[PATCH] Disable -Wunused warning for artificial decls (PR sanitizer/66452)

[Marek Polacek]

This PR is about a bogus -Wunused-variable warning about an internal
structure (*.Lubsan_data*), exposed by the debug-early merge.

I think the "defined but not used" warning should not be allowed for
the compiler-generated entities.

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

2015-06-08  Marek Polacek  <pola...@redhat.com>

        PR sanitizer/66452
        * toplev.c (check_global_declaration): Don't warn about artificial
        decls.

        * g++.dg/ubsan/pr66452.C: New test.

diff --git gcc/testsuite/g++.dg/ubsan/pr66452.C 
gcc/testsuite/g++.dg/ubsan/pr66452.C
index e69de29..473543c 100644
--- gcc/testsuite/g++.dg/ubsan/pr66452.C
+++ gcc/testsuite/g++.dg/ubsan/pr66452.C
@@ -0,0 +1,16 @@
+// PR sanitizer/66452
+// { dg-do compile }
+// { dg-options "-Wall -fsanitize=undefined" }
+
+class A {
+public:
+  A(int);
+};
+class B {
+  A m_fn1() const;
+};
+A B::m_fn1() const {
+  for (int i = 0;i;)
+    ;
+  return 0;
+}
diff --git gcc/toplev.c gcc/toplev.c
index fd2ac4e..eb8b8ac 100644
--- gcc/toplev.c
+++ gcc/toplev.c
@@ -534,6 +534,7 @@ check_global_declaration (tree decl)
         to handle multiple external decls in different scopes.  */
       && ! (DECL_NAME (decl) && TREE_USED (DECL_NAME (decl)))
       && ! DECL_EXTERNAL (decl)
+      && ! DECL_ARTIFICIAL (decl)
       && ! TREE_PUBLIC (decl)
       /* A volatile variable might be used in some non-obvious way.  */
       && ! TREE_THIS_VOLATILE (decl)

        Marek