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
|
//===- BasicAliasAnalysis.cpp - Local Alias Analysis Impl -----------------===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by the LLVM research group and is distributed under
// the University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the default implementation of the Alias Analysis interface
// that simply implements a few identities (two different globals cannot alias,
// etc), but otherwise does no analysis.
//
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/Passes.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/Function.h"
#include "llvm/ParameterAttributes.h"
#include "llvm/GlobalVariable.h"
#include "llvm/Instructions.h"
#include "llvm/Intrinsics.h"
#include "llvm/Pass.h"
#include "llvm/Target/TargetData.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringMap.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Support/ManagedStatic.h"
#include <algorithm>
using namespace llvm;
namespace {
/// NoAA - This class implements the -no-aa pass, which always returns "I
/// don't know" for alias queries. NoAA is unlike other alias analysis
/// implementations, in that it does not chain to a previous analysis. As
/// such it doesn't follow many of the rules that other alias analyses must.
///
struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
static char ID; // Class identification, replacement for typeinfo
NoAA() : ImmutablePass((intptr_t)&ID) {}
explicit NoAA(intptr_t PID) : ImmutablePass(PID) { }
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<TargetData>();
}
virtual void initializePass() {
TD = &getAnalysis<TargetData>();
}
virtual AliasResult alias(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size) {
return MayAlias;
}
virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
std::vector<PointerAccessInfo> *Info) {
return UnknownModRefBehavior;
}
virtual void getArgumentAccesses(Function *F, CallSite CS,
std::vector<PointerAccessInfo> &Info) {
assert(0 && "This method may not be called on this function!");
}
virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
virtual bool pointsToConstantMemory(const Value *P) { return false; }
virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
return ModRef;
}
virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
return ModRef;
}
virtual bool hasNoModRefInfoForCalls() const { return true; }
virtual void deleteValue(Value *V) {}
virtual void copyValue(Value *From, Value *To) {}
};
// Register this pass...
char NoAA::ID = 0;
RegisterPass<NoAA>
U("no-aa", "No Alias Analysis (always returns 'may' alias)");
// Declare that we implement the AliasAnalysis interface
RegisterAnalysisGroup<AliasAnalysis> V(U);
} // End of anonymous namespace
ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
namespace {
/// BasicAliasAnalysis - This is the default alias analysis implementation.
/// Because it doesn't chain to a previous alias analysis (like -no-aa), it
/// derives from the NoAA class.
struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA {
static char ID; // Class identification, replacement for typeinfo
BasicAliasAnalysis() : NoAA((intptr_t)&ID) { }
AliasResult alias(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size);
ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
return NoAA::getModRefInfo(CS1,CS2);
}
/// hasNoModRefInfoForCalls - We can provide mod/ref information against
/// non-escaping allocations.
virtual bool hasNoModRefInfoForCalls() const { return false; }
/// pointsToConstantMemory - Chase pointers until we find a (constant
/// global) or not.
bool pointsToConstantMemory(const Value *P);
virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
std::vector<PointerAccessInfo> *Info);
private:
// CheckGEPInstructions - Check two GEP instructions with known
// must-aliasing base pointers. This checks to see if the index expressions
// preclude the pointers from aliasing...
AliasResult
CheckGEPInstructions(const Type* BasePtr1Ty,
Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size,
const Type *BasePtr2Ty,
Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size);
};
// Register this pass...
char BasicAliasAnalysis::ID = 0;
RegisterPass<BasicAliasAnalysis>
X("basicaa", "Basic Alias Analysis (default AA impl)");
// Declare that we implement the AliasAnalysis interface
RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
} // End of anonymous namespace
ImmutablePass *llvm::createBasicAliasAnalysisPass() {
return new BasicAliasAnalysis();
}
// getUnderlyingObject - This traverses the use chain to figure out what object
// the specified value points to. If the value points to, or is derived from, a
// unique object or an argument, return it.
static const Value *getUnderlyingObject(const Value *V) {
if (!isa<PointerType>(V->getType())) return 0;
// If we are at some type of object, return it. GlobalValues and Allocations
// have unique addresses.
if (isa<GlobalValue>(V) || isa<AllocationInst>(V) || isa<Argument>(V))
return V;
// Traverse through different addressing mechanisms...
