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

[mpolacek at gcc dot 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;