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/GetElementPtrTypeIterator.h"
29 // Make sure that anything that uses AliasAnalysis pulls in this file...
30 void llvm::BasicAAStub() {}
33 /// NoAA - This class implements the -no-aa pass, which always returns "I
34 /// don't know" for alias queries. NoAA is unlike other alias analysis
35 /// implementations, in that it does not chain to a previous analysis. As
36 /// such it doesn't follow many of the rules that other alias analyses must.
38 struct NoAA : public ImmutablePass, public AliasAnalysis {
39 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
40 AU.addRequired<TargetData>();
43 virtual void initializePass() {
44 TD = &getAnalysis<TargetData>();
47 virtual AliasResult alias(const Value *V1, unsigned V1Size,
48 const Value *V2, unsigned V2Size) {
52 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
53 std::vector<PointerAccessInfo> *Info) {
54 return UnknownModRefBehavior;
57 virtual void getArgumentAccesses(Function *F, CallSite CS,
58 std::vector<PointerAccessInfo> &Info) {
59 assert(0 && "This method may not be called on this function!");
62 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
63 virtual bool pointsToConstantMemory(const Value *P) { return false; }
64 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
67 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
70 virtual bool hasNoModRefInfoForCalls() const { return true; }
72 virtual void deleteValue(Value *V) {}
73 virtual void copyValue(Value *From, Value *To) {}
76 // Register this pass...
78 U("no-aa", "No Alias Analysis (always returns 'may' alias)");
80 // Declare that we implement the AliasAnalysis interface
81 RegisterAnalysisGroup<AliasAnalysis, NoAA> V;
82 } // End of anonymous namespace
84 ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
87 /// BasicAliasAnalysis - This is the default alias analysis implementation.
88 /// Because it doesn't chain to a previous alias analysis (like -no-aa), it
89 /// derives from the NoAA class.
90 struct BasicAliasAnalysis : public NoAA {
91 AliasResult alias(const Value *V1, unsigned V1Size,
92 const Value *V2, unsigned V2Size);
94 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
95 ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
96 return NoAA::getModRefInfo(CS1,CS2);
99 /// hasNoModRefInfoForCalls - We can provide mod/ref information against
100 /// non-escaping allocations.
101 virtual bool hasNoModRefInfoForCalls() const { return false; }
103 /// pointsToConstantMemory - Chase pointers until we find a (constant
105 bool pointsToConstantMemory(const Value *P);
107 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
108 std::vector<PointerAccessInfo> *Info);
111 // CheckGEPInstructions - Check two GEP instructions with known
112 // must-aliasing base pointers. This checks to see if the index expressions
113 // preclude the pointers from aliasing...
115 CheckGEPInstructions(const Type* BasePtr1Ty, std::vector<Value*> &GEP1Ops,
117 const Type *BasePtr2Ty, std::vector<Value*> &GEP2Ops,
121 // Register this pass...
122 RegisterOpt<BasicAliasAnalysis>
123 X("basicaa", "Basic Alias Analysis (default AA impl)");
125 // Declare that we implement the AliasAnalysis interface
126 RegisterAnalysisGroup<AliasAnalysis, BasicAliasAnalysis, true> Y;
127 } // End of anonymous namespace
129 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
130 return new BasicAliasAnalysis();
133 // hasUniqueAddress - Return true if the specified value points to something
134 // with a unique, discernable, address.
135 static inline bool hasUniqueAddress(const Value *V) {
136 return isa<GlobalValue>(V) || isa<AllocationInst>(V);
139 // getUnderlyingObject - This traverses the use chain to figure out what object
140 // the specified value points to. If the value points to, or is derived from, a
141 // unique object or an argument, return it.
142 static const Value *getUnderlyingObject(const Value *V) {
143 if (!isa<PointerType>(V->getType())) return 0;
145 // If we are at some type of object... return it.
146 if (hasUniqueAddress(V) || isa<Argument>(V)) return V;
148 // Traverse through different addressing mechanisms...
