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/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 static const User *isGEP(const Value *V) {
40 if (isa<GetElementPtrInst>(V) ||
41 (isa<ConstantExpr>(V) &&
42 cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
47 static const Value *GetGEPOperands(const Value *V,
48 SmallVector<Value*, 16> &GEPOps) {
49 assert(GEPOps.empty() && "Expect empty list to populate!");
50 GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
51 cast<User>(V)->op_end());
53 // Accumulate all of the chained indexes into the operand array
54 V = cast<User>(V)->getOperand(0);
56 while (const User *G = isGEP(V)) {
57 if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
58 !cast<Constant>(GEPOps[0])->isNullValue())
59 break; // Don't handle folding arbitrary pointer offsets yet...
60 GEPOps.erase(GEPOps.begin()); // Drop the zero index
61 GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
67 /// isKnownNonNull - Return true if we know that the specified value is never
69 static bool isKnownNonNull(const Value *V) {
70 // Alloca never returns null, malloc might.
71 if (isa<AllocaInst>(V)) return true;
73 // A byval argument is never null.
74 if (const Argument *A = dyn_cast<Argument>(V))
75 return A->hasByValAttr();
77 // Global values are not null unless extern weak.
78 if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
79 return !GV->hasExternalWeakLinkage();
83 /// isNonEscapingLocalObject - Return true if the pointer is to a function-local
84 /// object that never escapes from the function.
85 static bool isNonEscapingLocalObject(const Value *V) {
86 // If this is a local allocation, check to see if it escapes.
87 if (isa<AllocationInst>(V) || isNoAliasCall(V))
88 return !PointerMayBeCaptured(V, false);
90 // If this is an argument that corresponds to a byval or noalias argument,
91 // then it has not escaped before entering the function. Check if it escapes
92 // inside the function.
93 if (const Argument *A = dyn_cast<Argument>(V))
94 if (A->hasByValAttr() || A->hasNoAliasAttr()) {
95 // Don't bother analyzing arguments already known not to escape.
96 if (A->hasNoCaptureAttr())
98 return !PointerMayBeCaptured(V, false);
104 /// isObjectSmallerThan - Return true if we can prove that the object specified
105 /// by V is smaller than Size.
106 static bool isObjectSmallerThan(const Value *V, unsigned Size,
107 const TargetData &TD) {
108 const Type *AccessTy;
109 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
110 AccessTy = GV->getType()->getElementType();
111 } else if (const AllocationInst *AI = dyn_cast<AllocationInst>(V)) {
112 if (!AI->isArrayAllocation())
113 AccessTy = AI->getType()->getElementType();
116 } else if (const Argument *A = dyn_cast<Argument>(V)) {
117 if (A->hasByValAttr())
118 AccessTy = cast<PointerType>(A->getType())->getElementType();
125 if (AccessTy->isSized())
126 return TD.getTypePaddedSize(AccessTy) < Size;
130 //===----------------------------------------------------------------------===//
132 //===----------------------------------------------------------------------===//
135 /// NoAA - This class implements the -no-aa pass, which always returns "I
136 /// don't know" for alias queries. NoAA is unlike other alias analysis
137 /// implementations, in that it does not chain to a previous analysis. As
138 /// such it doesn't follow many of the rules that other alias analyses must.
140 struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
141 static char ID; // Class identification, replacement for typeinfo
142 NoAA() : ImmutablePass(&ID) {}
143 explicit NoAA(void *PID) : ImmutablePass(PID) { }
145 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
146 AU.addRequired<TargetData>();
149 virtual void initializePass() {
150 TD = &getAnalysis<TargetData>();
153 virtual AliasResult alias(const Value *V1, unsigned V1Size,
154 const Value *V2, unsigned V2Size) {
158 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
159 std::vector<PointerAccessInfo> *Info) {
160 return UnknownModRefBehavior;
163 virtual void getArgumentAccesses(Function *F, CallSite CS,
164 std::vector<PointerAccessInfo> &Info) {
165 assert(0 && "This method may not be called on this function!");
168 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
169 virtual bool pointsToConstantMemory(const Value *P) { return false; }
170 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
173 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
176 virtual bool hasNoModRefInfoForCalls() const { return true; }
178 virtual void deleteValue(Value *V) {}
179 virtual void copyValue(Value *From, Value *To) {}
181 } // End of anonymous namespace
183 // Register this pass...
