On Thu, 18 Jul 2024, Jason Merrill wrote:
> On 7/18/24 12:45 PM, Patrick Palka wrote:
> > Bootstrapped and regtested on x86_64-pc-linux-gnu, does thi look
> > OK for trunk/14?
> >
> > -- >8 --
> >
> > As a followup of r15-2047-g7954bb4fcb6fa8, we also need to consider
> > dependent attributes when recursing into a non-template alias that names
> > a dependent alias template specialization (and so STF_STRIP_DEPENDENT
> > is set), otherwise in the first testcase below we undesirably strip B
> > all the way to T instead of to A<T>.
> >
> > We also need to move the typedef recursion case of strip_typedefs up to
> > get checked before the compound type recursion cases. Otherwise for C
> > below (which ultimately aliases T*) we end up stripping it to T* instead
> > of to A<T*> because the POINTER_TYPE recursion dominates the typedef
> > recursion. It also means we issue an unexpected extra error in the
> > third testcase below.
> >
> > Ideally we would also want to consider dependent attributes on
> > non-template aliases, so that we accept the second testcase below, but
> > making that work correctly would require broader changes to e.g.
> > spec_hasher which currently assumes all non-template aliases are
> > stripped and hence it'd conflate the dependent specializations A<T>
> > and A<B> even if we didn't strip B.
>
> Wouldn't that just be a matter of changing structural_comptypes to consider
> dependent attributes as well as dependent specializations?
Pretty much, it seems. ISTM we should check dependent attributes even
when !comparing_dependent_aliases since they affect type identity rather
than just SFINAE behavior.
>
> Or better, adding attributes to dependent_alias_template_spec_p (and changing
> its name)? It seems like other callers would also benefit from that change.
I ended up adding a new predicate opaque_alias_p separate from
dependent_alias_template_spec_p since ISTM we need to call it from
there and from alias_template_specialization_p to avoid looking through
such aliases.
So opaque_alias_p checks for type identity of an alias, whereas
dependent_alias_template_spec_p more broadly checks for SFINAE identity.
Something like the following (as an incremental patch on top of the
previous one, to consider separately for backportings since it's riskier):
-- >8 --
Subject: [PATCH 2/1] c++: non-template alias with dependent attributes
[PR115897]
PR c++/115897
gcc/cp/ChangeLog:
* cp-tree.h (opaque_alias_p): Declare.
* decl.cc (start_decl): Use structural equality for an
opaque alias.
* pt.cc (opaque_alias_p): Define.
(alias_template_specialization_p): Don't look through an
opaque alias.
(complex_alias_template_p): Use opaque_alias_p instead of
any_dependent_template_arguments_p directly.
(dependent_alias_template_spec_p): Don't look through an
opaque alias.
(get_underlying_template): Use opaque_alias_p instead of
any_dependent_template_arguments_p.
* tree.cc (strip_typedefs): Don't strip an opaque alias.
* typeck.cc (structural_comptypes): Compare declaration
attributes for an opaque alias.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/alias-decl-79.C: Remove xfails.
