Cleanup tree-ssa-alias and tree-ssa-dse use of modref summary

Cleanup tree-ssa-alias and tree-ssa-dse use of modref summary

Move code getting tree op from access_node and stmt to a common place.  I also
commonized logic to build ao_ref. While I was on it I also replaced FOR_EACH_*
by range for since they reads better.

gcc/ChangeLog:

2021-11-14  Jan Hubicka  <hubicka@ucw.cz>

	* ipa-modref-tree.c (modref_access_node::get_call_arg): New member
	function.
	(modref_access_node::get_ao_ref): Likewise.
	* ipa-modref-tree.h (modref_access_node::get_call_arg): Declare.
	(modref_access_node::get_ao_ref): Declare.
	* tree-ssa-alias.c (modref_may_conflict): Use new accessors.
	* tree-ssa-dse.c (dse_optimize_call): Use new accessors.

gcc/testsuite/ChangeLog:

2021-11-14  Jan Hubicka  <hubicka@ucw.cz>

	* c-c++-common/asan/null-deref-1.c: Update template.
	* c-c++-common/tsan/free_race.c: Update template.
	* c-c++-common/tsan/free_race2.c: Update template.
	* gcc.dg/ipa/ipa-sra-4.c: Update template.