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
|
//===- LoopIndexSplit.cpp - Loop Index Splitting Pass ---------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by Devang Patel and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements Loop Index Splitting Pass.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "loop-index-split"
#include "llvm/Transforms/Scalar.h"
#include "llvm/Analysis/LoopPass.h"
#include "llvm/Analysis/ScalarEvolutionExpander.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Transforms/Utils/Cloning.h"
#include "llvm/Support/Compiler.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/Statistic.h"
using namespace llvm;
STATISTIC(NumIndexSplit, "Number of loops index split");
namespace {
class VISIBILITY_HIDDEN LoopIndexSplit : public LoopPass {
public:
static char ID; // Pass ID, replacement for typeid
LoopIndexSplit() : LoopPass((intptr_t)&ID) {}
// Index split Loop L. Return true if loop is split.
bool runOnLoop(Loop *L, LPPassManager &LPM);
void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<ScalarEvolution>();
AU.addPreserved<ScalarEvolution>();
AU.addRequiredID(LCSSAID);
AU.addPreservedID(LCSSAID);
AU.addRequired<LoopInfo>();
AU.addPreserved<LoopInfo>();
AU.addRequiredID(LoopSimplifyID);
AU.addPreservedID(LoopSimplifyID);
AU.addRequired<DominatorTree>();
AU.addRequired<DominanceFrontier>();
AU.addPreserved<DominatorTree>();
AU.addPreserved<DominanceFrontier>();
}
private:
class SplitInfo {
public:
SplitInfo() : SplitValue(NULL), SplitCondition(NULL),
UseTrueBranchFirst(true), A_ExitValue(NULL),
B_StartValue(NULL) {}
// Induction variable's range is split at this value.
Value *SplitValue;
// This instruction compares IndVar against SplitValue.
Instruction *SplitCondition;
// True if after loop index split, first loop will execute split condition's
// true branch.
bool UseTrueBranchFirst;
// Exit value for first loop after loop split.
Value *A_ExitValue;
// Start value for second loop after loop split.
Value *B_StartValue;
// Clear split info.
void clear() {
SplitValue = NULL;
SplitCondition = NULL;
UseTrueBranchFirst = true;
A_ExitValue = NULL;
B_StartValue = NULL;
}
};
private:
// safeIcmpInst - CI is considered safe instruction if one of the operand
// is SCEVAddRecExpr based on induction variable and other operand is
// loop invariant. If CI is safe then populate SplitInfo object SD appropriately
// and return true;
bool safeICmpInst(ICmpInst *CI, SplitInfo &SD);
/// Find condition inside a loop that is suitable candidate for index split.
void findSplitCondition();
/// Find loop's exit condition.
void findLoopConditionals();
/// Return induction variable associated with value V.
void findIndVar(Value *V, Loop *L);
/// processOneIterationLoop - Current loop L contains compare instruction
/// that compares induction variable, IndVar, agains loop invariant. If
/// entire (i.e. meaningful) loop body is dominated by this compare
/// instruction then loop body is executed only for one iteration. In
/// such case eliminate loop structure surrounding this loop body. For
bool processOneIterationLoop(SplitInfo &SD);
/// If loop header includes loop variant instruction operands then
/// this loop may not be eliminated.
bool safeHeader(SplitInfo &SD, BasicBlock *BB);
/// If Exiting block includes loop variant instructions then this
/// loop may not be eliminated.
bool safeExitingBlock(SplitInfo &SD, BasicBlock *BB);
/// removeBlocks - Remove basic block DeadBB and all blocks dominated by DeadBB.
/// This routine is used to remove split condition's dead branch, dominated by
/// DeadBB. LiveBB dominates split conidition's other branch.
void removeBlocks(BasicBlock *DeadBB, Loop *LP, BasicBlock *LiveBB);
/// safeSplitCondition - Return true if it is possible to
/// split loop using given split condition.
bool safeSplitCondition(SplitInfo &SD);
/// calculateLoopBounds - ALoop exit value and BLoop start values are calculated
/// based on split value.
void calculateLoopBounds(SplitInfo &SD);
/// updatePHINodes - CFG has been changed.
/// Before
/// - ExitBB's single predecessor was Latch
/// - Latch's second successor was Header
/// Now
/// - ExitBB's single predecessor was Header
/// - Latch's one and only successor was Header
///
/// Update ExitBB PHINodes' to reflect this change.
void updatePHINodes(BasicBlock *ExitBB, BasicBlock *Latch,
BasicBlock *Header,
PHINode *IV, Instruction *IVIncrement);
/// moveExitCondition - Move exit condition EC into split condition block CondBB.
void moveExitCondition(BasicBlock *CondBB, BasicBlock *ActiveBB,
BasicBlock *ExitBB, ICmpInst *EC, ICmpInst *SC,
PHINode *IV, Instruction *IVAdd, Loop *LP);
/// splitLoop - Split current loop L in two loops using split information
/// SD. Update dominator information. Maintain LCSSA form.
bool splitLoop(SplitInfo &SD);
void initialize() {
IndVar = NULL;
IndVarIncrement = NULL;
ExitCondition = NULL;
StartValue = NULL;
ExitValueNum = 0;
SplitData.clear();
}
private:
// Current Loop.
Loop *L;
LPPassManager *LPM;
LoopInfo *LI;
ScalarEvolution *SE;
DominatorTree *DT;
DominanceFrontier *DF;
SmallVector<SplitInfo, 4> SplitData;
// Induction variable whose range is being split by this transformation.
PHINode *IndVar;
Instruction *IndVarIncrement;
// Loop exit condition.
ICmpInst *ExitCondition;
// Induction variable's initial value.
