analyzer: : Refactor callstring to work with pairs of supernodes.

analyzer: : Refactor callstring to work with pairs of supernodes.

2021-07-25  Ankur Saini  <arsenic@sourceware.org>

gcc/analyzer/ChangeLog:
	* call-string.cc (call_string::element_t::operator==): New operator.
	(call_String::element_t::operator!=): New operator.
	(call_string::element_t::get_caller_function): New function.
	(call_string::element_t::get_callee_function): New function.
	(call_string::call_string): Refactor to Initialise m_elements.
	(call_string::operator=): Refactor to work with m_elements.
	(call_string::operator==): Likewise.
	(call_string::to_json): Likewise.
	(call_string::hash): Refactor to hash e.m_caller.
	(call_string::push_call): Refactor to work with m_elements.
	(call_string::push_call): New overload to push call via supernodes.
	(call_string::pop): Refactor to work with m_elements.
	(call_string::calc_recursion_depth): Likewise.
	(call_string::cmp): Likewise.
	(call_string::validate): Likewise.
	(call_string::operator[]): Likewise.
	* call-string.h (class supernode): New forward decl.
	(struct call_string::element_t): New struct.
	(call_string::call_string): Refactor to initialise m_elements.
	(call_string::bool empty_p): Refactor to work with m_elements.
	(call_string::get_callee_node): New decl.
	(call_string::get_caller_node): New decl.
	(m_elements): Replaces m_return_edges.
	* program-point.cc (program_point::get_function_at_depth): Refactor to
	work with new call-string format.
	(program_point::validate): Likewise.
	(program_point::on_edge): Likewise.