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/ParameterAttributes.h"
22 #include "llvm/GlobalVariable.h"
23 #include "llvm/Instructions.h"
24 #include "llvm/IntrinsicInst.h"
25 #include "llvm/Pass.h"
26 #include "llvm/Target/TargetData.h"
27 #include "llvm/ADT/SmallVector.h"
28 #include "llvm/ADT/STLExtras.h"
29 #include "llvm/Support/Compiler.h"
30 #include "llvm/Support/GetElementPtrTypeIterator.h"
31 #include "llvm/Support/ManagedStatic.h"
36 /// NoAA - This class implements the -no-aa pass, which always returns "I
37 /// don't know" for alias queries. NoAA is unlike other alias analysis
38 /// implementations, in that it does not chain to a previous analysis. As
39 /// such it doesn't follow many of the rules that other alias analyses must.
41 struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
42 static char ID; // Class identification, replacement for typeinfo
43 NoAA() : ImmutablePass((intptr_t)&ID) {}
44 explicit NoAA(intptr_t PID) : ImmutablePass(PID) { }
46 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
47 AU.addRequired<TargetData>();
50 virtual void initializePass() {
51 TD = &getAnalysis<TargetData>();
54 virtual AliasResult alias(const Value *V1, unsigned V1Size,
55 const Value *V2, unsigned V2Size) {
59 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
60 std::vector<PointerAccessInfo> *Info) {
61 return UnknownModRefBehavior;
64 virtual void getArgumentAccesses(Function *F, CallSite CS,
65 std::vector<PointerAccessInfo> &Info) {
66 assert(0 && "This method may not be called on this function!");
69 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
70 virtual bool pointsToConstantMemory(const Value *P) { return false; }
71 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
74 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
77 virtual bool hasNoModRefInfoForCalls() const { return true; }
79 virtual void deleteValue(Value *V) {}
80 virtual void copyValue(Value *From, Value *To) {}
82 } // End of anonymous namespace
84 // Register this pass...
86 static RegisterPass<NoAA>
87 U("no-aa", "No Alias Analysis (always returns 'may' alias)", true, true);
89 // Declare that we implement the AliasAnalysis interface
90 static RegisterAnalysisGroup<AliasAnalysis> V(U);
92 ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
95 /// BasicAliasAnalysis - This is the default alias analysis implementation.
96 /// Because it doesn't chain to a previous alias analysis (like -no-aa), it
97 /// derives from the NoAA class.
98 struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA {
99 static char ID; // Class identification, replacement for typeinfo
100 BasicAliasAnalysis() : NoAA((intptr_t)&ID) { }
101 AliasResult alias(const Value *V1, unsigned V1Size,
102 const Value *V2, unsigned V2Size);
104 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
105 ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
106 return NoAA::getModRefInfo(CS1,CS2);
109 /// hasNoModRefInfoForCalls - We can provide mod/ref information against
110 /// non-escaping allocations.
111 virtual bool hasNoModRefInfoForCalls() const { return false; }
113 /// pointsToConstantMemory - Chase pointers until we find a (constant
115 bool pointsToConstantMemory(const Value *P);
118 // CheckGEPInstructions - Check two GEP instructions with known
119 // must-aliasing base pointers. This checks to see if the index expressions
120 // preclude the pointers from aliasing...
122 CheckGEPInstructions(const Type* BasePtr1Ty,
123 Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size,
124 const Type *BasePtr2Ty,
125 Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size);
127 } // End of anonymous namespace
129 // Register this pass...
130 char BasicAliasAnalysis::ID = 0;
131 static RegisterPass<BasicAliasAnalysis>
132 X("basicaa", "Basic Alias Analysis (default AA impl)", false, true);
134 // Declare that we implement the AliasAnalysis interface
135 static RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
137 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
138 return new BasicAliasAnalysis();
141 /// getUnderlyingObject - This traverses the use chain to figure out what object
142 /// the specified value points to. If the value points to, or is derived from,
143 /// a unique object or an argument, return it. This returns:
144 /// Arguments, GlobalVariables, Functions, Allocas, Mallocs.
145 static const Value *getUnderlyingObject(const Value *V) {
146 if (!isa<PointerType>(V->getType())) return V;
148 // If we are at some type of object, return it. GlobalValues and Allocations
149 // have unique addresses.
