1 //===- BasicAliasAnalysis.cpp - Local Alias Analysis Impl -----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines the default implementation of the Alias Analysis interface
11 // that simply implements a few identities (two different globals cannot alias,
12 // etc), but otherwise does no analysis.
14 //===----------------------------------------------------------------------===//
16 #include "llvm/Analysis/AliasAnalysis.h"
17 #include "llvm/Analysis/Passes.h"
18 #include "llvm/Constants.h"
19 #include "llvm/DerivedTypes.h"
20 #include "llvm/Function.h"
21 #include "llvm/GlobalVariable.h"
22 #include "llvm/Instructions.h"
23 #include "llvm/IntrinsicInst.h"
24 #include "llvm/Pass.h"
25 #include "llvm/Target/TargetData.h"
26 #include "llvm/ADT/SmallVector.h"
27 #include "llvm/ADT/STLExtras.h"
28 #include "llvm/Support/Compiler.h"
29 #include "llvm/Support/GetElementPtrTypeIterator.h"
30 #include "llvm/Support/ManagedStatic.h"
34 //===----------------------------------------------------------------------===//
36 //===----------------------------------------------------------------------===//
38 // Determine if an AllocationInst instruction escapes from the function it is
39 // contained in. If it does not escape, there is no way for another function to
40 // mod/ref it. We do this by looking at its uses and determining if the uses
41 // can escape (recursively).
42 static bool AddressMightEscape(const Value *V) {
43 for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
45 const Instruction *I = cast<Instruction>(*UI);
46 switch (I->getOpcode()) {
47 case Instruction::Load:
49 case Instruction::Store:
50 if (I->getOperand(0) == V)
51 return true; // Escapes if the pointer is stored.
53 case Instruction::GetElementPtr:
54 if (AddressMightEscape(I))
57 case Instruction::BitCast:
58 if (AddressMightEscape(I))
61 case Instruction::Ret:
62 // If returned, the address will escape to calling functions, but no
63 // callees could modify it.
65 case Instruction::Call:
66 // If the call is to a few known safe intrinsics, we know that it does
68 // TODO: Eventually just check the 'nocapture' attribute.
69 if (!isa<MemIntrinsic>(I))
79 static const User *isGEP(const Value *V) {
80 if (isa<GetElementPtrInst>(V) ||
81 (isa<ConstantExpr>(V) &&
82 cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
87 static const Value *GetGEPOperands(const Value *V,
88 SmallVector<Value*, 16> &GEPOps){
89 assert(GEPOps.empty() && "Expect empty list to populate!");
90 GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
91 cast<User>(V)->op_end());
93 // Accumulate all of the chained indexes into the operand array
94 V = cast<User>(V)->getOperand(0);
96 while (const User *G = isGEP(V)) {
97 if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
98 !cast<Constant>(GEPOps[0])->isNullValue())
99 break; // Don't handle folding arbitrary pointer offsets yet...
100 GEPOps.erase(GEPOps.begin()); // Drop the zero index
101 GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
102 V = G->getOperand(0);
107 /// isNoAliasCall - Return true if this pointer is returned by a noalias
109 static bool isNoAliasCall(const Value *V) {
110 if (isa<CallInst>(V) || isa<InvokeInst>(V))
111 return CallSite(const_cast<Instruction*>(cast<Instruction>(V)))
112 .paramHasAttr(0, Attribute::NoAlias);
116 /// isIdentifiedObject - Return true if this pointer refers to a distinct and
117 /// identifiable object. This returns true for:
118 /// Global Variables and Functions
119 /// Allocas and Mallocs
120 /// ByVal and NoAlias Arguments
123 static bool isIdentifiedObject(const Value *V) {
124 if (isa<GlobalValue>(V) || isa<AllocationInst>(V) || isNoAliasCall(V))
126 if (const Argument *A = dyn_cast<Argument>(V))
127 return A->hasNoAliasAttr() || A->hasByValAttr();
131 /// isKnownNonNull - Return true if we know that the specified value is never
133 static bool isKnownNonNull(const Value *V) {
134 // Alloca never returns null, malloc might.
135 if (isa<AllocaInst>(V)) return true;
137 // A byval argument is never null.
138 if (const Argument *A = dyn_cast<Argument>(V))
139 return A->hasByValAttr();
141 // Global values are not null unless extern weak.