185 static RegisterPass<NoAA>
186 U("no-aa", "No Alias Analysis (always returns 'may' alias)", true, true);
188 // Declare that we implement the AliasAnalysis interface
189 static RegisterAnalysisGroup<AliasAnalysis> V(U);
191 ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
193 //===----------------------------------------------------------------------===//
195 //===----------------------------------------------------------------------===//
198 /// BasicAliasAnalysis - This is the default alias analysis implementation.
199 /// Because it doesn't chain to a previous alias analysis (like -no-aa), it
200 /// derives from the NoAA class.
201 struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA {
202 static char ID; // Class identification, replacement for typeinfo
203 BasicAliasAnalysis() : NoAA(&ID) {}
204 AliasResult alias(const Value *V1, unsigned V1Size,
205 const Value *V2, unsigned V2Size);
207 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
208 ModRefResult getModRefInfo(CallSite CS1, CallSite CS2);
210 /// hasNoModRefInfoForCalls - We can provide mod/ref information against
211 /// non-escaping allocations.
212 virtual bool hasNoModRefInfoForCalls() const { return false; }
214 /// pointsToConstantMemory - Chase pointers until we find a (constant
216 bool pointsToConstantMemory(const Value *P);
219 // CheckGEPInstructions - Check two GEP instructions with known
220 // must-aliasing base pointers. This checks to see if the index expressions
221 // preclude the pointers from aliasing...
223 CheckGEPInstructions(const Type* BasePtr1Ty,
224 Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size,
225 const Type *BasePtr2Ty,
226 Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size);
228 } // End of anonymous namespace
230 // Register this pass...
231 char BasicAliasAnalysis::ID = 0;
232 static RegisterPass<BasicAliasAnalysis>
233 X("basicaa", "Basic Alias Analysis (default AA impl)", false, true);
235 // Declare that we implement the AliasAnalysis interface
236 static RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
238 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
239 return new BasicAliasAnalysis();
243 /// pointsToConstantMemory - Chase pointers until we find a (constant
245 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
246 if (const GlobalVariable *GV =
247 dyn_cast<GlobalVariable>(P->getUnderlyingObject()))
248 return GV->isConstant();
252 // getModRefInfo - Check to see if the specified callsite can clobber the
253 // specified memory object. Since we only look at local properties of this
254 // function, we really can't say much about this query. We do, however, use
255 // simple "address taken" analysis on local objects.
257 AliasAnalysis::ModRefResult
258 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
259 if (!isa<Constant>(P)) {
260 const Value *Object = P->getUnderlyingObject();
262 // If this is a tail call and P points to a stack location, we know that
263 // the tail call cannot access or modify the local stack.
264 // We cannot exclude byval arguments here; these belong to the caller of
265 // the current function not to the current function, and a tail callee
266 // may reference them.
267 if (isa<AllocaInst>(Object))
268 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
269 if (CI->isTailCall())
272 // If the pointer is to a locally allocated object that does not escape,
273 // then the call can not mod/ref the pointer unless the call takes the
274 // argument without capturing it.
275 if (isNonEscapingLocalObject(Object)) {
276 bool passedAsArg = false;
277 // TODO: Eventually only check 'nocapture' arguments.
278 for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
280 if (isa<PointerType>((*CI)->getType()) &&
281 alias(cast<Value>(CI), ~0U, P, ~0U) != NoAlias)
289 // The AliasAnalysis base class has some smarts, lets use them.
290 return AliasAnalysis::getModRefInfo(CS, P, Size);
294 AliasAnalysis::ModRefResult
295 BasicAliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) {
296 // If CS1 or CS2 are readnone, they don't interact.
