summaryrefslogtreecommitdiff
path: root/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
blob: cddf00bea775fdab99949963a8d1aa11f0ba59fc (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
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
//===- ObjCARCOpts.cpp - ObjC ARC Optimization ----------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
/// \file
/// This file defines ObjC ARC optimizations. ARC stands for Automatic
/// Reference Counting and is a system for managing reference counts for objects
/// in Objective C.
///
/// The optimizations performed include elimination of redundant, partially
/// redundant, and inconsequential reference count operations, elimination of
/// redundant weak pointer operations, and numerous minor simplifications.
///
/// WARNING: This file knows about certain library functions. It recognizes them
/// by name, and hardwires knowledge of their semantics.
///
/// WARNING: This file knows about how certain Objective-C library functions are
/// used. Naive LLVM IR transformations which would otherwise be
/// behavior-preserving may break these assumptions.
///
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "objc-arc-opts"
#include "ObjCARC.h"
#include "DependencyAnalysis.h"
#include "ObjCARCAliasAnalysis.h"
#include "ProvenanceAnalysis.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"

using namespace llvm;
using namespace llvm::objcarc;

/// \defgroup MiscUtils Miscellaneous utilities that are not ARC specific.
/// @{

namespace {
  /// \brief An associative container with fast insertion-order (deterministic)
  /// iteration over its elements. Plus the special blot operation.
  template<class KeyT, class ValueT>
  class MapVector {
    /// Map keys to indices in Vector.
    typedef DenseMap<KeyT, size_t> MapTy;
    MapTy Map;

    typedef std::vector<std::pair<KeyT, ValueT> > VectorTy;
    /// Keys and values.
    VectorTy Vector;

  public:
    typedef typename VectorTy::iterator iterator;
    typedef typename VectorTy::const_iterator const_iterator;
    iterator begin() { return Vector.begin(); }
    iterator end() { return Vector.end(); }
    const_iterator begin() const { return Vector.begin(); }
    const_iterator end() const { return Vector.end(); }

#ifdef XDEBUG
    ~MapVector() {
      assert(Vector.size() >= Map.size()); // May differ due to blotting.
      for (typename MapTy::const_iterator I = Map.begin(), E = Map.end();
           I != E; ++I) {
        assert(I->second < Vector.size());
        assert(Vector[I->second].first == I->first);
      }
      for (typename VectorTy::const_iterator I = Vector.begin(),
           E = Vector.end(); I != E; ++I)
        assert(!I->first ||
               (Map.count(I->first) &&
                Map[I->first] == size_t(I - Vector.begin())));
    }
#endif

    ValueT &operator[](const KeyT &Arg) {
      std::pair<typename MapTy::iterator, bool> Pair =
        Map.insert(std::make_pair(Arg, size_t(0)));
      if (Pair.second) {
        size_t Num = Vector.size();
        Pair.first->second = Num;
        Vector.push_back(std::make_pair(Arg, ValueT()));
        return Vector[Num].second;
      }
      return Vector[Pair.first->second].second;
    }

    std::pair<iterator, bool>
    insert(const std::pair<KeyT, ValueT> &InsertPair) {
      std::pair<typename MapTy::iterator, bool> Pair =
        Map.insert(std::make_pair(InsertPair.first, size_t(0)));
      if (Pair.second) {
        size_t Num = Vector.size();
        Pair.first->second = Num;
        Vector.push_back(InsertPair);
        return std::make_pair(Vector.begin() + Num, true);
      }
      return std::make_pair(Vector.begin() + Pair.first->second, false);
    }

    const_iterator find(const KeyT &Key) const {
      typename MapTy::const_iterator It = Map.find(Key);
      if (It == Map.end()) return Vector.end();
      return Vector.begin() + It->second;
    }

    /// This is similar to erase, but instead of removing the element from the
    /// vector, it just zeros out the key in the vector. This leaves iterators
    /// intact, but clients must be prepared for zeroed-out keys when iterating.
    void blot(const KeyT &Key) {
      typename MapTy::iterator It = Map.find(Key);
      if (It == Map.end()) return;
      Vector[It->second].first = KeyT();
      Map.erase(It);
    }

    void clear() {
      Map.clear();
      Vector.clear();
    }
  };
}

/// @}
///
/// \defgroup ARCUtilities Utility declarations/definitions specific to ARC.
/// @{

/// \brief This is similar to StripPointerCastsAndObjCCalls but it stops as soon
/// as it finds a value with multiple uses.
static const Value *FindSingleUseIdentifiedObject(const Value *Arg) {
  if (Arg->hasOneUse()) {
    if (const BitCastInst *BC = dyn_cast<BitCastInst>(Arg))
      return FindSingleUseIdentifiedObject(BC->getOperand(0));
    if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Arg))
      if (GEP->hasAllZeroIndices())
        return FindSingleUseIdentifiedObject(GEP->getPointerOperand());
    if (IsForwarding(GetBasicInstructionClass(Arg)))
      return FindSingleUseIdentifiedObject(
               cast<CallInst>(Arg)->getArgOperand(0));
    if (!IsObjCIdentifiedObject(Arg))
      return 0;
    return Arg;
  }

  // If we found an identifiable object but it has multiple uses, but they are
  // trivial uses, we can still consider this to be a single-use value.
  if (IsObjCIdentifiedObject(Arg)) {
    for (Value::const_use_iterator UI = Arg->use_begin(), UE = Arg->use_end();
         UI != UE; ++UI) {
      const User *U = *UI;
      if (!U->use_empty() || StripPointerCastsAndObjCCalls(U) != Arg)
         return 0;
    }

    return Arg;
  }

  return 0;
}

/// \brief Test whether the given retainable object pointer escapes.
///
/// This differs from regular escape analysis in that a use as an
/// argument to a call is not considered an escape.
///
static bool DoesRetainableObjPtrEscape(const User *Ptr) {
  DEBUG(dbgs() << "DoesRetainableObjPtrEscape: Target: " << *Ptr << "\n");

  // Walk the def-use chains.
  SmallVector<const Value *, 4> Worklist;
  Worklist.push_back(Ptr);
  // If Ptr has any operands add them as well.
  for (User::const_op_iterator I = Ptr->op_begin(), E = Ptr->op_end(); I != E;
       ++I) {
    Worklist.push_back(*I);
  }

  // Ensure we do not visit any value twice.
  SmallPtrSet<const Value *, 8> VisitedSet;

  do {
    const Value *V = Worklist.pop_back_val();

    DEBUG(dbgs() << "Visiting: " << *V << "\n");

    for (Value::const_use_iterator UI = V->use_begin(), UE = V->use_end();
         UI != UE; ++UI) {
      const User *UUser = *UI;

      DEBUG(dbgs() << "User: " << *UUser << "\n");

      // Special - Use by a call (callee or argument) is not considered
      // to be an escape.
      switch (GetBasicInstructionClass(UUser)) {
      case IC_StoreWeak:
      case IC_InitWeak:
      case IC_StoreStrong:
      case IC_Autorelease:
      case IC_AutoreleaseRV: {
        DEBUG(dbgs() << "User copies pointer arguments. Pointer Escapes!\n");
        // These special functions make copies of their pointer arguments.
        return true;
      }
      case IC_IntrinsicUser:
        // Use by the use intrinsic is not an escape.
        continue;
      case IC_User:
      case IC_None:
        // Use by an instruction which copies the value is an escape if the
        // result is an escape.
        if (isa<BitCastInst>(UUser) || isa<GetElementPtrInst>(UUser) ||
            isa<PHINode>(UUser) || isa<SelectInst>(UUser)) {

          if (VisitedSet.insert(UUser)) {
            DEBUG(dbgs() << "User copies value. Ptr escapes if result escapes."
                  " Adding to list.\n");
            Worklist.push_back(UUser);
          } else {
            DEBUG(dbgs() << "Already visited node.\n");
          }
          continue;
        }
        // Use by a load is not an escape.
        if (isa<LoadInst>(UUser))
          continue;
        // Use by a store is not an escape if the use is the address.
        if (const StoreInst *SI = dyn_cast<StoreInst>(UUser))
          if (V != SI->getValueOperand())
            continue;
        break;
      default:
        // Regular calls and other stuff are not considered escapes.
        continue;
      }
      // Otherwise, conservatively assume an escape.
      DEBUG(dbgs() << "Assuming ptr escapes.\n");
      return true;
    }
  } while (!Worklist.empty());

  // No escapes found.
  DEBUG(dbgs() << "Ptr does not escape.\n");
  return false;
}

/// @}
///
/// \defgroup ARCOpt ARC Optimization.
/// @{

// TODO: On code like this:
//
// objc_retain(%x)
// stuff_that_cannot_release()
// objc_autorelease(%x)
// stuff_that_cannot_release()
// objc_retain(%x)
// stuff_that_cannot_release()
// objc_autorelease(%x)
//
// The second retain and autorelease can be deleted.

// TODO: It should be possible to delete
// objc_autoreleasePoolPush and objc_autoreleasePoolPop
// pairs if nothing is actually autoreleased between them. Also, autorelease
// calls followed by objc_autoreleasePoolPop calls (perhaps in ObjC++ code
// after inlining) can be turned into plain release calls.

// TODO: Critical-edge splitting. If the optimial insertion point is
// a critical edge, the current algorithm has to fail, because it doesn't
// know how to split edges. It should be possible to make the optimizer
// think in terms of edges, rather than blocks, and then split critical
// edges on demand.

// TODO: OptimizeSequences could generalized to be Interprocedural.

// TODO: Recognize that a bunch of other objc runtime calls have
// non-escaping arguments and non-releasing arguments, and may be
// non-autoreleasing.

// TODO: Sink autorelease calls as far as possible. Unfortunately we
// usually can't sink them past other calls, which would be the main
// case where it would be useful.

// TODO: The pointer returned from objc_loadWeakRetained is retained.

// TODO: Delete release+retain pairs (rare).

STATISTIC(NumNoops,       "Number of no-op objc calls eliminated");
STATISTIC(NumPartialNoops, "Number of partially no-op objc calls eliminated");
STATISTIC(NumAutoreleases,"Number of autoreleases converted to releases");
STATISTIC(NumRets,        "Number of return value forwarding "
                          "retain+autoreleaes eliminated");
STATISTIC(NumRRs,         "Number of retain+release paths eliminated");
STATISTIC(NumPeeps,       "Number of calls peephole-optimized");

namespace {
  /// \enum Sequence
  ///
  /// \brief A sequence of states that a pointer may go through in which an
  /// objc_retain and objc_release are actually needed.
  enum Sequence {
    S_None,
    S_Retain,         ///< objc_retain(x).
    S_CanRelease,     ///< foo(x) -- x could possibly see a ref count decrement.
    S_Use,            ///< any use of x.
    S_Stop,           ///< like S_Release, but code motion is stopped.
    S_Release,        ///< objc_release(x).
    S_MovableRelease  ///< objc_release(x), !clang.imprecise_release.
  };

  raw_ostream &operator<<(raw_ostream &OS, const Sequence S)
    LLVM_ATTRIBUTE_UNUSED;
  raw_ostream &operator<<(raw_ostream &OS, const Sequence S) {
    switch (S) {
    case S_None:
      return OS << "S_None";
    case S_Retain:
      return OS << "S_Retain";
    case S_CanRelease:
      return OS << "S_CanRelease";
    case S_Use:
      return OS << "S_Use";
    case S_Release:
      return OS << "S_Release";
    case S_MovableRelease:
      return OS << "S_MovableRelease";
    case S_Stop:
      return OS << "S_Stop";
    }
    llvm_unreachable("Unknown sequence type.");
  }
}

static Sequence MergeSeqs(Sequence A, Sequence B, bool TopDown) {
  // The easy cases.
  if (A == B)
    return A;
  if (A == S_None || B == S_None)
    return S_None;

  if (A > B) std::swap(A, B);
  if (TopDown) {
    // Choose the side which is further along in the sequence.
    if ((A == S_Retain || A == S_CanRelease) &&
        (B == S_CanRelease || B == S_Use))
      return B;
  } else {
    // Choose the side which is further along in the sequence.
    if ((A == S_Use || A == S_CanRelease) &&
        (B == S_Use || B == S_Release || B == S_Stop || B == S_MovableRelease))
      return A;
    // If both sides are releases, choose the more conservative one.
    if (A == S_Stop && (B == S_Release || B == S_MovableRelease))
      return A;
    if (A == S_Release && B == S_MovableRelease)
      return A;
  }

  return S_None;
}

namespace {
  /// \brief Unidirectional information about either a
  /// retain-decrement-use-release sequence or release-use-decrement-retain
  /// reverse sequence.
  struct RRInfo {
    /// After an objc_retain, the reference count of the referenced
    /// object is known to be positive. Similarly, before an objc_release, the
    /// reference count of the referenced object is known to be positive. If
    /// there are retain-release pairs in code regions where the retain count
    /// is known to be positive, they can be eliminated, regardless of any side
    /// effects between them.
    ///
    /// Also, a retain+release pair nested within another retain+release
    /// pair all on the known same pointer value can be eliminated, regardless
    /// of any intervening side effects.
    ///
    /// KnownSafe is true when either of these conditions is satisfied.
    bool KnownSafe;

    /// True of the objc_release calls are all marked with the "tail" keyword.
    bool IsTailCallRelease;

    /// If the Calls are objc_release calls and they all have a
    /// clang.imprecise_release tag, this is the metadata tag.
    MDNode *ReleaseMetadata;

    /// For a top-down sequence, the set of objc_retains or
    /// objc_retainBlocks. For bottom-up, the set of objc_releases.
    SmallPtrSet<Instruction *, 2> Calls;

    /// The set of optimal insert positions for moving calls in the opposite
    /// sequence.
    SmallPtrSet<Instruction *, 2> ReverseInsertPts;

    RRInfo() :
      KnownSafe(false), IsTailCallRelease(false), ReleaseMetadata(0) {}

    void clear();

    bool IsTrackingImpreciseReleases() {
      return ReleaseMetadata != 0;
    }
  };
}

void RRInfo::clear() {
  KnownSafe = false;
  IsTailCallRelease = false;
  ReleaseMetadata = 0;
  Calls.clear();
  ReverseInsertPts.clear();
}

namespace {
  /// \brief This class summarizes several per-pointer runtime properties which
  /// are propogated through the flow graph.
  class PtrState {
    /// True if the reference count is known to be incremented.
    bool KnownPositiveRefCount;

