summaryrefslogtreecommitdiff
path: root/vala/valaflowanalyzer.vala
blob: 9f94a42ca6c16006b82d123796b2b0e8cbe3a78c (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
/* valaflowanalyzer.vala
 *
 * Copyright (C) 2008-2010  Jürg Billeter
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.

 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.

 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301  USA
 *
 * Author:
 * 	Jürg Billeter <j@bitron.ch>
 */

using GLib;

/**
 * Code visitor building the control flow graph.
 */
public class Vala.FlowAnalyzer : CodeVisitor {
	private class JumpTarget {
		public bool is_break_target { get; set; }
		public bool is_continue_target { get; set; }
		public bool is_return_target { get; set; }
		public bool is_exit_target { get; set; }
		public bool is_error_target { get; set; }
		public ErrorDomain? error_domain { get; set; }
		public ErrorCode? error_code { get; set; }
		public Class? error_class { get; set; }
		public bool is_finally_clause { get; set; }
		public BasicBlock basic_block { get; set; }
		public BasicBlock? last_block { get; set; }
		public CatchClause? catch_clause { get; set; }

		public JumpTarget.break_target (BasicBlock basic_block) {
			this.basic_block = basic_block;
			is_break_target = true;
		}

		public JumpTarget.continue_target (BasicBlock basic_block) {
			this.basic_block = basic_block;
			is_continue_target = true;
		}

		public JumpTarget.return_target (BasicBlock basic_block) {
			this.basic_block = basic_block;
			is_return_target = true;
		}

		public JumpTarget.exit_target (BasicBlock basic_block) {
			this.basic_block = basic_block;
			is_exit_target = true;
		}

		public JumpTarget.error_target (BasicBlock basic_block, CatchClause catch_clause, ErrorDomain? error_domain, ErrorCode? error_code, Class? error_class) {
			this.basic_block = basic_block;
			this.catch_clause = catch_clause;
			this.error_domain = error_domain;
			this.error_code = error_code;
			this.error_class = error_class;
			is_error_target = true;
		}

		public JumpTarget.any_target (BasicBlock basic_block) {
			this.basic_block = basic_block;
			is_break_target = true;
			is_continue_target = true;
			is_return_target = true;
			is_exit_target = true;
			is_error_target = true;
		}

		public JumpTarget.finally_clause (BasicBlock basic_block, BasicBlock last_block) {
			this.basic_block = basic_block;
			this.last_block = last_block;
			is_finally_clause = true;
		}
	}

	private CodeContext context;
	private BasicBlock current_block;
	private bool unreachable_reported;
	private List<JumpTarget> jump_stack = new ArrayList<JumpTarget> ();

	Map<Symbol, List<Variable>> var_map;
	Set<Variable> used_vars;
	Map<Variable, PhiFunction> phi_functions;

	public FlowAnalyzer () {
	}

	/**
	 * Build control flow graph in the specified context.
	 *
	 * @param context a code context
	 */
	public void analyze (CodeContext context) {
		this.context = context;

		/* we're only interested in non-pkg source files */
		var source_files = context.get_source_files ();
		foreach (SourceFile file in source_files) {
			if (file.file_type == SourceFileType.SOURCE) {
				file.accept (this);
			}
		}
	}

	public override void visit_source_file (SourceFile source_file) {
		source_file.accept_children (this);
	}

	public override void visit_class (Class cl) {
		cl.accept_children (this);
	}

	public override void visit_struct (Struct st) {
		st.accept_children (this);
	}

	public override void visit_interface (Interface iface) {
		iface.accept_children (this);
	}

	public override void visit_enum (Enum en) {
		en.accept_children (this);
	}

	public override void visit_error_domain (ErrorDomain ed) {
		ed.accept_children (this);
	}

	public override void visit_field (Field f) {
		if (f.is_internal_symbol () && !f.used) {
			if (!f.is_private_symbol () && (context.internal_header_filename != null || context.use_fast_vapi)) {
				// do not warn if internal member may be used outside this compilation unit
			} else {
				Report.warning (f.source_reference, "field `%s' never used".printf (f.get_full_name ()));
			}
		}
	}

	public override void visit_lambda_expression (LambdaExpression le) {
		var old_current_block = current_block;
		var old_unreachable_reported = unreachable_reported;
		var old_jump_stack = jump_stack;
		mark_unreachable ();
		jump_stack = new ArrayList<JumpTarget> ();

