aboutsummaryrefslogtreecommitdiffstats
path: root/gcc-4.9/gcc/tree-predcom.c
blob: 20b0e3b0ab8f9693b310d0d8a55f16bc417d69da (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
/* Predictive commoning.
   Copyright (C) 2005-2014 Free Software Foundation, Inc.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 3, or (at your option) any
later version.

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

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

/* This file implements the predictive commoning optimization.  Predictive
   commoning can be viewed as CSE around a loop, and with some improvements,
   as generalized strength reduction-- i.e., reusing values computed in
   earlier iterations of a loop in the later ones.  So far, the pass only
   handles the most useful case, that is, reusing values of memory references.
   If you think this is all just a special case of PRE, you are sort of right;
   however, concentrating on loops is simpler, and makes it possible to
   incorporate data dependence analysis to detect the opportunities, perform
   loop unrolling to avoid copies together with renaming immediately,
   and if needed, we could also take register pressure into account.

   Let us demonstrate what is done on an example:

   for (i = 0; i < 100; i++)
     {
       a[i+2] = a[i] + a[i+1];
       b[10] = b[10] + i;
       c[i] = c[99 - i];
       d[i] = d[i + 1];
     }

   1) We find data references in the loop, and split them to mutually
      independent groups (i.e., we find components of a data dependence
      graph).  We ignore read-read dependences whose distance is not constant.
      (TODO -- we could also ignore antidependences).  In this example, we
      find the following groups:

      a[i]{read}, a[i+1]{read}, a[i+2]{write}
      b[10]{read}, b[10]{write}
      c[99 - i]{read}, c[i]{write}
      d[i + 1]{read}, d[i]{write}

   2) Inside each of the group, we verify several conditions:
      a) all the references must differ in indices only, and the indices
	 must all have the same step
      b) the references must dominate loop latch (and thus, they must be
	 ordered by dominance relation).
      c) the distance of the indices must be a small multiple of the step
      We are then able to compute the difference of the references (# of
      iterations before they point to the same place as the first of them).
      Also, in case there are writes in the loop, we split the groups into
      chains whose head is the write whose values are used by the reads in
      the same chain.  The chains are then processed independently,
      making the further transformations simpler.  Also, the shorter chains
      need the same number of registers, but may require lower unrolling
      factor in order to get rid of the copies on the loop latch.

      In our example, we get the following chains (the chain for c is invalid).

      a[i]{read,+0}, a[i+1]{read,-1}, a[i+2]{write,-2}
      b[10]{read,+0}, b[10]{write,+0}
      d[i + 1]{read,+0}, d[i]{write,+1}

   3) For each read, we determine the read or write whose value it reuses,
      together with the distance of this reuse.  I.e. we take the last
      reference before it with distance 0, or the last of the references
      with the smallest positive distance to the read.  Then, we remove
      the references that are not used in any of these chains, discard the
      empty groups, and propagate all the links so that they point to the
      single root reference of the chain (adjusting their distance
      appropriately).  Some extra care needs to be taken for references with
      step 0.  In our example (the numbers indicate the distance of the
      reuse),

      a[i] --> (*) 2, a[i+1] --> (*) 1, a[i+2] (*)
      b[10] --> (*) 1, b[10] (*)

   4) The chains are combined together if possible.  If the corresponding
      elements of two chains are always combined together with the same
      operator, we remember just the result of this combination, instead
      of remembering the values separately.  We may need to perform
      reassociation to enable combining, for example

      e[i] + f[i+1] + e[i+1] + f[i]

      can be reassociated as

      (e[i] + f[i]) + (e[i+1] + f[i+1])

      and we can combine the chains for e and f into one chain.

   5) For each root reference (end of the chain) R, let N be maximum distance
      of a reference reusing its value.  Variables R0 up to RN are created,
      together with phi nodes that transfer values from R1 .. RN to
      R0 .. R(N-1).
      Initial values are loaded to R0..R(N-1) (in case not all references
      must necessarily be accessed and they may trap, we may fail here;
      TODO sometimes, the loads could be guarded by a check for the number
      of iterations).  Values loaded/stored in roots are also copied to
      RN.  Other reads are replaced with the appropriate variable Ri.
      Everything is put to SSA form.

      As a small improvement, if R0 is dead after the root (i.e., all uses of
      the value with the maximum distance dominate the root), we can avoid
      creating RN and use R0 instead of it.

      In our example, we get (only the parts concerning a and b are shown):
      for (i = 0; i < 100; i++)
	{
	  f = phi (a[0], s);
	  s = phi (a[1], f);
	  x = phi (b[10], x);

	  f = f + s;
	  a[i+2] = f;
	  x = x + i;
	  b[10] = x;
	}

   6) Factor F for unrolling is determined as the smallest common multiple of
      (N + 1) for each root reference (N for references for that we avoided
      creating RN).  If F and the loop is small enough, loop is unrolled F
      times.  The stores to RN (R0) in the copies of the loop body are
      periodically replaced with R0, R1, ... (R1, R2, ...), so that they can
      be coalesced and the copies can be eliminated.

      TODO -- copy propagation and other optimizations may change the live
      ranges of the temporary registers and prevent them from being coalesced;
      this may increase the register pressure.

      In our case, F = 2 and the (main loop of the) result is

      for (i = 0; i < ...; i += 2)
        {
          f = phi (a[0], f);
          s = phi (a[1], s);
          x = phi (b[10], x);

          f = f + s;
          a[i+2] = f;
          x = x + i;
          b[10] = x;

          s = s + f;
          a[i+3] = s;
          x = x + i;
          b[10] = x;
       }

   TODO -- stores killing other stores can be taken into account, e.g.,
   for (i = 0; i < n; i++)
     {
       a[i] = 1;
       a[i+2] = 2;
     }

   can be replaced with

   t0 = a[0];
   t1 = a[1];
   for (i = 0; i < n; i++)
     {
       a[i] = 1;
       t2 = 2;
       t0 = t1;
       t1 = t2;
     }
   a[n] = t0;
   a[n+1] = t1;

   The interesting part is that this would generalize store motion; still, since
   sm is performed elsewhere, it does not seem that important.

   Predictive commoning can be generalized for arbitrary computations (not
   just memory loads), and also nontrivial transfer functions (e.g., replacing
   i * i with ii_last + 2 * i + 1), to generalize strength reduction.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "tree.h"
#include "tm_p.h"
#include "cfgloop.h"
#include "basic-block.h"
#include "tree-ssa-alias.h"
#include "internal-fn.h"
#include "tree-eh.h"
#include "gimple-expr.h"
#include "is-a.h"
#include "gimple.h"
#include "gimplify.h"
#include "gimple-iterator.h"
#include "gimplify-me.h"
#include "gimple-ssa.h"
#include "tree-phinodes.h"
#include "ssa-iterators.h"
#include "stringpool.h"
#include "tree-ssanames.h"
#include "tree-ssa-loop-ivopts.h"
#include "tree-ssa-loop-manip.h"
#include "tree-ssa-loop-niter.h"
#include "tree-ssa-loop.h"
#include "tree-into-ssa.h"
#include "expr.h"
#include "tree-dfa.h"
#include "tree-ssa.h"
#include "tree-data-ref.h"
#include "tree-scalar-evolution.h"
#include "tree-chrec.h"
#include "params.h"
#include "gimple-pretty-print.h"
#include "tree-pass.h"
#include "tree-affine.h"
#include "tree-inline.h"

/* The maximum number of iterations between the considered memory
   references.  */

#define MAX_DISTANCE (target_avail_regs < 16 ? 4 : 8)

/* Data references (or phi nodes that carry data reference values across
   loop iterations).  */

typedef struct dref_d
{
  /* The reference itself.  */
  struct data_reference *ref;

  /* The statement in that the reference appears.  */
  gimple stmt;

  /* In case that STMT is a phi node, this field is set to the SSA name
     defined by it in replace_phis_by_defined_names (in order to avoid
     pointing to phi node that got reallocated in the meantime).  */
  tree name_defined_by_phi;

  /* Distance of the reference from the root of the chain (in number of
     iterations of the loop).  */
  unsigned distance;

  /* Number of iterations offset from the first reference in the component.  */
  double_int offset;

  /* Number of the reference in a component, in dominance ordering.  */
  unsigned pos;

  /* True if the memory reference is always accessed when the loop is
     entered.  */
  unsigned always_accessed : 1;
} *dref;


/* Type of the chain of the references.  */

enum chain_type
{
  /* The addresses of the references in the chain are constant.  */
  CT_INVARIANT,

  /* There are only loads in the chain.  */
  CT_LOAD,

  /* Root of the chain is store, the rest are loads.  */
  CT_STORE_LOAD,

  /* A combination of two chains.  */
  CT_COMBINATION
};

/* Chains of data references.  */

typedef struct chain
{
  /* Type of the chain.  */
  enum chain_type type;

  /* For combination chains, the operator and the two chains that are
     combined, and the type of the result.  */
  enum tree_code op;
  tree rslt_type;
  struct chain *ch1, *ch2;

  /* The references in the chain.  */
  vec<dref> refs;

  /* The maximum distance of the reference in the chain from the root.  */
  unsigned length;

  /* The variables used to copy the value throughout iterations.  */
  vec<tree> vars;

  /* Initializers for the variables.  */
  vec<tree> inits;

  /* True if there is a use of a variable with the maximal distance
     that comes after the root in the loop.  */
  unsigned has_max_use_after : 1;

  /* True if all the memory references in the chain are always accessed.  */
  unsigned all_always_accessed : 1;

  /* True if this chain was combined together with some other chain.  */
  unsigned combined : 1;
} *chain_p;


