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/MallocHelper.h"
19 #include "llvm/Analysis/Passes.h"
20 #include "llvm/Constants.h"
21 #include "llvm/DerivedTypes.h"
22 #include "llvm/Function.h"
23 #include "llvm/GlobalVariable.h"
24 #include "llvm/Instructions.h"
25 #include "llvm/IntrinsicInst.h"
26 #include "llvm/LLVMContext.h"
27 #include "llvm/Operator.h"
28 #include "llvm/Pass.h"
29 #include "llvm/Target/TargetData.h"
30 #include "llvm/ADT/SmallVector.h"
31 #include "llvm/ADT/STLExtras.h"
32 #include "llvm/Support/Compiler.h"
33 #include "llvm/Support/ErrorHandling.h"
34 #include "llvm/Support/GetElementPtrTypeIterator.h"
38 //===----------------------------------------------------------------------===//
40 //===----------------------------------------------------------------------===//
42 static const GEPOperator *isGEP(const Value *V) {
43 return dyn_cast<GEPOperator>(V);
46 static const Value *GetGEPOperands(const Value *V,
47 SmallVector<Value*, 16> &GEPOps) {
48 assert(GEPOps.empty() && "Expect empty list to populate!");
49 GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
50 cast<User>(V)->op_end());
52 // Accumulate all of the chained indexes into the operand array
53 V = cast<User>(V)->getOperand(0);
55 while (const User *G = isGEP(V)) {
56 if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
57 !cast<Constant>(GEPOps[0])->isNullValue())
58 break; // Don't handle folding arbitrary pointer offsets yet...
59 GEPOps.erase(GEPOps.begin()); // Drop the zero index
60 GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
66 /// isKnownNonNull - Return true if we know that the specified value is never
68 static bool isKnownNonNull(const Value *V) {
69 // Alloca never returns null, malloc might.
70 if (isa<AllocaInst>(V)) return true;
72 // A byval argument is never null.
73 if (const Argument *A = dyn_cast<Argument>(V))
74 return A->hasByValAttr();
76 // Global values are not null unless extern weak.
77 if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
78 return !GV->hasExternalWeakLinkage();
82 /// isNonEscapingLocalObject - Return true if the pointer is to a function-local
83 /// object that never escapes from the function.
84 static bool isNonEscapingLocalObject(const Value *V) {
85 // If this is a local allocation, check to see if it escapes.
86 if (isa<AllocationInst>(V) || isNoAliasCall(V))
87 return !PointerMayBeCaptured(V, false);
89 // If this is an argument that corresponds to a byval or noalias argument,
90 // then it has not escaped before entering the function. Check if it escapes
91 // inside the function.
92 if (const Argument *A = dyn_cast<Argument>(V))
93 if (A->hasByValAttr() || A->hasNoAliasAttr()) {
94 // Don't bother analyzing arguments already known not to escape.
95 if (A->hasNoCaptureAttr())
97 return !PointerMayBeCaptured(V, false);
103 /// isObjectSmallerThan - Return true if we can prove that the object specified
104 /// by V is smaller than Size.
105 static bool isObjectSmallerThan(const Value *V, unsigned Size,
106 LLVMContext &Context, const TargetData &TD) {
107 const Type *AccessTy;
108 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
109 AccessTy = GV->getType()->getElementType();
110 } else if (const AllocationInst *AI = dyn_cast<AllocationInst>(V)) {
111 if (!AI->isArrayAllocation())
112 AccessTy = AI->getType()->getElementType();
115 } else if (const CallInst* CI = extractMallocCall(V)) {
116 if (!isArrayMalloc(V, Context, &TD))
117 // The size is the argument to the malloc call.
