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 = 0;
168 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
169 AccessTy = GV->getType()->getElementType();
171 if (const AllocationInst *AI = dyn_cast<AllocationInst>(V))
172 if (!AI->isArrayAllocation())
173 AccessTy = AI->getType()->getElementType();
175 if (const Argument *A = dyn_cast<Argument>(V))
176 if (A->hasByValAttr())
177 AccessTy = cast<PointerType>(A->getType())->getElementType();
179 if (AccessTy && AccessTy->isSized())
180 return TD.getABITypeSize(AccessTy) < Size;
184 //===----------------------------------------------------------------------===//
186 //===----------------------------------------------------------------------===//
189 /// NoAA - This class implements the -no-aa pass, which always returns "I
190 /// don't know" for alias queries. NoAA is unlike other alias analysis
191 /// implementations, in that it does not chain to a previous analysis. As
192 /// such it doesn't follow many of the rules that other alias analyses must.
194 struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
195 static char ID; // Class identification, replacement for typeinfo
196 NoAA() : ImmutablePass(&ID) {}
197 explicit NoAA(void *PID) : ImmutablePass(PID) { }
199 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
200 AU.addRequired<TargetData>();
203 virtual void initializePass() {
204 TD = &getAnalysis<TargetData>();
207 virtual AliasResult alias(const Value *V1, unsigned V1Size,
208 const Value *V2, unsigned V2Size) {
212 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
213 std::vector<PointerAccessInfo> *Info) {
214 return UnknownModRefBehavior;
217 virtual void getArgumentAccesses(Function *F, CallSite CS,
218 std::vector<PointerAccessInfo> &Info) {
219 assert(0 && "This method may not be called on this function!");
222 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
223 virtual bool pointsToConstantMemory(const Value *P) { return false; }
224 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
227 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
230 virtual bool hasNoModRefInfoForCalls() const { return true; }
232 virtual void deleteValue(Value *V) {}
233 virtual void copyValue(Value *From, Value *To) {}
235 } // End of anonymous namespace
237 // Register this pass...
239 static RegisterPass<NoAA>
240 U("no-aa", "No Alias Analysis (always returns 'may' alias)", true, true);
242 // Declare that we implement the AliasAnalysis interface
243 static RegisterAnalysisGroup<AliasAnalysis> V(U);
245 ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
247 //===----------------------------------------------------------------------===//
249 //===----------------------------------------------------------------------===//
252 /// BasicAliasAnalysis - This is the default alias analysis implementation.
253 /// Because it doesn't chain to a previous alias analysis (like -no-aa), it
254 /// derives from the NoAA class.
255 struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA {
256 static char ID; // Class identification, replacement for typeinfo
257 BasicAliasAnalysis() : NoAA(&ID) {}
258 AliasResult alias(const Value *V1, unsigned V1Size,
259 const Value *V2, unsigned V2Size);
261 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
262 ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
263 return NoAA::getModRefInfo(CS1,CS2);
266 /// hasNoModRefInfoForCalls - We can provide mod/ref information against
267 /// non-escaping allocations.
268 virtual bool hasNoModRefInfoForCalls() const { return false; }
270 /// pointsToConstantMemory - Chase pointers until we find a (constant
272 bool pointsToConstantMemory(const Value *P);
275 // CheckGEPInstructions - Check two GEP instructions with known
276 // must-aliasing base pointers. This checks to see if the index expressions
277 // preclude the pointers from aliasing...
279 CheckGEPInstructions(const Type* BasePtr1Ty,
280 Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size,
281 const Type *BasePtr2Ty,
282 Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size);
284 } // End of anonymous namespace
286 // Register this pass...