if (const Instruction *I = dyn_cast<Instruction>(V)) {
if (isa<BitCastInst>(I) || isa<GetElementPtrInst>(I))
return getUnderlyingObject(I->getOperand(0));
} else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
if (CE->getOpcode() == Instruction::BitCast ||
CE->getOpcode() == Instruction::GetElementPtr)
return getUnderlyingObject(CE->getOperand(0));
}
return 0;
}
static const User *isGEP(const Value *V) {
if (isa<GetElementPtrInst>(V) ||
(isa<ConstantExpr>(V) &&
cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
return cast<User>(V);
return 0;
}
static const Value *GetGEPOperands(const Value *V,
SmallVector<Value*, 16> &GEPOps){
assert(GEPOps.empty() && "Expect empty list to populate!");
GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
cast<User>(V)->op_end());
// Accumulate all of the chained indexes into the operand array
V = cast<User>(V)->getOperand(0);
while (const User *G = isGEP(V)) {
if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
!cast<Constant>(GEPOps[0])->isNullValue())
break; // Don't handle folding arbitrary pointer offsets yet...
GEPOps.erase(GEPOps.begin()); // Drop the zero index
GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
V = G->getOperand(0);
}
return V;
}
/// pointsToConstantMemory - Chase pointers until we find a (constant
/// global) or not.
bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
if (const Value *V = getUnderlyingObject(P))
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
return GV->isConstant();
return false;
}
// Determine if an AllocationInst instruction escapes from the function it is
// contained in. If it does not escape, there is no way for another function to
// mod/ref it. We do this by looking at its uses and determining if the uses
// can escape (recursively).
static bool AddressMightEscape(const Value *V) {
for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
UI != E; ++UI) {
const Instruction *I = cast<Instruction>(*UI);
switch (I->getOpcode()) {
case Instruction::Load:
break; //next use.
case Instruction::Store:
if (I->getOperand(0) == V)
return true; // Escapes if the pointer is stored.
break; // next use.
case Instruction::GetElementPtr:
if (AddressMightEscape(I))
return true;
break; // next use.
case Instruction::BitCast:
if (!isa<PointerType>(I->getType()))
return true;
if (AddressMightEscape(I))
return true;
break; // next use
case Instruction::Ret:
// If returned, the address will escape to calling functions, but no
// callees could modify it.
break; // next use
default:
return true;
}
}
return false;
}
// getModRefInfo - Check to see if the specified callsite can clobber the
// specified memory object. Since we only look at local properties of this
// function, we really can't say much about this query. We do, however, use
// simple "address taken" analysis on local objects.
//
AliasAnalysis::ModRefResult
BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
if (!isa<Constant>(P))
if (const AllocationInst *AI =
dyn_cast_or_null<AllocationInst>(getUnderlyingObject(P))) {
// Okay, the pointer is to a stack allocated object. If we can prove that
// the pointer never "escapes", then we know the call cannot clobber it,
// because it simply can't get its address.
if (!AddressMightEscape(AI))
return NoModRef;
// If this is a tail call and P points to a stack location, we know that
// the tail call cannot access or modify the local stack.
if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
if (CI->isTailCall() && isa<AllocaInst>(AI))
return NoModRef;
}
// The AliasAnalysis base class has some smarts, lets use them.
return AliasAnalysis::getModRefInfo(CS, P, Size);
}
static bool isNoAliasArgument(const Argument *Arg) {
const Function *Func = Arg->getParent();
const ParamAttrsList *Attr = Func->getFunctionType()->getParamAttrs();
if (Attr) {
unsigned Idx = 1;
for (Function::const_arg_iterator I = Func->arg_begin(),
E = Func->arg_end(); I != E; ++I, ++Idx) {
if (&(*I) == Arg &&
Attr->paramHasAttr(Idx, ParamAttr::NoAlias))
return true;
}
}
return false;
}
// alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
// as array references. Note that this function is heavily tail recursive.
