On Sat, 2021-02-20 at 17:17 -0500, Antoni Boucher via Gcc-patches
wrote:
> Hi.
> Thanks for your feedback!
>
Sorry about the delay in responding.
In the past I was hesitant about adding more cast support to libgccjit
since I felt that the user could always just create a union to do the
cast. Then I tried actually using the libgccjit API to do this, and
realized how much work it adds, so I now think we do want to support
casting more types.
> See answers below:
>
> On Sat, Feb 20, 2021 at 11:20:35AM -0700, Tom Tromey wrote:
> > > > > > > "Antoni" == Antoni Boucher via Gcc-patches <
> > > > > > > gcc-patches@gcc.gnu.org> writes:
> >
> > Antoni> gcc/jit/
> > Antoni> PR target/95498
> > Antoni> * jit-playback.c: Add support to handle truncation
> > and extension
> > Antoni> in the convert function.
> >
> > Antoni> + switch (dst_code)
> > Antoni> + {
> > Antoni> + case INTEGER_TYPE:
> > Antoni> + case ENUMERAL_TYPE:
> > Antoni> + t_ret = convert_to_integer (dst_type, expr);
> > Antoni> + goto maybe_fold;
> > Antoni> +
> > Antoni> + default:
> > Antoni> + gcc_assert (gcc::jit::active_playback_ctxt);
> > Antoni> + gcc::jit::active_playback_ctxt->add_error (NULL,
> > "unhandled conversion");
> > Antoni> + fprintf (stderr, "input expression:\n");
> > Antoni> + debug_tree (expr);
> > Antoni> + fprintf (stderr, "requested type:\n");
> > Antoni> + debug_tree (dst_type);
> > Antoni> + return error_mark_node;
> > Antoni> +
> > Antoni> + maybe_fold:
> > Antoni> + if (TREE_CODE (t_ret) != C_MAYBE_CONST_EXPR)
Do we even get C_MAYBE_CONST_EXPR in libgccjit? That tree code is
defined in c-family/c-common.def; how can nodes of that kind be created
outside of the c-family?
> > Antoni> + t_ret = fold (t_ret);
> > Antoni> + return t_ret;
> >
> > It seems weird to have a single 'goto' to maybe_fold, especially
> > inside
> > a switch like this.
> >
> > If you think the maybe_fold code won't be reused, then it should just
> > be
> > hoisted up and the 'goto' removed.
>
> This actually depends on how the support for cast between integers and
> pointers will be implemented (see below).
> If we will support truncating pointers (does that even make sense? and
> I
> guess we cannot extend a pointer unless we add the support for
> uint128_t), that label will be reused for that case.
> Otherwise, it might not be reused.
>
> So, please tell me which option to choose and I'll update my patch.
FWIW I don't think we'll want to support truncating or extending
pointers.
>
> > On the other hand, if the maybe_fold code might be reused for some
> > other
> > case, then I suppose I would have the case end with 'break' and then
> > have this code outside the switch.
> >
> >
> > In another message, you wrote:
> >
> > Antoni> For your question, the current code already works with
> > boolean and
> > Antoni> reals and casts between integers and pointers is currently
> > not
> > Antoni> supported.
> >
> > I am curious why this wasn't supported. It seems like something that
> > one might want to do.
>
> I have no idea as this is my first contribution to gcc.
> But this would be indeed very useful and I opened an issue about this:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95438
>
> > thanks,
> > Tom
>
> Thanks!
>
