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/CaptureTracking.h"
18 #include "llvm/Analysis/Passes.h"
19 #include "llvm/Constants.h"
20 #include "llvm/DerivedTypes.h"
21 #include "llvm/Function.h"
22 #include "llvm/GlobalVariable.h"
23 #include "llvm/Instructions.h"
24 #include "llvm/IntrinsicInst.h"
25 #include "llvm/LLVMContext.h"
26 #include "llvm/Operator.h"
27 #include "llvm/Pass.h"
28 #include "llvm/Target/TargetData.h"
29 #include "llvm/ADT/SmallVector.h"
30 #include "llvm/ADT/STLExtras.h"
31 #include "llvm/Support/Compiler.h"
32 #include "llvm/Support/ErrorHandling.h"
33 #include "llvm/Support/GetElementPtrTypeIterator.h"
37 //===----------------------------------------------------------------------===//
39 //===----------------------------------------------------------------------===//
41 static const GEPOperator *isGEP(const Value *V) {
42 return dyn_cast<GEPOperator>(V);
45 static const Value *GetGEPOperands(const Value *V,
46 SmallVector<Value*, 16> &GEPOps) {
47 assert(GEPOps.empty() && "Expect empty list to populate!");
48 GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
49 cast<User>(V)->op_end());
51 // Accumulate all of the chained indexes into the operand array
52 V = cast<User>(V)->getOperand(0);
54 while (const User *G = isGEP(V)) {
55 if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
56 !cast<Constant>(GEPOps[0])->isNullValue())
57 break; // Don't handle folding arbitrary pointer offsets yet...
58 GEPOps.erase(GEPOps.begin()); // Drop the zero index
59 GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
65 /// isKnownNonNull - Return true if we know that the specified value is never
67 static bool isKnownNonNull(const Value *V) {
68 // Alloca never returns null, malloc might.
69 if (isa<AllocaInst>(V)) return true;
71 // A byval argument is never null.
72 if (const Argument *A = dyn_cast<Argument>(V))
73 return A->hasByValAttr();
75 // Global values are not null unless extern weak.
76 if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
77 return !GV->hasExternalWeakLinkage();
81 /// isNonEscapingLocalObject - Return true if the pointer is to a function-local
82 /// object that never escapes from the function.
83 static bool isNonEscapingLocalObject(const Value *V) {
84 // If this is a local allocation, check to see if it escapes.
85 if (isa<AllocationInst>(V) || isNoAliasCall(V))
86 return !PointerMayBeCaptured(V, false);
88 // If this is an argument that corresponds to a byval or noalias argument,
89 // then it has not escaped before entering the function. Check if it escapes
90 // inside the function.
91 if (const Argument *A = dyn_cast<Argument>(V))
92 if (A->hasByValAttr() || A->hasNoAliasAttr()) {
93 // Don't bother analyzing arguments already known not to escape.
94 if (A->hasNoCaptureAttr())
96 return !PointerMayBeCaptured(V, false);
102 /// isObjectSmallerThan - Return true if we can prove that the object specified
103 /// by V is smaller than Size.
104 static bool isObjectSmallerThan(const Value *V, unsigned Size,
105 const TargetData &TD) {
106 const Type *AccessTy;
107 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
108 AccessTy = GV->getType()->getElementType();
109 } else if (const AllocationInst *AI = dyn_cast<AllocationInst>(V)) {
110 if (!AI->isArrayAllocation())
111 AccessTy = AI->getType()->getElementType();
114 } else if (const Argument *A = dyn_cast<Argument>(V)) {
115 if (A->hasByValAttr())
116 AccessTy = cast<PointerType>(A->getType())->getElementType();
123 if (AccessTy->isSized())
124 return TD.getTypeAllocSize(AccessTy) < Size;
128 //===----------------------------------------------------------------------===//
130 //===----------------------------------------------------------------------===//
133 /// NoAA - This class implements the -no-aa pass, which always returns "I
134 /// don't know" for alias queries. NoAA is unlike other alias analysis
135 /// implementations, in that it does not chain to a previous analysis. As
136 /// such it doesn't follow many of the rules that other alias analyses must.
