RFA: PATCH to tree-inline.c:remap_decls for c++/70353 (ICE with __func__ and constexpr)

[Jason Merrill <jason at redhat dot com>]

The constexpr evaluation code uses the inlining code to remap the 
constexpr function body for evaluation so that recursion works properly. 
 In this testcase __func__ is declared as a static local variable, so 
rather than remap it, remap_decls tries to add it to the local_decls 
list for the function we're inlining into.  But there is no such 
function in this case, so we crash.

Avoid the add_local_decl call when cfun is null avoids the ICE (thanks 
Jakub), but results in an undefined symbol.  Calling 
varpool_node::finalize_decl instead allows cgraph to handle the 
reference from 'c' properly.

OK if testing passes?

commit d875b432434be92ab345c3851fa3ba4bef738399
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Mar 28 17:14:43 2016 -0400

    	PR c++/70353
    	* tree-inline.c (remap_decls): Use varpool_node::finalize_decl if
    	cfun is null.

diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-__func__2.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-__func__2.C
new file mode 100644
index 0000000..e678290
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-__func__2.C
@@ -0,0 +1,13 @@
+// PR c++/70353
+// { dg-do link { target c++11 } }
+
+constexpr const char* ce ()
+{
+  return __func__;
+}
+
+const char *c = ce();
+
+int main()
+{
+}
diff --git a/gcc/tree-inline.c b/gcc/tree-inline.c
index 9d4f8f7..74b0ca9 100644
--- a/gcc/tree-inline.c
+++ b/gcc/tree-inline.c
@@ -614,10 +614,16 @@ remap_decls (tree decls, vec<tree, va_gc> **nonlocalized_list,
       if (can_be_nonlocal (old_var, id))
 	{
 	  /* We need to add this variable to the local decls as otherwise
-	     nothing else will do so.  */
+	     nothing else will do so.  If we're not in a function,
+	     tell cgraph about it.  */
 	  if (TREE_CODE (old_var) == VAR_DECL
 	      && ! DECL_EXTERNAL (old_var))
-	    add_local_decl (cfun, old_var);
+	    {
+	      if (cfun)
+		add_local_decl (cfun, old_var);
+	      else
+		varpool_node::finalize_decl (old_var);
+	    }
 	  if ((!optimize || debug_info_level > DINFO_LEVEL_TERSE)
 	      && !DECL_IGNORED_P (old_var)
 	      && nonlocalized_list)