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/Intrinsics.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) {}
83 // Register this pass...
86 U("no-aa", "No Alias Analysis (always returns 'may' alias)");
88 // Declare that we implement the AliasAnalysis interface
89 RegisterAnalysisGroup<AliasAnalysis> V(U);
90 } // End of anonymous namespace
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);
128 // Register this pass...
129 char BasicAliasAnalysis::ID = 0;
130 RegisterPass<BasicAliasAnalysis>
131 X("basicaa", "Basic Alias Analysis (default AA impl)");
133 // Declare that we implement the AliasAnalysis interface
134 RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
135 } // End of anonymous namespace
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 0;
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 Value *V = getUnderlyingObject(P))
197 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
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 (!isa<PointerType>(I->getType()))
224 if (AddressMightEscape(I))
227 case Instruction::Ret:
228 // If returned, the address will escape to calling functions, but no
229 // callees could modify it.
238 // getModRefInfo - Check to see if the specified callsite can clobber the
239 // specified memory object. Since we only look at local properties of this
240 // function, we really can't say much about this query. We do, however, use
241 // simple "address taken" analysis on local objects.
243 AliasAnalysis::ModRefResult
244 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
245 if (!isa<Constant>(P)) {
246 const Value *Object = getUnderlyingObject(P);
247 // Allocations and byval arguments are "new" objects.
249 (isa<AllocationInst>(Object) ||
250 (isa<Argument>(Object) && cast<Argument>(Object)->hasByValAttr()))) {
251 // Okay, the pointer is to a stack allocated object. If we can prove that
252 // the pointer never "escapes", then we know the call cannot clobber it,
253 // because it simply can't get its address.
254 if (!AddressMightEscape(Object))
257 // If this is a tail call and P points to a stack location, we know that
258 // the tail call cannot access or modify the local stack.
259 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
260 if (CI->isTailCall() && !isa<MallocInst>(Object))
265 // The AliasAnalysis base class has some smarts, lets use them.
266 return AliasAnalysis::getModRefInfo(CS, P, Size);
269 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
270 // as array references. Note that this function is heavily tail recursive.
271 // Hopefully we have a smart C++ compiler. :)
273 AliasAnalysis::AliasResult
274 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
275 const Value *V2, unsigned V2Size) {
276 // Strip off any constant expression casts if they exist
277 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
278 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
279 V1 = CE->getOperand(0);
280 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
281 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
282 V2 = CE->getOperand(0);
284 // Are we checking for alias of the same value?
285 if (V1 == V2) return MustAlias;
287 if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
288 V1->getType() != Type::Int64Ty && V2->getType() != Type::Int64Ty)
289 return NoAlias; // Scalars cannot alias each other
291 // Strip off cast instructions...
292 if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
293 return alias(I->getOperand(0), V1Size, V2, V2Size);
294 if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
295 return alias(V1, V1Size, I->getOperand(0), V2Size);
297 // Figure out what objects these things are pointing to if we can...
298 const Value *O1 = getUnderlyingObject(V1);
299 const Value *O2 = getUnderlyingObject(V2);
301 // Pointing at a discernible object?
304 if (const Argument *O1Arg = dyn_cast<Argument>(O1)) {
305 // Incoming argument cannot alias locally allocated object!
306 if (isa<AllocationInst>(O2)) return NoAlias;
308 // If they are two different objects, and one is a noalias argument
309 // then they do not alias.
310 if (O1 != O2 && O1Arg->hasNoAliasAttr())
313 // Byval arguments can't alias globals or other arguments.
314 if (O1 != O2 && O1Arg->hasByValAttr()) return NoAlias;
316 // Otherwise, nothing is known...
319 if (const Argument *O2Arg = dyn_cast<Argument>(O2)) {
320 // Incoming argument cannot alias locally allocated object!
321 if (isa<AllocationInst>(O1)) return NoAlias;
323 // If they are two different objects, and one is a noalias argument
324 // then they do not alias.
325 if (O1 != O2 && O2Arg->hasNoAliasAttr())
328 // Byval arguments can't alias globals or other arguments.
329 if (O1 != O2 && O2Arg->hasByValAttr()) return NoAlias;
331 // Otherwise, nothing is known...
333 } else if (O1 != O2 && !isa<Argument>(O1)) {
334 // If they are two different objects, and neither is an argument,
335 // we know that we have no alias.
339 // If they are the same object, they we can look at the indexes. If they
340 // index off of the object is the same for both pointers, they must alias.
341 // If they are provably different, they must not alias. Otherwise, we
342 // can't tell anything.