118 if (const ConstantInt* C = dyn_cast<ConstantInt>(CI->getOperand(1)))
119 return (C->getZExtValue() < Size);
121 } else if (const Argument *A = dyn_cast<Argument>(V)) {
122 if (A->hasByValAttr())
123 AccessTy = cast<PointerType>(A->getType())->getElementType();
130 if (AccessTy->isSized())
131 return TD.getTypeAllocSize(AccessTy) < Size;
135 //===----------------------------------------------------------------------===//
137 //===----------------------------------------------------------------------===//
140 /// NoAA - This class implements the -no-aa pass, which always returns "I
141 /// don't know" for alias queries. NoAA is unlike other alias analysis
142 /// implementations, in that it does not chain to a previous analysis. As
143 /// such it doesn't follow many of the rules that other alias analyses must.
145 struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
146 static char ID; // Class identification, replacement for typeinfo
147 NoAA() : ImmutablePass(&ID) {}
148 explicit NoAA(void *PID) : ImmutablePass(PID) { }
150 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
153 virtual void initializePass() {
154 TD = getAnalysisIfAvailable<TargetData>();
157 virtual AliasResult alias(const Value *V1, unsigned V1Size,
158 const Value *V2, unsigned V2Size) {
162 virtual void getArgumentAccesses(Function *F, CallSite CS,
163 std::vector<PointerAccessInfo> &Info) {
164 llvm_unreachable("This method may not be called on this function!");
167 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
168 virtual bool pointsToConstantMemory(const Value *P) { return false; }
169 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
172 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
175 virtual bool hasNoModRefInfoForCalls() const { return true; }
177 virtual void deleteValue(Value *V) {}
178 virtual void copyValue(Value *From, Value *To) {}
180 } // End of anonymous namespace
182 // Register this pass...
184 static RegisterPass<NoAA>
185 U("no-aa", "No Alias Analysis (always returns 'may' alias)", true, true);
187 // Declare that we implement the AliasAnalysis interface
188 static RegisterAnalysisGroup<AliasAnalysis> V(U);
190 ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
192 //===----------------------------------------------------------------------===//
194 //===----------------------------------------------------------------------===//
197 /// BasicAliasAnalysis - This is the default alias analysis implementation.
198 /// Because it doesn't chain to a previous alias analysis (like -no-aa), it
199 /// derives from the NoAA class.
200 struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA {
201 static char ID; // Class identification, replacement for typeinfo
202 BasicAliasAnalysis() : NoAA(&ID) {}
203 AliasResult alias(const Value *V1, unsigned V1Size,
204 const Value *V2, unsigned V2Size);
206 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
207 ModRefResult getModRefInfo(CallSite CS1, CallSite CS2);
209 /// hasNoModRefInfoForCalls - We can provide mod/ref information against
210 /// non-escaping allocations.
211 virtual bool hasNoModRefInfoForCalls() const { return false; }
213 /// pointsToConstantMemory - Chase pointers until we find a (constant
215 bool pointsToConstantMemory(const Value *P);
218 // aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction
220 AliasResult aliasGEP(const Value *V1, unsigned V1Size,
221 const Value *V2, unsigned V2Size);
223 // CheckGEPInstructions - Check two GEP instructions with known
224 // must-aliasing base pointers. This checks to see if the index expressions
225 // preclude the pointers from aliasing...
227 CheckGEPInstructions(const Type* BasePtr1Ty,
228 Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size,
229 const Type *BasePtr2Ty,
230 Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size);
232 } // End of anonymous namespace
234 // Register this pass...
235 char BasicAliasAnalysis::ID = 0;
236 static RegisterPass<BasicAliasAnalysis>
237 X("basicaa", "Basic Alias Analysis (default AA impl)", false, true);
239 // Declare that we implement the AliasAnalysis interface
240 static RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
242 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
243 return new BasicAliasAnalysis();
247 /// pointsToConstantMemory - Chase pointers until we find a (constant
249 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
250 if (const GlobalVariable *GV =
251 dyn_cast<GlobalVariable>(P->getUnderlyingObject()))
252 return GV->isConstant();
257 // getModRefInfo - Check to see if the specified callsite can clobber the
258 // specified memory object. Since we only look at local properties of this
259 // function, we really can't say much about this query. We do, however, use
260 // simple "address taken" analysis on local objects.
