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"
34 //===----------------------------------------------------------------------===//
36 //===----------------------------------------------------------------------===//
38 static const User *isGEP(const Value *V) {
39 if (isa<GetElementPtrInst>(V) ||
40 (isa<ConstantExpr>(V) &&
41 cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
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 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 Argument *A = dyn_cast<Argument>(V)) {
116 if (A->hasByValAttr())
117 AccessTy = cast<PointerType>(A->getType())->getElementType();
124 if (AccessTy->isSized())
125 return TD.getTypeAllocSize(AccessTy) < Size;
129 //===----------------------------------------------------------------------===//
131 //===----------------------------------------------------------------------===//
134 /// NoAA - This class implements the -no-aa pass, which always returns "I
135 /// don't know" for alias queries. NoAA is unlike other alias analysis
136 /// implementations, in that it does not chain to a previous analysis. As
137 /// such it doesn't follow many of the rules that other alias analyses must.
139 struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
140 static char ID; // Class identification, replacement for typeinfo
141 NoAA() : ImmutablePass(&ID) {}
142 explicit NoAA(void *PID) : ImmutablePass(PID) { }
144 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
145 AU.addRequired<TargetData>();
148 virtual void initializePass() {
149 TD = &getAnalysis<TargetData>();
152 virtual AliasResult alias(const Value *V1, unsigned V1Size,
153 const Value *V2, unsigned V2Size) {
157 virtual void getArgumentAccesses(Function *F, CallSite CS,
158 std::vector<PointerAccessInfo> &Info) {
159 assert(0 && "This method may not be called on this function!");
162 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
163 virtual bool pointsToConstantMemory(const Value *P) { return false; }
164 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
167 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
170 virtual bool hasNoModRefInfoForCalls() const { return true; }
172 virtual void deleteValue(Value *V) {}
173 virtual void copyValue(Value *From, Value *To) {}
175 } // End of anonymous namespace
177 // Register this pass...
179 static RegisterPass<NoAA>
180 U("no-aa", "No Alias Analysis (always returns 'may' alias)", true, true);
182 // Declare that we implement the AliasAnalysis interface
183 static RegisterAnalysisGroup<AliasAnalysis> V(U);
185 ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
187 //===----------------------------------------------------------------------===//
189 //===----------------------------------------------------------------------===//
192 /// BasicAliasAnalysis - This is the default alias analysis implementation.
193 /// Because it doesn't chain to a previous alias analysis (like -no-aa), it
194 /// derives from the NoAA class.
195 struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA {
196 static char ID; // Class identification, replacement for typeinfo
197 BasicAliasAnalysis() : NoAA(&ID) {}
198 AliasResult alias(const Value *V1, unsigned V1Size,
199 const Value *V2, unsigned V2Size);
201 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
202 ModRefResult getModRefInfo(CallSite CS1, CallSite CS2);
204 /// hasNoModRefInfoForCalls - We can provide mod/ref information against
205 /// non-escaping allocations.
206 virtual bool hasNoModRefInfoForCalls() const { return false; }
208 /// pointsToConstantMemory - Chase pointers until we find a (constant
210 bool pointsToConstantMemory(const Value *P);
213 // CheckGEPInstructions - Check two GEP instructions with known
214 // must-aliasing base pointers. This checks to see if the index expressions
215 // preclude the pointers from aliasing...
217 CheckGEPInstructions(const Type* BasePtr1Ty,
218 Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size,
219 const Type *BasePtr2Ty,
220 Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size);
222 } // End of anonymous namespace
224 // Register this pass...
225 char BasicAliasAnalysis::ID = 0;
226 static RegisterPass<BasicAliasAnalysis>
227 X("basicaa", "Basic Alias Analysis (default AA impl)", false, true);
229 // Declare that we implement the AliasAnalysis interface
230 static RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
232 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
233 return new BasicAliasAnalysis();
237 /// pointsToConstantMemory - Chase pointers until we find a (constant
239 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
240 if (const GlobalVariable *GV =
241 dyn_cast<GlobalVariable>(P->getUnderlyingObject()))
242 return GV->isConstant();
247 // getModRefInfo - Check to see if the specified callsite can clobber the
248 // specified memory object. Since we only look at local properties of this
249 // function, we really can't say much about this query. We do, however, use
250 // simple "address taken" analysis on local objects.
252 AliasAnalysis::ModRefResult
253 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
254 if (!isa<Constant>(P)) {
255 const Value *Object = P->getUnderlyingObject();
257 // If this is a tail call and P points to a stack location, we know that
258 // the tail call cannot access or modify the local stack.