		le.accept_children (this);

		current_block = old_current_block;
		unreachable_reported = old_unreachable_reported;
		jump_stack = old_jump_stack;
	}

	public override void visit_method (Method m) {
		if (m.is_internal_symbol () && !m.used && !m.entry_point
		    && !m.overrides && (m.base_interface_method == null || m.base_interface_method == m)
		    && !(m is CreationMethod)) {
			if (!m.is_private_symbol () && (context.internal_header_filename != null || context.use_fast_vapi)) {
				// do not warn if internal member may be used outside this compilation unit
			} else {
				Report.warning (m.source_reference, "method `%s' never used".printf (m.get_full_name ()));
			}
		}

		visit_subroutine (m);
	}

	public override void visit_signal (Signal sig) {
		if (sig.default_handler != null) {
			visit_subroutine (sig.default_handler);
		}
	}

	void visit_subroutine (Subroutine m) {
		if (m.body == null) {
			return;
		}

		m.entry_block = new BasicBlock.entry ();
		m.return_block = new BasicBlock ();
		m.exit_block = new BasicBlock.exit ();

		m.return_block.connect (m.exit_block);

		if (m is Method) {
			// ensure out parameters are defined at end of method
			foreach (var param in ((Method) m).get_parameters ()) {
				if (param.direction == ParameterDirection.OUT) {
					var param_ma = new MemberAccess.simple (param.name, param.source_reference);
					param_ma.symbol_reference = param;
					m.return_block.add_node (param_ma);
				}
			}
		}

		current_block = new BasicBlock ();
		m.entry_block.connect (current_block);
		current_block.add_node (m);

		jump_stack.add (new JumpTarget.return_target (m.return_block));
		jump_stack.add (new JumpTarget.exit_target (m.exit_block));

		m.accept_children (this);

		jump_stack.remove_at (jump_stack.size - 1);

		if (current_block != null) {
			// end of method body reachable

			if (m.has_result) {
				Report.error (m.source_reference, "missing return statement at end of subroutine body");
				m.error = true;
			}

			current_block.connect (m.return_block);
		}

		analyze_body (m.entry_block);
	}

	void analyze_body (BasicBlock entry_block) {
		var block_list = get_depth_first_list (entry_block);

		build_dominator_tree (block_list, entry_block);
		build_dominator_frontier (block_list, entry_block);
		insert_phi_functions (block_list, entry_block);
		check_variables (entry_block);
	}

	// generates reverse postorder list
	List<BasicBlock> get_depth_first_list (BasicBlock entry_block) {
		var list = new ArrayList<BasicBlock> ();
		depth_first_traverse (entry_block, list);
		return list;
	}

	void depth_first_traverse (BasicBlock current, List<BasicBlock> list) {
		if (current.postorder_visited) {
			return;
		}
		current.postorder_visited = true;
		foreach (BasicBlock succ in current.get_successors ()) {
			depth_first_traverse (succ, list);
		}
		current.postorder_number = list.size;
		list.insert (0, current);
	}

	void build_dominator_tree (List<BasicBlock> block_list, BasicBlock entry_block) {
		// immediate dominators
		var idoms = new BasicBlock[block_list.size];
		idoms[entry_block.postorder_number] = entry_block;

		bool changed = true;
		while (changed) {
			changed = false;
			foreach (BasicBlock block in block_list) {
				if (block == entry_block) {
					continue;
				}

				// new immediate dominator
				BasicBlock new_idom = null;
				bool first = true;
				foreach (BasicBlock pred in block.get_predecessors ()) {
					if (idoms[pred.postorder_number] != null) {
						if (first) {
							new_idom = pred;
							first = false;
						} else {
							new_idom = intersect (idoms, pred, new_idom);
						}
					}
				}
				if (idoms[block.postorder_number] != new_idom) {
					idoms[block.postorder_number] = new_idom;
					changed = true;
				}
			}
		}

