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/Constants.h"
18 #include "llvm/DerivedTypes.h"
19 #include "llvm/Function.h"
20 #include "llvm/GlobalVariable.h"
21 #include "llvm/iOther.h"
22 #include "llvm/iMemory.h"
23 #include "llvm/Pass.h"
24 #include "llvm/Target/TargetData.h"
25 #include "llvm/Support/GetElementPtrTypeIterator.h"
28 // Make sure that anything that uses AliasAnalysis pulls in this file...
29 void llvm::BasicAAStub() {}
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 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 void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
52 virtual bool pointsToConstantMemory(const Value *P) { return false; }
53 virtual bool doesNotAccessMemory(Function *F) { return false; }
54 virtual bool onlyReadsMemory(Function *F) { return false; }
55 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
58 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
61 virtual bool hasNoModRefInfoForCalls() const { return true; }
63 virtual void deleteValue(Value *V) {}
64 virtual void copyValue(Value *From, Value *To) {}
67 // Register this pass...
69 U("no-aa", "No Alias Analysis (always returns 'may' alias)");
71 // Declare that we implement the AliasAnalysis interface
72 RegisterAnalysisGroup<AliasAnalysis, NoAA> V;
73 } // End of anonymous namespace
77 /// BasicAliasAnalysis - This is the default alias analysis implementation.
78 /// Because it doesn't chain to a previous alias analysis (like -no-aa), it
79 /// derives from the NoAA class.
80 struct BasicAliasAnalysis : public NoAA {
81 AliasResult alias(const Value *V1, unsigned V1Size,
82 const Value *V2, unsigned V2Size);
84 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
86 /// hasNoModRefInfoForCalls - We have no way to test one call against
87 /// another, unless they are pure or const.
88 virtual bool hasNoModRefInfoForCalls() const { return true; }
90 /// pointsToConstantMemory - Chase pointers until we find a (constant
92 bool pointsToConstantMemory(const Value *P);
94 virtual bool doesNotAccessMemory(Function *F);
95 virtual bool onlyReadsMemory(Function *F);
98 // CheckGEPInstructions - Check two GEP instructions with known
99 // must-aliasing base pointers. This checks to see if the index expressions
100 // preclude the pointers from aliasing...
102 CheckGEPInstructions(const Type* BasePtr1Ty, std::vector<Value*> &GEP1Ops,
104 const Type *BasePtr2Ty, std::vector<Value*> &GEP2Ops,
108 // Register this pass...
109 RegisterOpt<BasicAliasAnalysis>
110 X("basicaa", "Basic Alias Analysis (default AA impl)");
112 // Declare that we implement the AliasAnalysis interface
113 RegisterAnalysisGroup<AliasAnalysis, BasicAliasAnalysis, true> Y;
114 } // End of anonymous namespace
116 // hasUniqueAddress - Return true if the specified value points to something
117 // with a unique, discernable, address.
118 static inline bool hasUniqueAddress(const Value *V) {
119 return isa<GlobalValue>(V) || isa<AllocationInst>(V);
122 // getUnderlyingObject - This traverses the use chain to figure out what object
123 // the specified value points to. If the value points to, or is derived from, a
124 // unique object or an argument, return it.
125 static const Value *getUnderlyingObject(const Value *V) {
126 if (!isa<PointerType>(V->getType())) return 0;
128 // If we are at some type of object... return it.
129 if (hasUniqueAddress(V) || isa<Argument>(V)) return V;
131 // Traverse through different addressing mechanisms...
132 if (const Instruction *I = dyn_cast<Instruction>(V)) {
133 if (isa<CastInst>(I) || isa<GetElementPtrInst>(I))
134 return getUnderlyingObject(I->getOperand(0));
135 } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
136 if (CE->getOpcode() == Instruction::Cast ||
137 CE->getOpcode() == Instruction::GetElementPtr)
138 return getUnderlyingObject(CE->getOperand(0));
139 } else if (const GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
145 static const User *isGEP(const Value *V) {
146 if (isa<GetElementPtrInst>(V) ||
147 (isa<ConstantExpr>(V) &&
148 cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
149 return cast<User>(V);
153 static const Value *GetGEPOperands(const Value *V, std::vector<Value*> &GEPOps){
154 assert(GEPOps.empty() && "Expect empty list to populate!");
155 GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
156 cast<User>(V)->op_end());
158 // Accumulate all of the chained indexes into the operand array
159 V = cast<User>(V)->getOperand(0);
161 while (const User *G = isGEP(V)) {
162 if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
163 !cast<Constant>(GEPOps[0])->isNullValue())
164 break; // Don't handle folding arbitrary pointer offsets yet...