297 ModRefBehavior CS1B = AliasAnalysis::getModRefBehavior(CS1);
298 if (CS1B == DoesNotAccessMemory) return NoModRef;
300 ModRefBehavior CS2B = AliasAnalysis::getModRefBehavior(CS2);
301 if (CS2B == DoesNotAccessMemory) return NoModRef;
303 // If they both only read from memory, just return ref.
304 if (CS1B == OnlyReadsMemory && CS2B == OnlyReadsMemory)
307 // Otherwise, fall back to NoAA (mod+ref).
308 return NoAA::getModRefInfo(CS1, CS2);
312 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
313 // as array references.
315 AliasAnalysis::AliasResult
316 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
317 const Value *V2, unsigned V2Size) {
318 // Strip off any constant expression casts if they exist
319 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
320 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
321 V1 = CE->getOperand(0);
322 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
323 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
324 V2 = CE->getOperand(0);
326 // Are we checking for alias of the same value?
327 if (V1 == V2) return MustAlias;
329 if (!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType()))
330 return NoAlias; // Scalars cannot alias each other
332 // Strip off cast instructions. Since V1 and V2 are pointers, they must be
333 // pointer<->pointer bitcasts.
334 if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
335 return alias(I->getOperand(0), V1Size, V2, V2Size);
336 if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
337 return alias(V1, V1Size, I->getOperand(0), V2Size);
339 // Figure out what objects these things are pointing to if we can.
340 const Value *O1 = V1->getUnderlyingObject();
341 const Value *O2 = V2->getUnderlyingObject();
344 // If V1/V2 point to two different objects we know that we have no alias.
345 if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
348 // Arguments can't alias with local allocations or noalias calls.
349 if ((isa<Argument>(O1) && (isa<AllocationInst>(O2) || isNoAliasCall(O2))) ||
350 (isa<Argument>(O2) && (isa<AllocationInst>(O1) || isNoAliasCall(O1))))
353 // Most objects can't alias null.
354 if ((isa<ConstantPointerNull>(V2) && isKnownNonNull(O1)) ||
355 (isa<ConstantPointerNull>(V1) && isKnownNonNull(O2)))
359 // If the size of one access is larger than the entire object on the other
360 // side, then we know such behavior is undefined and can assume no alias.
361 const TargetData &TD = getTargetData();
362 if ((V1Size != ~0U && isObjectSmallerThan(O2, V1Size, TD)) ||
363 (V2Size != ~0U && isObjectSmallerThan(O1, V2Size, TD)))
366 // If one pointer is the result of a call/invoke and the other is a
367 // non-escaping local object, then we know the object couldn't escape to a
368 // point where the call could return it.
369 if ((isa<CallInst>(O1) || isa<InvokeInst>(O1)) &&
370 isNonEscapingLocalObject(O2))
372 if ((isa<CallInst>(O2) || isa<InvokeInst>(O2)) &&
373 isNonEscapingLocalObject(O1))
376 // If we have two gep instructions with must-alias'ing base pointers, figure
377 // out if the indexes to the GEP tell us anything about the derived pointer.
378 // Note that we also handle chains of getelementptr instructions as well as
379 // constant expression getelementptrs here.
381 if (isGEP(V1) && isGEP(V2)) {
382 const User *GEP1 = cast<User>(V1);
383 const User *GEP2 = cast<User>(V2);
385 // If V1 and V2 are identical GEPs, just recurse down on both of them.
386 // This allows us to analyze things like:
387 // P = gep A, 0, i, 1
388 // Q = gep B, 0, i, 1
389 // by just analyzing A and B. This is even safe for variable indices.
390 if (GEP1->getType() == GEP2->getType() &&
391 GEP1->getNumOperands() == GEP2->getNumOperands() &&
392 GEP1->getOperand(0)->getType() == GEP2->getOperand(0)->getType() &&
393 // All operands are the same, ignoring the base.