    /// True if we've seen an opportunity for partial RR elimination, such as
    /// pushing calls into a CFG triangle or into one side of a CFG diamond.
    bool Partial;

    /// The current position in the sequence.
    Sequence Seq : 8;

  public:
    /// Unidirectional information about the current sequence.
    ///
    /// TODO: Encapsulate this better.
    RRInfo RRI;

    PtrState() : KnownPositiveRefCount(false), Partial(false),
                 Seq(S_None) {}

    void SetKnownPositiveRefCount() {
      KnownPositiveRefCount = true;
    }

    void ClearKnownPositiveRefCount() {
      KnownPositiveRefCount = false;
    }

    bool HasKnownPositiveRefCount() const {
      return KnownPositiveRefCount;
    }

    void SetSeq(Sequence NewSeq) {
      DEBUG(dbgs() << "Old: " << Seq << "; New: " << NewSeq << "\n");
      Seq = NewSeq;
    }

    Sequence GetSeq() const {
      return Seq;
    }

    void ClearSequenceProgress() {
      ResetSequenceProgress(S_None);
    }

    void ResetSequenceProgress(Sequence NewSeq) {
      SetSeq(NewSeq);
      Partial = false;
      RRI.clear();
    }

    void Merge(const PtrState &Other, bool TopDown);
  };
}

void
PtrState::Merge(const PtrState &Other, bool TopDown) {
  Seq = MergeSeqs(Seq, Other.Seq, TopDown);
  KnownPositiveRefCount = KnownPositiveRefCount && Other.KnownPositiveRefCount;

  // If we're not in a sequence (anymore), drop all associated state.
  if (Seq == S_None) {
    Partial = false;
    RRI.clear();
  } else if (Partial || Other.Partial) {
    // If we're doing a merge on a path that's previously seen a partial
    // merge, conservatively drop the sequence, to avoid doing partial
    // RR elimination. If the branch predicates for the two merge differ,
    // mixing them is unsafe.
    ClearSequenceProgress();
  } else {
    // Conservatively merge the ReleaseMetadata information.
    if (RRI.ReleaseMetadata != Other.RRI.ReleaseMetadata)
      RRI.ReleaseMetadata = 0;

    RRI.KnownSafe = RRI.KnownSafe && Other.RRI.KnownSafe;
    RRI.IsTailCallRelease = RRI.IsTailCallRelease &&
                            Other.RRI.IsTailCallRelease;
    RRI.Calls.insert(Other.RRI.Calls.begin(), Other.RRI.Calls.end());

    // Merge the insert point sets. If there are any differences,
    // that makes this a partial merge.
    Partial = RRI.ReverseInsertPts.size() != Other.RRI.ReverseInsertPts.size();
    for (SmallPtrSet<Instruction *, 2>::const_iterator
         I = Other.RRI.ReverseInsertPts.begin(),
         E = Other.RRI.ReverseInsertPts.end(); I != E; ++I)
      Partial |= RRI.ReverseInsertPts.insert(*I);
  }
}

namespace {
  /// \brief Per-BasicBlock state.
  class BBState {
    /// The number of unique control paths from the entry which can reach this
    /// block.
    unsigned TopDownPathCount;

    /// The number of unique control paths to exits from this block.
    unsigned BottomUpPathCount;

    /// A type for PerPtrTopDown and PerPtrBottomUp.
    typedef MapVector<const Value *, PtrState> MapTy;

    /// The top-down traversal uses this to record information known about a
    /// pointer at the bottom of each block.
    MapTy PerPtrTopDown;

    /// The bottom-up traversal uses this to record information known about a
    /// pointer at the top of each block.
    MapTy PerPtrBottomUp;

    /// Effective predecessors of the current block ignoring ignorable edges and
    /// ignored backedges.
    SmallVector<BasicBlock *, 2> Preds;
    /// Effective successors of the current block ignoring ignorable edges and
    /// ignored backedges.
    SmallVector<BasicBlock *, 2> Succs;

  public:
    BBState() : TopDownPathCount(0), BottomUpPathCount(0) {}

    typedef MapTy::iterator ptr_iterator;
    typedef MapTy::const_iterator ptr_const_iterator;

    ptr_iterator top_down_ptr_begin() { return PerPtrTopDown.begin(); }
    ptr_iterator top_down_ptr_end() { return PerPtrTopDown.end(); }
    ptr_const_iterator top_down_ptr_begin() const {
      return PerPtrTopDown.begin();
    }
    ptr_const_iterator top_down_ptr_end() const {
      return PerPtrTopDown.end();
    }

    ptr_iterator bottom_up_ptr_begin() { return PerPtrBottomUp.begin(); }
    ptr_iterator bottom_up_ptr_end() { return PerPtrBottomUp.end(); }
    ptr_const_iterator bottom_up_ptr_begin() const {
      return PerPtrBottomUp.begin();
    }
    ptr_const_iterator bottom_up_ptr_end() const {
      return PerPtrBottomUp.end();
    }

    /// Mark this block as being an entry block, which has one path from the
    /// entry by definition.
    void SetAsEntry() { TopDownPathCount = 1; }

    /// Mark this block as being an exit block, which has one path to an exit by
    /// definition.
    void SetAsExit()  { BottomUpPathCount = 1; }

    PtrState &getPtrTopDownState(const Value *Arg) {
      return PerPtrTopDown[Arg];
    }

    PtrState &getPtrBottomUpState(const Value *Arg) {
      return PerPtrBottomUp[Arg];
    }

    void clearBottomUpPointers() {
      PerPtrBottomUp.clear();
    }

    void clearTopDownPointers() {
      PerPtrTopDown.clear();
    }

    void InitFromPred(const BBState &Other);
    void InitFromSucc(const BBState &Other);
    void MergePred(const BBState &Other);
    void MergeSucc(const BBState &Other);

    /// Return the number of possible unique paths from an entry to an exit
    /// which pass through this block. This is only valid after both the
    /// top-down and bottom-up traversals are complete.
    unsigned GetAllPathCount() const {
      assert(TopDownPathCount != 0);
      assert(BottomUpPathCount != 0);
      return TopDownPathCount * BottomUpPathCount;
    }

    // Specialized CFG utilities.
    typedef SmallVectorImpl<BasicBlock *>::const_iterator edge_iterator;
    edge_iterator pred_begin() { return Preds.begin(); }
    edge_iterator pred_end() { return Preds.end(); }
    edge_iterator succ_begin() { return Succs.begin(); }
    edge_iterator succ_end() { return Succs.end(); }

    void addSucc(BasicBlock *Succ) { Succs.push_back(Succ); }
    void addPred(BasicBlock *Pred) { Preds.push_back(Pred); }

    bool isExit() const { return Succs.empty(); }
  };
}

void BBState::InitFromPred(const BBState &Other) {
  PerPtrTopDown = Other.PerPtrTopDown;
  TopDownPathCount = Other.TopDownPathCount;
}

void BBState::InitFromSucc(const BBState &Other) {
  PerPtrBottomUp = Other.PerPtrBottomUp;
  BottomUpPathCount = Other.BottomUpPathCount;
}

/// The top-down traversal uses this to merge information about predecessors to
/// form the initial state for a new block.
void BBState::MergePred(const BBState &Other) {
  // Other.TopDownPathCount can be 0, in which case it is either dead or a
  // loop backedge. Loop backedges are special.
  TopDownPathCount += Other.TopDownPathCount;

  // Check for overflow. If we have overflow, fall back to conservative
  // behavior.
  if (TopDownPathCount < Other.TopDownPathCount) {
    clearTopDownPointers();
    return;
  }

  // For each entry in the other set, if our set has an entry with the same key,
  // merge the entries. Otherwise, copy the entry and merge it with an empty
  // entry.
  for (ptr_const_iterator MI = Other.top_down_ptr_begin(),
       ME = Other.top_down_ptr_end(); MI != ME; ++MI) {
    std::pair<ptr_iterator, bool> Pair = PerPtrTopDown.insert(*MI);
    Pair.first->second.Merge(Pair.second ? PtrState() : MI->second,
                             /*TopDown=*/true);
  }

  // For each entry in our set, if the other set doesn't have an entry with the
  // same key, force it to merge with an empty entry.
  for (ptr_iterator MI = top_down_ptr_begin(),
       ME = top_down_ptr_end(); MI != ME; ++MI)
    if (Other.PerPtrTopDown.find(MI->first) == Other.PerPtrTopDown.end())
      MI->second.Merge(PtrState(), /*TopDown=*/true);
}

/// The bottom-up traversal uses this to merge information about successors to
/// form the initial state for a new block.
void BBState::MergeSucc(const BBState &Other) {
  // Other.BottomUpPathCount can be 0, in which case it is either dead or a
  // loop backedge. Loop backedges are special.
  BottomUpPathCount += Other.BottomUpPathCount;

  // Check for overflow. If we have overflow, fall back to conservative
  // behavior.
  if (BottomUpPathCount < Other.BottomUpPathCount) {
    clearBottomUpPointers();
    return;
  }

  // For each entry in the other set, if our set has an entry with the
  // same key, merge the entries. Otherwise, copy the entry and merge
  // it with an empty entry.
  for (ptr_const_iterator MI = Other.bottom_up_ptr_begin(),
       ME = Other.bottom_up_ptr_end(); MI != ME; ++MI) {
    std::pair<ptr_iterator, bool> Pair = PerPtrBottomUp.insert(*MI);
    Pair.first->second.Merge(Pair.second ? PtrState() : MI->second,
                             /*TopDown=*/false);
  }

  // For each entry in our set, if the other set doesn't have an entry
  // with the same key, force it to merge with an empty entry.
  for (ptr_iterator MI = bottom_up_ptr_begin(),
       ME = bottom_up_ptr_end(); MI != ME; ++MI)
    if (Other.PerPtrBottomUp.find(MI->first) == Other.PerPtrBottomUp.end())
      MI->second.Merge(PtrState(), /*TopDown=*/false);
}

// Only enable ARC Annotations if we are building a debug version of
// libObjCARCOpts.
#ifndef NDEBUG
#define ARC_ANNOTATIONS
#endif

// Define some macros along the lines of DEBUG and some helper functions to make
// it cleaner to create annotations in the source code and to no-op when not
// building in debug mode.
#ifdef ARC_ANNOTATIONS

#include "llvm/Support/CommandLine.h"

/// Enable/disable ARC sequence annotations.
static cl::opt<bool>
EnableARCAnnotations("enable-objc-arc-annotations", cl::init(false));

/// This function appends a unique ARCAnnotationProvenanceSourceMDKind id to an
/// instruction so that we can track backwards when post processing via the llvm
/// arc annotation processor tool. If the function is an
static MDString *AppendMDNodeToSourcePtr(unsigned NodeId,
                                         Value *Ptr) {
  MDString *Hash = 0;

  // If pointer is a result of an instruction and it does not have a source
  // MDNode it, attach a new MDNode onto it. If pointer is a result of
  // an instruction and does have a source MDNode attached to it, return a
  // reference to said Node. Otherwise just return 0.
  if (Instruction *Inst = dyn_cast<Instruction>(Ptr)) {
    MDNode *Node;
    if (!(Node = Inst->getMetadata(NodeId))) {
      // We do not have any node. Generate and attatch the hash MDString to the
      // instruction.

      // We just use an MDString to ensure that this metadata gets written out
      // of line at the module level and to provide a very simple format
      // encoding the information herein. Both of these makes it simpler to
      // parse the annotations by a simple external program.
      std::string Str;
      raw_string_ostream os(Str);
      os << "(" << Inst->getParent()->getParent()->getName() << ",%"
         << Inst->getName() << ")";

      Hash = MDString::get(Inst->getContext(), os.str());
      Inst->setMetadata(NodeId, MDNode::get(Inst->getContext(),Hash));
    } else {
      // We have a node. Grab its hash and return it.
      assert(Node->getNumOperands() == 1 &&
        "An ARCAnnotationProvenanceSourceMDKind can only have 1 operand.");
      Hash = cast<MDString>(Node->getOperand(0));
    }
  } else if (Argument *Arg = dyn_cast<Argument>(Ptr)) {
    std::string str;
    raw_string_ostream os(str);
    os << "(" << Arg->getParent()->getName() << ",%" << Arg->getName()
       << ")";
    Hash = MDString::get(Arg->getContext(), os.str());
  }

  return Hash;
}

static std::string SequenceToString(Sequence A) {
  std::string str;
  raw_string_ostream os(str);
  os << A;
  return os.str();
}

/// Helper function to change a Sequence into a String object using our overload
/// for raw_ostream so we only have printing code in one location.
static MDString *SequenceToMDString(LLVMContext &Context,
                                    Sequence A) {
  return MDString::get(Context, SequenceToString(A));
}

/// A simple function to generate a MDNode which describes the change in state
/// for Value *Ptr caused by Instruction *Inst.
static void AppendMDNodeToInstForPtr(unsigned NodeId,
                                     Instruction *Inst,
                                     Value *Ptr,
                                     MDString *PtrSourceMDNodeID,
                                     Sequence OldSeq,
                                     Sequence NewSeq) {
  MDNode *Node = 0;
  Value *tmp[3] = {PtrSourceMDNodeID,
                   SequenceToMDString(Inst->getContext(),
                                      OldSeq),
                   SequenceToMDString(Inst->getContext(),
                                      NewSeq)};
  Node = MDNode::get(Inst->getContext(),
                     ArrayRef<Value*>(tmp, 3));

  Inst->setMetadata(NodeId, Node);
}

/// Add to the beginning of the basic block llvm.ptr.annotations which show the
/// state of a pointer at the entrance to a basic block.
static void GenerateARCBBEntranceAnnotation(const char *Name, BasicBlock *BB,
                                            Value *Ptr, Sequence Seq) {
  Module *M = BB->getParent()->getParent();
  LLVMContext &C = M->getContext();
  Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
  Type *I8XX = PointerType::getUnqual(I8X);
  Type *Params[] = {I8XX, I8XX};
  FunctionType *FTy = FunctionType::get(Type::getVoidTy(C),
                                        ArrayRef<Type*>(Params, 2),
                                        /*isVarArg=*/false);
  Constant *Callee = M->getOrInsertFunction(Name, FTy);

