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C++ PATCH to static auto in template
- From: Jason Merrill <jason at redhat dot com>
- To: gcc-patches List <gcc-patches at gcc dot gnu dot org>
- Date: Thu, 10 May 2018 22:52:12 -0400
- Subject: C++ PATCH to static auto in template
Normally we defer instantiation of static data member initializers
until they are needed, but we were doing it immediately for auto
variables.
Tested x86_64-pc-linux-gnu, applying to trunk.
commit a16c8170ac1c148087ee7798b9783656e53ab490
Author: Jason Merrill <jason@redhat.com>
Date: Wed Mar 14 20:11:38 2018 -0400
* decl.c (cp_finish_decl): Don't instantiate auto variable.
(check_static_variable_definition): Allow auto.
* constexpr.c (ensure_literal_type_for_constexpr_object): Likewise.
diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index b4bcc6a567d..d9a4cab9f37 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -91,6 +91,8 @@ ensure_literal_type_for_constexpr_object (tree decl)
if (CLASS_TYPE_P (stype) && !COMPLETE_TYPE_P (complete_type (stype)))
/* Don't complain here, we'll complain about incompleteness
when we try to initialize the variable. */;
+ else if (type_uses_auto (type))
+ /* We don't know the actual type yet. */;
else if (!literal_type_p (type))
{
if (DECL_DECLARED_CONSTEXPR_P (decl))
diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index d58964754b9..20ca28fc878 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -6803,24 +6803,18 @@ cp_finish_decl (tree decl, tree init, bool init_const_expr_p,
&& (DECL_INITIAL (decl) || init))
DECL_INITIALIZED_IN_CLASS_P (decl) = 1;
+ /* Do auto deduction unless decl is a function or an uninstantiated
+ template specialization. */
if (TREE_CODE (decl) != FUNCTION_DECL
+ && !(init == NULL_TREE
+ && DECL_LANG_SPECIFIC (decl)
+ && DECL_TEMPLATE_INSTANTIATION (decl)
+ && !DECL_TEMPLATE_INSTANTIATED (decl))
&& (auto_node = type_uses_auto (type)))
{
tree d_init;
if (init == NULL_TREE)
- {
- if (DECL_LANG_SPECIFIC (decl)
- && DECL_TEMPLATE_INSTANTIATION (decl)
- && !DECL_TEMPLATE_INSTANTIATED (decl))
- {
- /* init is null because we're deferring instantiating the
- initializer until we need it. Well, we need it now. */
- instantiate_decl (decl, /*defer_ok*/true, /*expl*/false);
- return;
- }
-
- gcc_assert (CLASS_PLACEHOLDER_TEMPLATE (auto_node));
- }
+ gcc_assert (CLASS_PLACEHOLDER_TEMPLATE (auto_node));
d_init = init;
if (d_init)
{
@@ -9368,6 +9362,7 @@ check_static_variable_definition (tree decl, tree type)
in check_initializer. Similarly for inline static data members. */
if (DECL_P (decl)
&& (DECL_DECLARED_CONSTEXPR_P (decl)
+ || undeduced_auto_decl (decl)
|| DECL_VAR_DECLARED_INLINE_P (decl)))
return 0;
else if (cxx_dialect >= cxx11 && !INTEGRAL_OR_ENUMERATION_TYPE_P (type))
diff --git a/gcc/testsuite/g++.dg/cpp1z/static2.C b/gcc/testsuite/g++.dg/cpp1z/static2.C
new file mode 100644
index 00000000000..b87bfec3aaa
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/static2.C
@@ -0,0 +1,17 @@
+// { dg-additional-options -std=c++17 }
+
+template <class T>
+struct A
+{
+ static constexpr auto x = T::x;
+};
+
+struct B;
+A<B> a;
+
+struct B
+{
+ static constexpr auto x = 42;
+};
+
+auto x = a.x;