1 //===- BasicAliasAnalysis.cpp - Local Alias Analysis Impl -----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source 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/Passes.h"
18 #include "llvm/Constants.h"
19 #include "llvm/DerivedTypes.h"
20 #include "llvm/Function.h"
21 #include "llvm/GlobalVariable.h"
22 #include "llvm/Instructions.h"
23 #include "llvm/Pass.h"
24 #include "llvm/Target/TargetData.h"
25 #include "llvm/Support/Compiler.h"
26 #include "llvm/Support/GetElementPtrTypeIterator.h"
27 #include "llvm/Support/ManagedStatic.h"
32 /// NoAA - This class implements the -no-aa pass, which always returns "I
33 /// don't know" for alias queries. NoAA is unlike other alias analysis
34 /// implementations, in that it does not chain to a previous analysis. As
35 /// such it doesn't follow many of the rules that other alias analyses must.
37 struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
38 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
39 AU.addRequired<TargetData>();
42 virtual void initializePass() {
43 TD = &getAnalysis<TargetData>();
46 virtual AliasResult alias(const Value *V1, unsigned V1Size,
47 const Value *V2, unsigned V2Size) {
51 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
52 std::vector<PointerAccessInfo> *Info) {
53 return UnknownModRefBehavior;
56 virtual void getArgumentAccesses(Function *F, CallSite CS,
57 std::vector<PointerAccessInfo> &Info) {
58 assert(0 && "This method may not be called on this function!");
61 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
62 virtual bool pointsToConstantMemory(const Value *P) { return false; }
63 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
66 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
69 virtual bool hasNoModRefInfoForCalls() const { return true; }
71 virtual void deleteValue(Value *V) {}
72 virtual void copyValue(Value *From, Value *To) {}
75 // Register this pass...
77 U("no-aa", "No Alias Analysis (always returns 'may' alias)");
79 // Declare that we implement the AliasAnalysis interface
80 RegisterAnalysisGroup<AliasAnalysis> V(U);
81 } // End of anonymous namespace
83 ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
86 /// BasicAliasAnalysis - This is the default alias analysis implementation.
87 /// Because it doesn't chain to a previous alias analysis (like -no-aa), it
88 /// derives from the NoAA class.
89 struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA {
90 AliasResult alias(const Value *V1, unsigned V1Size,
91 const Value *V2, unsigned V2Size);
93 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
94 ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
95 return NoAA::getModRefInfo(CS1,CS2);
98 /// hasNoModRefInfoForCalls - We can provide mod/ref information against
99 /// non-escaping allocations.
100 virtual bool hasNoModRefInfoForCalls() const { return false; }
102 /// pointsToConstantMemory - Chase pointers until we find a (constant
104 bool pointsToConstantMemory(const Value *P);
106 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
107 std::vector<PointerAccessInfo> *Info);
110 // CheckGEPInstructions - Check two GEP instructions with known
111 // must-aliasing base pointers. This checks to see if the index expressions
112 // preclude the pointers from aliasing...
114 CheckGEPInstructions(const Type* BasePtr1Ty, std::vector<Value*> &GEP1Ops,
116 const Type *BasePtr2Ty, std::vector<Value*> &GEP2Ops,
120 // Register this pass...
121 RegisterPass<BasicAliasAnalysis>
122 X("basicaa", "Basic Alias Analysis (default AA impl)");
124 // Declare that we implement the AliasAnalysis interface
125 RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
126 } // End of anonymous namespace
128 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
129 return new BasicAliasAnalysis();
132 // getUnderlyingObject - This traverses the use chain to figure out what object
133 // the specified value points to. If the value points to, or is derived from, a
134 // unique object or an argument, return it.
135 static const Value *getUnderlyingObject(const Value *V) {
136 if (!isa<PointerType>(V->getType())) return 0;
138 // If we are at some type of object, return it. GlobalValues and Allocations
139 // have unique addresses.