  IRBuilder<> Builder(BB, BB->getFirstInsertionPt());

  Value *PtrName;
  StringRef Tmp = Ptr->getName();
  if (0 == (PtrName = M->getGlobalVariable(Tmp, true))) {
    Value *ActualPtrName = Builder.CreateGlobalStringPtr(Tmp,
                                                         Tmp + "_STR");
    PtrName = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
                                 cast<Constant>(ActualPtrName), Tmp);
  }

  Value *S;
  std::string SeqStr = SequenceToString(Seq);
  if (0 == (S = M->getGlobalVariable(SeqStr, true))) {
    Value *ActualPtrName = Builder.CreateGlobalStringPtr(SeqStr,
                                                         SeqStr + "_STR");
    S = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
                           cast<Constant>(ActualPtrName), SeqStr);
  }

  Builder.CreateCall2(Callee, PtrName, S);
}

/// Add to the end of the basic block llvm.ptr.annotations which show the state
/// of the pointer at the bottom of the basic block.
static void GenerateARCBBTerminatorAnnotation(const char *Name, BasicBlock *BB,
                                              Value *Ptr, Sequence Seq) {
  Module *M = BB->getParent()->getParent();
  LLVMContext &C = M->getContext();
  Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
  Type *I8XX = PointerType::getUnqual(I8X);
  Type *Params[] = {I8XX, I8XX};
  FunctionType *FTy = FunctionType::get(Type::getVoidTy(C),
                                        ArrayRef<Type*>(Params, 2),
                                        /*isVarArg=*/false);
  Constant *Callee = M->getOrInsertFunction(Name, FTy);

  IRBuilder<> Builder(BB, llvm::prior(BB->end()));

  Value *PtrName;
  StringRef Tmp = Ptr->getName();
  if (0 == (PtrName = M->getGlobalVariable(Tmp, true))) {
    Value *ActualPtrName = Builder.CreateGlobalStringPtr(Tmp,
                                                         Tmp + "_STR");
    PtrName = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
                                 cast<Constant>(ActualPtrName), Tmp);
  }

  Value *S;
  std::string SeqStr = SequenceToString(Seq);
  if (0 == (S = M->getGlobalVariable(SeqStr, true))) {
    Value *ActualPtrName = Builder.CreateGlobalStringPtr(SeqStr,
                                                         SeqStr + "_STR");
    S = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
                           cast<Constant>(ActualPtrName), SeqStr);
  }
  Builder.CreateCall2(Callee, PtrName, S);
}

/// Adds a source annotation to pointer and a state change annotation to Inst
/// referencing the source annotation and the old/new state of pointer.
static void GenerateARCAnnotation(unsigned InstMDId,
                                  unsigned PtrMDId,
                                  Instruction *Inst,
                                  Value *Ptr,
                                  Sequence OldSeq,
                                  Sequence NewSeq) {
  if (EnableARCAnnotations) {
    // First generate the source annotation on our pointer. This will return an
    // MDString* if Ptr actually comes from an instruction implying we can put
    // in a source annotation. If AppendMDNodeToSourcePtr returns 0 (i.e. NULL),
    // then we know that our pointer is from an Argument so we put a reference
    // to the argument number.
    //
    // The point of this is to make it easy for the
    // llvm-arc-annotation-processor tool to cross reference where the source
    // pointer is in the LLVM IR since the LLVM IR parser does not submit such
    // information via debug info for backends to use (since why would anyone
    // need such a thing from LLVM IR besides in non standard cases
    // [i.e. this]).
    MDString *SourcePtrMDNode =
      AppendMDNodeToSourcePtr(PtrMDId, Ptr);
    AppendMDNodeToInstForPtr(InstMDId, Inst, Ptr, SourcePtrMDNode, OldSeq,
                             NewSeq);
  }
}

// The actual interface for accessing the above functionality is defined via
// some simple macros which are defined below. We do this so that the user does
// not need to pass in what metadata id is needed resulting in cleaner code and
// additionally since it provides an easy way to conditionally no-op all
// annotation support in a non-debug build.

/// Use this macro to annotate a sequence state change when processing
/// instructions bottom up,
#define ANNOTATE_BOTTOMUP(inst, ptr, old, new)                          \
  GenerateARCAnnotation(ARCAnnotationBottomUpMDKind,                    \
                        ARCAnnotationProvenanceSourceMDKind, (inst),    \
                        const_cast<Value*>(ptr), (old), (new))
/// Use this macro to annotate a sequence state change when processing
/// instructions top down.
#define ANNOTATE_TOPDOWN(inst, ptr, old, new)                           \
  GenerateARCAnnotation(ARCAnnotationTopDownMDKind,                     \
                        ARCAnnotationProvenanceSourceMDKind, (inst),    \
                        const_cast<Value*>(ptr), (old), (new))

#define ANNOTATE_BB(_states, _bb, _name, _type, _direction)                   \
  do {                                                                        \
    if (EnableARCAnnotations) {                                               \
      for(BBState::ptr_const_iterator I = (_states)._direction##_ptr_begin(), \
          E = (_states)._direction##_ptr_end(); I != E; ++I) {                \
        Value *Ptr = const_cast<Value*>(I->first);                            \
        Sequence Seq = I->second.GetSeq();                                    \
        GenerateARCBB ## _type ## Annotation(_name, (_bb), Ptr, Seq);         \
      }                                                                       \
    }                                                                         \
  } while (0)

#define ANNOTATE_BOTTOMUP_BBSTART(_states, _basicblock)                       \
    ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.bottomup.bbstart", \
                Entrance, bottom_up)
#define ANNOTATE_BOTTOMUP_BBEND(_states, _basicblock)                         \
    ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.bottomup.bbend",   \
                Terminator, bottom_up)
#define ANNOTATE_TOPDOWN_BBSTART(_states, _basicblock)                        \
    ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.topdown.bbstart",  \
                Entrance, top_down)
#define ANNOTATE_TOPDOWN_BBEND(_states, _basicblock)                          \
    ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.topdown.bbend",    \
                Terminator, top_down)

#else // !ARC_ANNOTATION
// If annotations are off, noop.
#define ANNOTATE_BOTTOMUP(inst, ptr, old, new)
#define ANNOTATE_TOPDOWN(inst, ptr, old, new)
#define ANNOTATE_BOTTOMUP_BBSTART(states, basicblock)
#define ANNOTATE_BOTTOMUP_BBEND(states, basicblock)
#define ANNOTATE_TOPDOWN_BBSTART(states, basicblock)
#define ANNOTATE_TOPDOWN_BBEND(states, basicblock)
#endif // !ARC_ANNOTATION

namespace {
  /// \brief The main ARC optimization pass.
  class ObjCARCOpt : public FunctionPass {
    bool Changed;
    ProvenanceAnalysis PA;

    /// A flag indicating whether this optimization pass should run.
    bool Run;

    /// Declarations for ObjC runtime functions, for use in creating calls to
    /// them. These are initialized lazily to avoid cluttering up the Module
    /// with unused declarations.

    /// Declaration for ObjC runtime function
    /// objc_retainAutoreleasedReturnValue.
    Constant *RetainRVCallee;
    /// Declaration for ObjC runtime function objc_autoreleaseReturnValue.
    Constant *AutoreleaseRVCallee;
    /// Declaration for ObjC runtime function objc_release.
    Constant *ReleaseCallee;
    /// Declaration for ObjC runtime function objc_retain.
    Constant *RetainCallee;
    /// Declaration for ObjC runtime function objc_retainBlock.
    Constant *RetainBlockCallee;
    /// Declaration for ObjC runtime function objc_autorelease.
    Constant *AutoreleaseCallee;

    /// Flags which determine whether each of the interesting runtine functions
    /// is in fact used in the current function.
    unsigned UsedInThisFunction;

    /// The Metadata Kind for clang.imprecise_release metadata.
    unsigned ImpreciseReleaseMDKind;

    /// The Metadata Kind for clang.arc.copy_on_escape metadata.
    unsigned CopyOnEscapeMDKind;

    /// The Metadata Kind for clang.arc.no_objc_arc_exceptions metadata.
    unsigned NoObjCARCExceptionsMDKind;

#ifdef ARC_ANNOTATIONS
    /// The Metadata Kind for llvm.arc.annotation.bottomup metadata.
    unsigned ARCAnnotationBottomUpMDKind;
    /// The Metadata Kind for llvm.arc.annotation.topdown metadata.
    unsigned ARCAnnotationTopDownMDKind;
    /// The Metadata Kind for llvm.arc.annotation.provenancesource metadata.
    unsigned ARCAnnotationProvenanceSourceMDKind;
#endif // ARC_ANNOATIONS

    Constant *getRetainRVCallee(Module *M);
    Constant *getAutoreleaseRVCallee(Module *M);
    Constant *getReleaseCallee(Module *M);
    Constant *getRetainCallee(Module *M);
    Constant *getRetainBlockCallee(Module *M);
    Constant *getAutoreleaseCallee(Module *M);

    bool IsRetainBlockOptimizable(const Instruction *Inst);

    void OptimizeRetainCall(Function &F, Instruction *Retain);
    bool OptimizeRetainRVCall(Function &F, Instruction *RetainRV);
    void OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV,
                                   InstructionClass &Class);
    bool OptimizeRetainBlockCall(Function &F, Instruction *RetainBlock,
                                 InstructionClass &Class);
    void OptimizeIndividualCalls(Function &F);

    void CheckForCFGHazards(const BasicBlock *BB,
                            DenseMap<const BasicBlock *, BBState> &BBStates,
                            BBState &MyStates) const;
    bool VisitInstructionBottomUp(Instruction *Inst,
                                  BasicBlock *BB,
                                  MapVector<Value *, RRInfo> &Retains,
                                  BBState &MyStates);
    bool VisitBottomUp(BasicBlock *BB,
                       DenseMap<const BasicBlock *, BBState> &BBStates,
                       MapVector<Value *, RRInfo> &Retains);
    bool VisitInstructionTopDown(Instruction *Inst,
                                 DenseMap<Value *, RRInfo> &Releases,
                                 BBState &MyStates);
    bool VisitTopDown(BasicBlock *BB,
                      DenseMap<const BasicBlock *, BBState> &BBStates,
                      DenseMap<Value *, RRInfo> &Releases);
    bool Visit(Function &F,
               DenseMap<const BasicBlock *, BBState> &BBStates,
               MapVector<Value *, RRInfo> &Retains,
               DenseMap<Value *, RRInfo> &Releases);

    void MoveCalls(Value *Arg, RRInfo &RetainsToMove, RRInfo &ReleasesToMove,
                   MapVector<Value *, RRInfo> &Retains,
                   DenseMap<Value *, RRInfo> &Releases,
                   SmallVectorImpl<Instruction *> &DeadInsts,
                   Module *M);

    bool ConnectTDBUTraversals(DenseMap<const BasicBlock *, BBState> &BBStates,
                               MapVector<Value *, RRInfo> &Retains,
                               DenseMap<Value *, RRInfo> &Releases,
                               Module *M,
                               SmallVector<Instruction *, 4> &NewRetains,
                               SmallVector<Instruction *, 4> &NewReleases,
                               SmallVector<Instruction *, 8> &DeadInsts,
                               RRInfo &RetainsToMove,
                               RRInfo &ReleasesToMove,
                               Value *Arg,
                               bool KnownSafe,
                               bool &AnyPairsCompletelyEliminated);

    bool PerformCodePlacement(DenseMap<const BasicBlock *, BBState> &BBStates,
                              MapVector<Value *, RRInfo> &Retains,
                              DenseMap<Value *, RRInfo> &Releases,
                              Module *M);

    void OptimizeWeakCalls(Function &F);

    bool OptimizeSequences(Function &F);

    void OptimizeReturns(Function &F);

    virtual void getAnalysisUsage(AnalysisUsage &AU) const;
    virtual bool doInitialization(Module &M);
    virtual bool runOnFunction(Function &F);
    virtual void releaseMemory();

  public:
    static char ID;
    ObjCARCOpt() : FunctionPass(ID) {
      initializeObjCARCOptPass(*PassRegistry::getPassRegistry());
    }
  };
}

char ObjCARCOpt::ID = 0;
INITIALIZE_PASS_BEGIN(ObjCARCOpt,
                      "objc-arc", "ObjC ARC optimization", false, false)
INITIALIZE_PASS_DEPENDENCY(ObjCARCAliasAnalysis)
INITIALIZE_PASS_END(ObjCARCOpt,
                    "objc-arc", "ObjC ARC optimization", false, false)

Pass *llvm::createObjCARCOptPass() {
  return new ObjCARCOpt();
}

void ObjCARCOpt::getAnalysisUsage(AnalysisUsage &AU) const {
  AU.addRequired<ObjCARCAliasAnalysis>();
  AU.addRequired<AliasAnalysis>();
  // ARC optimization doesn't currently split critical edges.
  AU.setPreservesCFG();
}

bool ObjCARCOpt::IsRetainBlockOptimizable(const Instruction *Inst) {
  // Without the magic metadata tag, we have to assume this might be an
  // objc_retainBlock call inserted to convert a block pointer to an id,
  // in which case it really is needed.
  if (!Inst->getMetadata(CopyOnEscapeMDKind))
    return false;

  // If the pointer "escapes" (not including being used in a call),
  // the copy may be needed.
  if (DoesRetainableObjPtrEscape(Inst))
    return false;

  // Otherwise, it's not needed.
  return true;
}

Constant *ObjCARCOpt::getRetainRVCallee(Module *M) {
  if (!RetainRVCallee) {
    LLVMContext &C = M->getContext();
    Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
    Type *Params[] = { I8X };
    FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false);
    AttributeSet Attribute =
      AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
                                  Attribute::NoUnwind);
    RetainRVCallee =
      M->getOrInsertFunction("objc_retainAutoreleasedReturnValue", FTy,
                             Attribute);
  }
  return RetainRVCallee;
}

Constant *ObjCARCOpt::getAutoreleaseRVCallee(Module *M) {
  if (!AutoreleaseRVCallee) {
    LLVMContext &C = M->getContext();
    Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
    Type *Params[] = { I8X };
    FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false);
    AttributeSet Attribute =
      AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
                                  Attribute::NoUnwind);
    AutoreleaseRVCallee =
      M->getOrInsertFunction("objc_autoreleaseReturnValue", FTy,
                             Attribute);
  }
  return AutoreleaseRVCallee;
}