---
gcc/cp/cp-tree.h | 1 +
gcc/cp/decl.cc | 3 ++
gcc/cp/pt.cc | 23 ++++++++----
gcc/cp/tree.cc | 7 ++--
gcc/cp/typeck.cc | 42 ++++++++++++++--------
gcc/testsuite/g++.dg/cpp0x/alias-decl-79.C | 16 ++++-----
6 files changed, 61 insertions(+), 31 deletions(-)
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index c6f102564ce..f2a64b63133 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -7622,6 +7622,7 @@ extern tree instantiate_non_dependent_or_null (tree);
extern bool variable_template_specialization_p (tree);
extern bool alias_type_or_template_p (tree);
enum { nt_opaque = false, nt_transparent = true };
+extern bool opaque_alias_p (const_tree);
extern tree alias_template_specialization_p (const_tree, bool);
extern tree dependent_alias_template_spec_p (const_tree, bool);
extern tree get_template_parm_object (tree expr, tree mangle);
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 66e8a973cce..755701fd8aa 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -6144,6 +6144,9 @@ start_decl (const cp_declarator *declarator,
if (decl == error_mark_node)
return error_mark_node;
+ if (opaque_alias_p (TREE_TYPE (decl)))
+ SET_TYPE_STRUCTURAL_EQUALITY (TREE_TYPE (decl));
+
if (VAR_P (decl)
&& DECL_NAMESPACE_SCOPE_P (decl) && !TREE_PUBLIC (decl) && !was_public
&& !DECL_THIS_STATIC (decl) && !DECL_ARTIFICIAL (decl)
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 0620c8c023a..4d4a5cef92c 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -6508,6 +6508,19 @@ alias_type_or_template_p (tree t)
|| DECL_ALIAS_TEMPLATE_P (t));
}
+/* Return true if substituting into T would yield a different type than
+ substituting into its expansion. */
+
+bool
+opaque_alias_p (const_tree t)
+{
+ return (TYPE_P (t)
+ && typedef_variant_p (t)
+ && uses_template_parms (DECL_ORIGINAL_TYPE (TYPE_NAME (t)))
+ && any_dependent_type_attributes_p (DECL_ATTRIBUTES
+ (TYPE_NAME (t))));
+}
+
/* If T is a specialization of an alias template, return it; otherwise return
NULL_TREE. If TRANSPARENT_TYPEDEFS is true, look through other aliases. */
@@ -6525,7 +6538,7 @@ alias_template_specialization_p (const_tree t,
if (tree tinfo = TYPE_ALIAS_TEMPLATE_INFO (t))
if (PRIMARY_TEMPLATE_P (TI_TEMPLATE (tinfo)))
return CONST_CAST_TREE (t);
- if (transparent_typedefs)
+ if (transparent_typedefs && !opaque_alias_p (t))
return alias_template_specialization_p (DECL_ORIGINAL_TYPE
(TYPE_NAME (t)),
transparent_typedefs);
@@ -6630,8 +6643,7 @@ complex_alias_template_p (const_tree tmpl, tree *seen_out)
return true;
/* An alias with dependent type attributes is complex. */
- if (any_dependent_type_attributes_p (DECL_ATTRIBUTES
- (DECL_TEMPLATE_RESULT (tmpl))))
+ if (opaque_alias_p (TREE_TYPE (tmpl)))
return true;
if (!complex_alias_tmpl_info)
@@ -6718,7 +6730,7 @@ dependent_alias_template_spec_p (const_tree t, bool
transparent_typedefs)
}
}
- if (transparent_typedefs)
+ if (transparent_typedefs && !opaque_alias_p (t))
{
tree utype = DECL_ORIGINAL_TYPE (TYPE_NAME (t));
return dependent_alias_template_spec_p (utype, transparent_typedefs);
@@ -6787,8 +6799,7 @@ get_underlying_template (tree tmpl)
break;
/* If TMPL adds dependent type attributes, it isn't equivalent. */
- if (any_dependent_type_attributes_p (DECL_ATTRIBUTES
- (DECL_TEMPLATE_RESULT (tmpl))))
+ if (opaque_alias_p (TREE_TYPE (tmpl)))
break;
/* Alias is equivalent. Strip it and repeat. */
diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc
index 0e6be8de59a..3a2283b4d65 100644
--- a/gcc/cp/tree.cc
+++ b/gcc/cp/tree.cc
@@ -1613,12 +1613,13 @@ strip_typedefs (tree t, bool *remove_attributes /* =
NULL */,
&& !user_facing_original_type_p (t))
return t;
+ if (opaque_alias_p (t))
+ return t;
+
if (alias_template_specialization_p (t, nt_opaque))
{
if (dependent_alias_template_spec_p (t, nt_opaque)
- && (!(flags & STF_STRIP_DEPENDENT)
- || any_dependent_type_attributes_p (DECL_ATTRIBUTES
- (TYPE_NAME (t)))))
+ && !(flags & STF_STRIP_DEPENDENT))
/* DR 1558: However, if the template-id is dependent, subsequent
template argument substitution still applies to the template-id.