140 if (isa<GlobalValue>(V) || isa<AllocationInst>(V) || isa<Argument>(V))
143 // Traverse through different addressing mechanisms...
144 if (const Instruction *I = dyn_cast<Instruction>(V)) {
145 if (isa<BitCastInst>(I) || isa<GetElementPtrInst>(I))
146 return getUnderlyingObject(I->getOperand(0));
147 } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
148 if (CE->getOpcode() == Instruction::BitCast ||
149 CE->getOpcode() == Instruction::GetElementPtr)
150 return getUnderlyingObject(CE->getOperand(0));
155 static const User *isGEP(const Value *V) {
156 if (isa<GetElementPtrInst>(V) ||
157 (isa<ConstantExpr>(V) &&
158 cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
159 return cast<User>(V);
163 static const Value *GetGEPOperands(const Value *V, std::vector<Value*> &GEPOps){
164 assert(GEPOps.empty() && "Expect empty list to populate!");
165 GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
166 cast<User>(V)->op_end());
168 // Accumulate all of the chained indexes into the operand array
169 V = cast<User>(V)->getOperand(0);
171 while (const User *G = isGEP(V)) {
172 if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
173 !cast<Constant>(GEPOps[0])->isNullValue())
174 break; // Don't handle folding arbitrary pointer offsets yet...
175 GEPOps.erase(GEPOps.begin()); // Drop the zero index
176 GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
177 V = G->getOperand(0);
182 /// pointsToConstantMemory - Chase pointers until we find a (constant
184 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
185 if (const Value *V = getUnderlyingObject(P))
186 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
187 return GV->isConstant();
191 // Determine if an AllocationInst instruction escapes from the function it is
192 // contained in. If it does not escape, there is no way for another function to
193 // mod/ref it. We do this by looking at its uses and determining if the uses
194 // can escape (recursively).
195 static bool AddressMightEscape(const Value *V) {
196 for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
198 const Instruction *I = cast<Instruction>(*UI);
199 switch (I->getOpcode()) {
200 case Instruction::Load:
202 case Instruction::Store:
203 if (I->getOperand(0) == V)
204 return true; // Escapes if the pointer is stored.
206 case Instruction::GetElementPtr:
207 if (AddressMightEscape(I))
209 case Instruction::BitCast:
210 if (!isa<PointerType>(I->getType()))
212 if (AddressMightEscape(I))
215 case Instruction::Ret:
216 // If returned, the address will escape to calling functions, but no
217 // callees could modify it.
226 // getModRefInfo - Check to see if the specified callsite can clobber the
227 // specified memory object. Since we only look at local properties of this
228 // function, we really can't say much about this query. We do, however, use
229 // simple "address taken" analysis on local objects.
231 AliasAnalysis::ModRefResult
232 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
233 if (!isa<Constant>(P))
234 if (const AllocationInst *AI =
235 dyn_cast_or_null<AllocationInst>(getUnderlyingObject(P))) {
236 // Okay, the pointer is to a stack allocated object. If we can prove that
237 // the pointer never "escapes", then we know the call cannot clobber it,
238 // because it simply can't get its address.
239 if (!AddressMightEscape(AI))
242 // If this is a tail call and P points to a stack location, we know that
243 // the tail call cannot access or modify the local stack.
244 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
245 if (CI->isTailCall() && isa<AllocaInst>(AI))
249 // The AliasAnalysis base class has some smarts, lets use them.
250 return AliasAnalysis::getModRefInfo(CS, P, Size);
253 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
254 // as array references. Note that this function is heavily tail recursive.
255 // Hopefully we have a smart C++ compiler. :)
257 AliasAnalysis::AliasResult
258 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
259 const Value *V2, unsigned V2Size) {
260 // Strip off any constant expression casts if they exist
261 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
262 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
263 V1 = CE->getOperand(0);
264 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
265 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
266 V2 = CE->getOperand(0);
268 // Are we checking for alias of the same value?