394 std::equal(GEP1->op_begin()+1, GEP1->op_end(), GEP2->op_begin()+1))
395 return alias(GEP1->getOperand(0), V1Size, GEP2->getOperand(0), V2Size);
398 // Drill down into the first non-gep value, to test for must-aliasing of
399 // the base pointers.
400 while (isGEP(GEP1->getOperand(0)) &&
401 GEP1->getOperand(1) ==
402 Constant::getNullValue(GEP1->getOperand(1)->getType()))
403 GEP1 = cast<User>(GEP1->getOperand(0));
404 const Value *BasePtr1 = GEP1->getOperand(0);
406 while (isGEP(GEP2->getOperand(0)) &&
407 GEP2->getOperand(1) ==
408 Constant::getNullValue(GEP2->getOperand(1)->getType()))
409 GEP2 = cast<User>(GEP2->getOperand(0));
410 const Value *BasePtr2 = GEP2->getOperand(0);
412 // Do the base pointers alias?
413 AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
414 if (BaseAlias == NoAlias) return NoAlias;
415 if (BaseAlias == MustAlias) {
416 // If the base pointers alias each other exactly, check to see if we can
417 // figure out anything about the resultant pointers, to try to prove
420 // Collect all of the chained GEP operands together into one simple place
421 SmallVector<Value*, 16> GEP1Ops, GEP2Ops;
422 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
423 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
425 // If GetGEPOperands were able to fold to the same must-aliased pointer,
426 // do the comparison.
427 if (BasePtr1 == BasePtr2) {
429 CheckGEPInstructions(BasePtr1->getType(),
430 &GEP1Ops[0], GEP1Ops.size(), V1Size,
432 &GEP2Ops[0], GEP2Ops.size(), V2Size);
433 if (GAlias != MayAlias)
439 // Check to see if these two pointers are related by a getelementptr
440 // instruction. If one pointer is a GEP with a non-zero index of the other
441 // pointer, we know they cannot alias.
445 std::swap(V1Size, V2Size);
448 if (V1Size != ~0U && V2Size != ~0U)
450 SmallVector<Value*, 16> GEPOperands;
451 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
453 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
454 if (R == MustAlias) {
455 // If there is at least one non-zero constant index, we know they cannot
457 bool ConstantFound = false;
458 bool AllZerosFound = true;
459 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
460 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
461 if (!C->isNullValue()) {
462 ConstantFound = true;
463 AllZerosFound = false;
467 AllZerosFound = false;
470 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
471 // the ptr, the end result is a must alias also.
476 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
479 // Otherwise we have to check to see that the distance is more than
480 // the size of the argument... build an index vector that is equal to
481 // the arguments provided, except substitute 0's for any variable
482 // indexes we find...
483 if (cast<PointerType>(
484 BasePtr->getType())->getElementType()->isSized()) {
485 for (unsigned i = 0; i != GEPOperands.size(); ++i)
486 if (!isa<ConstantInt>(GEPOperands[i]))
488 Constant::getNullValue(GEPOperands[i]->getType());
490 getTargetData().getIndexedOffset(BasePtr->getType(),
494 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
504 // This function is used to determine if the indices of two GEP instructions are
505 // equal. V1 and V2 are the indices.
506 static bool IndexOperandsEqual(Value *V1, Value *V2) {
507 if (V1->getType() == V2->getType())
509 if (Constant *C1 = dyn_cast<Constant>(V1))
510 if (Constant *C2 = dyn_cast<Constant>(V2)) {
511 // Sign extend the constants to long types, if necessary
512 if (C1->getType() != Type::Int64Ty)
513 C1 = ConstantExpr::getSExt(C1, Type::Int64Ty);
514 if (C2->getType() != Type::Int64Ty)
515 C2 = ConstantExpr::getSExt(C2, Type::Int64Ty);
521 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
522 /// base pointers. This checks to see if the index expressions preclude the
523 /// pointers from aliasing...
524 AliasAnalysis::AliasResult
525 BasicAliasAnalysis::CheckGEPInstructions(
526 const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
527 const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
528 // We currently can't handle the case when the base pointers have different
529 // primitive types. Since this is uncommon anyway, we are happy being
530 // extremely conservative.