150 if (isa<GlobalValue>(V) || isa<AllocationInst>(V) || isa<Argument>(V))
153 // Traverse through different addressing mechanisms...
154 if (const Instruction *I = dyn_cast<Instruction>(V)) {
155 if (isa<BitCastInst>(I) || isa<GetElementPtrInst>(I))
156 return getUnderlyingObject(I->getOperand(0));
157 } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
158 if (CE->getOpcode() == Instruction::BitCast ||
159 CE->getOpcode() == Instruction::GetElementPtr)
160 return getUnderlyingObject(CE->getOperand(0));
165 static const User *isGEP(const Value *V) {
166 if (isa<GetElementPtrInst>(V) ||
167 (isa<ConstantExpr>(V) &&
168 cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
169 return cast<User>(V);
173 static const Value *GetGEPOperands(const Value *V,
174 SmallVector<Value*, 16> &GEPOps){
175 assert(GEPOps.empty() && "Expect empty list to populate!");
176 GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
177 cast<User>(V)->op_end());
179 // Accumulate all of the chained indexes into the operand array
180 V = cast<User>(V)->getOperand(0);
182 while (const User *G = isGEP(V)) {
183 if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
184 !cast<Constant>(GEPOps[0])->isNullValue())
185 break; // Don't handle folding arbitrary pointer offsets yet...
186 GEPOps.erase(GEPOps.begin()); // Drop the zero index
187 GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
188 V = G->getOperand(0);
193 /// pointsToConstantMemory - Chase pointers until we find a (constant
195 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
196 if (const GlobalVariable *GV =
197 dyn_cast<GlobalVariable>(getUnderlyingObject(P)))
198 return GV->isConstant();
202 // Determine if an AllocationInst instruction escapes from the function it is
203 // contained in. If it does not escape, there is no way for another function to
204 // mod/ref it. We do this by looking at its uses and determining if the uses
205 // can escape (recursively).
206 static bool AddressMightEscape(const Value *V) {
207 for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
209 const Instruction *I = cast<Instruction>(*UI);
210 switch (I->getOpcode()) {
211 case Instruction::Load:
213 case Instruction::Store:
214 if (I->getOperand(0) == V)
215 return true; // Escapes if the pointer is stored.
217 case Instruction::GetElementPtr:
218 if (AddressMightEscape(I))
221 case Instruction::BitCast:
222 if (AddressMightEscape(I))
225 case Instruction::Ret:
226 // If returned, the address will escape to calling functions, but no
227 // callees could modify it.
229 case Instruction::Call:
230 // If the call is to a few known safe intrinsics, we know that it does
232 if (!isa<MemIntrinsic>(I))
242 // getModRefInfo - Check to see if the specified callsite can clobber the
243 // specified memory object. Since we only look at local properties of this
244 // function, we really can't say much about this query. We do, however, use
245 // simple "address taken" analysis on local objects.
247 AliasAnalysis::ModRefResult
248 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
249 if (!isa<Constant>(P)) {
250 const Value *Object = getUnderlyingObject(P);
252 // If this is a tail call and P points to a stack location, we know that
253 // the tail call cannot access or modify the local stack.
254 // We cannot exclude byval arguments here; these belong to the caller of
255 // the current function not to the current function, and a tail callee
256 // may reference them.
257 if (isa<AllocaInst>(Object))
258 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
259 if (CI->isTailCall())
262 // Allocations and byval arguments are "new" objects.
263 if (isa<AllocationInst>(Object) || isa<Argument>(Object)) {
264 // Okay, the pointer is to a stack allocated (or effectively so, for
265 // for noalias parameters) object. If the address of this object doesn't
266 // escape from this function body to a callee, then we know that no
267 // callees can mod/ref it unless they are actually passed it.
268 if (isa<AllocationInst>(Object) ||
269 cast<Argument>(Object)->hasByValAttr() ||
270 cast<Argument>(Object)->hasNoAliasAttr())
271 if (!AddressMightEscape(Object)) {
272 bool passedAsArg = false;
273 for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
275 if (isa<PointerType>((*CI)->getType()) &&
276 (getUnderlyingObject(*CI) == P ||
277 alias(cast<Value>(CI), ~0U, P, ~0U) != NoAlias))
286 // The AliasAnalysis base class has some smarts, lets use them.
