analyzer: fix false leak due to overeager state merging [PR103217]

analyzer: fix false leak due to overeager state merging [PR103217]

PR analyzer/103217 reports a false positive from -Wanalyzer-malloc-leak.

The root cause is due to overzealous state merger, where the
state-merging code decided to merge these two states by merging
the stores:

state A:
  clusters within frame: ‘main’@1
    cluster for: one_3: CONJURED(val_4 = strdup (src_2(D));, val_4)
    cluster for: two_4: UNKNOWN(char *)
    cluster for: one_21: CONJURED(val_4 = strdup (src_2(D));, val_4)

state B:
  clusters within frame: ‘main’@1
    cluster for: one_3: UNKNOWN(char *)
    cluster for: two_4: CONJURED(val_4 = strdup (src_2(D));, val_4)
    cluster for: two_18: CONJURED(val_4 = strdup (src_2(D));, val_4)

into:
  clusters within frame: ‘main’@1
    cluster for: one_3: UNKNOWN(char *)
    cluster for: two_4: UNKNOWN(char *)
    cluster for: one_21: UNKNOWN(char *)
    cluster for: two_18: UNKNOWN(char *)

despite "CONJURED(val_4 = strdup (src_2(D));, val_4)" having sm-state,
in this case malloc:nonnull ({free}), thus leading to both references
to the conjured svalue being lost at merger.

This patch tweaks the state merger code so that it will not consider
merging two different svalues for the value of a region if either svalue
has non-purgable sm-state (in the above example, malloc:nonnull).  This
fixes the false leak report above.

Doing so uncovered an issue with explode-2a.c in which the warnings
moved from the correct location to the "while" stmt.  This turned out
to be a missing call to detect_leaks in phi-handling, which the patch
also fixes (in the PK_BEFORE_SUPERNODE case in
exploded_graph::process_node).  Doing this fixed the regression in
explode-2a.c and also fixed the location of the leak warning in
explode-1.c.

The other side effect of the change is that pr94858-1.c now emits
a -Wanalyzer-too-complex warning, since pertinent state is no longer
being thrown away.  There doesn't seem to be a good way of avoiding
this, so the patch also adds -Wno-analyzer-too-complex to that test
case (restoring the default).

gcc/analyzer/ChangeLog:
	PR analyzer/103217
	* engine.cc (exploded_graph::get_or_create_node): Pass in
	m_ext_state to program_state::can_merge_with_p.
	(exploded_graph::process_worklist): Likewise.
	(exploded_graph::maybe_process_run_of_before_supernode_enodes):
	Likewise.
	(exploded_graph::process_node): Add missing call to detect_leaks
	when handling phi nodes.
	* program-state.cc (program_state::can_merge_with_p): Add
	"ext_state" param.  Pass it and state ptrs to
	region_model::can_merge_with_p.
	(selftest::test_program_state_merging): Update for new ext_state
	param of program_state::can_merge_with_p.
	(selftest::test_program_state_merging_2): Likewise.
	* program-state.h (program_state::can_purge_p): Make const.
	(program_state::can_merge_with_p): Add "ext_state" param.
	* region-model.cc: Include "analyzer/program-state.h".
	(region_model::can_merge_with_p): Add params "ext_state",
	"state_a", and "state_b", use them when creating model_merger
	object.
	(model_merger::mergeable_svalue_p): New.
	* region-model.h (region_model::can_merge_with_p): Add params
	"ext_state", "state_a", and "state_b".
	(model_merger::model_merger) Likewise, initializing new fields.
	(model_merger::mergeable_svalue_p): New decl.
	(model_merger::m_ext_state): New field.
	(model_merger::m_state_a): New field.
	(model_merger::m_state_b): New field.
	* svalue.cc (svalue::can_merge_p): Call
	model_merger::mergeable_svalue_p on both states and reject the
	merger accordingly.

gcc/testsuite/ChangeLog:
	PR analyzer/103217
	* gcc.dg/analyzer/explode-1.c: Update for improvement to location
	of leak warning.
	* gcc.dg/analyzer/pr103217.c: New test.
	* gcc.dg/analyzer/pr94858-1.c: Add -Wno-analyzer-too-complex.

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