142 if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
143 return !GV->hasExternalWeakLinkage();
147 /// isNonEscapingLocalObject - Return true if the pointer is to a function-local
148 /// object that never escapes from the function.
149 static bool isNonEscapingLocalObject(const Value *V) {
150 // If this is a local allocation, check to see if it escapes.
151 if (isa<AllocationInst>(V) || isNoAliasCall(V))
152 return !AddressMightEscape(V);
154 // If this is an argument that corresponds to a byval or noalias argument,
155 // it can't escape either.
156 if (const Argument *A = dyn_cast<Argument>(V))
157 if (A->hasByValAttr() || A->hasNoAliasAttr())
158 return !AddressMightEscape(V);
163 /// isObjectSmallerThan - Return true if we can prove that the object specified
164 /// by V is smaller than Size.
165 static bool isObjectSmallerThan(const Value *V, unsigned Size,
166 const TargetData &TD) {
167 const Type *AccessTy;
168 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
169 AccessTy = GV->getType()->getElementType();
170 } else if (const AllocationInst *AI = dyn_cast<AllocationInst>(V)) {
171 if (!AI->isArrayAllocation())
172 AccessTy = AI->getType()->getElementType();
175 } else if (const Argument *A = dyn_cast<Argument>(V)) {
176 if (A->hasByValAttr())
177 AccessTy = cast<PointerType>(A->getType())->getElementType();
184 if (AccessTy->isSized())
185 return TD.getABITypeSize(AccessTy) < Size;
189 //===----------------------------------------------------------------------===//
191 //===----------------------------------------------------------------------===//
194 /// NoAA - This class implements the -no-aa pass, which always returns "I
195 /// don't know" for alias queries. NoAA is unlike other alias analysis
196 /// implementations, in that it does not chain to a previous analysis. As
197 /// such it doesn't follow many of the rules that other alias analyses must.
199 struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
200 static char ID; // Class identification, replacement for typeinfo
201 NoAA() : ImmutablePass(&ID) {}
202 explicit NoAA(void *PID) : ImmutablePass(PID) { }
204 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
205 AU.addRequired<TargetData>();
208 virtual void initializePass() {
209 TD = &getAnalysis<TargetData>();
212 virtual AliasResult alias(const Value *V1, unsigned V1Size,
213 const Value *V2, unsigned V2Size) {
217 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
218 std::vector<PointerAccessInfo> *Info) {
219 return UnknownModRefBehavior;
222 virtual void getArgumentAccesses(Function *F, CallSite CS,
223 std::vector<PointerAccessInfo> &Info) {
224 assert(0 && "This method may not be called on this function!");
227 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
228 virtual bool pointsToConstantMemory(const Value *P) { return false; }
229 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
232 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
235 virtual bool hasNoModRefInfoForCalls() const { return true; }
237 virtual void deleteValue(Value *V) {}
238 virtual void copyValue(Value *From, Value *To) {}
240 } // End of anonymous namespace
242 // Register this pass...
244 static RegisterPass<NoAA>
245 U("no-aa", "No Alias Analysis (always returns 'may' alias)", true, true);
247 // Declare that we implement the AliasAnalysis interface
248 static RegisterAnalysisGroup<AliasAnalysis> V(U);
250 ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
252 //===----------------------------------------------------------------------===//
254 //===----------------------------------------------------------------------===//
257 /// BasicAliasAnalysis - This is the default alias analysis implementation.
258 /// Because it doesn't chain to a previous alias analysis (like -no-aa), it
259 /// derives from the NoAA class.
260 struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA {
261 static char ID; // Class identification, replacement for typeinfo
262 BasicAliasAnalysis() : NoAA(&ID) {}
263 AliasResult alias(const Value *V1, unsigned V1Size,
264 const Value *V2, unsigned V2Size);
266 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
267 ModRefResult getModRefInfo(CallSite CS1, CallSite CS2);
269 /// hasNoModRefInfoForCalls - We can provide mod/ref information against
270 /// non-escaping allocations.
271 virtual bool hasNoModRefInfoForCalls() const { return false; }
273 /// pointsToConstantMemory - Chase pointers until we find a (constant
275 bool pointsToConstantMemory(const Value *P);
278 // CheckGEPInstructions - Check two GEP instructions with known
279 // must-aliasing base pointers. This checks to see if the index expressions
280 // preclude the pointers from aliasing...