Constant *ObjCARCOpt::getReleaseCallee(Module *M) {
  if (!ReleaseCallee) {
    LLVMContext &C = M->getContext();
    Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
    AttributeSet Attribute =
      AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
                                  Attribute::NoUnwind);
    ReleaseCallee =
      M->getOrInsertFunction(
        "objc_release",
        FunctionType::get(Type::getVoidTy(C), Params, /*isVarArg=*/false),
        Attribute);
  }
  return ReleaseCallee;
}

Constant *ObjCARCOpt::getRetainCallee(Module *M) {
  if (!RetainCallee) {
    LLVMContext &C = M->getContext();
    Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
    AttributeSet Attribute =
      AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
                                  Attribute::NoUnwind);
    RetainCallee =
      M->getOrInsertFunction(
        "objc_retain",
        FunctionType::get(Params[0], Params, /*isVarArg=*/false),
        Attribute);
  }
  return RetainCallee;
}

Constant *ObjCARCOpt::getRetainBlockCallee(Module *M) {
  if (!RetainBlockCallee) {
    LLVMContext &C = M->getContext();
    Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
    // objc_retainBlock is not nounwind because it calls user copy constructors
    // which could theoretically throw.
    RetainBlockCallee =
      M->getOrInsertFunction(
        "objc_retainBlock",
        FunctionType::get(Params[0], Params, /*isVarArg=*/false),
        AttributeSet());
  }
  return RetainBlockCallee;
}

Constant *ObjCARCOpt::getAutoreleaseCallee(Module *M) {
  if (!AutoreleaseCallee) {
    LLVMContext &C = M->getContext();
    Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
    AttributeSet Attribute =
      AttributeSet().addAttribute(M->getContext(), AttributeSet::FunctionIndex,
                                  Attribute::NoUnwind);
    AutoreleaseCallee =
      M->getOrInsertFunction(
        "objc_autorelease",
        FunctionType::get(Params[0], Params, /*isVarArg=*/false),
        Attribute);
  }
  return AutoreleaseCallee;
}

/// Turn objc_retain into objc_retainAutoreleasedReturnValue if the operand is a
/// return value.
void
ObjCARCOpt::OptimizeRetainCall(Function &F, Instruction *Retain) {
  ImmutableCallSite CS(GetObjCArg(Retain));
  const Instruction *Call = CS.getInstruction();
  if (!Call) return;
  if (Call->getParent() != Retain->getParent()) return;

  // Check that the call is next to the retain.
  BasicBlock::const_iterator I = Call;
  ++I;
  while (IsNoopInstruction(I)) ++I;
  if (&*I != Retain)
    return;

  // Turn it to an objc_retainAutoreleasedReturnValue..
  Changed = true;
  ++NumPeeps;

  DEBUG(dbgs() << "Transforming objc_retain => "
                  "objc_retainAutoreleasedReturnValue since the operand is a "
                  "return value.\nOld: "<< *Retain << "\n");

  cast<CallInst>(Retain)->setCalledFunction(getRetainRVCallee(F.getParent()));

  DEBUG(dbgs() << "New: " << *Retain << "\n");
}

/// Turn objc_retainAutoreleasedReturnValue into objc_retain if the operand is
/// not a return value.  Or, if it can be paired with an
/// objc_autoreleaseReturnValue, delete the pair and return true.
bool
ObjCARCOpt::OptimizeRetainRVCall(Function &F, Instruction *RetainRV) {
  // Check for the argument being from an immediately preceding call or invoke.
  const Value *Arg = GetObjCArg(RetainRV);
  ImmutableCallSite CS(Arg);
  if (const Instruction *Call = CS.getInstruction()) {
    if (Call->getParent() == RetainRV->getParent()) {
      BasicBlock::const_iterator I = Call;
      ++I;
      while (IsNoopInstruction(I)) ++I;
      if (&*I == RetainRV)
        return false;
    } else if (const InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
      BasicBlock *RetainRVParent = RetainRV->getParent();
      if (II->getNormalDest() == RetainRVParent) {
        BasicBlock::const_iterator I = RetainRVParent->begin();
        while (IsNoopInstruction(I)) ++I;
        if (&*I == RetainRV)
          return false;
      }
    }
  }

  // Check for being preceded by an objc_autoreleaseReturnValue on the same
  // pointer. In this case, we can delete the pair.
  BasicBlock::iterator I = RetainRV, Begin = RetainRV->getParent()->begin();
  if (I != Begin) {
    do --I; while (I != Begin && IsNoopInstruction(I));
    if (GetBasicInstructionClass(I) == IC_AutoreleaseRV &&
        GetObjCArg(I) == Arg) {
      Changed = true;
      ++NumPeeps;

      DEBUG(dbgs() << "Erasing autoreleaseRV,retainRV pair: " << *I << "\n"
                   << "Erasing " << *RetainRV << "\n");

      EraseInstruction(I);
      EraseInstruction(RetainRV);
      return true;
    }
  }

  // Turn it to a plain objc_retain.
  Changed = true;
  ++NumPeeps;

  DEBUG(dbgs() << "Transforming objc_retainAutoreleasedReturnValue => "
                  "objc_retain since the operand is not a return value.\n"
                  "Old = " << *RetainRV << "\n");

  cast<CallInst>(RetainRV)->setCalledFunction(getRetainCallee(F.getParent()));

  DEBUG(dbgs() << "New = " << *RetainRV << "\n");

  return false;
}

/// Turn objc_autoreleaseReturnValue into objc_autorelease if the result is not
/// used as a return value.
void
ObjCARCOpt::OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV,
                                      InstructionClass &Class) {
  // Check for a return of the pointer value.
  const Value *Ptr = GetObjCArg(AutoreleaseRV);
  SmallVector<const Value *, 2> Users;
  Users.push_back(Ptr);
  do {
    Ptr = Users.pop_back_val();
    for (Value::const_use_iterator UI = Ptr->use_begin(), UE = Ptr->use_end();
         UI != UE; ++UI) {
      const User *I = *UI;
      if (isa<ReturnInst>(I) || GetBasicInstructionClass(I) == IC_RetainRV)
        return;
      if (isa<BitCastInst>(I))
        Users.push_back(I);
    }
  } while (!Users.empty());

  Changed = true;
  ++NumPeeps;

  DEBUG(dbgs() << "Transforming objc_autoreleaseReturnValue => "
                  "objc_autorelease since its operand is not used as a return "
                  "value.\n"
                  "Old = " << *AutoreleaseRV << "\n");

  CallInst *AutoreleaseRVCI = cast<CallInst>(AutoreleaseRV);
  AutoreleaseRVCI->
    setCalledFunction(getAutoreleaseCallee(F.getParent()));
  AutoreleaseRVCI->setTailCall(false); // Never tail call objc_autorelease.
  Class = IC_Autorelease;

  DEBUG(dbgs() << "New: " << *AutoreleaseRV << "\n");

}

// \brief Attempt to strength reduce objc_retainBlock calls to objc_retain
// calls.
//
// Specifically: If an objc_retainBlock call has the copy_on_escape metadata and
// does not escape (following the rules of block escaping), strength reduce the
// objc_retainBlock to an objc_retain.
//
// TODO: If an objc_retainBlock call is dominated period by a previous
// objc_retainBlock call, strength reduce the objc_retainBlock to an
// objc_retain.
bool
ObjCARCOpt::OptimizeRetainBlockCall(Function &F, Instruction *Inst,
                                    InstructionClass &Class) {
  assert(GetBasicInstructionClass(Inst) == Class);
  assert(IC_RetainBlock == Class);

  // If we can not optimize Inst, return false.
  if (!IsRetainBlockOptimizable(Inst))
    return false;

  CallInst *RetainBlock = cast<CallInst>(Inst);
  RetainBlock->setCalledFunction(getRetainCallee(F.getParent()));
  // Remove copy_on_escape metadata.
  RetainBlock->setMetadata(CopyOnEscapeMDKind, 0);
  Class = IC_Retain;

  return true;
}

/// Visit each call, one at a time, and make simplifications without doing any
/// additional analysis.
void ObjCARCOpt::OptimizeIndividualCalls(Function &F) {
  DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeIndividualCalls ==\n");
  // Reset all the flags in preparation for recomputing them.
  UsedInThisFunction = 0;

  // Visit all objc_* calls in F.
  for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
    Instruction *Inst = &*I++;

    InstructionClass Class = GetBasicInstructionClass(Inst);

    DEBUG(dbgs() << "Visiting: Class: " << Class << "; " << *Inst << "\n");

    switch (Class) {
    default: break;

    // Delete no-op casts. These function calls have special semantics, but
    // the semantics are entirely implemented via lowering in the front-end,
    // so by the time they reach the optimizer, they are just no-op calls
    // which return their argument.
    //
    // There are gray areas here, as the ability to cast reference-counted
    // pointers to raw void* and back allows code to break ARC assumptions,
    // however these are currently considered to be unimportant.
    case IC_NoopCast:
      Changed = true;
      ++NumNoops;
      DEBUG(dbgs() << "Erasing no-op cast: " << *Inst << "\n");
      EraseInstruction(Inst);
      continue;

    // If the pointer-to-weak-pointer is null, it's undefined behavior.
    case IC_StoreWeak:
    case IC_LoadWeak:
    case IC_LoadWeakRetained:
    case IC_InitWeak:
    case IC_DestroyWeak: {
      CallInst *CI = cast<CallInst>(Inst);
      if (IsNullOrUndef(CI->getArgOperand(0))) {
        Changed = true;
        Type *Ty = CI->getArgOperand(0)->getType();
        new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()),
                      Constant::getNullValue(Ty),
                      CI);
        llvm::Value *NewValue = UndefValue::get(CI->getType());
        DEBUG(dbgs() << "A null pointer-to-weak-pointer is undefined behavior."
                       "\nOld = " << *CI << "\nNew = " << *NewValue << "\n");
        CI->replaceAllUsesWith(NewValue);
        CI->eraseFromParent();
        continue;
      }
      break;
    }
    case IC_CopyWeak:
    case IC_MoveWeak: {
      CallInst *CI = cast<CallInst>(Inst);
      if (IsNullOrUndef(CI->getArgOperand(0)) ||
          IsNullOrUndef(CI->getArgOperand(1))) {
        Changed = true;
        Type *Ty = CI->getArgOperand(0)->getType();
        new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()),
                      Constant::getNullValue(Ty),
                      CI);

        llvm::Value *NewValue = UndefValue::get(CI->getType());
        DEBUG(dbgs() << "A null pointer-to-weak-pointer is undefined behavior."
                        "\nOld = " << *CI << "\nNew = " << *NewValue << "\n");

        CI->replaceAllUsesWith(NewValue);
        CI->eraseFromParent();
        continue;
      }
      break;
    }
    case IC_RetainBlock:
      // If we strength reduce an objc_retainBlock to amn objc_retain, continue
      // onto the objc_retain peephole optimizations. Otherwise break.
      if (!OptimizeRetainBlockCall(F, Inst, Class))
        break;
      // FALLTHROUGH
    case IC_Retain:
      OptimizeRetainCall(F, Inst);
      break;
    case IC_RetainRV:
      if (OptimizeRetainRVCall(F, Inst))
        continue;
      break;
    case IC_AutoreleaseRV:
      OptimizeAutoreleaseRVCall(F, Inst, Class);
      break;
    }

    // objc_autorelease(x) -> objc_release(x) if x is otherwise unused.
    if (IsAutorelease(Class) && Inst->use_empty()) {
      CallInst *Call = cast<CallInst>(Inst);
      const Value *Arg = Call->getArgOperand(0);
      Arg = FindSingleUseIdentifiedObject(Arg);
      if (Arg) {
        Changed = true;
        ++NumAutoreleases;

        // Create the declaration lazily.
        LLVMContext &C = Inst->getContext();
        CallInst *NewCall =
          CallInst::Create(getReleaseCallee(F.getParent()),
                           Call->getArgOperand(0), "", Call);
        NewCall->setMetadata(ImpreciseReleaseMDKind,
                             MDNode::get(C, ArrayRef<Value *>()));

        DEBUG(dbgs() << "Replacing autorelease{,RV}(x) with objc_release(x) "
              "since x is otherwise unused.\nOld: " << *Call << "\nNew: "
              << *NewCall << "\n");

        EraseInstruction(Call);
        Inst = NewCall;
        Class = IC_Release;
      }
    }

    // For functions which can never be passed stack arguments, add
    // a tail keyword.
    if (IsAlwaysTail(Class)) {
      Changed = true;
      DEBUG(dbgs() << "Adding tail keyword to function since it can never be "
                      "passed stack args: " << *Inst << "\n");
      cast<CallInst>(Inst)->setTailCall();
    }

    // Ensure that functions that can never have a "tail" keyword due to the
    // semantics of ARC truly do not do so.
    if (IsNeverTail(Class)) {
      Changed = true;
      DEBUG(dbgs() << "Removing tail keyword from function: " << *Inst <<
            "\n");
      cast<CallInst>(Inst)->setTailCall(false);
    }

    // Set nounwind as needed.
    if (IsNoThrow(Class)) {
      Changed = true;
      DEBUG(dbgs() << "Found no throw class. Setting nounwind on: " << *Inst
                   << "\n");
      cast<CallInst>(Inst)->setDoesNotThrow();
    }

    if (!IsNoopOnNull(Class)) {
      UsedInThisFunction |= 1 << Class;
      continue;
    }

    const Value *Arg = GetObjCArg(Inst);

    // ARC calls with null are no-ops. Delete them.
    if (IsNullOrUndef(Arg)) {
      Changed = true;
      ++NumNoops;
      DEBUG(dbgs() << "ARC calls with  null are no-ops. Erasing: " << *Inst
            << "\n");
      EraseInstruction(Inst);
      continue;
    }

    // Keep track of which of retain, release, autorelease, and retain_block
    // are actually present in this function.
    UsedInThisFunction |= 1 << Class;