259 // We cannot exclude byval arguments here; these belong to the caller of
260 // the current function not to the current function, and a tail callee
261 // may reference them.
262 if (isa<AllocaInst>(Object))
263 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
264 if (CI->isTailCall())
267 // If the pointer is to a locally allocated object that does not escape,
268 // then the call can not mod/ref the pointer unless the call takes the
269 // argument without capturing it.
270 if (isNonEscapingLocalObject(Object) && CS.getInstruction() != Object) {
271 bool passedAsArg = false;
272 // TODO: Eventually only check 'nocapture' arguments.
273 for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
275 if (isa<PointerType>((*CI)->getType()) &&
276 alias(cast<Value>(CI), ~0U, P, ~0U) != NoAlias)
284 // The AliasAnalysis base class has some smarts, lets use them.
285 return AliasAnalysis::getModRefInfo(CS, P, Size);
289 AliasAnalysis::ModRefResult
290 BasicAliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) {
291 // If CS1 or CS2 are readnone, they don't interact.
292 ModRefBehavior CS1B = AliasAnalysis::getModRefBehavior(CS1);
293 if (CS1B == DoesNotAccessMemory) return NoModRef;
295 ModRefBehavior CS2B = AliasAnalysis::getModRefBehavior(CS2);
296 if (CS2B == DoesNotAccessMemory) return NoModRef;
298 // If they both only read from memory, just return ref.
299 if (CS1B == OnlyReadsMemory && CS2B == OnlyReadsMemory)
302 // Otherwise, fall back to NoAA (mod+ref).
303 return NoAA::getModRefInfo(CS1, CS2);
307 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
308 // as array references.
310 AliasAnalysis::AliasResult
311 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
312 const Value *V2, unsigned V2Size) {
313 // Strip off any constant expression casts if they exist
314 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
315 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
316 V1 = CE->getOperand(0);
317 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
318 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
319 V2 = CE->getOperand(0);
321 // Are we checking for alias of the same value?
322 if (V1 == V2) return MustAlias;
324 if (!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType()))
325 return NoAlias; // Scalars cannot alias each other
327 // Strip off cast instructions. Since V1 and V2 are pointers, they must be
328 // pointer<->pointer bitcasts.
329 if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
330 return alias(I->getOperand(0), V1Size, V2, V2Size);
331 if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
332 return alias(V1, V1Size, I->getOperand(0), V2Size);
334 // Figure out what objects these things are pointing to if we can.
335 const Value *O1 = V1->getUnderlyingObject();
336 const Value *O2 = V2->getUnderlyingObject();
339 // If V1/V2 point to two different objects we know that we have no alias.
340 if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
343 // Arguments can't alias with local allocations or noalias calls.
344 if ((isa<Argument>(O1) && (isa<AllocationInst>(O2) || isNoAliasCall(O2))) ||
345 (isa<Argument>(O2) && (isa<AllocationInst>(O1) || isNoAliasCall(O1))))
348 // Most objects can't alias null.
349 if ((isa<ConstantPointerNull>(V2) && isKnownNonNull(O1)) ||
350 (isa<ConstantPointerNull>(V1) && isKnownNonNull(O2)))
354 // If the size of one access is larger than the entire object on the other
355 // side, then we know such behavior is undefined and can assume no alias.
356 const TargetData &TD = getTargetData();
357 if ((V1Size != ~0U && isObjectSmallerThan(O2, V1Size, TD)) ||
358 (V2Size != ~0U && isObjectSmallerThan(O1, V2Size, TD)))
361 // If one pointer is the result of a call/invoke and the other is a
362 // non-escaping local object, then we know the object couldn't escape to a
363 // point where the call could return it.
364 if ((isa<CallInst>(O1) || isa<InvokeInst>(O1)) &&
365 isNonEscapingLocalObject(O2) && O1 != O2)
367 if ((isa<CallInst>(O2) || isa<InvokeInst>(O2)) &&
368 isNonEscapingLocalObject(O1) && O1 != O2)
371 // If we have two gep instructions with must-alias'ing base pointers, figure
372 // out if the indexes to the GEP tell us anything about the derived pointer.
373 // Note that we also handle chains of getelementptr instructions as well as
374 // constant expression getelementptrs here.
376 if (isGEP(V1) && isGEP(V2)) {
377 const User *GEP1 = cast<User>(V1);
378 const User *GEP2 = cast<User>(V2);
380 // If V1 and V2 are identical GEPs, just recurse down on both of them.
