On Thu, May 23, 2024 at 2:00 PM Joseph Myers <josmy...@redhat.com> wrote:
>
> On Tue, 21 May 2024, Martin Uecker wrote:
> >
> > C: allow aliasing of compatible types derived from enumeral types
> > [PR115157]
> >
> > Aliasing of enumeral types with the underlying integer is now allowed
> > by setting the aliasing set to zero. But this does not allow aliasing
> > of derived types which are compatible as required by ISO C. Instead,
> > initially set structural equality. Then set TYPE_CANONICAL and update
> > pointers and main variants when the type is completed (as done for
> > structures and unions in C23).
> >
> > PR 115157
> >
> > gcc/c/
> > * c-decl.cc (shadow_tag-warned,parse_xref_tag,start_enum,
> > finish_enum): Set SET_TYPE_STRUCTURAL_EQUALITY / TYPE_CANONICAL.
> > * c-obj-common.cc (get_alias_set): Remove special case.
> > (get_aka_type): Add special case.
> >
> > gcc/
> > * godump.cc (go_output_typedef): use TYPE_MAIN_VARIANT instead
> > of TYPE_CANONICAL.
> >
> > gcc/testsuite/
> > * gcc.dg/enum-alias-1.c: New test.
> > * gcc.dg/enum-alias-2.c: New test.
> > * gcc.dg/enum-alias-3.c: New test.
>
> OK, in the absence of objections on middle-end or Go grounds within the
> next week.
The godump.cc patch is
&& (TYPE_CANONICAL (TREE_TYPE (decl)) == NULL_TREE
|| !container->decls_seen.contains
- (TYPE_CANONICAL (TREE_TYPE (decl)))))
+ (TYPE_MAIN_VARIANT (TREE_TYPE (decl)))))
{
What is the problem you are seeing?
This patch isn't right:
1) The code is saying if "X == NULL_TREE || !already_seen(X)". This
patch is changing the latter X but not the former. They should be
consistent.
2) At the bottom of that conditional block is code that adds a value
to container->decls_seen. Today that code is adding TYPE_CANONICAL.
If we change the condition to test TYPE_MAIN_VARIANT, then we need to
add TYPE_MAIN_VARIANT to decls_seen.
Hope that makes sense.
I don't know why the patch is required, but it's fine with those
changes as long as the libgo tests continue to pass.
Ian