269 if (V1 == V2) return MustAlias;
271 if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
272 V1->getType() != Type::Int64Ty && V2->getType() != Type::Int64Ty)
273 return NoAlias; // Scalars cannot alias each other
275 // Strip off cast instructions...
276 if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
277 return alias(I->getOperand(0), V1Size, V2, V2Size);
278 if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
279 return alias(V1, V1Size, I->getOperand(0), V2Size);
281 // Figure out what objects these things are pointing to if we can...
282 const Value *O1 = getUnderlyingObject(V1);
283 const Value *O2 = getUnderlyingObject(V2);
285 // Pointing at a discernible object?
288 if (isa<Argument>(O1)) {
289 // Incoming argument cannot alias locally allocated object!
290 if (isa<AllocationInst>(O2)) return NoAlias;
291 // Otherwise, nothing is known...
292 } else if (isa<Argument>(O2)) {
293 // Incoming argument cannot alias locally allocated object!
294 if (isa<AllocationInst>(O1)) return NoAlias;
295 // Otherwise, nothing is known...
296 } else if (O1 != O2) {
297 // If they are two different objects, we know that we have no alias...
301 // If they are the same object, they we can look at the indexes. If they
302 // index off of the object is the same for both pointers, they must alias.
303 // If they are provably different, they must not alias. Otherwise, we
304 // can't tell anything.
308 if (!isa<Argument>(O1) && isa<ConstantPointerNull>(V2))
309 return NoAlias; // Unique values don't alias null
311 if (isa<GlobalVariable>(O1) ||
312 (isa<AllocationInst>(O1) &&
313 !cast<AllocationInst>(O1)->isArrayAllocation()))
314 if (cast<PointerType>(O1->getType())->getElementType()->isSized()) {
315 // If the size of the other access is larger than the total size of the
316 // global/alloca/malloc, it cannot be accessing the global (it's
317 // undefined to load or store bytes before or after an object).
318 const Type *ElTy = cast<PointerType>(O1->getType())->getElementType();
319 unsigned GlobalSize = getTargetData().getTypeSize(ElTy);
320 if (GlobalSize < V2Size && V2Size != ~0U)
326 if (!isa<Argument>(O2) && isa<ConstantPointerNull>(V1))
327 return NoAlias; // Unique values don't alias null
329 if (isa<GlobalVariable>(O2) ||
330 (isa<AllocationInst>(O2) &&
331 !cast<AllocationInst>(O2)->isArrayAllocation()))
332 if (cast<PointerType>(O2->getType())->getElementType()->isSized()) {
333 // If the size of the other access is larger than the total size of the
334 // global/alloca/malloc, it cannot be accessing the object (it's
335 // undefined to load or store bytes before or after an object).
336 const Type *ElTy = cast<PointerType>(O2->getType())->getElementType();
337 unsigned GlobalSize = getTargetData().getTypeSize(ElTy);
338 if (GlobalSize < V1Size && V1Size != ~0U)
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 // Drill down into the first non-gep value, to test for must-aliasing of
350 // the base pointers.
351 const Value *BasePtr1 = V1, *BasePtr2 = V2;
353 BasePtr1 = cast<User>(BasePtr1)->getOperand(0);
354 } while (isGEP(BasePtr1) &&
355 cast<User>(BasePtr1)->getOperand(1) ==
356 Constant::getNullValue(cast<User>(BasePtr1)->getOperand(1)->getType()));
358 BasePtr2 = cast<User>(BasePtr2)->getOperand(0);
359 } while (isGEP(BasePtr2) &&
360 cast<User>(BasePtr2)->getOperand(1) ==
361 Constant::getNullValue(cast<User>(BasePtr2)->getOperand(1)->getType()));
363 // Do the base pointers alias?