/* Describes the knowledge about the step of the memory references in
   the component.  */

enum ref_step_type
{
  /* The step is zero.  */
  RS_INVARIANT,

  /* The step is nonzero.  */
  RS_NONZERO,

  /* The step may or may not be nonzero.  */
  RS_ANY
};

/* Components of the data dependence graph.  */

struct component
{
  /* The references in the component.  */
  vec<dref> refs;

  /* What we know about the step of the references in the component.  */
  enum ref_step_type comp_step;

  /* Next component in the list.  */
  struct component *next;
};

/* Bitmap of ssa names defined by looparound phi nodes covered by chains.  */

static bitmap looparound_phis;

/* Cache used by tree_to_aff_combination_expand.  */

static struct pointer_map_t *name_expansions;

/* Dumps data reference REF to FILE.  */

extern void dump_dref (FILE *, dref);
void
dump_dref (FILE *file, dref ref)
{
  if (ref->ref)
    {
      fprintf (file, "    ");
      print_generic_expr (file, DR_REF (ref->ref), TDF_SLIM);
      fprintf (file, " (id %u%s)\n", ref->pos,
	       DR_IS_READ (ref->ref) ? "" : ", write");

      fprintf (file, "      offset ");
      dump_double_int (file, ref->offset, false);
      fprintf (file, "\n");

      fprintf (file, "      distance %u\n", ref->distance);
    }
  else
    {
      if (gimple_code (ref->stmt) == GIMPLE_PHI)
	fprintf (file, "    looparound ref\n");
      else
	fprintf (file, "    combination ref\n");
      fprintf (file, "      in statement ");
      print_gimple_stmt (file, ref->stmt, 0, TDF_SLIM);
      fprintf (file, "\n");
      fprintf (file, "      distance %u\n", ref->distance);
    }

}

/* Dumps CHAIN to FILE.  */

extern void dump_chain (FILE *, chain_p);
void
dump_chain (FILE *file, chain_p chain)
{
  dref a;
  const char *chain_type;
  unsigned i;
  tree var;

  switch (chain->type)
    {
    case CT_INVARIANT:
      chain_type = "Load motion";
      break;

    case CT_LOAD:
      chain_type = "Loads-only";
      break;

    case CT_STORE_LOAD:
      chain_type = "Store-loads";
      break;

    case CT_COMBINATION:
      chain_type = "Combination";
      break;

    default:
      gcc_unreachable ();
    }

  fprintf (file, "%s chain %p%s\n", chain_type, (void *) chain,
	   chain->combined ? " (combined)" : "");
  if (chain->type != CT_INVARIANT)
    fprintf (file, "  max distance %u%s\n", chain->length,
	     chain->has_max_use_after ? "" : ", may reuse first");

  if (chain->type == CT_COMBINATION)
    {
      fprintf (file, "  equal to %p %s %p in type ",
	       (void *) chain->ch1, op_symbol_code (chain->op),
	       (void *) chain->ch2);
      print_generic_expr (file, chain->rslt_type, TDF_SLIM);
      fprintf (file, "\n");
    }

  if (chain->vars.exists ())
    {
      fprintf (file, "  vars");
      FOR_EACH_VEC_ELT (chain->vars, i, var)
	{
	  fprintf (file, " ");
	  print_generic_expr (file, var, TDF_SLIM);
	}
      fprintf (file, "\n");
    }

  if (chain->inits.exists ())
    {
      fprintf (file, "  inits");
      FOR_EACH_VEC_ELT (chain->inits, i, var)
	{
	  fprintf (file, " ");
	  print_generic_expr (file, var, TDF_SLIM);
	}
      fprintf (file, "\n");
    }

  fprintf (file, "  references:\n");
  FOR_EACH_VEC_ELT (chain->refs, i, a)
    dump_dref (file, a);

  fprintf (file, "\n");
}

/* Dumps CHAINS to FILE.  */

extern void dump_chains (FILE *, vec<chain_p> );
void
dump_chains (FILE *file, vec<chain_p> chains)
{
  chain_p chain;
  unsigned i;

  FOR_EACH_VEC_ELT (chains, i, chain)
    dump_chain (file, chain);
}

/* Dumps COMP to FILE.  */

extern void dump_component (FILE *, struct component *);
void
dump_component (FILE *file, struct component *comp)
{
  dref a;
  unsigned i;

  fprintf (file, "Component%s:\n",
	   comp->comp_step == RS_INVARIANT ? " (invariant)" : "");
  FOR_EACH_VEC_ELT (comp->refs, i, a)
    dump_dref (file, a);
  fprintf (file, "\n");
}

/* Dumps COMPS to FILE.  */

extern void dump_components (FILE *, struct component *);
void
dump_components (FILE *file, struct component *comps)
{
  struct component *comp;

  for (comp = comps; comp; comp = comp->next)
    dump_component (file, comp);
}

/* Frees a chain CHAIN.  */

static void
release_chain (chain_p chain)
{
  dref ref;
  unsigned i;

  if (chain == NULL)
    return;

  FOR_EACH_VEC_ELT (chain->refs, i, ref)
    free (ref);

  chain->refs.release ();
  chain->vars.release ();
  chain->inits.release ();

  free (chain);
}

/* Frees CHAINS.  */

static void
release_chains (vec<chain_p> chains)
{
  unsigned i;
  chain_p chain;

  FOR_EACH_VEC_ELT (chains, i, chain)
    release_chain (chain);
  chains.release ();
}

/* Frees a component COMP.  */

static void
release_component (struct component *comp)
{
  comp->refs.release ();
  free (comp);
}

/* Frees list of components COMPS.  */

static void
release_components (struct component *comps)
{
  struct component *act, *next;

  for (act = comps; act; act = next)
    {
      next = act->next;
      release_component (act);
    }
}

/* Finds a root of tree given by FATHERS containing A, and performs path
   shortening.  */

static unsigned
component_of (unsigned fathers[], unsigned a)
{
  unsigned root, n;

  for (root = a; root != fathers[root]; root = fathers[root])
    continue;

  for (; a != root; a = n)
    {
      n = fathers[a];
      fathers[a] = root;
    }

  return root;
}

/* Join operation for DFU.  FATHERS gives the tree, SIZES are sizes of the
   components, A and B are components to merge.  */

static void
merge_comps (unsigned fathers[], unsigned sizes[], unsigned a, unsigned b)
{
  unsigned ca = component_of (fathers, a);
  unsigned cb = component_of (fathers, b);

  if (ca == cb)
    return;

  if (sizes[ca] < sizes[cb])
    {
      sizes[cb] += sizes[ca];
      fathers[ca] = cb;
    }
  else
    {
      sizes[ca] += sizes[cb];
      fathers[cb] = ca;
    }
}

/* Returns true if A is a reference that is suitable for predictive commoning
   in the innermost loop that contains it.  REF_STEP is set according to the
   step of the reference A.  */

static bool
suitable_reference_p (struct data_reference *a, enum ref_step_type *ref_step)
{
  tree ref = DR_REF (a), step = DR_STEP (a);

  if (!step
      || TREE_THIS_VOLATILE (ref)
      || !is_gimple_reg_type (TREE_TYPE (ref))
      || tree_could_throw_p (ref))
    return false;

  if (integer_zerop (step))
    *ref_step = RS_INVARIANT;
  else if (integer_nonzerop (step))
    *ref_step = RS_NONZERO;
  else
    *ref_step = RS_ANY;

  return true;
}

/* Stores DR_OFFSET (DR) + DR_INIT (DR) to OFFSET.  */

static void
aff_combination_dr_offset (struct data_reference *dr, aff_tree *offset)
{
  tree type = TREE_TYPE (DR_OFFSET (dr));
  aff_tree delta;

  tree_to_aff_combination_expand (DR_OFFSET (dr), type, offset,
				  &name_expansions);
  aff_combination_const (&delta, type, tree_to_double_int (DR_INIT (dr)));
  aff_combination_add (offset, &delta);
}

/* Determines number of iterations of the innermost enclosing loop before B
   refers to exactly the same location as A and stores it to OFF.  If A and
   B do not have the same step, they never meet, or anything else fails,
   returns false, otherwise returns true.  Both A and B are assumed to
   satisfy suitable_reference_p.  */

static bool
determine_offset (struct data_reference *a, struct data_reference *b,
		  double_int *off)
{
  aff_tree diff, baseb, step;
  tree typea, typeb;

  /* Check that both the references access the location in the same type.  */
  typea = TREE_TYPE (DR_REF (a));
  typeb = TREE_TYPE (DR_REF (b));
  if (!useless_type_conversion_p (typeb, typea))
    return false;

  /* Check whether the base address and the step of both references is the
     same.  */
  if (!operand_equal_p (DR_STEP (a), DR_STEP (b), 0)
      || !operand_equal_p (DR_BASE_ADDRESS (a), DR_BASE_ADDRESS (b), 0))
    return false;

  if (integer_zerop (DR_STEP (a)))
    {
      /* If the references have loop invariant address, check that they access
	 exactly the same location.  */
      *off = double_int_zero;
      return (operand_equal_p (DR_OFFSET (a), DR_OFFSET (b), 0)
	      && operand_equal_p (DR_INIT (a), DR_INIT (b), 0));
    }

  /* Compare the offsets of the addresses, and check whether the difference
     is a multiple of step.  */
  aff_combination_dr_offset (a, &diff);
  aff_combination_dr_offset (b, &baseb);
  aff_combination_scale (&baseb, double_int_minus_one);
  aff_combination_add (&diff, &baseb);

  tree_to_aff_combination_expand (DR_STEP (a), TREE_TYPE (DR_STEP (a)),
				  &step, &name_expansions);
  return aff_combination_constant_multiple_p (&diff, &step, off);
}