531 if (BasePtr1Ty != BasePtr2Ty)
534 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
536 // Find the (possibly empty) initial sequence of equal values... which are not
537 // necessarily constants.
538 unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
539 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
540 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
541 unsigned UnequalOper = 0;
542 while (UnequalOper != MinOperands &&
543 IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
544 // Advance through the type as we go...
546 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
547 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
549 // If all operands equal each other, then the derived pointers must
550 // alias each other...
552 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
553 "Ran out of type nesting, but not out of operands?");
558 // If we have seen all constant operands, and run out of indexes on one of the
559 // getelementptrs, check to see if the tail of the leftover one is all zeros.
560 // If so, return mustalias.
561 if (UnequalOper == MinOperands) {
562 if (NumGEP1Ops < NumGEP2Ops) {
563 std::swap(GEP1Ops, GEP2Ops);
564 std::swap(NumGEP1Ops, NumGEP2Ops);
567 bool AllAreZeros = true;
568 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
569 if (!isa<Constant>(GEP1Ops[i]) ||
570 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
574 if (AllAreZeros) return MustAlias;
578 // So now we know that the indexes derived from the base pointers,
579 // which are known to alias, are different. We can still determine a
580 // no-alias result if there are differing constant pairs in the index
581 // chain. For example:
582 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
584 // We have to be careful here about array accesses. In particular, consider:
585 // A[1][0] vs A[0][i]
586 // In this case, we don't *know* that the array will be accessed in bounds:
587 // the index could even be negative. Because of this, we have to
588 // conservatively *give up* and return may alias. We disregard differing
589 // array subscripts that are followed by a variable index without going
592 unsigned SizeMax = std::max(G1S, G2S);
593 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
595 // Scan for the first operand that is constant and unequal in the
596 // two getelementptrs...
597 unsigned FirstConstantOper = UnequalOper;
598 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
599 const Value *G1Oper = GEP1Ops[FirstConstantOper];
600 const Value *G2Oper = GEP2Ops[FirstConstantOper];
602 if (G1Oper != G2Oper) // Found non-equal constant indexes...
603 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
604 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
605 if (G1OC->getType() != G2OC->getType()) {
606 // Sign extend both operands to long.
607 if (G1OC->getType() != Type::Int64Ty)
608 G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty);
609 if (G2OC->getType() != Type::Int64Ty)
610 G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty);
611 GEP1Ops[FirstConstantOper] = G1OC;
612 GEP2Ops[FirstConstantOper] = G2OC;
616 // Handle the "be careful" case above: if this is an array/vector
617 // subscript, scan for a subsequent variable array index.
618 if (isa<SequentialType>(BasePtr1Ty)) {
620 cast<SequentialType>(BasePtr1Ty)->getElementType();
621 bool isBadCase = false;
623 for (unsigned Idx = FirstConstantOper+1;
624 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
625 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
626 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
630 NextTy = cast<SequentialType>(NextTy)->getElementType();
633 if (isBadCase) G1OC = 0;
636 // Make sure they are comparable (ie, not constant expressions), and
637 // make sure the GEP with the smaller leading constant is GEP1.
639 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
641 if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
642 if (CV->getZExtValue()) { // If they are comparable and G2 > G1
643 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
644 std::swap(NumGEP1Ops, NumGEP2Ops);
651 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
654 // No shared constant operands, and we ran out of common operands. At this
655 // point, the GEP instructions have run through all of their operands, and we
656 // haven't found evidence that there are any deltas between the GEP's.
657 // However, one GEP may have more operands than the other. If this is the
658 // case, there may still be hope. Check this now.
659 if (FirstConstantOper == MinOperands) {
660 // Make GEP1Ops be the longer one if there is a longer one.
661 if (NumGEP1Ops < NumGEP2Ops) {
662 std::swap(GEP1Ops, GEP2Ops);
663 std::swap(NumGEP1Ops, NumGEP2Ops);
666 // Is there anything to check?
