coroutines: Do not assume parms are named [PR94752].

Parameters to user-defined coroutines might be unnamed.
In that case, we must synthesize a name for the coroutine
frame copy.

gcc/cp/ChangeLog:

2020-04-26  Iain Sandoe  <iain@sandoe.co.uk>

	PR c++/94752
	* coroutines.cc (morph_fn_to_coro): Ensure that
	unnamed function params have a usable and distinct
	frame field name.

gcc/testsuite/ChangeLog:

2020-04-26  Iain Sandoe  <iain@sandoe.co.uk>

	PR c++/94752
	* g++.dg/coroutines/pr94752.C: New test.

gcc/cp/ChangeLog

+2020-04-26  Iain Sandoe  <iain@sandoe.co.uk>
+
+	PR c++/94752
+	* coroutines.cc (morph_fn_to_coro): Ensure that
+	unnamed function params have a usable and distinct
+	frame field name.
+
 2020-04-24  Jason Merrill  <jason@redhat.com>
 
 	PR c++/94583

gcc/cp/coroutines.cc

@@ -3653,6 +3653,7 @@ morph_fn_to_coro (tree orig, tree *resumer, tree *destroyer)
 	  when we see uses.  */
       param_uses = new hash_map<tree, param_info>;
 
+      unsigned no_name_parm = 0;
       for (tree arg = DECL_ARGUMENTS (orig); arg != NULL;
 	   arg = DECL_CHAIN (arg))
 	{
@@ -3693,8 +3694,14 @@ morph_fn_to_coro (tree orig, tree *resumer, tree *destroyer)
 	    parm.frame_type = actual_type;
 	  parm.this_ptr = is_this_parameter (arg);
 	  parm.trivial_dtor = TYPE_HAS_TRIVIAL_DESTRUCTOR (parm.frame_type);
-	  tree pname = DECL_NAME (arg);
-	  char *buf = xasprintf ("__parm.%s", IDENTIFIER_POINTER (pname));
+	  char *buf;
+	  if (DECL_NAME (arg))
+	    {
+	      tree pname = DECL_NAME (arg);
+	      buf = xasprintf ("__parm.%s", IDENTIFIER_POINTER (pname));
+	    }
+	  else
+	    buf = xasprintf ("__unnamed_parm.%d", no_name_parm++);
 	  parm.field_id = coro_make_frame_entry
 	    (&field_list, buf, actual_type, DECL_SOURCE_LOCATION (arg));
 	  free (buf);

gcc/testsuite/ChangeLog

+2020-04-26  Iain Sandoe  <iain@sandoe.co.uk>
+
+	PR c++/94752
+	* g++.dg/coroutines/pr94752.C: New test.
+
 2020-04-26  Thomas Koenig  <tkoenig@gcc.gnu.org>
 
 	PR fortran/94737

gcc/testsuite/g++.dg/coroutines/pr94752.C

+//  { dg-additional-options  "-w" }
+
+#include "coro.h"
+
+using namespace std;
+
+struct task {
+    struct promise_type {
+        promise_type() {}
+        task get_return_object() { return {}; }
+        suspend_never initial_suspend() { return {}; }
+        suspend_never final_suspend() { return {}; }
+        void return_void() {}
+        void unhandled_exception() {}
+    };
+};
+
+task foo(int) {
+    co_return;
+}