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 // FIXME: This could be extended for a very simple form of mod/ref information.
15 // If a pointer is locally allocated (either malloc or alloca) and never passed
16 // into a call or stored to memory, then we know that calls will not mod/ref the
17 // memory. This can be important for tailcallelim, and can support CSE of loads
18 // and dead store elimination across calls. This is particularly important for
19 // stack allocated arrays.
21 //===----------------------------------------------------------------------===//
23 #include "llvm/Analysis/AliasAnalysis.h"
24 #include "llvm/Constants.h"
25 #include "llvm/DerivedTypes.h"
26 #include "llvm/Function.h"
27 #include "llvm/GlobalVariable.h"
28 #include "llvm/iOther.h"
29 #include "llvm/iMemory.h"
30 #include "llvm/Pass.h"
31 #include "llvm/Target/TargetData.h"
32 #include "llvm/Support/GetElementPtrTypeIterator.h"
35 // Make sure that anything that uses AliasAnalysis pulls in this file...
36 void llvm::BasicAAStub() {}
39 struct BasicAliasAnalysis : public ImmutablePass, public AliasAnalysis {
41 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
42 AliasAnalysis::getAnalysisUsage(AU);
45 virtual void initializePass();
47 AliasResult alias(const Value *V1, unsigned V1Size,
48 const Value *V2, unsigned V2Size);
50 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
52 /// pointsToConstantMemory - Chase pointers until we find a (constant
54 bool pointsToConstantMemory(const Value *P);
56 virtual bool doesNotAccessMemory(Function *F);
57 virtual bool onlyReadsMemory(Function *F);
60 // CheckGEPInstructions - Check two GEP instructions with known
61 // must-aliasing base pointers. This checks to see if the index expressions
62 // preclude the pointers from aliasing...
64 CheckGEPInstructions(const Type* BasePtr1Ty, std::vector<Value*> &GEP1Ops,
66 const Type *BasePtr2Ty, std::vector<Value*> &GEP2Ops,
70 // Register this pass...
71 RegisterOpt<BasicAliasAnalysis>
72 X("basicaa", "Basic Alias Analysis (default AA impl)");
74 // Declare that we implement the AliasAnalysis interface
75 RegisterAnalysisGroup<AliasAnalysis, BasicAliasAnalysis, true> Y;
76 } // End of anonymous namespace
78 void BasicAliasAnalysis::initializePass() {
79 InitializeAliasAnalysis(this);
82 // hasUniqueAddress - Return true if the specified value points to something
83 // with a unique, discernable, address.
84 static inline bool hasUniqueAddress(const Value *V) {
85 return isa<GlobalValue>(V) || isa<AllocationInst>(V);
88 // getUnderlyingObject - This traverses the use chain to figure out what object
89 // the specified value points to. If the value points to, or is derived from, a
90 // unique object or an argument, return it.
91 static const Value *getUnderlyingObject(const Value *V) {
92 if (!isa<PointerType>(V->getType())) return 0;
94 // If we are at some type of object... return it.
95 if (hasUniqueAddress(V) || isa<Argument>(V)) return V;
97 // Traverse through different addressing mechanisms...
98 if (const Instruction *I = dyn_cast<Instruction>(V)) {
99 if (isa<CastInst>(I) || isa<GetElementPtrInst>(I))
100 return getUnderlyingObject(I->getOperand(0));
101 } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
102 if (CE->getOpcode() == Instruction::Cast ||
103 CE->getOpcode() == Instruction::GetElementPtr)
104 return getUnderlyingObject(CE->getOperand(0));
105 } else if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V)) {
106 return CPR->getValue();
111 static const User *isGEP(const Value *V) {
112 if (isa<GetElementPtrInst>(V) ||
113 (isa<ConstantExpr>(V) &&
114 cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
115 return cast<User>(V);
119 static const Value *GetGEPOperands(const Value *V, std::vector<Value*> &GEPOps){
120 assert(GEPOps.empty() && "Expect empty list to populate!");
121 GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
122 cast<User>(V)->op_end());
124 // Accumulate all of the chained indexes into the operand array
125 V = cast<User>(V)->getOperand(0);
127 while (const User *G = isGEP(V)) {
128 if (!isa<Constant>(GEPOps[0]) ||
129 !cast<Constant>(GEPOps[0])->isNullValue())
130 break; // Don't handle folding arbitrary pointer offsets yet...