364 AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
365 if (BaseAlias == NoAlias) return NoAlias;
366 if (BaseAlias == MustAlias) {
367 // If the base pointers alias each other exactly, check to see if we can
368 // figure out anything about the resultant pointers, to try to prove
371 // Collect all of the chained GEP operands together into one simple place
372 std::vector<Value*> GEP1Ops, GEP2Ops;
373 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
374 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
376 // If GetGEPOperands were able to fold to the same must-aliased pointer,
377 // do the comparison.
378 if (BasePtr1 == BasePtr2) {
380 CheckGEPInstructions(BasePtr1->getType(), GEP1Ops, V1Size,
381 BasePtr2->getType(), GEP2Ops, V2Size);
382 if (GAlias != MayAlias)
388 // Check to see if these two pointers are related by a getelementptr
389 // instruction. If one pointer is a GEP with a non-zero index of the other
390 // pointer, we know they cannot alias.
394 std::swap(V1Size, V2Size);
397 if (V1Size != ~0U && V2Size != ~0U)
399 std::vector<Value*> GEPOperands;
400 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
402 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
403 if (R == MustAlias) {
404 // If there is at least one non-zero constant index, we know they cannot
406 bool ConstantFound = false;
407 bool AllZerosFound = true;
408 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
409 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
410 if (!C->isNullValue()) {
411 ConstantFound = true;
412 AllZerosFound = false;
416 AllZerosFound = false;
419 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
420 // the ptr, the end result is a must alias also.
425 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
428 // Otherwise we have to check to see that the distance is more than
429 // the size of the argument... build an index vector that is equal to
430 // the arguments provided, except substitute 0's for any variable
431 // indexes we find...
432 if (cast<PointerType>(
433 BasePtr->getType())->getElementType()->isSized()) {
434 for (unsigned i = 0; i != GEPOperands.size(); ++i)
435 if (!isa<ConstantInt>(GEPOperands[i]))
437 Constant::getNullValue(GEPOperands[i]->getType());
439 getTargetData().getIndexedOffset(BasePtr->getType(), GEPOperands);
441 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
451 // This function is used to determin if the indices of two GEP instructions are
452 // equal. V1 and V2 are the indices.
453 static bool IndexOperandsEqual(Value *V1, Value *V2) {
454 if (V1->getType() == V2->getType())
456 if (Constant *C1 = dyn_cast<Constant>(V1))
457 if (Constant *C2 = dyn_cast<Constant>(V2)) {
458 // Sign extend the constants to long types, if necessary
459 if (C1->getType() != Type::Int64Ty)
460 C1 = ConstantExpr::getSExt(C1, Type::Int64Ty);
461 if (C2->getType() != Type::Int64Ty)
462 C2 = ConstantExpr::getSExt(C2, Type::Int64Ty);
468 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
469 /// base pointers. This checks to see if the index expressions preclude the
470 /// pointers from aliasing...
471 AliasAnalysis::AliasResult
472 BasicAliasAnalysis::CheckGEPInstructions(
473 const Type* BasePtr1Ty, std::vector<Value*> &GEP1Ops, unsigned G1S,
474 const Type *BasePtr2Ty, std::vector<Value*> &GEP2Ops, unsigned G2S) {
475 // We currently can't handle the case when the base pointers have different
476 // primitive types. Since this is uncommon anyway, we are happy being
477 // extremely conservative.
478 if (BasePtr1Ty != BasePtr2Ty)
481 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
483 // Find the (possibly empty) initial sequence of equal values... which are not
484 // necessarily constants.
485 unsigned NumGEP1Operands = GEP1Ops.size(), NumGEP2Operands = GEP2Ops.size();
486 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
487 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
488 unsigned UnequalOper = 0;
489 while (UnequalOper != MinOperands &&
490 IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
491 // Advance through the type as we go...
493 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
494 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
496 // If all operands equal each other, then the derived pointers must
497 // alias each other...
499 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
500 "Ran out of type nesting, but not out of operands?");
505 // If we have seen all constant operands, and run out of indexes on one of the
506 // getelementptrs, check to see if the tail of the leftover one is all zeros.
