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 // Strip off any constant expression casts if they exist
316 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
317 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
318 V1 = CE->getOperand(0);
319 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
320 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
321 V2 = CE->getOperand(0);
323 // Are we checking for alias of the same value?
324 if (V1 == V2) return MustAlias;
326 if (!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType()))
327 return NoAlias; // Scalars cannot alias each other
329 // Strip off cast instructions. Since V1 and V2 are pointers, they must be
330 // pointer<->pointer bitcasts.
331 if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
332 return alias(I->getOperand(0), V1Size, V2, V2Size);
333 if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
334 return alias(V1, V1Size, I->getOperand(0), V2Size);
336 // Figure out what objects these things are pointing to if we can.
337 const Value *O1 = V1->getUnderlyingObject();
338 const Value *O2 = V2->getUnderlyingObject();
341 // If V1/V2 point to two different objects we know that we have no alias.
342 if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
345 // Arguments can't alias with local allocations or noalias calls.
346 if ((isa<Argument>(O1) && (isa<AllocationInst>(O2) || isNoAliasCall(O2))) ||
347 (isa<Argument>(O2) && (isa<AllocationInst>(O1) || isNoAliasCall(O1))))
350 // Most objects can't alias null.
351 if ((isa<ConstantPointerNull>(V2) && isKnownNonNull(O1)) ||
352 (isa<ConstantPointerNull>(V1) && isKnownNonNull(O2)))
356 // If the size of one access is larger than the entire object on the other
357 // side, then we know such behavior is undefined and can assume no alias.
358 const TargetData &TD = getTargetData();
359 if ((V1Size != ~0U && isObjectSmallerThan(O2, V1Size, TD)) ||
360 (V2Size != ~0U && isObjectSmallerThan(O1, V2Size, TD)))
363 // If one pointer is the result of a call/invoke and the other is a
364 // non-escaping local object, then we know the object couldn't escape to a
365 // point where the call could return it.
366 if ((isa<CallInst>(O1) || isa<InvokeInst>(O1)) &&
367 isNonEscapingLocalObject(O2) && O1 != O2)
369 if ((isa<CallInst>(O2) || isa<InvokeInst>(O2)) &&
370 isNonEscapingLocalObject(O1) && O1 != O2)
373 // If we have two gep instructions with must-alias'ing base pointers, figure
374 // out if the indexes to the GEP tell us anything about the derived pointer.
375 // Note that we also handle chains of getelementptr instructions as well as
376 // constant expression getelementptrs here.
378 if (isGEP(V1) && isGEP(V2)) {
379 const User *GEP1 = cast<User>(V1);
380 const User *GEP2 = cast<User>(V2);
382 // If V1 and V2 are identical GEPs, just recurse down on both of them.
383 // This allows us to analyze things like:
384 // P = gep A, 0, i, 1
385 // Q = gep B, 0, i, 1
386 // by just analyzing A and B. This is even safe for variable indices.
387 if (GEP1->getType() == GEP2->getType() &&
388 GEP1->getNumOperands() == GEP2->getNumOperands() &&
389 GEP1->getOperand(0)->getType() == GEP2->getOperand(0)->getType() &&
390 // All operands are the same, ignoring the base.
391 std::equal(GEP1->op_begin()+1, GEP1->op_end(), GEP2->op_begin()+1))
392 return alias(GEP1->getOperand(0), V1Size, GEP2->getOperand(0), V2Size);
395 // Drill down into the first non-gep value, to test for must-aliasing of
396 // the base pointers.
397 while (isGEP(GEP1->getOperand(0)) &&
398 GEP1->getOperand(1) ==
399 Context->getNullValue(GEP1->getOperand(1)->getType()))
400 GEP1 = cast<User>(GEP1->getOperand(0));
401 const Value *BasePtr1 = GEP1->getOperand(0);
403 while (isGEP(GEP2->getOperand(0)) &&
404 GEP2->getOperand(1) ==
405 Context->getNullValue(GEP2->getOperand(1)->getType()))
406 GEP2 = cast<User>(GEP2->getOperand(0));
407 const Value *BasePtr2 = GEP2->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 Context->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 determine if the indices of two GEP instructions are
502 // equal. V1 and V2 are the indices.
503 static bool IndexOperandsEqual(Value *V1, Value *V2, LLVMContext *Context) {
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 = Context->getConstantExprSExt(C1, Type::Int64Ty);
511 if (C2->getType() != Type::Int64Ty)
512 C2 = Context->getConstantExprSExt(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],
542 // Advance through the type as we go...