287 char BasicAliasAnalysis::ID = 0;
288 static RegisterPass<BasicAliasAnalysis>
289 X("basicaa", "Basic Alias Analysis (default AA impl)", false, true);
291 // Declare that we implement the AliasAnalysis interface
292 static RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
294 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
295 return new BasicAliasAnalysis();
299 /// pointsToConstantMemory - Chase pointers until we find a (constant
301 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
302 if (const GlobalVariable *GV =
303 dyn_cast<GlobalVariable>(P->getUnderlyingObject()))
304 return GV->isConstant();
308 // getModRefInfo - Check to see if the specified callsite can clobber the
309 // specified memory object. Since we only look at local properties of this
310 // function, we really can't say much about this query. We do, however, use
311 // simple "address taken" analysis on local objects.
313 AliasAnalysis::ModRefResult
314 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
315 if (!isa<Constant>(P)) {
316 const Value *Object = P->getUnderlyingObject();
318 // If this is a tail call and P points to a stack location, we know that
319 // the tail call cannot access or modify the local stack.
320 // We cannot exclude byval arguments here; these belong to the caller of
321 // the current function not to the current function, and a tail callee
322 // may reference them.
323 if (isa<AllocaInst>(Object))
324 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
325 if (CI->isTailCall())
328 // If the pointer is to a locally allocated object that does not escape,
329 // then the call can not mod/ref the pointer unless the call takes the
330 // argument without capturing it.
331 if (isNonEscapingLocalObject(Object)) {
332 bool passedAsArg = false;
333 // TODO: Eventually only check 'nocapture' arguments.
334 for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
336 if (isa<PointerType>((*CI)->getType()) &&
337 alias(cast<Value>(CI), ~0U, P, ~0U) != NoAlias)
345 // The AliasAnalysis base class has some smarts, lets use them.
346 return AliasAnalysis::getModRefInfo(CS, P, Size);
350 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
351 // as array references. Note that this function is heavily tail recursive.
352 // Hopefully we have a smart C++ compiler. :)
354 AliasAnalysis::AliasResult
355 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
356 const Value *V2, unsigned V2Size) {
357 // Strip off any constant expression casts if they exist
358 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
359 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
360 V1 = CE->getOperand(0);
361 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
362 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
363 V2 = CE->getOperand(0);
365 // Are we checking for alias of the same value?
366 if (V1 == V2) return MustAlias;
368 if (!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType()))
369 return NoAlias; // Scalars cannot alias each other
371 // Strip off cast instructions...
372 if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
373 return alias(I->getOperand(0), V1Size, V2, V2Size);
374 if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
375 return alias(V1, V1Size, I->getOperand(0), V2Size);
377 // Figure out what objects these things are pointing to if we can...
378 const Value *O1 = V1->getUnderlyingObject();
379 const Value *O2 = V2->getUnderlyingObject();
382 // If V1/V2 point to two different objects we know that we have no alias.
383 if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
386 // Local allocations can't alias with arguments or noalias functions.
387 if ((isa<AllocationInst>(O1) && (isa<Argument>(O2) || isNoAliasCall(O2))) ||
388 (isa<AllocationInst>(O2) && (isa<Argument>(O1) || isNoAliasCall(O1))))
391 // Most objects can't alias null.
392 if ((isa<ConstantPointerNull>(V2) && isKnownNonNull(O1)) ||
393 (isa<ConstantPointerNull>(V1) && isKnownNonNull(O2)))
397 // If the size of one access is larger than the entire object on the other
398 // side, then we know such behavior is undefined and can assume no alias.
399 const TargetData &TD = getTargetData();
400 if ((V1Size != ~0U && isObjectSmallerThan(O2, V1Size, TD)) ||
401 (V2Size != ~0U && isObjectSmallerThan(O1, V2Size, TD)))
404 // If one pointer is the result of a call/invoke and the other is a
405 // non-escaping local object, then we know the object couldn't escape to a
406 // point where the call could return it.
407 if ((isa<CallInst>(O1) || isa<InvokeInst>(O1)) &&
408 isNonEscapingLocalObject(O2))
410 if ((isa<CallInst>(O2) || isa<InvokeInst>(O2)) &&
411 isNonEscapingLocalObject(O1))
414 // If we have two gep instructions with must-alias'ing base pointers, figure
415 // out if the indexes to the GEP tell us anything about the derived pointer.