287 return AliasAnalysis::getModRefInfo(CS, P, Size);
290 /// isIdentifiedObject - Return true if this pointer refers to a distinct and
291 /// identifiable object. This returns true for:
292 /// Global Variables and Functions
293 /// Allocas and Mallocs
294 /// ByVal and NoAlias Arguments
296 static bool isIdentifiedObject(const Value *V) {
297 if (isa<GlobalValue>(V) || isa<AllocationInst>(V))
299 if (const Argument *A = dyn_cast<Argument>(V))
300 return A->hasNoAliasAttr() || A->hasByValAttr();
304 /// isKnownNonNull - Return true if we know that the specified value is never
306 static bool isKnownNonNull(const Value *V) {
307 // Alloca never returns null, malloc might.
308 if (isa<AllocaInst>(V)) return true;
310 // A byval argument is never null.
311 if (const Argument *A = dyn_cast<Argument>(V))
312 return A->hasByValAttr();
314 // Global values are not null unless extern weak.
315 if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
316 return !GV->hasExternalWeakLinkage();
320 /// isNonEscapingLocalObject - Return true if the pointer is to a function-local
321 /// object that never escapes from the function.
322 static bool isNonEscapingLocalObject(const Value *V) {
323 // If this is a local allocation, check to see if it escapes.
324 if (isa<AllocationInst>(V))
325 return !AddressMightEscape(V);
327 // If this is an argument that corresponds to a byval or noalias argument,
328 // it can't escape either.
329 if (const Argument *A = dyn_cast<Argument>(V))
330 if (A->hasByValAttr() || A->hasNoAliasAttr())
331 return !AddressMightEscape(V);
336 /// isObjectSmallerThan - Return true if we can prove that the object specified
337 /// by V is smaller than Size.
338 static bool isObjectSmallerThan(const Value *V, unsigned Size,
339 const TargetData &TD) {
340 const Type *AccessTy = 0;
341 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
342 AccessTy = GV->getType()->getElementType();
344 if (const AllocationInst *AI = dyn_cast<AllocationInst>(V))
345 if (!AI->isArrayAllocation())
346 AccessTy = AI->getType()->getElementType();
348 if (const Argument *A = dyn_cast<Argument>(V))
349 if (A->hasByValAttr())
350 AccessTy = cast<PointerType>(A->getType())->getElementType();
352 if (AccessTy && AccessTy->isSized())
353 return TD.getABITypeSize(AccessTy) < Size;
357 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
358 // as array references. Note that this function is heavily tail recursive.
359 // Hopefully we have a smart C++ compiler. :)
361 AliasAnalysis::AliasResult
362 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
363 const Value *V2, unsigned V2Size) {
364 // Strip off any constant expression casts if they exist
365 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
366 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
367 V1 = CE->getOperand(0);
368 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
369 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
370 V2 = CE->getOperand(0);
372 // Are we checking for alias of the same value?
373 if (V1 == V2) return MustAlias;
375 if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
376 V1->getType() != Type::Int64Ty && V2->getType() != Type::Int64Ty)
377 return NoAlias; // Scalars cannot alias each other
379 // Strip off cast instructions...
380 if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
381 return alias(I->getOperand(0), V1Size, V2, V2Size);
382 if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
383 return alias(V1, V1Size, I->getOperand(0), V2Size);
385 // Figure out what objects these things are pointing to if we can...
386 const Value *O1 = getUnderlyingObject(V1);
387 const Value *O2 = getUnderlyingObject(V2);
390 // If V1/V2 point to two different objects we know that we have no alias.
391 if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
394 // Incoming argument cannot alias locally allocated object!
395 if ((isa<Argument>(O1) && isa<AllocationInst>(O2)) ||
396 (isa<Argument>(O2) && isa<AllocationInst>(O1)))
399 // Most objects can't alias null.
400 if ((isa<ConstantPointerNull>(V2) && isKnownNonNull(O1)) ||
401 (isa<ConstantPointerNull>(V1) && isKnownNonNull(O2)))
405 // If the size of one access is larger than the entire object on the other
406 // side, then we know such behavior is undefined and can assume no alias.