Value *StartValue;
// Induction variable's final loop exit value operand number in exit condition..
unsigned ExitValueNum;
};
char LoopIndexSplit::ID = 0;
RegisterPass<LoopIndexSplit> X ("loop-index-split", "Index Split Loops");
}
LoopPass *llvm::createLoopIndexSplitPass() {
return new LoopIndexSplit();
}
// Index split Loop L. Return true if loop is split.
bool LoopIndexSplit::runOnLoop(Loop *IncomingLoop, LPPassManager &LPM_Ref) {
bool Changed = false;
L = IncomingLoop;
LPM = &LPM_Ref;
// FIXME - Nested loops make dominator info updates tricky.
if (!L->getSubLoops().empty())
return false;
SE = &getAnalysis<ScalarEvolution>();
DT = &getAnalysis<DominatorTree>();
LI = &getAnalysis<LoopInfo>();
DF = &getAnalysis<DominanceFrontier>();
initialize();
findLoopConditionals();
if (!ExitCondition)
return false;
findSplitCondition();
if (SplitData.empty())
return false;
// First see if it is possible to eliminate loop itself or not.
for (SmallVector<SplitInfo, 4>::iterator SI = SplitData.begin(),
E = SplitData.end(); SI != E;) {
SplitInfo &SD = *SI;
ICmpInst *CI = dyn_cast<ICmpInst>(SD.SplitCondition);
if (CI && CI->getPredicate() == ICmpInst::ICMP_EQ) {
Changed = processOneIterationLoop(SD);
if (Changed) {
++NumIndexSplit;
// If is loop is eliminated then nothing else to do here.
return Changed;
} else {
SmallVector<SplitInfo, 4>::iterator Delete_SI = SI;
++SI;
SplitData.erase(Delete_SI);
}
} else
++SI;
}
if (SplitData.empty())
return false;
// Split most profitiable condition.
// FIXME : Implement cost analysis.
unsigned MostProfitableSDIndex = 0;
Changed = splitLoop(SplitData[MostProfitableSDIndex]);
if (Changed)
++NumIndexSplit;
return Changed;
}
/// Return true if V is a induction variable or induction variable's
/// increment for loop L.
void LoopIndexSplit::findIndVar(Value *V, Loop *L) {
Instruction *I = dyn_cast<Instruction>(V);
if (!I)
return;
// Check if I is a phi node from loop header or not.
if (PHINode *PN = dyn_cast<PHINode>(V)) {
if (PN->getParent() == L->getHeader()) {
IndVar = PN;
return;
}
}
// Check if I is a add instruction whose one operand is
// phi node from loop header and second operand is constant.
if (I->getOpcode() != Instruction::Add)
return;
Value *Op0 = I->getOperand(0);
Value *Op1 = I->getOperand(1);
if (PHINode *PN = dyn_cast<PHINode>(Op0)) {
if (PN->getParent() == L->getHeader()
&& isa<ConstantInt>(Op1)) {
IndVar = PN;
IndVarIncrement = I;
return;
}
}
if (PHINode *PN = dyn_cast<PHINode>(Op1)) {
if (PN->getParent() == L->getHeader()
&& isa<ConstantInt>(Op0)) {
IndVar = PN;
IndVarIncrement = I;
return;
}
}
return;
}
// Find loop's exit condition and associated induction variable.
void LoopIndexSplit::findLoopConditionals() {
BasicBlock *ExitingBlock = NULL;
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
I != E; ++I) {
BasicBlock *BB = *I;
if (!L->isLoopExit(BB))
continue;
if (ExitingBlock)
return;
ExitingBlock = BB;
}
if (!ExitingBlock)
return;
// If exiting block is neither loop header nor loop latch then this loop is
// not suitable.
if (ExitingBlock != L->getHeader() && ExitingBlock != L->getLoopLatch())
return;
// If exit block's terminator is conditional branch inst then we have found
// exit condition.
BranchInst *BR = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
if (!BR || BR->isUnconditional())
return;
ICmpInst *CI = dyn_cast<ICmpInst>(BR->getCondition());
if (!CI)
return;
// FIXME
if (CI->getPredicate() == ICmpInst::ICMP_EQ
|| CI->getPredicate() == ICmpInst::ICMP_NE)
return;
if (CI->getPredicate() == ICmpInst::ICMP_SGT
|| CI->getPredicate() == ICmpInst::ICMP_UGT
|| CI->getPredicate() == ICmpInst::ICMP_SGE
|| CI->getPredicate() == ICmpInst::ICMP_UGE) {
BasicBlock *FirstSuccessor = BR->getSuccessor(0);
// splitLoop() is expecting LT/LE as exit condition predicate.
// Swap operands here if possible to meet this requirement.
if (!L->contains(FirstSuccessor))
CI->swapOperands();
else
return;
}
ExitCondition = CI;
// Exit condition's one operand is loop invariant exit value and second
// operand is SCEVAddRecExpr based on induction variable.
Value *V0 = CI->getOperand(0);
Value *V1 = CI->getOperand(1);
SCEVHandle SH0 = SE->getSCEV(V0);
SCEVHandle SH1 = SE->getSCEV(V1);
if (SH0->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH1)) {
ExitValueNum = 0;
findIndVar(V1, L);
}
else if (SH1->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH0)) {
ExitValueNum = 1;
findIndVar(V0, L);
}
if (!IndVar)
ExitCondition = NULL;
else if (IndVar) {
BasicBlock *Preheader = L->getLoopPreheader();
StartValue = IndVar->getIncomingValueForBlock(Preheader);
}
}
/// Find condition inside a loop that is suitable candidate for index split.
void LoopIndexSplit::findSplitCondition() {
SplitInfo SD;
// Check all basic block's terminators.
for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
I != E; ++I) {
SD.clear();
BasicBlock *BB = *I;
// If this basic block does not terminate in a conditional branch
// then terminator is not a suitable split condition.
