re PR tree-optimization/81455 (Compile-time hog w/ -O1 -funswitch-loops)

2017-07-25  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/81455
	* tree-ssa-loop-unswitch.c (find_loop_guard): Make sure to
	not walk in cycles when looking for guards.

	* gcc.dg/pr81455.c: New testcase.

From-SVN: r250518

gcc/ChangeLog

 2017-07-25  Richard Biener  <rguenther@suse.de>
 
+	PR tree-optimization/81455
+	* tree-ssa-loop-unswitch.c (find_loop_guard): Make sure to
+	not walk in cycles when looking for guards.
+
+2017-07-25  Richard Biener  <rguenther@suse.de>
+
 	PR tree-optimization/81529
 	* tree-vect-stmts.c (process_use): Disregard live induction PHIs
 	when optimizing backedge uses.

gcc/testsuite/ChangeLog

 2017-07-25  Richard Biener  <rguenther@suse.de>
 
+	PR tree-optimization/81455
+	* gcc.dg/pr81455.c: New testcase.
+
+2017-07-25  Richard Biener  <rguenther@suse.de>
+
 	PR tree-optimization/81529
 	* gfortran.dg/pr81529.f90: New testcase.
 

gcc/testsuite/gcc.dg/pr81455.c

+/* { dg-do compile } */
+/* { dg-options "-O -funswitch-loops" } */
+
+void
+jh (unsigned int aw, int sn)
+{
+  int xs;
+
+  for (xs = 0; xs < 1; ++xs)
+    aw &= 1;
+
+  while (aw < 1 || ++sn < 1)
+    {
+    }
+}

gcc/tree-ssa-loop-unswitch.c

@@ -582,8 +582,9 @@ find_loop_guard (struct loop *loop)
   gcond *cond;
   do
     {
+      basic_block next = NULL;
       if (single_succ_p (header))
-	header = single_succ (header);
+	next = single_succ (header);
       else
 	{
 	  cond = dyn_cast <gcond *> (last_stmt (header));
@@ -593,12 +594,16 @@ find_loop_guard (struct loop *loop)
 	  /* Make sure to skip earlier hoisted guards that are left
 	     in place as if (true).  */
 	  if (gimple_cond_true_p (cond))
-	    header = te->dest;
+	    next = te->dest;
 	  else if (gimple_cond_false_p (cond))
-	    header = fe->dest;
+	    next = fe->dest;
 	  else
 	    break;
 	}
+      /* Never traverse a backedge.  */
+      if (header->loop_father->header == next)
+	return NULL;
+      header = next;
     }
   while (1);
   if (!flow_bb_inside_loop_p (loop, te->dest)