re PR c++/85462 (internal compiler error: in inc_refcount_use, at cp/pt.c:8955)

	PR c++/85462
	* cp-tree.h (tinst_level): Remove in_system_header_p member,
	change refcount member from unsigned char to unsigned short,
	add refcount_infinity static data member, adjust comments.
	* pt.c (tinst_level::refcount_infinity): Define.
	(inc_refcount_use): Remove assert, don't increment if refcount
	is already refcount_infinity, adjust comment.
	(dec_refcount_use): Remove assert, don't decrement if refcount
	is refcount_infinity, adjust comment.
	(push_tinst_level_loc): Formatting fix.

	* g++.dg/cpp0x/pr85462.C: New test.

From-SVN: r259516

3 files changed, 35 insertions, 18 deletions

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index e4c3deb..099407b 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,16 @@
+2018-04-20  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/85462
+	* cp-tree.h (tinst_level): Remove in_system_header_p member,
+	change refcount member from unsigned char to unsigned short,
+	add refcount_infinity static data member, adjust comments.
+	* pt.c (tinst_level::refcount_infinity): Define.
+	(inc_refcount_use): Remove assert, don't increment if refcount
+	is already refcount_infinity, adjust comment.
+	(dec_refcount_use): Remove assert, don't decrement if refcount
+	is refcount_infinity, adjust comment.
+	(push_tinst_level_loc): Formatting fix.
+
 2018-04-19  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	PR c++/84611
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 8c5c84e..5af4928 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -5927,14 +5927,19 @@ struct GTY((chain_next ("%h.next"))) tinst_level {
   /* The location where the template is instantiated.  */
   location_t locus;
 
-  /* errorcount+sorrycount when we pushed this level.  */
+  /* errorcount + sorrycount when we pushed this level.  */
   unsigned short errors;
 
-  /* True if the location is in a system header.  */
-  bool in_system_header_p;
+  /* Count references to this object.  If refcount reaches
+     refcount_infinity value, we don't increment or decrement the
+     refcount anymore, as the refcount isn't accurate anymore.
+     The object can be still garbage collected if unreferenced from
+     anywhere, which might keep referenced objects referenced longer than
+     otherwise necessary.  Hitting the infinity is rare though.  */
+  unsigned short refcount;
 
-  /* Count references to this object.  */
-  unsigned char refcount;
+  /* Infinity value for the above refcount.  */
+  static const unsigned short refcount_infinity = (unsigned short) ~0;
 };
 
 bool decl_spec_seq_has_spec_p (const cp_decl_specifier_seq *, cp_decl_spec);
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 1370e21..e2a12b9 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -8945,15 +8945,14 @@ tinst_level::to_list ()
   return ret;
 }
 
-/* Increment OBJ's refcount.  */
+const unsigned short tinst_level::refcount_infinity;
+
+/* Increment OBJ's refcount unless it is already infinite.  */
 static tinst_level *
 inc_refcount_use (tinst_level *obj)
 {
-  if (obj)
-    {
-      ++obj->refcount;
-      gcc_assert (obj->refcount != 0);
-    }
+  if (obj && obj->refcount != tinst_level::refcount_infinity)
+    ++obj->refcount;
   return obj;
 }
 
@@ -8966,15 +8965,16 @@ tinst_level::free (tinst_level *obj)
   tinst_level_freelist ().free (obj);
 }
 
-/* Decrement OBJ's refcount.  If it reaches zero, release OBJ's DECL
-   and OBJ, and start over with the tinst_level object that used to be
-   referenced by OBJ's NEXT.  */
+/* Decrement OBJ's refcount if not infinite.  If it reaches zero, release
+   OBJ's DECL and OBJ, and start over with the tinst_level object that
+   used to be referenced by OBJ's NEXT.  */
 static void
 dec_refcount_use (tinst_level *obj)
 {
-  while (obj && !--obj->refcount)
+  while (obj
+	 && obj->refcount != tinst_level::refcount_infinity
+	 && !--obj->refcount)
     {
-      gcc_assert (obj->refcount+1 != 0);
       tinst_level *next = obj->next;
       tinst_level::free (obj);
       obj = next;
@@ -10145,8 +10145,7 @@ push_tinst_level_loc (tree tldcl, tree targs, location_t loc)
   new_level->tldcl = tldcl;
   new_level->targs = targs;
   new_level->locus = loc;
-  new_level->errors = errorcount+sorrycount;
-  new_level->in_system_header_p = in_system_header_at (input_location);
+  new_level->errors = errorcount + sorrycount;
   new_level->next = NULL;
   new_level->refcount = 0;
   set_refcount_ptr (new_level->next, current_tinst_level);