BranchInst *BR = dyn_cast<BranchInst>(BB->getTerminator());
if (!BR)
continue;
if (BR->isUnconditional())
continue;
ICmpInst *CI = dyn_cast<ICmpInst>(BR->getCondition());
if (!CI || CI == ExitCondition)
continue;
if (CI->getPredicate() == ICmpInst::ICMP_NE)
continue;
// If split condition predicate is GT or GE then first execute
// false branch of split condition.
if (CI->getPredicate() == ICmpInst::ICMP_UGT
|| CI->getPredicate() == ICmpInst::ICMP_SGT
|| CI->getPredicate() == ICmpInst::ICMP_UGE
|| CI->getPredicate() == ICmpInst::ICMP_SGE)
SD.UseTrueBranchFirst = false;
// If one operand is loop invariant and second operand is SCEVAddRecExpr
// based on induction variable then CI is a candidate split condition.
if (safeICmpInst(CI, SD))
SplitData.push_back(SD);
}
}
// safeIcmpInst - CI is considered safe instruction if one of the operand
// is SCEVAddRecExpr based on induction variable and other operand is
// loop invariant. If CI is safe then populate SplitInfo object SD appropriately
// and return true;
bool LoopIndexSplit::safeICmpInst(ICmpInst *CI, SplitInfo &SD) {
Value *V0 = CI->getOperand(0);
Value *V1 = CI->getOperand(1);
SCEVHandle SH0 = SE->getSCEV(V0);
SCEVHandle SH1 = SE->getSCEV(V1);
if (SH0->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH1)) {
SD.SplitValue = V0;
SD.SplitCondition = CI;
if (PHINode *PN = dyn_cast<PHINode>(V1)) {
if (PN == IndVar)
return true;
}
else if (Instruction *Insn = dyn_cast<Instruction>(V1)) {
if (IndVarIncrement && IndVarIncrement == Insn)
return true;
}
}
else if (SH1->isLoopInvariant(L) && isa<SCEVAddRecExpr>(SH0)) {
SD.SplitValue = V1;
SD.SplitCondition = CI;
if (PHINode *PN = dyn_cast<PHINode>(V0)) {
if (PN == IndVar)
return true;
}
else if (Instruction *Insn = dyn_cast<Instruction>(V0)) {
if (IndVarIncrement && IndVarIncrement == Insn)
return true;
}
}
return false;
}
/// processOneIterationLoop - Current loop L contains compare instruction
/// that compares induction variable, IndVar, against loop invariant. If
/// entire (i.e. meaningful) loop body is dominated by this compare
/// instruction then loop body is executed only once. In such case eliminate
/// loop structure surrounding this loop body. For example,
/// for (int i = start; i < end; ++i) {
/// if ( i == somevalue) {
/// loop_body
/// }
/// }
/// can be transformed into
/// if (somevalue >= start && somevalue < end) {
/// i = somevalue;
/// loop_body
/// }
bool LoopIndexSplit::processOneIterationLoop(SplitInfo &SD) {
BasicBlock *Header = L->getHeader();
// First of all, check if SplitCondition dominates entire loop body
// or not.
// If SplitCondition is not in loop header then this loop is not suitable
// for this transformation.
if (SD.SplitCondition->getParent() != Header)
return false;
// If loop header includes loop variant instruction operands then
// this loop may not be eliminated.
if (!safeHeader(SD, Header))
return false;
// If Exiting block includes loop variant instructions then this
// loop may not be eliminated.
if (!safeExitingBlock(SD, ExitCondition->getParent()))
return false;
// Update CFG.
// Replace index variable with split value in loop body. Loop body is executed
// only when index variable is equal to split value.
IndVar->replaceAllUsesWith(SD.SplitValue);
// Remove Latch to Header edge.
BasicBlock *Latch = L->getLoopLatch();
BasicBlock *LatchSucc = NULL;
BranchInst *BR = dyn_cast<BranchInst>(Latch->getTerminator());
if (!BR)
return false;
Header->removePredecessor(Latch);
for (succ_iterator SI = succ_begin(Latch), E = succ_end(Latch);
SI != E; ++SI) {
if (Header != *SI)
LatchSucc = *SI;
}
BR->setUnconditionalDest(LatchSucc);
Instruction *Terminator = Header->getTerminator();
Value *ExitValue = ExitCondition->getOperand(ExitValueNum);
// Replace split condition in header.
// Transform
// SplitCondition : icmp eq i32 IndVar, SplitValue
// into
// c1 = icmp uge i32 SplitValue, StartValue
// c2 = icmp ult i32 SplitValue, ExitValue
// and i32 c1, c2
bool SignedPredicate = ExitCondition->isSignedPredicate();
Instruction *C1 = new ICmpInst(SignedPredicate ?
ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE,
SD.SplitValue, StartValue, "lisplit",
Terminator);
Instruction *C2 = new ICmpInst(SignedPredicate ?
ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
SD.SplitValue, ExitValue, "lisplit",
Terminator);
Instruction *NSplitCond = BinaryOperator::createAnd(C1, C2, "lisplit",
Terminator);
SD.SplitCondition->replaceAllUsesWith(NSplitCond);
SD.SplitCondition->eraseFromParent();
// Now, clear latch block. Remove instructions that are responsible
// to increment induction variable.