    // If Arg is a PHI, and one or more incoming values to the
    // PHI are null, and the call is control-equivalent to the PHI, and there
    // are no relevant side effects between the PHI and the call, the call
    // could be pushed up to just those paths with non-null incoming values.
    // For now, don't bother splitting critical edges for this.
    SmallVector<std::pair<Instruction *, const Value *>, 4> Worklist;
    Worklist.push_back(std::make_pair(Inst, Arg));
    do {
      std::pair<Instruction *, const Value *> Pair = Worklist.pop_back_val();
      Inst = Pair.first;
      Arg = Pair.second;

      const PHINode *PN = dyn_cast<PHINode>(Arg);
      if (!PN) continue;

      // Determine if the PHI has any null operands, or any incoming
      // critical edges.
      bool HasNull = false;
      bool HasCriticalEdges = false;
      for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
        Value *Incoming =
          StripPointerCastsAndObjCCalls(PN->getIncomingValue(i));
        if (IsNullOrUndef(Incoming))
          HasNull = true;
        else if (cast<TerminatorInst>(PN->getIncomingBlock(i)->back())
                   .getNumSuccessors() != 1) {
          HasCriticalEdges = true;
          break;
        }
      }
      // If we have null operands and no critical edges, optimize.
      if (!HasCriticalEdges && HasNull) {
        SmallPtrSet<Instruction *, 4> DependingInstructions;
        SmallPtrSet<const BasicBlock *, 4> Visited;

        // Check that there is nothing that cares about the reference
        // count between the call and the phi.
        switch (Class) {
        case IC_Retain:
        case IC_RetainBlock:
          // These can always be moved up.
          break;
        case IC_Release:
          // These can't be moved across things that care about the retain
          // count.
          FindDependencies(NeedsPositiveRetainCount, Arg,
                           Inst->getParent(), Inst,
                           DependingInstructions, Visited, PA);
          break;
        case IC_Autorelease:
          // These can't be moved across autorelease pool scope boundaries.
          FindDependencies(AutoreleasePoolBoundary, Arg,
                           Inst->getParent(), Inst,
                           DependingInstructions, Visited, PA);
          break;
        case IC_RetainRV:
        case IC_AutoreleaseRV:
          // Don't move these; the RV optimization depends on the autoreleaseRV
          // being tail called, and the retainRV being immediately after a call
          // (which might still happen if we get lucky with codegen layout, but
          // it's not worth taking the chance).
          continue;
        default:
          llvm_unreachable("Invalid dependence flavor");
        }

        if (DependingInstructions.size() == 1 &&
            *DependingInstructions.begin() == PN) {
          Changed = true;
          ++NumPartialNoops;
          // Clone the call into each predecessor that has a non-null value.
          CallInst *CInst = cast<CallInst>(Inst);
          Type *ParamTy = CInst->getArgOperand(0)->getType();
          for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
            Value *Incoming =
              StripPointerCastsAndObjCCalls(PN->getIncomingValue(i));
            if (!IsNullOrUndef(Incoming)) {
              CallInst *Clone = cast<CallInst>(CInst->clone());
              Value *Op = PN->getIncomingValue(i);
              Instruction *InsertPos = &PN->getIncomingBlock(i)->back();
              if (Op->getType() != ParamTy)
                Op = new BitCastInst(Op, ParamTy, "", InsertPos);
              Clone->setArgOperand(0, Op);
              Clone->insertBefore(InsertPos);

              DEBUG(dbgs() << "Cloning "
                           << *CInst << "\n"
                           "And inserting clone at " << *InsertPos << "\n");
              Worklist.push_back(std::make_pair(Clone, Incoming));
            }
          }
          // Erase the original call.
          DEBUG(dbgs() << "Erasing: " << *CInst << "\n");
          EraseInstruction(CInst);
          continue;
        }
      }
    } while (!Worklist.empty());
  }
}

/// Check for critical edges, loop boundaries, irreducible control flow, or
/// other CFG structures where moving code across the edge would result in it
/// being executed more.
void
ObjCARCOpt::CheckForCFGHazards(const BasicBlock *BB,
                               DenseMap<const BasicBlock *, BBState> &BBStates,
                               BBState &MyStates) const {
  // If any top-down local-use or possible-dec has a succ which is earlier in
  // the sequence, forget it.
  for (BBState::ptr_iterator I = MyStates.top_down_ptr_begin(),
       E = MyStates.top_down_ptr_end(); I != E; ++I)
    switch (I->second.GetSeq()) {
    default: break;
    case S_Use: {
      const Value *Arg = I->first;
      const TerminatorInst *TI = cast<TerminatorInst>(&BB->back());
      bool SomeSuccHasSame = false;
      bool AllSuccsHaveSame = true;
      PtrState &S = I->second;
      succ_const_iterator SI(TI), SE(TI, false);

      for (; SI != SE; ++SI) {
        Sequence SuccSSeq = S_None;
        bool SuccSRRIKnownSafe = false;
        // If VisitBottomUp has pointer information for this successor, take
        // what we know about it.
        DenseMap<const BasicBlock *, BBState>::iterator BBI =
          BBStates.find(*SI);
        assert(BBI != BBStates.end());
        const PtrState &SuccS = BBI->second.getPtrBottomUpState(Arg);
        SuccSSeq = SuccS.GetSeq();
        SuccSRRIKnownSafe = SuccS.RRI.KnownSafe;
        switch (SuccSSeq) {
        case S_None:
        case S_CanRelease: {
          if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe) {
            S.ClearSequenceProgress();
            break;
          }
          continue;
        }
        case S_Use:
          SomeSuccHasSame = true;
          break;
        case S_Stop:
        case S_Release:
        case S_MovableRelease:
          if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe)
            AllSuccsHaveSame = false;
          break;
        case S_Retain:
          llvm_unreachable("bottom-up pointer in retain state!");
        }
      }
      // If the state at the other end of any of the successor edges
      // matches the current state, require all edges to match. This
      // guards against loops in the middle of a sequence.
      if (SomeSuccHasSame && !AllSuccsHaveSame)
        S.ClearSequenceProgress();
      break;
    }
    case S_CanRelease: {
      const Value *Arg = I->first;
      const TerminatorInst *TI = cast<TerminatorInst>(&BB->back());
      bool SomeSuccHasSame = false;
      bool AllSuccsHaveSame = true;
      PtrState &S = I->second;
      succ_const_iterator SI(TI), SE(TI, false);

      for (; SI != SE; ++SI) {
        Sequence SuccSSeq = S_None;
        bool SuccSRRIKnownSafe = false;
        // If VisitBottomUp has pointer information for this successor, take
        // what we know about it.
        DenseMap<const BasicBlock *, BBState>::iterator BBI =
          BBStates.find(*SI);
        assert(BBI != BBStates.end());
        const PtrState &SuccS = BBI->second.getPtrBottomUpState(Arg);
        SuccSSeq = SuccS.GetSeq();
        SuccSRRIKnownSafe = SuccS.RRI.KnownSafe;
        switch (SuccSSeq) {
        case S_None: {
          if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe) {
            S.ClearSequenceProgress();
            break;
          }
          continue;
        }
        case S_CanRelease:
          SomeSuccHasSame = true;
          break;
        case S_Stop:
        case S_Release:
        case S_MovableRelease:
        case S_Use:
          if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe)
            AllSuccsHaveSame = false;
          break;
        case S_Retain:
          llvm_unreachable("bottom-up pointer in retain state!");
        }
      }
      // If the state at the other end of any of the successor edges
      // matches the current state, require all edges to match. This
      // guards against loops in the middle of a sequence.
      if (SomeSuccHasSame && !AllSuccsHaveSame)
        S.ClearSequenceProgress();
      break;
    }
    }
}

bool
ObjCARCOpt::VisitInstructionBottomUp(Instruction *Inst,
                                     BasicBlock *BB,
                                     MapVector<Value *, RRInfo> &Retains,
                                     BBState &MyStates) {
  bool NestingDetected = false;
  InstructionClass Class = GetInstructionClass(Inst);
  const Value *Arg = 0;

  DEBUG(dbgs() << "Class: " << Class << "\n");

  switch (Class) {
  case IC_Release: {
    Arg = GetObjCArg(Inst);

    PtrState &S = MyStates.getPtrBottomUpState(Arg);

    // If we see two releases in a row on the same pointer. If so, make
    // a note, and we'll cicle back to revisit it after we've
    // hopefully eliminated the second release, which may allow us to
    // eliminate the first release too.
    // Theoretically we could implement removal of nested retain+release
    // pairs by making PtrState hold a stack of states, but this is
    // simple and avoids adding overhead for the non-nested case.
    if (S.GetSeq() == S_Release || S.GetSeq() == S_MovableRelease) {
      DEBUG(dbgs() << "Found nested releases (i.e. a release pair)\n");
      NestingDetected = true;
    }

    MDNode *ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind);
    Sequence NewSeq = ReleaseMetadata ? S_MovableRelease : S_Release;
    ANNOTATE_BOTTOMUP(Inst, Arg, S.GetSeq(), NewSeq);
    S.ResetSequenceProgress(NewSeq);
    S.RRI.ReleaseMetadata = ReleaseMetadata;
    S.RRI.KnownSafe = S.HasKnownPositiveRefCount();
    S.RRI.IsTailCallRelease = cast<CallInst>(Inst)->isTailCall();
    S.RRI.Calls.insert(Inst);
    S.SetKnownPositiveRefCount();
    break;
  }
  case IC_RetainBlock:
    // In OptimizeIndividualCalls, we have strength reduced all optimizable
    // objc_retainBlocks to objc_retains. Thus at this point any
    // objc_retainBlocks that we see are not optimizable.
    break;
  case IC_Retain:
  case IC_RetainRV: {
    Arg = GetObjCArg(Inst);

    PtrState &S = MyStates.getPtrBottomUpState(Arg);
    S.SetKnownPositiveRefCount();

    Sequence OldSeq = S.GetSeq();
    switch (OldSeq) {
    case S_Stop:
    case S_Release:
    case S_MovableRelease:
    case S_Use:
      // If OldSeq is not S_Use or OldSeq is S_Use and we are tracking an
      // imprecise release, clear our reverse insertion points.
      if (OldSeq != S_Use || S.RRI.IsTrackingImpreciseReleases())
        S.RRI.ReverseInsertPts.clear();
      // FALL THROUGH
    case S_CanRelease:
      // Don't do retain+release tracking for IC_RetainRV, because it's
      // better to let it remain as the first instruction after a call.
      if (Class != IC_RetainRV)
        Retains[Inst] = S.RRI;
      S.ClearSequenceProgress();
      break;
    case S_None:
      break;
    case S_Retain:
      llvm_unreachable("bottom-up pointer in retain state!");
    }
    ANNOTATE_BOTTOMUP(Inst, Arg, OldSeq, S.GetSeq());
    // A retain moving bottom up can be a use.
    break;
  }
  case IC_AutoreleasepoolPop:
    // Conservatively, clear MyStates for all known pointers.
    MyStates.clearBottomUpPointers();
    return NestingDetected;
  case IC_AutoreleasepoolPush:
  case IC_None:
    // These are irrelevant.
    return NestingDetected;
  default:
    break;
  }

  // Consider any other possible effects of this instruction on each
  // pointer being tracked.
  for (BBState::ptr_iterator MI = MyStates.bottom_up_ptr_begin(),
       ME = MyStates.bottom_up_ptr_end(); MI != ME; ++MI) {
    const Value *Ptr = MI->first;
    if (Ptr == Arg)
      continue; // Handled above.
    PtrState &S = MI->second;
    Sequence Seq = S.GetSeq();

    // Check for possible releases.
    if (CanAlterRefCount(Inst, Ptr, PA, Class)) {
      DEBUG(dbgs() << "CanAlterRefCount: Seq: " << Seq << "; " << *Ptr
            << "\n");
      S.ClearKnownPositiveRefCount();
      switch (Seq) {
      case S_Use:
        S.SetSeq(S_CanRelease);
        ANNOTATE_BOTTOMUP(Inst, Ptr, Seq, S.GetSeq());
        continue;
      case S_CanRelease:
      case S_Release:
      case S_MovableRelease:
      case S_Stop:
      case S_None:
        break;
      case S_Retain:
        llvm_unreachable("bottom-up pointer in retain state!");
      }
    }

    // Check for possible direct uses.
    switch (Seq) {
    case S_Release:
    case S_MovableRelease:
      if (CanUse(Inst, Ptr, PA, Class)) {
        DEBUG(dbgs() << "CanUse: Seq: " << Seq << "; " << *Ptr
              << "\n");
        assert(S.RRI.ReverseInsertPts.empty());
        // If this is an invoke instruction, we're scanning it as part of
        // one of its successor blocks, since we can't insert code after it
        // in its own block, and we don't want to split critical edges.
        if (isa<InvokeInst>(Inst))
          S.RRI.ReverseInsertPts.insert(BB->getFirstInsertionPt());
        else
          S.RRI.ReverseInsertPts.insert(llvm::next(BasicBlock::iterator(Inst)));
        S.SetSeq(S_Use);
        ANNOTATE_BOTTOMUP(Inst, Ptr, Seq, S_Use);
      } else if (Seq == S_Release && IsUser(Class)) {
        DEBUG(dbgs() << "PreciseReleaseUse: Seq: " << Seq << "; " << *Ptr
              << "\n");
        // Non-movable releases depend on any possible objc pointer use.
        S.SetSeq(S_Stop);
        ANNOTATE_BOTTOMUP(Inst, Ptr, S_Release, S_Stop);
        assert(S.RRI.ReverseInsertPts.empty());
        // As above; handle invoke specially.
        if (isa<InvokeInst>(Inst))
          S.RRI.ReverseInsertPts.insert(BB->getFirstInsertionPt());
        else
          S.RRI.ReverseInsertPts.insert(llvm::next(BasicBlock::iterator(Inst)));
      }
      break;
    case S_Stop:
      if (CanUse(Inst, Ptr, PA, Class)) {
        DEBUG(dbgs() << "PreciseStopUse: Seq: " << Seq << "; " << *Ptr
              << "\n");
        S.SetSeq(S_Use);
        ANNOTATE_BOTTOMUP(Inst, Ptr, Seq, S_Use);
      }
      break;
    case S_CanRelease:
    case S_Use:
    case S_None:
      break;
    case S_Retain:
      llvm_unreachable("bottom-up pointer in retain state!");
    }
  }

  return NestingDetected;
}

bool
ObjCARCOpt::VisitBottomUp(BasicBlock *BB,
                          DenseMap<const BasicBlock *, BBState> &BBStates,
                          MapVector<Value *, RRInfo> &Retains) {