262 AliasAnalysis::ModRefResult
263 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
264 if (!isa<Constant>(P)) {
265 const Value *Object = P->getUnderlyingObject();
267 // If this is a tail call and P points to a stack location, we know that
268 // the tail call cannot access or modify the local stack.
269 // We cannot exclude byval arguments here; these belong to the caller of
270 // the current function not to the current function, and a tail callee
271 // may reference them.
272 if (isa<AllocaInst>(Object))
273 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
274 if (CI->isTailCall())
277 // If the pointer is to a locally allocated object that does not escape,
278 // then the call can not mod/ref the pointer unless the call takes the
279 // argument without capturing it.
280 if (isNonEscapingLocalObject(Object) && CS.getInstruction() != Object) {
281 bool passedAsArg = false;
282 // TODO: Eventually only check 'nocapture' arguments.
283 for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
285 if (isa<PointerType>((*CI)->getType()) &&
286 alias(cast<Value>(CI), ~0U, P, ~0U) != NoAlias)
293 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction())) {
294 switch (II->getIntrinsicID()) {
296 case Intrinsic::atomic_cmp_swap:
297 case Intrinsic::atomic_swap:
298 case Intrinsic::atomic_load_add:
299 case Intrinsic::atomic_load_sub:
300 case Intrinsic::atomic_load_and:
301 case Intrinsic::atomic_load_nand:
302 case Intrinsic::atomic_load_or:
303 case Intrinsic::atomic_load_xor:
304 case Intrinsic::atomic_load_max:
305 case Intrinsic::atomic_load_min:
306 case Intrinsic::atomic_load_umax:
307 case Intrinsic::atomic_load_umin:
308 if (alias(II->getOperand(1), Size, P, Size) == NoAlias)
315 // The AliasAnalysis base class has some smarts, lets use them.
316 return AliasAnalysis::getModRefInfo(CS, P, Size);
320 AliasAnalysis::ModRefResult
321 BasicAliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) {
322 // If CS1 or CS2 are readnone, they don't interact.
323 ModRefBehavior CS1B = AliasAnalysis::getModRefBehavior(CS1);
324 if (CS1B == DoesNotAccessMemory) return NoModRef;
326 ModRefBehavior CS2B = AliasAnalysis::getModRefBehavior(CS2);
327 if (CS2B == DoesNotAccessMemory) return NoModRef;
329 // If they both only read from memory, just return ref.
330 if (CS1B == OnlyReadsMemory && CS2B == OnlyReadsMemory)
333 // Otherwise, fall back to NoAA (mod+ref).
334 return NoAA::getModRefInfo(CS1, CS2);
337 // aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction
340 AliasAnalysis::AliasResult
341 BasicAliasAnalysis::aliasGEP(const Value *V1, unsigned V1Size,
342 const Value *V2, unsigned V2Size) {
343 // If we have two gep instructions with must-alias'ing base pointers, figure
344 // out if the indexes to the GEP tell us anything about the derived pointer.
345 // Note that we also handle chains of getelementptr instructions as well as
346 // constant expression getelementptrs here.
348 if (isGEP(V1) && isGEP(V2)) {
349 const User *GEP1 = cast<User>(V1);
350 const User *GEP2 = cast<User>(V2);
352 // If V1 and V2 are identical GEPs, just recurse down on both of them.
353 // This allows us to analyze things like:
354 // P = gep A, 0, i, 1
355 // Q = gep B, 0, i, 1
356 // by just analyzing A and B. This is even safe for variable indices.
357 if (GEP1->getType() == GEP2->getType() &&
358 GEP1->getNumOperands() == GEP2->getNumOperands() &&
359 GEP1->getOperand(0)->getType() == GEP2->getOperand(0)->getType() &&
360 // All operands are the same, ignoring the base.
361 std::equal(GEP1->op_begin()+1, GEP1->op_end(), GEP2->op_begin()+1))
362 return alias(GEP1->getOperand(0), V1Size, GEP2->getOperand(0), V2Size);
365 // Drill down into the first non-gep value, to test for must-aliasing of
366 // the base pointers.