507 // If so, return mustalias.
508 if (UnequalOper == MinOperands) {
509 if (GEP1Ops.size() < GEP2Ops.size()) std::swap(GEP1Ops, GEP2Ops);
511 bool AllAreZeros = true;
512 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
513 if (!isa<Constant>(GEP1Ops[i]) ||
514 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
518 if (AllAreZeros) return MustAlias;
522 // So now we know that the indexes derived from the base pointers,
523 // which are known to alias, are different. We can still determine a
524 // no-alias result if there are differing constant pairs in the index
525 // chain. For example:
526 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
528 // We have to be careful here about array accesses. In particular, consider:
529 // A[1][0] vs A[0][i]
530 // In this case, we don't *know* that the array will be accessed in bounds:
531 // the index could even be negative. Because of this, we have to
532 // conservatively *give up* and return may alias. We disregard differing
533 // array subscripts that are followed by a variable index without going
536 unsigned SizeMax = std::max(G1S, G2S);
537 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
539 // Scan for the first operand that is constant and unequal in the
540 // two getelementptrs...
541 unsigned FirstConstantOper = UnequalOper;
542 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
543 const Value *G1Oper = GEP1Ops[FirstConstantOper];
544 const Value *G2Oper = GEP2Ops[FirstConstantOper];
546 if (G1Oper != G2Oper) // Found non-equal constant indexes...
547 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
548 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
549 if (G1OC->getType() != G2OC->getType()) {
550 // Sign extend both operands to long.
551 if (G1OC->getType() != Type::Int64Ty)
552 G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty);
553 if (G2OC->getType() != Type::Int64Ty)
554 G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty);
555 GEP1Ops[FirstConstantOper] = G1OC;
556 GEP2Ops[FirstConstantOper] = G2OC;
560 // Handle the "be careful" case above: if this is an array/packed
561 // subscript, scan for a subsequent variable array index.
562 if (isa<SequentialType>(BasePtr1Ty)) {
564 cast<SequentialType>(BasePtr1Ty)->getElementType();
565 bool isBadCase = false;
567 for (unsigned Idx = FirstConstantOper+1;
568 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
569 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
570 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
574 NextTy = cast<SequentialType>(NextTy)->getElementType();
577 if (isBadCase) G1OC = 0;
580 // Make sure they are comparable (ie, not constant expressions), and
581 // make sure the GEP with the smaller leading constant is GEP1.
583 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
585 if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
586 if (CV->getZExtValue()) // If they are comparable and G2 > G1
587 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
593 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
596 // No shared constant operands, and we ran out of common operands. At this
597 // point, the GEP instructions have run through all of their operands, and we
598 // haven't found evidence that there are any deltas between the GEP's.
599 // However, one GEP may have more operands than the other. If this is the
600 // case, there may still be hope. Check this now.
601 if (FirstConstantOper == MinOperands) {
602 // Make GEP1Ops be the longer one if there is a longer one.
603 if (GEP1Ops.size() < GEP2Ops.size())
604 std::swap(GEP1Ops, GEP2Ops);
606 // Is there anything to check?
607 if (GEP1Ops.size() > MinOperands) {
608 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
609 if (isa<ConstantInt>(GEP1Ops[i]) &&
610 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
611 // Yup, there's a constant in the tail. Set all variables to
612 // constants in the GEP instruction to make it suiteable for
613 // TargetData::getIndexedOffset.
614 for (i = 0; i != MaxOperands; ++i)
615 if (!isa<ConstantInt>(GEP1Ops[i]))
616 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
617 // Okay, now get the offset. This is the relative offset for the full
619 const TargetData &TD = getTargetData();
620 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops);
622 // Now crop off any constants from the end...
623 GEP1Ops.resize(MinOperands);
624 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops);
626 // If the tail provided a bit enough offset, return noalias!
627 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
632 // Couldn't find anything useful.
