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/Pass.h"
27 #include "llvm/Target/TargetData.h"
28 #include "llvm/ADT/SmallVector.h"
29 #include "llvm/ADT/STLExtras.h"
30 #include "llvm/Support/Compiler.h"
31 #include "llvm/Support/ErrorHandling.h"
32 #include "llvm/Support/GetElementPtrTypeIterator.h"
36 //===----------------------------------------------------------------------===//
38 //===----------------------------------------------------------------------===//
40 static const User *isGEP(const Value *V) {
41 if (isa<GetElementPtrInst>(V) ||
42 (isa<ConstantExpr>(V) &&
43 cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
48 static const Value *GetGEPOperands(const Value *V,
49 SmallVector<Value*, 16> &GEPOps) {
50 assert(GEPOps.empty() && "Expect empty list to populate!");
51 GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
52 cast<User>(V)->op_end());
54 // Accumulate all of the chained indexes into the operand array
55 V = cast<User>(V)->getOperand(0);
57 while (const User *G = isGEP(V)) {
58 if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
59 !cast<Constant>(GEPOps[0])->isNullValue())
60 break; // Don't handle folding arbitrary pointer offsets yet...
61 GEPOps.erase(GEPOps.begin()); // Drop the zero index
62 GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
68 /// isKnownNonNull - Return true if we know that the specified value is never
70 static bool isKnownNonNull(const Value *V) {
71 // Alloca never returns null, malloc might.
72 if (isa<AllocaInst>(V)) return true;
74 // A byval argument is never null.
75 if (const Argument *A = dyn_cast<Argument>(V))
76 return A->hasByValAttr();
78 // Global values are not null unless extern weak.
79 if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
80 return !GV->hasExternalWeakLinkage();
84 /// isNonEscapingLocalObject - Return true if the pointer is to a function-local
85 /// object that never escapes from the function.
86 static bool isNonEscapingLocalObject(const Value *V) {
87 // If this is a local allocation, check to see if it escapes.
88 if (isa<AllocationInst>(V) || isNoAliasCall(V))
89 return !PointerMayBeCaptured(V, false);
91 // If this is an argument that corresponds to a byval or noalias argument,
92 // then it has not escaped before entering the function. Check if it escapes
93 // inside the function.
94 if (const Argument *A = dyn_cast<Argument>(V))
95 if (A->hasByValAttr() || A->hasNoAliasAttr()) {
96 // Don't bother analyzing arguments already known not to escape.
97 if (A->hasNoCaptureAttr())
99 return !PointerMayBeCaptured(V, false);
105 /// isObjectSmallerThan - Return true if we can prove that the object specified
106 /// by V is smaller than Size.
107 static bool isObjectSmallerThan(const Value *V, unsigned Size,
108 const TargetData &TD) {
109 const Type *AccessTy;
110 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
111 AccessTy = GV->getType()->getElementType();
112 } else if (const AllocationInst *AI = dyn_cast<AllocationInst>(V)) {
113 if (!AI->isArrayAllocation())
114 AccessTy = AI->getType()->getElementType();
117 } else if (const Argument *A = dyn_cast<Argument>(V)) {
118 if (A->hasByValAttr())
119 AccessTy = cast<PointerType>(A->getType())->getElementType();
126 if (AccessTy->isSized())
127 return TD.getTypeAllocSize(AccessTy) < Size;
131 //===----------------------------------------------------------------------===//
133 //===----------------------------------------------------------------------===//
136 /// NoAA - This class implements the -no-aa pass, which always returns "I
137 /// don't know" for alias queries. NoAA is unlike other alias analysis
138 /// implementations, in that it does not chain to a previous analysis. As
139 /// such it doesn't follow many of the rules that other alias analyses must.
141 struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
142 static char ID; // Class identification, replacement for typeinfo
143 NoAA() : ImmutablePass(&ID) {}
144 explicit NoAA(void *PID) : ImmutablePass(PID) { }
146 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
147 AU.addRequired<TargetData>();
150 virtual void initializePass() {
151 TD = &getAnalysis<TargetData>();
154 virtual AliasResult alias(const Value *V1, unsigned V1Size,
155 const Value *V2, unsigned V2Size) {
159 virtual void getArgumentAccesses(Function *F, CallSite CS,
160 std::vector<PointerAccessInfo> &Info) {
161 llvm_unreachable("This method may not be called on this function!");
164 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
165 virtual bool pointsToConstantMemory(const Value *P) { return false; }
166 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
169 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
172 virtual bool hasNoModRefInfoForCalls() const { return true; }
174 virtual void deleteValue(Value *V) {}
175 virtual void copyValue(Value *From, Value *To) {}
177 } // End of anonymous namespace
179 // Register this pass...