282 CheckGEPInstructions(const Type* BasePtr1Ty,
283 Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size,
284 const Type *BasePtr2Ty,
285 Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size);
287 } // End of anonymous namespace
289 // Register this pass...
290 char BasicAliasAnalysis::ID = 0;
291 static RegisterPass<BasicAliasAnalysis>
292 X("basicaa", "Basic Alias Analysis (default AA impl)", false, true);
294 // Declare that we implement the AliasAnalysis interface
295 static RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
297 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
298 return new BasicAliasAnalysis();
302 /// pointsToConstantMemory - Chase pointers until we find a (constant
304 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
305 if (const GlobalVariable *GV =
306 dyn_cast<GlobalVariable>(P->getUnderlyingObject()))
307 return GV->isConstant();
311 // getModRefInfo - Check to see if the specified callsite can clobber the
312 // specified memory object. Since we only look at local properties of this
313 // function, we really can't say much about this query. We do, however, use
314 // simple "address taken" analysis on local objects.
316 AliasAnalysis::ModRefResult
317 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
318 if (!isa<Constant>(P)) {
319 const Value *Object = P->getUnderlyingObject();
321 // If this is a tail call and P points to a stack location, we know that
322 // the tail call cannot access or modify the local stack.
323 // We cannot exclude byval arguments here; these belong to the caller of
324 // the current function not to the current function, and a tail callee
325 // may reference them.
326 if (isa<AllocaInst>(Object))
327 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
328 if (CI->isTailCall())
331 // If the pointer is to a locally allocated object that does not escape,
332 // then the call can not mod/ref the pointer unless the call takes the
333 // argument without capturing it.
334 if (isNonEscapingLocalObject(Object)) {
335 bool passedAsArg = false;
336 // TODO: Eventually only check 'nocapture' arguments.
337 for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
339 if (isa<PointerType>((*CI)->getType()) &&
340 alias(cast<Value>(CI), ~0U, P, ~0U) != NoAlias)
348 // The AliasAnalysis base class has some smarts, lets use them.
349 return AliasAnalysis::getModRefInfo(CS, P, Size);
353 AliasAnalysis::ModRefResult
354 BasicAliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) {
355 // If CS1 or CS2 are readnone, they don't interact.
356 ModRefBehavior CS1B = AliasAnalysis::getModRefBehavior(CS1);
357 if (CS1B == DoesNotAccessMemory) return NoModRef;
359 ModRefBehavior CS2B = AliasAnalysis::getModRefBehavior(CS2);
360 if (CS2B == DoesNotAccessMemory) return NoModRef;
362 // If they both only read from memory, just return ref.
363 if (CS1B == OnlyReadsMemory && CS2B == OnlyReadsMemory)
366 // Otherwise, fall back to NoAA (mod+ref).
367 return NoAA::getModRefInfo(CS1, CS2);
371 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
372 // as array references. Note that this function is heavily tail recursive.
373 // Hopefully we have a smart C++ compiler. :)
375 AliasAnalysis::AliasResult
376 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
377 const Value *V2, unsigned V2Size) {
378 // Strip off any constant expression casts if they exist
379 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
380 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
381 V1 = CE->getOperand(0);
382 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
383 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
384 V2 = CE->getOperand(0);
386 // Are we checking for alias of the same value?
387 if (V1 == V2) return MustAlias;
389 if (!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType()))
390 return NoAlias; // Scalars cannot alias each other
392 // Strip off cast instructions...
393 if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
394 return alias(I->getOperand(0), V1Size, V2, V2Size);
395 if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
396 return alias(V1, V1Size, I->getOperand(0), V2Size);
398 // Figure out what objects these things are pointing to if we can...
399 const Value *O1 = V1->getUnderlyingObject();
400 const Value *O2 = V2->getUnderlyingObject();
403 // If V1/V2 point to two different objects we know that we have no alias.
404 if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
407 // Arguments can't alias with local allocations or noalias calls.
408 if ((isa<Argument>(O1) && (isa<AllocationInst>(O2) || isNoAliasCall(O2))) ||
409 (isa<Argument>(O2) && (isa<AllocationInst>(O1) || isNoAliasCall(O1))))
412 // Most objects can't alias null.