416 // Note that we also handle chains of getelementptr instructions as well as
417 // constant expression getelementptrs here.
419 if (isGEP(V1) && isGEP(V2)) {
420 // Drill down into the first non-gep value, to test for must-aliasing of
421 // the base pointers.
422 const User *G = cast<User>(V1);
423 while (isGEP(G->getOperand(0)) &&
425 Constant::getNullValue(G->getOperand(1)->getType()))
426 G = cast<User>(G->getOperand(0));
427 const Value *BasePtr1 = G->getOperand(0);
430 while (isGEP(G->getOperand(0)) &&
432 Constant::getNullValue(G->getOperand(1)->getType()))
433 G = cast<User>(G->getOperand(0));
434 const Value *BasePtr2 = G->getOperand(0);
436 // Do the base pointers alias?
437 AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
438 if (BaseAlias == NoAlias) return NoAlias;
439 if (BaseAlias == MustAlias) {
440 // If the base pointers alias each other exactly, check to see if we can
441 // figure out anything about the resultant pointers, to try to prove
444 // Collect all of the chained GEP operands together into one simple place
445 SmallVector<Value*, 16> GEP1Ops, GEP2Ops;
446 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
447 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
449 // If GetGEPOperands were able to fold to the same must-aliased pointer,
450 // do the comparison.
451 if (BasePtr1 == BasePtr2) {
453 CheckGEPInstructions(BasePtr1->getType(),
454 &GEP1Ops[0], GEP1Ops.size(), V1Size,
456 &GEP2Ops[0], GEP2Ops.size(), V2Size);
457 if (GAlias != MayAlias)
463 // Check to see if these two pointers are related by a getelementptr
464 // instruction. If one pointer is a GEP with a non-zero index of the other
465 // pointer, we know they cannot alias.
469 std::swap(V1Size, V2Size);
472 if (V1Size != ~0U && V2Size != ~0U)
474 SmallVector<Value*, 16> GEPOperands;
475 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
477 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
478 if (R == MustAlias) {
479 // If there is at least one non-zero constant index, we know they cannot
481 bool ConstantFound = false;
482 bool AllZerosFound = true;
483 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
484 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
485 if (!C->isNullValue()) {
486 ConstantFound = true;
487 AllZerosFound = false;
491 AllZerosFound = false;
494 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
495 // the ptr, the end result is a must alias also.
500 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
503 // Otherwise we have to check to see that the distance is more than
504 // the size of the argument... build an index vector that is equal to
505 // the arguments provided, except substitute 0's for any variable
506 // indexes we find...
507 if (cast<PointerType>(
508 BasePtr->getType())->getElementType()->isSized()) {
509 for (unsigned i = 0; i != GEPOperands.size(); ++i)
510 if (!isa<ConstantInt>(GEPOperands[i]))
512 Constant::getNullValue(GEPOperands[i]->getType());
514 getTargetData().getIndexedOffset(BasePtr->getType(),
518 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
528 // This function is used to determin if the indices of two GEP instructions are
529 // equal. V1 and V2 are the indices.
530 static bool IndexOperandsEqual(Value *V1, Value *V2) {
531 if (V1->getType() == V2->getType())
533 if (Constant *C1 = dyn_cast<Constant>(V1))
534 if (Constant *C2 = dyn_cast<Constant>(V2)) {
535 // Sign extend the constants to long types, if necessary
536 if (C1->getType() != Type::Int64Ty)
537 C1 = ConstantExpr::getSExt(C1, Type::Int64Ty);
538 if (C2->getType() != Type::Int64Ty)
539 C2 = ConstantExpr::getSExt(C2, Type::Int64Ty);
545 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
546 /// base pointers. This checks to see if the index expressions preclude the
547 /// pointers from aliasing...
548 AliasAnalysis::AliasResult
549 BasicAliasAnalysis::CheckGEPInstructions(
550 const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
551 const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
552 // We currently can't handle the case when the base pointers have different
553 // primitive types. Since this is uncommon anyway, we are happy being
554 // extremely conservative.