Instruction *LTerminator = Latch->getTerminator();
for (BasicBlock::iterator LB = Latch->begin(), LE = Latch->end();
LB != LE; ) {
Instruction *I = LB;
++LB;
if (isa<PHINode>(I) || I == LTerminator)
continue;
if (I == IndVarIncrement)
I->replaceAllUsesWith(ExitValue);
else
I->replaceAllUsesWith(UndefValue::get(I->getType()));
I->eraseFromParent();
}
LPM->deleteLoopFromQueue(L);
// Update Dominator Info.
// Only CFG change done is to remove Latch to Header edge. This
// does not change dominator tree because Latch did not dominate
// Header.
if (DF) {
DominanceFrontier::iterator HeaderDF = DF->find(Header);
if (HeaderDF != DF->end())
DF->removeFromFrontier(HeaderDF, Header);
DominanceFrontier::iterator LatchDF = DF->find(Latch);
if (LatchDF != DF->end())
DF->removeFromFrontier(LatchDF, Header);
}
return true;
}
// If loop header includes loop variant instruction operands then
// this loop can not be eliminated. This is used by processOneIterationLoop().
bool LoopIndexSplit::safeHeader(SplitInfo &SD, BasicBlock *Header) {
Instruction *Terminator = Header->getTerminator();
for(BasicBlock::iterator BI = Header->begin(), BE = Header->end();
BI != BE; ++BI) {
Instruction *I = BI;
// PHI Nodes are OK.
if (isa<PHINode>(I))
continue;
// SplitCondition itself is OK.
if (I == SD.SplitCondition)
continue;
// Induction variable is OK.
if (I == IndVar)
continue;
// Induction variable increment is OK.
if (I == IndVarIncrement)
continue;
// Terminator is also harmless.
if (I == Terminator)
continue;
// Otherwise we have a instruction that may not be safe.
return false;
}
return true;
}
// If Exiting block includes loop variant instructions then this
// loop may not be eliminated. This is used by processOneIterationLoop().
bool LoopIndexSplit::safeExitingBlock(SplitInfo &SD,
BasicBlock *ExitingBlock) {
for (BasicBlock::iterator BI = ExitingBlock->begin(),
BE = ExitingBlock->end(); BI != BE; ++BI) {
Instruction *I = BI;
// PHI Nodes are OK.
if (isa<PHINode>(I))
continue;
// Induction variable increment is OK.
if (IndVarIncrement && IndVarIncrement == I)
continue;
// Check if I is induction variable increment instruction.
if (!IndVarIncrement && I->getOpcode() == Instruction::Add) {
Value *Op0 = I->getOperand(0);
Value *Op1 = I->getOperand(1);
PHINode *PN = NULL;
ConstantInt *CI = NULL;
if ((PN = dyn_cast<PHINode>(Op0))) {
if ((CI = dyn_cast<ConstantInt>(Op1)))
IndVarIncrement = I;
} else
if ((PN = dyn_cast<PHINode>(Op1))) {
if ((CI = dyn_cast<ConstantInt>(Op0)))
IndVarIncrement = I;
}
if (IndVarIncrement && PN == IndVar && CI->isOne())
continue;
}
// I is an Exit condition if next instruction is block terminator.
// Exit condition is OK if it compares loop invariant exit value,
// which is checked below.
else if (ICmpInst *EC = dyn_cast<ICmpInst>(I)) {
if (EC == ExitCondition)
continue;
}
if (I == ExitingBlock->getTerminator())
continue;
// Otherwise we have instruction that may not be safe.
return false;
}
// We could not find any reason to consider ExitingBlock unsafe.
return true;
}
/// removeBlocks - Remove basic block DeadBB and all blocks dominated by DeadBB.
/// This routine is used to remove split condition's dead branch, dominated by
/// DeadBB. LiveBB dominates split conidition's other branch.
void LoopIndexSplit::removeBlocks(BasicBlock *DeadBB, Loop *LP,
BasicBlock *LiveBB) {
// First update DeadBB's dominance frontier.
SmallVector<BasicBlock *, 8> FrontierBBs;
DominanceFrontier::iterator DeadBBDF = DF->find(DeadBB);
if (DeadBBDF != DF->end()) {
SmallVector<BasicBlock *, 8> PredBlocks;
DominanceFrontier::DomSetType DeadBBSet = DeadBBDF->second;
for (DominanceFrontier::DomSetType::iterator DeadBBSetI = DeadBBSet.begin(),
DeadBBSetE = DeadBBSet.end(); DeadBBSetI != DeadBBSetE; ++DeadBBSetI) {
BasicBlock *FrontierBB = *DeadBBSetI;
FrontierBBs.push_back(FrontierBB);
// Rremove any PHI incoming edge from blocks dominated by DeadBB.
PredBlocks.clear();
for(pred_iterator PI = pred_begin(FrontierBB), PE = pred_end(FrontierBB);
PI != PE; ++PI) {
BasicBlock *P = *PI;
if (P == DeadBB || DT->dominates(DeadBB, P))
PredBlocks.push_back(P);
}
for(BasicBlock::iterator FBI = FrontierBB->begin(), FBE = FrontierBB->end();
FBI != FBE; ++FBI) {
if (PHINode *PN = dyn_cast<PHINode>(FBI)) {
for(SmallVector<BasicBlock *, 8>::iterator PI = PredBlocks.begin(),
PE = PredBlocks.end(); PI != PE; ++PI) {
BasicBlock *P = *PI;
PN->removeIncomingValue(P);
}
}
else
break;
}
}
}
// Now remove DeadBB and all nodes dominated by DeadBB in df order.