407 const TargetData &TD = getTargetData();
408 if ((V1Size != ~0U && isObjectSmallerThan(O2, V1Size, TD)) ||
409 (V2Size != ~0U && isObjectSmallerThan(O1, V2Size, TD)))
412 // If one pointer is the result of a call/invoke and the other is a
413 // non-escaping local object, then we know the object couldn't escape to a
414 // point where the call could return it.
415 if ((isa<CallInst>(O1) || isa<InvokeInst>(O1)) &&
416 isNonEscapingLocalObject(O2))
418 if ((isa<CallInst>(O2) || isa<InvokeInst>(O2)) &&
419 isNonEscapingLocalObject(O1))
422 // If we have two gep instructions with must-alias'ing base pointers, figure
423 // out if the indexes to the GEP tell us anything about the derived pointer.
424 // Note that we also handle chains of getelementptr instructions as well as
425 // constant expression getelementptrs here.
427 if (isGEP(V1) && isGEP(V2)) {
428 // Drill down into the first non-gep value, to test for must-aliasing of
429 // the base pointers.
430 const User *G = cast<User>(V1);
431 while (isGEP(G->getOperand(0)) &&
433 Constant::getNullValue(G->getOperand(1)->getType()))
434 G = cast<User>(G->getOperand(0));
435 const Value *BasePtr1 = G->getOperand(0);
438 while (isGEP(G->getOperand(0)) &&
440 Constant::getNullValue(G->getOperand(1)->getType()))
441 G = cast<User>(G->getOperand(0));
442 const Value *BasePtr2 = G->getOperand(0);
444 // Do the base pointers alias?
445 AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
446 if (BaseAlias == NoAlias) return NoAlias;
447 if (BaseAlias == MustAlias) {
448 // If the base pointers alias each other exactly, check to see if we can
449 // figure out anything about the resultant pointers, to try to prove
452 // Collect all of the chained GEP operands together into one simple place
453 SmallVector<Value*, 16> GEP1Ops, GEP2Ops;
454 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
455 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
457 // If GetGEPOperands were able to fold to the same must-aliased pointer,
458 // do the comparison.
459 if (BasePtr1 == BasePtr2) {
461 CheckGEPInstructions(BasePtr1->getType(),
462 &GEP1Ops[0], GEP1Ops.size(), V1Size,
464 &GEP2Ops[0], GEP2Ops.size(), V2Size);
465 if (GAlias != MayAlias)
471 // Check to see if these two pointers are related by a getelementptr
472 // instruction. If one pointer is a GEP with a non-zero index of the other
473 // pointer, we know they cannot alias.
477 std::swap(V1Size, V2Size);
480 if (V1Size != ~0U && V2Size != ~0U)
482 SmallVector<Value*, 16> GEPOperands;
483 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
485 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
486 if (R == MustAlias) {
487 // If there is at least one non-zero constant index, we know they cannot
489 bool ConstantFound = false;
490 bool AllZerosFound = true;
491 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
492 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
493 if (!C->isNullValue()) {
494 ConstantFound = true;
495 AllZerosFound = false;
499 AllZerosFound = false;
502 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
503 // the ptr, the end result is a must alias also.
508 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
511 // Otherwise we have to check to see that the distance is more than
512 // the size of the argument... build an index vector that is equal to
513 // the arguments provided, except substitute 0's for any variable
514 // indexes we find...
515 if (cast<PointerType>(
516 BasePtr->getType())->getElementType()->isSized()) {
517 for (unsigned i = 0; i != GEPOperands.size(); ++i)
518 if (!isa<ConstantInt>(GEPOperands[i]))
520 Constant::getNullValue(GEPOperands[i]->getType());
522 getTargetData().getIndexedOffset(BasePtr->getType(),
526 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
536 // This function is used to determin if the indices of two GEP instructions are
537 // equal. V1 and V2 are the indices.
538 static bool IndexOperandsEqual(Value *V1, Value *V2) {
539 if (V1->getType() == V2->getType())
541 if (Constant *C1 = dyn_cast<Constant>(V1))
542 if (Constant *C2 = dyn_cast<Constant>(V2)) {
543 // Sign extend the constants to long types, if necessary
544 if (C1->getType() != Type::Int64Ty)
545 C1 = ConstantExpr::getSExt(C1, Type::Int64Ty);
546 if (C2->getType() != Type::Int64Ty)
547 C2 = ConstantExpr::getSExt(C2, Type::Int64Ty);
553 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
554 /// base pointers. This checks to see if the index expressions preclude the
555 /// pointers from aliasing...