555 if (BasePtr1Ty != BasePtr2Ty)
558 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
560 // Find the (possibly empty) initial sequence of equal values... which are not
561 // necessarily constants.
562 unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
563 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
564 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
565 unsigned UnequalOper = 0;
566 while (UnequalOper != MinOperands &&
567 IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
568 // Advance through the type as we go...
570 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
571 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
573 // If all operands equal each other, then the derived pointers must
574 // alias each other...
576 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
577 "Ran out of type nesting, but not out of operands?");
582 // If we have seen all constant operands, and run out of indexes on one of the
583 // getelementptrs, check to see if the tail of the leftover one is all zeros.
584 // If so, return mustalias.
585 if (UnequalOper == MinOperands) {
586 if (NumGEP1Ops < NumGEP2Ops) {
587 std::swap(GEP1Ops, GEP2Ops);
588 std::swap(NumGEP1Ops, NumGEP2Ops);
591 bool AllAreZeros = true;
592 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
593 if (!isa<Constant>(GEP1Ops[i]) ||
594 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
598 if (AllAreZeros) return MustAlias;
602 // So now we know that the indexes derived from the base pointers,
603 // which are known to alias, are different. We can still determine a
604 // no-alias result if there are differing constant pairs in the index
605 // chain. For example:
606 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
608 // We have to be careful here about array accesses. In particular, consider:
609 // A[1][0] vs A[0][i]
610 // In this case, we don't *know* that the array will be accessed in bounds:
611 // the index could even be negative. Because of this, we have to
612 // conservatively *give up* and return may alias. We disregard differing
613 // array subscripts that are followed by a variable index without going
616 unsigned SizeMax = std::max(G1S, G2S);
617 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
619 // Scan for the first operand that is constant and unequal in the
620 // two getelementptrs...
621 unsigned FirstConstantOper = UnequalOper;
622 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
623 const Value *G1Oper = GEP1Ops[FirstConstantOper];
624 const Value *G2Oper = GEP2Ops[FirstConstantOper];
626 if (G1Oper != G2Oper) // Found non-equal constant indexes...
627 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
628 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
629 if (G1OC->getType() != G2OC->getType()) {
630 // Sign extend both operands to long.
631 if (G1OC->getType() != Type::Int64Ty)
632 G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty);
633 if (G2OC->getType() != Type::Int64Ty)
634 G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty);
635 GEP1Ops[FirstConstantOper] = G1OC;
636 GEP2Ops[FirstConstantOper] = G2OC;
640 // Handle the "be careful" case above: if this is an array/vector
641 // subscript, scan for a subsequent variable array index.
642 if (isa<SequentialType>(BasePtr1Ty)) {
644 cast<SequentialType>(BasePtr1Ty)->getElementType();
645 bool isBadCase = false;
647 for (unsigned Idx = FirstConstantOper+1;
648 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
649 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
650 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
654 NextTy = cast<SequentialType>(NextTy)->getElementType();
657 if (isBadCase) G1OC = 0;
660 // Make sure they are comparable (ie, not constant expressions), and
661 // make sure the GEP with the smaller leading constant is GEP1.
663 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
665 if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
666 if (CV->getZExtValue()) { // If they are comparable and G2 > G1
667 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
668 std::swap(NumGEP1Ops, NumGEP2Ops);
675 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
678 // No shared constant operands, and we ran out of common operands. At this
679 // point, the GEP instructions have run through all of their operands, and we
680 // haven't found evidence that there are any deltas between the GEP's.
681 // However, one GEP may have more operands than the other. If this is the
682 // case, there may still be hope. Check this now.
683 if (FirstConstantOper == MinOperands) {
684 // Make GEP1Ops be the longer one if there is a longer one.
685 if (NumGEP1Ops < NumGEP2Ops) {
686 std::swap(GEP1Ops, GEP2Ops);
687 std::swap(NumGEP1Ops, NumGEP2Ops);
690 // Is there anything to check?