636 // If there are non-equal constants arguments, then we can figure
637 // out a minimum known delta between the two index expressions... at
638 // this point we know that the first constant index of GEP1 is less
639 // than the first constant index of GEP2.
641 // Advance BasePtr[12]Ty over this first differing constant operand.
642 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
643 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
644 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
645 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
647 // We are going to be using TargetData::getIndexedOffset to determine the
648 // offset that each of the GEP's is reaching. To do this, we have to convert
649 // all variable references to constant references. To do this, we convert the
650 // initial sequence of array subscripts into constant zeros to start with.
651 const Type *ZeroIdxTy = GEPPointerTy;
652 for (unsigned i = 0; i != FirstConstantOper; ++i) {
653 if (!isa<StructType>(ZeroIdxTy))
654 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty);
656 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
657 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
660 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
662 // Loop over the rest of the operands...
663 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
664 const Value *Op1 = i < GEP1Ops.size() ? GEP1Ops[i] : 0;
665 const Value *Op2 = i < GEP2Ops.size() ? GEP2Ops[i] : 0;
666 // If they are equal, use a zero index...
667 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
668 if (!isa<ConstantInt>(Op1))
669 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
670 // Otherwise, just keep the constants we have.
673 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
674 // If this is an array index, make sure the array element is in range.
675 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
676 if (Op1C->getZExtValue() >= AT->getNumElements())
677 return MayAlias; // Be conservative with out-of-range accesses
678 } else if (const PackedType *PT = dyn_cast<PackedType>(BasePtr1Ty)) {
679 if (Op1C->getZExtValue() >= PT->getNumElements())
680 return MayAlias; // Be conservative with out-of-range accesses
684 // GEP1 is known to produce a value less than GEP2. To be
685 // conservatively correct, we must assume the largest possible
686 // constant is used in this position. This cannot be the initial
687 // index to the GEP instructions (because we know we have at least one
688 // element before this one with the different constant arguments), so
689 // we know that the current index must be into either a struct or
690 // array. Because we know it's not constant, this cannot be a
691 // structure index. Because of this, we can calculate the maximum
694 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
695 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1);
696 else if (const PackedType *PT = dyn_cast<PackedType>(BasePtr1Ty))
697 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,PT->getNumElements()-1);
703 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
704 // If this is an array index, make sure the array element is in range.
705 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
706 if (Op2C->getZExtValue() >= AT->getNumElements())
707 return MayAlias; // Be conservative with out-of-range accesses
708 } else if (const PackedType *PT = dyn_cast<PackedType>(BasePtr1Ty)) {
709 if (Op2C->getZExtValue() >= PT->getNumElements())
710 return MayAlias; // Be conservative with out-of-range accesses
712 } else { // Conservatively assume the minimum value for this index
713 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
718 if (BasePtr1Ty && Op1) {
719 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
720 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
725 if (BasePtr2Ty && Op2) {
726 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
727 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
733 if (GEPPointerTy->getElementType()->isSized()) {
734 int64_t Offset1 = getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops);
735 int64_t Offset2 = getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops);
736 assert(Offset1<Offset2 && "There is at least one different constant here!");
738 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
739 //cerr << "Determined that these two GEP's don't alias ["
740 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
748 struct StringCompare {
749 bool operator()(const char *LHS, const char *RHS) {
750 return strcmp(LHS, RHS) < 0;
755 // Note that this list cannot contain libm functions (such as acos and sqrt)
756 // that set errno on a domain or other error.