381 // This allows us to analyze things like:
382 // P = gep A, 0, i, 1
383 // Q = gep B, 0, i, 1
384 // by just analyzing A and B. This is even safe for variable indices.
385 if (GEP1->getType() == GEP2->getType() &&
386 GEP1->getNumOperands() == GEP2->getNumOperands() &&
387 GEP1->getOperand(0)->getType() == GEP2->getOperand(0)->getType() &&
388 // All operands are the same, ignoring the base.
389 std::equal(GEP1->op_begin()+1, GEP1->op_end(), GEP2->op_begin()+1))
390 return alias(GEP1->getOperand(0), V1Size, GEP2->getOperand(0), V2Size);
393 // Drill down into the first non-gep value, to test for must-aliasing of
394 // the base pointers.
395 while (isGEP(GEP1->getOperand(0)) &&
396 GEP1->getOperand(1) ==
397 Constant::getNullValue(GEP1->getOperand(1)->getType()))
398 GEP1 = cast<User>(GEP1->getOperand(0));
399 const Value *BasePtr1 = GEP1->getOperand(0);
401 while (isGEP(GEP2->getOperand(0)) &&
402 GEP2->getOperand(1) ==
403 Constant::getNullValue(GEP2->getOperand(1)->getType()))
404 GEP2 = cast<User>(GEP2->getOperand(0));
405 const Value *BasePtr2 = GEP2->getOperand(0);
407 // Do the base pointers alias?
408 AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
409 if (BaseAlias == NoAlias) return NoAlias;
410 if (BaseAlias == MustAlias) {
411 // If the base pointers alias each other exactly, check to see if we can
412 // figure out anything about the resultant pointers, to try to prove
415 // Collect all of the chained GEP operands together into one simple place
416 SmallVector<Value*, 16> GEP1Ops, GEP2Ops;
417 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
418 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
420 // If GetGEPOperands were able to fold to the same must-aliased pointer,
421 // do the comparison.
422 if (BasePtr1 == BasePtr2) {
424 CheckGEPInstructions(BasePtr1->getType(),
425 &GEP1Ops[0], GEP1Ops.size(), V1Size,
427 &GEP2Ops[0], GEP2Ops.size(), V2Size);
428 if (GAlias != MayAlias)
434 // Check to see if these two pointers are related by a getelementptr
435 // instruction. If one pointer is a GEP with a non-zero index of the other
436 // pointer, we know they cannot alias.
440 std::swap(V1Size, V2Size);
443 if (V1Size != ~0U && V2Size != ~0U)
445 SmallVector<Value*, 16> GEPOperands;
446 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
448 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
449 if (R == MustAlias) {
450 // If there is at least one non-zero constant index, we know they cannot
452 bool ConstantFound = false;
453 bool AllZerosFound = true;
454 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
455 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
456 if (!C->isNullValue()) {
457 ConstantFound = true;
458 AllZerosFound = false;
462 AllZerosFound = false;
465 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
466 // the ptr, the end result is a must alias also.
471 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
474 // Otherwise we have to check to see that the distance is more than
475 // the size of the argument... build an index vector that is equal to
476 // the arguments provided, except substitute 0's for any variable
477 // indexes we find...
478 if (cast<PointerType>(
479 BasePtr->getType())->getElementType()->isSized()) {
480 for (unsigned i = 0; i != GEPOperands.size(); ++i)
481 if (!isa<ConstantInt>(GEPOperands[i]))
483 Constant::getNullValue(GEPOperands[i]->getType());
485 getTargetData().getIndexedOffset(BasePtr->getType(),
489 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
499 // This function is used to determine if the indices of two GEP instructions are
500 // equal. V1 and V2 are the indices.
501 static bool IndexOperandsEqual(Value *V1, Value *V2) {
502 if (V1->getType() == V2->getType())
504 if (Constant *C1 = dyn_cast<Constant>(V1))
505 if (Constant *C2 = dyn_cast<Constant>(V2)) {
506 // Sign extend the constants to long types, if necessary
507 if (C1->getType() != Type::Int64Ty)
508 C1 = ConstantExpr::getSExt(C1, Type::Int64Ty);
509 if (C2->getType() != Type::Int64Ty)
510 C2 = ConstantExpr::getSExt(C2, Type::Int64Ty);
516 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
517 /// base pointers. This checks to see if the index expressions preclude the
518 /// pointers from aliasing...