131 GEPOps.erase(GEPOps.begin()); // Drop the zero index
132 GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
133 V = G->getOperand(0);
138 /// pointsToConstantMemory - Chase pointers until we find a (constant
140 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
141 if (const Value *V = getUnderlyingObject(P))
142 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
143 return GV->isConstant();
147 static bool AddressMightEscape(const Value *V) {
148 for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
150 const Instruction *I = cast<Instruction>(*UI);
151 switch (I->getOpcode()) {
152 case Instruction::Load: break;
153 case Instruction::Store:
154 if (I->getOperand(0) == V)
155 return true; // Escapes if the pointer is stored.
157 case Instruction::GetElementPtr:
158 if (AddressMightEscape(I)) return true;
160 case Instruction::Cast:
161 if (!isa<PointerType>(I->getType()))
163 if (AddressMightEscape(I)) return true;
172 // getModRefInfo - Check to see if the specified callsite can clobber the
173 // specified memory object. Since we only look at local properties of this
174 // function, we really can't say much about this query. We do, however, use
175 // simple "address taken" analysis on local objects.
177 AliasAnalysis::ModRefResult
178 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
179 if (!isa<Constant>(P) && !isa<GlobalValue>(P))
180 if (const AllocationInst *AI =
181 dyn_cast_or_null<AllocationInst>(getUnderlyingObject(P))) {
182 // Okay, the pointer is to a stack allocated object. If we can prove that
183 // the pointer never "escapes", then we know the call cannot clobber it,
184 // because it simply can't get its address.
185 if (!AddressMightEscape(AI))
189 // The AliasAnalysis base class has some smarts, lets use them.
190 return AliasAnalysis::getModRefInfo(CS, P, Size);
193 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
194 // as array references. Note that this function is heavily tail recursive.
195 // Hopefully we have a smart C++ compiler. :)
197 AliasAnalysis::AliasResult
198 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
199 const Value *V2, unsigned V2Size) {
200 // Strip off any constant expression casts if they exist
201 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
202 if (CE->getOpcode() == Instruction::Cast)
203 V1 = CE->getOperand(0);
204 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
205 if (CE->getOpcode() == Instruction::Cast)
206 V2 = CE->getOperand(0);
208 // Strip off constant pointer refs if they exist
209 if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V1))
210 V1 = CPR->getValue();
211 if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V2))
212 V2 = CPR->getValue();
214 // Are we checking for alias of the same value?
215 if (V1 == V2) return MustAlias;
217 if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
218 V1->getType() != Type::LongTy && V2->getType() != Type::LongTy)
219 return NoAlias; // Scalars cannot alias each other
221 // Strip off cast instructions...
222 if (const Instruction *I = dyn_cast<CastInst>(V1))
223 return alias(I->getOperand(0), V1Size, V2, V2Size);
224 if (const Instruction *I = dyn_cast<CastInst>(V2))
225 return alias(V1, V1Size, I->getOperand(0), V2Size);
227 // Figure out what objects these things are pointing to if we can...
228 const Value *O1 = getUnderlyingObject(V1);
229 const Value *O2 = getUnderlyingObject(V2);
231 // Pointing at a discernible object?
233 if (isa<Argument>(O1)) {
234 // Incoming argument cannot alias locally allocated object!
235 if (isa<AllocationInst>(O2)) return NoAlias;
236 // Otherwise, nothing is known...
237 } else if (isa<Argument>(O2)) {
238 // Incoming argument cannot alias locally allocated object!
239 if (isa<AllocationInst>(O1)) return NoAlias;
240 // Otherwise, nothing is known...
242 // If they are two different objects, we know that we have no alias...
243 if (O1 != O2) return NoAlias;
246 // If they are the same object, they we can look at the indexes. If they
247 // index off of the object is the same for both pointers, they must alias.