		// build tree
		foreach (BasicBlock block in block_list) {
			if (block == entry_block) {
				continue;
			}

			idoms[block.postorder_number].add_child (block);
		}
	}

	BasicBlock intersect (BasicBlock[] idoms, BasicBlock b1, BasicBlock b2) {
		while (b1 != b2) {
			while (b1.postorder_number < b2.postorder_number) {
				b1 = idoms[b2.postorder_number];
			}
			while (b2.postorder_number < b1.postorder_number) {
				b2 = idoms[b2.postorder_number];
			}
		}
		return b1;
	}

	void build_dominator_frontier (List<BasicBlock> block_list, BasicBlock entry_block) {
		for (int i = block_list.size - 1; i >= 0; i--) {
			var block = block_list[i];

			foreach (BasicBlock succ in block.get_successors ()) {
				// if idom(succ) != block
				if (succ.parent != block) {
					block.add_dominator_frontier (succ);
				}
			}

			foreach (BasicBlock child in block.get_children ()) {
				foreach (BasicBlock child_frontier in child.get_dominator_frontier ()) {
					// if idom(child_frontier) != block
					if (child_frontier.parent != block) {
						block.add_dominator_frontier (child_frontier);
					}
				}
			}
		}
	}

	Map<Variable, Set<BasicBlock>> get_assignment_map (List<BasicBlock> block_list, BasicBlock entry_block) {
		var map = new HashMap<Variable, Set<BasicBlock>> ();
		foreach (BasicBlock block in block_list) {
			var defined_variables = new ArrayList<Variable> ();
			foreach (CodeNode node in block.get_nodes ()) {
				node.get_defined_variables (defined_variables);
			}

			foreach (Variable variable in defined_variables) {
				var block_set = map.get (variable);
				if (block_set == null) {
					block_set = new HashSet<BasicBlock> ();
					map.set (variable, block_set);
				}
				block_set.add (block);
			}
		}
		return map;
	}

	void insert_phi_functions (List<BasicBlock> block_list, BasicBlock entry_block) {
		var assign = get_assignment_map (block_list, entry_block);

		int counter = 0;
		var work_list = new ArrayList<BasicBlock> ();

		var added = new HashMap<BasicBlock, int> ();
		var phi = new HashMap<BasicBlock, int> ();
		foreach (BasicBlock block in block_list) {
			added.set (block, 0);
			phi.set (block, 0);
		}

		foreach (Variable variable in assign.get_keys ()) {
			counter++;
			foreach (BasicBlock block in assign.get (variable)) {
				work_list.add (block);
				added.set (block, counter);
			}
			while (work_list.size > 0) {
				BasicBlock block = work_list.get (0);
				work_list.remove_at (0);
				foreach (BasicBlock frontier in block.get_dominator_frontier ()) {
					int blockPhi = phi.get (frontier);
					if (blockPhi < counter) {
						frontier.add_phi_function (new PhiFunction (variable, frontier.get_predecessors ().size));
						phi.set (frontier, counter);
						int block_added = added.get (frontier);
						if (block_added < counter) {
							added.set (frontier, counter);
							work_list.add (frontier);
						}
					}
				}
			}
		}
	}

	void check_variables (BasicBlock entry_block) {
		var_map = new HashMap<Symbol, List<Variable>>();
		used_vars = new HashSet<Variable> ();
		phi_functions = new HashMap<Variable, PhiFunction> ();

		check_block_variables (entry_block);

		// check for variables used before initialization
		var used_vars_queue = new ArrayList<Variable> ();
		foreach (Variable variable in used_vars) {
			used_vars_queue.add (variable);
		}
		while (used_vars_queue.size > 0) {
			Variable used_var = used_vars_queue[0];
			used_vars_queue.remove_at (0);

			PhiFunction phi = phi_functions.get (used_var);
			if (phi != null) {
				foreach (Variable variable in phi.operands) {
					if (variable == null) {
						if (used_var is LocalVariable) {
							Report.error (used_var.source_reference, "use of possibly unassigned local variable `%s'".printf (used_var.name));
						} else {
							// parameter
							Report.warning (used_var.source_reference, "use of possibly unassigned parameter `%s'".printf (used_var.name));
						}
						continue;
					}
					if (!(variable in used_vars)) {
						variable.source_reference = used_var.source_reference;
						used_vars.add (variable);
						used_vars_queue.add (variable);
					}
				}
			}
		}
	}

	void check_block_variables (BasicBlock block) {
		foreach (PhiFunction phi in block.get_phi_functions ()) {
			Variable versioned_var = process_assignment (var_map, phi.original_variable);