181 static RegisterPass<NoAA>
182 U("no-aa", "No Alias Analysis (always returns 'may' alias)", true, true);
184 // Declare that we implement the AliasAnalysis interface
185 static RegisterAnalysisGroup<AliasAnalysis> V(U);
187 ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
189 //===----------------------------------------------------------------------===//
191 //===----------------------------------------------------------------------===//
194 /// BasicAliasAnalysis - This is the default alias analysis implementation.
195 /// Because it doesn't chain to a previous alias analysis (like -no-aa), it
196 /// derives from the NoAA class.
197 struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA {
198 static char ID; // Class identification, replacement for typeinfo
199 BasicAliasAnalysis() : NoAA(&ID) {}
200 AliasResult alias(const Value *V1, unsigned V1Size,
201 const Value *V2, unsigned V2Size);
203 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
204 ModRefResult getModRefInfo(CallSite CS1, CallSite CS2);
206 /// hasNoModRefInfoForCalls - We can provide mod/ref information against
207 /// non-escaping allocations.
208 virtual bool hasNoModRefInfoForCalls() const { return false; }
210 /// pointsToConstantMemory - Chase pointers until we find a (constant
212 bool pointsToConstantMemory(const Value *P);
215 // CheckGEPInstructions - Check two GEP instructions with known
216 // must-aliasing base pointers. This checks to see if the index expressions
217 // preclude the pointers from aliasing...
219 CheckGEPInstructions(const Type* BasePtr1Ty,
220 Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size,
221 const Type *BasePtr2Ty,
222 Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size);
224 } // End of anonymous namespace
226 // Register this pass...
227 char BasicAliasAnalysis::ID = 0;
228 static RegisterPass<BasicAliasAnalysis>
229 X("basicaa", "Basic Alias Analysis (default AA impl)", false, true);
231 // Declare that we implement the AliasAnalysis interface
232 static RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
234 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
235 return new BasicAliasAnalysis();
239 /// pointsToConstantMemory - Chase pointers until we find a (constant
241 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
242 if (const GlobalVariable *GV =
243 dyn_cast<GlobalVariable>(P->getUnderlyingObject()))
244 return GV->isConstant();
249 // getModRefInfo - Check to see if the specified callsite can clobber the
250 // specified memory object. Since we only look at local properties of this
251 // function, we really can't say much about this query. We do, however, use
252 // simple "address taken" analysis on local objects.
254 AliasAnalysis::ModRefResult
255 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
256 if (!isa<Constant>(P)) {
257 const Value *Object = P->getUnderlyingObject();
259 // If this is a tail call and P points to a stack location, we know that
260 // the tail call cannot access or modify the local stack.
261 // We cannot exclude byval arguments here; these belong to the caller of
262 // the current function not to the current function, and a tail callee
263 // may reference them.
264 if (isa<AllocaInst>(Object))
265 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
266 if (CI->isTailCall())
269 // If the pointer is to a locally allocated object that does not escape,
270 // then the call can not mod/ref the pointer unless the call takes the
271 // argument without capturing it.
272 if (isNonEscapingLocalObject(Object) && CS.getInstruction() != Object) {
273 bool passedAsArg = false;
274 // TODO: Eventually only check 'nocapture' arguments.
275 for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
277 if (isa<PointerType>((*CI)->getType()) &&
278 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);
291 AliasAnalysis::ModRefResult
292 BasicAliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) {
293 // If CS1 or CS2 are readnone, they don't interact.
294 ModRefBehavior CS1B = AliasAnalysis::getModRefBehavior(CS1);
295 if (CS1B == DoesNotAccessMemory) return NoModRef;
297 ModRefBehavior CS2B = AliasAnalysis::getModRefBehavior(CS2);
298 if (CS2B == DoesNotAccessMemory) return NoModRef;
300 // If they both only read from memory, just return ref.