544 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
545 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
547 // If all operands equal each other, then the derived pointers must
548 // alias each other...
550 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
551 "Ran out of type nesting, but not out of operands?");
556 // If we have seen all constant operands, and run out of indexes on one of the
557 // getelementptrs, check to see if the tail of the leftover one is all zeros.
558 // If so, return mustalias.
559 if (UnequalOper == MinOperands) {
560 if (NumGEP1Ops < NumGEP2Ops) {
561 std::swap(GEP1Ops, GEP2Ops);
562 std::swap(NumGEP1Ops, NumGEP2Ops);
565 bool AllAreZeros = true;
566 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
567 if (!isa<Constant>(GEP1Ops[i]) ||
568 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
572 if (AllAreZeros) return MustAlias;
576 // So now we know that the indexes derived from the base pointers,
577 // which are known to alias, are different. We can still determine a
578 // no-alias result if there are differing constant pairs in the index
579 // chain. For example:
580 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
582 // We have to be careful here about array accesses. In particular, consider:
583 // A[1][0] vs A[0][i]
584 // In this case, we don't *know* that the array will be accessed in bounds:
585 // the index could even be negative. Because of this, we have to
586 // conservatively *give up* and return may alias. We disregard differing
587 // array subscripts that are followed by a variable index without going
590 unsigned SizeMax = std::max(G1S, G2S);
591 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
593 // Scan for the first operand that is constant and unequal in the
594 // two getelementptrs...
595 unsigned FirstConstantOper = UnequalOper;
596 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
597 const Value *G1Oper = GEP1Ops[FirstConstantOper];
598 const Value *G2Oper = GEP2Ops[FirstConstantOper];
600 if (G1Oper != G2Oper) // Found non-equal constant indexes...
601 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
602 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
603 if (G1OC->getType() != G2OC->getType()) {
604 // Sign extend both operands to long.
605 if (G1OC->getType() != Type::Int64Ty)
606 G1OC = Context->getConstantExprSExt(G1OC, Type::Int64Ty);
607 if (G2OC->getType() != Type::Int64Ty)
608 G2OC = Context->getConstantExprSExt(G2OC, Type::Int64Ty);
609 GEP1Ops[FirstConstantOper] = G1OC;
610 GEP2Ops[FirstConstantOper] = G2OC;
614 // Handle the "be careful" case above: if this is an array/vector
615 // subscript, scan for a subsequent variable array index.
616 if (const SequentialType *STy =
617 dyn_cast<SequentialType>(BasePtr1Ty)) {
618 const Type *NextTy = STy;
619 bool isBadCase = false;
621 for (unsigned Idx = FirstConstantOper;
622 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
623 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
624 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
628 // If the array is indexed beyond the bounds of the static type
629 // at this level, it will also fall into the "be careful" case.
630 // It would theoretically be possible to analyze these cases,
631 // but for now just be conservatively correct.
632 if (const ArrayType *ATy = dyn_cast<ArrayType>(STy))
633 if (cast<ConstantInt>(G1OC)->getZExtValue() >=
634 ATy->getNumElements() ||
635 cast<ConstantInt>(G2OC)->getZExtValue() >=
636 ATy->getNumElements()) {
640 if (const VectorType *VTy = dyn_cast<VectorType>(STy))
641 if (cast<ConstantInt>(G1OC)->getZExtValue() >=
642 VTy->getNumElements() ||
643 cast<ConstantInt>(G2OC)->getZExtValue() >=
644 VTy->getNumElements()) {
648 STy = cast<SequentialType>(NextTy);
649 NextTy = cast<SequentialType>(NextTy)->getElementType();
652 if (isBadCase) G1OC = 0;
655 // Make sure they are comparable (ie, not constant expressions), and
656 // make sure the GEP with the smaller leading constant is GEP1.
658 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
660 if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
661 if (CV->getZExtValue()) { // If they are comparable and G2 > G1
662 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
663 std::swap(NumGEP1Ops, NumGEP2Ops);
670 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
673 // No shared constant operands, and we ran out of common operands. At this
674 // point, the GEP instructions have run through all of their operands, and we
675 // haven't found evidence that there are any deltas between the GEP's.
676 // However, one GEP may have more operands than the other. If this is the
677 // case, there may still be hope. Check this now.
678 if (FirstConstantOper == MinOperands) {
679 // Make GEP1Ops be the longer one if there is a longer one.
680 if (NumGEP1Ops < NumGEP2Ops) {
681 std::swap(GEP1Ops, GEP2Ops);
682 std::swap(NumGEP1Ops, NumGEP2Ops);
685 // Is there anything to check?