			phi_functions.set (versioned_var, phi);
		}

		foreach (CodeNode node in block.get_nodes ()) {
			var used_variables = new ArrayList<Variable> ();
			node.get_used_variables (used_variables);
			
			foreach (Variable var_symbol in used_variables) {
				var variable_stack = var_map.get (var_symbol);
				if (variable_stack == null || variable_stack.size == 0) {
					if (var_symbol is LocalVariable) {
						Report.error (node.source_reference, "use of possibly unassigned local variable `%s'".printf (var_symbol.name));
					} else {
						// parameter
						Report.warning (node.source_reference, "use of possibly unassigned parameter `%s'".printf (var_symbol.name));
					}
					continue;
				}
				var versioned_variable = variable_stack.get (variable_stack.size - 1);
				if (!(versioned_variable in used_vars)) {
					versioned_variable.source_reference = node.source_reference;
				}
				used_vars.add (versioned_variable);
			}

			var defined_variables = new ArrayList<Variable> ();
			node.get_defined_variables (defined_variables);

			foreach (Variable variable in defined_variables) {
				process_assignment (var_map, variable);
			}
		}

		foreach (BasicBlock succ in block.get_successors ()) {
			int j = 0;
			foreach (BasicBlock pred in succ.get_predecessors ()) {
				if (pred == block) {
					break;
				}
				j++;
			}

			foreach (PhiFunction phi in succ.get_phi_functions ()) {
				var variable_stack = var_map.get (phi.original_variable);
				if (variable_stack != null && variable_stack.size > 0) {
					phi.operands.set (j, variable_stack.get (variable_stack.size - 1));
				}
			}
		}

		foreach (BasicBlock child in block.get_children ()) {
			check_block_variables (child);
		}

		foreach (PhiFunction phi in block.get_phi_functions ()) {
			var variable_stack = var_map.get (phi.original_variable);
			variable_stack.remove_at (variable_stack.size - 1);
		}
		foreach (CodeNode node in block.get_nodes ()) {
			var defined_variables = new ArrayList<Variable> ();
			node.get_defined_variables (defined_variables);

			foreach (Variable variable in defined_variables) {
				var variable_stack = var_map.get (variable);
				variable_stack.remove_at (variable_stack.size - 1);
			}
		}
	}

	Variable process_assignment (Map<Symbol, List<Variable>> var_map, Variable var_symbol) {
		var variable_stack = var_map.get (var_symbol);
		if (variable_stack == null) {
			variable_stack = new ArrayList<Variable> ();
			var_map.set (var_symbol, variable_stack);
			var_symbol.single_assignment = true;
		} else {
			var_symbol.single_assignment = false;
		}
		Variable versioned_var;
		if (var_symbol is LocalVariable) {
			versioned_var = new LocalVariable (var_symbol.variable_type.copy (), var_symbol.name, null, var_symbol.source_reference);
		} else {
			// parameter
			versioned_var = new Parameter (var_symbol.name, var_symbol.variable_type.copy (), var_symbol.source_reference);
		}
		variable_stack.add (versioned_var);
		return versioned_var;
	}

	public override void visit_creation_method (CreationMethod m) {
		visit_method (m);
	}

	public override void visit_property (Property prop) {
		prop.accept_children (this);
	}

	public override void visit_property_accessor (PropertyAccessor acc) {
		visit_subroutine (acc);
	}

	public override void visit_block (Block b) {
		b.accept_children (this);
	}

	public override void visit_declaration_statement (DeclarationStatement stmt) {
		stmt.accept_children (this);

		if (unreachable (stmt)) {
			stmt.declaration.unreachable = true;
			return;
		}

		if (!stmt.declaration.used) {
			Report.warning (stmt.declaration.source_reference, "local variable `%s' declared but never used".printf (stmt.declaration.name));
		}

		current_block.add_node (stmt);

		var local = stmt.declaration as LocalVariable;
		if (local != null && local.initializer != null) {
			handle_errors (local.initializer);
		}
	}

	public override void visit_local_variable (LocalVariable local) {
		if (local.initializer != null) {
			local.initializer.accept (this);
		}
	}

	public override void visit_expression_statement (ExpressionStatement stmt) {
		stmt.accept_children (this);

		if (unreachable (stmt)) {
			return;
		}

		current_block.add_node (stmt);

		handle_errors (stmt);

		if (stmt.expression is MethodCall) {
			var expr = (MethodCall) stmt.expression;
			var ma = expr.call as MemberAccess;
			if (ma != null && ma.symbol_reference != null && ma.symbol_reference.get_attribute ("NoReturn") != null) {
				mark_unreachable ();
				return;
			}
		}
	}

	bool always_true (Expression condition) {
		var literal = condition as BooleanLiteral;
		return (literal != null && literal.value);
	}

	bool always_false (Expression condition) {
		var literal = condition as BooleanLiteral;
		return (literal != null && !literal.value);
	}

	public override void visit_if_statement (IfStatement stmt) {
		if (unreachable (stmt)) {
			return;
		}