519 AliasAnalysis::AliasResult
520 BasicAliasAnalysis::CheckGEPInstructions(
521 const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
522 const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
523 // We currently can't handle the case when the base pointers have different
524 // primitive types. Since this is uncommon anyway, we are happy being
525 // extremely conservative.
526 if (BasePtr1Ty != BasePtr2Ty)
529 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
531 // Find the (possibly empty) initial sequence of equal values... which are not
532 // necessarily constants.
533 unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
534 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
535 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
536 unsigned UnequalOper = 0;
537 while (UnequalOper != MinOperands &&
538 IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
539 // Advance through the type as we go...
541 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
542 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
544 // If all operands equal each other, then the derived pointers must
545 // alias each other...
547 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
548 "Ran out of type nesting, but not out of operands?");
553 // If we have seen all constant operands, and run out of indexes on one of the
554 // getelementptrs, check to see if the tail of the leftover one is all zeros.
555 // If so, return mustalias.
556 if (UnequalOper == MinOperands) {
557 if (NumGEP1Ops < NumGEP2Ops) {
558 std::swap(GEP1Ops, GEP2Ops);
559 std::swap(NumGEP1Ops, NumGEP2Ops);
562 bool AllAreZeros = true;
563 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
564 if (!isa<Constant>(GEP1Ops[i]) ||
565 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
569 if (AllAreZeros) return MustAlias;
573 // So now we know that the indexes derived from the base pointers,
574 // which are known to alias, are different. We can still determine a
575 // no-alias result if there are differing constant pairs in the index
576 // chain. For example:
577 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
579 // We have to be careful here about array accesses. In particular, consider:
580 // A[1][0] vs A[0][i]
581 // In this case, we don't *know* that the array will be accessed in bounds:
582 // the index could even be negative. Because of this, we have to
583 // conservatively *give up* and return may alias. We disregard differing
584 // array subscripts that are followed by a variable index without going
587 unsigned SizeMax = std::max(G1S, G2S);
588 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
590 // Scan for the first operand that is constant and unequal in the
591 // two getelementptrs...
592 unsigned FirstConstantOper = UnequalOper;
593 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
594 const Value *G1Oper = GEP1Ops[FirstConstantOper];
595 const Value *G2Oper = GEP2Ops[FirstConstantOper];
597 if (G1Oper != G2Oper) // Found non-equal constant indexes...
598 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
599 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
600 if (G1OC->getType() != G2OC->getType()) {
601 // Sign extend both operands to long.
602 if (G1OC->getType() != Type::Int64Ty)
603 G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty);
604 if (G2OC->getType() != Type::Int64Ty)
605 G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty);
606 GEP1Ops[FirstConstantOper] = G1OC;
607 GEP2Ops[FirstConstantOper] = G2OC;
611 // Handle the "be careful" case above: if this is an array/vector
612 // subscript, scan for a subsequent variable array index.
613 if (const SequentialType *STy =
614 dyn_cast<SequentialType>(BasePtr1Ty)) {
615 const Type *NextTy = STy;
616 bool isBadCase = false;
618 for (unsigned Idx = FirstConstantOper;
619 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
620 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
621 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
625 // If the array is indexed beyond the bounds of the static type
626 // at this level, it will also fall into the "be careful" case.
627 // It would theoretically be possible to analyze these cases,
628 // but for now just be conservatively correct.
629 if (const ArrayType *ATy = dyn_cast<ArrayType>(STy))
630 if (cast<ConstantInt>(G1OC)->getZExtValue() >=
631 ATy->getNumElements() ||
632 cast<ConstantInt>(G2OC)->getZExtValue() >=
633 ATy->getNumElements()) {
637 if (const VectorType *VTy = dyn_cast<VectorType>(STy))
638 if (cast<ConstantInt>(G1OC)->getZExtValue() >=
639 VTy->getNumElements() ||
640 cast<ConstantInt>(G2OC)->getZExtValue() >=
641 VTy->getNumElements()) {
645 STy = cast<SequentialType>(NextTy);
646 NextTy = cast<SequentialType>(NextTy)->getElementType();
649 if (isBadCase) G1OC = 0;
652 // Make sure they are comparable (ie, not constant expressions), and
653 // make sure the GEP with the smaller leading constant is GEP1.
655 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
657 if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
658 if (CV->getZExtValue()) { // If they are comparable and G2 > G1
659 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
660 std::swap(NumGEP1Ops, NumGEP2Ops);
667 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
670 // No shared constant operands, and we ran out of common operands. At this
671 // point, the GEP instructions have run through all of their operands, and we
672 // haven't found evidence that there are any deltas between the GEP's.