413 if ((isa<ConstantPointerNull>(V2) && isKnownNonNull(O1)) ||
414 (isa<ConstantPointerNull>(V1) && isKnownNonNull(O2)))
418 // If the size of one access is larger than the entire object on the other
419 // side, then we know such behavior is undefined and can assume no alias.
420 const TargetData &TD = getTargetData();
421 if ((V1Size != ~0U && isObjectSmallerThan(O2, V1Size, TD)) ||
422 (V2Size != ~0U && isObjectSmallerThan(O1, V2Size, TD)))
425 // If one pointer is the result of a call/invoke and the other is a
426 // non-escaping local object, then we know the object couldn't escape to a
427 // point where the call could return it.
428 if ((isa<CallInst>(O1) || isa<InvokeInst>(O1)) &&
429 isNonEscapingLocalObject(O2))
431 if ((isa<CallInst>(O2) || isa<InvokeInst>(O2)) &&
432 isNonEscapingLocalObject(O1))
435 // If we have two gep instructions with must-alias'ing base pointers, figure
436 // out if the indexes to the GEP tell us anything about the derived pointer.
437 // Note that we also handle chains of getelementptr instructions as well as
438 // constant expression getelementptrs here.
440 if (isGEP(V1) && isGEP(V2)) {
441 // Drill down into the first non-gep value, to test for must-aliasing of
442 // the base pointers.
443 const User *G = cast<User>(V1);
444 while (isGEP(G->getOperand(0)) &&
446 Constant::getNullValue(G->getOperand(1)->getType()))
447 G = cast<User>(G->getOperand(0));
448 const Value *BasePtr1 = G->getOperand(0);
451 while (isGEP(G->getOperand(0)) &&
453 Constant::getNullValue(G->getOperand(1)->getType()))
454 G = cast<User>(G->getOperand(0));
455 const Value *BasePtr2 = G->getOperand(0);
457 // Do the base pointers alias?
458 AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
459 if (BaseAlias == NoAlias) return NoAlias;
460 if (BaseAlias == MustAlias) {
461 // If the base pointers alias each other exactly, check to see if we can
462 // figure out anything about the resultant pointers, to try to prove
465 // Collect all of the chained GEP operands together into one simple place
466 SmallVector<Value*, 16> GEP1Ops, GEP2Ops;
467 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
468 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
470 // If GetGEPOperands were able to fold to the same must-aliased pointer,
471 // do the comparison.
472 if (BasePtr1 == BasePtr2) {
474 CheckGEPInstructions(BasePtr1->getType(),
475 &GEP1Ops[0], GEP1Ops.size(), V1Size,
477 &GEP2Ops[0], GEP2Ops.size(), V2Size);
478 if (GAlias != MayAlias)
484 // Check to see if these two pointers are related by a getelementptr
485 // instruction. If one pointer is a GEP with a non-zero index of the other
486 // pointer, we know they cannot alias.
490 std::swap(V1Size, V2Size);
493 if (V1Size != ~0U && V2Size != ~0U)
495 SmallVector<Value*, 16> GEPOperands;
496 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
498 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
499 if (R == MustAlias) {
500 // If there is at least one non-zero constant index, we know they cannot
502 bool ConstantFound = false;
503 bool AllZerosFound = true;
504 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
505 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
506 if (!C->isNullValue()) {
507 ConstantFound = true;
508 AllZerosFound = false;
512 AllZerosFound = false;
515 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
516 // the ptr, the end result is a must alias also.
521 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
524 // Otherwise we have to check to see that the distance is more than
525 // the size of the argument... build an index vector that is equal to
526 // the arguments provided, except substitute 0's for any variable
527 // indexes we find...
528 if (cast<PointerType>(
529 BasePtr->getType())->getElementType()->isSized()) {
530 for (unsigned i = 0; i != GEPOperands.size(); ++i)
531 if (!isa<ConstantInt>(GEPOperands[i]))
533 Constant::getNullValue(GEPOperands[i]->getType());
535 getTargetData().getIndexedOffset(BasePtr->getType(),
539 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
549 // This function is used to determine if the indices of two GEP instructions are
550 // equal. V1 and V2 are the indices.