/* Returns the last basic block in LOOP for that we are sure that
   it is executed whenever the loop is entered.  */

static basic_block
last_always_executed_block (struct loop *loop)
{
  unsigned i;
  vec<edge> exits = get_loop_exit_edges (loop);
  edge ex;
  basic_block last = loop->latch;

  FOR_EACH_VEC_ELT (exits, i, ex)
    last = nearest_common_dominator (CDI_DOMINATORS, last, ex->src);
  exits.release ();

  return last;
}

/* Splits dependence graph on DATAREFS described by DEPENDS to components.  */

static struct component *
split_data_refs_to_components (struct loop *loop,
			       vec<data_reference_p> datarefs,
			       vec<ddr_p> depends)
{
  unsigned i, n = datarefs.length ();
  unsigned ca, ia, ib, bad;
  unsigned *comp_father = XNEWVEC (unsigned, n + 1);
  unsigned *comp_size = XNEWVEC (unsigned, n + 1);
  struct component **comps;
  struct data_reference *dr, *dra, *drb;
  struct data_dependence_relation *ddr;
  struct component *comp_list = NULL, *comp;
  dref dataref;
  basic_block last_always_executed = last_always_executed_block (loop);

  FOR_EACH_VEC_ELT (datarefs, i, dr)
    {
      if (!DR_REF (dr))
	{
	  /* A fake reference for call or asm_expr that may clobber memory;
	     just fail.  */
	  goto end;
	}
      /* predcom pass isn't prepared to handle calls with data references.  */
      if (is_gimple_call (DR_STMT (dr)))
	goto end;
      dr->aux = (void *) (size_t) i;
      comp_father[i] = i;
      comp_size[i] = 1;
    }

  /* A component reserved for the "bad" data references.  */
  comp_father[n] = n;
  comp_size[n] = 1;

  FOR_EACH_VEC_ELT (datarefs, i, dr)
    {
      enum ref_step_type dummy;

      if (!suitable_reference_p (dr, &dummy))
	{
	  ia = (unsigned) (size_t) dr->aux;
	  merge_comps (comp_father, comp_size, n, ia);
	}
    }

  FOR_EACH_VEC_ELT (depends, i, ddr)
    {
      double_int dummy_off;

      if (DDR_ARE_DEPENDENT (ddr) == chrec_known)
	continue;

      dra = DDR_A (ddr);
      drb = DDR_B (ddr);
      ia = component_of (comp_father, (unsigned) (size_t) dra->aux);
      ib = component_of (comp_father, (unsigned) (size_t) drb->aux);
      if (ia == ib)
	continue;

      bad = component_of (comp_father, n);

      /* If both A and B are reads, we may ignore unsuitable dependences.  */
      if (DR_IS_READ (dra) && DR_IS_READ (drb))
	{
	  if (ia == bad || ib == bad
	      || !determine_offset (dra, drb, &dummy_off))
	    continue;
	}
      /* If A is read and B write or vice versa and there is unsuitable
	 dependence, instead of merging both components into a component
	 that will certainly not pass suitable_component_p, just put the
	 read into bad component, perhaps at least the write together with
	 all the other data refs in it's component will be optimizable.  */
      else if (DR_IS_READ (dra) && ib != bad)
	{
	  if (ia == bad)
	    continue;
	  else if (!determine_offset (dra, drb, &dummy_off))
	    {
	      merge_comps (comp_father, comp_size, bad, ia);
	      continue;
	    }
	}
      else if (DR_IS_READ (drb) && ia != bad)
	{
	  if (ib == bad)
	    continue;
	  else if (!determine_offset (dra, drb, &dummy_off))
	    {
	      merge_comps (comp_father, comp_size, bad, ib);
	      continue;
	    }
	}

      merge_comps (comp_father, comp_size, ia, ib);
    }

  comps = XCNEWVEC (struct component *, n);
  bad = component_of (comp_father, n);
  FOR_EACH_VEC_ELT (datarefs, i, dr)
    {
      ia = (unsigned) (size_t) dr->aux;
      ca = component_of (comp_father, ia);
      if (ca == bad)
	continue;

      comp = comps[ca];
      if (!comp)
	{
	  comp = XCNEW (struct component);
	  comp->refs.create (comp_size[ca]);
	  comps[ca] = comp;
	}

      dataref = XCNEW (struct dref_d);
      dataref->ref = dr;
      dataref->stmt = DR_STMT (dr);
      dataref->offset = double_int_zero;
      dataref->distance = 0;

      dataref->always_accessed
	      = dominated_by_p (CDI_DOMINATORS, last_always_executed,
				gimple_bb (dataref->stmt));
      dataref->pos = comp->refs.length ();
      comp->refs.quick_push (dataref);
    }

  for (i = 0; i < n; i++)
    {
      comp = comps[i];
      if (comp)
	{
	  comp->next = comp_list;
	  comp_list = comp;
	}
    }
  free (comps);

end:
  free (comp_father);
  free (comp_size);
  return comp_list;
}

/* Returns true if the component COMP satisfies the conditions
   described in 2) at the beginning of this file.  LOOP is the current
   loop.  */

static bool
suitable_component_p (struct loop *loop, struct component *comp)
{
  unsigned i;
  dref a, first;
  basic_block ba, bp = loop->header;
  bool ok, has_write = false;

  FOR_EACH_VEC_ELT (comp->refs, i, a)
    {
      ba = gimple_bb (a->stmt);

      if (!just_once_each_iteration_p (loop, ba))
	return false;

      gcc_assert (dominated_by_p (CDI_DOMINATORS, ba, bp));
      bp = ba;

      if (DR_IS_WRITE (a->ref))
	has_write = true;
    }

  first = comp->refs[0];
  ok = suitable_reference_p (first->ref, &comp->comp_step);
  gcc_assert (ok);
  first->offset = double_int_zero;

  for (i = 1; comp->refs.iterate (i, &a); i++)
    {
      if (!determine_offset (first->ref, a->ref, &a->offset))
	return false;

#ifdef ENABLE_CHECKING
      {
	enum ref_step_type a_step;
	ok = suitable_reference_p (a->ref, &a_step);
	gcc_assert (ok && a_step == comp->comp_step);
      }
#endif
    }

  /* If there is a write inside the component, we must know whether the
     step is nonzero or not -- we would not otherwise be able to recognize
     whether the value accessed by reads comes from the OFFSET-th iteration
     or the previous one.  */
  if (has_write && comp->comp_step == RS_ANY)
    return false;

  return true;
}

/* Check the conditions on references inside each of components COMPS,
   and remove the unsuitable components from the list.  The new list
   of components is returned.  The conditions are described in 2) at
   the beginning of this file.  LOOP is the current loop.  */

static struct component *
filter_suitable_components (struct loop *loop, struct component *comps)
{
  struct component **comp, *act;

  for (comp = &comps; *comp; )
    {
      act = *comp;
      if (suitable_component_p (loop, act))
	comp = &act->next;
      else
	{
	  dref ref;
	  unsigned i;

	  *comp = act->next;
	  FOR_EACH_VEC_ELT (act->refs, i, ref)
	    free (ref);
	  release_component (act);
	}
    }

  return comps;
}

/* Compares two drefs A and B by their offset and position.  Callback for
   qsort.  */

static int
order_drefs (const void *a, const void *b)
{
  const dref *const da = (const dref *) a;
  const dref *const db = (const dref *) b;
  int offcmp = (*da)->offset.scmp ((*db)->offset);

  if (offcmp != 0)
    return offcmp;

  return (*da)->pos - (*db)->pos;
}

/* Returns root of the CHAIN.  */

static inline dref
get_chain_root (chain_p chain)
{
  return chain->refs[0];
}

/* Adds REF to the chain CHAIN.  */

static void
add_ref_to_chain (chain_p chain, dref ref)
{
  dref root = get_chain_root (chain);
  double_int dist;

  gcc_assert (root->offset.sle (ref->offset));
  dist = ref->offset - root->offset;
  if (double_int::from_uhwi (MAX_DISTANCE).ule (dist))
    {
      free (ref);
      return;
    }
  gcc_assert (dist.fits_uhwi ());

  chain->refs.safe_push (ref);

  ref->distance = dist.to_uhwi ();

  if (ref->distance >= chain->length)
    {
      chain->length = ref->distance;
      chain->has_max_use_after = false;
    }

  if (ref->distance == chain->length
      && ref->pos > root->pos)
    chain->has_max_use_after = true;

  chain->all_always_accessed &= ref->always_accessed;
}

/* Returns the chain for invariant component COMP.  */

static chain_p
make_invariant_chain (struct component *comp)
{
  chain_p chain = XCNEW (struct chain);
  unsigned i;
  dref ref;

  chain->type = CT_INVARIANT;

  chain->all_always_accessed = true;

  FOR_EACH_VEC_ELT (comp->refs, i, ref)
    {
      chain->refs.safe_push (ref);
      chain->all_always_accessed &= ref->always_accessed;
    }

  return chain;
}

/* Make a new chain rooted at REF.  */

static chain_p
make_rooted_chain (dref ref)
{
  chain_p chain = XCNEW (struct chain);

  chain->type = DR_IS_READ (ref->ref) ? CT_LOAD : CT_STORE_LOAD;

  chain->refs.safe_push (ref);
  chain->all_always_accessed = ref->always_accessed;

  ref->distance = 0;

  return chain;
}

/* Returns true if CHAIN is not trivial.  */

static bool
nontrivial_chain_p (chain_p chain)
{
  return chain != NULL && chain->refs.length () > 1;
}