138 struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
139 static char ID; // Class identification, replacement for typeinfo
140 NoAA() : ImmutablePass(&ID) {}
141 explicit NoAA(void *PID) : ImmutablePass(PID) { }
143 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
146 virtual void initializePass() {
147 TD = getAnalysisIfAvailable<TargetData>();
150 virtual AliasResult alias(const Value *V1, unsigned V1Size,
151 const Value *V2, unsigned V2Size) {
155 virtual void getArgumentAccesses(Function *F, CallSite CS,
156 std::vector<PointerAccessInfo> &Info) {
157 llvm_unreachable("This method may not be called on this function!");
160 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
161 virtual bool pointsToConstantMemory(const Value *P) { return false; }
162 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
165 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
168 virtual bool hasNoModRefInfoForCalls() const { return true; }
170 virtual void deleteValue(Value *V) {}
171 virtual void copyValue(Value *From, Value *To) {}
173 } // End of anonymous namespace
175 // Register this pass...
177 static RegisterPass<NoAA>
178 U("no-aa", "No Alias Analysis (always returns 'may' alias)", true, true);
180 // Declare that we implement the AliasAnalysis interface
181 static RegisterAnalysisGroup<AliasAnalysis> V(U);
183 ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
185 //===----------------------------------------------------------------------===//
187 //===----------------------------------------------------------------------===//
190 /// BasicAliasAnalysis - This is the default alias analysis implementation.
191 /// Because it doesn't chain to a previous alias analysis (like -no-aa), it
192 /// derives from the NoAA class.
193 struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA {
194 static char ID; // Class identification, replacement for typeinfo
195 BasicAliasAnalysis() : NoAA(&ID) {}
196 AliasResult alias(const Value *V1, unsigned V1Size,
197 const Value *V2, unsigned V2Size);
199 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
200 ModRefResult getModRefInfo(CallSite CS1, CallSite CS2);
202 /// hasNoModRefInfoForCalls - We can provide mod/ref information against
203 /// non-escaping allocations.
204 virtual bool hasNoModRefInfoForCalls() const { return false; }
206 /// pointsToConstantMemory - Chase pointers until we find a (constant
208 bool pointsToConstantMemory(const Value *P);
211 // CheckGEPInstructions - Check two GEP instructions with known
212 // must-aliasing base pointers. This checks to see if the index expressions
213 // preclude the pointers from aliasing...
215 CheckGEPInstructions(const Type* BasePtr1Ty,
216 Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size,
217 const Type *BasePtr2Ty,
218 Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size);
220 } // End of anonymous namespace
222 // Register this pass...
223 char BasicAliasAnalysis::ID = 0;
224 static RegisterPass<BasicAliasAnalysis>
225 X("basicaa", "Basic Alias Analysis (default AA impl)", false, true);
227 // Declare that we implement the AliasAnalysis interface
228 static RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
230 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
231 return new BasicAliasAnalysis();
235 /// pointsToConstantMemory - Chase pointers until we find a (constant
237 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
238 if (const GlobalVariable *GV =
239 dyn_cast<GlobalVariable>(P->getUnderlyingObject()))
240 return GV->isConstant();
245 // getModRefInfo - Check to see if the specified callsite can clobber the
246 // specified memory object. Since we only look at local properties of this
247 // function, we really can't say much about this query. We do, however, use
248 // simple "address taken" analysis on local objects.
250 AliasAnalysis::ModRefResult
251 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
252 if (!isa<Constant>(P)) {
253 const Value *Object = P->getUnderlyingObject();
255 // If this is a tail call and P points to a stack location, we know that
256 // the tail call cannot access or modify the local stack.
257 // We cannot exclude byval arguments here; these belong to the caller of
258 // the current function not to the current function, and a tail callee
259 // may reference them.
260 if (isa<AllocaInst>(Object))
261 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
262 if (CI->isTailCall())
265 // If the pointer is to a locally allocated object that does not escape,
266 // then the call can not mod/ref the pointer unless the call takes the
267 // argument without capturing it.
268 if (isNonEscapingLocalObject(Object) && CS.getInstruction() != Object) {
269 bool passedAsArg = false;
270 // TODO: Eventually only check 'nocapture' arguments.
271 for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
273 if (isa<PointerType>((*CI)->getType()) &&
274 alias(cast<Value>(CI), ~0U, P, ~0U) != NoAlias)
282 // The AliasAnalysis base class has some smarts, lets use them.
283 return AliasAnalysis::getModRefInfo(CS, P, Size);
287 AliasAnalysis::ModRefResult
288 BasicAliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) {
289 // If CS1 or CS2 are readnone, they don't interact.
