analyzer: Fix allocation size false positive on conjured svalue [PR109577]

analyzer: Fix allocation size false positive on conjured svalue [PR109577]

Currently, the analyzer tries to prove that the allocation size is a
multiple of the pointee's type size.  This patch reverses the behavior
to try to prove that the expression is not a multiple of the pointee's
type size.  With this change, each unhandled case should be gracefully
considered as correct.  This fixes the bug reported in PR 109577 by
Paul Eggert.

Regression-tested on Linux x86-64 with -m32 and -m64.

2023-06-09  Tim Lange  <mail@tim-lange.me>

	PR analyzer/109577

gcc/analyzer/ChangeLog:

	* constraint-manager.cc (class sval_finder): Visitor to find
	childs in svalue trees.
	(constraint_manager::sval_constrained_p): Add new function to
	check whether a sval might be part of an constraint.
	* constraint-manager.h: Add sval_constrained_p function.
	* region-model.cc (class size_visitor): Reverse behavior to not
	emit a warning on not explicitly considered cases.
	(region_model::check_region_size):
	Adapt to size_visitor changes.

gcc/testsuite/ChangeLog:

	* gcc.dg/analyzer/allocation-size-2.c: Change expected output
	and add new test case.
	* gcc.dg/analyzer/pr109577.c: New test.