analyzer: add support for plugin-supplied known function behaviors

analyzer: add support for plugin-supplied known function behaviors

This patch adds the ability for plugins to register "known functions"
with the analyzer, identified by name.  If -fanalyzer sees a call to
such a function (with no body), it will use a plugin-provided subclass
of the new known_function abstract base class to model the possible
outcomes of the function call.

gcc/ChangeLog:
	* Makefile.in (ANALYZER_OBJS): Add
	analyzer/known-function-manager.o.

gcc/analyzer/ChangeLog:
	* analyzer.h (class known_function_manager): New forward decl.
	(class known_function): New.
	(plugin_analyzer_init_iface::register_known_function): New.
	* engine.cc: Include "analyzer/known-function-manager.h".
	(plugin_analyzer_init_impl::plugin_analyzer_init_impl): Add
	known_fn_mgr param.
	(plugin_analyzer_init_impl::register_state_machine): Add
	LOC_SCOPE.
	(plugin_analyzer_init_impl::register_known_function): New.
	(plugin_analyzer_init_impl::m_known_fn_mgr): New.
	(impl_run_checkers): Update plugin callback invocation to use
	eng's known_function_manager.
	* known-function-manager.cc: New file.
	* known-function-manager.h: New file.
	* region-model-manager.cc
	(region_model_manager::region_model_manager): Pass logger to
	m_known_fn_mgr's ctor.
	* region-model.cc (region_model::update_for_zero_return): New.
	(region_model::update_for_nonzero_return): New.
	(maybe_simplify_upper_bound): New.
	(region_model::maybe_get_copy_bounds): New.
	(region_model::get_known_function): New.
	(region_model::on_call_pre): Handle plugin-supplied known
	functions.
	* region-model.h: Include "analyzer/known-function-manager.h".
	(region_model_manager::get_known_function_manager): New.
	(region_model_manager::m_known_fn_mgr): New.
	(call_details::get_model): New accessor.
	(region_model::maybe_get_copy_bounds): New decl.
	(region_model::update_for_zero_return): New decl.
	(region_model::update_for_nonzero_return): New decl.
	(region_model::get_known_function): New decl.
	(region_model::get_known_function_manager): New.

gcc/testsuite/ChangeLog:
	* gcc.dg/plugin/analyzer_known_fns_plugin.c: New test plugin.
	* gcc.dg/plugin/known-fns-1.c: New test.
	* gcc.dg/plugin/plugin.exp (plugin_test_list): Add the new plugin
	and test.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>