cp-tree.h (OVL_HIDDEN_P): New.

	gcc/cp/
	* cp-tree.h (OVL_HIDDEN_P): New.
	(ovl_iterator::hidden_p, ovl_iterator::reveal_node): New.
	(ovl_iterator::reveal_node): Declare.
	* tree.c (ovl_copy): Copy OVL_HIDDEN_P.
	(ovl_insert): Order on hiddenness.
	(ovl_iterator::reveal_node): New.
	* name-lookup.c (anticipated_builtin_p): New.
	(supplement_binding_1): Use it.
	(set_local_extern_decl_linkage): Use hidden_p.
	(do_pushdecl): Deal with unhiding a hidden decl, use
	anticipated_builtin_p.
	(do_nonmember_using_decl): Use anticipated_decl_p.
	(lookup_name_real_1): Use DECL_HIDDEN_P.

	gcc/testsuite/
	* g++.dg/lookup/extern-c-hidden.C: New.
	* g++.dg/lookup/extern-redecl1.C: New.

From-SVN: r248406

7 files changed, 144 insertions, 21 deletions

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 785dfc5..16e30fa 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,19 @@
+2017-05-24  Nathan Sidwell  <nathan@acm.org>
+
+	* cp-tree.h (OVL_HIDDEN_P): New.
+	(ovl_iterator::hidden_p, ovl_iterator::reveal_node): New.
+	(ovl_iterator::reveal_node): Declare.
+	* tree.c (ovl_copy): Copy OVL_HIDDEN_P.
+	(ovl_insert): Order on hiddenness.
+	(ovl_iterator::reveal_node): New.
+	* name-lookup.c (anticipated_builtin_p): New.
+	(supplement_binding_1): Use it.
+	(set_local_extern_decl_linkage): Use hidden_p.
+	(do_pushdecl): Deal with unhiding a hidden decl, use
+	anticipated_builtin_p.
+	(do_nonmember_using_decl): Use anticipated_decl_p.
+	(lookup_name_real_1): Use DECL_HIDDEN_P.
+
 2017-05-23  Jason Merrill  <jason@redhat.com>
 
 	-Wunused and C++17 structured bindings
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 2ed9e5a..7f1c632 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -378,6 +378,7 @@ extern GTY(()) tree cp_global_trees[CPTI_MAX];
       REF_PARENTHESIZED_P (in COMPONENT_REF, INDIRECT_REF, SCOPE_REF)
       AGGR_INIT_ZERO_FIRST (in AGGR_INIT_EXPR)
       CONSTRUCTOR_MUTABLE_POISON (in CONSTRUCTOR)
+      OVL_HIDDEN_P (in OVERLOAD)
    3: (TREE_REFERENCE_EXPR) (in NON_LVALUE_EXPR) (commented-out).
       ICS_BAD_FLAG (in _CONV)
       FN_TRY_BLOCK_P (in TRY_BLOCK)
@@ -659,6 +660,8 @@ typedef struct ptrmem_cst * ptrmem_cst_t;
 
 /* If set, this was imported in a using declaration.   */
 #define OVL_USING_P(NODE)	TREE_LANG_FLAG_1 (OVERLOAD_CHECK (NODE))
+/* If set, this overload is a hidden decl.  */
+#define OVL_HIDDEN_P(NODE)	TREE_LANG_FLAG_2 (OVERLOAD_CHECK (NODE))
 /* If set, this overload contains a nested overload.  */
 #define OVL_NESTED_P(NODE)	TREE_LANG_FLAG_3 (OVERLOAD_CHECK (NODE))
 /* If set, this overload was constructed during lookup.  */
@@ -729,15 +732,26 @@ class ovl_iterator
   {
     return TREE_CODE (ovl) == OVERLOAD && OVL_USING_P (ovl);
   }
+  bool hidden_p () const
+  {
+    return TREE_CODE (ovl) == OVERLOAD && OVL_HIDDEN_P (ovl);
+  }
+
+ public:
   tree remove_node (tree head)
   {
     return remove_node (head, ovl);
   }
+  tree reveal_node (tree head)
+  {
+    return reveal_node (head, ovl);
+  }
 
  private:
-  /* We make this a static function to avoid the address of the
+  /* We make these static functions to avoid the address of the
      iterator escaping the local context.  */
   static tree remove_node (tree head, tree node);
+  static tree reveal_node (tree ovl, tree node);
 };
 
 /* Iterator over a (potentially) 2 dimensional overload, which is
diff --git a/gcc/cp/name-lookup.c b/gcc/cp/name-lookup.c
index 89d4e2a..57d85a5 100644
--- a/gcc/cp/name-lookup.c
+++ b/gcc/cp/name-lookup.c
@@ -1077,6 +1077,26 @@ strip_using_decl (tree decl)
   return decl;
 }
 
