analyzer: fix missing check for uninit of return values

analyzer: fix missing check for uninit of return values

When moving the -fanalyzer tests for -ftrivial-auto-var-init to the
"torture" subdirectory of gcc.dg/analyzer I noticed that -fanalyzer
wasn't always properly checking for initialization of return values.

The issue was that some "return" handling was using
region_model::copy_region to copy to the RESULT_DECL, and copy_region
wasn't checking for poisoned svalues.

This patch eliminates region_model::copy_region in favor of simply
doing a get_ravlue/set_value pair, fixing the issue.

gcc/analyzer/ChangeLog:
	* region-model.cc (region_model::on_return): Replace usage of
	copy_region with get_rvalue/set_value pair.
	(region_model::pop_frame): Likewise.
	(selftest::test_compound_assignment): Likewise.
	* region-model.h (region_model::copy_region): Delete decl.
	* region.cc (region_model::copy_region): Delete.

gcc/testsuite/ChangeLog:
	* gcc.dg/analyzer/torture/ubsan-1.c: Add missing return stmts.
	* gcc.dg/analyzer/uninit-trivial-auto-var-init-pattern.c: Move
	to...
	* gcc.dg/analyzer/torture/uninit-trivial-auto-var-init-pattern.c:
	...here.
	* gcc.dg/analyzer/uninit-trivial-auto-var-init-uninitialized.c:
	Move to...
	* gcc.dg/analyzer/torture/uninit-trivial-auto-var-init-uninitialized.c:
	...here.
	* gcc.dg/analyzer/uninit-trivial-auto-var-init-zero.c: Move to...
	* gcc.dg/analyzer/torture/uninit-trivial-auto-var-init-zero.c: ...here.

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