C++ PATCH to static auto in template

Message ID CADzB+2=rPhS+XB0dnC_prS=kwraTU0RzZ_oGwKyJ56sKqZ=S-A@mail.gmail.com
State New
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  • C++ PATCH to static auto in template
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Commit Message

Jason Merrill May 11, 2018, 2:52 a.m.
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.

Patch

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;