  DEBUG(dbgs() << "\n== ObjCARCOpt::VisitBottomUp ==\n");

  bool NestingDetected = false;
  BBState &MyStates = BBStates[BB];

  // Merge the states from each successor to compute the initial state
  // for the current block.
  BBState::edge_iterator SI(MyStates.succ_begin()),
                         SE(MyStates.succ_end());
  if (SI != SE) {
    const BasicBlock *Succ = *SI;
    DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Succ);
    assert(I != BBStates.end());
    MyStates.InitFromSucc(I->second);
    ++SI;
    for (; SI != SE; ++SI) {
      Succ = *SI;
      I = BBStates.find(Succ);
      assert(I != BBStates.end());
      MyStates.MergeSucc(I->second);
    }
  }

  // If ARC Annotations are enabled, output the current state of pointers at the
  // bottom of the basic block.
  ANNOTATE_BOTTOMUP_BBEND(MyStates, BB);

  // Visit all the instructions, bottom-up.
  for (BasicBlock::iterator I = BB->end(), E = BB->begin(); I != E; --I) {
    Instruction *Inst = llvm::prior(I);

    // Invoke instructions are visited as part of their successors (below).
    if (isa<InvokeInst>(Inst))
      continue;

    DEBUG(dbgs() << "Visiting " << *Inst << "\n");

    NestingDetected |= VisitInstructionBottomUp(Inst, BB, Retains, MyStates);
  }

  // If there's a predecessor with an invoke, visit the invoke as if it were
  // part of this block, since we can't insert code after an invoke in its own
  // block, and we don't want to split critical edges.
  for (BBState::edge_iterator PI(MyStates.pred_begin()),
       PE(MyStates.pred_end()); PI != PE; ++PI) {
    BasicBlock *Pred = *PI;
    if (InvokeInst *II = dyn_cast<InvokeInst>(&Pred->back()))
      NestingDetected |= VisitInstructionBottomUp(II, BB, Retains, MyStates);
  }

  // If ARC Annotations are enabled, output the current state of pointers at the
  // top of the basic block.
  ANNOTATE_BOTTOMUP_BBSTART(MyStates, BB);

  return NestingDetected;
}

bool
ObjCARCOpt::VisitInstructionTopDown(Instruction *Inst,
                                    DenseMap<Value *, RRInfo> &Releases,
                                    BBState &MyStates) {
  bool NestingDetected = false;
  InstructionClass Class = GetInstructionClass(Inst);
  const Value *Arg = 0;

  switch (Class) {
  case IC_RetainBlock:
    // In OptimizeIndividualCalls, we have strength reduced all optimizable
    // objc_retainBlocks to objc_retains. Thus at this point any
    // objc_retainBlocks that we see are not optimizable.
    break;
  case IC_Retain:
  case IC_RetainRV: {
    Arg = GetObjCArg(Inst);

    PtrState &S = MyStates.getPtrTopDownState(Arg);

    // Don't do retain+release tracking for IC_RetainRV, because it's
    // better to let it remain as the first instruction after a call.
    if (Class != IC_RetainRV) {
      // If we see two retains in a row on the same pointer. If so, make
      // a note, and we'll cicle back to revisit it after we've
      // hopefully eliminated the second retain, which may allow us to
      // eliminate the first retain too.
      // Theoretically we could implement removal of nested retain+release
      // pairs by making PtrState hold a stack of states, but this is
      // simple and avoids adding overhead for the non-nested case.
      if (S.GetSeq() == S_Retain)
        NestingDetected = true;

      ANNOTATE_TOPDOWN(Inst, Arg, S.GetSeq(), S_Retain);
      S.ResetSequenceProgress(S_Retain);
      S.RRI.KnownSafe = S.HasKnownPositiveRefCount();
      S.RRI.Calls.insert(Inst);
    }

    S.SetKnownPositiveRefCount();

    // A retain can be a potential use; procede to the generic checking
    // code below.
    break;
  }
  case IC_Release: {
    Arg = GetObjCArg(Inst);

    PtrState &S = MyStates.getPtrTopDownState(Arg);
    S.ClearKnownPositiveRefCount();

    Sequence OldSeq = S.GetSeq();

    MDNode *ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind);

    switch (OldSeq) {
    case S_Retain:
    case S_CanRelease:
      if (OldSeq == S_Retain || ReleaseMetadata != 0)
        S.RRI.ReverseInsertPts.clear();
      // FALL THROUGH
    case S_Use:
      S.RRI.ReleaseMetadata = ReleaseMetadata;
      S.RRI.IsTailCallRelease = cast<CallInst>(Inst)->isTailCall();
      Releases[Inst] = S.RRI;
      ANNOTATE_TOPDOWN(Inst, Arg, S.GetSeq(), S_None);
      S.ClearSequenceProgress();
      break;
    case S_None:
      break;
    case S_Stop:
    case S_Release:
    case S_MovableRelease:
      llvm_unreachable("top-down pointer in release state!");
    }
    break;
  }
  case IC_AutoreleasepoolPop:
    // Conservatively, clear MyStates for all known pointers.
    MyStates.clearTopDownPointers();
    return NestingDetected;
  case IC_AutoreleasepoolPush:
  case IC_None:
    // These are irrelevant.
    return NestingDetected;
  default:
    break;
  }

  // Consider any other possible effects of this instruction on each
  // pointer being tracked.
  for (BBState::ptr_iterator MI = MyStates.top_down_ptr_begin(),
       ME = MyStates.top_down_ptr_end(); MI != ME; ++MI) {
    const Value *Ptr = MI->first;
    if (Ptr == Arg)
      continue; // Handled above.
    PtrState &S = MI->second;
    Sequence Seq = S.GetSeq();

    // Check for possible releases.
    if (CanAlterRefCount(Inst, Ptr, PA, Class)) {
      DEBUG(dbgs() << "CanAlterRefCount: Seq: " << Seq << "; " << *Ptr
            << "\n");
      S.ClearKnownPositiveRefCount();
      switch (Seq) {
      case S_Retain:
        S.SetSeq(S_CanRelease);
        ANNOTATE_TOPDOWN(Inst, Ptr, Seq, S_CanRelease);
        assert(S.RRI.ReverseInsertPts.empty());
        S.RRI.ReverseInsertPts.insert(Inst);

        // One call can't cause a transition from S_Retain to S_CanRelease
        // and S_CanRelease to S_Use. If we've made the first transition,
        // we're done.
        continue;
      case S_Use:
      case S_CanRelease:
      case S_None:
        break;
      case S_Stop:
      case S_Release:
      case S_MovableRelease:
        llvm_unreachable("top-down pointer in release state!");
      }
    }

    // Check for possible direct uses.
    switch (Seq) {
    case S_CanRelease:
      if (CanUse(Inst, Ptr, PA, Class)) {
        DEBUG(dbgs() << "CanUse: Seq: " << Seq << "; " << *Ptr
              << "\n");
        S.SetSeq(S_Use);
        ANNOTATE_TOPDOWN(Inst, Ptr, Seq, S_Use);
      }
      break;
    case S_Retain:
    case S_Use:
    case S_None:
      break;
    case S_Stop:
    case S_Release:
    case S_MovableRelease:
      llvm_unreachable("top-down pointer in release state!");
    }
  }

  return NestingDetected;
}

bool
ObjCARCOpt::VisitTopDown(BasicBlock *BB,
                         DenseMap<const BasicBlock *, BBState> &BBStates,
                         DenseMap<Value *, RRInfo> &Releases) {
  DEBUG(dbgs() << "\n== ObjCARCOpt::VisitTopDown ==\n");
  bool NestingDetected = false;
  BBState &MyStates = BBStates[BB];

  // Merge the states from each predecessor to compute the initial state
  // for the current block.
  BBState::edge_iterator PI(MyStates.pred_begin()),
                         PE(MyStates.pred_end());
  if (PI != PE) {
    const BasicBlock *Pred = *PI;
    DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Pred);
    assert(I != BBStates.end());
    MyStates.InitFromPred(I->second);
    ++PI;
    for (; PI != PE; ++PI) {
      Pred = *PI;
      I = BBStates.find(Pred);
      assert(I != BBStates.end());
      MyStates.MergePred(I->second);
    }
  }

  // If ARC Annotations are enabled, output the current state of pointers at the
  // top of the basic block.
  ANNOTATE_TOPDOWN_BBSTART(MyStates, BB);

  // Visit all the instructions, top-down.
  for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
    Instruction *Inst = I;

    DEBUG(dbgs() << "Visiting " << *Inst << "\n");

    NestingDetected |= VisitInstructionTopDown(Inst, Releases, MyStates);
  }

  // If ARC Annotations are enabled, output the current state of pointers at the
  // bottom of the basic block.
  ANNOTATE_TOPDOWN_BBEND(MyStates, BB);

  CheckForCFGHazards(BB, BBStates, MyStates);
  return NestingDetected;
}

static void
ComputePostOrders(Function &F,
                  SmallVectorImpl<BasicBlock *> &PostOrder,
                  SmallVectorImpl<BasicBlock *> &ReverseCFGPostOrder,
                  unsigned NoObjCARCExceptionsMDKind,
                  DenseMap<const BasicBlock *, BBState> &BBStates) {
  /// The visited set, for doing DFS walks.
  SmallPtrSet<BasicBlock *, 16> Visited;

  // Do DFS, computing the PostOrder.
  SmallPtrSet<BasicBlock *, 16> OnStack;
  SmallVector<std::pair<BasicBlock *, succ_iterator>, 16> SuccStack;

  // Functions always have exactly one entry block, and we don't have
  // any other block that we treat like an entry block.
  BasicBlock *EntryBB = &F.getEntryBlock();
  BBState &MyStates = BBStates[EntryBB];
  MyStates.SetAsEntry();
  TerminatorInst *EntryTI = cast<TerminatorInst>(&EntryBB->back());
  SuccStack.push_back(std::make_pair(EntryBB, succ_iterator(EntryTI)));
  Visited.insert(EntryBB);
  OnStack.insert(EntryBB);
  do {
  dfs_next_succ:
    BasicBlock *CurrBB = SuccStack.back().first;
    TerminatorInst *TI = cast<TerminatorInst>(&CurrBB->back());
    succ_iterator SE(TI, false);

    while (SuccStack.back().second != SE) {
      BasicBlock *SuccBB = *SuccStack.back().second++;
      if (Visited.insert(SuccBB)) {
        TerminatorInst *TI = cast<TerminatorInst>(&SuccBB->back());
        SuccStack.push_back(std::make_pair(SuccBB, succ_iterator(TI)));
        BBStates[CurrBB].addSucc(SuccBB);
        BBState &SuccStates = BBStates[SuccBB];
        SuccStates.addPred(CurrBB);
        OnStack.insert(SuccBB);
        goto dfs_next_succ;
      }

      if (!OnStack.count(SuccBB)) {
        BBStates[CurrBB].addSucc(SuccBB);
        BBStates[SuccBB].addPred(CurrBB);
      }
    }
    OnStack.erase(CurrBB);
    PostOrder.push_back(CurrBB);
    SuccStack.pop_back();
  } while (!SuccStack.empty());

  Visited.clear();

  // Do reverse-CFG DFS, computing the reverse-CFG PostOrder.
  // Functions may have many exits, and there also blocks which we treat
  // as exits due to ignored edges.
  SmallVector<std::pair<BasicBlock *, BBState::edge_iterator>, 16> PredStack;
  for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
    BasicBlock *ExitBB = I;
    BBState &MyStates = BBStates[ExitBB];
    if (!MyStates.isExit())
      continue;

    MyStates.SetAsExit();

    PredStack.push_back(std::make_pair(ExitBB, MyStates.pred_begin()));
    Visited.insert(ExitBB);
    while (!PredStack.empty()) {
    reverse_dfs_next_succ:
      BBState::edge_iterator PE = BBStates[PredStack.back().first].pred_end();
      while (PredStack.back().second != PE) {
        BasicBlock *BB = *PredStack.back().second++;
        if (Visited.insert(BB)) {
          PredStack.push_back(std::make_pair(BB, BBStates[BB].pred_begin()));
          goto reverse_dfs_next_succ;
        }
      }
      ReverseCFGPostOrder.push_back(PredStack.pop_back_val().first);
    }
  }
}

// Visit the function both top-down and bottom-up.
bool
ObjCARCOpt::Visit(Function &F,
                  DenseMap<const BasicBlock *, BBState> &BBStates,
                  MapVector<Value *, RRInfo> &Retains,
                  DenseMap<Value *, RRInfo> &Releases) {

  // Use reverse-postorder traversals, because we magically know that loops
  // will be well behaved, i.e. they won't repeatedly call retain on a single
  // pointer without doing a release. We can't use the ReversePostOrderTraversal
  // class here because we want the reverse-CFG postorder to consider each
  // function exit point, and we want to ignore selected cycle edges.
  SmallVector<BasicBlock *, 16> PostOrder;
  SmallVector<BasicBlock *, 16> ReverseCFGPostOrder;
  ComputePostOrders(F, PostOrder, ReverseCFGPostOrder,
                    NoObjCARCExceptionsMDKind,
                    BBStates);

  // Use reverse-postorder on the reverse CFG for bottom-up.
  bool BottomUpNestingDetected = false;
  for (SmallVectorImpl<BasicBlock *>::const_reverse_iterator I =
       ReverseCFGPostOrder.rbegin(), E = ReverseCFGPostOrder.rend();
       I != E; ++I)
    BottomUpNestingDetected |= VisitBottomUp(*I, BBStates, Retains);

  // Use reverse-postorder for top-down.
  bool TopDownNestingDetected = false;
  for (SmallVectorImpl<BasicBlock *>::const_reverse_iterator I =
       PostOrder.rbegin(), E = PostOrder.rend();
       I != E; ++I)
    TopDownNestingDetected |= VisitTopDown(*I, BBStates, Releases);

  return TopDownNestingDetected && BottomUpNestingDetected;
}

/// Move the calls in RetainsToMove and ReleasesToMove.
void ObjCARCOpt::MoveCalls(Value *Arg,
                           RRInfo &RetainsToMove,
                           RRInfo &ReleasesToMove,
                           MapVector<Value *, RRInfo> &Retains,
                           DenseMap<Value *, RRInfo> &Releases,
                           SmallVectorImpl<Instruction *> &DeadInsts,
                           Module *M) {
  Type *ArgTy = Arg->getType();
  Type *ParamTy = PointerType::getUnqual(Type::getInt8Ty(ArgTy->getContext()));

