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"
35 //===----------------------------------------------------------------------===//
37 //===----------------------------------------------------------------------===//
39 // Determine if an AllocationInst instruction escapes from the function it is
40 // contained in. If it does not escape, there is no way for another function to
41 // mod/ref it. We do this by looking at its uses and determining if the uses
42 // can escape (recursively).
43 static bool AddressMightEscape(const Value *V) {
44 for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
46 const Instruction *I = cast<Instruction>(*UI);
47 switch (I->getOpcode()) {
48 case Instruction::Load:
50 case Instruction::Store:
51 if (I->getOperand(0) == V)
52 return true; // Escapes if the pointer is stored.
54 case Instruction::GetElementPtr:
55 if (AddressMightEscape(I))
58 case Instruction::BitCast:
59 if (AddressMightEscape(I))
62 case Instruction::Ret:
63 // If returned, the address will escape to calling functions, but no
64 // callees could modify it.
66 case Instruction::Call:
67 // If the call is to a few known safe intrinsics, we know that it does
69 // TODO: Eventually just check the 'nocapture' attribute.
70 if (!isa<MemIntrinsic>(I))
80 /// getUnderlyingObject - This traverses the use chain to figure out what object
81 /// the specified value points to. If the value points to, or is derived from,
82 /// a unique object or an argument, return it. This returns:
83 /// Arguments, GlobalVariables, Functions, Allocas, Mallocs.
84 static const Value *getUnderlyingObject(const Value *V) {
85 if (!isa<PointerType>(V->getType())) return V;
87 // If we are at some type of object, return it. GlobalValues and Allocations
88 // have unique addresses.
89 if (isa<GlobalValue>(V) || isa<AllocationInst>(V) || isa<Argument>(V))
92 // Traverse through different addressing mechanisms...
93 if (const Instruction *I = dyn_cast<Instruction>(V)) {
94 if (isa<BitCastInst>(I) || isa<GetElementPtrInst>(I))
95 return getUnderlyingObject(I->getOperand(0));
96 } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
97 if (CE->getOpcode() == Instruction::BitCast ||
98 CE->getOpcode() == Instruction::GetElementPtr)
99 return getUnderlyingObject(CE->getOperand(0));
104 static const User *isGEP(const Value *V) {
105 if (isa<GetElementPtrInst>(V) ||
106 (isa<ConstantExpr>(V) &&
107 cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
108 return cast<User>(V);
112 static const Value *GetGEPOperands(const Value *V,
113 SmallVector<Value*, 16> &GEPOps){
114 assert(GEPOps.empty() && "Expect empty list to populate!");
115 GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
116 cast<User>(V)->op_end());
118 // Accumulate all of the chained indexes into the operand array
119 V = cast<User>(V)->getOperand(0);
121 while (const User *G = isGEP(V)) {
122 if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
123 !cast<Constant>(GEPOps[0])->isNullValue())
124 break; // Don't handle folding arbitrary pointer offsets yet...
125 GEPOps.erase(GEPOps.begin()); // Drop the zero index
126 GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
127 V = G->getOperand(0);
132 /// isIdentifiedObject - Return true if this pointer refers to a distinct and
133 /// identifiable object. This returns true for:
134 /// Global Variables and Functions
135 /// Allocas and Mallocs
136 /// ByVal and NoAlias Arguments
138 static bool isIdentifiedObject(const Value *V) {
139 if (isa<GlobalValue>(V) || isa<AllocationInst>(V))
141 if (const Argument *A = dyn_cast<Argument>(V))
142 return A->hasNoAliasAttr() || A->hasByValAttr();
146 /// isKnownNonNull - Return true if we know that the specified value is never
148 static bool isKnownNonNull(const Value *V) {
149 // Alloca never returns null, malloc might.
150 if (isa<AllocaInst>(V)) return true;
152 // A byval argument is never null.
153 if (const Argument *A = dyn_cast<Argument>(V))
154 return A->hasByValAttr();
156 // Global values are not null unless extern weak.
157 if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
158 return !GV->hasExternalWeakLinkage();
162 /// isNonEscapingLocalObject - Return true if the pointer is to a function-local
163 /// object that never escapes from the function.