// Hopefully we have a smart C++ compiler. :)
//
AliasAnalysis::AliasResult
BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
const Value *V2, unsigned V2Size) {
// Strip off any constant expression casts if they exist
if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
V1 = CE->getOperand(0);
if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
V2 = CE->getOperand(0);
// Are we checking for alias of the same value?
if (V1 == V2) return MustAlias;
if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
V1->getType() != Type::Int64Ty && V2->getType() != Type::Int64Ty)
return NoAlias; // Scalars cannot alias each other
// Strip off cast instructions...
if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
return alias(I->getOperand(0), V1Size, V2, V2Size);
if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
return alias(V1, V1Size, I->getOperand(0), V2Size);
// Figure out what objects these things are pointing to if we can...
const Value *O1 = getUnderlyingObject(V1);
const Value *O2 = getUnderlyingObject(V2);
// Pointing at a discernible object?
if (O1) {
if (O2) {
if (const Argument *O1Arg = dyn_cast<Argument>(O1)) {
// Incoming argument cannot alias locally allocated object!
if (isa<AllocationInst>(O2)) return NoAlias;
// If they are two different objects, and one is a noalias argument
// then they do not alias.
if (O1 != O2 && isNoAliasArgument(O1Arg))
return NoAlias;
// Otherwise, nothing is known...
}
if (const Argument *O2Arg = dyn_cast<Argument>(O2)) {
// Incoming argument cannot alias locally allocated object!
if (isa<AllocationInst>(O1)) return NoAlias;
// If they are two different objects, and one is a noalias argument
// then they do not alias.
if (O1 != O2 && isNoAliasArgument(O2Arg))
return NoAlias;
// Otherwise, nothing is known...
} else if (O1 != O2) {
// If they are two different objects, we know that we have no alias...
return NoAlias;
}
// If they are the same object, they we can look at the indexes. If they
// index off of the object is the same for both pointers, they must alias.
// If they are provably different, they must not alias. Otherwise, we
// can't tell anything.
}
if (!isa<Argument>(O1) && isa<ConstantPointerNull>(V2))
return NoAlias; // Unique values don't alias null
if (isa<GlobalVariable>(O1) ||
(isa<AllocationInst>(O1) &&
!cast<AllocationInst>(O1)->isArrayAllocation()))
if (cast<PointerType>(O1->getType())->getElementType()->isSized()) {
// If the size of the other access is larger than the total size of the
// global/alloca/malloc, it cannot be accessing the global (it's
// undefined to load or store bytes before or after an object).
const Type *ElTy = cast<PointerType>(O1->getType())->getElementType();
unsigned GlobalSize = getTargetData().getTypeSize(ElTy);
if (GlobalSize < V2Size && V2Size != ~0U)
return NoAlias;
}
}
if (O2) {
if (!isa<Argument>(O2) && isa<ConstantPointerNull>(V1))
return NoAlias; // Unique values don't alias null
if (isa<GlobalVariable>(O2) ||
(isa<AllocationInst>(O2) &&
!cast<AllocationInst>(O2)->isArrayAllocation()))
if (cast<PointerType>(O2->getType())->getElementType()->isSized()) {
// If the size of the other access is larger than the total size of the
// global/alloca/malloc, it cannot be accessing the object (it's
// undefined to load or store bytes before or after an object).
const Type *ElTy = cast<PointerType>(O2->getType())->getElementType();
unsigned GlobalSize = getTargetData().getTypeSize(ElTy);
if (GlobalSize < V1Size && V1Size != ~0U)
return NoAlias;
}
}
// If we have two gep instructions with must-alias'ing base pointers, figure
// out if the indexes to the GEP tell us anything about the derived pointer.
// Note that we also handle chains of getelementptr instructions as well as
// constant expression getelementptrs here.
//
if (isGEP(V1) && isGEP(V2)) {
// Drill down into the first non-gep value, to test for must-aliasing of
// the base pointers.
const Value *BasePtr1 = V1, *BasePtr2 = V2;
do {
BasePtr1 = cast<User>(BasePtr1)->getOperand(0);
} while (isGEP(BasePtr1) &&
cast<User>(BasePtr1)->getOperand(1) ==
Constant::getNullValue(cast<User>(BasePtr1)->getOperand(1)->getType()));
do {
BasePtr2 = cast<User>(BasePtr2)->getOperand(0);
} while (isGEP(BasePtr2) &&
cast<User>(BasePtr2)->getOperand(1) ==
Constant::getNullValue(cast<User>(BasePtr2)->getOperand(1)->getType()));
// Do the base pointers alias?
AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
if (BaseAlias == NoAlias) return NoAlias;
if (BaseAlias == MustAlias) {
// If the base pointers alias each other exactly, check to see if we can
// figure out anything about the resultant pointers, to try to prove
// non-aliasing.
// Collect all of the chained GEP operands together into one simple place
SmallVector<Value*, 16> GEP1Ops, GEP2Ops;
BasePtr1 = GetGEPOperands(V1, GEP1Ops);
BasePtr2 = GetGEPOperands(V2, GEP2Ops);
// If GetGEPOperands were able to fold to the same must-aliased pointer,
// do the comparison.
if (BasePtr1 == BasePtr2) {
AliasResult GAlias =
CheckGEPInstructions(BasePtr1->getType(),
&GEP1Ops[0], GEP1Ops.size(), V1Size,
BasePtr2->getType(),
&GEP2Ops[0], GEP2Ops.size(), V2Size);
if (GAlias != MayAlias)
return GAlias;
}
}
}
// Check to see if these two pointers are related by a getelementptr
// instruction. If one pointer is a GEP with a non-zero index of the other
// pointer, we know they cannot alias.
//
if (isGEP(V2)) {
std::swap(V1, V2);
std::swap(V1Size, V2Size);
}
if (V1Size != ~0U && V2Size != ~0U)
if (isGEP(V1)) {
SmallVector<Value*, 16> GEPOperands;
const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
if (R == MustAlias) {
// If there is at least one non-zero constant index, we know they cannot
// alias.
bool ConstantFound = false;
bool AllZerosFound = true;
for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
if (!C->isNullValue()) {
ConstantFound = true;
AllZerosFound = false;
break;
}
} else {
AllZerosFound = false;
}
// If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
// the ptr, the end result is a must alias also.
if (AllZerosFound)
return MustAlias;
if (ConstantFound) {
if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
return NoAlias;
// Otherwise we have to check to see that the distance is more than
// the size of the argument... build an index vector that is equal to
// the arguments provided, except substitute 0's for any variable
// indexes we find...
if (cast<PointerType>(
BasePtr->getType())->getElementType()->isSized()) {
for (unsigned i = 0; i != GEPOperands.size(); ++i)
if (!isa<ConstantInt>(GEPOperands[i]))
GEPOperands[i] =
Constant::getNullValue(GEPOperands[i]->getType());
int64_t Offset =
getTargetData().getIndexedOffset(BasePtr->getType(),
&GEPOperands[0],
GEPOperands.size());
if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
return NoAlias;
}
}
}
}
return MayAlias;
}
// This function is used to determin if the indices of two GEP instructions are
// equal. V1 and V2 are the indices.
static bool IndexOperandsEqual(Value *V1, Value *V2) {
if (V1->getType() == V2->getType())
return V1 == V2;
if (Constant *C1 = dyn_cast<Constant>(V1))
if (Constant *C2 = dyn_cast<Constant>(V2)) {
// Sign extend the constants to long types, if necessary
if (C1->getType() != Type::Int64Ty)
C1 = ConstantExpr::getSExt(C1, Type::Int64Ty);
if (C2->getType() != Type::Int64Ty)
C2 = ConstantExpr::getSExt(C2, Type::Int64Ty);
return C1 == C2;
}
return false;
}
/// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
/// base pointers. This checks to see if the index expressions preclude the
/// pointers from aliasing...
AliasAnalysis::AliasResult
BasicAliasAnalysis::CheckGEPInstructions(
const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
// We currently can't handle the case when the base pointers have different
// primitive types. Since this is uncommon anyway, we are happy being
// extremely conservative.
if (BasePtr1Ty != BasePtr2Ty)
return MayAlias;
const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
// Find the (possibly empty) initial sequence of equal values... which are not
// necessarily constants.
unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
unsigned UnequalOper = 0;
while (UnequalOper != MinOperands &&
IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
// Advance through the type as we go...
++UnequalOper;
if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
else {
// If all operands equal each other, then the derived pointers must
// alias each other...
BasePtr1Ty = 0;
assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
"Ran out of type nesting, but not out of operands?");
return MustAlias;
}
}
// If we have seen all constant operands, and run out of indexes on one of the
// getelementptrs, check to see if the tail of the leftover one is all zeros.