686 if (NumGEP1Ops > MinOperands) {
687 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
688 if (isa<ConstantInt>(GEP1Ops[i]) &&
689 !cast<ConstantInt>(GEP1Ops[i])->isZero()) {
690 // Yup, there's a constant in the tail. Set all variables to
691 // constants in the GEP instruction to make it suitable for
692 // TargetData::getIndexedOffset.
693 for (i = 0; i != MaxOperands; ++i)
694 if (!isa<ConstantInt>(GEP1Ops[i]))
695 GEP1Ops[i] = Context->getNullValue(GEP1Ops[i]->getType());
696 // Okay, now get the offset. This is the relative offset for the full
698 const TargetData &TD = getTargetData();
699 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
702 // Now check without any constants at the end.
703 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
706 // Make sure we compare the absolute difference.
707 if (Offset1 > Offset2)
708 std::swap(Offset1, Offset2);
710 // If the tail provided a bit enough offset, return noalias!
711 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
713 // Otherwise break - we don't look for another constant in the tail.
718 // Couldn't find anything useful.
722 // If there are non-equal constants arguments, then we can figure
723 // out a minimum known delta between the two index expressions... at
724 // this point we know that the first constant index of GEP1 is less
725 // than the first constant index of GEP2.
727 // Advance BasePtr[12]Ty over this first differing constant operand.
728 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
729 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
730 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
731 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
733 // We are going to be using TargetData::getIndexedOffset to determine the
734 // offset that each of the GEP's is reaching. To do this, we have to convert
735 // all variable references to constant references. To do this, we convert the
736 // initial sequence of array subscripts into constant zeros to start with.
737 const Type *ZeroIdxTy = GEPPointerTy;
738 for (unsigned i = 0; i != FirstConstantOper; ++i) {
739 if (!isa<StructType>(ZeroIdxTy))
740 GEP1Ops[i] = GEP2Ops[i] = Context->getNullValue(Type::Int32Ty);
742 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
743 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
746 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
748 // Loop over the rest of the operands...
749 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
750 const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
751 const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
752 // If they are equal, use a zero index...
753 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
754 if (!isa<ConstantInt>(Op1))
755 GEP1Ops[i] = GEP2Ops[i] = Context->getNullValue(Op1->getType());
756 // Otherwise, just keep the constants we have.
759 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
760 // If this is an array index, make sure the array element is in range.
761 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
762 if (Op1C->getZExtValue() >= AT->getNumElements())
763 return MayAlias; // Be conservative with out-of-range accesses
764 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) {
765 if (Op1C->getZExtValue() >= VT->getNumElements())
766 return MayAlias; // Be conservative with out-of-range accesses
770 // GEP1 is known to produce a value less than GEP2. To be
771 // conservatively correct, we must assume the largest possible
772 // constant is used in this position. This cannot be the initial
773 // index to the GEP instructions (because we know we have at least one
774 // element before this one with the different constant arguments), so
775 // we know that the current index must be into either a struct or
776 // array. Because we know it's not constant, this cannot be a
777 // structure index. Because of this, we can calculate the maximum
780 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
782 Context->getConstantInt(Type::Int64Ty,AT->getNumElements()-1);
783 else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty))
785 Context->getConstantInt(Type::Int64Ty,VT->getNumElements()-1);
790 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
791 // If this is an array index, make sure the array element is in range.
792 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr2Ty)) {
793 if (Op2C->getZExtValue() >= AT->getNumElements())
794 return MayAlias; // Be conservative with out-of-range accesses
795 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr2Ty)) {
796 if (Op2C->getZExtValue() >= VT->getNumElements())
797 return MayAlias; // Be conservative with out-of-range accesses
799 } else { // Conservatively assume the minimum value for this index
800 GEP2Ops[i] = Context->getNullValue(Op2->getType());
805 if (BasePtr1Ty && Op1) {
806 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
807 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
812 if (BasePtr2Ty && Op2) {
813 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
814 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
820 if (GEPPointerTy->getElementType()->isSized()) {
822 getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
824 getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
825 assert(Offset1 != Offset2 &&
826 "There is at least one different constant here!");
828 // Make sure we compare the absolute difference.
829 if (Offset1 > Offset2)
830 std::swap(Offset1, Offset2);
832 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
833 //cerr << "Determined that these two GEP's don't alias ["
834 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
841 // Make sure that anything that uses AliasAnalysis pulls in this file...
842 DEFINING_FILE_FOR(BasicAliasAnalysis)