164 static bool isNonEscapingLocalObject(const Value *V) {
165 // If this is a local allocation, check to see if it escapes.
166 if (isa<AllocationInst>(V))
167 return !AddressMightEscape(V);
169 // If this is an argument that corresponds to a byval or noalias argument,
170 // it can't escape either.
171 if (const Argument *A = dyn_cast<Argument>(V))
172 if (A->hasByValAttr() || A->hasNoAliasAttr())
173 return !AddressMightEscape(V);
178 /// isObjectSmallerThan - Return true if we can prove that the object specified
179 /// by V is smaller than Size.
180 static bool isObjectSmallerThan(const Value *V, unsigned Size,
181 const TargetData &TD) {
182 const Type *AccessTy = 0;
183 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
184 AccessTy = GV->getType()->getElementType();
186 if (const AllocationInst *AI = dyn_cast<AllocationInst>(V))
187 if (!AI->isArrayAllocation())
188 AccessTy = AI->getType()->getElementType();
190 if (const Argument *A = dyn_cast<Argument>(V))
191 if (A->hasByValAttr())
192 AccessTy = cast<PointerType>(A->getType())->getElementType();
194 if (AccessTy && AccessTy->isSized())
195 return TD.getABITypeSize(AccessTy) < Size;
199 //===----------------------------------------------------------------------===//
201 //===----------------------------------------------------------------------===//
204 /// NoAA - This class implements the -no-aa pass, which always returns "I
205 /// don't know" for alias queries. NoAA is unlike other alias analysis
206 /// implementations, in that it does not chain to a previous analysis. As
207 /// such it doesn't follow many of the rules that other alias analyses must.
209 struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
210 static char ID; // Class identification, replacement for typeinfo
211 NoAA() : ImmutablePass((intptr_t)&ID) {}
212 explicit NoAA(intptr_t PID) : ImmutablePass(PID) { }
214 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
215 AU.addRequired<TargetData>();
218 virtual void initializePass() {
219 TD = &getAnalysis<TargetData>();
222 virtual AliasResult alias(const Value *V1, unsigned V1Size,
223 const Value *V2, unsigned V2Size) {
227 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
228 std::vector<PointerAccessInfo> *Info) {
229 return UnknownModRefBehavior;
232 virtual void getArgumentAccesses(Function *F, CallSite CS,
233 std::vector<PointerAccessInfo> &Info) {
234 assert(0 && "This method may not be called on this function!");
237 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
238 virtual bool pointsToConstantMemory(const Value *P) { return false; }
239 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
242 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
245 virtual bool hasNoModRefInfoForCalls() const { return true; }
247 virtual void deleteValue(Value *V) {}
248 virtual void copyValue(Value *From, Value *To) {}
250 } // End of anonymous namespace
252 // Register this pass...
254 static RegisterPass<NoAA>
255 U("no-aa", "No Alias Analysis (always returns 'may' alias)", true, true);
257 // Declare that we implement the AliasAnalysis interface
258 static RegisterAnalysisGroup<AliasAnalysis> V(U);
260 ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
262 //===----------------------------------------------------------------------===//
264 //===----------------------------------------------------------------------===//
267 /// BasicAliasAnalysis - This is the default alias analysis implementation.
268 /// Because it doesn't chain to a previous alias analysis (like -no-aa), it
269 /// derives from the NoAA class.
270 struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA {
271 static char ID; // Class identification, replacement for typeinfo
272 BasicAliasAnalysis() : NoAA((intptr_t)&ID) { }
273 AliasResult alias(const Value *V1, unsigned V1Size,
274 const Value *V2, unsigned V2Size);
276 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
277 ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
278 return NoAA::getModRefInfo(CS1,CS2);
281 /// hasNoModRefInfoForCalls - We can provide mod/ref information against
282 /// non-escaping allocations.
283 virtual bool hasNoModRefInfoForCalls() const { return false; }
285 /// pointsToConstantMemory - Chase pointers until we find a (constant
287 bool pointsToConstantMemory(const Value *P);
290 // CheckGEPInstructions - Check two GEP instructions with known
291 // must-aliasing base pointers. This checks to see if the index expressions
292 // preclude the pointers from aliasing...
