Fix phi arg location in find_implicit_erroneous_behavior

2017-07-20  Tom de Vries  <tom@codesourcery.com>

	PR tree-optimization/81489
	* gimple-ssa-isolate-paths.c (find_implicit_erroneous_behavior): Move
	read of phi arg location to before loop that modifies phi.

From-SVN: r250378

gcc/ChangeLog

+2017-07-20  Tom de Vries  <tom@codesourcery.com>
+
+	PR tree-optimization/81489
+	* gimple-ssa-isolate-paths.c (find_implicit_erroneous_behavior): Move
+	read of phi arg location to before loop that modifies phi.
+
 2017-07-20  Naveen H.S  <Naveen.Hurugalawadi@cavium.com>
 
 	* match.pd (((m1 >/</>=/<= m2) * d -> (m1 >/</>=/<= m2) ? d : 0):

gcc/gimple-ssa-isolate-paths.c

@@ -442,6 +442,8 @@ find_implicit_erroneous_behavior (void)
 	      if (!integer_zerop (op))
 		continue;
 
+	      location_t phi_arg_loc = gimple_phi_arg_location (phi, i);
+
 	      /* We've got a NULL PHI argument.  Now see if the
  	         PHI's result is dereferenced within BB.  */
 	      FOR_EACH_IMM_USE_STMT (use_stmt, iter, lhs)
@@ -454,7 +456,7 @@ find_implicit_erroneous_behavior (void)
 
 		  location_t loc = gimple_location (use_stmt)
 		    ? gimple_location (use_stmt)
-		    : gimple_phi_arg_location (phi, i);
+		    : phi_arg_loc;
 
 		  if (stmt_uses_name_in_undefined_way (use_stmt, lhs, loc))
 		    {