+/* Return true if OVL is an overload for an anticipated builtin.  */
+
+static bool
+anticipated_builtin_p (tree ovl)
+{
+  if (TREE_CODE (ovl) != OVERLOAD)
+    return false;
+
+  if (!OVL_HIDDEN_P (ovl))
+    return false;
+
+  tree fn = OVL_FUNCTION (ovl);
+  gcc_checking_assert (DECL_ANTICIPATED (fn));
+
+  if (DECL_HIDDEN_FRIEND_P (fn))
+    return false;
+
+  return true;
+}
+
 /* BINDING records an existing declaration for a name in the current scope.
    But, DECL is another declaration for that same identifier in the
    same scope.  This is the `struct stat' hack whereby a non-typedef
@@ -1131,9 +1151,7 @@ supplement_binding_1 (cxx_binding *binding, tree decl)
 	   || target_bval == error_mark_node
 	   /* If TARGET_BVAL is anticipated but has not yet been
 	      declared, pretend it is not there at all.  */
-	   || (TREE_CODE (target_bval) == FUNCTION_DECL
-	       && DECL_ANTICIPATED (target_bval)
-	       && !DECL_HIDDEN_FRIEND_P (target_bval)))
+	   || anticipated_builtin_p (target_bval))
     binding->value = decl;
   else if (TREE_CODE (target_bval) == TYPE_DECL
 	   && DECL_ARTIFICIAL (target_bval)
@@ -1803,7 +1821,7 @@ set_local_extern_decl_linkage (tree decl, bool shadowed)
 	loc_value = NULL_TREE;
 
       for (ovl_iterator iter (loc_value); iter; ++iter)
-	if (!DECL_HIDDEN_P (*iter)
+	if (!iter.hidden_p ()
 	    && (TREE_STATIC (*iter) || DECL_EXTERNAL (*iter))
 	    && decls_match (*iter, decl))
 	  {
@@ -1931,15 +1949,34 @@ do_pushdecl (tree decl, bool is_friend)
 	if (iter.using_p ())
 	  ; /* Ignore using decls here.  */
 	else if (tree match = duplicate_decls (decl, *iter, is_friend))
-	  return match;
+	  {
+	    if (iter.hidden_p ()
+		&& match != error_mark_node
+		&& !DECL_HIDDEN_P (match))
+	      {
+		/* Unhiding a previously hidden decl.  */
+		tree head = iter.reveal_node (old);
+		if (head != old)
+		  {
+		    if (!ns)
+		      update_local_overload (binding, head);
+		    binding->value = head;
+		  }
+
+		if (TREE_CODE (match) == FUNCTION_DECL
+		    && DECL_EXTERN_C_P (match))
+		  /* We need to check and register the fn now.  */
+		  check_extern_c_conflict (match);
+	      }
+	    return match;
+	  }
 
       /* We are pushing a new decl.  */
 
-      /* Skip a hidden builtin we failed to match already.  */
-      if (old && TREE_CODE (old) == FUNCTION_DECL
-	  && DECL_ANTICIPATED (old)
-	  && !DECL_HIDDEN_FRIEND_P (old))
-	old = NULL_TREE;
+      /* Skip a hidden builtin we failed to match already.  There can
+	 only be one.  */
+      if (old && anticipated_builtin_p (old))
+	old = OVL_CHAIN (old);
 
       check_template_shadow (decl);
 
@@ -3045,8 +3082,7 @@ do_nonmember_using_decl (tree scope, tree name, tree *value_p, tree *type_p)
 		    found = true;
 		  else if (old.using_p ())
 		    continue; /* This is a using decl. */
-		  else if (DECL_ANTICIPATED (old_fn)
-			   && !DECL_HIDDEN_FRIEND_P (old_fn))
+		  else if (old.hidden_p () && !DECL_HIDDEN_FRIEND_P (old_fn))
 		    continue; /* This is an anticipated builtin.  */
 		  else if (!matching_fn_p (new_fn, old_fn))
 		    continue; /* Parameters do not match.  */
@@ -3069,9 +3105,7 @@ do_nonmember_using_decl (tree scope, tree name, tree *value_p, tree *type_p)
 	}
       else if (value
 	       /* Ignore anticipated builtins.  */
-	       && !(TREE_CODE (value) == FUNCTION_DECL
-		    && DECL_ANTICIPATED (value)
-		    && !DECL_HIDDEN_FRIEND_P (value))
+	       && !anticipated_builtin_p (value)
 	       && !decls_match (lookup.value, value))
 	diagnose_name_conflict (lookup.value, value);
       else
@@ -5244,7 +5278,7 @@ lookup_name_real_1 (tree name, int prefer_type, int nonclass, bool block_p,
 
 	if (binding)
 	  {
-	    if (hidden_name_p (binding))
+	    if (TREE_CODE (binding) == TYPE_DECL && DECL_HIDDEN_P (binding))
 	      {
 		/* A non namespace-scope binding can only be hidden in the
 		   presence of a local class, due to friend declarations.
diff --git a/gcc/cp/tree.c b/gcc/cp/tree.c
index 8490c81..5ae9601 100644
--- a/gcc/cp/tree.c
+++ b/gcc/cp/tree.c
@@ -2143,7 +2143,8 @@ ovl_copy (tree ovl)
   TREE_TYPE (result) = TREE_TYPE (ovl);
   OVL_FUNCTION (result) = OVL_FUNCTION (ovl);
   OVL_CHAIN (result) = OVL_CHAIN (ovl);
-  OVL_USING_P (ovl) = OVL_USING_P (ovl);
+  OVL_HIDDEN_P (result) = OVL_HIDDEN_P (ovl);
+  OVL_USING_P (result) = OVL_USING_P (ovl);
 