301 if (CS1B == OnlyReadsMemory && CS2B == OnlyReadsMemory)
304 // Otherwise, fall back to NoAA (mod+ref).
305 return NoAA::getModRefInfo(CS1, CS2);
309 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
310 // as array references.
312 AliasAnalysis::AliasResult
313 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
314 const Value *V2, unsigned V2Size) {
315 Context = &V1->getType()->getContext();
317 // Strip off any constant expression casts if they exist
318 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
319 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
320 V1 = CE->getOperand(0);
321 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
322 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
323 V2 = CE->getOperand(0);
325 // Are we checking for alias of the same value?
326 if (V1 == V2) return MustAlias;
328 if (!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType()))
329 return NoAlias; // Scalars cannot alias each other
331 // Strip off cast instructions. Since V1 and V2 are pointers, they must be
332 // pointer<->pointer bitcasts.
333 if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
334 return alias(I->getOperand(0), V1Size, V2, V2Size);
335 if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
336 return alias(V1, V1Size, I->getOperand(0), V2Size);
338 // Figure out what objects these things are pointing to if we can.
339 const Value *O1 = V1->getUnderlyingObject();
340 const Value *O2 = V2->getUnderlyingObject();
343 // If V1/V2 point to two different objects we know that we have no alias.
344 if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
347 // Arguments can't alias with local allocations or noalias calls.
348 if ((isa<Argument>(O1) && (isa<AllocationInst>(O2) || isNoAliasCall(O2))) ||
349 (isa<Argument>(O2) && (isa<AllocationInst>(O1) || isNoAliasCall(O1))))
352 // Most objects can't alias null.
353 if ((isa<ConstantPointerNull>(V2) && isKnownNonNull(O1)) ||
354 (isa<ConstantPointerNull>(V1) && isKnownNonNull(O2)))
358 // If the size of one access is larger than the entire object on the other
359 // side, then we know such behavior is undefined and can assume no alias.
360 const TargetData &TD = getTargetData();
361 if ((V1Size != ~0U && isObjectSmallerThan(O2, V1Size, TD)) ||
362 (V2Size != ~0U && isObjectSmallerThan(O1, V2Size, TD)))
365 // If one pointer is the result of a call/invoke and the other is a
366 // non-escaping local object, then we know the object couldn't escape to a
367 // point where the call could return it.
368 if ((isa<CallInst>(O1) || isa<InvokeInst>(O1)) &&
369 isNonEscapingLocalObject(O2) && O1 != O2)
371 if ((isa<CallInst>(O2) || isa<InvokeInst>(O2)) &&
372 isNonEscapingLocalObject(O1) && O1 != O2)
375 // If we have two gep instructions with must-alias'ing base pointers, figure
376 // out if the indexes to the GEP tell us anything about the derived pointer.
377 // Note that we also handle chains of getelementptr instructions as well as
378 // constant expression getelementptrs here.
380 if (isGEP(V1) && isGEP(V2)) {
381 const User *GEP1 = cast<User>(V1);
382 const User *GEP2 = cast<User>(V2);
384 // If V1 and V2 are identical GEPs, just recurse down on both of them.
385 // This allows us to analyze things like:
386 // P = gep A, 0, i, 1
387 // Q = gep B, 0, i, 1
388 // by just analyzing A and B. This is even safe for variable indices.
389 if (GEP1->getType() == GEP2->getType() &&
390 GEP1->getNumOperands() == GEP2->getNumOperands() &&
391 GEP1->getOperand(0)->getType() == GEP2->getOperand(0)->getType() &&
392 // All operands are the same, ignoring the base.
393 std::equal(GEP1->op_begin()+1, GEP1->op_end(), GEP2->op_begin()+1))
394 return alias(GEP1->getOperand(0), V1Size, GEP2->getOperand(0), V2Size);
397 // Drill down into the first non-gep value, to test for must-aliasing of
398 // the base pointers.
399 while (isGEP(GEP1->getOperand(0)) &&
400 GEP1->getOperand(1) ==
401 Context->getNullValue(GEP1->getOperand(1)->getType()))
402 GEP1 = cast<User>(GEP1->getOperand(0));
403 const Value *BasePtr1 = GEP1->getOperand(0);
405 while (isGEP(GEP2->getOperand(0)) &&
406 GEP2->getOperand(1) ==
407 Context->getNullValue(GEP2->getOperand(1)->getType()))
408 GEP2 = cast<User>(GEP2->getOperand(0));
409 const Value *BasePtr2 = GEP2->getOperand(0);
411 // Do the base pointers alias?
