re PR tree-optimization/87693 (ICE in thread_around_empty_blocks, at tree-ssa-threadedge.c:984)

2018-10-23  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/87693
	* tree-ssa-threadedge.c (thread_around_empty_blocks): Handle
	the case we do not find the taken edge.

	* gcc.dg/torture/pr87693.c: New testcase.

From-SVN: r265413

gcc/ChangeLog

+2018-10-23  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/87693
+	* tree-ssa-threadedge.c (thread_around_empty_blocks): Handle
+	the case we do not find the taken edge.
+
 2018-10-22  Paul Koning  <ni1d@arrl.net>
 
 	* symtab.c (symtab_node::increase_alignment): Correct max

gcc/testsuite/ChangeLog

+2018-10-23  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/87693
+	* gcc.dg/torture/pr87693.c: New testcase.
+
 2018-10-23  Paul Thomas  <pault@gcc.gnu.org>
 
 	PR fortran/85603

gcc/testsuite/gcc.dg/torture/pr87693.c

+/* { dg-do compile } */
+
+void f (void);
+void g (void);
+void h (int a)
+{
+  void *p, **q;
+  if (a)
+    p = (void *)f;
+  else
+    p = (void *)g;
+  q = (void *)p;
+  if (*q == (void *)0)
+    goto *p;
+L0:
+  return;
+}

gcc/tree-ssa-threadedge.c

@@ -981,7 +981,8 @@ thread_around_empty_blocks (edge taken_edge,
       else
 	taken_edge = find_taken_edge (bb, cond);
 
-      if ((taken_edge->flags & EDGE_DFS_BACK) != 0)
+      if (!taken_edge
+	  || (taken_edge->flags & EDGE_DFS_BACK) != 0)
 	return false;
 
       if (bitmap_bit_p (visited, taken_edge->dest->index))