SmallVector<BasicBlock *, 32> WorkList;
DomTreeNode *DN = DT->getNode(DeadBB);
for (df_iterator<DomTreeNode*> DI = df_begin(DN),
E = df_end(DN); DI != E; ++DI) {
BasicBlock *BB = DI->getBlock();
WorkList.push_back(BB);
BB->replaceAllUsesWith(UndefValue::get(Type::LabelTy));
}
while (!WorkList.empty()) {
BasicBlock *BB = WorkList.back(); WorkList.pop_back();
for(BasicBlock::iterator BBI = BB->begin(), BBE = BB->end();
BBI != BBE; ++BBI) {
Instruction *I = BBI;
I->replaceAllUsesWith(UndefValue::get(I->getType()));
I->eraseFromParent();
}
LPM->deleteSimpleAnalysisValue(BB, LP);
DT->eraseNode(BB);
DF->removeBlock(BB);
LI->removeBlock(BB);
BB->eraseFromParent();
}
// Update Frontier BBs' dominator info.
while (!FrontierBBs.empty()) {
BasicBlock *FBB = FrontierBBs.back(); FrontierBBs.pop_back();
BasicBlock *NewDominator = FBB->getSinglePredecessor();
if (!NewDominator) {
pred_iterator PI = pred_begin(FBB), PE = pred_end(FBB);
NewDominator = *PI;
++PI;
if (NewDominator != LiveBB) {
for(; PI != PE; ++PI) {
BasicBlock *P = *PI;
if (P == LiveBB) {
NewDominator = LiveBB;
break;
}
NewDominator = DT->findNearestCommonDominator(NewDominator, P);
}
}
}
assert (NewDominator && "Unable to fix dominator info.");
DT->changeImmediateDominator(FBB, NewDominator);
DF->changeImmediateDominator(FBB, NewDominator, DT);
}
}
/// safeSplitCondition - Return true if it is possible to
/// split loop using given split condition.
bool LoopIndexSplit::safeSplitCondition(SplitInfo &SD) {
BasicBlock *SplitCondBlock = SD.SplitCondition->getParent();
// Unable to handle triange loops at the moment.
// In triangle loop, split condition is in header and one of the
// the split destination is loop latch. If split condition is EQ
// then such loops are already handle in processOneIterationLoop().
BasicBlock *Latch = L->getLoopLatch();
BranchInst *SplitTerminator =
cast<BranchInst>(SplitCondBlock->getTerminator());
BasicBlock *Succ0 = SplitTerminator->getSuccessor(0);
BasicBlock *Succ1 = SplitTerminator->getSuccessor(1);
if (L->getHeader() == SplitCondBlock
&& (Latch == Succ0 || Latch == Succ1))
return false;
// If split condition branches heads do not have single predecessor,
// SplitCondBlock, then is not possible to remove inactive branch.
if (!Succ0->getSinglePredecessor() || !Succ1->getSinglePredecessor())
return false;
// Finally this split condition is safe only if merge point for
// split condition branch is loop latch. This check along with previous
// check, to ensure that exit condition is in either loop latch or header,
// filters all loops with non-empty loop body between merge point
// and exit condition.
DominanceFrontier::iterator Succ0DF = DF->find(Succ0);
assert (Succ0DF != DF->end() && "Unable to find Succ0 dominance frontier");
if (Succ0DF->second.count(Latch))
return true;
DominanceFrontier::iterator Succ1DF = DF->find(Succ1);
assert (Succ1DF != DF->end() && "Unable to find Succ1 dominance frontier");
if (Succ1DF->second.count(Latch))
return true;
return false;
}
/// calculateLoopBounds - ALoop exit value and BLoop start values are calculated
/// based on split value.
void LoopIndexSplit::calculateLoopBounds(SplitInfo &SD) {
ICmpInst *SC = cast<ICmpInst>(SD.SplitCondition);
ICmpInst::Predicate SP = SC->getPredicate();
const Type *Ty = SD.SplitValue->getType();
bool Sign = ExitCondition->isSignedPredicate();
BasicBlock *Preheader = L->getLoopPreheader();
Instruction *PHTerminator = Preheader->getTerminator();
// Initially use split value as upper loop bound for first loop and lower loop
// bound for second loop.