/* Returns the ssa name that contains the value of REF, or NULL_TREE if there
   is no such name.  */

static tree
name_for_ref (dref ref)
{
  tree name;

  if (is_gimple_assign (ref->stmt))
    {
      if (!ref->ref || DR_IS_READ (ref->ref))
	name = gimple_assign_lhs (ref->stmt);
      else
	name = gimple_assign_rhs1 (ref->stmt);
    }
  else
    name = PHI_RESULT (ref->stmt);

  return (TREE_CODE (name) == SSA_NAME ? name : NULL_TREE);
}

/* Returns true if REF is a valid initializer for ROOT with given DISTANCE (in
   iterations of the innermost enclosing loop).  */

static bool
valid_initializer_p (struct data_reference *ref,
		     unsigned distance, struct data_reference *root)
{
  aff_tree diff, base, step;
  double_int off;

  /* Both REF and ROOT must be accessing the same object.  */
  if (!operand_equal_p (DR_BASE_ADDRESS (ref), DR_BASE_ADDRESS (root), 0))
    return false;

  /* The initializer is defined outside of loop, hence its address must be
     invariant inside the loop.  */
  gcc_assert (integer_zerop (DR_STEP (ref)));

  /* If the address of the reference is invariant, initializer must access
     exactly the same location.  */
  if (integer_zerop (DR_STEP (root)))
    return (operand_equal_p (DR_OFFSET (ref), DR_OFFSET (root), 0)
	    && operand_equal_p (DR_INIT (ref), DR_INIT (root), 0));

  /* Verify that this index of REF is equal to the root's index at
     -DISTANCE-th iteration.  */
  aff_combination_dr_offset (root, &diff);
  aff_combination_dr_offset (ref, &base);
  aff_combination_scale (&base, double_int_minus_one);
  aff_combination_add (&diff, &base);

  tree_to_aff_combination_expand (DR_STEP (root), TREE_TYPE (DR_STEP (root)),
				  &step, &name_expansions);
  if (!aff_combination_constant_multiple_p (&diff, &step, &off))
    return false;

  if (off != double_int::from_uhwi (distance))
    return false;

  return true;
}

/* Finds looparound phi node of LOOP that copies the value of REF, and if its
   initial value is correct (equal to initial value of REF shifted by one
   iteration), returns the phi node.  Otherwise, NULL_TREE is returned.  ROOT
   is the root of the current chain.  */

static gimple
find_looparound_phi (struct loop *loop, dref ref, dref root)
{
  tree name, init, init_ref;
  gimple phi = NULL, init_stmt;
  edge latch = loop_latch_edge (loop);
  struct data_reference init_dr;
  gimple_stmt_iterator psi;

  if (is_gimple_assign (ref->stmt))
    {
      if (DR_IS_READ (ref->ref))
	name = gimple_assign_lhs (ref->stmt);
      else
	name = gimple_assign_rhs1 (ref->stmt);
    }
  else
    name = PHI_RESULT (ref->stmt);
  if (!name)
    return NULL;

  for (psi = gsi_start_phis (loop->header); !gsi_end_p (psi); gsi_next (&psi))
    {
      phi = gsi_stmt (psi);
      if (PHI_ARG_DEF_FROM_EDGE (phi, latch) == name)
	break;
    }

  if (gsi_end_p (psi))
    return NULL;

  init = PHI_ARG_DEF_FROM_EDGE (phi, loop_preheader_edge (loop));
  if (TREE_CODE (init) != SSA_NAME)
    return NULL;
  init_stmt = SSA_NAME_DEF_STMT (init);
  if (gimple_code (init_stmt) != GIMPLE_ASSIGN)
    return NULL;
  gcc_assert (gimple_assign_lhs (init_stmt) == init);

  init_ref = gimple_assign_rhs1 (init_stmt);
  if (!REFERENCE_CLASS_P (init_ref)
      && !DECL_P (init_ref))
    return NULL;

  /* Analyze the behavior of INIT_REF with respect to LOOP (innermost
     loop enclosing PHI).  */
  memset (&init_dr, 0, sizeof (struct data_reference));
  DR_REF (&init_dr) = init_ref;
  DR_STMT (&init_dr) = phi;
  if (!dr_analyze_innermost (&init_dr, loop))
    return NULL;

  if (!valid_initializer_p (&init_dr, ref->distance + 1, root->ref))
    return NULL;

  return phi;
}

/* Adds a reference for the looparound copy of REF in PHI to CHAIN.  */

static void
insert_looparound_copy (chain_p chain, dref ref, gimple phi)
{
  dref nw = XCNEW (struct dref_d), aref;
  unsigned i;

  nw->stmt = phi;
  nw->distance = ref->distance + 1;
  nw->always_accessed = 1;

  FOR_EACH_VEC_ELT (chain->refs, i, aref)
    if (aref->distance >= nw->distance)
      break;
  chain->refs.safe_insert (i, nw);

  if (nw->distance > chain->length)
    {
      chain->length = nw->distance;
      chain->has_max_use_after = false;
    }
}

/* For references in CHAIN that are copied around the LOOP (created previously
   by PRE, or by user), add the results of such copies to the chain.  This
   enables us to remove the copies by unrolling, and may need less registers
   (also, it may allow us to combine chains together).  */

static void
add_looparound_copies (struct loop *loop, chain_p chain)
{
  unsigned i;
  dref ref, root = get_chain_root (chain);
  gimple phi;

  FOR_EACH_VEC_ELT (chain->refs, i, ref)
    {
      phi = find_looparound_phi (loop, ref, root);
      if (!phi)
	continue;

      bitmap_set_bit (looparound_phis, SSA_NAME_VERSION (PHI_RESULT (phi)));
      insert_looparound_copy (chain, ref, phi);
    }
}

/* Find roots of the values and determine distances in the component COMP.
   The references are redistributed into CHAINS.  LOOP is the current
   loop.  */

static void
determine_roots_comp (struct loop *loop,
		      struct component *comp,
		      vec<chain_p> *chains)
{
  unsigned i;
  dref a;
  chain_p chain = NULL;
  double_int last_ofs = double_int_zero;

  /* Invariants are handled specially.  */
  if (comp->comp_step == RS_INVARIANT)
    {
      chain = make_invariant_chain (comp);
      chains->safe_push (chain);
      return;
    }

  comp->refs.qsort (order_drefs);

  FOR_EACH_VEC_ELT (comp->refs, i, a)
    {
      if (!chain || DR_IS_WRITE (a->ref)
	  || double_int::from_uhwi (MAX_DISTANCE).ule (a->offset - last_ofs))
	{
	  if (nontrivial_chain_p (chain))
	    {
	      add_looparound_copies (loop, chain);
	      chains->safe_push (chain);
	    }
	  else
	    release_chain (chain);
	  chain = make_rooted_chain (a);
	  last_ofs = a->offset;
	  continue;
	}

      add_ref_to_chain (chain, a);
    }

  if (nontrivial_chain_p (chain))
    {
      add_looparound_copies (loop, chain);
      chains->safe_push (chain);
    }
  else
    release_chain (chain);
}

/* Find roots of the values and determine distances in components COMPS, and
   separates the references to CHAINS.  LOOP is the current loop.  */

static void
determine_roots (struct loop *loop,
		 struct component *comps, vec<chain_p> *chains)
{
  struct component *comp;

  for (comp = comps; comp; comp = comp->next)
    determine_roots_comp (loop, comp, chains);
}

/* Replace the reference in statement STMT with temporary variable
   NEW_TREE.  If SET is true, NEW_TREE is instead initialized to the value of
   the reference in the statement.  IN_LHS is true if the reference
   is in the lhs of STMT, false if it is in rhs.  */

static void
replace_ref_with (gimple stmt, tree new_tree, bool set, bool in_lhs)
{
  tree val;
  gimple new_stmt;
  gimple_stmt_iterator bsi, psi;

  if (gimple_code (stmt) == GIMPLE_PHI)
    {
      gcc_assert (!in_lhs && !set);

      val = PHI_RESULT (stmt);
      bsi = gsi_after_labels (gimple_bb (stmt));
      psi = gsi_for_stmt (stmt);
      remove_phi_node (&psi, false);

      /* Turn the phi node into GIMPLE_ASSIGN.  */
      new_stmt = gimple_build_assign (val, new_tree);
      gsi_insert_before (&bsi, new_stmt, GSI_NEW_STMT);
      return;
    }

  /* Since the reference is of gimple_reg type, it should only
     appear as lhs or rhs of modify statement.  */
  gcc_assert (is_gimple_assign (stmt));

  bsi = gsi_for_stmt (stmt);

  /* If we do not need to initialize NEW_TREE, just replace the use of OLD.  */
  if (!set)
    {
      gcc_assert (!in_lhs);
      gimple_assign_set_rhs_from_tree (&bsi, new_tree);
      stmt = gsi_stmt (bsi);
      update_stmt (stmt);
      return;
    }

  if (in_lhs)
    {
      /* We have statement

	 OLD = VAL

	 If OLD is a memory reference, then VAL is gimple_val, and we transform
	 this to

	 OLD = VAL
	 NEW = VAL

	 Otherwise, we are replacing a combination chain,
	 VAL is the expression that performs the combination, and OLD is an
	 SSA name.  In this case, we transform the assignment to