149 if (const Instruction *I = dyn_cast<Instruction>(V)) {
150 if (isa<CastInst>(I) || isa<GetElementPtrInst>(I))
151 return getUnderlyingObject(I->getOperand(0));
152 } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
153 if (CE->getOpcode() == Instruction::Cast ||
154 CE->getOpcode() == Instruction::GetElementPtr)
155 return getUnderlyingObject(CE->getOperand(0));
156 } else if (const GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
162 static const User *isGEP(const Value *V) {
163 if (isa<GetElementPtrInst>(V) ||
164 (isa<ConstantExpr>(V) &&
165 cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
166 return cast<User>(V);
170 static const Value *GetGEPOperands(const Value *V, std::vector<Value*> &GEPOps){
171 assert(GEPOps.empty() && "Expect empty list to populate!");
172 GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
173 cast<User>(V)->op_end());
175 // Accumulate all of the chained indexes into the operand array
176 V = cast<User>(V)->getOperand(0);
178 while (const User *G = isGEP(V)) {
179 if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
180 !cast<Constant>(GEPOps[0])->isNullValue())
181 break; // Don't handle folding arbitrary pointer offsets yet...
182 GEPOps.erase(GEPOps.begin()); // Drop the zero index
183 GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
184 V = G->getOperand(0);
189 /// pointsToConstantMemory - Chase pointers until we find a (constant
191 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
192 if (const Value *V = getUnderlyingObject(P))
193 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
194 return GV->isConstant();
198 static bool AddressMightEscape(const Value *V) {
199 for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
201 const Instruction *I = cast<Instruction>(*UI);
202 switch (I->getOpcode()) {
203 case Instruction::Load: break;
204 case Instruction::Store:
205 if (I->getOperand(0) == V)
206 return true; // Escapes if the pointer is stored.
208 case Instruction::GetElementPtr:
209 if (AddressMightEscape(I)) return true;
211 case Instruction::Cast:
212 if (!isa<PointerType>(I->getType()))
214 if (AddressMightEscape(I)) return true;
216 case Instruction::Ret:
217 // If returned, the address will escape to calling functions, but no
218 // callees could modify it.
227 // getModRefInfo - Check to see if the specified callsite can clobber the
228 // specified memory object. Since we only look at local properties of this
229 // function, we really can't say much about this query. We do, however, use
230 // simple "address taken" analysis on local objects.
232 AliasAnalysis::ModRefResult
233 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
234 if (!isa<Constant>(P))
235 if (const AllocationInst *AI =
236 dyn_cast_or_null<AllocationInst>(getUnderlyingObject(P))) {
237 // Okay, the pointer is to a stack allocated object. If we can prove that
238 // the pointer never "escapes", then we know the call cannot clobber it,
239 // because it simply can't get its address.
240 if (!AddressMightEscape(AI))
243 // If this is a tail call and P points to a stack location, we know that
244 // the tail call cannot access or modify the local stack.
245 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
246 if (CI->isTailCall() && isa<AllocaInst>(AI))
250 // The AliasAnalysis base class has some smarts, lets use them.
251 return AliasAnalysis::getModRefInfo(CS, P, Size);
254 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
255 // as array references. Note that this function is heavily tail recursive.
256 // Hopefully we have a smart C++ compiler. :)
258 AliasAnalysis::AliasResult
259 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
260 const Value *V2, unsigned V2Size) {
261 // Strip off any constant expression casts if they exist
262 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
263 if (CE->getOpcode() == Instruction::Cast &&
264 isa<PointerType>(CE->getOperand(0)->getType()))
265 V1 = CE->getOperand(0);
266 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
267 if (CE->getOpcode() == Instruction::Cast &&
268 isa<PointerType>(CE->getOperand(0)->getType()))
269 V2 = CE->getOperand(0);
271 // Are we checking for alias of the same value?
272 if (V1 == V2) return MustAlias;
274 if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
275 V1->getType() != Type::LongTy && V2->getType() != Type::LongTy)
276 return NoAlias; // Scalars cannot alias each other
278 // Strip off cast instructions...
279 if (const Instruction *I = dyn_cast<CastInst>(V1))
280 if (isa<PointerType>(I->getOperand(0)->getType()))
281 return alias(I->getOperand(0), V1Size, V2, V2Size);
282 if (const Instruction *I = dyn_cast<CastInst>(V2))
283 if (isa<PointerType>(I->getOperand(0)->getType()))
284 return alias(V1, V1Size, I->getOperand(0), V2Size);
286 // Figure out what objects these things are pointing to if we can...
287 const Value *O1 = getUnderlyingObject(V1);
288 const Value *O2 = getUnderlyingObject(V2);
290 // Pointing at a discernible object?
293 if (isa<Argument>(O1)) {
294 // Incoming argument cannot alias locally allocated object!
295 if (isa<AllocationInst>(O2)) return NoAlias;
296 // Otherwise, nothing is known...
297 } else if (isa<Argument>(O2)) {
298 // Incoming argument cannot alias locally allocated object!
299 if (isa<AllocationInst>(O1)) return NoAlias;
300 // Otherwise, nothing is known...