		// condition
		current_block.add_node (stmt.condition);

		handle_errors (stmt.condition);

		// true block
		var last_block = current_block;
		if (always_false (stmt.condition)) {
			mark_unreachable ();
		} else {
			current_block = new BasicBlock ();
			last_block.connect (current_block);
		}
		stmt.true_statement.accept (this);

		// false block
		var last_true_block = current_block;
		if (always_true (stmt.condition)) {
			mark_unreachable ();
		} else {
			current_block = new BasicBlock ();
			last_block.connect (current_block);
		}
		if (stmt.false_statement != null) {
			stmt.false_statement.accept (this);
		}

		// after if/else
		var last_false_block = current_block;
		// reachable?
		if (last_true_block != null || last_false_block != null) {
			current_block = new BasicBlock ();
			if (last_true_block != null) {
				last_true_block.connect (current_block);
			}
			if (last_false_block != null) {
				last_false_block.connect (current_block);
			}
		}
	}

	public override void visit_switch_statement (SwitchStatement stmt) {
		if (unreachable (stmt)) {
			return;
		}

		var after_switch_block = new BasicBlock ();
		jump_stack.add (new JumpTarget.break_target (after_switch_block));

		// condition
		current_block.add_node (stmt.expression);
		var condition_block = current_block;

		handle_errors (stmt.expression);

		bool has_default_label = false;

		foreach (SwitchSection section in stmt.get_sections ()) {
			current_block = new BasicBlock ();
			condition_block.connect (current_block);
			foreach (Statement section_stmt in section.get_statements ()) {
				section_stmt.accept (this);
			}

			if (section.has_default_label ()) {
				has_default_label = true;
			}

			if (current_block != null) {
				// end of switch section reachable
				// we don't allow fall-through

				Report.error (section.source_reference, "missing break statement at end of switch section");
				section.error = true;

				current_block.connect (after_switch_block);
			}
		}

		if (!has_default_label) {
			condition_block.connect (after_switch_block);
		}

		// after switch
		// reachable?
		if (after_switch_block.get_predecessors ().size > 0) {
			current_block = after_switch_block;
		} else {
			mark_unreachable ();
		}

		jump_stack.remove_at (jump_stack.size - 1);
	}

	public override void visit_loop (Loop stmt) {
		if (unreachable (stmt)) {
			return;
		}

		var loop_block = new BasicBlock ();
		jump_stack.add (new JumpTarget.continue_target (loop_block));
		var after_loop_block = new BasicBlock ();
		jump_stack.add (new JumpTarget.break_target (after_loop_block));

		// loop block
		var last_block = current_block;
		last_block.connect (loop_block);
		current_block = loop_block;

		stmt.body.accept (this);
		// end of loop block reachable?
		if (current_block != null) {
			current_block.connect (loop_block);
		}

		// after loop
		// reachable?
		if (after_loop_block.get_predecessors ().size == 0) {
			// after loop block not reachable
			mark_unreachable ();
		} else {
			// after loop block reachable
			current_block = after_loop_block;
		}

		jump_stack.remove_at (jump_stack.size - 1);
		jump_stack.remove_at (jump_stack.size - 1);
	}

	public override void visit_foreach_statement (ForeachStatement stmt) {
		if (unreachable (stmt)) {
			return;
		}

		// collection
		current_block.add_node (stmt.collection);
		handle_errors (stmt.collection);

		var loop_block = new BasicBlock ();
		jump_stack.add (new JumpTarget.continue_target (loop_block));
		var after_loop_block = new BasicBlock ();
		jump_stack.add (new JumpTarget.break_target (after_loop_block));

