re PR tree-optimization/70614 (GCC gets stuck with -O)

2016-04-14  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/70614
	* tree-scalar-evolution.c (analyze_evolution_in_loop): Terminate
	loop if the evolution dropped to chrec_dont_know.
	(interpret_condition_phi): Likewise.

From-SVN: r234972

gcc/ChangeLog

 2016-04-14  Richard Biener  <rguenther@suse.de>
 
+	PR tree-optimization/70614
+	* tree-scalar-evolution.c (analyze_evolution_in_loop): Terminate
+	loop if the evolution dropped to chrec_dont_know.
+	(interpret_condition_phi): Likewise.
+
+2016-04-14  Richard Biener  <rguenther@suse.de>
+
 	PR tree-optimization/70623
 	* tree-ssa-pre.c (changed_blocks): Make global ...
 	(compute_antic): ... local here.  Move and fix worklist

gcc/tree-scalar-evolution.c

@@ -1510,6 +1510,9 @@ analyze_evolution_in_loop (gphi *loop_phi_node,
       /* When there are multiple back edges of the loop (which in fact never
 	 happens currently, but nevertheless), merge their evolutions.  */
       evolution_function = chrec_merge (evolution_function, ev_fn);
+
+      if (evolution_function == chrec_dont_know)
+	break;
     }
 
   if (dump_file && (dump_flags & TDF_SCEV))
@@ -1687,6 +1690,8 @@ interpret_condition_phi (struct loop *loop, gphi *condition_phi)
 	(loop, PHI_ARG_DEF (condition_phi, i));
 
       res = chrec_merge (res, branch_chrec);
+      if (res == chrec_dont_know)
+	break;
     }
 
   return res;