691 if (NumGEP1Ops > MinOperands) {
692 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
693 if (isa<ConstantInt>(GEP1Ops[i]) &&
694 !cast<ConstantInt>(GEP1Ops[i])->isZero()) {
695 // Yup, there's a constant in the tail. Set all variables to
696 // constants in the GEP instruction to make it suitable for
697 // TargetData::getIndexedOffset.
698 for (i = 0; i != MaxOperands; ++i)
699 if (!isa<ConstantInt>(GEP1Ops[i]))
700 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
701 // Okay, now get the offset. This is the relative offset for the full
703 const TargetData &TD = getTargetData();
704 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
707 // Now check without any constants at the end.
708 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
711 // Make sure we compare the absolute difference.
712 if (Offset1 > Offset2)
713 std::swap(Offset1, Offset2);
715 // If the tail provided a bit enough offset, return noalias!
716 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
718 // Otherwise break - we don't look for another constant in the tail.
723 // Couldn't find anything useful.
727 // If there are non-equal constants arguments, then we can figure
728 // out a minimum known delta between the two index expressions... at
729 // this point we know that the first constant index of GEP1 is less
730 // than the first constant index of GEP2.
732 // Advance BasePtr[12]Ty over this first differing constant operand.
733 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
734 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
735 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
736 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
738 // We are going to be using TargetData::getIndexedOffset to determine the
739 // offset that each of the GEP's is reaching. To do this, we have to convert
740 // all variable references to constant references. To do this, we convert the
741 // initial sequence of array subscripts into constant zeros to start with.
742 const Type *ZeroIdxTy = GEPPointerTy;
743 for (unsigned i = 0; i != FirstConstantOper; ++i) {
744 if (!isa<StructType>(ZeroIdxTy))
745 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty);
747 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
748 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
751 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
753 // Loop over the rest of the operands...
754 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
755 const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
756 const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
757 // If they are equal, use a zero index...
758 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
759 if (!isa<ConstantInt>(Op1))
760 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
761 // Otherwise, just keep the constants we have.
764 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
765 // If this is an array index, make sure the array element is in range.
766 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
767 if (Op1C->getZExtValue() >= AT->getNumElements())
768 return MayAlias; // Be conservative with out-of-range accesses
769 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) {
770 if (Op1C->getZExtValue() >= VT->getNumElements())
771 return MayAlias; // Be conservative with out-of-range accesses
775 // GEP1 is known to produce a value less than GEP2. To be
776 // conservatively correct, we must assume the largest possible
777 // constant is used in this position. This cannot be the initial
778 // index to the GEP instructions (because we know we have at least one
779 // element before this one with the different constant arguments), so
780 // we know that the current index must be into either a struct or
781 // array. Because we know it's not constant, this cannot be a
782 // structure index. Because of this, we can calculate the maximum
785 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
786 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1);
787 else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty))
788 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,VT->getNumElements()-1);
793 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
794 // If this is an array index, make sure the array element is in range.
795 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr2Ty)) {
796 if (Op2C->getZExtValue() >= AT->getNumElements())
797 return MayAlias; // Be conservative with out-of-range accesses
798 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr2Ty)) {
799 if (Op2C->getZExtValue() >= VT->getNumElements())
800 return MayAlias; // Be conservative with out-of-range accesses
802 } else { // Conservatively assume the minimum value for this index
803 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
808 if (BasePtr1Ty && Op1) {
809 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
810 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
815 if (BasePtr2Ty && Op2) {
816 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
817 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
823 if (GEPPointerTy->getElementType()->isSized()) {
825 getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
827 getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
828 assert(Offset1 != Offset2 &&
829 "There is at least one different constant here!");
831 // Make sure we compare the absolute difference.
832 if (Offset1 > Offset2)
833 std::swap(Offset1, Offset2);
835 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
836 //cerr << "Determined that these two GEP's don't alias ["
837 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
844 // Make sure that anything that uses AliasAnalysis pulls in this file...
845 DEFINING_FILE_FOR(BasicAliasAnalysis)