	 OLD = VAL
	 NEW = OLD

	 */

      val = gimple_assign_lhs (stmt);
      if (TREE_CODE (val) != SSA_NAME)
	{
	  val = gimple_assign_rhs1 (stmt);
	  gcc_assert (gimple_assign_single_p (stmt));
	  if (TREE_CLOBBER_P (val))
	    val = get_or_create_ssa_default_def (cfun, SSA_NAME_VAR (new_tree));
	  else
	    gcc_assert (gimple_assign_copy_p (stmt));
	}
    }
  else
    {
      /* VAL = OLD

	 is transformed to

	 VAL = OLD
	 NEW = VAL  */

      val = gimple_assign_lhs (stmt);
    }

  new_stmt = gimple_build_assign (new_tree, unshare_expr (val));
  gsi_insert_after (&bsi, new_stmt, GSI_NEW_STMT);
}

/* Returns a memory reference to DR in the ITER-th iteration of
   the loop it was analyzed in.  Append init stmts to STMTS.  */

static tree 
ref_at_iteration (data_reference_p dr, int iter, gimple_seq *stmts)
{
  tree off = DR_OFFSET (dr);
  tree coff = DR_INIT (dr);
  if (iter == 0)
    ;
  else if (TREE_CODE (DR_STEP (dr)) == INTEGER_CST)
    coff = size_binop (PLUS_EXPR, coff,
		       size_binop (MULT_EXPR, DR_STEP (dr), ssize_int (iter)));
  else
    off = size_binop (PLUS_EXPR, off,
		      size_binop (MULT_EXPR, DR_STEP (dr), ssize_int (iter)));
  tree addr = fold_build_pointer_plus (DR_BASE_ADDRESS (dr), off);
  addr = force_gimple_operand_1 (unshare_expr (addr), stmts,
				 is_gimple_mem_ref_addr, NULL_TREE);
  tree alias_ptr = fold_convert (reference_alias_ptr_type (DR_REF (dr)), coff);
  /* While data-ref analysis punts on bit offsets it still handles
     bitfield accesses at byte boundaries.  Cope with that.  Note that
     we cannot simply re-apply the outer COMPONENT_REF because the
     byte-granular portion of it is already applied via DR_INIT and
     DR_OFFSET, so simply build a BIT_FIELD_REF knowing that the bits
     start at offset zero.  */
  if (TREE_CODE (DR_REF (dr)) == COMPONENT_REF
      && DECL_BIT_FIELD (TREE_OPERAND (DR_REF (dr), 1)))
    {
      tree field = TREE_OPERAND (DR_REF (dr), 1);
      return build3 (BIT_FIELD_REF, TREE_TYPE (DR_REF (dr)),
		     build2 (MEM_REF, DECL_BIT_FIELD_TYPE (field),
			     addr, alias_ptr),
		     DECL_SIZE (field), bitsize_zero_node);
    }
  else
    return fold_build2 (MEM_REF, TREE_TYPE (DR_REF (dr)), addr, alias_ptr);
}

/* Get the initialization expression for the INDEX-th temporary variable
   of CHAIN.  */

static tree
get_init_expr (chain_p chain, unsigned index)
{
  if (chain->type == CT_COMBINATION)
    {
      tree e1 = get_init_expr (chain->ch1, index);
      tree e2 = get_init_expr (chain->ch2, index);

      return fold_build2 (chain->op, chain->rslt_type, e1, e2);
    }
  else
    return chain->inits[index];
}

/* Returns a new temporary variable used for the I-th variable carrying
   value of REF.  The variable's uid is marked in TMP_VARS.  */

static tree
predcom_tmp_var (tree ref, unsigned i, bitmap tmp_vars)
{
  tree type = TREE_TYPE (ref);
  /* We never access the components of the temporary variable in predictive
     commoning.  */
  tree var = create_tmp_reg (type, get_lsm_tmp_name (ref, i));
  bitmap_set_bit (tmp_vars, DECL_UID (var));
  return var;
}

/* Creates the variables for CHAIN, as well as phi nodes for them and
   initialization on entry to LOOP.  Uids of the newly created
   temporary variables are marked in TMP_VARS.  */

static void
initialize_root_vars (struct loop *loop, chain_p chain, bitmap tmp_vars)
{
  unsigned i;
  unsigned n = chain->length;
  dref root = get_chain_root (chain);
  bool reuse_first = !chain->has_max_use_after;
  tree ref, init, var, next;
  gimple phi;
  gimple_seq stmts;
  edge entry = loop_preheader_edge (loop), latch = loop_latch_edge (loop);

  /* If N == 0, then all the references are within the single iteration.  And
     since this is an nonempty chain, reuse_first cannot be true.  */
  gcc_assert (n > 0 || !reuse_first);

  chain->vars.create (n + 1);

  if (chain->type == CT_COMBINATION)
    ref = gimple_assign_lhs (root->stmt);
  else
    ref = DR_REF (root->ref);

  for (i = 0; i < n + (reuse_first ? 0 : 1); i++)
    {
      var = predcom_tmp_var (ref, i, tmp_vars);
      chain->vars.quick_push (var);
    }
  if (reuse_first)
    chain->vars.quick_push (chain->vars[0]);

  FOR_EACH_VEC_ELT (chain->vars, i, var)
    chain->vars[i] = make_ssa_name (var, NULL);

  for (i = 0; i < n; i++)
    {
      var = chain->vars[i];
      next = chain->vars[i + 1];
      init = get_init_expr (chain, i);

      init = force_gimple_operand (init, &stmts, true, NULL_TREE);
      if (stmts)
	gsi_insert_seq_on_edge_immediate (entry, stmts);

      phi = create_phi_node (var, loop->header);
      add_phi_arg (phi, init, entry, UNKNOWN_LOCATION);
      add_phi_arg (phi, next, latch, UNKNOWN_LOCATION);
    }
}

/* Create the variables and initialization statement for root of chain
   CHAIN.  Uids of the newly created temporary variables are marked
   in TMP_VARS.  */

static void
initialize_root (struct loop *loop, chain_p chain, bitmap tmp_vars)
{
  dref root = get_chain_root (chain);
  bool in_lhs = (chain->type == CT_STORE_LOAD
		 || chain->type == CT_COMBINATION);

  initialize_root_vars (loop, chain, tmp_vars);
  replace_ref_with (root->stmt,
		    chain->vars[chain->length],
		    true, in_lhs);
}

/* Initializes a variable for load motion for ROOT and prepares phi nodes and
   initialization on entry to LOOP if necessary.  The ssa name for the variable
   is stored in VARS.  If WRITTEN is true, also a phi node to copy its value
   around the loop is created.  Uid of the newly created temporary variable
   is marked in TMP_VARS.  INITS is the list containing the (single)
   initializer.  */

static void
initialize_root_vars_lm (struct loop *loop, dref root, bool written,
			 vec<tree> *vars, vec<tree> inits,
			 bitmap tmp_vars)
{
  unsigned i;
  tree ref = DR_REF (root->ref), init, var, next;
  gimple_seq stmts;
  gimple phi;
  edge entry = loop_preheader_edge (loop), latch = loop_latch_edge (loop);

  /* Find the initializer for the variable, and check that it cannot
     trap.  */
  init = inits[0];

  vars->create (written ? 2 : 1);
  var = predcom_tmp_var (ref, 0, tmp_vars);
  vars->quick_push (var);
  if (written)
    vars->quick_push ((*vars)[0]);

  FOR_EACH_VEC_ELT (*vars, i, var)
    (*vars)[i] = make_ssa_name (var, NULL);

  var = (*vars)[0];

  init = force_gimple_operand (init, &stmts, written, NULL_TREE);
  if (stmts)
    gsi_insert_seq_on_edge_immediate (entry, stmts);

  if (written)
    {
      next = (*vars)[1];
      phi = create_phi_node (var, loop->header);
      add_phi_arg (phi, init, entry, UNKNOWN_LOCATION);
      add_phi_arg (phi, next, latch, UNKNOWN_LOCATION);
    }
  else
    {
      gimple init_stmt = gimple_build_assign (var, init);
      gsi_insert_on_edge_immediate (entry, init_stmt);
    }
}


/* Execute load motion for references in chain CHAIN.  Uids of the newly
   created temporary variables are marked in TMP_VARS.  */

static void
execute_load_motion (struct loop *loop, chain_p chain, bitmap tmp_vars)
{
  auto_vec<tree> vars;
  dref a;
  unsigned n_writes = 0, ridx, i;
  tree var;

  gcc_assert (chain->type == CT_INVARIANT);
  gcc_assert (!chain->combined);
  FOR_EACH_VEC_ELT (chain->refs, i, a)
    if (DR_IS_WRITE (a->ref))
      n_writes++;

  /* If there are no reads in the loop, there is nothing to do.  */
  if (n_writes == chain->refs.length ())
    return;

  initialize_root_vars_lm (loop, get_chain_root (chain), n_writes > 0,
			   &vars, chain->inits, tmp_vars);

  ridx = 0;
  FOR_EACH_VEC_ELT (chain->refs, i, a)
    {
      bool is_read = DR_IS_READ (a->ref);

      if (DR_IS_WRITE (a->ref))
	{
	  n_writes--;
	  if (n_writes)
	    {
	      var = vars[0];
	      var = make_ssa_name (SSA_NAME_VAR (var), NULL);
	      vars[0] = var;
	    }
	  else
	    ridx = 1;
	}

      replace_ref_with (a->stmt, vars[ridx],
			!is_read, !is_read);
    }
}

/* Returns the single statement in that NAME is used, excepting
   the looparound phi nodes contained in one of the chains.  If there is no
   such statement, or more statements, NULL is returned.  */

static gimple
single_nonlooparound_use (tree name)
{
  use_operand_p use;
  imm_use_iterator it;
  gimple stmt, ret = NULL;