551 static bool IndexOperandsEqual(Value *V1, Value *V2) {
552 if (V1->getType() == V2->getType())
554 if (Constant *C1 = dyn_cast<Constant>(V1))
555 if (Constant *C2 = dyn_cast<Constant>(V2)) {
556 // Sign extend the constants to long types, if necessary
557 if (C1->getType() != Type::Int64Ty)
558 C1 = ConstantExpr::getSExt(C1, Type::Int64Ty);
559 if (C2->getType() != Type::Int64Ty)
560 C2 = ConstantExpr::getSExt(C2, Type::Int64Ty);
566 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
567 /// base pointers. This checks to see if the index expressions preclude the
568 /// pointers from aliasing...
569 AliasAnalysis::AliasResult
570 BasicAliasAnalysis::CheckGEPInstructions(
571 const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
572 const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
573 // We currently can't handle the case when the base pointers have different
574 // primitive types. Since this is uncommon anyway, we are happy being
575 // extremely conservative.
576 if (BasePtr1Ty != BasePtr2Ty)
579 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
581 // Find the (possibly empty) initial sequence of equal values... which are not
582 // necessarily constants.
583 unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
584 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
585 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
586 unsigned UnequalOper = 0;
587 while (UnequalOper != MinOperands &&
588 IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
589 // Advance through the type as we go...
591 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
592 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
594 // If all operands equal each other, then the derived pointers must
595 // alias each other...
597 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
598 "Ran out of type nesting, but not out of operands?");
603 // If we have seen all constant operands, and run out of indexes on one of the
604 // getelementptrs, check to see if the tail of the leftover one is all zeros.
605 // If so, return mustalias.
606 if (UnequalOper == MinOperands) {
607 if (NumGEP1Ops < NumGEP2Ops) {
608 std::swap(GEP1Ops, GEP2Ops);
609 std::swap(NumGEP1Ops, NumGEP2Ops);
612 bool AllAreZeros = true;
613 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
614 if (!isa<Constant>(GEP1Ops[i]) ||
615 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
619 if (AllAreZeros) return MustAlias;
623 // So now we know that the indexes derived from the base pointers,
624 // which are known to alias, are different. We can still determine a
625 // no-alias result if there are differing constant pairs in the index
626 // chain. For example:
627 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
629 // We have to be careful here about array accesses. In particular, consider:
630 // A[1][0] vs A[0][i]
631 // In this case, we don't *know* that the array will be accessed in bounds:
632 // the index could even be negative. Because of this, we have to
633 // conservatively *give up* and return may alias. We disregard differing
634 // array subscripts that are followed by a variable index without going
637 unsigned SizeMax = std::max(G1S, G2S);
638 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
640 // Scan for the first operand that is constant and unequal in the
641 // two getelementptrs...
642 unsigned FirstConstantOper = UnequalOper;
643 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
644 const Value *G1Oper = GEP1Ops[FirstConstantOper];
645 const Value *G2Oper = GEP2Ops[FirstConstantOper];
647 if (G1Oper != G2Oper) // Found non-equal constant indexes...
648 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
649 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
650 if (G1OC->getType() != G2OC->getType()) {
651 // Sign extend both operands to long.
652 if (G1OC->getType() != Type::Int64Ty)
653 G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty);
654 if (G2OC->getType() != Type::Int64Ty)
655 G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty);
656 GEP1Ops[FirstConstantOper] = G1OC;
657 GEP2Ops[FirstConstantOper] = G2OC;
661 // Handle the "be careful" case above: if this is an array/vector
662 // subscript, scan for a subsequent variable array index.
663 if (isa<SequentialType>(BasePtr1Ty)) {
665 cast<SequentialType>(BasePtr1Ty)->getElementType();
666 bool isBadCase = false;
668 for (unsigned Idx = FirstConstantOper+1;
669 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
670 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
671 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
675 NextTy = cast<SequentialType>(NextTy)->getElementType();
678 if (isBadCase) G1OC = 0;
681 // Make sure they are comparable (ie, not constant expressions), and
682 // make sure the GEP with the smaller leading constant is GEP1.
684 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
686 if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
687 if (CV->getZExtValue()) { // If they are comparable and G2 > G1
688 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
689 std::swap(NumGEP1Ops, NumGEP2Ops);
696 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
699 // No shared constant operands, and we ran out of common operands. At this
700 // point, the GEP instructions have run through all of their operands, and we
701 // haven't found evidence that there are any deltas between the GEP's.
702 // However, one GEP may have more operands than the other. If this is the
703 // case, there may still be hope. Check this now.