Value *AEV = SD.SplitValue;
Value *BSV = SD.SplitValue;
switch (ExitCondition->getPredicate()) {
case ICmpInst::ICMP_SGT:
case ICmpInst::ICMP_UGT:
case ICmpInst::ICMP_SGE:
case ICmpInst::ICMP_UGE:
default:
assert (0 && "Unexpected exit condition predicate");
case ICmpInst::ICMP_SLT:
case ICmpInst::ICMP_ULT:
{
switch (SP) {
case ICmpInst::ICMP_SLT:
case ICmpInst::ICMP_ULT:
//
// for (i = LB; i < UB; ++i) { if (i < SV) A; else B; }
//
// is transformed into
// AEV = BSV = SV
// for (i = LB; i < min(UB, AEV); ++i)
// A;
// for (i = max(LB, BSV); i < UB; ++i);
// B;
break;
case ICmpInst::ICMP_SLE:
case ICmpInst::ICMP_ULE:
{
//
// for (i = LB; i < UB; ++i) { if (i <= SV) A; else B; }
//
// is transformed into
//
// AEV = SV + 1
// BSV = SV + 1
// for (i = LB; i < min(UB, AEV); ++i)
// A;
// for (i = max(LB, BSV); i < UB; ++i)
// B;
BSV = BinaryOperator::createAdd(SD.SplitValue,
ConstantInt::get(Ty, 1, Sign),
"lsplit.add", PHTerminator);
AEV = BSV;
}
break;
case ICmpInst::ICMP_SGE:
case ICmpInst::ICMP_UGE:
//
// for (i = LB; i < UB; ++i) { if (i >= SV) A; else B; }
//
// is transformed into
// AEV = BSV = SV
// for (i = LB; i < min(UB, AEV); ++i)
// B;
// for (i = max(BSV, LB); i < UB; ++i)
// A;
break;
case ICmpInst::ICMP_SGT:
case ICmpInst::ICMP_UGT:
{
//
// for (i = LB; i < UB; ++i) { if (i > SV) A; else B; }
//
// is transformed into
//
// BSV = AEV = SV + 1
// for (i = LB; i < min(UB, AEV); ++i)
// B;
// for (i = max(LB, BSV); i < UB; ++i)
// A;
BSV = BinaryOperator::createAdd(SD.SplitValue,
ConstantInt::get(Ty, 1, Sign),
"lsplit.add", PHTerminator);
AEV = BSV;
}
break;
default:
assert (0 && "Unexpected split condition predicate");
break;
} // end switch (SP)
}
break;
case ICmpInst::ICMP_SLE:
case ICmpInst::ICMP_ULE:
{
switch (SP) {
case ICmpInst::ICMP_SLT:
case ICmpInst::ICMP_ULT:
//
// for (i = LB; i <= UB; ++i) { if (i < SV) A; else B; }
//
// is transformed into
// AEV = SV - 1;
// BSV = SV;
// for (i = LB; i <= min(UB, AEV); ++i)
// A;
// for (i = max(LB, BSV); i <= UB; ++i)
// B;
AEV = BinaryOperator::createSub(SD.SplitValue,
ConstantInt::get(Ty, 1, Sign),
"lsplit.sub", PHTerminator);
break;
case ICmpInst::ICMP_SLE:
case ICmpInst::ICMP_ULE:
//
// for (i = LB; i <= UB; ++i) { if (i <= SV) A; else B; }
//
// is transformed into
// AEV = SV;
// BSV = SV + 1;
// for (i = LB; i <= min(UB, AEV); ++i)
// A;
// for (i = max(LB, BSV); i <= UB; ++i)
// B;
BSV = BinaryOperator::createAdd(SD.SplitValue,
ConstantInt::get(Ty, 1, Sign),
"lsplit.add", PHTerminator);
break;
case ICmpInst::ICMP_SGT:
case ICmpInst::ICMP_UGT:
//
// for (i = LB; i <= UB; ++i) { if (i > SV) A; else B; }
//
// is transformed into
// AEV = SV;
// BSV = SV + 1;
// for (i = LB; i <= min(AEV, UB); ++i)
// B;
// for (i = max(LB, BSV); i <= UB; ++i)
// A;
BSV = BinaryOperator::createAdd(SD.SplitValue,
ConstantInt::get(Ty, 1, Sign),
"lsplit.add", PHTerminator);
break;
case ICmpInst::ICMP_SGE:
case ICmpInst::ICMP_UGE:
// ** TODO **
//
// for (i = LB; i <= UB; ++i) { if (i >= SV) A; else B; }
//
// is transformed into
// AEV = SV - 1;
// BSV = SV;
// for (i = LB; i <= min(AEV, UB); ++i)
// B;
// for (i = max(LB, BSV); i <= UB; ++i)
// A;
AEV = BinaryOperator::createSub(SD.SplitValue,
ConstantInt::get(Ty, 1, Sign),
"lsplit.sub", PHTerminator);
break;
default:
assert (0 && "Unexpected split condition predicate");
break;
} // end switch (SP)
}
break;
}
// Calculate ALoop induction variable's new exiting value and
// BLoop induction variable's new starting value. Calculuate these
// values in original loop's preheader.
// A_ExitValue = min(SplitValue, OrignalLoopExitValue)
// B_StartValue = max(SplitValue, OriginalLoopStartValue)
Value *C1 = new ICmpInst(Sign ?
ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
AEV,
ExitCondition->getOperand(ExitValueNum),
"lsplit.ev", PHTerminator);
SD.A_ExitValue = new SelectInst(C1, AEV,
ExitCondition->getOperand(ExitValueNum),
"lsplit.ev", PHTerminator);
Value *C2 = new ICmpInst(Sign ?
ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT,
BSV, StartValue, "lsplit.sv",
PHTerminator);
SD.B_StartValue = new SelectInst(C2, StartValue, BSV,
"lsplit.sv", PHTerminator);
}
/// splitLoop - Split current loop L in two loops using split information
/// SD. Update dominator information. Maintain LCSSA form.
bool LoopIndexSplit::splitLoop(SplitInfo &SD) {
if (!safeSplitCondition(SD))
return false;
// After loop is cloned there are two loops.
//
// First loop, referred as ALoop, executes first part of loop's iteration
// space split. Second loop, referred as BLoop, executes remaining
// part of loop's iteration space.
//
// ALoop's exit edge enters BLoop's header through a forwarding block which
// acts as a BLoop's preheader.
BasicBlock *Preheader = L->getLoopPreheader();
// Calculate ALoop induction variable's new exiting value and
// BLoop induction variable's new starting value.
calculateLoopBounds(SD);
//[*] Clone loop.
DenseMap<const Value *, Value *> ValueMap;
Loop *BLoop = CloneLoop(L, LPM, LI, ValueMap, this);
Loop *ALoop = L;
BasicBlock *B_Header = BLoop->getHeader();
//[*] ALoop's exiting edge BLoop's header.
// ALoop's original exit block becomes BLoop's exit block.