  FOR_EACH_IMM_USE_FAST (use, it, name)
    {
      stmt = USE_STMT (use);

      if (gimple_code (stmt) == GIMPLE_PHI)
	{
	  /* Ignore uses in looparound phi nodes.  Uses in other phi nodes
	     could not be processed anyway, so just fail for them.  */
	  if (bitmap_bit_p (looparound_phis,
			    SSA_NAME_VERSION (PHI_RESULT (stmt))))
	    continue;

	  return NULL;
	}
      else if (is_gimple_debug (stmt))
	continue;
      else if (ret != NULL)
	return NULL;
      else
	ret = stmt;
    }

  return ret;
}

/* Remove statement STMT, as well as the chain of assignments in that it is
   used.  */

static void
remove_stmt (gimple stmt)
{
  tree name;
  gimple next;
  gimple_stmt_iterator psi;

  if (gimple_code (stmt) == GIMPLE_PHI)
    {
      name = PHI_RESULT (stmt);
      next = single_nonlooparound_use (name);
      reset_debug_uses (stmt);
      psi = gsi_for_stmt (stmt);
      remove_phi_node (&psi, true);

      if (!next
	  || !gimple_assign_ssa_name_copy_p (next)
	  || gimple_assign_rhs1 (next) != name)
	return;

      stmt = next;
    }

  while (1)
    {
      gimple_stmt_iterator bsi;

      bsi = gsi_for_stmt (stmt);

      name = gimple_assign_lhs (stmt);
      gcc_assert (TREE_CODE (name) == SSA_NAME);

      next = single_nonlooparound_use (name);
      reset_debug_uses (stmt);

      unlink_stmt_vdef (stmt);
      gsi_remove (&bsi, true);
      release_defs (stmt);

      if (!next
	  || !gimple_assign_ssa_name_copy_p (next)
	  || gimple_assign_rhs1 (next) != name)
	return;

      stmt = next;
    }
}

/* Perform the predictive commoning optimization for a chain CHAIN.
   Uids of the newly created temporary variables are marked in TMP_VARS.*/

static void
execute_pred_commoning_chain (struct loop *loop, chain_p chain,
			     bitmap tmp_vars)
{
  unsigned i;
  dref a;
  tree var;

  if (chain->combined)
    {
      /* For combined chains, just remove the statements that are used to
	 compute the values of the expression (except for the root one).  */
      for (i = 1; chain->refs.iterate (i, &a); i++)
	remove_stmt (a->stmt);
    }
  else
    {
      /* For non-combined chains, set up the variables that hold its value,
	 and replace the uses of the original references by these
	 variables.  */
      initialize_root (loop, chain, tmp_vars);
      for (i = 1; chain->refs.iterate (i, &a); i++)
	{
	  var = chain->vars[chain->length - a->distance];
	  replace_ref_with (a->stmt, var, false, false);
	}
    }
}

/* Determines the unroll factor necessary to remove as many temporary variable
   copies as possible.  CHAINS is the list of chains that will be
   optimized.  */

static unsigned
determine_unroll_factor (vec<chain_p> chains)
{
  chain_p chain;
  unsigned factor = 1, af, nfactor, i;
  unsigned max = PARAM_VALUE (PARAM_MAX_UNROLL_TIMES);

  FOR_EACH_VEC_ELT (chains, i, chain)
    {
      if (chain->type == CT_INVARIANT || chain->combined)
	continue;

      /* The best unroll factor for this chain is equal to the number of
	 temporary variables that we create for it.  */
      af = chain->length;
      if (chain->has_max_use_after)
	af++;

      nfactor = factor * af / gcd (factor, af);
      if (nfactor <= max)
	factor = nfactor;
    }

  return factor;
}

/* Perform the predictive commoning optimization for CHAINS.
   Uids of the newly created temporary variables are marked in TMP_VARS.  */

static void
execute_pred_commoning (struct loop *loop, vec<chain_p> chains,
			bitmap tmp_vars)
{
  chain_p chain;
  unsigned i;

  FOR_EACH_VEC_ELT (chains, i, chain)
    {
      if (chain->type == CT_INVARIANT)
	execute_load_motion (loop, chain, tmp_vars);
      else
	execute_pred_commoning_chain (loop, chain, tmp_vars);
    }

  update_ssa (TODO_update_ssa_only_virtuals);
}

/* For each reference in CHAINS, if its defining statement is
   phi node, record the ssa name that is defined by it.  */

static void
replace_phis_by_defined_names (vec<chain_p> chains)
{
  chain_p chain;
  dref a;
  unsigned i, j;

  FOR_EACH_VEC_ELT (chains, i, chain)
    FOR_EACH_VEC_ELT (chain->refs, j, a)
      {
	if (gimple_code (a->stmt) == GIMPLE_PHI)
	  {
	    a->name_defined_by_phi = PHI_RESULT (a->stmt);
	    a->stmt = NULL;
	  }
      }
}

/* For each reference in CHAINS, if name_defined_by_phi is not
   NULL, use it to set the stmt field.  */

static void
replace_names_by_phis (vec<chain_p> chains)
{
  chain_p chain;
  dref a;
  unsigned i, j;

  FOR_EACH_VEC_ELT (chains, i, chain)
    FOR_EACH_VEC_ELT (chain->refs, j, a)
      if (a->stmt == NULL)
	{
	  a->stmt = SSA_NAME_DEF_STMT (a->name_defined_by_phi);
	  gcc_assert (gimple_code (a->stmt) == GIMPLE_PHI);
	  a->name_defined_by_phi = NULL_TREE;
	}
}

/* Wrapper over execute_pred_commoning, to pass it as a callback
   to tree_transform_and_unroll_loop.  */

struct epcc_data
{
  vec<chain_p> chains;
  bitmap tmp_vars;
};

static void
execute_pred_commoning_cbck (struct loop *loop, void *data)
{
  struct epcc_data *const dta = (struct epcc_data *) data;

  /* Restore phi nodes that were replaced by ssa names before
     tree_transform_and_unroll_loop (see detailed description in
     tree_predictive_commoning_loop).  */
  replace_names_by_phis (dta->chains);
  execute_pred_commoning (loop, dta->chains, dta->tmp_vars);
}

/* Base NAME and all the names in the chain of phi nodes that use it
   on variable VAR.  The phi nodes are recognized by being in the copies of
   the header of the LOOP.  */

static void
base_names_in_chain_on (struct loop *loop, tree name, tree var)
{
  gimple stmt, phi;
  imm_use_iterator iter;

  replace_ssa_name_symbol (name, var);

  while (1)
    {
      phi = NULL;
      FOR_EACH_IMM_USE_STMT (stmt, iter, name)
	{
	  if (gimple_code (stmt) == GIMPLE_PHI
	      && flow_bb_inside_loop_p (loop, gimple_bb (stmt)))
	    {
	      phi = stmt;
	      BREAK_FROM_IMM_USE_STMT (iter);
	    }
	}
      if (!phi)
	return;

      name = PHI_RESULT (phi);
      replace_ssa_name_symbol (name, var);
    }
}

/* Given an unrolled LOOP after predictive commoning, remove the
   register copies arising from phi nodes by changing the base
   variables of SSA names.  TMP_VARS is the set of the temporary variables
   for those we want to perform this.  */

static void
eliminate_temp_copies (struct loop *loop, bitmap tmp_vars)
{
  edge e;
  gimple phi, stmt;
  tree name, use, var;
  gimple_stmt_iterator psi;

  e = loop_latch_edge (loop);
  for (psi = gsi_start_phis (loop->header); !gsi_end_p (psi); gsi_next (&psi))
    {
      phi = gsi_stmt (psi);
      name = PHI_RESULT (phi);
      var = SSA_NAME_VAR (name);
      if (!var || !bitmap_bit_p (tmp_vars, DECL_UID (var)))
	continue;
      use = PHI_ARG_DEF_FROM_EDGE (phi, e);
      gcc_assert (TREE_CODE (use) == SSA_NAME);

      /* Base all the ssa names in the ud and du chain of NAME on VAR.  */
      stmt = SSA_NAME_DEF_STMT (use);
      while (gimple_code (stmt) == GIMPLE_PHI
	     /* In case we could not unroll the loop enough to eliminate
		all copies, we may reach the loop header before the defining
		statement (in that case, some register copies will be present
		in loop latch in the final code, corresponding to the newly
		created looparound phi nodes).  */
	     && gimple_bb (stmt) != loop->header)
	{
	  gcc_assert (single_pred_p (gimple_bb (stmt)));
	  use = PHI_ARG_DEF (stmt, 0);
	  stmt = SSA_NAME_DEF_STMT (use);
	}

      base_names_in_chain_on (loop, use, var);
    }
}

/* Returns true if CHAIN is suitable to be combined.  */

static bool
chain_can_be_combined_p (chain_p chain)
{
  return (!chain->combined
	  && (chain->type == CT_LOAD || chain->type == CT_COMBINATION));
}

/* Returns the modify statement that uses NAME.  Skips over assignment
   statements, NAME is replaced with the actual name used in the returned
   statement.  */

static gimple
find_use_stmt (tree *name)
{
  gimple stmt;
  tree rhs, lhs;

  /* Skip over assignments.  */
  while (1)
    {
      stmt = single_nonlooparound_use (*name);
      if (!stmt)
	return NULL;

      if (gimple_code (stmt) != GIMPLE_ASSIGN)
	return NULL;

      lhs = gimple_assign_lhs (stmt);
      if (TREE_CODE (lhs) != SSA_NAME)
	return NULL;

      if (gimple_assign_copy_p (stmt))
	{
	  rhs = gimple_assign_rhs1 (stmt);
	  if (rhs != *name)
	    return NULL;