704 if (FirstConstantOper == MinOperands) {
705 // Make GEP1Ops be the longer one if there is a longer one.
706 if (NumGEP1Ops < NumGEP2Ops) {
707 std::swap(GEP1Ops, GEP2Ops);
708 std::swap(NumGEP1Ops, NumGEP2Ops);
711 // Is there anything to check?
712 if (NumGEP1Ops > MinOperands) {
713 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
714 if (isa<ConstantInt>(GEP1Ops[i]) &&
715 !cast<ConstantInt>(GEP1Ops[i])->isZero()) {
716 // Yup, there's a constant in the tail. Set all variables to
717 // constants in the GEP instruction to make it suitable for
718 // TargetData::getIndexedOffset.
719 for (i = 0; i != MaxOperands; ++i)
720 if (!isa<ConstantInt>(GEP1Ops[i]))
721 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
722 // Okay, now get the offset. This is the relative offset for the full
724 const TargetData &TD = getTargetData();
725 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
728 // Now check without any constants at the end.
729 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
732 // Make sure we compare the absolute difference.
733 if (Offset1 > Offset2)
734 std::swap(Offset1, Offset2);
736 // If the tail provided a bit enough offset, return noalias!
737 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
739 // Otherwise break - we don't look for another constant in the tail.
744 // Couldn't find anything useful.
748 // If there are non-equal constants arguments, then we can figure
749 // out a minimum known delta between the two index expressions... at
750 // this point we know that the first constant index of GEP1 is less
751 // than the first constant index of GEP2.
753 // Advance BasePtr[12]Ty over this first differing constant operand.
754 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
755 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
756 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
757 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
759 // We are going to be using TargetData::getIndexedOffset to determine the
760 // offset that each of the GEP's is reaching. To do this, we have to convert
761 // all variable references to constant references. To do this, we convert the
762 // initial sequence of array subscripts into constant zeros to start with.
763 const Type *ZeroIdxTy = GEPPointerTy;
764 for (unsigned i = 0; i != FirstConstantOper; ++i) {
765 if (!isa<StructType>(ZeroIdxTy))
766 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty);
768 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
769 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
772 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
774 // Loop over the rest of the operands...
775 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
776 const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
777 const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
778 // If they are equal, use a zero index...
779 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
780 if (!isa<ConstantInt>(Op1))
781 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
782 // Otherwise, just keep the constants we have.
785 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
786 // If this is an array index, make sure the array element is in range.
787 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
788 if (Op1C->getZExtValue() >= AT->getNumElements())
789 return MayAlias; // Be conservative with out-of-range accesses
790 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) {
791 if (Op1C->getZExtValue() >= VT->getNumElements())
792 return MayAlias; // Be conservative with out-of-range accesses
796 // GEP1 is known to produce a value less than GEP2. To be
797 // conservatively correct, we must assume the largest possible
798 // constant is used in this position. This cannot be the initial
799 // index to the GEP instructions (because we know we have at least one
800 // element before this one with the different constant arguments), so
801 // we know that the current index must be into either a struct or
802 // array. Because we know it's not constant, this cannot be a
803 // structure index. Because of this, we can calculate the maximum
806 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
807 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1);
808 else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty))
809 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,VT->getNumElements()-1);
814 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
815 // If this is an array index, make sure the array element is in range.
816 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr2Ty)) {
817 if (Op2C->getZExtValue() >= AT->getNumElements())
818 return MayAlias; // Be conservative with out-of-range accesses
819 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr2Ty)) {
820 if (Op2C->getZExtValue() >= VT->getNumElements())
821 return MayAlias; // Be conservative with out-of-range accesses
823 } else { // Conservatively assume the minimum value for this index
824 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
829 if (BasePtr1Ty && Op1) {
830 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
831 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
836 if (BasePtr2Ty && Op2) {
837 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
838 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
844 if (GEPPointerTy->getElementType()->isSized()) {
846 getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
848 getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
849 assert(Offset1 != Offset2 &&
850 "There is at least one different constant here!");
852 // Make sure we compare the absolute difference.
853 if (Offset1 > Offset2)
854 std::swap(Offset1, Offset2);
856 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
857 //cerr << "Determined that these two GEP's don't alias ["
858 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
865 // Make sure that anything that uses AliasAnalysis pulls in this file...
866 DEFINING_FILE_FOR(BasicAliasAnalysis)