re PR tree-optimization/63168 (loop header copying fails - not vectorized: latch block not empty)

2014-10-16  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/63168
	* tree-cfg.c (gimple_can_merge_blocks_p): Only protect
	latches if after merging they are no longer simple.
	* cfghooks.c (merge_blocks): Handle merging a latch block
	into another block.

	* gcc.dg/tree-ssa/loop-40.c: New testcase.

From-SVN: r216304

gcc/ChangeLog

+2014-10-16  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/63168
+	* tree-cfg.c (gimple_can_merge_blocks_p): Only protect
+	latches if after merging they are no longer simple.
+	* cfghooks.c (merge_blocks): Handle merging a latch block
+	into another block.
+
 2014-10-16  Alexander Ivchenko  <alexander.ivchenko@intel.com>
 	    Maxim Kuznetsov  <maxim.kuznetsov@intel.com>
 	    Anna Tikhonova  <anna.tikhonova@intel.com>

gcc/cfghooks.c

@@ -766,6 +766,11 @@ merge_blocks (basic_block a, basic_block b)
 	  add_bb_to_loop  (a, b->loop_father);
 	  a->loop_father->header = a;
 	}
+      /* If we merge a loop latch into its predecessor, update the loop
+         structure.  */
+      if (b->loop_father->latch
+	  && b->loop_father->latch == b)
+	b->loop_father->latch = a;
       remove_bb_from_loops (b);
     }
 

gcc/testsuite/ChangeLog

+2014-10-16  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/63168
+	* gcc.dg/tree-ssa/loop-40.c: New testcase.
+
 2014-10-16  Andreas Schwab  <schwab@suse.de>
 
 	* gcc.target/m68k/crash1.c: Fix implicit declaration.

gcc/testsuite/gcc.dg/tree-ssa/loop-40.c

+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-ch-details" } */
+
+int mymax2(int *it, int *end)
+{
+  int max = *it;
+  while (++it != end)
+    if (*it > max)
+      max = *it;
+  return max;
+}
+
+/* { dg-final { scan-tree-dump "Duplicating header" "ch" } } */
+/* { dg-final { cleanup-tree-dump "ch" } } */

gcc/tree-cfg.c

@@ -1674,8 +1674,12 @@ gimple_can_merge_blocks_p (basic_block a, basic_block b)
 	return false;
     }
 
-  /* Protect the loop latches.  */
-  if (current_loops && b->loop_father->latch == b)
+  /* Protect simple loop latches.  We only want to avoid merging
+     the latch with the loop header in this case.  */
+  if (current_loops
+      && b->loop_father->latch == b
+      && loops_state_satisfies_p (LOOPS_HAVE_SIMPLE_LATCHES)
+      && b->loop_father->header == a)
     return false;
 
   /* It must be possible to eliminate all phi nodes in B.  If ssa form