Re: [C++ PATCH] Fix up decl_in_std_namespace_p handling of --enable-symvers=gnu-versioned-namespace

[Jakub Jelinek <jakub at redhat dot com>]

On Fri, Oct 25, 2019 at 10:44:18AM -0400, Marek Polacek wrote:
> That is... sneaky.  I guess I/we need to test with
> --enable-symvers=gnu-versioned-namespace every now and then.

Indeed.

> Probably deserves a comment.

Ok, here it is with a comment, bootstrapped/regtested again last night:

2019-10-30  Jakub Jelinek  <jakub@redhat.com>

	* typeck.c (decl_in_std_namespace_p): Return true also for decls
	in inline namespaces inside of std namespace.

	* g++.dg/cpp0x/Wpessimizing-move6.C: New test.

--- gcc/cp/typeck.c.jj	2019-10-23 20:38:00.022871653 +0200
+++ gcc/cp/typeck.c	2019-10-24 11:36:14.982981481 +0200
@@ -9395,8 +9395,19 @@ maybe_warn_about_returning_address_of_lo
 bool
 decl_in_std_namespace_p (tree decl)
 {
-  return (decl != NULL_TREE
-	  && DECL_NAMESPACE_STD_P (decl_namespace_context (decl)));
+  while (decl)
+    {
+      decl = decl_namespace_context (decl);
+      if (DECL_NAMESPACE_STD_P (decl))
+	return true;
+      /* Allow inline namespaces inside of std namespace, e.g. with
+	 --enable-symvers=gnu-versioned-namespace std::forward would be
+	 actually std::_8::forward.  */
+      if (!DECL_NAMESPACE_INLINE_P (decl))
+	return false;
+      decl = CP_DECL_CONTEXT (decl);
+    }
+  return false;
 }
 
 /* Returns true if FN, a CALL_EXPR, is a call to std::forward.  */
--- gcc/testsuite/g++.dg/cpp0x/Wpessimizing-move6.C.jj	2019-10-24 11:26:17.535148996 +0200
+++ gcc/testsuite/g++.dg/cpp0x/Wpessimizing-move6.C	2019-10-24 11:27:17.359232014 +0200
@@ -0,0 +1,135 @@
+// PR c++/86981
+// { dg-do compile { target c++11 } }
+// { dg-options "-Wpessimizing-move" }
+
+// Define std::move.
+namespace std {
+  inline namespace _8 { }
+  namespace _8 {
+    template<typename _Tp>
+      struct remove_reference
+      { typedef _Tp   type; };
+
+    template<typename _Tp>
+      struct remove_reference<_Tp&>
+      { typedef _Tp   type; };
+
+    template<typename _Tp>
+      struct remove_reference<_Tp&&>
+      { typedef _Tp   type; };
+
+    template<typename _Tp>
+      constexpr typename std::remove_reference<_Tp>::type&&
+      move(_Tp&& __t) noexcept
+      { return static_cast<typename std::remove_reference<_Tp>::type&&>(__t); }
+  }
+}
+
+struct T {
+  T() { }
+  T(const T&) { }
+  T(T&&) { }
+};
+struct U {
+  U() { }
+  U(const U&) { }
+  U(U&&) { }
+  U(T) { }
+};
+
+T g;
+
+T
+fn1 ()
+{
+  T t;
+  return std::move (t); // { dg-warning "moving a local object in a return statement prevents copy elision" }
+}
+
+T
+fn2 ()
+{
+  // Not a local variable.
+  return std::move (g);
+}
+
+int
+fn3 ()
+{
+  int i = 42;
+  // Not a class type.
+  return std::move (i);
+}
+
+T
+fn4 (bool b)
+{
+  T t;
+  if (b)
+    throw std::move (t);
+  return std::move (t); // { dg-warning "moving a local object in a return statement prevents copy elision" }
+}
+
+T
+fn5 (T t)
+{
+  // Function parameter; std::move is redundant but not pessimizing.
+  return std::move (t);
+}
+
+U
+fn6 (T t, U u, bool b)
+{
+  if (b)
+    return std::move (t);
+  else
+    // Function parameter; std::move is redundant but not pessimizing.
+    return std::move (u);
+}
+
+U
+fn6 (bool b)
+{
+  T t;
+  U u;
+  if (b)
+    return std::move (t);
+  else
+    return std::move (u); // { dg-warning "moving a local object in a return statement prevents copy elision" }
+}
+
+T
+fn7 ()
+{
+  static T t;
+  // Non-local; don't warn.
+  return std::move (t);
+}
+
+T
+fn8 ()
+{
+  return T();
+}
+
+T
+fn9 (int i)
+{
+  T t;
+
+  switch (i)
+    {
+    case 1:
+      return std::move ((t)); // { dg-warning "moving a local object in a return statement prevents copy elision" }
+    case 2:
+      return (std::move (t)); // { dg-warning "moving a local object in a return statement prevents copy elision" }
+    default:
+      return (std::move ((t))); // { dg-warning "moving a local object in a return statement prevents copy elision" }
+    }
+}
+
+int
+fn10 ()
+{
+  return std::move (42);
+}


	Jakub