// If so, return mustalias.
if (UnequalOper == MinOperands) {
if (NumGEP1Ops < NumGEP2Ops) {
std::swap(GEP1Ops, GEP2Ops);
std::swap(NumGEP1Ops, NumGEP2Ops);
}
bool AllAreZeros = true;
for (unsigned i = UnequalOper; i != MaxOperands; ++i)
if (!isa<Constant>(GEP1Ops[i]) ||
!cast<Constant>(GEP1Ops[i])->isNullValue()) {
AllAreZeros = false;
break;
}
if (AllAreZeros) return MustAlias;
}
// So now we know that the indexes derived from the base pointers,
// which are known to alias, are different. We can still determine a
// no-alias result if there are differing constant pairs in the index
// chain. For example:
// A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
//
// We have to be careful here about array accesses. In particular, consider:
// A[1][0] vs A[0][i]
// In this case, we don't *know* that the array will be accessed in bounds:
// the index could even be negative. Because of this, we have to
// conservatively *give up* and return may alias. We disregard differing
// array subscripts that are followed by a variable index without going
// through a struct.
//
unsigned SizeMax = std::max(G1S, G2S);
if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
// Scan for the first operand that is constant and unequal in the
// two getelementptrs...
unsigned FirstConstantOper = UnequalOper;
for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
const Value *G1Oper = GEP1Ops[FirstConstantOper];
const Value *G2Oper = GEP2Ops[FirstConstantOper];
if (G1Oper != G2Oper) // Found non-equal constant indexes...
if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
if (G1OC->getType() != G2OC->getType()) {
// Sign extend both operands to long.
if (G1OC->getType() != Type::Int64Ty)
G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty);
if (G2OC->getType() != Type::Int64Ty)
G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty);
GEP1Ops[FirstConstantOper] = G1OC;
GEP2Ops[FirstConstantOper] = G2OC;
}
if (G1OC != G2OC) {
// Handle the "be careful" case above: if this is an array/vector
// subscript, scan for a subsequent variable array index.
if (isa<SequentialType>(BasePtr1Ty)) {
const Type *NextTy =
cast<SequentialType>(BasePtr1Ty)->getElementType();
bool isBadCase = false;
for (unsigned Idx = FirstConstantOper+1;
Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
isBadCase = true;
break;
}
NextTy = cast<SequentialType>(NextTy)->getElementType();
}
if (isBadCase) G1OC = 0;
}
// Make sure they are comparable (ie, not constant expressions), and
// make sure the GEP with the smaller leading constant is GEP1.
if (G1OC) {
Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
G1OC, G2OC);
if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
if (CV->getZExtValue()) { // If they are comparable and G2 > G1
std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
std::swap(NumGEP1Ops, NumGEP2Ops);
}
break;
}
}
}
}
BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
}
// No shared constant operands, and we ran out of common operands. At this
// point, the GEP instructions have run through all of their operands, and we
// haven't found evidence that there are any deltas between the GEP's.
// However, one GEP may have more operands than the other. If this is the
// case, there may still be hope. Check this now.
if (FirstConstantOper == MinOperands) {
// Make GEP1Ops be the longer one if there is a longer one.
if (NumGEP1Ops < NumGEP2Ops) {
std::swap(GEP1Ops, GEP2Ops);
std::swap(NumGEP1Ops, NumGEP2Ops);
}
// Is there anything to check?
if (NumGEP1Ops > MinOperands) {
for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
if (isa<ConstantInt>(GEP1Ops[i]) &&
!cast<ConstantInt>(GEP1Ops[i])->isZero()) {
// Yup, there's a constant in the tail. Set all variables to
// constants in the GEP instruction to make it suiteable for
// TargetData::getIndexedOffset.
for (i = 0; i != MaxOperands; ++i)
if (!isa<ConstantInt>(GEP1Ops[i]))
GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
// Okay, now get the offset. This is the relative offset for the full
// instruction.
const TargetData &TD = getTargetData();
int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
NumGEP1Ops);
// Now check without any constants at the end.
int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
MinOperands);
// If the tail provided a bit enough offset, return noalias!
if ((uint64_t)(Offset2-Offset1) >= SizeMax)
return NoAlias;
}
}
// Couldn't find anything useful.
return MayAlias;
}
// If there are non-equal constants arguments, then we can figure
// out a minimum known delta between the two index expressions... at
// this point we know that the first constant index of GEP1 is less
// than the first constant index of GEP2.