165 GEPOps.erase(GEPOps.begin()); // Drop the zero index
166 GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
167 V = G->getOperand(0);
172 /// pointsToConstantMemory - Chase pointers until we find a (constant
174 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
175 if (const Value *V = getUnderlyingObject(P))
176 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
177 return GV->isConstant();
181 static bool AddressMightEscape(const Value *V) {
182 for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
184 const Instruction *I = cast<Instruction>(*UI);
185 switch (I->getOpcode()) {
186 case Instruction::Load: break;
187 case Instruction::Store:
188 if (I->getOperand(0) == V)
189 return true; // Escapes if the pointer is stored.
191 case Instruction::GetElementPtr:
192 if (AddressMightEscape(I)) return true;
194 case Instruction::Cast:
195 if (!isa<PointerType>(I->getType()))
197 if (AddressMightEscape(I)) return true;
206 // getModRefInfo - Check to see if the specified callsite can clobber the
207 // specified memory object. Since we only look at local properties of this
208 // function, we really can't say much about this query. We do, however, use
209 // simple "address taken" analysis on local objects.
211 AliasAnalysis::ModRefResult
212 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
213 if (!isa<Constant>(P))
214 if (const AllocationInst *AI =
215 dyn_cast_or_null<AllocationInst>(getUnderlyingObject(P))) {
216 // Okay, the pointer is to a stack allocated object. If we can prove that
217 // the pointer never "escapes", then we know the call cannot clobber it,
218 // because it simply can't get its address.
219 if (!AddressMightEscape(AI))
223 // The AliasAnalysis base class has some smarts, lets use them.
224 return AliasAnalysis::getModRefInfo(CS, P, Size);
227 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
228 // as array references. Note that this function is heavily tail recursive.
229 // Hopefully we have a smart C++ compiler. :)
231 AliasAnalysis::AliasResult
232 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
233 const Value *V2, unsigned V2Size) {
234 // Strip off any constant expression casts if they exist
235 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
236 if (CE->getOpcode() == Instruction::Cast &&
237 isa<PointerType>(CE->getOperand(0)->getType()))
238 V1 = CE->getOperand(0);
239 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
240 if (CE->getOpcode() == Instruction::Cast &&
241 isa<PointerType>(CE->getOperand(0)->getType()))
242 V2 = CE->getOperand(0);
244 // Are we checking for alias of the same value?
245 if (V1 == V2) return MustAlias;
247 if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
248 V1->getType() != Type::LongTy && V2->getType() != Type::LongTy)
249 return NoAlias; // Scalars cannot alias each other
251 // Strip off cast instructions...
252 if (const Instruction *I = dyn_cast<CastInst>(V1))
253 if (isa<PointerType>(I->getOperand(0)->getType()))
254 return alias(I->getOperand(0), V1Size, V2, V2Size);
255 if (const Instruction *I = dyn_cast<CastInst>(V2))
256 if (isa<PointerType>(I->getOperand(0)->getType()))
257 return alias(V1, V1Size, I->getOperand(0), V2Size);
259 // Figure out what objects these things are pointing to if we can...
260 const Value *O1 = getUnderlyingObject(V1);
261 const Value *O2 = getUnderlyingObject(V2);
263 // Pointing at a discernible object?
265 if (isa<Argument>(O1)) {
266 // Incoming argument cannot alias locally allocated object!
267 if (isa<AllocationInst>(O2)) return NoAlias;
268 // Otherwise, nothing is known...
269 } else if (isa<Argument>(O2)) {
270 // Incoming argument cannot alias locally allocated object!