673 // However, one GEP may have more operands than the other. If this is the
674 // case, there may still be hope. Check this now.
675 if (FirstConstantOper == MinOperands) {
676 // Make GEP1Ops be the longer one if there is a longer one.
677 if (NumGEP1Ops < NumGEP2Ops) {
678 std::swap(GEP1Ops, GEP2Ops);
679 std::swap(NumGEP1Ops, NumGEP2Ops);
682 // Is there anything to check?
683 if (NumGEP1Ops > MinOperands) {
684 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
685 if (isa<ConstantInt>(GEP1Ops[i]) &&
686 !cast<ConstantInt>(GEP1Ops[i])->isZero()) {
687 // Yup, there's a constant in the tail. Set all variables to
688 // constants in the GEP instruction to make it suitable for
689 // TargetData::getIndexedOffset.
690 for (i = 0; i != MaxOperands; ++i)
691 if (!isa<ConstantInt>(GEP1Ops[i]))
692 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
693 // Okay, now get the offset. This is the relative offset for the full
695 const TargetData &TD = getTargetData();
696 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
699 // Now check without any constants at the end.
700 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
703 // Make sure we compare the absolute difference.
704 if (Offset1 > Offset2)
705 std::swap(Offset1, Offset2);
707 // If the tail provided a bit enough offset, return noalias!
708 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
710 // Otherwise break - we don't look for another constant in the tail.
715 // Couldn't find anything useful.
719 // If there are non-equal constants arguments, then we can figure
720 // out a minimum known delta between the two index expressions... at
721 // this point we know that the first constant index of GEP1 is less
722 // than the first constant index of GEP2.
724 // Advance BasePtr[12]Ty over this first differing constant operand.
725 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
726 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
727 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
728 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
730 // We are going to be using TargetData::getIndexedOffset to determine the
731 // offset that each of the GEP's is reaching. To do this, we have to convert
732 // all variable references to constant references. To do this, we convert the
733 // initial sequence of array subscripts into constant zeros to start with.
734 const Type *ZeroIdxTy = GEPPointerTy;
735 for (unsigned i = 0; i != FirstConstantOper; ++i) {
736 if (!isa<StructType>(ZeroIdxTy))
737 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty);
739 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
740 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
743 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
745 // Loop over the rest of the operands...
746 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
747 const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
748 const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
749 // If they are equal, use a zero index...
750 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
751 if (!isa<ConstantInt>(Op1))
752 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
753 // Otherwise, just keep the constants we have.
756 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
757 // If this is an array index, make sure the array element is in range.
758 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
759 if (Op1C->getZExtValue() >= AT->getNumElements())
760 return MayAlias; // Be conservative with out-of-range accesses
761 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) {
762 if (Op1C->getZExtValue() >= VT->getNumElements())
763 return MayAlias; // Be conservative with out-of-range accesses
767 // GEP1 is known to produce a value less than GEP2. To be
768 // conservatively correct, we must assume the largest possible
769 // constant is used in this position. This cannot be the initial
770 // index to the GEP instructions (because we know we have at least one
771 // element before this one with the different constant arguments), so
772 // we know that the current index must be into either a struct or
773 // array. Because we know it's not constant, this cannot be a
774 // structure index. Because of this, we can calculate the maximum
777 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
778 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1);
779 else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty))
780 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,VT->getNumElements()-1);
785 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
786 // If this is an array index, make sure the array element is in range.
787 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr2Ty)) {
788 if (Op2C->getZExtValue() >= AT->getNumElements())
789 return MayAlias; // Be conservative with out-of-range accesses
790 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr2Ty)) {
791 if (Op2C->getZExtValue() >= VT->getNumElements())
792 return MayAlias; // Be conservative with out-of-range accesses
794 } else { // Conservatively assume the minimum value for this index
795 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
800 if (BasePtr1Ty && Op1) {
801 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
802 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
807 if (BasePtr2Ty && Op2) {
808 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
809 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
815 if (GEPPointerTy->getElementType()->isSized()) {
817 getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
819 getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
820 assert(Offset1 != Offset2 &&
821 "There is at least one different constant here!");
823 // Make sure we compare the absolute difference.
824 if (Offset1 > Offset2)
825 std::swap(Offset1, Offset2);
827 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
828 //cerr << "Determined that these two GEP's don't alias ["
829 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
836 // Make sure that anything that uses AliasAnalysis pulls in this file...
837 DEFINING_FILE_FOR(BasicAliasAnalysis)