	  *name = lhs;
	}
      else if (get_gimple_rhs_class (gimple_assign_rhs_code (stmt))
	       == GIMPLE_BINARY_RHS)
	return stmt;
      else
	return NULL;
    }
}

/* Returns true if we may perform reassociation for operation CODE in TYPE.  */

static bool
may_reassociate_p (tree type, enum tree_code code)
{
  if (FLOAT_TYPE_P (type)
      && !flag_unsafe_math_optimizations)
    return false;

  return (commutative_tree_code (code)
	  && associative_tree_code (code));
}

/* If the operation used in STMT is associative and commutative, go through the
   tree of the same operations and returns its root.  Distance to the root
   is stored in DISTANCE.  */

static gimple
find_associative_operation_root (gimple stmt, unsigned *distance)
{
  tree lhs;
  gimple next;
  enum tree_code code = gimple_assign_rhs_code (stmt);
  tree type = TREE_TYPE (gimple_assign_lhs (stmt));
  unsigned dist = 0;

  if (!may_reassociate_p (type, code))
    return NULL;

  while (1)
    {
      lhs = gimple_assign_lhs (stmt);
      gcc_assert (TREE_CODE (lhs) == SSA_NAME);

      next = find_use_stmt (&lhs);
      if (!next
	  || gimple_assign_rhs_code (next) != code)
	break;

      stmt = next;
      dist++;
    }

  if (distance)
    *distance = dist;
  return stmt;
}

/* Returns the common statement in that NAME1 and NAME2 have a use.  If there
   is no such statement, returns NULL_TREE.  In case the operation used on
   NAME1 and NAME2 is associative and commutative, returns the root of the
   tree formed by this operation instead of the statement that uses NAME1 or
   NAME2.  */

static gimple
find_common_use_stmt (tree *name1, tree *name2)
{
  gimple stmt1, stmt2;

  stmt1 = find_use_stmt (name1);
  if (!stmt1)
    return NULL;

  stmt2 = find_use_stmt (name2);
  if (!stmt2)
    return NULL;

  if (stmt1 == stmt2)
    return stmt1;

  stmt1 = find_associative_operation_root (stmt1, NULL);
  if (!stmt1)
    return NULL;
  stmt2 = find_associative_operation_root (stmt2, NULL);
  if (!stmt2)
    return NULL;

  return (stmt1 == stmt2 ? stmt1 : NULL);
}

/* Checks whether R1 and R2 are combined together using CODE, with the result
   in RSLT_TYPE, in order R1 CODE R2 if SWAP is false and in order R2 CODE R1
   if it is true.  If CODE is ERROR_MARK, set these values instead.  */

static bool
combinable_refs_p (dref r1, dref r2,
		   enum tree_code *code, bool *swap, tree *rslt_type)
{
  enum tree_code acode;
  bool aswap;
  tree atype;
  tree name1, name2;
  gimple stmt;

  name1 = name_for_ref (r1);
  name2 = name_for_ref (r2);
  gcc_assert (name1 != NULL_TREE && name2 != NULL_TREE);

  stmt = find_common_use_stmt (&name1, &name2);

  if (!stmt
      /* A simple post-dominance check - make sure the combination
         is executed under the same condition as the references.  */
      || (gimple_bb (stmt) != gimple_bb (r1->stmt)
	  && gimple_bb (stmt) != gimple_bb (r2->stmt)))
    return false;

  acode = gimple_assign_rhs_code (stmt);
  aswap = (!commutative_tree_code (acode)
	   && gimple_assign_rhs1 (stmt) != name1);
  atype = TREE_TYPE (gimple_assign_lhs (stmt));

  if (*code == ERROR_MARK)
    {
      *code = acode;
      *swap = aswap;
      *rslt_type = atype;
      return true;
    }

  return (*code == acode
	  && *swap == aswap
	  && *rslt_type == atype);
}

/* Remove OP from the operation on rhs of STMT, and replace STMT with
   an assignment of the remaining operand.  */

static void
remove_name_from_operation (gimple stmt, tree op)
{
  tree other_op;
  gimple_stmt_iterator si;

  gcc_assert (is_gimple_assign (stmt));

  if (gimple_assign_rhs1 (stmt) == op)
    other_op = gimple_assign_rhs2 (stmt);
  else
    other_op = gimple_assign_rhs1 (stmt);

  si = gsi_for_stmt (stmt);
  gimple_assign_set_rhs_from_tree (&si, other_op);

  /* We should not have reallocated STMT.  */
  gcc_assert (gsi_stmt (si) == stmt);

  update_stmt (stmt);
}

/* Reassociates the expression in that NAME1 and NAME2 are used so that they
   are combined in a single statement, and returns this statement.  */

static gimple
reassociate_to_the_same_stmt (tree name1, tree name2)
{
  gimple stmt1, stmt2, root1, root2, s1, s2;
  gimple new_stmt, tmp_stmt;
  tree new_name, tmp_name, var, r1, r2;
  unsigned dist1, dist2;
  enum tree_code code;
  tree type = TREE_TYPE (name1);
  gimple_stmt_iterator bsi;

  stmt1 = find_use_stmt (&name1);
  stmt2 = find_use_stmt (&name2);
  root1 = find_associative_operation_root (stmt1, &dist1);
  root2 = find_associative_operation_root (stmt2, &dist2);
  code = gimple_assign_rhs_code (stmt1);

  gcc_assert (root1 && root2 && root1 == root2
	      && code == gimple_assign_rhs_code (stmt2));

  /* Find the root of the nearest expression in that both NAME1 and NAME2
     are used.  */
  r1 = name1;
  s1 = stmt1;
  r2 = name2;
  s2 = stmt2;

  while (dist1 > dist2)
    {
      s1 = find_use_stmt (&r1);
      r1 = gimple_assign_lhs (s1);
      dist1--;
    }
  while (dist2 > dist1)
    {
      s2 = find_use_stmt (&r2);
      r2 = gimple_assign_lhs (s2);
      dist2--;
    }

  while (s1 != s2)
    {
      s1 = find_use_stmt (&r1);
      r1 = gimple_assign_lhs (s1);
      s2 = find_use_stmt (&r2);
      r2 = gimple_assign_lhs (s2);
    }

  /* Remove NAME1 and NAME2 from the statements in that they are used
     currently.  */
  remove_name_from_operation (stmt1, name1);
  remove_name_from_operation (stmt2, name2);

  /* Insert the new statement combining NAME1 and NAME2 before S1, and
     combine it with the rhs of S1.  */
  var = create_tmp_reg (type, "predreastmp");
  new_name = make_ssa_name (var, NULL);
  new_stmt = gimple_build_assign_with_ops (code, new_name, name1, name2);

  var = create_tmp_reg (type, "predreastmp");
  tmp_name = make_ssa_name (var, NULL);

  /* Rhs of S1 may now be either a binary expression with operation
     CODE, or gimple_val (in case that stmt1 == s1 or stmt2 == s1,
     so that name1 or name2 was removed from it).  */
  tmp_stmt = gimple_build_assign_with_ops (gimple_assign_rhs_code (s1),
					   tmp_name,
					   gimple_assign_rhs1 (s1),
					   gimple_assign_rhs2 (s1));

  bsi = gsi_for_stmt (s1);
  gimple_assign_set_rhs_with_ops (&bsi, code, new_name, tmp_name);
  s1 = gsi_stmt (bsi);
  update_stmt (s1);

  gsi_insert_before (&bsi, new_stmt, GSI_SAME_STMT);
  gsi_insert_before (&bsi, tmp_stmt, GSI_SAME_STMT);

  return new_stmt;
}

/* Returns the statement that combines references R1 and R2.  In case R1
   and R2 are not used in the same statement, but they are used with an
   associative and commutative operation in the same expression, reassociate
   the expression so that they are used in the same statement.  */

static gimple
stmt_combining_refs (dref r1, dref r2)
{
  gimple stmt1, stmt2;
  tree name1 = name_for_ref (r1);
  tree name2 = name_for_ref (r2);

  stmt1 = find_use_stmt (&name1);
  stmt2 = find_use_stmt (&name2);
  if (stmt1 == stmt2)
    return stmt1;

  return reassociate_to_the_same_stmt (name1, name2);
}

/* Tries to combine chains CH1 and CH2 together.  If this succeeds, the
   description of the new chain is returned, otherwise we return NULL.  */

static chain_p
combine_chains (chain_p ch1, chain_p ch2)
{
  dref r1, r2, nw;
  enum tree_code op = ERROR_MARK;
  bool swap = false;
  chain_p new_chain;
  unsigned i;
  gimple root_stmt;
  tree rslt_type = NULL_TREE;

  if (ch1 == ch2)
    return NULL;
  if (ch1->length != ch2->length)
    return NULL;

  if (ch1->refs.length () != ch2->refs.length ())
    return NULL;

  for (i = 0; (ch1->refs.iterate (i, &r1)
	       && ch2->refs.iterate (i, &r2)); i++)
    {
      if (r1->distance != r2->distance)
	return NULL;

      if (!combinable_refs_p (r1, r2, &op, &swap, &rslt_type))
	return NULL;
    }

  if (swap)
    {
      chain_p tmp = ch1;
      ch1 = ch2;
      ch2 = tmp;
    }

  new_chain = XCNEW (struct chain);
  new_chain->type = CT_COMBINATION;
  new_chain->op = op;
  new_chain->ch1 = ch1;
  new_chain->ch2 = ch2;
  new_chain->rslt_type = rslt_type;
  new_chain->length = ch1->length;

  for (i = 0; (ch1->refs.iterate (i, &r1)
	       && ch2->refs.iterate (i, &r2)); i++)
    {
      nw = XCNEW (struct dref_d);
      nw->stmt = stmt_combining_refs (r1, r2);
      nw->distance = r1->distance;

      new_chain->refs.safe_push (nw);
    }

  new_chain->has_max_use_after = false;
  root_stmt = get_chain_root (new_chain)->stmt;
  for (i = 1; new_chain->refs.iterate (i, &nw); i++)
    {
      if (nw->distance == new_chain->length
	  && !stmt_dominates_stmt_p (nw->stmt, root_stmt))
	{
	  new_chain->has_max_use_after = true;
	  break;
	}
    }

  ch1->combined = true;
  ch2->combined = true;
  return new_chain;
}

/* Try to combine the CHAINS.  */

static void
try_combine_chains (vec<chain_p> *chains)
{
  unsigned i, j;
  chain_p ch1, ch2, cch;
  auto_vec<chain_p> worklist;