345 // Unique values don't alias null, except non-byval arguments.
346 if (isa<ConstantPointerNull>(V2)) {
347 if (const Argument *O1Arg = dyn_cast<Argument>(O1)) {
348 if (O1Arg->hasByValAttr())
355 if (isa<GlobalVariable>(O1) ||
356 (isa<AllocationInst>(O1) &&
357 !cast<AllocationInst>(O1)->isArrayAllocation()))
358 if (cast<PointerType>(O1->getType())->getElementType()->isSized()) {
359 // If the size of the other access is larger than the total size of the
360 // global/alloca/malloc, it cannot be accessing the global (it's
361 // undefined to load or store bytes before or after an object).
362 const Type *ElTy = cast<PointerType>(O1->getType())->getElementType();
363 unsigned GlobalSize = getTargetData().getABITypeSize(ElTy);
364 if (GlobalSize < V2Size && V2Size != ~0U)
370 if (!isa<Argument>(O2) && isa<ConstantPointerNull>(V1))
371 return NoAlias; // Unique values don't alias null
373 if (isa<GlobalVariable>(O2) ||
374 (isa<AllocationInst>(O2) &&
375 !cast<AllocationInst>(O2)->isArrayAllocation()))
376 if (cast<PointerType>(O2->getType())->getElementType()->isSized()) {
377 // If the size of the other access is larger than the total size of the
378 // global/alloca/malloc, it cannot be accessing the object (it's
379 // undefined to load or store bytes before or after an object).
380 const Type *ElTy = cast<PointerType>(O2->getType())->getElementType();
381 unsigned GlobalSize = getTargetData().getABITypeSize(ElTy);
382 if (GlobalSize < V1Size && V1Size != ~0U)
387 // If we have two gep instructions with must-alias'ing base pointers, figure
388 // out if the indexes to the GEP tell us anything about the derived pointer.
389 // Note that we also handle chains of getelementptr instructions as well as
390 // constant expression getelementptrs here.
392 if (isGEP(V1) && isGEP(V2)) {
393 // Drill down into the first non-gep value, to test for must-aliasing of
394 // the base pointers.
395 const User *G = cast<User>(V1);
396 while (isGEP(G->getOperand(0)) &&
398 Constant::getNullValue(G->getOperand(1)->getType()))
399 G = cast<User>(G->getOperand(0));
400 const Value *BasePtr1 = G->getOperand(0);
403 while (isGEP(G->getOperand(0)) &&
405 Constant::getNullValue(G->getOperand(1)->getType()))
406 G = cast<User>(G->getOperand(0));
407 const Value *BasePtr2 = G->getOperand(0);
409 // Do the base pointers alias?
410 AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
411 if (BaseAlias == NoAlias) return NoAlias;
412 if (BaseAlias == MustAlias) {
413 // If the base pointers alias each other exactly, check to see if we can
414 // figure out anything about the resultant pointers, to try to prove
417 // Collect all of the chained GEP operands together into one simple place
418 SmallVector<Value*, 16> GEP1Ops, GEP2Ops;
419 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
420 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
422 // If GetGEPOperands were able to fold to the same must-aliased pointer,
423 // do the comparison.
424 if (BasePtr1 == BasePtr2) {
426 CheckGEPInstructions(BasePtr1->getType(),
427 &GEP1Ops[0], GEP1Ops.size(), V1Size,
429 &GEP2Ops[0], GEP2Ops.size(), V2Size);
430 if (GAlias != MayAlias)
436 // Check to see if these two pointers are related by a getelementptr
437 // instruction. If one pointer is a GEP with a non-zero index of the other
438 // pointer, we know they cannot alias.
442 std::swap(V1Size, V2Size);
445 if (V1Size != ~0U && V2Size != ~0U)
447 SmallVector<Value*, 16> GEPOperands;
448 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
450 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
451 if (R == MustAlias) {
452 // If there is at least one non-zero constant index, we know they cannot
454 bool ConstantFound = false;
455 bool AllZerosFound = true;
456 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
457 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
458 if (!C->isNullValue()) {
459 ConstantFound = true;
460 AllZerosFound = false;
464 AllZerosFound = false;
467 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
468 // the ptr, the end result is a must alias also.
473 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
476 // Otherwise we have to check to see that the distance is more than
477 // the size of the argument... build an index vector that is equal to
478 // the arguments provided, except substitute 0's for any variable
479 // indexes we find...