667 if (NumGEP1Ops > MinOperands) {
668 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
669 if (isa<ConstantInt>(GEP1Ops[i]) &&
670 !cast<ConstantInt>(GEP1Ops[i])->isZero()) {
671 // Yup, there's a constant in the tail. Set all variables to
672 // constants in the GEP instruction to make it suitable for
673 // TargetData::getIndexedOffset.
674 for (i = 0; i != MaxOperands; ++i)
675 if (!isa<ConstantInt>(GEP1Ops[i]))
676 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
677 // Okay, now get the offset. This is the relative offset for the full
679 const TargetData &TD = getTargetData();
680 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
683 // Now check without any constants at the end.
684 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
687 // Make sure we compare the absolute difference.
688 if (Offset1 > Offset2)
689 std::swap(Offset1, Offset2);
691 // If the tail provided a bit enough offset, return noalias!
692 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
694 // Otherwise break - we don't look for another constant in the tail.
699 // Couldn't find anything useful.
703 // If there are non-equal constants arguments, then we can figure
704 // out a minimum known delta between the two index expressions... at
705 // this point we know that the first constant index of GEP1 is less
706 // than the first constant index of GEP2.
708 // Advance BasePtr[12]Ty over this first differing constant operand.
709 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
710 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
711 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
712 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
714 // We are going to be using TargetData::getIndexedOffset to determine the
715 // offset that each of the GEP's is reaching. To do this, we have to convert
716 // all variable references to constant references. To do this, we convert the
717 // initial sequence of array subscripts into constant zeros to start with.
718 const Type *ZeroIdxTy = GEPPointerTy;
719 for (unsigned i = 0; i != FirstConstantOper; ++i) {
720 if (!isa<StructType>(ZeroIdxTy))
721 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty);
723 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
724 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
727 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
729 // Loop over the rest of the operands...
730 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
731 const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
732 const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
733 // If they are equal, use a zero index...
734 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
735 if (!isa<ConstantInt>(Op1))
736 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
737 // Otherwise, just keep the constants we have.
740 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
741 // If this is an array index, make sure the array element is in range.
742 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
743 if (Op1C->getZExtValue() >= AT->getNumElements())
744 return MayAlias; // Be conservative with out-of-range accesses
745 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) {
746 if (Op1C->getZExtValue() >= VT->getNumElements())
747 return MayAlias; // Be conservative with out-of-range accesses
751 // GEP1 is known to produce a value less than GEP2. To be
752 // conservatively correct, we must assume the largest possible
753 // constant is used in this position. This cannot be the initial
754 // index to the GEP instructions (because we know we have at least one
755 // element before this one with the different constant arguments), so
756 // we know that the current index must be into either a struct or
757 // array. Because we know it's not constant, this cannot be a
758 // structure index. Because of this, we can calculate the maximum
761 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
762 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1);
763 else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty))
764 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,VT->getNumElements()-1);
769 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
770 // If this is an array index, make sure the array element is in range.
771 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr2Ty)) {
772 if (Op2C->getZExtValue() >= AT->getNumElements())
773 return MayAlias; // Be conservative with out-of-range accesses
774 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr2Ty)) {
775 if (Op2C->getZExtValue() >= VT->getNumElements())
776 return MayAlias; // Be conservative with out-of-range accesses
778 } else { // Conservatively assume the minimum value for this index
779 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
784 if (BasePtr1Ty && Op1) {
785 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
786 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
791 if (BasePtr2Ty && Op2) {
792 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
793 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
799 if (GEPPointerTy->getElementType()->isSized()) {
801 getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
803 getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
804 assert(Offset1 != Offset2 &&
805 "There is at least one different constant here!");
807 // Make sure we compare the absolute difference.
808 if (Offset1 > Offset2)
809 std::swap(Offset1, Offset2);
811 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
812 //cerr << "Determined that these two GEP's don't alias ["
813 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
820 // Make sure that anything that uses AliasAnalysis pulls in this file...
821 DEFINING_FILE_FOR(BasicAliasAnalysis)