367 while (isGEP(GEP1->getOperand(0)) &&
368 GEP1->getOperand(1) ==
369 Constant::getNullValue(GEP1->getOperand(1)->getType()))
370 GEP1 = cast<User>(GEP1->getOperand(0));
371 const Value *BasePtr1 = GEP1->getOperand(0);
373 while (isGEP(GEP2->getOperand(0)) &&
374 GEP2->getOperand(1) ==
375 Constant::getNullValue(GEP2->getOperand(1)->getType()))
376 GEP2 = cast<User>(GEP2->getOperand(0));
377 const Value *BasePtr2 = GEP2->getOperand(0);
379 // Do the base pointers alias?
380 AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
381 if (BaseAlias == NoAlias) return NoAlias;
382 if (BaseAlias == MustAlias) {
383 // If the base pointers alias each other exactly, check to see if we can
384 // figure out anything about the resultant pointers, to try to prove
387 // Collect all of the chained GEP operands together into one simple place
388 SmallVector<Value*, 16> GEP1Ops, GEP2Ops;
389 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
390 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
392 // If GetGEPOperands were able to fold to the same must-aliased pointer,
393 // do the comparison.
394 if (BasePtr1 == BasePtr2) {
396 CheckGEPInstructions(BasePtr1->getType(),
397 &GEP1Ops[0], GEP1Ops.size(), V1Size,
399 &GEP2Ops[0], GEP2Ops.size(), V2Size);
400 if (GAlias != MayAlias)
406 // Check to see if these two pointers are related by a getelementptr
407 // instruction. If one pointer is a GEP with a non-zero index of the other
408 // pointer, we know they cannot alias.
410 if (V1Size == ~0U || V2Size == ~0U)
413 SmallVector<Value*, 16> GEPOperands;
414 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
416 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
417 if (R == MustAlias) {
418 // If there is at least one non-zero constant index, we know they cannot
420 bool ConstantFound = false;
421 bool AllZerosFound = true;
422 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
423 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
424 if (!C->isNullValue()) {
425 ConstantFound = true;
426 AllZerosFound = false;
430 AllZerosFound = false;
433 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
434 // the ptr, the end result is a must alias also.
439 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
442 // Otherwise we have to check to see that the distance is more than
443 // the size of the argument... build an index vector that is equal to
444 // the arguments provided, except substitute 0's for any variable
445 // indexes we find...
447 cast<PointerType>(BasePtr->getType())->getElementType()->isSized()) {
448 for (unsigned i = 0; i != GEPOperands.size(); ++i)
449 if (!isa<ConstantInt>(GEPOperands[i]))
450 GEPOperands[i] = Constant::getNullValue(GEPOperands[i]->getType());
452 TD->getIndexedOffset(BasePtr->getType(),
456 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
465 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
466 // as array references.
468 AliasAnalysis::AliasResult
469 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
470 const Value *V2, unsigned V2Size) {
471 // Strip off any casts if they exist.
472 V1 = V1->stripPointerCasts();
473 V2 = V2->stripPointerCasts();
475 // Are we checking for alias of the same value?
476 if (V1 == V2) return MustAlias;
478 if (!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType()))
479 return NoAlias; // Scalars cannot alias each other
481 // Figure out what objects these things are pointing to if we can.
482 const Value *O1 = V1->getUnderlyingObject();
483 const Value *O2 = V2->getUnderlyingObject();
486 // If V1/V2 point to two different objects we know that we have no alias.
487 if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
490 // Arguments can't alias with local allocations or noalias calls.
491 if ((isa<Argument>(O1) && (isa<AllocationInst>(O2) || isNoAliasCall(O2))) ||
492 (isa<Argument>(O2) && (isa<AllocationInst>(O1) || isNoAliasCall(O1))))
495 // Most objects can't alias null.