757 static const char *DoesntAccessMemoryFns[] = {
758 "abs", "labs", "llabs", "imaxabs", "fabs", "fabsf", "fabsl",
759 "trunc", "truncf", "truncl", "ldexp",
761 "atan", "atanf", "atanl", "atan2", "atan2f", "atan2l",
763 "cos", "cosf", "cosl",
764 "exp", "expf", "expl",
766 "sin", "sinf", "sinl",
767 "tan", "tanf", "tanl", "tanh", "tanhf", "tanhl",
769 "floor", "floorf", "floorl", "ceil", "ceilf", "ceill",
772 "isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower", "isprint"
773 "ispunct", "isspace", "isupper", "isxdigit", "tolower", "toupper",
776 "iswalnum", "iswalpha", "iswcntrl", "iswdigit", "iswgraph", "iswlower",
777 "iswprint", "iswpunct", "iswspace", "iswupper", "iswxdigit",
779 "iswctype", "towctrans", "towlower", "towupper",
783 "isinf", "isnan", "finite",
785 // C99 math functions
786 "copysign", "copysignf", "copysignd",
787 "nexttoward", "nexttowardf", "nexttowardd",
788 "nextafter", "nextafterf", "nextafterd",
791 "__signbit", "__signbitf", "__signbitl",
795 static const char *OnlyReadsMemoryFns[] = {
796 "atoi", "atol", "atof", "atoll", "atoq", "a64l",
797 "bcmp", "memcmp", "memchr", "memrchr", "wmemcmp", "wmemchr",
800 "strcmp", "strcasecmp", "strcoll", "strncmp", "strncasecmp",
801 "strchr", "strcspn", "strlen", "strpbrk", "strrchr", "strspn", "strstr",
805 "wcschr", "wcscmp", "wcscoll", "wcscspn", "wcslen", "wcsncmp", "wcspbrk",
806 "wcsrchr", "wcsspn", "wcsstr",
809 "alphasort", "alphasort64", "versionsort", "versionsort64",
812 "nan", "nanf", "nand",
815 "feof", "ferror", "fileno",
816 "feof_unlocked", "ferror_unlocked", "fileno_unlocked"
819 static ManagedStatic<std::vector<const char*> > NoMemoryTable;
820 static ManagedStatic<std::vector<const char*> > OnlyReadsMemoryTable;
823 AliasAnalysis::ModRefBehavior
824 BasicAliasAnalysis::getModRefBehavior(Function *F, CallSite CS,
825 std::vector<PointerAccessInfo> *Info) {
826 if (!F->isExternal()) return UnknownModRefBehavior;
828 static bool Initialized = false;
830 NoMemoryTable->insert(NoMemoryTable->end(),
831 DoesntAccessMemoryFns,
832 DoesntAccessMemoryFns+
833 sizeof(DoesntAccessMemoryFns)/sizeof(DoesntAccessMemoryFns[0]));
835 OnlyReadsMemoryTable->insert(OnlyReadsMemoryTable->end(),
838 sizeof(OnlyReadsMemoryFns)/sizeof(OnlyReadsMemoryFns[0]));
839 #define GET_MODREF_BEHAVIOR
840 #include "llvm/Intrinsics.gen"
841 #undef GET_MODREF_BEHAVIOR
843 // Sort the table the first time through.
844 std::sort(NoMemoryTable->begin(), NoMemoryTable->end(), StringCompare());
845 std::sort(OnlyReadsMemoryTable->begin(), OnlyReadsMemoryTable->end(),
850 std::vector<const char*>::iterator Ptr =
851 std::lower_bound(NoMemoryTable->begin(), NoMemoryTable->end(),
852 F->getName().c_str(), StringCompare());
853 if (Ptr != NoMemoryTable->end() && *Ptr == F->getName())
854 return DoesNotAccessMemory;
856 Ptr = std::lower_bound(OnlyReadsMemoryTable->begin(),
857 OnlyReadsMemoryTable->end(),
858 F->getName().c_str(), StringCompare());
859 if (Ptr != OnlyReadsMemoryTable->end() && *Ptr == F->getName())
860 return OnlyReadsMemory;
862 return UnknownModRefBehavior;
865 // Make sure that anything that uses AliasAnalysis pulls in this file...
866 DEFINING_FILE_FOR(BasicAliasAnalysis)