analyzer: add svalue::can_have_associated_state_p [PR101503]

PR analyzer/101503 reports an assertion failure due to an unexpected
"UNKNOWN" value (due to using --param analyzer-max-svalue-depth=0).

This patch fixes this by rejecting attempts to purge state involving
unknown/poisoned svalues (in region_model::purge_state_involving),
as these svalues should not have state associated with them - they
are singletons w.r.t each type.

To be more systematic about this, the patch also introduces a new
svalue::can_have_associated_state_p which returns false for
unknown/poisoned svalues, so that we can reject adding constraints
or sm-state on them, or building various kinds of svalue in terms
of them (e.g. unary ops, binary ops, etc).

gcc/analyzer/ChangeLog:
	PR analyzer/101503
	* constraint-manager.cc (constraint_manager::add_constraint): Use
	can_have_associated_state_p rather than testing for unknown.
	(constraint_manager::get_or_add_equiv_class): Likewise.
	* program-state.cc (sm_state_map::set_state): Likewise.
	(sm_state_map::impl_set_state): Add assertion.
	* region-model-manager.cc
	(region_model_manager::maybe_fold_unaryop): Handle poisoned
	values.
	(region_model_manager::maybe_fold_binop): Move handling of unknown
	values...
	(region_model_manager::get_or_create_binop): ...to here, and
	generalize to use can_have_associated_state_p.
	(region_model_manager::maybe_fold_sub_svalue): Use
	can_have_associated_state_p rather than testing for unknown.
	(region_model_manager::maybe_fold_repeated_svalue): Use unknown
	when the size or repeated value is "unknown"/"poisoned".
	* region-model.cc (region_model::purge_state_involving): Reject
	attempts to purge unknown/poisoned svalues, as these svalues
	should not have state associated with them.
	* svalue.cc (sub_svalue::sub_svalue): Assert that we're building
	on top of an svalue with can_have_associated_state_p.
	(repeated_svalue::repeated_svalue): Likewise.
	(bits_within_svalue::bits_within_svalue): Likewise.
	* svalue.h (svalue::can_have_associated_state_p): New.
	(unknown_svalue::can_have_associated_state_p): New.
	(poisoned_svalue::can_have_associated_state_p): New.
	(unaryop_svalue::unaryop_svalue): Assert that we're building on
	top of an svalue with can_have_associated_state_p.
	(binop_svalue::binop_svalue): Likewise.
	(widening_svalue::widening_svalue): Likewise.

gcc/testsuite/ChangeLog:
	PR analyzer/101503
	* gcc.dg/analyzer/pr101503.c: New test.

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

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