496 if ((isa<ConstantPointerNull>(V2) && isKnownNonNull(O1)) ||
497 (isa<ConstantPointerNull>(V1) && isKnownNonNull(O2)))
501 // If the size of one access is larger than the entire object on the other
502 // side, then we know such behavior is undefined and can assume no alias.
503 LLVMContext &Context = V1->getContext();
505 if ((V1Size != ~0U && isObjectSmallerThan(O2, V1Size, Context, *TD)) ||
506 (V2Size != ~0U && isObjectSmallerThan(O1, V2Size, Context, *TD)))
509 // If one pointer is the result of a call/invoke and the other is a
510 // non-escaping local object, then we know the object couldn't escape to a
511 // point where the call could return it.
512 if ((isa<CallInst>(O1) || isa<InvokeInst>(O1)) &&
513 isNonEscapingLocalObject(O2) && O1 != O2)
515 if ((isa<CallInst>(O2) || isa<InvokeInst>(O2)) &&
516 isNonEscapingLocalObject(O1) && O1 != O2)
519 if (!isGEP(V1) && isGEP(V2)) {
521 std::swap(V1Size, V2Size);
524 return aliasGEP(V1, V1Size, V2, V2Size);
529 // This function is used to determine if the indices of two GEP instructions are
530 // equal. V1 and V2 are the indices.
531 static bool IndexOperandsEqual(Value *V1, Value *V2, LLVMContext &Context) {
532 if (V1->getType() == V2->getType())
534 if (Constant *C1 = dyn_cast<Constant>(V1))
535 if (Constant *C2 = dyn_cast<Constant>(V2)) {
536 // Sign extend the constants to long types, if necessary
537 if (C1->getType() != Type::getInt64Ty(Context))
538 C1 = ConstantExpr::getSExt(C1, Type::getInt64Ty(Context));
539 if (C2->getType() != Type::getInt64Ty(Context))
540 C2 = ConstantExpr::getSExt(C2, Type::getInt64Ty(Context));
546 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
547 /// base pointers. This checks to see if the index expressions preclude the
548 /// pointers from aliasing...
549 AliasAnalysis::AliasResult
550 BasicAliasAnalysis::CheckGEPInstructions(
551 const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
552 const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
553 // We currently can't handle the case when the base pointers have different
554 // primitive types. Since this is uncommon anyway, we are happy being
555 // extremely conservative.
556 if (BasePtr1Ty != BasePtr2Ty)
559 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
561 LLVMContext &Context = GEPPointerTy->getContext();
563 // Find the (possibly empty) initial sequence of equal values... which are not
564 // necessarily constants.
565 unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
566 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
567 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
568 unsigned UnequalOper = 0;
569 while (UnequalOper != MinOperands &&
570 IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper],
572 // Advance through the type as we go...
574 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
575 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
577 // If all operands equal each other, then the derived pointers must
578 // alias each other...
580 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
581 "Ran out of type nesting, but not out of operands?");
586 // If we have seen all constant operands, and run out of indexes on one of the
587 // getelementptrs, check to see if the tail of the leftover one is all zeros.
588 // If so, return mustalias.
589 if (UnequalOper == MinOperands) {
590 if (NumGEP1Ops < NumGEP2Ops) {
591 std::swap(GEP1Ops, GEP2Ops);
592 std::swap(NumGEP1Ops, NumGEP2Ops);
595 bool AllAreZeros = true;
596 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
597 if (!isa<Constant>(GEP1Ops[i]) ||
598 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
602 if (AllAreZeros) return MustAlias;
606 // So now we know that the indexes derived from the base pointers,
607 // which are known to alias, are different. We can still determine a
608 // no-alias result if there are differing constant pairs in the index
609 // chain. For example:
610 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
612 // We have to be careful here about array accesses. In particular, consider:
613 // A[1][0] vs A[0][i]
614 // In this case, we don't *know* that the array will be accessed in bounds:
615 // the index could even be negative. Because of this, we have to
616 // conservatively *give up* and return may alias. We disregard differing
617 // array subscripts that are followed by a variable index without going
620 unsigned SizeMax = std::max(G1S, G2S);
621 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
623 // Scan for the first operand that is constant and unequal in the
624 // two getelementptrs...
