[Bug rtl-optimization/56181] [4.8 Regression] ICE in verify_loop_structure, at cfgloop.c:1581 with -ftracer

["mpolacek at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56181

--- Comment #6 from Marek Polacek <mpolacek at gcc dot gnu.org> 2013-02-05 16:33:45 UTC ---
Hmm, maybe I should have put it this way: we don't want to duplicate a BB,
which may be a preheader.  Does it sound sane?  Thus, something like

--- a/gcc/tracer.c
+++ b/gcc/tracer.c
@@ -217,6 +217,21 @@ find_trace (basic_block bb, basic_block *trace)
   return i;
 }

+/* Return true if basic block BB may be a preheader.  */
+
+static bool
+maybe_preheader_p (basic_block bb)
+{
+  edge e;
+  edge_iterator ei;
+
+  FOR_EACH_EDGE (e, ei, bb->succs)
+    if (e->dest->loop_father->header == e->dest)
+      return true;
+
+  return false;
+}
+
 /* Look for basic blocks in frequency order, construct traces and tail
duplicate
    if profitable.  */

@@ -310,7 +325,8 @@ tail_duplicate (void)
          not profitable and it might create a loop with multiple
          entries or at least rotate the loop.  */
           && (!current_loops
-          || bb2->loop_father->header != bb2))
+          || bb2->loop_father->header != bb2)
+          && !maybe_preheader_p (bb2))
         {
           edge e;
           basic_block copy;