556 AliasAnalysis::AliasResult
557 BasicAliasAnalysis::CheckGEPInstructions(
558 const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
559 const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
560 // We currently can't handle the case when the base pointers have different
561 // primitive types. Since this is uncommon anyway, we are happy being
562 // extremely conservative.
563 if (BasePtr1Ty != BasePtr2Ty)
566 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
568 // Find the (possibly empty) initial sequence of equal values... which are not
569 // necessarily constants.
570 unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
571 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
572 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
573 unsigned UnequalOper = 0;
574 while (UnequalOper != MinOperands &&
575 IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
576 // Advance through the type as we go...
578 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
579 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
581 // If all operands equal each other, then the derived pointers must
582 // alias each other...
584 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
585 "Ran out of type nesting, but not out of operands?");
590 // If we have seen all constant operands, and run out of indexes on one of the
591 // getelementptrs, check to see if the tail of the leftover one is all zeros.
592 // If so, return mustalias.
593 if (UnequalOper == MinOperands) {
594 if (NumGEP1Ops < NumGEP2Ops) {
595 std::swap(GEP1Ops, GEP2Ops);
596 std::swap(NumGEP1Ops, NumGEP2Ops);
599 bool AllAreZeros = true;
600 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
601 if (!isa<Constant>(GEP1Ops[i]) ||
602 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
606 if (AllAreZeros) return MustAlias;
610 // So now we know that the indexes derived from the base pointers,
611 // which are known to alias, are different. We can still determine a
612 // no-alias result if there are differing constant pairs in the index
613 // chain. For example:
614 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
616 // We have to be careful here about array accesses. In particular, consider:
617 // A[1][0] vs A[0][i]
618 // In this case, we don't *know* that the array will be accessed in bounds:
619 // the index could even be negative. Because of this, we have to
620 // conservatively *give up* and return may alias. We disregard differing
621 // array subscripts that are followed by a variable index without going
624 unsigned SizeMax = std::max(G1S, G2S);
625 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
627 // Scan for the first operand that is constant and unequal in the
628 // two getelementptrs...
629 unsigned FirstConstantOper = UnequalOper;
630 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
631 const Value *G1Oper = GEP1Ops[FirstConstantOper];
632 const Value *G2Oper = GEP2Ops[FirstConstantOper];
634 if (G1Oper != G2Oper) // Found non-equal constant indexes...
635 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
636 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
637 if (G1OC->getType() != G2OC->getType()) {
638 // Sign extend both operands to long.
639 if (G1OC->getType() != Type::Int64Ty)
640 G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty);
641 if (G2OC->getType() != Type::Int64Ty)
642 G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty);
643 GEP1Ops[FirstConstantOper] = G1OC;
644 GEP2Ops[FirstConstantOper] = G2OC;
648 // Handle the "be careful" case above: if this is an array/vector
649 // subscript, scan for a subsequent variable array index.
650 if (isa<SequentialType>(BasePtr1Ty)) {
652 cast<SequentialType>(BasePtr1Ty)->getElementType();
653 bool isBadCase = false;
655 for (unsigned Idx = FirstConstantOper+1;
656 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
657 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
658 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
662 NextTy = cast<SequentialType>(NextTy)->getElementType();
665 if (isBadCase) G1OC = 0;
668 // Make sure they are comparable (ie, not constant expressions), and
669 // make sure the GEP with the smaller leading constant is GEP1.
671 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
673 if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
674 if (CV->getZExtValue()) { // If they are comparable and G2 > G1
675 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
676 std::swap(NumGEP1Ops, NumGEP2Ops);
683 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
686 // No shared constant operands, and we ran out of common operands. At this
687 // point, the GEP instructions have run through all of their operands, and we
688 // haven't found evidence that there are any deltas between the GEP's.
689 // However, one GEP may have more operands than the other. If this is the
690 // case, there may still be hope. Check this now.
691 if (FirstConstantOper == MinOperands) {
692 // Make GEP1Ops be the longer one if there is a longer one.