625 unsigned FirstConstantOper = UnequalOper;
626 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
627 const Value *G1Oper = GEP1Ops[FirstConstantOper];
628 const Value *G2Oper = GEP2Ops[FirstConstantOper];
630 if (G1Oper != G2Oper) // Found non-equal constant indexes...
631 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
632 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
633 if (G1OC->getType() != G2OC->getType()) {
634 // Sign extend both operands to long.
635 if (G1OC->getType() != Type::getInt64Ty(Context))
636 G1OC = ConstantExpr::getSExt(G1OC, Type::getInt64Ty(Context));
637 if (G2OC->getType() != Type::getInt64Ty(Context))
638 G2OC = ConstantExpr::getSExt(G2OC, Type::getInt64Ty(Context));
639 GEP1Ops[FirstConstantOper] = G1OC;
640 GEP2Ops[FirstConstantOper] = G2OC;
644 // Handle the "be careful" case above: if this is an array/vector
645 // subscript, scan for a subsequent variable array index.
646 if (const SequentialType *STy =
647 dyn_cast<SequentialType>(BasePtr1Ty)) {
648 const Type *NextTy = STy;
649 bool isBadCase = false;
651 for (unsigned Idx = FirstConstantOper;
652 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
653 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
654 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
658 // If the array is indexed beyond the bounds of the static type
659 // at this level, it will also fall into the "be careful" case.
660 // It would theoretically be possible to analyze these cases,
661 // but for now just be conservatively correct.
662 if (const ArrayType *ATy = dyn_cast<ArrayType>(STy))
663 if (cast<ConstantInt>(G1OC)->getZExtValue() >=
664 ATy->getNumElements() ||
665 cast<ConstantInt>(G2OC)->getZExtValue() >=
666 ATy->getNumElements()) {
670 if (const VectorType *VTy = dyn_cast<VectorType>(STy))
671 if (cast<ConstantInt>(G1OC)->getZExtValue() >=
672 VTy->getNumElements() ||
673 cast<ConstantInt>(G2OC)->getZExtValue() >=
674 VTy->getNumElements()) {
678 STy = cast<SequentialType>(NextTy);
679 NextTy = cast<SequentialType>(NextTy)->getElementType();
682 if (isBadCase) G1OC = 0;
685 // Make sure they are comparable (ie, not constant expressions), and
686 // make sure the GEP with the smaller leading constant is GEP1.
688 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
690 if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
691 if (CV->getZExtValue()) { // If they are comparable and G2 > G1
692 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
693 std::swap(NumGEP1Ops, NumGEP2Ops);
700 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
703 // No shared constant operands, and we ran out of common operands. At this
704 // point, the GEP instructions have run through all of their operands, and we
705 // haven't found evidence that there are any deltas between the GEP's.
706 // However, one GEP may have more operands than the other. If this is the
707 // case, there may still be hope. Check this now.
708 if (FirstConstantOper == MinOperands) {
709 // Without TargetData, we won't know what the offsets are.
713 // Make GEP1Ops be the longer one if there is a longer one.
714 if (NumGEP1Ops < NumGEP2Ops) {
715 std::swap(GEP1Ops, GEP2Ops);
716 std::swap(NumGEP1Ops, NumGEP2Ops);
719 // Is there anything to check?
720 if (NumGEP1Ops > MinOperands) {
721 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
722 if (isa<ConstantInt>(GEP1Ops[i]) &&
723 !cast<ConstantInt>(GEP1Ops[i])->isZero()) {
724 // Yup, there's a constant in the tail. Set all variables to
725 // constants in the GEP instruction to make it suitable for
726 // TargetData::getIndexedOffset.