271 if (isa<AllocationInst>(O1)) return NoAlias;
272 // Otherwise, nothing is known...
274 // If they are two different objects, we know that we have no alias...
275 if (O1 != O2) return NoAlias;
278 // If they are the same object, they we can look at the indexes. If they
279 // index off of the object is the same for both pointers, they must alias.
280 // If they are provably different, they must not alias. Otherwise, we can't
282 } else if (O1 && !isa<Argument>(O1) && isa<ConstantPointerNull>(V2)) {
283 return NoAlias; // Unique values don't alias null
284 } else if (O2 && !isa<Argument>(O2) && isa<ConstantPointerNull>(V1)) {
285 return NoAlias; // Unique values don't alias null
288 // If we have two gep instructions with must-alias'ing base pointers, figure
289 // out if the indexes to the GEP tell us anything about the derived pointer.
290 // Note that we also handle chains of getelementptr instructions as well as
291 // constant expression getelementptrs here.
293 if (isGEP(V1) && isGEP(V2)) {
294 // Drill down into the first non-gep value, to test for must-aliasing of
295 // the base pointers.
296 const Value *BasePtr1 = V1, *BasePtr2 = V2;
298 BasePtr1 = cast<User>(BasePtr1)->getOperand(0);
299 } while (isGEP(BasePtr1) &&
300 cast<User>(BasePtr1)->getOperand(1) ==
301 Constant::getNullValue(cast<User>(BasePtr1)->getOperand(1)->getType()));
303 BasePtr2 = cast<User>(BasePtr2)->getOperand(0);
304 } while (isGEP(BasePtr2) &&
305 cast<User>(BasePtr2)->getOperand(1) ==
306 Constant::getNullValue(cast<User>(BasePtr2)->getOperand(1)->getType()));
308 // Do the base pointers alias?
309 AliasResult BaseAlias = alias(BasePtr1, V1Size, BasePtr2, V2Size);
310 if (BaseAlias == NoAlias) return NoAlias;
311 if (BaseAlias == MustAlias) {
312 // If the base pointers alias each other exactly, check to see if we can
313 // figure out anything about the resultant pointers, to try to prove
316 // Collect all of the chained GEP operands together into one simple place
317 std::vector<Value*> GEP1Ops, GEP2Ops;
318 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
319 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
322 CheckGEPInstructions(BasePtr1->getType(), GEP1Ops, V1Size,
323 BasePtr2->getType(), GEP2Ops, V2Size);
324 if (GAlias != MayAlias)
329 // Check to see if these two pointers are related by a getelementptr
330 // instruction. If one pointer is a GEP with a non-zero index of the other
331 // pointer, we know they cannot alias.
335 std::swap(V1Size, V2Size);
338 if (V1Size != ~0U && V2Size != ~0U)
339 if (const User *GEP = isGEP(V1)) {
340 std::vector<Value*> GEPOperands;
341 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
343 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
344 if (R == MustAlias) {
345 // If there is at least one non-zero constant index, we know they cannot
347 bool ConstantFound = false;
348 bool AllZerosFound = true;
349 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
350 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
351 if (!C->isNullValue()) {
352 ConstantFound = true;
353 AllZerosFound = false;
357 AllZerosFound = false;
360 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
361 // the ptr, the end result is a must alias also.
366 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
369 // Otherwise we have to check to see that the distance is more than
370 // the size of the argument... build an index vector that is equal to
371 // the arguments provided, except substitute 0's for any variable
372 // indexes we find...
373 for (unsigned i = 0; i != GEPOperands.size(); ++i)
374 if (!isa<Constant>(GEPOperands[i]) || isa<GlobalValue>(GEPOperands[i]) ||
375 isa<ConstantExpr>(GEPOperands[i]))
376 GEPOperands[i] =Constant::getNullValue(GEPOperands[i]->getType());
377 int64_t Offset = getTargetData().getIndexedOffset(BasePtr->getType(),
379 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
388 static bool ValuesEqual(Value *V1, Value *V2) {
389 if (V1->getType() == V2->getType())
391 if (Constant *C1 = dyn_cast<Constant>(V1))
392 if (Constant *C2 = dyn_cast<Constant>(V2)) {
393 // Sign extend the constants to long types.
