re PR tree-optimization/72772 (Missed SCEV after pass reordering@236440)

2016-08-11  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/72772
	* cfgloopmanip.c (create_preheader): Use split_edge if there
	is a single loop entry, avoiding degenerate PHIs.

	* gcc.dg/graphite/pr35356-1.c: Adjust.
	* gcc.dg/tree-ssa/pr59597.c: Likewise.

From-SVN: r239357

gcc/ChangeLog

 2016-08-11  Richard Biener  <rguenther@suse.de>
 
+	PR tree-optimization/72772
+	* cfgloopmanip.c (create_preheader): Use split_edge if there
+	is a single loop entry, avoiding degenerate PHIs.
+
+2016-08-11  Richard Biener  <rguenther@suse.de>
+
 	* tree-ssa-threadbackward.c (pass_data_thread_jumps): Remove
 	unconditional TODO_cleanup_cfg.
 	(pass_thread_jumps::execute): Initialize loops, perform a CFG

gcc/cfgloopmanip.c

@@ -1497,7 +1497,7 @@ has_preds_from_loop (basic_block block, struct loop *loop)
 basic_block
 create_preheader (struct loop *loop, int flags)
 {
-  edge e, fallthru;
+  edge e;
   basic_block dummy;
   int nentry = 0;
   bool irred = false;
@@ -1544,9 +1544,14 @@ create_preheader (struct loop *loop, int flags)
 
   mfb_kj_edge = loop_latch_edge (loop);
   latch_edge_was_fallthru = (mfb_kj_edge->flags & EDGE_FALLTHRU) != 0;
-  fallthru = make_forwarder_block (loop->header, mfb_keep_just, NULL);
-  dummy = fallthru->src;
-  loop->header = fallthru->dest;
+  if (nentry == 1)
+    dummy = split_edge (single_entry);
+  else
+    {
+      edge fallthru = make_forwarder_block (loop->header, mfb_keep_just, NULL);
+      dummy = fallthru->src;
+      loop->header = fallthru->dest;
+    }
 
   /* Try to be clever in placing the newly created preheader.  The idea is to
      avoid breaking any "fallthruness" relationship between blocks.

gcc/testsuite/ChangeLog

+2016-08-11  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/72772
+	* gcc.dg/graphite/pr35356-1.c: Adjust.
+	* gcc.dg/tree-ssa/pr59597.c: Likewise.
+
 2016-08-11  Janne Blomqvist  <jb@gcc.gnu.org>
 
 	* gfortran.dg/random_7.f90: Take into account that the last seed

gcc/testsuite/gcc.dg/graphite/pr35356-1.c

@@ -34,4 +34,4 @@ if (n >= k + 1 && k >= 0) {
 
 */
 
-/* { dg-final { scan-tree-dump "if \\\(P_9 >= P_10 \\\+ 1 && P_10 >= 0\\\) \\\{" "graphite" } } */
+/* { dg-final { scan-tree-dump "if \\\(P_8 >= P_9 \\\+ 1 && P_9 >= 0\\\) \\\{" "graphite" } } */

gcc/testsuite/gcc.dg/tree-ssa/pr59597.c

@@ -54,5 +54,6 @@ main (int argc, char argv[])
   return crc;
 }
 
-/* { dg-final { scan-tree-dump "Cancelling" "vrp1" } } */
-
+/* { dg-final { scan-tree-dump-times "Registering jump thread" 3 "vrp1" } } */
+/* { dg-final { scan-tree-dump-not "joiner" "vrp1" } } */
+/* { dg-final { scan-tree-dump-times "Threaded jump" 3 "vrp1" } } */