  DEBUG(dbgs() << "== ObjCARCOpt::MoveCalls ==\n");

  // Insert the new retain and release calls.
  for (SmallPtrSet<Instruction *, 2>::const_iterator
       PI = ReleasesToMove.ReverseInsertPts.begin(),
       PE = ReleasesToMove.ReverseInsertPts.end(); PI != PE; ++PI) {
    Instruction *InsertPt = *PI;
    Value *MyArg = ArgTy == ParamTy ? Arg :
                   new BitCastInst(Arg, ParamTy, "", InsertPt);
    CallInst *Call =
      CallInst::Create(getRetainCallee(M), MyArg, "", InsertPt);
    Call->setDoesNotThrow();
    Call->setTailCall();

    DEBUG(dbgs() << "Inserting new Release: " << *Call << "\n"
                    "At insertion point: " << *InsertPt << "\n");
  }
  for (SmallPtrSet<Instruction *, 2>::const_iterator
       PI = RetainsToMove.ReverseInsertPts.begin(),
       PE = RetainsToMove.ReverseInsertPts.end(); PI != PE; ++PI) {
    Instruction *InsertPt = *PI;
    Value *MyArg = ArgTy == ParamTy ? Arg :
                   new BitCastInst(Arg, ParamTy, "", InsertPt);
    CallInst *Call = CallInst::Create(getReleaseCallee(M), MyArg,
                                      "", InsertPt);
    // Attach a clang.imprecise_release metadata tag, if appropriate.
    if (MDNode *M = ReleasesToMove.ReleaseMetadata)
      Call->setMetadata(ImpreciseReleaseMDKind, M);
    Call->setDoesNotThrow();
    if (ReleasesToMove.IsTailCallRelease)
      Call->setTailCall();

    DEBUG(dbgs() << "Inserting new Release: " << *Call << "\n"
                    "At insertion point: " << *InsertPt << "\n");
  }

  // Delete the original retain and release calls.
  for (SmallPtrSet<Instruction *, 2>::const_iterator
       AI = RetainsToMove.Calls.begin(),
       AE = RetainsToMove.Calls.end(); AI != AE; ++AI) {
    Instruction *OrigRetain = *AI;
    Retains.blot(OrigRetain);
    DeadInsts.push_back(OrigRetain);
    DEBUG(dbgs() << "Deleting retain: " << *OrigRetain << "\n");
  }
  for (SmallPtrSet<Instruction *, 2>::const_iterator
       AI = ReleasesToMove.Calls.begin(),
       AE = ReleasesToMove.Calls.end(); AI != AE; ++AI) {
    Instruction *OrigRelease = *AI;
    Releases.erase(OrigRelease);
    DeadInsts.push_back(OrigRelease);
    DEBUG(dbgs() << "Deleting release: " << *OrigRelease << "\n");
  }

}

bool
ObjCARCOpt::ConnectTDBUTraversals(DenseMap<const BasicBlock *, BBState>
                                    &BBStates,
                                  MapVector<Value *, RRInfo> &Retains,
                                  DenseMap<Value *, RRInfo> &Releases,
                                  Module *M,
                                  SmallVector<Instruction *, 4> &NewRetains,
                                  SmallVector<Instruction *, 4> &NewReleases,
                                  SmallVector<Instruction *, 8> &DeadInsts,
                                  RRInfo &RetainsToMove,
                                  RRInfo &ReleasesToMove,
                                  Value *Arg,
                                  bool KnownSafe,
                                  bool &AnyPairsCompletelyEliminated) {
  // If a pair happens in a region where it is known that the reference count
  // is already incremented, we can similarly ignore possible decrements.
  bool KnownSafeTD = true, KnownSafeBU = true;

  // Connect the dots between the top-down-collected RetainsToMove and
  // bottom-up-collected ReleasesToMove to form sets of related calls.
  // This is an iterative process so that we connect multiple releases
  // to multiple retains if needed.
  unsigned OldDelta = 0;
  unsigned NewDelta = 0;
  unsigned OldCount = 0;
  unsigned NewCount = 0;
  bool FirstRelease = true;
  for (;;) {
    for (SmallVectorImpl<Instruction *>::const_iterator
           NI = NewRetains.begin(), NE = NewRetains.end(); NI != NE; ++NI) {
      Instruction *NewRetain = *NI;
      MapVector<Value *, RRInfo>::const_iterator It = Retains.find(NewRetain);
      assert(It != Retains.end());
      const RRInfo &NewRetainRRI = It->second;
      KnownSafeTD &= NewRetainRRI.KnownSafe;
      for (SmallPtrSet<Instruction *, 2>::const_iterator
             LI = NewRetainRRI.Calls.begin(),
             LE = NewRetainRRI.Calls.end(); LI != LE; ++LI) {
        Instruction *NewRetainRelease = *LI;
        DenseMap<Value *, RRInfo>::const_iterator Jt =
          Releases.find(NewRetainRelease);
        if (Jt == Releases.end())
          return false;
        const RRInfo &NewRetainReleaseRRI = Jt->second;
        assert(NewRetainReleaseRRI.Calls.count(NewRetain));
        if (ReleasesToMove.Calls.insert(NewRetainRelease)) {
          OldDelta -=
            BBStates[NewRetainRelease->getParent()].GetAllPathCount();

          // Merge the ReleaseMetadata and IsTailCallRelease values.
          if (FirstRelease) {
            ReleasesToMove.ReleaseMetadata =
              NewRetainReleaseRRI.ReleaseMetadata;
            ReleasesToMove.IsTailCallRelease =
              NewRetainReleaseRRI.IsTailCallRelease;
            FirstRelease = false;
          } else {
            if (ReleasesToMove.ReleaseMetadata !=
                NewRetainReleaseRRI.ReleaseMetadata)
              ReleasesToMove.ReleaseMetadata = 0;
            if (ReleasesToMove.IsTailCallRelease !=
                NewRetainReleaseRRI.IsTailCallRelease)
              ReleasesToMove.IsTailCallRelease = false;
          }

          // Collect the optimal insertion points.
          if (!KnownSafe)
            for (SmallPtrSet<Instruction *, 2>::const_iterator
                   RI = NewRetainReleaseRRI.ReverseInsertPts.begin(),
                   RE = NewRetainReleaseRRI.ReverseInsertPts.end();
                 RI != RE; ++RI) {
              Instruction *RIP = *RI;
              if (ReleasesToMove.ReverseInsertPts.insert(RIP))
                NewDelta -= BBStates[RIP->getParent()].GetAllPathCount();
            }
          NewReleases.push_back(NewRetainRelease);
        }
      }
    }
    NewRetains.clear();
    if (NewReleases.empty()) break;

    // Back the other way.
    for (SmallVectorImpl<Instruction *>::const_iterator
           NI = NewReleases.begin(), NE = NewReleases.end(); NI != NE; ++NI) {
      Instruction *NewRelease = *NI;
      DenseMap<Value *, RRInfo>::const_iterator It =
        Releases.find(NewRelease);
      assert(It != Releases.end());
      const RRInfo &NewReleaseRRI = It->second;
      KnownSafeBU &= NewReleaseRRI.KnownSafe;
      for (SmallPtrSet<Instruction *, 2>::const_iterator
             LI = NewReleaseRRI.Calls.begin(),
             LE = NewReleaseRRI.Calls.end(); LI != LE; ++LI) {
        Instruction *NewReleaseRetain = *LI;
        MapVector<Value *, RRInfo>::const_iterator Jt =
          Retains.find(NewReleaseRetain);
        if (Jt == Retains.end())
          return false;
        const RRInfo &NewReleaseRetainRRI = Jt->second;
        assert(NewReleaseRetainRRI.Calls.count(NewRelease));
        if (RetainsToMove.Calls.insert(NewReleaseRetain)) {
          unsigned PathCount =
            BBStates[NewReleaseRetain->getParent()].GetAllPathCount();
          OldDelta += PathCount;
          OldCount += PathCount;

          // Collect the optimal insertion points.
          if (!KnownSafe)
            for (SmallPtrSet<Instruction *, 2>::const_iterator
                   RI = NewReleaseRetainRRI.ReverseInsertPts.begin(),
                   RE = NewReleaseRetainRRI.ReverseInsertPts.end();
                 RI != RE; ++RI) {
              Instruction *RIP = *RI;
              if (RetainsToMove.ReverseInsertPts.insert(RIP)) {
                PathCount = BBStates[RIP->getParent()].GetAllPathCount();
                NewDelta += PathCount;
                NewCount += PathCount;
              }
            }
          NewRetains.push_back(NewReleaseRetain);
        }
      }
    }
    NewReleases.clear();
    if (NewRetains.empty()) break;
  }

  // If the pointer is known incremented or nested, we can safely delete the
  // pair regardless of what's between them.
  if (KnownSafeTD || KnownSafeBU) {
    RetainsToMove.ReverseInsertPts.clear();
    ReleasesToMove.ReverseInsertPts.clear();
    NewCount = 0;
  } else {
    // Determine whether the new insertion points we computed preserve the
    // balance of retain and release calls through the program.
    // TODO: If the fully aggressive solution isn't valid, try to find a
    // less aggressive solution which is.
    if (NewDelta != 0)
      return false;
  }

  // Determine whether the original call points are balanced in the retain and
  // release calls through the program. If not, conservatively don't touch
  // them.
  // TODO: It's theoretically possible to do code motion in this case, as
  // long as the existing imbalances are maintained.
  if (OldDelta != 0)
    return false;

  Changed = true;
  assert(OldCount != 0 && "Unreachable code?");
  NumRRs += OldCount - NewCount;
  // Set to true if we completely removed any RR pairs.
  AnyPairsCompletelyEliminated = NewCount == 0;

  // We can move calls!
  return true;
}

/// Identify pairings between the retains and releases, and delete and/or move
/// them.
bool
ObjCARCOpt::PerformCodePlacement(DenseMap<const BasicBlock *, BBState>
                                   &BBStates,
                                 MapVector<Value *, RRInfo> &Retains,
                                 DenseMap<Value *, RRInfo> &Releases,
                                 Module *M) {
  DEBUG(dbgs() << "\n== ObjCARCOpt::PerformCodePlacement ==\n");

  bool AnyPairsCompletelyEliminated = false;
  RRInfo RetainsToMove;
  RRInfo ReleasesToMove;
  SmallVector<Instruction *, 4> NewRetains;
  SmallVector<Instruction *, 4> NewReleases;
  SmallVector<Instruction *, 8> DeadInsts;

  // Visit each retain.
  for (MapVector<Value *, RRInfo>::const_iterator I = Retains.begin(),
       E = Retains.end(); I != E; ++I) {
    Value *V = I->first;
    if (!V) continue; // blotted

    Instruction *Retain = cast<Instruction>(V);

    DEBUG(dbgs() << "Visiting: " << *Retain << "\n");

    Value *Arg = GetObjCArg(Retain);

    // If the object being released is in static or stack storage, we know it's
    // not being managed by ObjC reference counting, so we can delete pairs
    // regardless of what possible decrements or uses lie between them.
    bool KnownSafe = isa<Constant>(Arg) || isa<AllocaInst>(Arg);

    // A constant pointer can't be pointing to an object on the heap. It may
    // be reference-counted, but it won't be deleted.
    if (const LoadInst *LI = dyn_cast<LoadInst>(Arg))
      if (const GlobalVariable *GV =
            dyn_cast<GlobalVariable>(
              StripPointerCastsAndObjCCalls(LI->getPointerOperand())))
        if (GV->isConstant())
          KnownSafe = true;

    // Connect the dots between the top-down-collected RetainsToMove and
    // bottom-up-collected ReleasesToMove to form sets of related calls.
    NewRetains.push_back(Retain);
    bool PerformMoveCalls =
      ConnectTDBUTraversals(BBStates, Retains, Releases, M, NewRetains,
                            NewReleases, DeadInsts, RetainsToMove,
                            ReleasesToMove, Arg, KnownSafe,
                            AnyPairsCompletelyEliminated);

#ifdef ARC_ANNOTATIONS
    // Do not move calls if ARC annotations are requested. If we were to move
    // calls in this case, we would not be able
    PerformMoveCalls = PerformMoveCalls && !EnableARCAnnotations;
#endif // ARC_ANNOTATIONS

    if (PerformMoveCalls) {
      // Ok, everything checks out and we're all set. Let's move/delete some
      // code!
      MoveCalls(Arg, RetainsToMove, ReleasesToMove,
                Retains, Releases, DeadInsts, M);
    }

    // Clean up state for next retain.
    NewReleases.clear();
    NewRetains.clear();
    RetainsToMove.clear();
    ReleasesToMove.clear();
  }

  // Now that we're done moving everything, we can delete the newly dead
  // instructions, as we no longer need them as insert points.
  while (!DeadInsts.empty())
    EraseInstruction(DeadInsts.pop_back_val());

  return AnyPairsCompletelyEliminated;
}

/// Weak pointer optimizations.
void ObjCARCOpt::OptimizeWeakCalls(Function &F) {
  DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeWeakCalls ==\n");

  // First, do memdep-style RLE and S2L optimizations. We can't use memdep
  // itself because it uses AliasAnalysis and we need to do provenance
  // queries instead.
  for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
    Instruction *Inst = &*I++;

    DEBUG(dbgs() << "Visiting: " << *Inst << "\n");

    InstructionClass Class = GetBasicInstructionClass(Inst);
    if (Class != IC_LoadWeak && Class != IC_LoadWeakRetained)
      continue;

    // Delete objc_loadWeak calls with no users.
    if (Class == IC_LoadWeak && Inst->use_empty()) {
      Inst->eraseFromParent();
      continue;
    }

