Const parameters are always unmodified

2016-05-18  Martin Jambor  <mjambor@suse.cz>

	PR ipa/69708
	* ipa-prop.c (parm_preserved_before_stmt_p): Return true for loads
	from TREE_READONLY parameters.

From-SVN: r236417

gcc/ChangeLog

 2016-05-18  Martin Jambor  <mjambor@suse.cz>
 
 	PR ipa/69708
+	* ipa-prop.c (parm_preserved_before_stmt_p): Return true for loads
+	from TREE_READONLY parameters.
+
+2016-05-18  Martin Jambor  <mjambor@suse.cz>
+
+	PR ipa/69708
 	* cgraph.h (cgraph_indirect_call_info): New field
 	guaranteed_unmodified.
 	* ipa-cp.c (ipa_get_indirect_edge_target_1): Also pass parameter value

gcc/ipa-prop.c

@@ -803,6 +803,11 @@ parm_preserved_before_stmt_p (struct ipa_func_body_info *fbi, int index,
   bool modified = false;
   ao_ref refd;
 
+  tree base = get_base_address (parm_load);
+  gcc_assert (TREE_CODE (base) == PARM_DECL);
+  if (TREE_READONLY (base))
+    return true;
+
   /* FIXME: FBI can be NULL if we are being called from outside
      ipa_node_analysis or ipcp_transform_function, which currently happens
      during inlining analysis.  It would be great to extend fbi's lifetime and