PR ipa/61602 (ICE in single_use propagation)

Index: testsuite/gcc.dg/torture/pr61602.c
===================================================================
--- testsuite/gcc.dg/torture/pr61602.c	(revision 0)
+++ testsuite/gcc.dg/torture/pr61602.c	(revision 0)
@@ -0,0 +1,8 @@ 
+int a;
+int *b = &a, **c = &b;
+int
+main ()
+{
+  int **d = &b;
+  *d = 0;
+}
Index: cgraph.h
===================================================================
--- cgraph.h	(revision 218726)
+++ cgraph.h	(working copy)
@@ -2188,7 +2188,7 @@  void record_references_in_initializer (t
 
 /* In ipa.c  */
 void cgraph_build_static_cdtor (char which, tree body, int priority);
-void ipa_discover_readonly_nonaddressable_vars (void);
+bool ipa_discover_readonly_nonaddressable_vars (void);
 
 /* In varpool.c  */
 tree ctor_for_folding (tree);
Index: ipa.c
===================================================================
--- ipa.c	(revision 218730)
+++ ipa.c	(working copy)
@@ -714,14 +714,18 @@  set_readonly_bit (varpool_node *vnode, v
 /* Set writeonly bit and clear the initalizer, since it will not be needed.  */
 
 bool
-set_writeonly_bit (varpool_node *vnode, void *data ATTRIBUTE_UNUSED)
+set_writeonly_bit (varpool_node *vnode, void *data)
 {
   vnode->writeonly = true;
   if (optimize)
     {
       DECL_INITIAL (vnode->decl) = NULL;
       if (!vnode->alias)
-	vnode->remove_all_references ();
+	{
+	  if (vnode->num_references ())
+	    *(bool *)data = true;
+	  vnode->remove_all_references ();
+	}
     }
   return false;
 }
@@ -739,15 +743,18 @@  clear_addressable_bit (varpool_node *vno
 /* Discover variables that have no longer address taken or that are read only
    and update their flags.
 
+   Return true when unreachable symbol removan should be done.
+
    FIXME: This can not be done in between gimplify and omp_expand since
    readonly flag plays role on what is shared and what is not.  Currently we do
    this transformation as part of whole program visibility and re-do at
    ipa-reference pass (to take into account clonning), but it would
    make sense to do it before early optimizations.  */
 
-void
+bool
 ipa_discover_readonly_nonaddressable_vars (void)
 {
+  bool remove_p = false;
   varpool_node *vnode;
   if (dump_file)
     fprintf (dump_file, "Clearing variable flags:");
@@ -762,14 +769,16 @@  ipa_discover_readonly_nonaddressable_var
 	bool read = false;
 	bool explicit_refs = true;
 
-	process_references (vnode, &written, &address_taken, &read, &explicit_refs);
+	process_references (vnode, &written, &address_taken, &read,
+			    &explicit_refs);
 	if (!explicit_refs)
 	  continue;
 	if (!address_taken)
 	  {
 	    if (TREE_ADDRESSABLE (vnode->decl) && dump_file)
 	      fprintf (dump_file, " %s (non-addressable)", vnode->name ());
-	    vnode->call_for_node_and_aliases (clear_addressable_bit, NULL, true);
+	    vnode->call_for_node_and_aliases (clear_addressable_bit, NULL,
+					      true);
 	  }
 	if (!address_taken && !written
 	    /* Making variable in explicit section readonly can cause section
@@ -785,11 +794,13 @@  ipa_discover_readonly_nonaddressable_var
 	  {
 	    if (dump_file)
 	      fprintf (dump_file, " %s (write-only)", vnode->name ());
-	    vnode->call_for_node_and_aliases (set_writeonly_bit, NULL, true);
+	    vnode->call_for_node_and_aliases (set_writeonly_bit, &remove_p, 
+					     true);
 	  }
       }
   if (dump_file)
     fprintf (dump_file, "\n");
+  return remove_p;
 }
 
 /* Free inline summary.  */
Index: ipa-reference.c
===================================================================
--- ipa-reference.c	(revision 218726)
+++ ipa-reference.c	(working copy)
@@ -676,11 +676,12 @@  propagate (void)
     XCNEWVEC (struct cgraph_node *, symtab->cgraph_count);
   int order_pos;
   int i;
+  bool remove_p;
 
   if (dump_file)
     cgraph_node::dump_cgraph (dump_file);
 
-  ipa_discover_readonly_nonaddressable_vars ();
+  remove_p = ipa_discover_readonly_nonaddressable_vars ();
   generate_summary ();
 
   /* Propagate the local information through the call graph to produce
@@ -867,7 +868,7 @@  propagate (void)
   if (dump_file)
     splay_tree_delete (reference_vars_to_consider);
   reference_vars_to_consider = NULL;
-  return 0;
+  return remove_p ? TODO_remove_functions : 0;
 }
 
 /* Return true if we need to write summary of NODE. */