301 } else if (O1 != O2) {
302 // If they are two different objects, we know that we have no alias...
306 // If they are the same object, they we can look at the indexes. If they
307 // index off of the object is the same for both pointers, they must alias.
308 // If they are provably different, they must not alias. Otherwise, we
309 // can't tell anything.
313 if (!isa<Argument>(O1) && isa<ConstantPointerNull>(V2))
314 return NoAlias; // Unique values don't alias null
316 if (isa<GlobalVariable>(O1) ||
317 (isa<AllocationInst>(O1) &&
318 !cast<AllocationInst>(O1)->isArrayAllocation()))
319 if (cast<PointerType>(O1->getType())->getElementType()->isSized()) {
320 // If the size of the other access is larger than the total size of the
321 // global/alloca/malloc, it cannot be accessing the global (it's
322 // undefined to load or store bytes before or after an object).
323 const Type *ElTy = cast<PointerType>(O1->getType())->getElementType();
324 unsigned GlobalSize = getTargetData().getTypeSize(ElTy);
325 if (GlobalSize < V2Size && V2Size != ~0U)
331 if (!isa<Argument>(O2) && isa<ConstantPointerNull>(V1))
332 return NoAlias; // Unique values don't alias null
334 if (isa<GlobalVariable>(O2) ||
335 (isa<AllocationInst>(O2) &&
336 !cast<AllocationInst>(O2)->isArrayAllocation()))
337 if (cast<PointerType>(O2->getType())->getElementType()->isSized()) {
338 // If the size of the other access is larger than the total size of the
339 // global/alloca/malloc, it cannot be accessing the object (it's
340 // undefined to load or store bytes before or after an object).
341 const Type *ElTy = cast<PointerType>(O2->getType())->getElementType();
342 unsigned GlobalSize = getTargetData().getTypeSize(ElTy);
343 if (GlobalSize < V1Size && V1Size != ~0U)
348 // If we have two gep instructions with must-alias'ing base pointers, figure
349 // out if the indexes to the GEP tell us anything about the derived pointer.
350 // Note that we also handle chains of getelementptr instructions as well as
351 // constant expression getelementptrs here.
353 if (isGEP(V1) && isGEP(V2)) {
354 // Drill down into the first non-gep value, to test for must-aliasing of
355 // the base pointers.
356 const Value *BasePtr1 = V1, *BasePtr2 = V2;
358 BasePtr1 = cast<User>(BasePtr1)->getOperand(0);
359 } while (isGEP(BasePtr1) &&
360 cast<User>(BasePtr1)->getOperand(1) ==
361 Constant::getNullValue(cast<User>(BasePtr1)->getOperand(1)->getType()));
363 BasePtr2 = cast<User>(BasePtr2)->getOperand(0);
364 } while (isGEP(BasePtr2) &&
365 cast<User>(BasePtr2)->getOperand(1) ==
366 Constant::getNullValue(cast<User>(BasePtr2)->getOperand(1)->getType()));
368 // Do the base pointers alias?
369 AliasResult BaseAlias = alias(BasePtr1, V1Size, BasePtr2, V2Size);
370 if (BaseAlias == NoAlias) return NoAlias;
371 if (BaseAlias == MustAlias) {
372 // If the base pointers alias each other exactly, check to see if we can
373 // figure out anything about the resultant pointers, to try to prove
376 // Collect all of the chained GEP operands together into one simple place
377 std::vector<Value*> GEP1Ops, GEP2Ops;
378 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
379 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
381 // If GetGEPOperands were able to fold to the same must-aliased pointer,
382 // do the comparison.
383 if (BasePtr1 == BasePtr2) {
385 CheckGEPInstructions(BasePtr1->getType(), GEP1Ops, V1Size,
386 BasePtr2->getType(), GEP2Ops, V2Size);
387 if (GAlias != MayAlias)
393 // Check to see if these two pointers are related by a getelementptr
394 // instruction. If one pointer is a GEP with a non-zero index of the other
395 // pointer, we know they cannot alias.
399 std::swap(V1Size, V2Size);
402 if (V1Size != ~0U && V2Size != ~0U)
403 if (const User *GEP = isGEP(V1)) {
404 std::vector<Value*> GEPOperands;
405 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
407 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
408 if (R == MustAlias) {
409 // If there is at least one non-zero constant index, we know they cannot
411 bool ConstantFound = false;
412 bool AllZerosFound = true;
413 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
414 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
415 if (!C->isNullValue()) {
416 ConstantFound = true;
417 AllZerosFound = false;
421 AllZerosFound = false;
424 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
425 // the ptr, the end result is a must alias also.