// Advance BasePtr[12]Ty over this first differing constant operand.
BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
getTypeAtIndex(GEP2Ops[FirstConstantOper]);
BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
getTypeAtIndex(GEP1Ops[FirstConstantOper]);
// We are going to be using TargetData::getIndexedOffset to determine the
// offset that each of the GEP's is reaching. To do this, we have to convert
// all variable references to constant references. To do this, we convert the
// initial sequence of array subscripts into constant zeros to start with.
const Type *ZeroIdxTy = GEPPointerTy;
for (unsigned i = 0; i != FirstConstantOper; ++i) {
if (!isa<StructType>(ZeroIdxTy))
GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty);
if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
}
// We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
// Loop over the rest of the operands...
for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
// If they are equal, use a zero index...
if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
if (!isa<ConstantInt>(Op1))
GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
// Otherwise, just keep the constants we have.
} else {
if (Op1) {
if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
// If this is an array index, make sure the array element is in range.
if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
if (Op1C->getZExtValue() >= AT->getNumElements())
return MayAlias; // Be conservative with out-of-range accesses
} else if (const VectorType *PT = dyn_cast<VectorType>(BasePtr1Ty)) {
if (Op1C->getZExtValue() >= PT->getNumElements())
return MayAlias; // Be conservative with out-of-range accesses
}
} else {
// GEP1 is known to produce a value less than GEP2. To be
// conservatively correct, we must assume the largest possible
// constant is used in this position. This cannot be the initial
// index to the GEP instructions (because we know we have at least one
// element before this one with the different constant arguments), so
// we know that the current index must be into either a struct or
// array. Because we know it's not constant, this cannot be a
// structure index. Because of this, we can calculate the maximum
// value possible.
//
if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1);
else if (const VectorType *PT = dyn_cast<VectorType>(BasePtr1Ty))
GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,PT->getNumElements()-1);
}
}
if (Op2) {
if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
// If this is an array index, make sure the array element is in range.
if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
if (Op2C->getZExtValue() >= AT->getNumElements())
return MayAlias; // Be conservative with out-of-range accesses
} else if (const VectorType *PT = dyn_cast<VectorType>(BasePtr1Ty)) {
if (Op2C->getZExtValue() >= PT->getNumElements())
return MayAlias; // Be conservative with out-of-range accesses
}
} else { // Conservatively assume the minimum value for this index
GEP2Ops[i] = Constant::getNullValue(Op2->getType());
}
}
}
if (BasePtr1Ty && Op1) {
if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
else
BasePtr1Ty = 0;
}
if (BasePtr2Ty && Op2) {
if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
else
BasePtr2Ty = 0;
}
}
if (GEPPointerTy->getElementType()->isSized()) {
int64_t Offset1 =
getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
int64_t Offset2 =
getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
assert(Offset1<Offset2 && "There is at least one different constant here!");
if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
//cerr << "Determined that these two GEP's don't alias ["
// << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
return NoAlias;
}
}
return MayAlias;
}
namespace {
struct VISIBILITY_HIDDEN StringCompare {
bool operator()(const char *LHS, const char *RHS) {
return strcmp(LHS, RHS) < 0;
}
};
}
// Note that this list cannot contain libm functions (such as acos and sqrt)
// that set errno on a domain or other error.
