analyzer: fixes to memcpy [PR103872]

analyzer: fixes to memcpy [PR103872]

PR analyzer/103872 reports a failure of gcc.dg/analyzer/pr103526.c on
riscv64-unknown-elf-gcc.  The issue is that I wrote the test on x86_64
where a memcpy in the test is optimized to a write to a read/write pair,
whereas due to alignment differences the analyzer can see it as a
memcpy call, revealing problems with the analyzer's implementation
of memcpy.

This patch reimplements region_model::impl_call_memcpy in terms of a
get_store_value followed by a set_value, fixing the issue.

gcc/analyzer/ChangeLog:
	PR analyzer/103872
	* region-model-impl-calls.cc (region_model::impl_call_memcpy):
	Reimplement in terms of a get_store_value followed by a set_value.

gcc/testsuite/ChangeLog:
	PR analyzer/103872
	* gcc.dg/analyzer/memcpy-1.c: Add alternate versions of test cases
	in which the calls to memcpy are hidden from the optimizer.  Add
	further test cases.
	* gcc.dg/analyzer/taint-size-1.c: Add test coverage for memcpy
	with tainted size.

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