394 C1 = ConstantExpr::getSignExtend(C1, Type::LongTy);
395 C2 = ConstantExpr::getSignExtend(C2, Type::LongTy);
401 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
402 /// base pointers. This checks to see if the index expressions preclude the
403 /// pointers from aliasing...
404 AliasAnalysis::AliasResult BasicAliasAnalysis::
405 CheckGEPInstructions(const Type* BasePtr1Ty, std::vector<Value*> &GEP1Ops,
407 const Type *BasePtr2Ty, std::vector<Value*> &GEP2Ops,
409 // We currently can't handle the case when the base pointers have different
410 // primitive types. Since this is uncommon anyway, we are happy being
411 // extremely conservative.
412 if (BasePtr1Ty != BasePtr2Ty)
415 const Type *GEPPointerTy = BasePtr1Ty;
417 // Find the (possibly empty) initial sequence of equal values... which are not
418 // necessarily constants.
419 unsigned NumGEP1Operands = GEP1Ops.size(), NumGEP2Operands = GEP2Ops.size();
420 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
421 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
422 unsigned UnequalOper = 0;
423 while (UnequalOper != MinOperands &&
424 ValuesEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
425 // Advance through the type as we go...
427 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
428 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
430 // If all operands equal each other, then the derived pointers must
431 // alias each other...
433 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
434 "Ran out of type nesting, but not out of operands?");
439 // If we have seen all constant operands, and run out of indexes on one of the
440 // getelementptrs, check to see if the tail of the leftover one is all zeros.
441 // If so, return mustalias.
442 if (UnequalOper == MinOperands) {
443 if (GEP1Ops.size() < GEP2Ops.size()) std::swap(GEP1Ops, GEP2Ops);
445 bool AllAreZeros = true;
446 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
447 if (!isa<Constant>(GEP1Ops[i]) ||
448 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
452 if (AllAreZeros) return MustAlias;
456 // So now we know that the indexes derived from the base pointers,
457 // which are known to alias, are different. We can still determine a
458 // no-alias result if there are differing constant pairs in the index
459 // chain. For example:
460 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
462 unsigned SizeMax = std::max(G1S, G2S);
463 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work...
465 // Scan for the first operand that is constant and unequal in the
466 // two getelementptrs...
467 unsigned FirstConstantOper = UnequalOper;
468 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
469 const Value *G1Oper = GEP1Ops[FirstConstantOper];
470 const Value *G2Oper = GEP2Ops[FirstConstantOper];
472 if (G1Oper != G2Oper) // Found non-equal constant indexes...
473 if (Constant *G1OC = dyn_cast<Constant>(const_cast<Value*>(G1Oper)))
474 if (Constant *G2OC = dyn_cast<Constant>(const_cast<Value*>(G2Oper))) {
475 if (G1OC->getType() != G2OC->getType()) {
476 // Sign extend both operands to long.
477 G1OC = ConstantExpr::getSignExtend(G1OC, Type::LongTy);
478 G2OC = ConstantExpr::getSignExtend(G2OC, Type::LongTy);
479 GEP1Ops[FirstConstantOper] = G1OC;
480 GEP2Ops[FirstConstantOper] = G2OC;
484 // Make sure they are comparable (ie, not constant expressions)...
485 // and make sure the GEP with the smaller leading constant is GEP1.
486 Constant *Compare = ConstantExpr::getSetGT(G1OC, G2OC);
487 if (ConstantBool *CV = dyn_cast<ConstantBool>(Compare)) {
488 if (CV->getValue()) // If they are comparable and G2 > G1
489 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
494 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
497 // No shared constant operands, and we ran out of common operands. At this
498 // point, the GEP instructions have run through all of their operands, and we
499 // haven't found evidence that there are any deltas between the GEP's.
500 // However, one GEP may have more operands than the other. If this is the
501 // case, there may still be hope. Check this now.
502 if (FirstConstantOper == MinOperands) {
503 // Make GEP1Ops be the longer one if there is a longer one.
