Detect EAF flags in ipa-modref

Detect EAF flags in ipa-modref

A minimal patch for the EAF flags discovery.  It works only in local ipa-modref
and gives up on cyclic SSA graphs.  It improves pt_solution_includes
disambiguations twice.

gcc/Changelog:

	* gimple.c: Include ipa-modref-tree.h and ipa-modref.h.
	(gimple_call_arg_flags): Use modref to determine flags.
	* ipa-modref.c: Include gimple-ssa.h, tree-phinodes.h,
	tree-ssa-operands.h, stringpool.h and tree-ssanames.h.
	(analyze_ssa_name_flags): Declare.
	(modref_summary::useful_p): Summary is also useful if arg flags are
	known.
	(dump_eaf_flags): New function.
	(modref_summary::dump): Use it.
	(get_modref_function_summary): Be read for current_function_decl
	being NULL.
	(memory_access_to): New function.
	(deref_flags): New function.
	(call_lhs_flags): New function.
	(analyze_parms): New function.
	(analyze_function): Use it.
	* ipa-modref.h (struct modref_summary): Add arg_flags.
	* doc/invoke.texi (ipa-modref-max-depth): Document.
	* params.opt (ipa-modref-max-depth): New param.