		// loop block
		var last_block = current_block;
		last_block.connect (loop_block);
		current_block = loop_block;
		current_block.add_node (stmt);
		stmt.body.accept (this);
		if (current_block != null) {
			current_block.connect (loop_block);
		}

		// after loop
		last_block.connect (after_loop_block);
		if (current_block != null) {
			current_block.connect (after_loop_block);
		}
		current_block = after_loop_block;

		jump_stack.remove_at (jump_stack.size - 1);
		jump_stack.remove_at (jump_stack.size - 1);
	}

	public override void visit_break_statement (BreakStatement stmt) {
		if (unreachable (stmt)) {
			return;
		}

		current_block.add_node (stmt);

		for (int i = jump_stack.size - 1; i >= 0; i--) {
			var jump_target = jump_stack[i];
			if (jump_target.is_break_target) {
				current_block.connect (jump_target.basic_block);
				mark_unreachable ();
				return;
			} else if (jump_target.is_finally_clause) {
				current_block.connect (jump_target.basic_block);
				current_block = jump_target.last_block;
			}
		}

		Report.error (stmt.source_reference, "no enclosing loop or switch statement found");
		stmt.error = true;
	}

	public override void visit_continue_statement (ContinueStatement stmt) {
		if (unreachable (stmt)) {
			return;
		}

		current_block.add_node (stmt);

		for (int i = jump_stack.size - 1; i >= 0; i--) {
			var jump_target = jump_stack[i];
			if (jump_target.is_continue_target) {
				current_block.connect (jump_target.basic_block);
				mark_unreachable ();
				return;
			} else if (jump_target.is_finally_clause) {
				current_block.connect (jump_target.basic_block);
				current_block = jump_target.last_block;
			}
		}

		Report.error (stmt.source_reference, "no enclosing loop found");
		stmt.error = true;
	}

	public override void visit_return_statement (ReturnStatement stmt) {
		stmt.accept_children (this);

		if (unreachable (stmt)) {
			return;
		}

		current_block.add_node (stmt);

		if (stmt.return_expression != null) {
			handle_errors (stmt.return_expression);
		}

		for (int i = jump_stack.size - 1; i >= 0; i--) {
			var jump_target = jump_stack[i];
			if (jump_target.is_return_target) {
				current_block.connect (jump_target.basic_block);
				mark_unreachable ();
				return;
			} else if (jump_target.is_finally_clause) {
				current_block.connect (jump_target.basic_block);
				current_block = jump_target.last_block;
			}
		}

		Report.error (stmt.source_reference, "no enclosing loop found");
		stmt.error = true;
	}

	private void handle_errors (CodeNode node, bool always_fail = false) {
		if (node.tree_can_fail) {
			var last_block = current_block;

			// exceptional control flow
			foreach (DataType error_data_type in node.get_error_types()) {
				var error_type = error_data_type as ErrorType;
				current_block = last_block;
				unreachable_reported = true;

				for (int i = jump_stack.size - 1; i >= 0; i--) {
					var jump_target = jump_stack[i];
					if (jump_target.is_exit_target) {
						current_block.connect (jump_target.basic_block);
						mark_unreachable ();
						break;
					} else if (jump_target.is_error_target) {
						if (jump_target.error_domain == null
						    || (jump_target.error_domain == error_type.error_domain
							&& (jump_target.error_code == null
							    || jump_target.error_code == error_type.error_code))) {
							// error can always be caught by this catch clause
							// following catch clauses cannot be reached by this error
							current_block.connect (jump_target.basic_block);
							mark_unreachable ();
							break;
						} else if (error_type.error_domain == null
							   || (error_type.error_domain == jump_target.error_domain
							       && (error_type.error_code == null
							           || error_type.error_code == jump_target.error_code))) {
							// error might be caught by this catch clause
							// unknown at compile time
							// following catch clauses might still be reached by this error
							current_block.connect (jump_target.basic_block);
						}
					} else if (jump_target.is_finally_clause) {
						current_block.connect (jump_target.basic_block);
						current_block = jump_target.last_block;
					}
				}
			}

			// normal control flow
			if (!always_fail) {
				current_block = new BasicBlock ();
				last_block.connect (current_block);
			}
		}
	}

	public override void visit_yield_statement (YieldStatement stmt) {
		if (unreachable (stmt)) {
			return;
		}

		stmt.accept_children (this);
	}

	public override void visit_throw_statement (ThrowStatement stmt) {
		if (unreachable (stmt)) {
			return;
		}

		current_block.add_node (stmt);
		handle_errors (stmt, true);
	}

	public override void visit_try_statement (TryStatement stmt) {
		if (unreachable (stmt)) {
			return;
		}

		var before_try_block = current_block;
		var after_try_block = new BasicBlock ();