290 ModRefBehavior CS1B = AliasAnalysis::getModRefBehavior(CS1);
291 if (CS1B == DoesNotAccessMemory) return NoModRef;
293 ModRefBehavior CS2B = AliasAnalysis::getModRefBehavior(CS2);
294 if (CS2B == DoesNotAccessMemory) return NoModRef;
296 // If they both only read from memory, just return ref.
297 if (CS1B == OnlyReadsMemory && CS2B == OnlyReadsMemory)
300 // Otherwise, fall back to NoAA (mod+ref).
301 return NoAA::getModRefInfo(CS1, CS2);
305 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
306 // as array references.
308 AliasAnalysis::AliasResult
309 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
310 const Value *V2, unsigned V2Size) {
311 // Strip off any constant expression casts if they exist
312 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
313 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
314 V1 = CE->getOperand(0);
315 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
316 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
317 V2 = CE->getOperand(0);
319 // Are we checking for alias of the same value?
320 if (V1 == V2) return MustAlias;
322 if (!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType()))
323 return NoAlias; // Scalars cannot alias each other
325 // Strip off cast instructions. Since V1 and V2 are pointers, they must be
326 // pointer<->pointer bitcasts.
327 if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
328 return alias(I->getOperand(0), V1Size, V2, V2Size);
329 if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
330 return alias(V1, V1Size, I->getOperand(0), V2Size);
332 // Figure out what objects these things are pointing to if we can.
333 const Value *O1 = V1->getUnderlyingObject();
334 const Value *O2 = V2->getUnderlyingObject();
337 // If V1/V2 point to two different objects we know that we have no alias.
338 if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
341 // Arguments can't alias with local allocations or noalias calls.
342 if ((isa<Argument>(O1) && (isa<AllocationInst>(O2) || isNoAliasCall(O2))) ||
343 (isa<Argument>(O2) && (isa<AllocationInst>(O1) || isNoAliasCall(O1))))
346 // Most objects can't alias null.
347 if ((isa<ConstantPointerNull>(V2) && isKnownNonNull(O1)) ||
348 (isa<ConstantPointerNull>(V1) && isKnownNonNull(O2)))
352 // If the size of one access is larger than the entire object on the other
353 // side, then we know such behavior is undefined and can assume no alias.
355 if ((V1Size != ~0U && isObjectSmallerThan(O2, V1Size, *TD)) ||
356 (V2Size != ~0U && isObjectSmallerThan(O1, V2Size, *TD)))
359 // If one pointer is the result of a call/invoke and the other is a
360 // non-escaping local object, then we know the object couldn't escape to a
361 // point where the call could return it.
362 if ((isa<CallInst>(O1) || isa<InvokeInst>(O1)) &&
363 isNonEscapingLocalObject(O2) && O1 != O2)
365 if ((isa<CallInst>(O2) || isa<InvokeInst>(O2)) &&
366 isNonEscapingLocalObject(O1) && O1 != O2)
369 // If we have two gep instructions with must-alias'ing base pointers, figure
370 // out if the indexes to the GEP tell us anything about the derived pointer.
371 // Note that we also handle chains of getelementptr instructions as well as
372 // constant expression getelementptrs here.
374 if (isGEP(V1) && isGEP(V2)) {
375 const User *GEP1 = cast<User>(V1);
376 const User *GEP2 = cast<User>(V2);
378 // If V1 and V2 are identical GEPs, just recurse down on both of them.
379 // This allows us to analyze things like:
380 // P = gep A, 0, i, 1
381 // Q = gep B, 0, i, 1
382 // by just analyzing A and B. This is even safe for variable indices.
383 if (GEP1->getType() == GEP2->getType() &&
384 GEP1->getNumOperands() == GEP2->getNumOperands() &&
385 GEP1->getOperand(0)->getType() == GEP2->getOperand(0)->getType() &&
386 // All operands are the same, ignoring the base.
387 std::equal(GEP1->op_begin()+1, GEP1->op_end(), GEP2->op_begin()+1))
388 return alias(GEP1->getOperand(0), V1Size, GEP2->getOperand(0), V2Size);
391 // Drill down into the first non-gep value, to test for must-aliasing of
392 // the base pointers.