504 if (GEP1Ops.size() < GEP2Ops.size())
505 std::swap(GEP1Ops, GEP2Ops);
507 // Is there anything to check?
508 if (GEP1Ops.size() > MinOperands) {
509 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
510 if (isa<ConstantInt>(GEP1Ops[i]) &&
511 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
512 // Yup, there's a constant in the tail. Set all variables to
513 // constants in the GEP instruction to make it suiteable for
514 // TargetData::getIndexedOffset.
515 for (i = 0; i != MaxOperands; ++i)
516 if (!isa<ConstantInt>(GEP1Ops[i]))
517 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
518 // Okay, now get the offset. This is the relative offset for the full
520 const TargetData &TD = getTargetData();
521 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops);
523 // Now crop off any constants from the end...
524 GEP1Ops.resize(MinOperands);
525 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops);
527 // If the tail provided a bit enough offset, return noalias!
528 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
533 // Couldn't find anything useful.
537 // If there are non-equal constants arguments, then we can figure
538 // out a minimum known delta between the two index expressions... at
539 // this point we know that the first constant index of GEP1 is less
540 // than the first constant index of GEP2.
542 // Advance BasePtr[12]Ty over this first differing constant operand.
543 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(GEP2Ops[FirstConstantOper]);
544 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(GEP1Ops[FirstConstantOper]);
546 // We are going to be using TargetData::getIndexedOffset to determine the
547 // offset that each of the GEP's is reaching. To do this, we have to convert
548 // all variable references to constant references. To do this, we convert the
549 // initial equal sequence of variables into constant zeros to start with.
550 for (unsigned i = 0; i != FirstConstantOper; ++i) {
551 if (!isa<Constant>(GEP1Ops[i]) || isa<ConstantExpr>(GEP1Ops[i]) ||
552 !isa<Constant>(GEP2Ops[i]) || isa<ConstantExpr>(GEP2Ops[i]))
553 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::UIntTy);
556 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
558 // Loop over the rest of the operands...
559 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
560 const Value *Op1 = i < GEP1Ops.size() ? GEP1Ops[i] : 0;
561 const Value *Op2 = i < GEP2Ops.size() ? GEP2Ops[i] : 0;
562 // If they are equal, use a zero index...
563 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
564 if (!isa<Constant>(Op1) || isa<ConstantExpr>(Op1))
565 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
566 // Otherwise, just keep the constants we have.
569 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
570 // If this is an array index, make sure the array element is in range.
571 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
572 if (Op1C->getRawValue() >= AT->getNumElements())
573 return MayAlias; // Be conservative with out-of-range accesses
576 // GEP1 is known to produce a value less than GEP2. To be
577 // conservatively correct, we must assume the largest possible
578 // constant is used in this position. This cannot be the initial
579 // index to the GEP instructions (because we know we have at least one
580 // element before this one with the different constant arguments), so
581 // we know that the current index must be into either a struct or
582 // array. Because we know it's not constant, this cannot be a
583 // structure index. Because of this, we can calculate the maximum
586 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
587 GEP1Ops[i] = ConstantSInt::get(Type::LongTy,AT->getNumElements()-1);
592 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
593 // If this is an array index, make sure the array element is in range.
594 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
595 if (Op2C->getRawValue() >= AT->getNumElements())
596 return MayAlias; // Be conservative with out-of-range accesses
597 } else { // Conservatively assume the minimum value for this index
598 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
603 if (BasePtr1Ty && Op1) {
604 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
605 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
610 if (BasePtr2Ty && Op2) {
611 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
612 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
618 int64_t Offset1 = getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops);
619 int64_t Offset2 = getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops);
620 assert(Offset1 < Offset2 &&"There is at least one different constant here!");
622 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
623 //std::cerr << "Determined that these two GEP's don't alias ["
624 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
631 struct StringCompare {
632 bool operator()(const char *LHS, const char *RHS) {
633 return strcmp(LHS, RHS) < 0;
638 // Note that this list cannot contain libm functions (such as acos and sqrt)
639 // that set errno on a domain or other error.
