Avoid redundant entries in modref access lists.

Avoid redundant entries in modref access lists.

In PR101296 Richard noticed that modref is giving up on analysis in milc by
hitting --param=modref-max-accesses limit.  While cleaning up original modref
patch I removed code that tried to do smart things while merging accesses
because it had bugs and wanted to reimplement it later which I later forgot.

This patch adds logic that avoids adding access and its subaccess to the list
which is just waste of memory and compile time.  Incrementally I will add logic
merging the ranges.

gcc/ChangeLog:

2021-08-23  Jan Hubicka  <hubicka@ucw.cz>

	* ipa-modref-tree.h (modref_access_node::range_info_useful_p):
	Improve range compare.
	(modref_access_node::contains): New member function.
	(modref_access_node::search): Remove.
	(modref_access_node::insert): Be smarter about subaccesses.

gcc/testsuite/ChangeLog:

2021-08-23  Jan Hubicka  <hubicka@ucw.cz>

	* gcc.dg/tree-ssa/modref-7.c: New test.