On 12/23/23 14:46, Nathan Sidwell wrote:
On 12/18/23 17:10, Jason Merrill wrote:
On 12/18/23 16:57, Nathan Sidwell wrote:
On 12/18/23 16:31, Jason Merrill wrote:
Tested x86_64-pc-linux-gnu. Does this make sense? Did you have
another theory
about how to merge these?
Why isn't push_abi_namespace doing the right setup here? (and I think
get_global_binding might be similarly problematic?)
What would the right setup be? It pushes into the global module, but
before this change lookup doesn't find things imported into the global
module, and so we get two independent (and so non-equivalent)
declarations.
The comment for get_namespace_binding says "Users of this who, having
found nothing, push a new decl must be prepared for that pushing to
match an existing decl." But if lookup_elaborated_type fails, so we
pushtag a new type, check_module_override doesn't try to merge them
because TREE_PUBLIC isn't set on the TYPE_DECL yet at that point, and
they coexist until we complain about redeclaring __dynamic_cast with
non-matching parameter types.
I tried setting TREE_PUBLIC on the TYPE_DECL, and then
check_module_override called duplicate_decls, and rejected the
redeclaration as a different type.
sigh, it seems that doesn't work as intended, I guess your approace is a
pragmatic workaround, much as I dislike special-casing particular
identifier. Perhaps comment with an appropriate FIXME?
I've realized there's problems with completeness here -- the 'invisible'
type may be complete, but the current TU only forward-declares it. Our
AST can't represent that right now. And I'm not sure if there are
template instantiation issues -- is the type complete or not in any
particular instantiaton?
My understanding of https://eel.is/c++draft/module#reach-4 is that this
doesn't matter: if there is a reachable definition of the class, the
class is complete, even if the current TU only forward-declares it.
Here's an alternate approach that handles this merging in
check_module_override; this makes P1811 include-after-import a bit
worse, but it's already not well supported, so perhaps that's OK for
now. But I'm inclined to go with my earlier patch for GCC 14. What do
you think?
Jason
From a4ccd4664d6acb696db3263de8286721e75a0d2b Mon Sep 17 00:00:00 2001
From: Jason Merrill <ja...@redhat.com>
Date: Mon, 18 Dec 2023 15:47:10 -0500
Subject: [PATCH 1/2] c++: __class_type_info and modules
To: gcc-patches@gcc.gnu.org
Doing a dynamic_cast in both TUs broke because we were declaring a new
__class_type_info in _b that conflicted with the one imported in the global
module from _a. check_module_override wasn't merging them because
TREE_PUBLIC wasn't set yet. Fixing that led to errors from duplicate_decls
about the decls having different types; let's avoid that in
check_module_override.
gcc/cp/ChangeLog:
* name-lookup.cc (pushtag): Set TREE_PUBLIC sooner.
(check_module_override): Merge classes.
(lookup_elaborated_type): Update comment.
gcc/testsuite/ChangeLog:
* g++.dg/lookup/builtin4.C: Expect warning.
* g++.dg/lookup/hidden-class10.C: Likewise.
* g++.dg/modules/pr106304_b.C: Add dynamic_cast.
---
gcc/cp/name-lookup.cc | 33 ++++++++++++++++----
gcc/testsuite/g++.dg/lookup/builtin4.C | 2 +-
gcc/testsuite/g++.dg/lookup/hidden-class10.C | 2 +-
gcc/testsuite/g++.dg/modules/pr106304_b.C | 1 +
4 files changed, 30 insertions(+), 8 deletions(-)
diff --git a/gcc/cp/name-lookup.cc b/gcc/cp/name-lookup.cc
index 4e2d5b03015..37724ea0e65 100644
--- a/gcc/cp/name-lookup.cc
+++ b/gcc/cp/name-lookup.cc
@@ -3794,7 +3794,22 @@ check_module_override (tree decl, tree mvec, bool hiding,
for (ovl_iterator iter (mergeable); iter; ++iter)
{
- match = duplicate_decls (decl, *iter, hiding);
+ if (!named_module_p ()
+ && DECL_IMPLICIT_TYPEDEF_P (decl)
+ && DECL_IMPLICIT_TYPEDEF_P (*iter)
+ && !IDENTIFIER_ANON_P (DECL_NAME (decl)))
+ /* Merge classes of the same name in the global module;
+ duplicate_decls would complain about different types. This test
+ is similar to the one in check_mergeable_decl, but only
+ considers implicit typedefs, since explicit typedefs should
+ actually have the same type.
+
+ ??? If we eventually want to do consistency checking for P1811
+ redefinition, we'll probably need to delay this merging until
+ the end of the class definition. */
+ match = *iter;
+ else
+ match = duplicate_decls (decl, *iter, hiding);
if (match)
goto matched;
}
@@ -8087,11 +8102,9 @@ lookup_elaborated_type (tree name, TAG_how how)
if (!module_purview_p ())
{
- /* We're in the global module, perhaps there's a tag
- there? */
- // FIXME: This isn't quite right, if we find something
- // here, from the language PoV we're not supposed to
- // know it?
+ /* We're in the global module, perhaps there's a tag there?
+ We'll find it in check_module_override when we try to push a
+ new one, no need to handle it specially here. */
}
}
}
@@ -8277,10 +8290,18 @@ pushtag (tree name, tree type, TAG_how how)
}
else
{
+ /* Set TREE_PUBLIC now for built-in warnings and module merging. */
+ if (b->kind == sk_namespace
+ && TREE_PUBLIC (b->this_entity))
+ TREE_PUBLIC (decl) = 1;
+
decl = do_pushdecl_with_scope
(decl, b, /*hiding=*/(how == TAG_how::HIDDEN_FRIEND));
if (decl == error_mark_node)
return decl;
+ if (TREE_TYPE (decl) != type)
+ /* Found an imported version of the same type. */
+ return TREE_TYPE (decl);
if (DECL_CONTEXT (decl) == std_node
&& init_list_identifier == DECL_NAME (TYPE_NAME (type))
diff --git a/gcc/testsuite/g++.dg/lookup/builtin4.C b/gcc/testsuite/g++.dg/lookup/builtin4.C
index b1785dcc7fb..e71131b5a99 100644
--- a/gcc/testsuite/g++.dg/lookup/builtin4.C
+++ b/gcc/testsuite/g++.dg/lookup/builtin4.C
@@ -10,6 +10,6 @@ namespace std
union abort;
}
-union abort;
+union abort; // { dg-warning "built-in" }
using std::abort; // { dg-error "" }
diff --git a/gcc/testsuite/g++.dg/lookup/hidden-class10.C b/gcc/testsuite/g++.dg/lookup/hidden-class10.C
index c9b5ca9f663..986241558a6 100644
--- a/gcc/testsuite/g++.dg/lookup/hidden-class10.C
+++ b/gcc/testsuite/g++.dg/lookup/hidden-class10.C
@@ -6,6 +6,6 @@
// function name.
class A {
- friend class abort;
+ friend class abort; // { dg-warning "built-in" }
abort *b; // { dg-error "type|expected" }
};
diff --git a/gcc/testsuite/g++.dg/modules/pr106304_b.C b/gcc/testsuite/g++.dg/modules/pr106304_b.C
index e8333909c8d..0d1da086176 100644
--- a/gcc/testsuite/g++.dg/modules/pr106304_b.C
+++ b/gcc/testsuite/g++.dg/modules/pr106304_b.C
@@ -5,4 +5,5 @@ module pr106304;
void f(A& a) {
as_b(a);
+ dynamic_cast<B*>(&a);
}
--
2.39.3
