C++ PATCH for c++/84707, ICE with nested anonymous namespace

[Marek Polacek]

Since Nathan's r253489 we seem to not use anon_identifier anymore; rather, the
DECL_NAME is simply NULL.  This crashed in duplicate_decls on this invalid code
because UDLIT_OPER_P was blithely used on a possibly null tree.  Other spots in
this function check this, too.

Bootstrapped/regtested on x86_64-linux, ok for trunk?

2018-03-05  Marek Polacek  <pola...@redhat.com>

        PR c++/84707
        * decl.c (duplicate_decls): Check DECL_NAME before accessing
        UDLIT_OPER_P.

        * g++.dg/cpp0x/inline-ns10.C: New test.

diff --git gcc/cp/decl.c gcc/cp/decl.c
index 1866e8f3574..b2e19a6549d 100644
--- gcc/cp/decl.c
+++ gcc/cp/decl.c
@@ -1410,7 +1410,9 @@ duplicate_decls (tree newdecl, tree olddecl, bool 
newdecl_is_friend)
       || TREE_TYPE (olddecl) == error_mark_node)
     return error_mark_node;
 
-  if (UDLIT_OPER_P (DECL_NAME (newdecl))
+  if (DECL_NAME (newdecl)
+      && DECL_NAME (olddecl)
+      && UDLIT_OPER_P (DECL_NAME (newdecl))
       && UDLIT_OPER_P (DECL_NAME (olddecl)))
     {
       if (TREE_CODE (newdecl) == TEMPLATE_DECL
diff --git gcc/testsuite/g++.dg/cpp0x/inline-ns10.C 
gcc/testsuite/g++.dg/cpp0x/inline-ns10.C
index e69de29bb2d..3ab425f7be4 100644
--- gcc/testsuite/g++.dg/cpp0x/inline-ns10.C
+++ gcc/testsuite/g++.dg/cpp0x/inline-ns10.C
@@ -0,0 +1,8 @@
+// PR c++/84707
+// { dg-do compile { target c++11 } }
+
+inline namespace {
+  namespace {}
+}
+
+namespace {} // { dg-error "conflicts" }

        Marek