412 AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
413 if (BaseAlias == NoAlias) return NoAlias;
414 if (BaseAlias == MustAlias) {
415 // If the base pointers alias each other exactly, check to see if we can
416 // figure out anything about the resultant pointers, to try to prove
419 // Collect all of the chained GEP operands together into one simple place
420 SmallVector<Value*, 16> GEP1Ops, GEP2Ops;
421 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
422 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
424 // If GetGEPOperands were able to fold to the same must-aliased pointer,
425 // do the comparison.
426 if (BasePtr1 == BasePtr2) {
428 CheckGEPInstructions(BasePtr1->getType(),
429 &GEP1Ops[0], GEP1Ops.size(), V1Size,
431 &GEP2Ops[0], GEP2Ops.size(), V2Size);
432 if (GAlias != MayAlias)
438 // Check to see if these two pointers are related by a getelementptr
439 // instruction. If one pointer is a GEP with a non-zero index of the other
440 // pointer, we know they cannot alias.
444 std::swap(V1Size, V2Size);
447 if (V1Size != ~0U && V2Size != ~0U)
449 SmallVector<Value*, 16> GEPOperands;
450 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
452 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
453 if (R == MustAlias) {
454 // If there is at least one non-zero constant index, we know they cannot
456 bool ConstantFound = false;
457 bool AllZerosFound = true;
458 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
459 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
460 if (!C->isNullValue()) {
461 ConstantFound = true;
462 AllZerosFound = false;
466 AllZerosFound = false;
469 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
470 // the ptr, the end result is a must alias also.
475 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
478 // Otherwise we have to check to see that the distance is more than
479 // the size of the argument... build an index vector that is equal to
480 // the arguments provided, except substitute 0's for any variable
481 // indexes we find...
482 if (cast<PointerType>(
483 BasePtr->getType())->getElementType()->isSized()) {
484 for (unsigned i = 0; i != GEPOperands.size(); ++i)
485 if (!isa<ConstantInt>(GEPOperands[i]))
487 Context->getNullValue(GEPOperands[i]->getType());
489 getTargetData().getIndexedOffset(BasePtr->getType(),
493 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
503 // This function is used to determine if the indices of two GEP instructions are
504 // equal. V1 and V2 are the indices.
505 static bool IndexOperandsEqual(Value *V1, Value *V2, LLVMContext *Context) {
506 if (V1->getType() == V2->getType())
508 if (Constant *C1 = dyn_cast<Constant>(V1))
509 if (Constant *C2 = dyn_cast<Constant>(V2)) {
510 // Sign extend the constants to long types, if necessary
511 if (C1->getType() != Type::Int64Ty)
512 C1 = Context->getConstantExprSExt(C1, Type::Int64Ty);
513 if (C2->getType() != Type::Int64Ty)
514 C2 = Context->getConstantExprSExt(C2, Type::Int64Ty);
520 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
521 /// base pointers. This checks to see if the index expressions preclude the
522 /// pointers from aliasing...
523 AliasAnalysis::AliasResult
524 BasicAliasAnalysis::CheckGEPInstructions(
525 const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
526 const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
527 // We currently can't handle the case when the base pointers have different
528 // primitive types. Since this is uncommon anyway, we are happy being
529 // extremely conservative.
530 if (BasePtr1Ty != BasePtr2Ty)
533 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
535 Context = &GEPPointerTy->getContext();
537 // Find the (possibly empty) initial sequence of equal values... which are not
538 // necessarily constants.
539 unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
540 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
541 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
542 unsigned UnequalOper = 0;
543 while (UnequalOper != MinOperands &&
544 IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper],
546 // Advance through the type as we go...
548 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
549 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
551 // If all operands equal each other, then the derived pointers must
552 // alias each other...
554 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
555 "Ran out of type nesting, but not out of operands?");
560 // If we have seen all constant operands, and run out of indexes on one of the
561 // getelementptrs, check to see if the tail of the leftover one is all zeros.
562 // If so, return mustalias.