294 CheckGEPInstructions(const Type* BasePtr1Ty,
295 Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size,
296 const Type *BasePtr2Ty,
297 Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size);
299 } // End of anonymous namespace
301 // Register this pass...
302 char BasicAliasAnalysis::ID = 0;
303 static RegisterPass<BasicAliasAnalysis>
304 X("basicaa", "Basic Alias Analysis (default AA impl)", false, true);
306 // Declare that we implement the AliasAnalysis interface
307 static RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
309 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
310 return new BasicAliasAnalysis();
314 /// pointsToConstantMemory - Chase pointers until we find a (constant
316 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
317 if (const GlobalVariable *GV =
318 dyn_cast<GlobalVariable>(getUnderlyingObject(P)))
319 return GV->isConstant();
323 // getModRefInfo - Check to see if the specified callsite can clobber the
324 // specified memory object. Since we only look at local properties of this
325 // function, we really can't say much about this query. We do, however, use
326 // simple "address taken" analysis on local objects.
328 AliasAnalysis::ModRefResult
329 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
330 if (!isa<Constant>(P)) {
331 const Value *Object = getUnderlyingObject(P);
333 // If this is a tail call and P points to a stack location, we know that
334 // the tail call cannot access or modify the local stack.
335 // We cannot exclude byval arguments here; these belong to the caller of
336 // the current function not to the current function, and a tail callee
337 // may reference them.
338 if (isa<AllocaInst>(Object))
339 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
340 if (CI->isTailCall())
343 // If the pointer is to a locally allocated object that does not escape,
344 // then the call can not mod/ref the pointer unless the call takes the
345 // argument without capturing it.
346 if (isNonEscapingLocalObject(Object)) {
347 bool passedAsArg = false;
348 // TODO: Eventually only check 'nocapture' arguments.
349 for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
351 if (isa<PointerType>((*CI)->getType()) &&
352 alias(cast<Value>(CI), ~0U, P, ~0U) != NoAlias)
360 // The AliasAnalysis base class has some smarts, lets use them.
361 return AliasAnalysis::getModRefInfo(CS, P, Size);
365 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
366 // as array references. Note that this function is heavily tail recursive.
367 // Hopefully we have a smart C++ compiler. :)
369 AliasAnalysis::AliasResult
370 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
371 const Value *V2, unsigned V2Size) {
372 // Strip off any constant expression casts if they exist
373 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
374 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
375 V1 = CE->getOperand(0);
376 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
377 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
378 V2 = CE->getOperand(0);
380 // Are we checking for alias of the same value?
381 if (V1 == V2) return MustAlias;
383 if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
384 V1->getType() != Type::Int64Ty && V2->getType() != Type::Int64Ty)
385 return NoAlias; // Scalars cannot alias each other
387 // Strip off cast instructions...
388 if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
389 return alias(I->getOperand(0), V1Size, V2, V2Size);
390 if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
391 return alias(V1, V1Size, I->getOperand(0), V2Size);
393 // Figure out what objects these things are pointing to if we can...
394 const Value *O1 = getUnderlyingObject(V1);
395 const Value *O2 = getUnderlyingObject(V2);
398 // If V1/V2 point to two different objects we know that we have no alias.
399 if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
402 // Incoming argument cannot alias locally allocated object!
403 if ((isa<Argument>(O1) && isa<AllocationInst>(O2)) ||
404 (isa<Argument>(O2) && isa<AllocationInst>(O1)))
407 // Most objects can't alias null.
408 if ((isa<ConstantPointerNull>(V2) && isKnownNonNull(O1)) ||
409 (isa<ConstantPointerNull>(V1) && isKnownNonNull(O2)))
413 // If the size of one access is larger than the entire object on the other
414 // side, then we know such behavior is undefined and can assume no alias.
415 const TargetData &TD = getTargetData();
416 if ((V1Size != ~0U && isObjectSmallerThan(O2, V1Size, TD)) ||
417 (V2Size != ~0U && isObjectSmallerThan(O1, V2Size, TD)))
420 // If one pointer is the result of a call/invoke and the other is a
421 // non-escaping local object, then we know the object couldn't escape to a
422 // point where the call could return it.