393 while (isGEP(GEP1->getOperand(0)) &&
394 GEP1->getOperand(1) ==
395 Constant::getNullValue(GEP1->getOperand(1)->getType()))
396 GEP1 = cast<User>(GEP1->getOperand(0));
397 const Value *BasePtr1 = GEP1->getOperand(0);
399 while (isGEP(GEP2->getOperand(0)) &&
400 GEP2->getOperand(1) ==
401 Constant::getNullValue(GEP2->getOperand(1)->getType()))
402 GEP2 = cast<User>(GEP2->getOperand(0));
403 const Value *BasePtr2 = GEP2->getOperand(0);
405 // Do the base pointers alias?
406 AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
407 if (BaseAlias == NoAlias) return NoAlias;
408 if (BaseAlias == MustAlias) {
409 // If the base pointers alias each other exactly, check to see if we can
410 // figure out anything about the resultant pointers, to try to prove
413 // Collect all of the chained GEP operands together into one simple place
414 SmallVector<Value*, 16> GEP1Ops, GEP2Ops;
415 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
416 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
418 // If GetGEPOperands were able to fold to the same must-aliased pointer,
419 // do the comparison.
420 if (BasePtr1 == BasePtr2) {
422 CheckGEPInstructions(BasePtr1->getType(),
423 &GEP1Ops[0], GEP1Ops.size(), V1Size,
425 &GEP2Ops[0], GEP2Ops.size(), V2Size);
426 if (GAlias != MayAlias)
432 // Check to see if these two pointers are related by a getelementptr
433 // instruction. If one pointer is a GEP with a non-zero index of the other
434 // pointer, we know they cannot alias.
438 std::swap(V1Size, V2Size);
441 if (V1Size != ~0U && V2Size != ~0U)
443 SmallVector<Value*, 16> GEPOperands;
444 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
446 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
447 if (R == MustAlias) {
448 // If there is at least one non-zero constant index, we know they cannot
450 bool ConstantFound = false;
451 bool AllZerosFound = true;
452 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
453 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
454 if (!C->isNullValue()) {
455 ConstantFound = true;
456 AllZerosFound = false;
460 AllZerosFound = false;
463 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
464 // the ptr, the end result is a must alias also.
469 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
472 // Otherwise we have to check to see that the distance is more than
473 // the size of the argument... build an index vector that is equal to
474 // the arguments provided, except substitute 0's for any variable
475 // indexes we find...
476 if (TD && cast<PointerType>(
477 BasePtr->getType())->getElementType()->isSized()) {
478 for (unsigned i = 0; i != GEPOperands.size(); ++i)
479 if (!isa<ConstantInt>(GEPOperands[i]))
481 Constant::getNullValue(GEPOperands[i]->getType());
483 TD->getIndexedOffset(BasePtr->getType(),
487 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
497 // This function is used to determine if the indices of two GEP instructions are
498 // equal. V1 and V2 are the indices.
499 static bool IndexOperandsEqual(Value *V1, Value *V2, LLVMContext &Context) {
500 if (V1->getType() == V2->getType())
502 if (Constant *C1 = dyn_cast<Constant>(V1))
503 if (Constant *C2 = dyn_cast<Constant>(V2)) {
504 // Sign extend the constants to long types, if necessary
505 if (C1->getType() != Type::Int64Ty)
506 C1 = ConstantExpr::getSExt(C1, Type::Int64Ty);
507 if (C2->getType() != Type::Int64Ty)
508 C2 = ConstantExpr::getSExt(C2, Type::Int64Ty);
514 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
515 /// base pointers. This checks to see if the index expressions preclude the
516 /// pointers from aliasing...
517 AliasAnalysis::AliasResult
518 BasicAliasAnalysis::CheckGEPInstructions(
519 const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
520 const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
521 // We currently can't handle the case when the base pointers have different
522 // primitive types. Since this is uncommon anyway, we are happy being
523 // extremely conservative.
524 if (BasePtr1Ty != BasePtr2Ty)
527 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
529 LLVMContext &Context = GEPPointerTy->getContext();
531 // Find the (possibly empty) initial sequence of equal values... which are not
532 // necessarily constants.
533 unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
534 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
535 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
536 unsigned UnequalOper = 0;
537 while (UnequalOper != MinOperands &&
538 IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper],
540 // Advance through the type as we go...
542 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
543 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
545 // If all operands equal each other, then the derived pointers must
546 // alias each other...