PHINode *B_IndVar = cast<PHINode>(ValueMap[IndVar]);
BasicBlock *A_ExitingBlock = ExitCondition->getParent();
BranchInst *A_ExitInsn =
dyn_cast<BranchInst>(A_ExitingBlock->getTerminator());
assert (A_ExitInsn && "Unable to find suitable loop exit branch");
BasicBlock *B_ExitBlock = A_ExitInsn->getSuccessor(1);
if (L->contains(B_ExitBlock)) {
B_ExitBlock = A_ExitInsn->getSuccessor(0);
A_ExitInsn->setSuccessor(0, B_Header);
} else
A_ExitInsn->setSuccessor(1, B_Header);
//[*] Update ALoop's exit value using new exit value.
ExitCondition->setOperand(ExitValueNum, SD.A_ExitValue);
// [*] Update BLoop's header phi nodes. Remove incoming PHINode's from
// original loop's preheader. Add incoming PHINode values from
// ALoop's exiting block. Update BLoop header's domiantor info.
// Collect inverse map of Header PHINodes.
DenseMap<Value *, Value *> InverseMap;
for (BasicBlock::iterator BI = L->getHeader()->begin(),
BE = L->getHeader()->end(); BI != BE; ++BI) {
if (PHINode *PN = dyn_cast<PHINode>(BI)) {
PHINode *PNClone = cast<PHINode>(ValueMap[PN]);
InverseMap[PNClone] = PN;
} else
break;
}
for (BasicBlock::iterator BI = B_Header->begin(), BE = B_Header->end();
BI != BE; ++BI) {
if (PHINode *PN = dyn_cast<PHINode>(BI)) {
// Remove incoming value from original preheader.
PN->removeIncomingValue(Preheader);
// Add incoming value from A_ExitingBlock.
if (PN == B_IndVar)
PN->addIncoming(SD.B_StartValue, A_ExitingBlock);
else {
PHINode *OrigPN = cast<PHINode>(InverseMap[PN]);
Value *V2 = OrigPN->getIncomingValueForBlock(A_ExitingBlock);
PN->addIncoming(V2, A_ExitingBlock);
}
} else
break;
}
DT->changeImmediateDominator(B_Header, A_ExitingBlock);
DF->changeImmediateDominator(B_Header, A_ExitingBlock, DT);
// [*] Update BLoop's exit block. Its new predecessor is BLoop's exit
// block. Remove incoming PHINode values from ALoop's exiting block.
// Add new incoming values from BLoop's incoming exiting value.
// Update BLoop exit block's dominator info..
BasicBlock *B_ExitingBlock = cast<BasicBlock>(ValueMap[A_ExitingBlock]);
for (BasicBlock::iterator BI = B_ExitBlock->begin(), BE = B_ExitBlock->end();
BI != BE; ++BI) {
if (PHINode *PN = dyn_cast<PHINode>(BI)) {
PN->addIncoming(ValueMap[PN->getIncomingValueForBlock(A_ExitingBlock)],
B_ExitingBlock);
PN->removeIncomingValue(A_ExitingBlock);
} else
break;
}
DT->changeImmediateDominator(B_ExitBlock, B_ExitingBlock);
DF->changeImmediateDominator(B_ExitBlock, B_ExitingBlock, DT);
//[*] Split ALoop's exit edge. This creates a new block which
// serves two purposes. First one is to hold PHINode defnitions
// to ensure that ALoop's LCSSA form. Second use it to act
// as a preheader for BLoop.
BasicBlock *A_ExitBlock = SplitEdge(A_ExitingBlock, B_Header, this);
//[*] Preserve ALoop's LCSSA form. Create new forwarding PHINodes
// in A_ExitBlock to redefine outgoing PHI definitions from ALoop.
for(BasicBlock::iterator BI = B_Header->begin(), BE = B_Header->end();
BI != BE; ++BI) {
if (PHINode *PN = dyn_cast<PHINode>(BI)) {
Value *V1 = PN->getIncomingValueForBlock(A_ExitBlock);
PHINode *newPHI = new PHINode(PN->getType(), PN->getName());
newPHI->addIncoming(V1, A_ExitingBlock);
A_ExitBlock->getInstList().push_front(newPHI);
PN->removeIncomingValue(A_ExitBlock);
PN->addIncoming(newPHI, A_ExitBlock);
} else
break;
}
//[*] Eliminate split condition's inactive branch from ALoop.
BasicBlock *A_SplitCondBlock = SD.SplitCondition->getParent();
BranchInst *A_BR = cast<BranchInst>(A_SplitCondBlock->getTerminator());
BasicBlock *A_InactiveBranch = NULL;
BasicBlock *A_ActiveBranch = NULL;
if (SD.UseTrueBranchFirst) {
A_ActiveBranch = A_BR->getSuccessor(0);
A_InactiveBranch = A_BR->getSuccessor(1);
} else {
A_ActiveBranch = A_BR->getSuccessor(1);
A_InactiveBranch = A_BR->getSuccessor(0);
}
A_BR->setUnconditionalDest(A_ActiveBranch);
removeBlocks(A_InactiveBranch, L, A_ActiveBranch);
//[*] Eliminate split condition's inactive branch in from BLoop.
BasicBlock *B_SplitCondBlock = cast<BasicBlock>(ValueMap[A_SplitCondBlock]);
BranchInst *B_BR = cast<BranchInst>(B_SplitCondBlock->getTerminator());
BasicBlock *B_InactiveBranch = NULL;
BasicBlock *B_ActiveBranch = NULL;
if (SD.UseTrueBranchFirst) {
B_ActiveBranch = B_BR->getSuccessor(1);
B_InactiveBranch = B_BR->getSuccessor(0);
} else {
B_ActiveBranch = B_BR->getSuccessor(0);
B_InactiveBranch = B_BR->getSuccessor(1);
}
B_BR->setUnconditionalDest(B_ActiveBranch);
removeBlocks(B_InactiveBranch, BLoop, B_ActiveBranch);
BasicBlock *A_Header = L->getHeader();
if (A_ExitingBlock == A_Header)
return true;
//[*] Move exit condition into split condition block to avoid
// executing dead loop iteration.
