c++: duplicate block-scope extern [PR 97877]

c++: duplicate block-scope extern [PR 97877]

[Nathan Sidwell]

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We ICED	with a duplicated block-scope extern, as duplicate_decls was
dropping the decl_lang_specific	of olddecl.  Simplys adding
appropriate retrofitting and copying turned out to be insufficient
because you can get a block-scope using	decl also matching the extern.
The latter seems a little suspicious and I have asked CWG for advice.
While there robustified the assert about releasing olddecls'
lang-specific -- if it had one,	the new	decl better have one.

         PR c++/97877
         gcc/cp/
         * decl.c (duplicate_decls): Deal with duplicated DECL_LOCAL_DECL_P
         decls.  Extend decl_lang_specific checking assert.
         gcc/testsuite/
         * g++.dg/lookup/pr97877.C: New.


pushing to trunk

-- 
Nathan Sidwell

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diff --git i/gcc/cp/decl.c w/gcc/cp/decl.c
index 89bae06cd6b..d90e9840f40 100644
--- i/gcc/cp/decl.c
+++ w/gcc/cp/decl.c
@@ -2452,6 +2452,20 @@ duplicate_decls (tree newdecl, tree olddecl, bool hiding, bool was_hidden)
   if (! DECL_COMDAT (olddecl))
     DECL_COMDAT (newdecl) = 0;
 
+  if (VAR_OR_FUNCTION_DECL_P (newdecl) && DECL_LOCAL_DECL_P (newdecl))
+    {
+      if (!DECL_LOCAL_DECL_P (olddecl))
+	/* This can happen if olddecl was brought in from the
+	   enclosing namespace via a using-decl.  The new decl is
+	   then not a block-scope extern at all.  */
+	DECL_LOCAL_DECL_P (newdecl) = false;
+      else
+	{
+	  retrofit_lang_decl (newdecl);
+	  DECL_LOCAL_DECL_ALIAS (newdecl) = DECL_LOCAL_DECL_ALIAS (olddecl);
+	}
+    }
+
   new_template_info = NULL_TREE;
   if (DECL_LANG_SPECIFIC (newdecl) && DECL_LANG_SPECIFIC (olddecl))
     {
@@ -2735,8 +2749,9 @@ duplicate_decls (tree newdecl, tree olddecl, bool hiding, bool was_hidden)
      with that from NEWDECL below.  */
   if (DECL_LANG_SPECIFIC (olddecl))
     {
-      gcc_assert (DECL_LANG_SPECIFIC (olddecl)
-		  != DECL_LANG_SPECIFIC (newdecl));
+      gcc_checking_assert (DECL_LANG_SPECIFIC (newdecl)
+			   && (DECL_LANG_SPECIFIC (olddecl)
+			       != DECL_LANG_SPECIFIC (newdecl)));
       ggc_free (DECL_LANG_SPECIFIC (olddecl));
     }