548 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
549 "Ran out of type nesting, but not out of operands?");
554 // If we have seen all constant operands, and run out of indexes on one of the
555 // getelementptrs, check to see if the tail of the leftover one is all zeros.
556 // If so, return mustalias.
557 if (UnequalOper == MinOperands) {
558 if (NumGEP1Ops < NumGEP2Ops) {
559 std::swap(GEP1Ops, GEP2Ops);
560 std::swap(NumGEP1Ops, NumGEP2Ops);
563 bool AllAreZeros = true;
564 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
565 if (!isa<Constant>(GEP1Ops[i]) ||
566 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
570 if (AllAreZeros) return MustAlias;
574 // So now we know that the indexes derived from the base pointers,
575 // which are known to alias, are different. We can still determine a
576 // no-alias result if there are differing constant pairs in the index
577 // chain. For example:
578 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
580 // We have to be careful here about array accesses. In particular, consider:
581 // A[1][0] vs A[0][i]
582 // In this case, we don't *know* that the array will be accessed in bounds:
583 // the index could even be negative. Because of this, we have to
584 // conservatively *give up* and return may alias. We disregard differing
585 // array subscripts that are followed by a variable index without going
588 unsigned SizeMax = std::max(G1S, G2S);
589 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
591 // Scan for the first operand that is constant and unequal in the
592 // two getelementptrs...
593 unsigned FirstConstantOper = UnequalOper;
594 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
595 const Value *G1Oper = GEP1Ops[FirstConstantOper];
596 const Value *G2Oper = GEP2Ops[FirstConstantOper];
598 if (G1Oper != G2Oper) // Found non-equal constant indexes...
599 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
600 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
601 if (G1OC->getType() != G2OC->getType()) {
602 // Sign extend both operands to long.
603 if (G1OC->getType() != Type::Int64Ty)
604 G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty);
605 if (G2OC->getType() != Type::Int64Ty)
606 G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty);
607 GEP1Ops[FirstConstantOper] = G1OC;
608 GEP2Ops[FirstConstantOper] = G2OC;
612 // Handle the "be careful" case above: if this is an array/vector
613 // subscript, scan for a subsequent variable array index.
614 if (const SequentialType *STy =
615 dyn_cast<SequentialType>(BasePtr1Ty)) {
616 const Type *NextTy = STy;
617 bool isBadCase = false;
619 for (unsigned Idx = FirstConstantOper;
620 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
621 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
622 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
626 // If the array is indexed beyond the bounds of the static type
627 // at this level, it will also fall into the "be careful" case.
628 // It would theoretically be possible to analyze these cases,
629 // but for now just be conservatively correct.
630 if (const ArrayType *ATy = dyn_cast<ArrayType>(STy))
631 if (cast<ConstantInt>(G1OC)->getZExtValue() >=
632 ATy->getNumElements() ||
633 cast<ConstantInt>(G2OC)->getZExtValue() >=
634 ATy->getNumElements()) {
638 if (const VectorType *VTy = dyn_cast<VectorType>(STy))
639 if (cast<ConstantInt>(G1OC)->getZExtValue() >=
640 VTy->getNumElements() ||
641 cast<ConstantInt>(G2OC)->getZExtValue() >=
642 VTy->getNumElements()) {
646 STy = cast<SequentialType>(NextTy);
647 NextTy = cast<SequentialType>(NextTy)->getElementType();
650 if (isBadCase) G1OC = 0;
653 // Make sure they are comparable (ie, not constant expressions), and
654 // make sure the GEP with the smaller leading constant is GEP1.
656 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
658 if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
659 if (CV->getZExtValue()) { // If they are comparable and G2 > G1
660 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
661 std::swap(NumGEP1Ops, NumGEP2Ops);
668 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
671 // No shared constant operands, and we ran out of common operands. At this
672 // point, the GEP instructions have run through all of their operands, and we
673 // haven't found evidence that there are any deltas between the GEP's.
674 // However, one GEP may have more operands than the other. If this is the
675 // case, there may still be hope. Check this now.
676 if (FirstConstantOper == MinOperands) {
677 // Without TargetData, we won't know what the offsets are.
681 // Make GEP1Ops be the longer one if there is a longer one.
682 if (NumGEP1Ops < NumGEP2Ops) {
683 std::swap(GEP1Ops, GEP2Ops);
684 std::swap(NumGEP1Ops, NumGEP2Ops);
687 // Is there anything to check?