693 if (NumGEP1Ops < NumGEP2Ops) {
694 std::swap(GEP1Ops, GEP2Ops);
695 std::swap(NumGEP1Ops, NumGEP2Ops);
698 // Is there anything to check?
699 if (NumGEP1Ops > MinOperands) {
700 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
701 if (isa<ConstantInt>(GEP1Ops[i]) &&
702 !cast<ConstantInt>(GEP1Ops[i])->isZero()) {
703 // Yup, there's a constant in the tail. Set all variables to
704 // constants in the GEP instruction to make it suitable for
705 // TargetData::getIndexedOffset.
706 for (i = 0; i != MaxOperands; ++i)
707 if (!isa<ConstantInt>(GEP1Ops[i]))
708 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
709 // Okay, now get the offset. This is the relative offset for the full
711 const TargetData &TD = getTargetData();
712 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
715 // Now check without any constants at the end.
716 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
719 // Make sure we compare the absolute difference.
720 if (Offset1 > Offset2)
721 std::swap(Offset1, Offset2);
723 // If the tail provided a bit enough offset, return noalias!
724 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
726 // Otherwise break - we don't look for another constant in the tail.
731 // Couldn't find anything useful.
735 // If there are non-equal constants arguments, then we can figure
736 // out a minimum known delta between the two index expressions... at
737 // this point we know that the first constant index of GEP1 is less
738 // than the first constant index of GEP2.
740 // Advance BasePtr[12]Ty over this first differing constant operand.
741 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
742 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
743 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
744 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
746 // We are going to be using TargetData::getIndexedOffset to determine the
747 // offset that each of the GEP's is reaching. To do this, we have to convert
748 // all variable references to constant references. To do this, we convert the
749 // initial sequence of array subscripts into constant zeros to start with.
750 const Type *ZeroIdxTy = GEPPointerTy;
751 for (unsigned i = 0; i != FirstConstantOper; ++i) {
752 if (!isa<StructType>(ZeroIdxTy))
753 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty);
755 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
756 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
759 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
761 // Loop over the rest of the operands...
762 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
763 const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
764 const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
765 // If they are equal, use a zero index...
766 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
767 if (!isa<ConstantInt>(Op1))
768 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
769 // Otherwise, just keep the constants we have.
772 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
773 // If this is an array index, make sure the array element is in range.
774 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
775 if (Op1C->getZExtValue() >= AT->getNumElements())
776 return MayAlias; // Be conservative with out-of-range accesses
777 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) {
778 if (Op1C->getZExtValue() >= VT->getNumElements())
779 return MayAlias; // Be conservative with out-of-range accesses
783 // GEP1 is known to produce a value less than GEP2. To be
784 // conservatively correct, we must assume the largest possible
785 // constant is used in this position. This cannot be the initial
786 // index to the GEP instructions (because we know we have at least one
787 // element before this one with the different constant arguments), so
788 // we know that the current index must be into either a struct or
789 // array. Because we know it's not constant, this cannot be a
790 // structure index. Because of this, we can calculate the maximum
793 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
794 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1);
795 else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty))
796 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,VT->getNumElements()-1);
801 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
802 // If this is an array index, make sure the array element is in range.
803 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr2Ty)) {
804 if (Op2C->getZExtValue() >= AT->getNumElements())
805 return MayAlias; // Be conservative with out-of-range accesses
806 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr2Ty)) {
807 if (Op2C->getZExtValue() >= VT->getNumElements())
808 return MayAlias; // Be conservative with out-of-range accesses
810 } else { // Conservatively assume the minimum value for this index
811 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
816 if (BasePtr1Ty && Op1) {
817 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
818 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
823 if (BasePtr2Ty && Op2) {
824 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
825 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
831 if (GEPPointerTy->getElementType()->isSized()) {
833 getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
835 getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
836 assert(Offset1 != Offset2 &&
837 "There is at least one different constant here!");
839 // Make sure we compare the absolute difference.
840 if (Offset1 > Offset2)
841 std::swap(Offset1, Offset2);
843 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
844 //cerr << "Determined that these two GEP's don't alias ["
845 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
852 // Make sure that anything that uses AliasAnalysis pulls in this file...
853 DEFINING_FILE_FOR(BasicAliasAnalysis)