248 // If they are provably different, they must not alias. Otherwise, we can't
250 } else if (O1 && !isa<Argument>(O1) && isa<ConstantPointerNull>(V2)) {
251 return NoAlias; // Unique values don't alias null
252 } else if (O2 && !isa<Argument>(O2) && isa<ConstantPointerNull>(V1)) {
253 return NoAlias; // Unique values don't alias null
256 // If we have two gep instructions with must-alias'ing base pointers, figure
257 // out if the indexes to the GEP tell us anything about the derived pointer.
258 // Note that we also handle chains of getelementptr instructions as well as
259 // constant expression getelementptrs here.
261 if (isGEP(V1) && isGEP(V2)) {
262 // Drill down into the first non-gep value, to test for must-aliasing of
263 // the base pointers.
264 const Value *BasePtr1 = V1, *BasePtr2 = V2;
266 BasePtr1 = cast<User>(BasePtr1)->getOperand(0);
267 } while (isGEP(BasePtr1) &&
268 cast<User>(BasePtr1)->getOperand(1) ==
269 Constant::getNullValue(cast<User>(BasePtr1)->getOperand(1)->getType()));
271 BasePtr2 = cast<User>(BasePtr2)->getOperand(0);
272 } while (isGEP(BasePtr2) &&
273 cast<User>(BasePtr2)->getOperand(1) ==
274 Constant::getNullValue(cast<User>(BasePtr2)->getOperand(1)->getType()));
276 // Do the base pointers alias?
277 AliasResult BaseAlias = alias(BasePtr1, V1Size, BasePtr2, V2Size);
278 if (BaseAlias == NoAlias) return NoAlias;
279 if (BaseAlias == MustAlias) {
280 // If the base pointers alias each other exactly, check to see if we can
281 // figure out anything about the resultant pointers, to try to prove
284 // Collect all of the chained GEP operands together into one simple place
285 std::vector<Value*> GEP1Ops, GEP2Ops;
286 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
287 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
290 CheckGEPInstructions(BasePtr1->getType(), GEP1Ops, V1Size,
291 BasePtr2->getType(), GEP2Ops, V2Size);
292 if (GAlias != MayAlias)
297 // Check to see if these two pointers are related by a getelementptr
298 // instruction. If one pointer is a GEP with a non-zero index of the other
299 // pointer, we know they cannot alias.
303 std::swap(V1Size, V2Size);
306 if (V1Size != ~0U && V2Size != ~0U)
307 if (const User *GEP = isGEP(V1)) {
308 std::vector<Value*> GEPOperands;
309 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
311 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
312 if (R == MustAlias) {
313 // If there is at least one non-zero constant index, we know they cannot
315 bool ConstantFound = false;
316 bool AllZerosFound = true;
317 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
318 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
319 if (!C->isNullValue()) {
320 ConstantFound = true;
321 AllZerosFound = false;
325 AllZerosFound = false;
328 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
329 // the ptr, the end result is a must alias also.
334 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
337 // Otherwise we have to check to see that the distance is more than
338 // the size of the argument... build an index vector that is equal to
339 // the arguments provided, except substitute 0's for any variable
340 // indexes we find...
341 for (unsigned i = 0; i != GEPOperands.size(); ++i)
342 if (!isa<Constant>(GEPOperands[i]) ||
343 isa<ConstantExpr>(GEPOperands[i]))
344 GEPOperands[i] =Constant::getNullValue(GEPOperands[i]->getType());
345 int64_t Offset = getTargetData().getIndexedOffset(BasePtr->getType(),
347 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
356 static bool ValuesEqual(Value *V1, Value *V2) {
357 if (V1->getType() == V2->getType())
359 if (Constant *C1 = dyn_cast<Constant>(V1))
360 if (Constant *C2 = dyn_cast<Constant>(V2)) {
361 // Sign extend the constants to long types.
362 C1 = ConstantExpr::getSignExtend(C1, Type::LongTy);
363 C2 = ConstantExpr::getSignExtend(C2, Type::LongTy);
369 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
370 /// base pointers. This checks to see if the index expressions preclude the
371 /// pointers from aliasing...