688 if (NumGEP1Ops > MinOperands) {
689 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
690 if (isa<ConstantInt>(GEP1Ops[i]) &&
691 !cast<ConstantInt>(GEP1Ops[i])->isZero()) {
692 // Yup, there's a constant in the tail. Set all variables to
693 // constants in the GEP instruction to make it suitable for
694 // TargetData::getIndexedOffset.
695 for (i = 0; i != MaxOperands; ++i)
696 if (!isa<ConstantInt>(GEP1Ops[i]))
697 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
698 // Okay, now get the offset. This is the relative offset for the full
700 int64_t Offset1 = TD->getIndexedOffset(GEPPointerTy, GEP1Ops,
703 // Now check without any constants at the end.
704 int64_t Offset2 = TD->getIndexedOffset(GEPPointerTy, GEP1Ops,
707 // Make sure we compare the absolute difference.
708 if (Offset1 > Offset2)
709 std::swap(Offset1, Offset2);
711 // If the tail provided a bit enough offset, return noalias!
712 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
714 // Otherwise break - we don't look for another constant in the tail.
719 // Couldn't find anything useful.
723 // If there are non-equal constants arguments, then we can figure
724 // out a minimum known delta between the two index expressions... at
725 // this point we know that the first constant index of GEP1 is less
726 // than the first constant index of GEP2.
728 // Advance BasePtr[12]Ty over this first differing constant operand.
729 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
730 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
731 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
732 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
734 // We are going to be using TargetData::getIndexedOffset to determine the
735 // offset that each of the GEP's is reaching. To do this, we have to convert
736 // all variable references to constant references. To do this, we convert the
737 // initial sequence of array subscripts into constant zeros to start with.
738 const Type *ZeroIdxTy = GEPPointerTy;
739 for (unsigned i = 0; i != FirstConstantOper; ++i) {
740 if (!isa<StructType>(ZeroIdxTy))
741 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty);
743 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
744 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
747 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
749 // Loop over the rest of the operands...
750 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
751 const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
752 const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
753 // If they are equal, use a zero index...
754 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
755 if (!isa<ConstantInt>(Op1))
756 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
757 // Otherwise, just keep the constants we have.
760 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
761 // If this is an array index, make sure the array element is in range.
762 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
763 if (Op1C->getZExtValue() >= AT->getNumElements())
764 return MayAlias; // Be conservative with out-of-range accesses
765 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) {
766 if (Op1C->getZExtValue() >= VT->getNumElements())
767 return MayAlias; // Be conservative with out-of-range accesses
771 // GEP1 is known to produce a value less than GEP2. To be
772 // conservatively correct, we must assume the largest possible
773 // constant is used in this position. This cannot be the initial
774 // index to the GEP instructions (because we know we have at least one
775 // element before this one with the different constant arguments), so
776 // we know that the current index must be into either a struct or
777 // array. Because we know it's not constant, this cannot be a
778 // structure index. Because of this, we can calculate the maximum
781 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
783 ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1);
784 else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty))
786 ConstantInt::get(Type::Int64Ty,VT->getNumElements()-1);
791 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
792 // If this is an array index, make sure the array element is in range.
793 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr2Ty)) {
794 if (Op2C->getZExtValue() >= AT->getNumElements())
795 return MayAlias; // Be conservative with out-of-range accesses
796 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr2Ty)) {
797 if (Op2C->getZExtValue() >= VT->getNumElements())
798 return MayAlias; // Be conservative with out-of-range accesses
800 } else { // Conservatively assume the minimum value for this index
801 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
806 if (BasePtr1Ty && Op1) {
807 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
808 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
813 if (BasePtr2Ty && Op2) {
814 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
815 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
821 if (TD && GEPPointerTy->getElementType()->isSized()) {
823 TD->getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
825 TD->getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
826 assert(Offset1 != Offset2 &&
827 "There is at least one different constant here!");
829 // Make sure we compare the absolute difference.
830 if (Offset1 > Offset2)
831 std::swap(Offset1, Offset2);
833 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
834 //cerr << "Determined that these two GEP's don't alias ["
835 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
842 // Make sure that anything that uses AliasAnalysis pulls in this file...
843 DEFINING_FILE_FOR(BasicAliasAnalysis)