libstdc++: Define noop coroutine details private and inline [PR 95917]

This moves the __noop_coro_frame type, the __noop_coro_fr global
variable, and the __dummy_resume_destroy function from namespace scope,
replacing them with private members of the specialization
coroutine_handle<noop_coroutine_promise>.

The function and variable are also declared inline, so that they
generate no code unless used.

libstdc++-v3/ChangeLog:

	PR libstdc++/95917
	* include/std/coroutine (__noop_coro_frame): Replace with
	noop_coroutine_handle::__frame.
	(__dummy_resume_destroy): Define inline in __frame.
	(__noop_coro_fr): Replace with noop_coroutine_handle::_S_fr
	and define as inline.
	* testsuite/18_support/coroutines/95917.cc: New test.

2 files changed, 48 insertions, 13 deletions

diff --git a/libstdc++-v3/include/std/coroutine b/libstdc++-v3/include/std/coroutine
index 6e1cf14..2b635b9 100644
--- a/libstdc++-v3/include/std/coroutine
+++ b/libstdc++-v3/include/std/coroutine
@@ -249,16 +249,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   {
   };
 
-  void __dummy_resume_destroy() __attribute__((__weak__));
-  void __dummy_resume_destroy() {}
-
-  struct __noop_coro_frame
-  {
-    void (*__r)() = __dummy_resume_destroy;
-    void (*__d)() = __dummy_resume_destroy;
-    struct noop_coroutine_promise __p;
-  } __noop_coro_fr __attribute__((__weak__));
-
   // 17.12.4.1 Class noop_coroutine_promise
   /// [coroutine.promise.noop]
   template <>
@@ -284,7 +274,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       // [coroutine.handle.noop.promise], promise access
       noop_coroutine_promise& promise() const noexcept
-      { return __noop_coro_fr.__p; }
+      { return _S_fr.__p; }
 
       // [coroutine.handle.noop.address], address
       constexpr void* address() const noexcept { return _M_fr_ptr; }
@@ -292,13 +282,27 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     private:
       friend coroutine_handle noop_coroutine() noexcept;
 
-      coroutine_handle() = default;
+      struct __frame
+      {
+	static void __dummy_resume_destroy() { }
+
+	void (*__r)() = __dummy_resume_destroy;
+	void (*__d)() = __dummy_resume_destroy;
+	struct noop_coroutine_promise __p;
+      };
+
+      static __frame _S_fr;
 
-      void* _M_fr_ptr = (void*) &__noop_coro_fr;
+      explicit coroutine_handle() noexcept = default;
+
+      void* _M_fr_ptr = &_S_fr;
     };
 
   using noop_coroutine_handle = coroutine_handle<noop_coroutine_promise>;
 
+  inline noop_coroutine_handle::__frame
+  noop_coroutine_handle::_S_fr{};
+
   inline noop_coroutine_handle noop_coroutine() noexcept
   {
     return noop_coroutine_handle();
diff --git a/libstdc++-v3/testsuite/18_support/coroutines/95917.cc b/libstdc++-v3/testsuite/18_support/coroutines/95917.cc
new file mode 100644
index 0000000..5c9cf57
--- /dev/null
+++ b/libstdc++-v3/testsuite/18_support/coroutines/95917.cc
@@ -0,0 +1,31 @@
+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a -g0" }
+// { dg-do compile { target c++2a } }
+// { dg-final { scan-assembler-not "dummy_resume_destroy" } }
+// { dg-final { scan-assembler-not "noop_coro" } }
+
+#include <coroutine>
+
+// PR libstdc++/95917
+
+void
+test01()
+{
+  std::coroutine_handle<> h;
+}