[PATCH RFC] c++: lambda mangling alias issues [PR107897]

[Jason Merrill <jason@redhat.com>]

Tested x86_64-pc-linux-gnu.  Does this look good, or do we want to factor the
flag clearing into a symtab_node counterpart to cgraph_node::reset?

-- 8< --

In 107897, by the time we are looking at the mangling clash, the
alias has already been removed from the symbol table by analyze_functions,
so we can't look at n->cpp_implicit_alias.  So just assume that it's an
alias if it's internal.

In 108887 the problem is that removing the mangling alias from the symbol
table confuses analyze_functions, because it ended up as first_analyzed
somehow, so it becomes a dangling pointer.  Fixed by clearing various flags
to neutralize the alias.

	PR c++/107897
	PR c++/108887

gcc/cp/ChangeLog:

	* decl2.cc (record_mangling): Improve symbol table handling.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-lambda3.C: Use -flto if supported.
	* g++.dg/cpp0x/lambda/lambda-mangle7.C: New test.
---
 gcc/cp/decl2.cc                               | 25 +++++--
 .../g++.dg/cpp0x/lambda/lambda-mangle7.C      | 70 +++++++++++++++++++
 gcc/testsuite/g++.dg/cpp2a/concepts-lambda3.C |  1 +
 3 files changed, 91 insertions(+), 5 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/lambda/lambda-mangle7.C

diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
index 387e24542cd..e6e58b08de4 100644
--- a/gcc/cp/decl2.cc
+++ b/gcc/cp/decl2.cc
@@ -4742,15 +4742,30 @@ record_mangling (tree decl, bool need_warning)
     = mangled_decls->find_slot_with_hash (id, IDENTIFIER_HASH_VALUE (id),
 					  INSERT);
 
-  /* If this is already an alias, remove the alias, because the real
+  /* If this is already an alias, cancel the alias, because the real
      decl takes precedence.  */
   if (*slot && DECL_ARTIFICIAL (*slot) && DECL_IGNORED_P (*slot))
-    if (symtab_node *n = symtab_node::get (*slot))
-      if (n->cpp_implicit_alias)
+    {
+      if (symtab_node *n = symtab_node::get (*slot))
 	{
-	  n->remove ();
-	  *slot = NULL_TREE;
+	  if (n->cpp_implicit_alias)
+	    {
+	      /* Actually removing the node isn't safe if other code is already
+		 holding a pointer to it, so just neutralize it.  */
+	      n->remove_from_same_comdat_group ();
+	      n->analyzed = false;
+	      n->definition = false;
+	      n->alias = false;
+	      n->cpp_implicit_alias = false;
+	    }
 	}
+      else
+	/* analyze_functions might have already removed the alias from the
+	   symbol table if it's internal.  */
+	gcc_checking_assert (!TREE_PUBLIC (*slot));
+
+      *slot = NULL_TREE;
+    }
 
   if (!*slot)
     *slot = decl;
diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-mangle7.C b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-mangle7.C
new file mode 100644
index 00000000000..c7946a2be08
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-mangle7.C
@@ -0,0 +1,70 @@
+// PR c++/108887
+// { dg-do compile { target c++11 } }
+
+template <int __v> struct integral_constant {
+  static constexpr int value = __v;
+};
+using false_type = integral_constant<false>;
+template <bool, bool, typename...> struct __result_of_impl;
+template <typename _Functor, typename... _ArgTypes>
+struct __result_of_impl<false, false, _Functor, _ArgTypes...> {
+  typedef decltype(0) type;
+};
+template <typename... _ArgTypes>
+struct __invoke_result
+    : __result_of_impl<false_type::value, false_type::value, _ArgTypes...> {};
+template <typename, typename _Fn, typename... _Args>
+void __invoke_impl(_Fn __f, _Args... __args) {
+  __f(__args...);
+}
+template <typename, typename _Callable, typename... _Args>
+void __invoke_r(_Callable __fn, _Args... __args) {
+  using __result = __invoke_result<_Args...>;
+  using __type = typename __result::type;
+  __invoke_impl<__type>(__fn, __args...);
+}
+struct QString {
+  QString(const char *);
+};
+template <typename> class function;
+template <typename _Functor> struct _Base_manager {
+  static _Functor _M_get_pointer(int) { __builtin_abort (); }
+};
+template <typename, typename> class _Function_handler;
+template <typename _Res, typename _Functor, typename... _ArgTypes>
+struct _Function_handler<_Res(_ArgTypes...), _Functor> {
+  using _Base = _Base_manager<_Functor>;
+  static _Res _M_invoke(const int &__functor, _ArgTypes &&...__args) {
+    auto __trans_tmp_1 = _Base::_M_get_pointer(__functor);
+    __invoke_r<_Res>(__trans_tmp_1, __args...);
+  }
+};
+template <typename _Res, typename... _ArgTypes>
+struct function<_Res(_ArgTypes...)> {
+  template <typename _Functor>
+  using _Handler = _Function_handler<_Res(_ArgTypes...), _Functor>;
+  template <typename _Functor> function(_Functor) {
+    using _My_handler = _Handler<_Functor>;
+    _M_invoker = _My_handler::_M_invoke;
+  }
+  using _Invoker_type = _Res (*)(const int &, _ArgTypes &&...);
+  _Invoker_type _M_invoker;
+};
+struct QRegularExpression {
+  QRegularExpression(QString);
+};
+struct AbstractAccount {
+  void get(function<void(AbstractAccount *)>,
+           function<void(AbstractAccount *)>);
+};
+struct AbstractTimelineModel {
+  AbstractAccount m_account;
+};
+struct LinkPaginationTimelineModel : AbstractTimelineModel {
+  void fillTimeline();
+};
+void LinkPaginationTimelineModel::fillTimeline() {
+  [] {};
+  m_account.get([](AbstractAccount *) { static QRegularExpression re(""); },
+                [](AbstractAccount *) {});
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-lambda3.C b/gcc/testsuite/g++.dg/cpp2a/concepts-lambda3.C
index 291e451ca1a..a7cb6c5dece 100644
--- a/gcc/testsuite/g++.dg/cpp2a/concepts-lambda3.C
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-lambda3.C
@@ -1,4 +1,5 @@
 // { dg-do run { target c++20 } }
+// { dg-additional-options "-flto" { target lto } } (PR107897)
 
 template<typename T>
 concept C1 = __is_same_as(T, int)

base-commit: 4f181f9c7ee3efc509d185fdfda33be9018f1611
-- 
2.31.1