    // TODO: For now, just look for an earlier available version of this value
    // within the same block. Theoretically, we could do memdep-style non-local
    // analysis too, but that would want caching. A better approach would be to
    // use the technique that EarlyCSE uses.
    inst_iterator Current = llvm::prior(I);
    BasicBlock *CurrentBB = Current.getBasicBlockIterator();
    for (BasicBlock::iterator B = CurrentBB->begin(),
                              J = Current.getInstructionIterator();
         J != B; --J) {
      Instruction *EarlierInst = &*llvm::prior(J);
      InstructionClass EarlierClass = GetInstructionClass(EarlierInst);
      switch (EarlierClass) {
      case IC_LoadWeak:
      case IC_LoadWeakRetained: {
        // If this is loading from the same pointer, replace this load's value
        // with that one.
        CallInst *Call = cast<CallInst>(Inst);
        CallInst *EarlierCall = cast<CallInst>(EarlierInst);
        Value *Arg = Call->getArgOperand(0);
        Value *EarlierArg = EarlierCall->getArgOperand(0);
        switch (PA.getAA()->alias(Arg, EarlierArg)) {
        case AliasAnalysis::MustAlias:
          Changed = true;
          // If the load has a builtin retain, insert a plain retain for it.
          if (Class == IC_LoadWeakRetained) {
            CallInst *CI =
              CallInst::Create(getRetainCallee(F.getParent()), EarlierCall,
                               "", Call);
            CI->setTailCall();
          }
          // Zap the fully redundant load.
          Call->replaceAllUsesWith(EarlierCall);
          Call->eraseFromParent();
          goto clobbered;
        case AliasAnalysis::MayAlias:
        case AliasAnalysis::PartialAlias:
          goto clobbered;
        case AliasAnalysis::NoAlias:
          break;
        }
        break;
      }
      case IC_StoreWeak:
      case IC_InitWeak: {
        // If this is storing to the same pointer and has the same size etc.
        // replace this load's value with the stored value.
        CallInst *Call = cast<CallInst>(Inst);
        CallInst *EarlierCall = cast<CallInst>(EarlierInst);
        Value *Arg = Call->getArgOperand(0);
        Value *EarlierArg = EarlierCall->getArgOperand(0);
        switch (PA.getAA()->alias(Arg, EarlierArg)) {
        case AliasAnalysis::MustAlias:
          Changed = true;
          // If the load has a builtin retain, insert a plain retain for it.
          if (Class == IC_LoadWeakRetained) {
            CallInst *CI =
              CallInst::Create(getRetainCallee(F.getParent()), EarlierCall,
                               "", Call);
            CI->setTailCall();
          }
          // Zap the fully redundant load.
          Call->replaceAllUsesWith(EarlierCall->getArgOperand(1));
          Call->eraseFromParent();
          goto clobbered;
        case AliasAnalysis::MayAlias:
        case AliasAnalysis::PartialAlias:
          goto clobbered;
        case AliasAnalysis::NoAlias:
          break;
        }
        break;
      }
      case IC_MoveWeak:
      case IC_CopyWeak:
        // TOOD: Grab the copied value.
        goto clobbered;
      case IC_AutoreleasepoolPush:
      case IC_None:
      case IC_IntrinsicUser:
      case IC_User:
        // Weak pointers are only modified through the weak entry points
        // (and arbitrary calls, which could call the weak entry points).
        break;
      default:
        // Anything else could modify the weak pointer.
        goto clobbered;
      }
    }
  clobbered:;
  }

  // Then, for each destroyWeak with an alloca operand, check to see if
  // the alloca and all its users can be zapped.
  for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
    Instruction *Inst = &*I++;
    InstructionClass Class = GetBasicInstructionClass(Inst);
    if (Class != IC_DestroyWeak)
      continue;

    CallInst *Call = cast<CallInst>(Inst);
    Value *Arg = Call->getArgOperand(0);
    if (AllocaInst *Alloca = dyn_cast<AllocaInst>(Arg)) {
      for (Value::use_iterator UI = Alloca->use_begin(),
           UE = Alloca->use_end(); UI != UE; ++UI) {
        const Instruction *UserInst = cast<Instruction>(*UI);
        switch (GetBasicInstructionClass(UserInst)) {
        case IC_InitWeak:
        case IC_StoreWeak:
        case IC_DestroyWeak:
          continue;
        default:
          goto done;
        }
      }
      Changed = true;
      for (Value::use_iterator UI = Alloca->use_begin(),
           UE = Alloca->use_end(); UI != UE; ) {
        CallInst *UserInst = cast<CallInst>(*UI++);
        switch (GetBasicInstructionClass(UserInst)) {
        case IC_InitWeak:
        case IC_StoreWeak:
          // These functions return their second argument.
          UserInst->replaceAllUsesWith(UserInst->getArgOperand(1));
          break;
        case IC_DestroyWeak:
          // No return value.
          break;
        default:
          llvm_unreachable("alloca really is used!");
        }
        UserInst->eraseFromParent();
      }
      Alloca->eraseFromParent();
    done:;
    }
  }
}

/// Identify program paths which execute sequences of retains and releases which
/// can be eliminated.
bool ObjCARCOpt::OptimizeSequences(Function &F) {
  /// Releases, Retains - These are used to store the results of the main flow
  /// analysis. These use Value* as the key instead of Instruction* so that the
  /// map stays valid when we get around to rewriting code and calls get
  /// replaced by arguments.
  DenseMap<Value *, RRInfo> Releases;
  MapVector<Value *, RRInfo> Retains;

  /// This is used during the traversal of the function to track the
  /// states for each identified object at each block.
  DenseMap<const BasicBlock *, BBState> BBStates;

  // Analyze the CFG of the function, and all instructions.
  bool NestingDetected = Visit(F, BBStates, Retains, Releases);

  // Transform.
  return PerformCodePlacement(BBStates, Retains, Releases, F.getParent()) &&
         NestingDetected;
}

/// Check if there is a dependent call earlier that does not have anything in
/// between the Retain and the call that can affect the reference count of their
/// shared pointer argument. Note that Retain need not be in BB.
static bool
HasSafePathToPredecessorCall(const Value *Arg, Instruction *Retain,
                             SmallPtrSet<Instruction *, 4> &DepInsts,
                             SmallPtrSet<const BasicBlock *, 4> &Visited,
                             ProvenanceAnalysis &PA) {
  FindDependencies(CanChangeRetainCount, Arg, Retain->getParent(), Retain,
                   DepInsts, Visited, PA);
  if (DepInsts.size() != 1)
    return false;

  CallInst *Call =
    dyn_cast_or_null<CallInst>(*DepInsts.begin());

  // Check that the pointer is the return value of the call.
  if (!Call || Arg != Call)
    return false;

  // Check that the call is a regular call.
  InstructionClass Class = GetBasicInstructionClass(Call);
  if (Class != IC_CallOrUser && Class != IC_Call)
    return false;

  return true;
}

/// Find a dependent retain that precedes the given autorelease for which there
/// is nothing in between the two instructions that can affect the ref count of
/// Arg.
static CallInst *
FindPredecessorRetainWithSafePath(const Value *Arg, BasicBlock *BB,
                                  Instruction *Autorelease,
                                  SmallPtrSet<Instruction *, 4> &DepInsts,
                                  SmallPtrSet<const BasicBlock *, 4> &Visited,
                                  ProvenanceAnalysis &PA) {
  FindDependencies(CanChangeRetainCount, Arg,
                   BB, Autorelease, DepInsts, Visited, PA);
  if (DepInsts.size() != 1)
    return 0;

  CallInst *Retain =
    dyn_cast_or_null<CallInst>(*DepInsts.begin());

  // Check that we found a retain with the same argument.
  if (!Retain ||
      !IsRetain(GetBasicInstructionClass(Retain)) ||
      GetObjCArg(Retain) != Arg) {
    return 0;
  }

  return Retain;
}

/// Look for an ``autorelease'' instruction dependent on Arg such that there are
/// no instructions dependent on Arg that need a positive ref count in between
/// the autorelease and the ret.
static CallInst *
FindPredecessorAutoreleaseWithSafePath(const Value *Arg, BasicBlock *BB,
                                       ReturnInst *Ret,
                                       SmallPtrSet<Instruction *, 4> &DepInsts,
                                       SmallPtrSet<const BasicBlock *, 4> &V,
                                       ProvenanceAnalysis &PA) {
  FindDependencies(NeedsPositiveRetainCount, Arg,
                   BB, Ret, DepInsts, V, PA);
  if (DepInsts.size() != 1)
    return 0;

  CallInst *Autorelease =
    dyn_cast_or_null<CallInst>(*DepInsts.begin());
  if (!Autorelease)
    return 0;
  InstructionClass AutoreleaseClass = GetBasicInstructionClass(Autorelease);
  if (!IsAutorelease(AutoreleaseClass))
    return 0;
  if (GetObjCArg(Autorelease) != Arg)
    return 0;

  return Autorelease;
}

/// Look for this pattern:
/// \code
///    %call = call i8* @something(...)
///    %2 = call i8* @objc_retain(i8* %call)
///    %3 = call i8* @objc_autorelease(i8* %2)
///    ret i8* %3
/// \endcode
/// And delete the retain and autorelease.
void ObjCARCOpt::OptimizeReturns(Function &F) {
  if (!F.getReturnType()->isPointerTy())
    return;

  DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeReturns ==\n");

  SmallPtrSet<Instruction *, 4> DependingInstructions;
  SmallPtrSet<const BasicBlock *, 4> Visited;
  for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
    BasicBlock *BB = FI;
    ReturnInst *Ret = dyn_cast<ReturnInst>(&BB->back());

    DEBUG(dbgs() << "Visiting: " << *Ret << "\n");

    if (!Ret)
      continue;

    const Value *Arg = StripPointerCastsAndObjCCalls(Ret->getOperand(0));

    // Look for an ``autorelease'' instruction that is a predecssor of Ret and
    // dependent on Arg such that there are no instructions dependent on Arg
    // that need a positive ref count in between the autorelease and Ret.
    CallInst *Autorelease =
      FindPredecessorAutoreleaseWithSafePath(Arg, BB, Ret,
                                             DependingInstructions, Visited,
                                             PA);
    if (Autorelease) {
      DependingInstructions.clear();
      Visited.clear();

      CallInst *Retain =
        FindPredecessorRetainWithSafePath(Arg, BB, Autorelease,
                                          DependingInstructions, Visited, PA);
      if (Retain) {
        DependingInstructions.clear();
        Visited.clear();

        // Check that there is nothing that can affect the reference count
        // between the retain and the call.  Note that Retain need not be in BB.
        if (HasSafePathToPredecessorCall(Arg, Retain, DependingInstructions,
                                         Visited, PA)) {
          // If so, we can zap the retain and autorelease.
          Changed = true;
          ++NumRets;
          DEBUG(dbgs() << "Erasing: " << *Retain << "\nErasing: "
                       << *Autorelease << "\n");
          EraseInstruction(Retain);
          EraseInstruction(Autorelease);
        }
      }
    }

    DependingInstructions.clear();
    Visited.clear();
  }
}

bool ObjCARCOpt::doInitialization(Module &M) {
  if (!EnableARCOpts)
    return false;

  // If nothing in the Module uses ARC, don't do anything.
  Run = ModuleHasARC(M);
  if (!Run)
    return false;

  // Identify the imprecise release metadata kind.
  ImpreciseReleaseMDKind =
    M.getContext().getMDKindID("clang.imprecise_release");
  CopyOnEscapeMDKind =
    M.getContext().getMDKindID("clang.arc.copy_on_escape");
  NoObjCARCExceptionsMDKind =
    M.getContext().getMDKindID("clang.arc.no_objc_arc_exceptions");
#ifdef ARC_ANNOTATIONS
  ARCAnnotationBottomUpMDKind =
    M.getContext().getMDKindID("llvm.arc.annotation.bottomup");
  ARCAnnotationTopDownMDKind =
    M.getContext().getMDKindID("llvm.arc.annotation.topdown");
  ARCAnnotationProvenanceSourceMDKind =
    M.getContext().getMDKindID("llvm.arc.annotation.provenancesource");
#endif // ARC_ANNOTATIONS

  // Intuitively, objc_retain and others are nocapture, however in practice
  // they are not, because they return their argument value. And objc_release
  // calls finalizers which can have arbitrary side effects.

  // These are initialized lazily.
  RetainRVCallee = 0;
  AutoreleaseRVCallee = 0;
  ReleaseCallee = 0;
  RetainCallee = 0;
  RetainBlockCallee = 0;
  AutoreleaseCallee = 0;

  return false;
}

bool ObjCARCOpt::runOnFunction(Function &F) {
  if (!EnableARCOpts)
    return false;

  // If nothing in the Module uses ARC, don't do anything.
  if (!Run)
    return false;

  Changed = false;

  DEBUG(dbgs() << "<<< ObjCARCOpt: Visiting Function: " << F.getName() << " >>>"
        "\n");

  PA.setAA(&getAnalysis<AliasAnalysis>());

  // This pass performs several distinct transformations. As a compile-time aid
  // when compiling code that isn't ObjC, skip these if the relevant ObjC
  // library functions aren't declared.

  // Preliminary optimizations. This also computs UsedInThisFunction.
  OptimizeIndividualCalls(F);

  // Optimizations for weak pointers.
  if (UsedInThisFunction & ((1 << IC_LoadWeak) |
                            (1 << IC_LoadWeakRetained) |
                            (1 << IC_StoreWeak) |
                            (1 << IC_InitWeak) |
                            (1 << IC_CopyWeak) |
                            (1 << IC_MoveWeak) |
                            (1 << IC_DestroyWeak)))
    OptimizeWeakCalls(F);

  // Optimizations for retain+release pairs.
  if (UsedInThisFunction & ((1 << IC_Retain) |
                            (1 << IC_RetainRV) |
                            (1 << IC_RetainBlock)))
    if (UsedInThisFunction & (1 << IC_Release))
      // Run OptimizeSequences until it either stops making changes or
      // no retain+release pair nesting is detected.
      while (OptimizeSequences(F)) {}

  // Optimizations if objc_autorelease is used.
  if (UsedInThisFunction & ((1 << IC_Autorelease) |
                            (1 << IC_AutoreleaseRV)))
    OptimizeReturns(F);

  DEBUG(dbgs() << "\n");

  return Changed;
}

void ObjCARCOpt::releaseMemory() {
  PA.clear();
}

/// @}
///