*/
return t;
diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index 15e5577f670..e966bcd9d03 100644
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -1658,20 +1658,34 @@ structural_comptypes (tree t1, tree t2, int strict)
return false;
check_alias:
- if (comparing_dependent_aliases)
- {
- /* Don't treat an alias template specialization with dependent
- arguments as equivalent to its underlying type when used as a
- template argument; we need them to be distinct so that we
- substitute into the specialization arguments at instantiation
- time. And aliases can't be equivalent without being ==, so
- we don't need to look any deeper. */
- ++processing_template_decl;
- tree dep1 = dependent_alias_template_spec_p (t1, nt_transparent);
- tree dep2 = dependent_alias_template_spec_p (t2, nt_transparent);
- --processing_template_decl;
- if ((dep1 || dep2) && dep1 != dep2)
- return false;
+ if (typedef_variant_p (t1) || typedef_variant_p (t2))
+ {
+ tree o1 = opaque_alias_p (t1) ? t1 : NULL_TREE;
+ tree o2 = opaque_alias_p (t2) ? t2 : NULL_TREE;
+ if (o1 || o2)
+ {
+ if (!o1 || !o2)
+ return false;
+ if (!comp_type_attributes (DECL_ATTRIBUTES (TYPE_NAME (o1)),
+ DECL_ATTRIBUTES (TYPE_NAME (o2))))
+ return false;
+ }
+
+ if (comparing_dependent_aliases)
+ {
+ /* Don't treat an alias template specialization with dependent
+ arguments as equivalent to its underlying type when used as a
+ template argument; we need them to be distinct so that we
+ substitute into the specialization arguments at instantiation
+ time. And aliases can't be equivalent without being ==, so
+ we don't need to look any deeper. */
+ ++processing_template_decl;
+ tree dep1 = dependent_alias_template_spec_p (t1, nt_transparent);
+ tree dep2 = dependent_alias_template_spec_p (t2, nt_transparent);
+ --processing_template_decl;
+ if ((dep1 || dep2) && dep1 != dep2)
+ return false;
+ }
}
return true;
diff --git a/gcc/testsuite/g++.dg/cpp0x/alias-decl-79.C
b/gcc/testsuite/g++.dg/cpp0x/alias-decl-79.C
index e0f07475cc1..58436f907ef 100644
--- a/gcc/testsuite/g++.dg/cpp0x/alias-decl-79.C
+++ b/gcc/testsuite/g++.dg/cpp0x/alias-decl-79.C
@@ -14,22 +14,22 @@ template<class T> struct A;
template<class T>
void f() {
using B [[gnu::vector_size(16)]] = T;
- static_assert(!is_same<T, B>::value, ""); // { dg-bogus "" "" { xfail
*-*-* } }
- static_assert(!is_same<A<T>, A<B>>::value, ""); // { dg-bogus "" "" { xfail
*-*-* } }
+ static_assert(!is_same<T, B>::value, "");
+ static_assert(!is_same<A<T>, A<B>>::value, "");
#if __cpp_variable_templates
- static_assert(!is_same_v<T, B>, ""); // { dg-bogus "" "" { xfail
c++14 } }
- static_assert(!is_same_v<A<T>, A<B>>, ""); // { dg-bogus "" "" { xfail
c++14 } }
+ static_assert(!is_same_v<T, B>, "");
+ static_assert(!is_same_v<A<T>, A<B>>, "");
#endif
};
template<class T>
void g() {
using C [[gnu::vector_size(16)]] = T*;
- static_assert(!is_same<T*, C>::value, ""); // { dg-bogus "" "" { xfail
*-*-* } }
- static_assert(!is_same<A<T*>, A<C>>::value, ""); // { dg-bogus "" "" { xfail
*-*-* } }
+ static_assert(!is_same<T*, C>::value, "");
+ static_assert(!is_same<A<T*>, A<C>>::value, "");
#if __cpp_variable_templates
- static_assert(!is_same_v<T*, C>, ""); // { dg-bogus "" "" { xfail
c++14 } }
- static_assert(!is_same_v<A<T*>, A<C>>, ""); // { dg-bogus "" "" { xfail
c++14 } }
+ static_assert(!is_same_v<T*, C>, "");
+ static_assert(!is_same_v<A<T*>, A<C>>, "");
#endif
};
--
2.46.0.rc0.106.g1c4a234a1c