640 static const char *DoesntAccessMemoryTable[] = {
642 "llvm.frameaddress", "llvm.returnaddress", "llvm.readport", "llvm.isunordered",
644 "abs", "labs", "llabs", "imaxabs", "fabs", "fabsf", "fabsl",
645 "trunc", "truncf", "truncl", "ldexp",
647 "atan", "atanf", "atanl", "atan2", "atan2f", "atan2l",
649 "cos", "cosf", "cosl", "cosh", "coshf", "coshl",
650 "exp", "expf", "expl",
652 "sin", "sinf", "sinl", "sinh", "sinhf", "sinhl",
653 "tan", "tanf", "tanl", "tanh", "tanhf", "tanhl",
656 "isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower", "isprint"
657 "ispunct", "isspace", "isupper", "isxdigit", "tolower", "toupper",
660 "iswalnum", "iswalpha", "iswcntrl", "iswdigit", "iswgraph", "iswlower",
661 "iswprint", "iswpunct", "iswspace", "iswupper", "iswxdigit",
663 "iswctype", "towctrans", "towlower", "towupper",
667 "isinf", "isnan", "finite",
669 // C99 math functions
670 "copysign", "copysignf", "copysignd",
671 "nexttoward", "nexttowardf", "nexttowardd",
672 "nextafter", "nextafterf", "nextafterd",
675 "__fpclassify", "__fpclassifyf", "__fpclassifyl",
676 "__signbit", "__signbitf", "__signbitl",
679 static const unsigned DAMTableSize =
680 sizeof(DoesntAccessMemoryTable)/sizeof(DoesntAccessMemoryTable[0]);
682 /// doesNotAccessMemory - Return true if we know that the function does not
683 /// access memory at all. Since basicaa does no analysis, we can only do simple
684 /// things here. In particular, if we have an external function with the name
685 /// of a standard C library function, we are allowed to assume it will be
686 /// resolved by libc, so we can hardcode some entries in here.
687 bool BasicAliasAnalysis::doesNotAccessMemory(Function *F) {
688 if (!F->isExternal()) return false;
690 static bool Initialized = false;
692 // Sort the table the first time through.
693 std::sort(DoesntAccessMemoryTable, DoesntAccessMemoryTable+DAMTableSize,
698 const char **Ptr = std::lower_bound(DoesntAccessMemoryTable,
699 DoesntAccessMemoryTable+DAMTableSize,
700 F->getName().c_str(), StringCompare());
701 return Ptr != DoesntAccessMemoryTable+DAMTableSize && *Ptr == F->getName();
705 static const char *OnlyReadsMemoryTable[] = {
706 "atoi", "atol", "atof", "atoll", "atoq", "a64l",
707 "bcmp", "memcmp", "memchr", "memrchr", "wmemcmp", "wmemchr",
710 "strcmp", "strcasecmp", "strcoll", "strncmp", "strncasecmp",
711 "strchr", "strcspn", "strlen", "strpbrk", "strrchr", "strspn", "strstr",
715 "wcschr", "wcscmp", "wcscoll", "wcscspn", "wcslen", "wcsncmp", "wcspbrk",
716 "wcsrchr", "wcsspn", "wcsstr",
719 "alphasort", "alphasort64", "versionsort", "versionsort64",
722 "nan", "nanf", "nand",
725 "feof", "ferror", "fileno",
726 "feof_unlocked", "ferror_unlocked", "fileno_unlocked"
729 static const unsigned ORMTableSize =
730 sizeof(OnlyReadsMemoryTable)/sizeof(OnlyReadsMemoryTable[0]);
732 bool BasicAliasAnalysis::onlyReadsMemory(Function *F) {
733 if (doesNotAccessMemory(F)) return true;
734 if (!F->isExternal()) return false;
736 static bool Initialized = false;
738 // Sort the table the first time through.
739 std::sort(OnlyReadsMemoryTable, OnlyReadsMemoryTable+ORMTableSize,
744 const char **Ptr = std::lower_bound(OnlyReadsMemoryTable,
745 OnlyReadsMemoryTable+ORMTableSize,
746 F->getName().c_str(), StringCompare());
747 return Ptr != OnlyReadsMemoryTable+ORMTableSize && *Ptr == F->getName();