563 if (UnequalOper == MinOperands) {
564 if (NumGEP1Ops < NumGEP2Ops) {
565 std::swap(GEP1Ops, GEP2Ops);
566 std::swap(NumGEP1Ops, NumGEP2Ops);
569 bool AllAreZeros = true;
570 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
571 if (!isa<Constant>(GEP1Ops[i]) ||
572 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
576 if (AllAreZeros) return MustAlias;
580 // So now we know that the indexes derived from the base pointers,
581 // which are known to alias, are different. We can still determine a
582 // no-alias result if there are differing constant pairs in the index
583 // chain. For example:
584 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
586 // We have to be careful here about array accesses. In particular, consider:
587 // A[1][0] vs A[0][i]
588 // In this case, we don't *know* that the array will be accessed in bounds:
589 // the index could even be negative. Because of this, we have to
590 // conservatively *give up* and return may alias. We disregard differing
591 // array subscripts that are followed by a variable index without going
594 unsigned SizeMax = std::max(G1S, G2S);
595 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
597 // Scan for the first operand that is constant and unequal in the
598 // two getelementptrs...
599 unsigned FirstConstantOper = UnequalOper;
600 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
601 const Value *G1Oper = GEP1Ops[FirstConstantOper];
602 const Value *G2Oper = GEP2Ops[FirstConstantOper];
604 if (G1Oper != G2Oper) // Found non-equal constant indexes...
605 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
606 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
607 if (G1OC->getType() != G2OC->getType()) {
608 // Sign extend both operands to long.
609 if (G1OC->getType() != Type::Int64Ty)
610 G1OC = Context->getConstantExprSExt(G1OC, Type::Int64Ty);
611 if (G2OC->getType() != Type::Int64Ty)
612 G2OC = Context->getConstantExprSExt(G2OC, Type::Int64Ty);
613 GEP1Ops[FirstConstantOper] = G1OC;
614 GEP2Ops[FirstConstantOper] = G2OC;
618 // Handle the "be careful" case above: if this is an array/vector
619 // subscript, scan for a subsequent variable array index.
620 if (const SequentialType *STy =
621 dyn_cast<SequentialType>(BasePtr1Ty)) {
622 const Type *NextTy = STy;
623 bool isBadCase = false;
625 for (unsigned Idx = FirstConstantOper;
626 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
627 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
628 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
632 // If the array is indexed beyond the bounds of the static type
633 // at this level, it will also fall into the "be careful" case.
634 // It would theoretically be possible to analyze these cases,
635 // but for now just be conservatively correct.
636 if (const ArrayType *ATy = dyn_cast<ArrayType>(STy))
637 if (cast<ConstantInt>(G1OC)->getZExtValue() >=
638 ATy->getNumElements() ||
639 cast<ConstantInt>(G2OC)->getZExtValue() >=
640 ATy->getNumElements()) {
644 if (const VectorType *VTy = dyn_cast<VectorType>(STy))
645 if (cast<ConstantInt>(G1OC)->getZExtValue() >=
646 VTy->getNumElements() ||
647 cast<ConstantInt>(G2OC)->getZExtValue() >=
648 VTy->getNumElements()) {
652 STy = cast<SequentialType>(NextTy);
653 NextTy = cast<SequentialType>(NextTy)->getElementType();
656 if (isBadCase) G1OC = 0;
659 // Make sure they are comparable (ie, not constant expressions), and
660 // make sure the GEP with the smaller leading constant is GEP1.
662 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
664 if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
665 if (CV->getZExtValue()) { // If they are comparable and G2 > G1
666 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
667 std::swap(NumGEP1Ops, NumGEP2Ops);
674 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
677 // No shared constant operands, and we ran out of common operands. At this
678 // point, the GEP instructions have run through all of their operands, and we
679 // haven't found evidence that there are any deltas between the GEP's.
680 // However, one GEP may have more operands than the other. If this is the
681 // case, there may still be hope. Check this now.
682 if (FirstConstantOper == MinOperands) {
683 // Make GEP1Ops be the longer one if there is a longer one.
684 if (NumGEP1Ops < NumGEP2Ops) {
685 std::swap(GEP1Ops, GEP2Ops);
686 std::swap(NumGEP1Ops, NumGEP2Ops);
689 // Is there anything to check?