		BasicBlock finally_block = null;
		if (stmt.finally_body != null) {
			finally_block = new BasicBlock ();
			current_block = finally_block;

			// trap all forbidden jumps
			var invalid_block = new BasicBlock ();
			jump_stack.add (new JumpTarget.any_target (invalid_block));

			stmt.finally_body.accept (this);

			if (invalid_block.get_predecessors ().size > 0) {
				// don't allow finally blocks with e.g. return statements
				Report.error (stmt.source_reference, "jump out of finally block not permitted");
				stmt.error = true;
				return;
			}
			jump_stack.remove_at (jump_stack.size - 1);

			jump_stack.add (new JumpTarget.finally_clause (finally_block, current_block));
		}

		int finally_jump_stack_size = jump_stack.size;

		var catch_clauses = stmt.get_catch_clauses ();
		for (int i = catch_clauses.size - 1; i >= 0; i--) {
			var catch_clause = catch_clauses[i];
			if (catch_clause.error_type != null) {
				var error_type = (ErrorType) catch_clause.error_type;
				jump_stack.add (new JumpTarget.error_target (new BasicBlock (), catch_clause, catch_clause.error_type.data_type as ErrorDomain, error_type.error_code, null));
			} else {
				jump_stack.add (new JumpTarget.error_target (new BasicBlock (), catch_clause, null, null, null));
			}
		}

		current_block = before_try_block;

		stmt.body.accept (this);

		if (current_block != null) {
			if (finally_block != null) {
				current_block.connect (finally_block);
				current_block = finally_block;
			}
			current_block.connect (after_try_block);
		}

		// remove catch clauses from jump stack
		List<JumpTarget> catch_stack = new ArrayList<JumpTarget> ();
		for (int i = jump_stack.size - 1; i >= finally_jump_stack_size; i--) {
			var jump_target = jump_stack[i];
			catch_stack.add (jump_target);
			jump_stack.remove_at (i);
		}

		foreach (JumpTarget jump_target in catch_stack) {

			foreach (JumpTarget prev_target in catch_stack) {
				if (prev_target == jump_target) {
					break;
				}

				if (prev_target.error_domain == jump_target.error_domain &&
				    prev_target.error_code == jump_target.error_code) {
					Report.error (stmt.source_reference, "double catch clause of same error detected");
					stmt.error = true;
					return;
				}
			}

			if (jump_target.basic_block.get_predecessors ().size == 0) {
				// unreachable
				Report.warning (jump_target.catch_clause.source_reference, "unreachable catch clause detected");
			} else {
				current_block = jump_target.basic_block;
				current_block.add_node (jump_target.catch_clause);
				jump_target.catch_clause.body.accept (this);
				if (current_block != null) {
					if (finally_block != null) {
						current_block.connect (finally_block);
						current_block = finally_block;
					}
					current_block.connect (after_try_block);
				}
			}
		}

		if (finally_block != null) {
			jump_stack.remove_at (jump_stack.size - 1);
		}

		// after try statement
		// reachable?
		if (after_try_block.get_predecessors ().size > 0) {
			current_block = after_try_block;
		} else {
			stmt.after_try_block_reachable = false;
			mark_unreachable ();
		}
	}

	public override void visit_lock_statement (LockStatement stmt) {
		if (unreachable (stmt)) {
			return;
		}
	}

	public override void visit_unlock_statement (UnlockStatement stmt) {
		if (unreachable (stmt)) {
			return;
		}
	}

	public override void visit_expression (Expression expr) {
		// lambda expression is handled separately
		if (!(expr is LambdaExpression)) {
			expr.accept_children (this);
		}
	}

	private bool unreachable (CodeNode node) {
		if (current_block == null) {
			node.unreachable = true;
			if (!unreachable_reported) {
				Report.warning (node.source_reference, "unreachable code detected");
				unreachable_reported = true;
			}
			return true;
		}

		return false;
	}

	void mark_unreachable () {
		current_block = null;
		unreachable_reported = false;
	}
}