423 if ((isa<CallInst>(O1) || isa<InvokeInst>(O1)) &&
424 isNonEscapingLocalObject(O2))
426 if ((isa<CallInst>(O2) || isa<InvokeInst>(O2)) &&
427 isNonEscapingLocalObject(O1))
430 // If we have two gep instructions with must-alias'ing base pointers, figure
431 // out if the indexes to the GEP tell us anything about the derived pointer.
432 // Note that we also handle chains of getelementptr instructions as well as
433 // constant expression getelementptrs here.
435 if (isGEP(V1) && isGEP(V2)) {
436 // Drill down into the first non-gep value, to test for must-aliasing of
437 // the base pointers.
438 const User *G = cast<User>(V1);
439 while (isGEP(G->getOperand(0)) &&
441 Constant::getNullValue(G->getOperand(1)->getType()))
442 G = cast<User>(G->getOperand(0));
443 const Value *BasePtr1 = G->getOperand(0);
446 while (isGEP(G->getOperand(0)) &&
448 Constant::getNullValue(G->getOperand(1)->getType()))
449 G = cast<User>(G->getOperand(0));
450 const Value *BasePtr2 = G->getOperand(0);
452 // Do the base pointers alias?
453 AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
454 if (BaseAlias == NoAlias) return NoAlias;
455 if (BaseAlias == MustAlias) {
456 // If the base pointers alias each other exactly, check to see if we can
457 // figure out anything about the resultant pointers, to try to prove
460 // Collect all of the chained GEP operands together into one simple place
461 SmallVector<Value*, 16> GEP1Ops, GEP2Ops;
462 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
463 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
465 // If GetGEPOperands were able to fold to the same must-aliased pointer,
466 // do the comparison.
467 if (BasePtr1 == BasePtr2) {
469 CheckGEPInstructions(BasePtr1->getType(),
470 &GEP1Ops[0], GEP1Ops.size(), V1Size,
472 &GEP2Ops[0], GEP2Ops.size(), V2Size);
473 if (GAlias != MayAlias)
479 // Check to see if these two pointers are related by a getelementptr
480 // instruction. If one pointer is a GEP with a non-zero index of the other
481 // pointer, we know they cannot alias.
485 std::swap(V1Size, V2Size);
488 if (V1Size != ~0U && V2Size != ~0U)
490 SmallVector<Value*, 16> GEPOperands;
491 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
493 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
494 if (R == MustAlias) {
495 // If there is at least one non-zero constant index, we know they cannot
497 bool ConstantFound = false;
498 bool AllZerosFound = true;
499 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
500 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
501 if (!C->isNullValue()) {
502 ConstantFound = true;
503 AllZerosFound = false;
507 AllZerosFound = false;
510 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
511 // the ptr, the end result is a must alias also.
516 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
519 // Otherwise we have to check to see that the distance is more than
520 // the size of the argument... build an index vector that is equal to
521 // the arguments provided, except substitute 0's for any variable
522 // indexes we find...
523 if (cast<PointerType>(
524 BasePtr->getType())->getElementType()->isSized()) {
525 for (unsigned i = 0; i != GEPOperands.size(); ++i)
526 if (!isa<ConstantInt>(GEPOperands[i]))
528 Constant::getNullValue(GEPOperands[i]->getType());
530 getTargetData().getIndexedOffset(BasePtr->getType(),
534 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
544 // This function is used to determin if the indices of two GEP instructions are
545 // equal. V1 and V2 are the indices.
546 static bool IndexOperandsEqual(Value *V1, Value *V2) {
547 if (V1->getType() == V2->getType())
549 if (Constant *C1 = dyn_cast<Constant>(V1))
550 if (Constant *C2 = dyn_cast<Constant>(V2)) {
551 // Sign extend the constants to long types, if necessary
552 if (C1->getType() != Type::Int64Ty)
553 C1 = ConstantExpr::getSExt(C1, Type::Int64Ty);
554 if (C2->getType() != Type::Int64Ty)
555 C2 = ConstantExpr::getSExt(C2, Type::Int64Ty);
561 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
562 /// base pointers. This checks to see if the index expressions preclude the
563 /// pointers from aliasing...