  FOR_EACH_VEC_ELT (*chains, i, ch1)
    if (chain_can_be_combined_p (ch1))
      worklist.safe_push (ch1);

  while (!worklist.is_empty ())
    {
      ch1 = worklist.pop ();
      if (!chain_can_be_combined_p (ch1))
	continue;

      FOR_EACH_VEC_ELT (*chains, j, ch2)
	{
	  if (!chain_can_be_combined_p (ch2))
	    continue;

	  cch = combine_chains (ch1, ch2);
	  if (cch)
	    {
	      worklist.safe_push (cch);
	      chains->safe_push (cch);
	      break;
	    }
	}
    }
}

/* Prepare initializers for CHAIN in LOOP.  Returns false if this is
   impossible because one of these initializers may trap, true otherwise.  */

static bool
prepare_initializers_chain (struct loop *loop, chain_p chain)
{
  unsigned i, n = (chain->type == CT_INVARIANT) ? 1 : chain->length;
  struct data_reference *dr = get_chain_root (chain)->ref;
  tree init;
  gimple_seq stmts;
  dref laref;
  edge entry = loop_preheader_edge (loop);

  /* Find the initializers for the variables, and check that they cannot
     trap.  */
  chain->inits.create (n);
  for (i = 0; i < n; i++)
    chain->inits.quick_push (NULL_TREE);

  /* If we have replaced some looparound phi nodes, use their initializers
     instead of creating our own.  */
  FOR_EACH_VEC_ELT (chain->refs, i, laref)
    {
      if (gimple_code (laref->stmt) != GIMPLE_PHI)
	continue;

      gcc_assert (laref->distance > 0);
      chain->inits[n - laref->distance] 
	= PHI_ARG_DEF_FROM_EDGE (laref->stmt, entry);
    }

  for (i = 0; i < n; i++)
    {
      if (chain->inits[i] != NULL_TREE)
	continue;

      init = ref_at_iteration (dr, (int) i - n, &stmts);
      if (!chain->all_always_accessed && tree_could_trap_p (init))
	return false;

      if (stmts)
	gsi_insert_seq_on_edge_immediate (entry, stmts);

      chain->inits[i] = init;
    }

  return true;
}

/* Prepare initializers for CHAINS in LOOP, and free chains that cannot
   be used because the initializers might trap.  */

static void
prepare_initializers (struct loop *loop, vec<chain_p> chains)
{
  chain_p chain;
  unsigned i;

  for (i = 0; i < chains.length (); )
    {
      chain = chains[i];
      if (prepare_initializers_chain (loop, chain))
	i++;
      else
	{
	  release_chain (chain);
	  chains.unordered_remove (i);
	}
    }
}

/* Performs predictive commoning for LOOP.  Returns true if LOOP was
   unrolled.  */

static bool
tree_predictive_commoning_loop (struct loop *loop)
{
  vec<data_reference_p> datarefs;
  vec<ddr_p> dependences;
  struct component *components;
  vec<chain_p> chains = vNULL;
  unsigned unroll_factor;
  struct tree_niter_desc desc;
  bool unroll = false;
  edge exit;
  bitmap tmp_vars;

  if (dump_file && (dump_flags & TDF_DETAILS))
    fprintf (dump_file, "Processing loop %d\n",  loop->num);

  /* Find the data references and split them into components according to their
     dependence relations.  */
  auto_vec<loop_p, 3> loop_nest;
  dependences.create (10);
  datarefs.create (10);
  if (! compute_data_dependences_for_loop (loop, true, &loop_nest, &datarefs,
					   &dependences))
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
	fprintf (dump_file, "Cannot analyze data dependencies\n");
      free_data_refs (datarefs);
      free_dependence_relations (dependences);
      return false;
    }

  if (dump_file && (dump_flags & TDF_DETAILS))
    dump_data_dependence_relations (dump_file, dependences);

  components = split_data_refs_to_components (loop, datarefs, dependences);
  loop_nest.release ();
  free_dependence_relations (dependences);
  if (!components)
    {
      free_data_refs (datarefs);
      free_affine_expand_cache (&name_expansions);
      return false;
    }

  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file, "Initial state:\n\n");
      dump_components (dump_file, components);
    }

  /* Find the suitable components and split them into chains.  */
  components = filter_suitable_components (loop, components);

  tmp_vars = BITMAP_ALLOC (NULL);
  looparound_phis = BITMAP_ALLOC (NULL);
  determine_roots (loop, components, &chains);
  release_components (components);

  if (!chains.exists ())
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
	fprintf (dump_file,
		 "Predictive commoning failed: no suitable chains\n");
      goto end;
    }
  prepare_initializers (loop, chains);

  /* Try to combine the chains that are always worked with together.  */
  try_combine_chains (&chains);

  if (dump_file && (dump_flags & TDF_DETAILS))
    {
      fprintf (dump_file, "Before commoning:\n\n");
      dump_chains (dump_file, chains);
    }

  /* Determine the unroll factor, and if the loop should be unrolled, ensure
     that its number of iterations is divisible by the factor.  */
  unroll_factor = determine_unroll_factor (chains);
  scev_reset ();
  unroll = (unroll_factor > 1
	    && can_unroll_loop_p (loop, unroll_factor, &desc));
  exit = single_dom_exit (loop);

  /* Execute the predictive commoning transformations, and possibly unroll the
     loop.  */
  if (unroll)
    {
      struct epcc_data dta;

      if (dump_file && (dump_flags & TDF_DETAILS))
	fprintf (dump_file, "Unrolling %u times.\n", unroll_factor);

      dta.chains = chains;
      dta.tmp_vars = tmp_vars;

      update_ssa (TODO_update_ssa_only_virtuals);

      /* Cfg manipulations performed in tree_transform_and_unroll_loop before
	 execute_pred_commoning_cbck is called may cause phi nodes to be
	 reallocated, which is a problem since CHAINS may point to these
	 statements.  To fix this, we store the ssa names defined by the
	 phi nodes here instead of the phi nodes themselves, and restore
	 the phi nodes in execute_pred_commoning_cbck.  A bit hacky.  */
      replace_phis_by_defined_names (chains);

      tree_transform_and_unroll_loop (loop, unroll_factor, exit, &desc,
				      execute_pred_commoning_cbck, &dta);
      eliminate_temp_copies (loop, tmp_vars);
    }
  else
    {
      if (dump_file && (dump_flags & TDF_DETAILS))
	fprintf (dump_file,
		 "Executing predictive commoning without unrolling.\n");
      execute_pred_commoning (loop, chains, tmp_vars);
    }

end: ;
  release_chains (chains);
  free_data_refs (datarefs);
  BITMAP_FREE (tmp_vars);
  BITMAP_FREE (looparound_phis);

  free_affine_expand_cache (&name_expansions);

  return unroll;
}

/* Runs predictive commoning.  */

unsigned
tree_predictive_commoning (void)
{
  bool unrolled = false;
  struct loop *loop;
  unsigned ret = 0;

  initialize_original_copy_tables ();
  FOR_EACH_LOOP (loop, LI_ONLY_INNERMOST)
    if (optimize_loop_for_speed_p (loop))
      {
	unrolled |= tree_predictive_commoning_loop (loop);
      }

  if (unrolled)
    {
      scev_reset ();
      ret = TODO_cleanup_cfg;
    }
  free_original_copy_tables ();

  return ret;
}

/* Predictive commoning Pass.  */

static unsigned
run_tree_predictive_commoning (void)
{
  if (!current_loops)
    return 0;

  return tree_predictive_commoning ();
}

static bool
gate_tree_predictive_commoning (void)
{
  return flag_predictive_commoning != 0;
}

namespace {

const pass_data pass_data_predcom =
{
  GIMPLE_PASS, /* type */
  "pcom", /* name */
  OPTGROUP_LOOP, /* optinfo_flags */
  true, /* has_gate */
  true, /* has_execute */
  TV_PREDCOM, /* tv_id */
  PROP_cfg, /* properties_required */
  0, /* properties_provided */
  0, /* properties_destroyed */
  0, /* todo_flags_start */
  TODO_update_ssa_only_virtuals, /* todo_flags_finish */
};

class pass_predcom : public gimple_opt_pass
{
public:
  pass_predcom (gcc::context *ctxt)
    : gimple_opt_pass (pass_data_predcom, ctxt)
  {}

  /* opt_pass methods: */
  bool gate () { return gate_tree_predictive_commoning (); }
  unsigned int execute () { return run_tree_predictive_commoning (); }

}; // class pass_predcom

} // anon namespace

gimple_opt_pass *
make_pass_predcom (gcc::context *ctxt)
{
  return new pass_predcom (ctxt);
}