PR analyzer/94378 reports a false -Wanalyzer-malloc-leak
when returning a struct containing a malloc-ed pointer.

The issue is that the assignment code was not handling
compound copies, only copying top-level values from region to region,
and not copying child values.

This patch introduces a region_model::copy_region function, using
it for assignments and when analyzing function return values.
It recursively copies nested values within structs, unions, and
arrays, fixing the bug.

gcc/analyzer/ChangeLog:
	PR analyzer/94378
	* checker-path.cc: Include "bitmap.h".
	* constraint-manager.cc: Likewise.
	* diagnostic-manager.cc: Likewise.
	* engine.cc: Likewise.
	(exploded_node::detect_leaks): Pass null region_id to pop_frame.
	* program-point.cc: Include "bitmap.h".
	* program-state.cc: Likewise.
	* region-model.cc (id_set<region_id>::id_set): Convert to...
	(region_id_set::region_id_set): ...this.
	(svalue_id_set::svalue_id_set): New ctor.
	(region_model::copy_region): New function.
	(region_model::copy_struct_region): New function.
	(region_model::copy_union_region): New function.
	(region_model::copy_array_region): New function.
	(stack_region::pop_frame): Drop return value.  Add
	"result_dst_rid" param; if it is non-null, use copy_region to copy
	the result to it.  Rather than capture and pass a single "known
	used" return value to be used by purge_unused_values, instead
	gather and pass a set of known used return values.
	(root_region::pop_frame): Drop return value.  Add "result_dst_rid"
	param.
	(region_model::on_assignment): Use copy_region.
	(region_model::on_return): Likewise for the result.
	(region_model::on_longjmp): Pass null for pop_frame's
	result_dst_rid.
	(region_model::update_for_return_superedge): Pass the region for the
	return value of the call, if any, to pop_frame, rather than setting
	the lvalue for the lhs of the result.
	(region_model::pop_frame): Drop return value.  Add
	"result_dst_rid" param.
	(region_model::purge_unused_svalues): Convert third param from an
	svalue_id * to an svalue_id_set *, updating the initial populating
	of the "used" bitmap accordingly.  Don't remap it when done.
	(struct selftest::coord_test): New selftest fixture, extracted from...
	(selftest::test_dump_2): ...here.
	(selftest::test_compound_assignment): New selftest.
	(selftest::test_stack_frames): Pass null to new param of pop_frame.
	(selftest::analyzer_region_model_cc_tests): Call the new selftest.
	* region-model.h (class id_set): Delete template.
	(class region_id_set): Reimplement, using old id_set implementation.
	(class svalue_id_set): Likewise.  Convert from auto_sbitmap to
	auto_bitmap.
	(region::get_active_view): New accessor.
	(stack_region::pop_frame): Drop return value.  Add
	"result_dst_rid" param.
	(root_region::pop_frame): Likewise.
	(region_model::pop_frame): Likewise.
	(region_model::copy_region): New decl.
	(region_model::purge_unused_svalues): Convert third param from an
	svalue_id * to an svalue_id_set *.
	(region_model::copy_struct_region): New decl.
	(region_model::copy_union_region): New decl.
	(region_model::copy_array_region): New decl.

gcc/testsuite/ChangeLog:
	PR analyzer/94378
	* gcc.dg/analyzer/compound-assignment-1.c: New test.
	* gcc.dg/analyzer/compound-assignment-2.c: New test.
	* gcc.dg/analyzer/compound-assignment-3.c: New test.