372 AliasAnalysis::AliasResult BasicAliasAnalysis::
373 CheckGEPInstructions(const Type* BasePtr1Ty, std::vector<Value*> &GEP1Ops,
375 const Type *BasePtr2Ty, std::vector<Value*> &GEP2Ops,
377 // We currently can't handle the case when the base pointers have different
378 // primitive types. Since this is uncommon anyway, we are happy being
379 // extremely conservative.
380 if (BasePtr1Ty != BasePtr2Ty)
383 const Type *GEPPointerTy = BasePtr1Ty;
385 // Find the (possibly empty) initial sequence of equal values... which are not
386 // necessarily constants.
387 unsigned NumGEP1Operands = GEP1Ops.size(), NumGEP2Operands = GEP2Ops.size();
388 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
389 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
390 unsigned UnequalOper = 0;
391 while (UnequalOper != MinOperands &&
392 ValuesEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
393 // Advance through the type as we go...
395 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
396 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
398 // If all operands equal each other, then the derived pointers must
399 // alias each other...
401 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
402 "Ran out of type nesting, but not out of operands?");
407 // If we have seen all constant operands, and run out of indexes on one of the
408 // getelementptrs, check to see if the tail of the leftover one is all zeros.
409 // If so, return mustalias.
410 if (UnequalOper == MinOperands) {
411 if (GEP1Ops.size() < GEP2Ops.size()) std::swap(GEP1Ops, GEP2Ops);
413 bool AllAreZeros = true;
414 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
415 if (!isa<Constant>(GEP1Ops[i]) ||
416 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
420 if (AllAreZeros) return MustAlias;
424 // So now we know that the indexes derived from the base pointers,
425 // which are known to alias, are different. We can still determine a
426 // no-alias result if there are differing constant pairs in the index
427 // chain. For example:
428 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
430 unsigned SizeMax = std::max(G1S, G2S);
431 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work...
433 // Scan for the first operand that is constant and unequal in the
434 // two getelementptrs...
435 unsigned FirstConstantOper = UnequalOper;
436 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
437 const Value *G1Oper = GEP1Ops[FirstConstantOper];
438 const Value *G2Oper = GEP2Ops[FirstConstantOper];
440 if (G1Oper != G2Oper) // Found non-equal constant indexes...
441 if (Constant *G1OC = dyn_cast<Constant>(const_cast<Value*>(G1Oper)))
442 if (Constant *G2OC = dyn_cast<Constant>(const_cast<Value*>(G2Oper))) {
443 if (G1OC->getType() != G2OC->getType()) {
444 // Sign extend both operands to long.
445 G1OC = ConstantExpr::getSignExtend(G1OC, Type::LongTy);
446 G2OC = ConstantExpr::getSignExtend(G2OC, Type::LongTy);
447 GEP1Ops[FirstConstantOper] = G1OC;
448 GEP2Ops[FirstConstantOper] = G2OC;
452 // Make sure they are comparable (ie, not constant expressions)...
453 // and make sure the GEP with the smaller leading constant is GEP1.
454 Constant *Compare = ConstantExpr::getSetGT(G1OC, G2OC);
455 if (ConstantBool *CV = dyn_cast<ConstantBool>(Compare)) {
456 if (CV->getValue()) // If they are comparable and G2 > G1
457 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
462 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
465 // No shared constant operands, and we ran out of common operands. At this
466 // point, the GEP instructions have run through all of their operands, and we
467 // haven't found evidence that there are any deltas between the GEP's.
468 // However, one GEP may have more operands than the other. If this is the
469 // case, there may still be hope. Check this now.
470 if (FirstConstantOper == MinOperands) {
471 // Make GEP1Ops be the longer one if there is a longer one.
472 if (GEP1Ops.size() < GEP2Ops.size())
473 std::swap(GEP1Ops, GEP2Ops);
475 // Is there anything to check?
