[patch c++]: Fix for PR c++/51344 - cc1plus hangs when compiling

[Kai Tietz]

Hello,

this hang is caused by an end-less loop in private_lookup_attribute
caused by double-chaining of attributes in decl2.c's
save_template_attributes function.  In save_template_attributes we
need to check that attribute-list isn't equal to late_attrs before
chaining them.

ChangeLog gcc/cp

2012-01-17  Kai Tietz  <kti...@redhat.com>

        PR c++/51344
        * decl2.c (save_template_attributes): Don't chain late-attributes with
        attribute-list, if they are same.

ChangeLog gcc/cp

2012-01-17  Kai Tietz  <kti...@redhat.com>

        g++.dg/torture/pr51344.C: New test.

Bootstrapped and regression tested for x86_64-unknown-linux-gnu,
x86_64-w64-mingw32, and i686-w64-mingw32. Ok for apply?

Regards,
Kai

Index: gcc/cp/decl2.c
===================================================================
--- gcc/cp/decl2.c      (revision 183106)
+++ gcc/cp/decl2.c      (working copy)
@@ -1202,7 +1202,8 @@

   /* Place the late attributes at the beginning of the attribute
      list.  */
-  TREE_CHAIN (tree_last (late_attrs)) = *q;
+  if (late_attrs != *q)
+    TREE_CHAIN (tree_last (late_attrs)) = *q;
   *q = late_attrs;

   if (!DECL_P (*decl_p) && *decl_p == TYPE_MAIN_VARIANT (*decl_p))

Index: gcc/gcc/testsuite/g++.dg/torture/pr51344.C
===================================================================
--- /dev/null
+++ gcc/gcc/testsuite/g++.dg/torture/pr51344.C
@@ -0,0 +1,9 @@
+/* { dg-do compile } */
+template <class T>
+class B
+{
+  friend __attribute__((cdecl)) A& operator >>(A& a, B& b)
+  {
+    return a;
+  }
+};