564 AliasAnalysis::AliasResult
565 BasicAliasAnalysis::CheckGEPInstructions(
566 const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
567 const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
568 // We currently can't handle the case when the base pointers have different
569 // primitive types. Since this is uncommon anyway, we are happy being
570 // extremely conservative.
571 if (BasePtr1Ty != BasePtr2Ty)
574 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
576 // Find the (possibly empty) initial sequence of equal values... which are not
577 // necessarily constants.
578 unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
579 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
580 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
581 unsigned UnequalOper = 0;
582 while (UnequalOper != MinOperands &&
583 IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
584 // Advance through the type as we go...
586 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
587 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
589 // If all operands equal each other, then the derived pointers must
590 // alias each other...
592 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
593 "Ran out of type nesting, but not out of operands?");
598 // If we have seen all constant operands, and run out of indexes on one of the
599 // getelementptrs, check to see if the tail of the leftover one is all zeros.
600 // If so, return mustalias.
601 if (UnequalOper == MinOperands) {
602 if (NumGEP1Ops < NumGEP2Ops) {
603 std::swap(GEP1Ops, GEP2Ops);
604 std::swap(NumGEP1Ops, NumGEP2Ops);
607 bool AllAreZeros = true;
608 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
609 if (!isa<Constant>(GEP1Ops[i]) ||
610 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
614 if (AllAreZeros) return MustAlias;
618 // So now we know that the indexes derived from the base pointers,
619 // which are known to alias, are different. We can still determine a
620 // no-alias result if there are differing constant pairs in the index
621 // chain. For example:
622 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
624 // We have to be careful here about array accesses. In particular, consider:
625 // A[1][0] vs A[0][i]
626 // In this case, we don't *know* that the array will be accessed in bounds:
627 // the index could even be negative. Because of this, we have to
628 // conservatively *give up* and return may alias. We disregard differing
629 // array subscripts that are followed by a variable index without going
632 unsigned SizeMax = std::max(G1S, G2S);
633 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
635 // Scan for the first operand that is constant and unequal in the
636 // two getelementptrs...
637 unsigned FirstConstantOper = UnequalOper;
638 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
639 const Value *G1Oper = GEP1Ops[FirstConstantOper];
640 const Value *G2Oper = GEP2Ops[FirstConstantOper];
642 if (G1Oper != G2Oper) // Found non-equal constant indexes...
643 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
644 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
645 if (G1OC->getType() != G2OC->getType()) {
646 // Sign extend both operands to long.
647 if (G1OC->getType() != Type::Int64Ty)
648 G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty);
649 if (G2OC->getType() != Type::Int64Ty)
650 G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty);
651 GEP1Ops[FirstConstantOper] = G1OC;
652 GEP2Ops[FirstConstantOper] = G2OC;
656 // Handle the "be careful" case above: if this is an array/vector
657 // subscript, scan for a subsequent variable array index.
658 if (isa<SequentialType>(BasePtr1Ty)) {
660 cast<SequentialType>(BasePtr1Ty)->getElementType();
661 bool isBadCase = false;
663 for (unsigned Idx = FirstConstantOper+1;
664 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
665 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
666 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
670 NextTy = cast<SequentialType>(NextTy)->getElementType();
673 if (isBadCase) G1OC = 0;
676 // Make sure they are comparable (ie, not constant expressions), and
677 // make sure the GEP with the smaller leading constant is GEP1.
679 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
681 if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
682 if (CV->getZExtValue()) { // If they are comparable and G2 > G1
683 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
684 std::swap(NumGEP1Ops, NumGEP2Ops);
691 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
694 // No shared constant operands, and we ran out of common operands. At this
695 // point, the GEP instructions have run through all of their operands, and we
696 // haven't found evidence that there are any deltas between the GEP's.
697 // However, one GEP may have more operands than the other. If this is the
698 // case, there may still be hope. Check this now.
699 if (FirstConstantOper == MinOperands) {
700 // Make GEP1Ops be the longer one if there is a longer one.