480 if (cast<PointerType>(
481 BasePtr->getType())->getElementType()->isSized()) {
482 for (unsigned i = 0; i != GEPOperands.size(); ++i)
483 if (!isa<ConstantInt>(GEPOperands[i]))
485 Constant::getNullValue(GEPOperands[i]->getType());
487 getTargetData().getIndexedOffset(BasePtr->getType(),
491 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
501 // This function is used to determin if the indices of two GEP instructions are
502 // equal. V1 and V2 are the indices.
503 static bool IndexOperandsEqual(Value *V1, Value *V2) {
504 if (V1->getType() == V2->getType())
506 if (Constant *C1 = dyn_cast<Constant>(V1))
507 if (Constant *C2 = dyn_cast<Constant>(V2)) {
508 // Sign extend the constants to long types, if necessary
509 if (C1->getType() != Type::Int64Ty)
510 C1 = ConstantExpr::getSExt(C1, Type::Int64Ty);
511 if (C2->getType() != Type::Int64Ty)
512 C2 = ConstantExpr::getSExt(C2, Type::Int64Ty);
518 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
519 /// base pointers. This checks to see if the index expressions preclude the
520 /// pointers from aliasing...
521 AliasAnalysis::AliasResult
522 BasicAliasAnalysis::CheckGEPInstructions(
523 const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
524 const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
525 // We currently can't handle the case when the base pointers have different
526 // primitive types. Since this is uncommon anyway, we are happy being
527 // extremely conservative.
528 if (BasePtr1Ty != BasePtr2Ty)
531 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
533 // Find the (possibly empty) initial sequence of equal values... which are not
534 // necessarily constants.
535 unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
536 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
537 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
538 unsigned UnequalOper = 0;
539 while (UnequalOper != MinOperands &&
540 IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
541 // Advance through the type as we go...
543 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
544 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
546 // If all operands equal each other, then the derived pointers must
547 // alias each other...
549 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
550 "Ran out of type nesting, but not out of operands?");
555 // If we have seen all constant operands, and run out of indexes on one of the
556 // getelementptrs, check to see if the tail of the leftover one is all zeros.
557 // If so, return mustalias.
558 if (UnequalOper == MinOperands) {
559 if (NumGEP1Ops < NumGEP2Ops) {
560 std::swap(GEP1Ops, GEP2Ops);
561 std::swap(NumGEP1Ops, NumGEP2Ops);
564 bool AllAreZeros = true;
565 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
566 if (!isa<Constant>(GEP1Ops[i]) ||
567 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
571 if (AllAreZeros) return MustAlias;
575 // So now we know that the indexes derived from the base pointers,
576 // which are known to alias, are different. We can still determine a
577 // no-alias result if there are differing constant pairs in the index
578 // chain. For example:
579 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
581 // We have to be careful here about array accesses. In particular, consider:
582 // A[1][0] vs A[0][i]
583 // In this case, we don't *know* that the array will be accessed in bounds:
584 // the index could even be negative. Because of this, we have to
585 // conservatively *give up* and return may alias. We disregard differing
586 // array subscripts that are followed by a variable index without going
589 unsigned SizeMax = std::max(G1S, G2S);
590 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
592 // Scan for the first operand that is constant and unequal in the
593 // two getelementptrs...
594 unsigned FirstConstantOper = UnequalOper;
595 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
596 const Value *G1Oper = GEP1Ops[FirstConstantOper];
597 const Value *G2Oper = GEP2Ops[FirstConstantOper];
599 if (G1Oper != G2Oper) // Found non-equal constant indexes...
600 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
601 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
602 if (G1OC->getType() != G2OC->getType()) {
603 // Sign extend both operands to long.
604 if (G1OC->getType() != Type::Int64Ty)
605 G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty);
606 if (G2OC->getType() != Type::Int64Ty)
607 G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty);
608 GEP1Ops[FirstConstantOper] = G1OC;
609 GEP2Ops[FirstConstantOper] = G2OC;
613 // Handle the "be careful" case above: if this is an array/vector
614 // subscript, scan for a subsequent variable array index.
615 if (isa<SequentialType>(BasePtr1Ty)) {
617 cast<SequentialType>(BasePtr1Ty)->getElementType();
618 bool isBadCase = false;
620 for (unsigned Idx = FirstConstantOper+1;
621 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
622 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
623 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
627 NextTy = cast<SequentialType>(NextTy)->getElementType();
630 if (isBadCase) G1OC = 0;
633 // Make sure they are comparable (ie, not constant expressions), and
634 // make sure the GEP with the smaller leading constant is GEP1.
