[Bug middle-end/60418] [4.9 Regression] 435.gromacs in SPEC CPU 2006 is miscompiled

["hjl.tools at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60418

--- Comment #1 from H.J. Lu <hjl.tools at gmail dot com> ---
Do we need to verify that basic block DEST has a single predecessor?
This patch works for me:

diff --git a/gcc/tree-cfgcleanup.c b/gcc/tree-cfgcleanup.c
index 926d300..0ed15df 100644
--- a/gcc/tree-cfgcleanup.c
+++ b/gcc/tree-cfgcleanup.c
@@ -316,6 +316,8 @@ tree_forwarder_block_p (basic_block bb, bool phi_wanted)
       /* Protect loop preheaders and latches if requested.  */
       if (dest->loop_father->header == dest)
   {
+    if (single_pred_p (dest))
+      {
         if (bb->loop_father == dest->loop_father)
      {
        if (loops_state_satisfies_p (LOOPS_HAVE_SIMPLE_LATCHES))
@@ -329,6 +331,7 @@ tree_forwarder_block_p (basic_block bb, bool phi_wanted)
      }
         else if (bb->loop_father == loop_outer (dest->loop_father))
      return !loops_state_satisfies_p (LOOPS_HAVE_PREHEADERS);
+      }
     /* Always preserve other edges into loop headers that are
        not simple latches or preheaders.  */
     return false;