476 if (GEP1Ops.size() > MinOperands) {
477 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
478 if (isa<Constant>(GEP1Ops[i]) && !isa<ConstantExpr>(GEP1Ops[i]) &&
479 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
480 // Yup, there's a constant in the tail. Set all variables to
481 // constants in the GEP instruction to make it suiteable for
482 // TargetData::getIndexedOffset.
483 for (i = 0; i != MaxOperands; ++i)
484 if (!isa<Constant>(GEP1Ops[i]) || isa<ConstantExpr>(GEP1Ops[i]))
485 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
486 // Okay, now get the offset. This is the relative offset for the full
488 const TargetData &TD = getTargetData();
489 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops);
491 // Now crop off any constants from the end...
492 GEP1Ops.resize(MinOperands);
493 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops);
495 // If the tail provided a bit enough offset, return noalias!
496 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
501 // Couldn't find anything useful.
505 // If there are non-equal constants arguments, then we can figure
506 // out a minimum known delta between the two index expressions... at
507 // this point we know that the first constant index of GEP1 is less
508 // than the first constant index of GEP2.
510 // Advance BasePtr[12]Ty over this first differing constant operand.
511 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(GEP2Ops[FirstConstantOper]);
512 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(GEP1Ops[FirstConstantOper]);
514 // We are going to be using TargetData::getIndexedOffset to determine the
515 // offset that each of the GEP's is reaching. To do this, we have to convert
516 // all variable references to constant references. To do this, we convert the
517 // initial equal sequence of variables into constant zeros to start with.
518 for (unsigned i = 0; i != FirstConstantOper; ++i) {
519 if (!isa<Constant>(GEP1Ops[i]) || isa<ConstantExpr>(GEP1Ops[i]) ||
520 !isa<Constant>(GEP2Ops[i]) || isa<ConstantExpr>(GEP2Ops[i]))
521 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::UIntTy);
524 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
526 // Loop over the rest of the operands...
527 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
528 const Value *Op1 = i < GEP1Ops.size() ? GEP1Ops[i] : 0;
529 const Value *Op2 = i < GEP2Ops.size() ? GEP2Ops[i] : 0;
530 // If they are equal, use a zero index...
531 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
532 if (!isa<Constant>(Op1) || isa<ConstantExpr>(Op1))
533 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
534 // Otherwise, just keep the constants we have.
537 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
538 // If this is an array index, make sure the array element is in range.
539 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
540 if (Op1C->getRawValue() >= AT->getNumElements())
541 return MayAlias; // Be conservative with out-of-range accesses
544 // GEP1 is known to produce a value less than GEP2. To be
545 // conservatively correct, we must assume the largest possible
546 // constant is used in this position. This cannot be the initial
547 // index to the GEP instructions (because we know we have at least one
548 // element before this one with the different constant arguments), so
549 // we know that the current index must be into either a struct or
550 // array. Because we know it's not constant, this cannot be a
551 // structure index. Because of this, we can calculate the maximum
554 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
555 GEP1Ops[i] = ConstantSInt::get(Type::LongTy,AT->getNumElements()-1);
560 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
561 // If this is an array index, make sure the array element is in range.
562 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
563 if (Op2C->getRawValue() >= AT->getNumElements())
564 return MayAlias; // Be conservative with out-of-range accesses
565 } else { // Conservatively assume the minimum value for this index
566 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
571 if (BasePtr1Ty && Op1) {
572 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
573 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
578 if (BasePtr2Ty && Op2) {
579 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
580 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
586 int64_t Offset1 = getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops);
587 int64_t Offset2 = getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops);
588 assert(Offset1 < Offset2 &&"There is at least one different constant here!");
590 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
591 //std::cerr << "Determined that these two GEP's don't alias ["
592 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
599 struct StringCompare {
600 bool operator()(const char *LHS, const char *RHS) {
601 return strcmp(LHS, RHS) < 0;
606 // Note that this list cannot contain libm functions (such as acos and sqrt)
607 // that set errno on a domain or other error.