636 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
638 if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
639 if (CV->getZExtValue()) { // If they are comparable and G2 > G1
640 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
641 std::swap(NumGEP1Ops, NumGEP2Ops);
648 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
651 // No shared constant operands, and we ran out of common operands. At this
652 // point, the GEP instructions have run through all of their operands, and we
653 // haven't found evidence that there are any deltas between the GEP's.
654 // However, one GEP may have more operands than the other. If this is the
655 // case, there may still be hope. Check this now.
656 if (FirstConstantOper == MinOperands) {
657 // Make GEP1Ops be the longer one if there is a longer one.
658 if (NumGEP1Ops < NumGEP2Ops) {
659 std::swap(GEP1Ops, GEP2Ops);
660 std::swap(NumGEP1Ops, NumGEP2Ops);
663 // Is there anything to check?
664 if (NumGEP1Ops > MinOperands) {
665 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
666 if (isa<ConstantInt>(GEP1Ops[i]) &&
667 !cast<ConstantInt>(GEP1Ops[i])->isZero()) {
668 // Yup, there's a constant in the tail. Set all variables to
669 // constants in the GEP instruction to make it suiteable for
670 // TargetData::getIndexedOffset.
671 for (i = 0; i != MaxOperands; ++i)
672 if (!isa<ConstantInt>(GEP1Ops[i]))
673 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
674 // Okay, now get the offset. This is the relative offset for the full
676 const TargetData &TD = getTargetData();
677 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
680 // Now check without any constants at the end.
681 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
684 // If the tail provided a bit enough offset, return noalias!
685 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
690 // Couldn't find anything useful.
694 // If there are non-equal constants arguments, then we can figure
695 // out a minimum known delta between the two index expressions... at
696 // this point we know that the first constant index of GEP1 is less
697 // than the first constant index of GEP2.
699 // Advance BasePtr[12]Ty over this first differing constant operand.
700 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
701 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
702 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
703 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
705 // We are going to be using TargetData::getIndexedOffset to determine the
706 // offset that each of the GEP's is reaching. To do this, we have to convert
707 // all variable references to constant references. To do this, we convert the
708 // initial sequence of array subscripts into constant zeros to start with.
709 const Type *ZeroIdxTy = GEPPointerTy;
710 for (unsigned i = 0; i != FirstConstantOper; ++i) {
711 if (!isa<StructType>(ZeroIdxTy))
712 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty);
714 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
715 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
718 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
720 // Loop over the rest of the operands...
721 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
722 const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
723 const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
724 // If they are equal, use a zero index...
725 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
726 if (!isa<ConstantInt>(Op1))
727 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
728 // Otherwise, just keep the constants we have.
731 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
732 // If this is an array index, make sure the array element is in range.
733 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
734 if (Op1C->getZExtValue() >= AT->getNumElements())
735 return MayAlias; // Be conservative with out-of-range accesses
736 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) {
737 if (Op1C->getZExtValue() >= VT->getNumElements())
738 return MayAlias; // Be conservative with out-of-range accesses
742 // GEP1 is known to produce a value less than GEP2. To be
743 // conservatively correct, we must assume the largest possible
744 // constant is used in this position. This cannot be the initial
745 // index to the GEP instructions (because we know we have at least one
746 // element before this one with the different constant arguments), so
747 // we know that the current index must be into either a struct or
748 // array. Because we know it's not constant, this cannot be a
749 // structure index. Because of this, we can calculate the maximum
752 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
753 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1);
754 else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty))
755 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,VT->getNumElements()-1);
760 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
761 // If this is an array index, make sure the array element is in range.
762 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr2Ty)) {
763 if (Op2C->getZExtValue() >= AT->getNumElements())
764 return MayAlias; // Be conservative with out-of-range accesses
765 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr2Ty)) {
766 if (Op2C->getZExtValue() >= VT->getNumElements())
767 return MayAlias; // Be conservative with out-of-range accesses
769 } else { // Conservatively assume the minimum value for this index
770 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
775 if (BasePtr1Ty && Op1) {
776 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
777 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
782 if (BasePtr2Ty && Op2) {
783 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
784 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
790 if (GEPPointerTy->getElementType()->isSized()) {
792 getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
794 getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
795 assert(Offset1 != Offset2 &&
796 "There is at least one different constant here!");
798 // Make sure we compare the absolute difference.
799 if (Offset1 > Offset2)
800 std::swap(Offset1, Offset2);
802 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
803 //cerr << "Determined that these two GEP's don't alias ["
804 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
811 // Make sure that anything that uses AliasAnalysis pulls in this file...
812 DEFINING_FILE_FOR(BasicAliasAnalysis)