   return result;
 }
@@ -2156,14 +2157,16 @@ tree
 ovl_insert (tree fn, tree maybe_ovl, bool using_p)
 {
   bool copying = false; /* Checking use only.  */
-  int weight = using_p;
+  bool hidden_p = DECL_HIDDEN_P (fn);
+  int weight = (hidden_p << 1) | (using_p << 0);
 
   tree result = NULL_TREE;
   tree insert_after = NULL_TREE;
 
   /* Find insertion point.  */
   while (maybe_ovl && TREE_CODE (maybe_ovl) == OVERLOAD
-	 && (weight < OVL_USING_P (maybe_ovl)))
+	 && (weight < ((OVL_HIDDEN_P (maybe_ovl) << 1)
+		       | (OVL_USING_P (maybe_ovl) << 0))))
     {
       gcc_checking_assert (!OVL_LOOKUP_P (maybe_ovl)
 			   && (!OVL_USED_P (maybe_ovl) || !copying));
@@ -2181,9 +2184,11 @@ ovl_insert (tree fn, tree maybe_ovl, bool using_p)
     }
 
   tree trail = fn;
-  if (maybe_ovl || using_p || TREE_CODE (fn) == TEMPLATE_DECL)
+  if (maybe_ovl || using_p || hidden_p || TREE_CODE (fn) == TEMPLATE_DECL)
     {
       trail = ovl_make (fn, maybe_ovl);
+      if (hidden_p)
+	OVL_HIDDEN_P (trail) = true;
       if (using_p)
 	OVL_USING_P (trail) = true;
     }
@@ -2199,6 +2204,28 @@ ovl_insert (tree fn, tree maybe_ovl, bool using_p)
   return result;
 }
 
+/* NODE is an OVL_HIDDEN_P node which is now revealed.  */
+
+tree
+ovl_iterator::reveal_node (tree overload, tree node)
+{
+  /* We cannot have returned NODE as part of a lookup overload, so it
+     cannot be USED.  */
+  gcc_checking_assert (!OVL_USED_P (node));
+
+  OVL_HIDDEN_P (node) = false;
+  if (tree chain = OVL_CHAIN (node))
+    if (TREE_CODE (chain) == OVERLOAD
+	&& (OVL_USING_P (chain) || OVL_HIDDEN_P (chain)))
+      {
+	/* The node needs moving, and the simplest way is to remove it
+	   and reinsert.  */
+	overload = remove_node (overload, node);
+	overload = ovl_insert (OVL_FUNCTION (node), overload);
+      }
+  return overload;
+}
+
 /* NODE is on the overloads of OVL.  Remove it.  If a predecessor is
    OVL_USED_P we must copy OVL nodes, because those are immutable.
    The removed node is unaltered and may continue to be iterated
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index f536dda..d8d16ee 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,8 @@
 2017-05-23  Nathan Sidwell  <nathan@acm.org>
 
+	* g++.dg/lookup/extern-c-hidden.C: New.
+	* g++.dg/lookup/extern-redecl1.C: New.
+
 	PR c++/80866
 	* g++.dg/parse/pr80866.C: New.
 
diff --git a/gcc/testsuite/g++.dg/lookup/extern-c-hidden.C b/gcc/testsuite/g++.dg/lookup/extern-c-hidden.C
new file mode 100644
index 0000000..a03dea0
--- /dev/null
+++ b/gcc/testsuite/g++.dg/lookup/extern-c-hidden.C
@@ -0,0 +1,11 @@
+// Make sure unhidding an extern-c still checks it is compatible
+
+extern "C" float fabsf (float);  // { dg-error "conflicts with previous declaration" }
+
+namespace Bob 
+{
+  extern "C" float fabsf (float, float); // { dg-error "C language" }
+  extern "C" double fabs (double, double); // { dg-error "conflicts with previous declaration" }
+}
+
+extern "C" double fabs (double); // { dg-error "C language" }
diff --git a/gcc/testsuite/g++.dg/lookup/extern-redecl1.C b/gcc/testsuite/g++.dg/lookup/extern-redecl1.C
new file mode 100644
index 0000000..18e675b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/lookup/extern-redecl1.C
@@ -0,0 +1,18 @@
+extern int X; // { dg-message "previous declaration" }
+extern int Y (int);  // { dg-message "previous declaration" }
+extern int Y (float);
+
+static int Z (int s)
+{
+  return s;
+}
+
+void Foo ()
+{
+  extern char X; // { dg-error "local external declaration" }
+  extern char Y (int); // { dg-error "local external declaration" }
+  extern int Y (float);
+  extern void Y (double);
+  extern char Z (int);
+}
+