690 if (NumGEP1Ops > MinOperands) {
691 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
692 if (isa<ConstantInt>(GEP1Ops[i]) &&
693 !cast<ConstantInt>(GEP1Ops[i])->isZero()) {
694 // Yup, there's a constant in the tail. Set all variables to
695 // constants in the GEP instruction to make it suitable for
696 // TargetData::getIndexedOffset.
697 for (i = 0; i != MaxOperands; ++i)
698 if (!isa<ConstantInt>(GEP1Ops[i]))
699 GEP1Ops[i] = Context->getNullValue(GEP1Ops[i]->getType());
700 // Okay, now get the offset. This is the relative offset for the full
702 const TargetData &TD = getTargetData();
703 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
706 // Now check without any constants at the end.
707 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
710 // Make sure we compare the absolute difference.
711 if (Offset1 > Offset2)
712 std::swap(Offset1, Offset2);
714 // If the tail provided a bit enough offset, return noalias!
715 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
717 // Otherwise break - we don't look for another constant in the tail.
722 // Couldn't find anything useful.
726 // If there are non-equal constants arguments, then we can figure
727 // out a minimum known delta between the two index expressions... at
728 // this point we know that the first constant index of GEP1 is less
729 // than the first constant index of GEP2.
731 // Advance BasePtr[12]Ty over this first differing constant operand.
732 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
733 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
734 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
735 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
737 // We are going to be using TargetData::getIndexedOffset to determine the
738 // offset that each of the GEP's is reaching. To do this, we have to convert
739 // all variable references to constant references. To do this, we convert the
740 // initial sequence of array subscripts into constant zeros to start with.
741 const Type *ZeroIdxTy = GEPPointerTy;
742 for (unsigned i = 0; i != FirstConstantOper; ++i) {
743 if (!isa<StructType>(ZeroIdxTy))
744 GEP1Ops[i] = GEP2Ops[i] = Context->getNullValue(Type::Int32Ty);
746 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
747 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
750 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
752 // Loop over the rest of the operands...
753 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
754 const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
755 const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
756 // If they are equal, use a zero index...
757 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
758 if (!isa<ConstantInt>(Op1))
759 GEP1Ops[i] = GEP2Ops[i] = Context->getNullValue(Op1->getType());
760 // Otherwise, just keep the constants we have.
763 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
764 // If this is an array index, make sure the array element is in range.
765 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
766 if (Op1C->getZExtValue() >= AT->getNumElements())
767 return MayAlias; // Be conservative with out-of-range accesses
768 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) {
769 if (Op1C->getZExtValue() >= VT->getNumElements())
770 return MayAlias; // Be conservative with out-of-range accesses
774 // GEP1 is known to produce a value less than GEP2. To be
775 // conservatively correct, we must assume the largest possible
776 // constant is used in this position. This cannot be the initial
777 // index to the GEP instructions (because we know we have at least one
778 // element before this one with the different constant arguments), so
779 // we know that the current index must be into either a struct or
780 // array. Because we know it's not constant, this cannot be a
781 // structure index. Because of this, we can calculate the maximum
784 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
786 Context->getConstantInt(Type::Int64Ty,AT->getNumElements()-1);
787 else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty))
789 Context->getConstantInt(Type::Int64Ty,VT->getNumElements()-1);
794 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
795 // If this is an array index, make sure the array element is in range.
796 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr2Ty)) {
797 if (Op2C->getZExtValue() >= AT->getNumElements())
798 return MayAlias; // Be conservative with out-of-range accesses
799 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr2Ty)) {
800 if (Op2C->getZExtValue() >= VT->getNumElements())
801 return MayAlias; // Be conservative with out-of-range accesses
803 } else { // Conservatively assume the minimum value for this index
804 GEP2Ops[i] = Context->getNullValue(Op2->getType());
809 if (BasePtr1Ty && Op1) {
810 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
811 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
816 if (BasePtr2Ty && Op2) {
817 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
818 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
824 if (GEPPointerTy->getElementType()->isSized()) {
826 getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
828 getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
829 assert(Offset1 != Offset2 &&
830 "There is at least one different constant here!");
832 // Make sure we compare the absolute difference.
833 if (Offset1 > Offset2)
834 std::swap(Offset1, Offset2);
836 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
837 //cerr << "Determined that these two GEP's don't alias ["
838 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
845 // Make sure that anything that uses AliasAnalysis pulls in this file...
846 DEFINING_FILE_FOR(BasicAliasAnalysis)