analyzer: fix ICE reporting NULL dereference (PR 93647)

gcc/analyzer/ChangeLog:
	PR analyzer/93647
	* diagnostic-manager.cc
	(diagnostic_manager::prune_for_sm_diagnostic): Bulletproof against
	VAR being constant.
	* region-model.cc (region_model::get_lvalue_1): Provide a better
	error message when encountering an unhandled tree code.

gcc/testsuite/ChangeLog:
	PR analyzer/93647
	* gcc.dg/analyzer/torture/pr93647.c: New test.

gcc/analyzer/ChangeLog

 2020-02-10  David Malcolm  <dmalcolm@redhat.com>
 
+	PR analyzer/93647
+	* diagnostic-manager.cc
+	(diagnostic_manager::prune_for_sm_diagnostic): Bulletproof against
+	VAR being constant.
+	* region-model.cc (region_model::get_lvalue_1): Provide a better
+	error message when encountering an unhandled tree code.
+
+2020-02-10  David Malcolm  <dmalcolm@redhat.com>
+
 	PR analyzer/93405
 	* region-model.cc (region_model::get_lvalue_1): Implement
 	CONST_DECL.

gcc/analyzer/diagnostic-manager.cc

@@ -965,6 +965,12 @@ diagnostic_manager::prune_for_sm_diagnostic (checker_path *path,
 					     tree var,
 					     state_machine::state_t state) const
 {
+  /* If we have a constant (such as NULL), assume its state is also
+     constant, so as not to attempt to get its lvalue whilst tracking the
+     origin of the state.  */
+  if (var && CONSTANT_CLASS_P (var))
+    var = NULL_TREE;
+
   int idx = path->num_events () - 1;
   while (idx >= 0 && idx < (signed)path->num_events ())
     {

gcc/analyzer/region-model.cc

@@ -4614,6 +4614,8 @@ region_model::get_lvalue_1 (path_var pv, region_model_context *ctxt)
   switch (TREE_CODE (expr))
     {
     default:
+      internal_error ("unhandled tree code in region_model::get_lvalue_1: %qs",
+		      get_tree_code_name (TREE_CODE (expr)));
       gcc_unreachable ();
 
     case ARRAY_REF:

gcc/testsuite/ChangeLog

+2020-02-10  David Malcolm  <dmalcolm@redhat.com>
+
+	PR analyzer/93647
+	* gcc.dg/analyzer/torture/pr93647.c: New test.
+
 2020-02-10  Jakub Jelinek  <jakub@redhat.com>
 
 	PR target/93637

gcc/testsuite/gcc.dg/analyzer/torture/pr93647.c

+/* { dg-skip-if "" { *-*-* } { "-fno-fat-lto-objects" } { "" } } */
+
+int *tz;
+
+void
+ky (int);
+
+void
+wd (void)
+{
+  tz = 0;
+  ky (*tz); /* { dg-warning "dereference of NULL" } */
+}
+