727 for (i = 0; i != MaxOperands; ++i)
728 if (!isa<ConstantInt>(GEP1Ops[i]))
729 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
730 // Okay, now get the offset. This is the relative offset for the full
732 int64_t Offset1 = TD->getIndexedOffset(GEPPointerTy, GEP1Ops,
735 // Now check without any constants at the end.
736 int64_t Offset2 = TD->getIndexedOffset(GEPPointerTy, GEP1Ops,
739 // Make sure we compare the absolute difference.
740 if (Offset1 > Offset2)
741 std::swap(Offset1, Offset2);
743 // If the tail provided a bit enough offset, return noalias!
744 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
746 // Otherwise break - we don't look for another constant in the tail.
751 // Couldn't find anything useful.
755 // If there are non-equal constants arguments, then we can figure
756 // out a minimum known delta between the two index expressions... at
757 // this point we know that the first constant index of GEP1 is less
758 // than the first constant index of GEP2.
760 // Advance BasePtr[12]Ty over this first differing constant operand.
761 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
762 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
763 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
764 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
766 // We are going to be using TargetData::getIndexedOffset to determine the
767 // offset that each of the GEP's is reaching. To do this, we have to convert
768 // all variable references to constant references. To do this, we convert the
769 // initial sequence of array subscripts into constant zeros to start with.
770 const Type *ZeroIdxTy = GEPPointerTy;
771 for (unsigned i = 0; i != FirstConstantOper; ++i) {
772 if (!isa<StructType>(ZeroIdxTy))
773 GEP1Ops[i] = GEP2Ops[i] =
774 Constant::getNullValue(Type::getInt32Ty(Context));
776 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
777 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
780 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
782 // Loop over the rest of the operands...
783 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
784 const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
785 const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
786 // If they are equal, use a zero index...
787 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
788 if (!isa<ConstantInt>(Op1))
789 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
790 // Otherwise, just keep the constants we have.
793 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
794 // If this is an array index, make sure the array element is in range.
795 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
796 if (Op1C->getZExtValue() >= AT->getNumElements())
797 return MayAlias; // Be conservative with out-of-range accesses
798 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) {
799 if (Op1C->getZExtValue() >= VT->getNumElements())
800 return MayAlias; // Be conservative with out-of-range accesses
804 // GEP1 is known to produce a value less than GEP2. To be
805 // conservatively correct, we must assume the largest possible
806 // constant is used in this position. This cannot be the initial
807 // index to the GEP instructions (because we know we have at least one
808 // element before this one with the different constant arguments), so
809 // we know that the current index must be into either a struct or
810 // array. Because we know it's not constant, this cannot be a
811 // structure index. Because of this, we can calculate the maximum
814 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
816 ConstantInt::get(Type::getInt64Ty(Context),
817 AT->getNumElements()-1);
818 else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty))
820 ConstantInt::get(Type::getInt64Ty(Context),
821 VT->getNumElements()-1);
826 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
827 // If this is an array index, make sure the array element is in range.
828 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr2Ty)) {
829 if (Op2C->getZExtValue() >= AT->getNumElements())
830 return MayAlias; // Be conservative with out-of-range accesses
831 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr2Ty)) {
832 if (Op2C->getZExtValue() >= VT->getNumElements())
833 return MayAlias; // Be conservative with out-of-range accesses
835 } else { // Conservatively assume the minimum value for this index
836 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
841 if (BasePtr1Ty && Op1) {
842 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
843 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
848 if (BasePtr2Ty && Op2) {
849 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
850 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
856 if (TD && GEPPointerTy->getElementType()->isSized()) {
858 TD->getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
860 TD->getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
861 assert(Offset1 != Offset2 &&
862 "There is at least one different constant here!");
864 // Make sure we compare the absolute difference.
865 if (Offset1 > Offset2)
866 std::swap(Offset1, Offset2);
868 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
869 //cerr << "Determined that these two GEP's don't alias ["
870 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
877 // Make sure that anything that uses AliasAnalysis pulls in this file...
878 DEFINING_FILE_FOR(BasicAliasAnalysis)