_nop_conversion was done already.
> >
> > Also from my description of the patch
> >     STRIP_USELESS_TYPE_CONVERSION is mostly used inside the gimplifier
> >     and the places where it is used outside of the gimplifier would not
> >     be adding too much overhead.
> >
> > Though I think Richard Biener's patch is better really. It would be
> > interesting to see how the C++ front-end handles this case, I remember
> > it using integer_type_node in some locations after an error for a
> > type.
>
> If the fix to the C frontend doesn't work out I'd indeed prefer your variant.
> Nit:
>
> +  outer_type = TREE_TYPE (expr);
> +  inner_type = TREE_TYPE (TREE_OPERAND (expr, 0));
> +
> +  if (!inner_type || inner_type == error_mark_node)
> +    return false;
>
> unless we get to a case where inner_type == NULL I would not bother
> checking that.

Understood, I will remove it, I was just copying exactly what was done
in tree_nop_conversion really. The history on the null check seems to
date to 2000 without any explanation really.

Thanks,
Andrew Pinski

>
> As said, that TREE_TYPE (error_mark_node) is not a type is IMHO bad
> for error recovery.  Maybe we really need ERROR_TYPE here.
>
> > Thanks,
> > Andrew Pinski
> >
> > >
> > >
> > >
> > > gcc/testsuite/ChangeLog
> > >
> > > PR c/104506
> > >
> > > * gcc.dg/pr104506.c: New test case.
> > >
> > >
> > >
> > >
> > >
> > > Roger
> > >
> > > --
> > >
> > >