static const char *DoesntAccessMemoryFns[] = {
"abs", "labs", "llabs", "imaxabs", "fabs", "fabsf", "fabsl",
"trunc", "truncf", "truncl", "ldexp",
"atan", "atanf", "atanl", "atan2", "atan2f", "atan2l",
"cbrt",
"cos", "cosf", "cosl",
"exp", "expf", "expl",
"hypot",
"sin", "sinf", "sinl",
"tan", "tanf", "tanl", "tanh", "tanhf", "tanhl",
"floor", "floorf", "floorl", "ceil", "ceilf", "ceill",
// ctype.h
"isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower", "isprint"
"ispunct", "isspace", "isupper", "isxdigit", "tolower", "toupper",
// wctype.h"
"iswalnum", "iswalpha", "iswcntrl", "iswdigit", "iswgraph", "iswlower",
"iswprint", "iswpunct", "iswspace", "iswupper", "iswxdigit",
"iswctype", "towctrans", "towlower", "towupper",
"btowc", "wctob",
"isinf", "isnan", "finite",
// C99 math functions
"copysign", "copysignf", "copysignd",
"nexttoward", "nexttowardf", "nexttowardd",
"nextafter", "nextafterf", "nextafterd",
// ISO C99:
"__signbit", "__signbitf", "__signbitl",
};
static const char *OnlyReadsMemoryFns[] = {
"atoi", "atol", "atof", "atoll", "atoq", "a64l",
"bcmp", "memcmp", "memchr", "memrchr", "wmemcmp", "wmemchr",
// Strings
"strcmp", "strcasecmp", "strcoll", "strncmp", "strncasecmp",
"strchr", "strcspn", "strlen", "strpbrk", "strrchr", "strspn", "strstr",
"index", "rindex",
// Wide char strings
"wcschr", "wcscmp", "wcscoll", "wcscspn", "wcslen", "wcsncmp", "wcspbrk",
"wcsrchr", "wcsspn", "wcsstr",
// glibc
"alphasort", "alphasort64", "versionsort", "versionsort64",
// C99
"nan", "nanf", "nand",
// File I/O
"feof", "ferror", "fileno",
"feof_unlocked", "ferror_unlocked", "fileno_unlocked"
};
static ManagedStatic<std::vector<const char*> > NoMemoryTable;
static ManagedStatic<std::vector<const char*> > OnlyReadsMemoryTable;
static ManagedStatic<BitVector> NoMemoryIntrinsics;
static ManagedStatic<BitVector> OnlyReadsMemoryIntrinsics;
AliasAnalysis::ModRefBehavior
BasicAliasAnalysis::getModRefBehavior(Function *F, CallSite CS,
std::vector<PointerAccessInfo> *Info) {
if (!F->isDeclaration()) return UnknownModRefBehavior;
static bool Initialized = false;
if (!Initialized) {
NoMemoryTable->insert(NoMemoryTable->end(),
DoesntAccessMemoryFns,
array_endof(DoesntAccessMemoryFns));
OnlyReadsMemoryTable->insert(OnlyReadsMemoryTable->end(),
OnlyReadsMemoryFns,
array_endof(OnlyReadsMemoryFns));
// Sort the table the first time through.
std::sort(NoMemoryTable->begin(), NoMemoryTable->end(), StringCompare());
std::sort(OnlyReadsMemoryTable->begin(), OnlyReadsMemoryTable->end(),
StringCompare());
NoMemoryIntrinsics->resize(Intrinsic::num_intrinsics);
OnlyReadsMemoryIntrinsics->resize(Intrinsic::num_intrinsics);
#define GET_MODREF_BEHAVIOR
#include "llvm/Intrinsics.gen"
#undef GET_MODREF_BEHAVIOR
Initialized = true;
}
// If this is an intrinsic, we can use lookup tables
if (unsigned id = F->getIntrinsicID()) {
if (NoMemoryIntrinsics->test(id))
return DoesNotAccessMemory;
if (OnlyReadsMemoryIntrinsics->test(id))
return OnlyReadsMemory;
return UnknownModRefBehavior;
}
ValueName *Name = F->getValueName();
unsigned NameLen = Name->getKeyLength();
const char *NamePtr = Name->getKeyData();
// If there is an embedded nul character in the function name, we can never
// match it.
if (strlen(NamePtr) != NameLen)
return UnknownModRefBehavior;
std::vector<const char*>::iterator Ptr =
std::lower_bound(NoMemoryTable->begin(), NoMemoryTable->end(),
NamePtr, StringCompare());
if (Ptr != NoMemoryTable->end() && strcmp(*Ptr, NamePtr) == 0)
return DoesNotAccessMemory;
Ptr = std::lower_bound(OnlyReadsMemoryTable->begin(),
OnlyReadsMemoryTable->end(),
NamePtr, StringCompare());
if (Ptr != OnlyReadsMemoryTable->end() && strcmp(*Ptr, NamePtr) == 0)
return OnlyReadsMemory;
return UnknownModRefBehavior;
}
// Make sure that anything that uses AliasAnalysis pulls in this file...
DEFINING_FILE_FOR(BasicAliasAnalysis)
|