701 if (NumGEP1Ops < NumGEP2Ops) {
702 std::swap(GEP1Ops, GEP2Ops);
703 std::swap(NumGEP1Ops, NumGEP2Ops);
706 // Is there anything to check?
707 if (NumGEP1Ops > MinOperands) {
708 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
709 if (isa<ConstantInt>(GEP1Ops[i]) &&
710 !cast<ConstantInt>(GEP1Ops[i])->isZero()) {
711 // Yup, there's a constant in the tail. Set all variables to
712 // constants in the GEP instruction to make it suitable for
713 // TargetData::getIndexedOffset.
714 for (i = 0; i != MaxOperands; ++i)
715 if (!isa<ConstantInt>(GEP1Ops[i]))
716 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
717 // Okay, now get the offset. This is the relative offset for the full
719 const TargetData &TD = getTargetData();
720 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
723 // Now check without any constants at the end.
724 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
727 // Make sure we compare the absolute difference.
728 if (Offset1 > Offset2)
729 std::swap(Offset1, Offset2);
731 // If the tail provided a bit enough offset, return noalias!
732 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
734 // Otherwise break - we don't look for another constant in the tail.
739 // Couldn't find anything useful.
743 // If there are non-equal constants arguments, then we can figure
744 // out a minimum known delta between the two index expressions... at
745 // this point we know that the first constant index of GEP1 is less
746 // than the first constant index of GEP2.
748 // Advance BasePtr[12]Ty over this first differing constant operand.
749 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
750 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
751 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
752 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
754 // We are going to be using TargetData::getIndexedOffset to determine the
755 // offset that each of the GEP's is reaching. To do this, we have to convert
756 // all variable references to constant references. To do this, we convert the
757 // initial sequence of array subscripts into constant zeros to start with.
758 const Type *ZeroIdxTy = GEPPointerTy;
759 for (unsigned i = 0; i != FirstConstantOper; ++i) {
760 if (!isa<StructType>(ZeroIdxTy))
761 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty);
763 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
764 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
767 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
769 // Loop over the rest of the operands...
770 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
771 const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
772 const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
773 // If they are equal, use a zero index...
774 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
775 if (!isa<ConstantInt>(Op1))
776 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
777 // Otherwise, just keep the constants we have.
780 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
781 // If this is an array index, make sure the array element is in range.
782 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
783 if (Op1C->getZExtValue() >= AT->getNumElements())
784 return MayAlias; // Be conservative with out-of-range accesses
785 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) {
786 if (Op1C->getZExtValue() >= VT->getNumElements())
787 return MayAlias; // Be conservative with out-of-range accesses
791 // GEP1 is known to produce a value less than GEP2. To be
792 // conservatively correct, we must assume the largest possible
793 // constant is used in this position. This cannot be the initial
794 // index to the GEP instructions (because we know we have at least one
795 // element before this one with the different constant arguments), so
796 // we know that the current index must be into either a struct or
797 // array. Because we know it's not constant, this cannot be a
798 // structure index. Because of this, we can calculate the maximum
801 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
802 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1);
803 else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty))
804 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,VT->getNumElements()-1);
809 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
810 // If this is an array index, make sure the array element is in range.
811 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr2Ty)) {
812 if (Op2C->getZExtValue() >= AT->getNumElements())
813 return MayAlias; // Be conservative with out-of-range accesses
814 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr2Ty)) {
815 if (Op2C->getZExtValue() >= VT->getNumElements())
816 return MayAlias; // Be conservative with out-of-range accesses
818 } else { // Conservatively assume the minimum value for this index
819 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
824 if (BasePtr1Ty && Op1) {
825 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
826 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
831 if (BasePtr2Ty && Op2) {
832 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
833 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
839 if (GEPPointerTy->getElementType()->isSized()) {
841 getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
843 getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
844 assert(Offset1 != Offset2 &&
845 "There is at least one different constant here!");
847 // Make sure we compare the absolute difference.
848 if (Offset1 > Offset2)
849 std::swap(Offset1, Offset2);
851 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
852 //cerr << "Determined that these two GEP's don't alias ["
853 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
860 // Make sure that anything that uses AliasAnalysis pulls in this file...
861 DEFINING_FILE_FOR(BasicAliasAnalysis)