608 static const char *DoesntAccessMemoryTable[] = {
610 "llvm.frameaddress", "llvm.returnaddress", "llvm.readport",
612 "abs", "labs", "llabs", "imaxabs", "fabs", "fabsf", "fabsl",
613 "trunc", "truncf", "truncl", "ldexp",
615 "atan", "atanf", "atanl", "atan2", "atan2f", "atan2l",
617 "cos", "cosf", "cosl", "cosh", "coshf", "coshl",
618 "exp", "expf", "expl",
620 "sin", "sinf", "sinl", "sinh", "sinhf", "sinhl",
621 "tan", "tanf", "tanl", "tanh", "tanhf", "tanhl",
624 "isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower", "isprint"
625 "ispunct", "isspace", "isupper", "isxdigit", "tolower", "toupper",
628 "iswalnum", "iswalpha", "iswcntrl", "iswdigit", "iswgraph", "iswlower",
629 "iswprint", "iswpunct", "iswspace", "iswupper", "iswxdigit",
631 "iswctype", "towctrans", "towlower", "towupper",
635 "isinf", "isnan", "finite",
637 // C99 math functions
638 "copysign", "copysignf", "copysignd",
639 "nexttoward", "nexttowardf", "nexttowardd",
640 "nextafter", "nextafterf", "nextafterd",
643 "__fpclassify", "__fpclassifyf", "__fpclassifyl",
644 "__signbit", "__signbitf", "__signbitl",
647 static const unsigned DAMTableSize =
648 sizeof(DoesntAccessMemoryTable)/sizeof(DoesntAccessMemoryTable[0]);
650 /// doesNotAccessMemory - Return true if we know that the function does not
651 /// access memory at all. Since basicaa does no analysis, we can only do simple
652 /// things here. In particular, if we have an external function with the name
653 /// of a standard C library function, we are allowed to assume it will be
654 /// resolved by libc, so we can hardcode some entries in here.
655 bool BasicAliasAnalysis::doesNotAccessMemory(Function *F) {
656 if (!F->isExternal()) return false;
658 static bool Initialized = false;
660 // Sort the table the first time through.
661 std::sort(DoesntAccessMemoryTable, DoesntAccessMemoryTable+DAMTableSize,
666 const char **Ptr = std::lower_bound(DoesntAccessMemoryTable,
667 DoesntAccessMemoryTable+DAMTableSize,
668 F->getName().c_str(), StringCompare());
669 return Ptr != DoesntAccessMemoryTable+DAMTableSize && *Ptr == F->getName();
673 static const char *OnlyReadsMemoryTable[] = {
674 "atoi", "atol", "atof", "atoll", "atoq", "a64l",
675 "bcmp", "memcmp", "memchr", "memrchr", "wmemcmp", "wmemchr",
678 "strcmp", "strcasecmp", "strcoll", "strncmp", "strncasecmp",
679 "strchr", "strcspn", "strlen", "strpbrk", "strrchr", "strspn", "strstr",
683 "wcschr", "wcscmp", "wcscoll", "wcscspn", "wcslen", "wcsncmp", "wcspbrk",
684 "wcsrchr", "wcsspn", "wcsstr",
687 "alphasort", "alphasort64", "versionsort", "versionsort64",
690 "nan", "nanf", "nand",
693 "feof", "ferror", "fileno",
694 "feof_unlocked", "ferror_unlocked", "fileno_unlocked"
697 static const unsigned ORMTableSize =
698 sizeof(OnlyReadsMemoryTable)/sizeof(OnlyReadsMemoryTable[0]);
700 bool BasicAliasAnalysis::onlyReadsMemory(Function *F) {
701 if (doesNotAccessMemory(F)) return true;
702 if (!F->isExternal()) return false;
704 static bool Initialized = false;
706 // Sort the table the first time through.
707 std::sort(OnlyReadsMemoryTable, OnlyReadsMemoryTable+ORMTableSize,
712 const char **Ptr = std::lower_bound(OnlyReadsMemoryTable,
713 OnlyReadsMemoryTable+ORMTableSize,
714 F->getName().c_str(), StringCompare());
715 return Ptr != OnlyReadsMemoryTable+ORMTableSize && *Ptr == F->getName();