ICmpInst *B_ExitCondition = cast<ICmpInst>(ValueMap[ExitCondition]);
Instruction *B_IndVarIncrement = cast<Instruction>(ValueMap[IndVarIncrement]);
ICmpInst *B_SplitCondition = cast<ICmpInst>(ValueMap[SD.SplitCondition]);
moveExitCondition(A_SplitCondBlock, A_ActiveBranch, A_ExitBlock, ExitCondition,
cast<ICmpInst>(SD.SplitCondition), IndVar, IndVarIncrement,
ALoop);
moveExitCondition(B_SplitCondBlock, B_ActiveBranch, B_ExitBlock, B_ExitCondition,
B_SplitCondition, B_IndVar, B_IndVarIncrement, BLoop);
return true;
}
// moveExitCondition - Move exit condition EC into split condition block CondBB.
void LoopIndexSplit::moveExitCondition(BasicBlock *CondBB, BasicBlock *ActiveBB,
BasicBlock *ExitBB, ICmpInst *EC, ICmpInst *SC,
PHINode *IV, Instruction *IVAdd, Loop *LP) {
BasicBlock *ExitingBB = EC->getParent();
Instruction *CurrentBR = CondBB->getTerminator();
// Move exit condition into split condition block.
EC->moveBefore(CurrentBR);
EC->setOperand(ExitValueNum == 0 ? 1 : 0, IV);
// Move exiting block's branch into split condition block. Update its branch
// destination.
BranchInst *ExitingBR = cast<BranchInst>(ExitingBB->getTerminator());
ExitingBR->moveBefore(CurrentBR);
if (ExitingBR->getSuccessor(0) == ExitBB)
ExitingBR->setSuccessor(1, ActiveBB);
else
ExitingBR->setSuccessor(0, ActiveBB);
// Remove split condition and current split condition branch.
SC->eraseFromParent();
CurrentBR->eraseFromParent();
// Connect exiting block to split condition block.
new BranchInst(CondBB, ExitingBB);
// Update PHINodes
updatePHINodes(ExitBB, ExitingBB, CondBB, IV, IVAdd);
// Fix dominator info.
// ExitBB is now dominated by CondBB
DT->changeImmediateDominator(ExitBB, CondBB);
DF->changeImmediateDominator(ExitBB, CondBB, DT);
// Basicblocks dominated by ActiveBB may have ExitingBB or
// a basic block outside the loop in their DF list. If so,
// replace it with CondBB.
DomTreeNode *Node = DT->getNode(ActiveBB);
for (df_iterator<DomTreeNode *> DI = df_begin(Node), DE = df_end(Node);
DI != DE; ++DI) {
BasicBlock *BB = DI->getBlock();
DominanceFrontier::iterator BBDF = DF->find(BB);
DominanceFrontier::DomSetType::iterator DomSetI = BBDF->second.begin();
DominanceFrontier::DomSetType::iterator DomSetE = BBDF->second.end();
while (DomSetI != DomSetE) {
DominanceFrontier::DomSetType::iterator CurrentItr = DomSetI;
++DomSetI;
BasicBlock *DFBB = *CurrentItr;
if (DFBB == ExitingBB || !L->contains(DFBB)) {
BBDF->second.erase(DFBB);
BBDF->second.insert(CondBB);
}
}
}
}
/// updatePHINodes - CFG has been changed.
/// Before
/// - ExitBB's single predecessor was Latch
/// - Latch's second successor was Header
/// Now
/// - ExitBB's single predecessor was Header
/// - Latch's one and only successor was Header
///
/// Update ExitBB PHINodes' to reflect this change.
void LoopIndexSplit::updatePHINodes(BasicBlock *ExitBB, BasicBlock *Latch,
BasicBlock *Header,
PHINode *IV, Instruction *IVIncrement) {
for (BasicBlock::iterator BI = ExitBB->begin(), BE = ExitBB->end();
BI != BE; ++BI) {
PHINode *PN = dyn_cast<PHINode>(BI);
if (!PN)
break;
Value *V = PN->getIncomingValueForBlock(Latch);
if (PHINode *PHV = dyn_cast<PHINode>(V)) {
// PHV is in Latch. PHV has two uses, one use is in ExitBB PHINode
// (i.e. PN :)).
// The second use is in Header and it is new incoming value for PN.
PHINode *U1 = NULL;
PHINode *U2 = NULL;
Value *NewV = NULL;
for (Value::use_iterator UI = PHV->use_begin(), E = PHV->use_end();
UI != E; ++UI) {
if (!U1)
U1 = cast<PHINode>(*UI);
else if (!U2)
U2 = cast<PHINode>(*UI);
else
assert ( 0 && "Unexpected third use of this PHINode");
}
assert (U1 && U2 && "Unable to find two uses");
if (U1->getParent() == Header)
NewV = U1;
else
NewV = U2;
PN->addIncoming(NewV, Header);
} else if (Instruction *PHI = dyn_cast<Instruction>(V)) {
// If this instruction is IVIncrement then IV is new incoming value
// from header otherwise this instruction must be incoming value from
// header because loop is in LCSSA form.
if (PHI == IVIncrement)
PN->addIncoming(IV, Header);
else
PN->addIncoming(V, Header);
} else
// Otherwise this is an incoming value from header because loop is in
// LCSSA form.
PN->addIncoming(V, Header);
// Remove incoming value from Latch.
PN->removeIncomingValue(Latch);
}
}
|