430 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
433 // Otherwise we have to check to see that the distance is more than
434 // the size of the argument... build an index vector that is equal to
435 // the arguments provided, except substitute 0's for any variable
436 // indexes we find...
437 if (cast<PointerType>(
438 BasePtr->getType())->getElementType()->isSized()) {
439 for (unsigned i = 0; i != GEPOperands.size(); ++i)
440 if (!isa<ConstantInt>(GEPOperands[i]))
442 Constant::getNullValue(GEPOperands[i]->getType());
444 getTargetData().getIndexedOffset(BasePtr->getType(), GEPOperands);
446 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
456 static bool ValuesEqual(Value *V1, Value *V2) {
457 if (V1->getType() == V2->getType())
459 if (Constant *C1 = dyn_cast<Constant>(V1))
460 if (Constant *C2 = dyn_cast<Constant>(V2)) {
461 // Sign extend the constants to long types.
462 C1 = ConstantExpr::getSignExtend(C1, Type::LongTy);
463 C2 = ConstantExpr::getSignExtend(C2, Type::LongTy);
469 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
470 /// base pointers. This checks to see if the index expressions preclude the
471 /// pointers from aliasing...
472 AliasAnalysis::AliasResult BasicAliasAnalysis::
473 CheckGEPInstructions(const Type* BasePtr1Ty, std::vector<Value*> &GEP1Ops,
475 const Type *BasePtr2Ty, std::vector<Value*> &GEP2Ops,
477 // We currently can't handle the case when the base pointers have different
478 // primitive types. Since this is uncommon anyway, we are happy being
479 // extremely conservative.
480 if (BasePtr1Ty != BasePtr2Ty)
483 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
485 // Find the (possibly empty) initial sequence of equal values... which are not
486 // necessarily constants.
487 unsigned NumGEP1Operands = GEP1Ops.size(), NumGEP2Operands = GEP2Ops.size();
488 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
489 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
490 unsigned UnequalOper = 0;
491 while (UnequalOper != MinOperands &&
492 ValuesEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
493 // Advance through the type as we go...
495 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
496 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
498 // If all operands equal each other, then the derived pointers must
499 // alias each other...
501 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
502 "Ran out of type nesting, but not out of operands?");
507 // If we have seen all constant operands, and run out of indexes on one of the
508 // getelementptrs, check to see if the tail of the leftover one is all zeros.
509 // If so, return mustalias.
510 if (UnequalOper == MinOperands) {
511 if (GEP1Ops.size() < GEP2Ops.size()) std::swap(GEP1Ops, GEP2Ops);
513 bool AllAreZeros = true;
514 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
515 if (!isa<Constant>(GEP1Ops[i]) ||
516 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
520 if (AllAreZeros) return MustAlias;
524 // So now we know that the indexes derived from the base pointers,
525 // which are known to alias, are different. We can still determine a
526 // no-alias result if there are differing constant pairs in the index
527 // chain. For example:
528 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
530 unsigned SizeMax = std::max(G1S, G2S);
531 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
533 // Scan for the first operand that is constant and unequal in the
534 // two getelementptrs...
535 unsigned FirstConstantOper = UnequalOper;
536 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
537 const Value *G1Oper = GEP1Ops[FirstConstantOper];
538 const Value *G2Oper = GEP2Ops[FirstConstantOper];
540 if (G1Oper != G2Oper) // Found non-equal constant indexes...
541 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
542 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
543 if (G1OC->getType() != G2OC->getType()) {
544 // Sign extend both operands to long.
545 G1OC = ConstantExpr::getSignExtend(G1OC, Type::LongTy);
546 G2OC = ConstantExpr::getSignExtend(G2OC, Type::LongTy);
547 GEP1Ops[FirstConstantOper] = G1OC;
548 GEP2Ops[FirstConstantOper] = G2OC;
552 // Make sure they are comparable (ie, not constant expressions), and
553 // make sure the GEP with the smaller leading constant is GEP1.
554 Constant *Compare = ConstantExpr::getSetGT(G1OC, G2OC);
555 if (ConstantBool *CV = dyn_cast<ConstantBool>(Compare)) {
556 if (CV->getValue()) // If they are comparable and G2 > G1
557 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
562 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
565 // No shared constant operands, and we ran out of common operands. At this
566 // point, the GEP instructions have run through all of their operands, and we
567 // haven't found evidence that there are any deltas between the GEP's.
568 // However, one GEP may have more operands than the other. If this is the
569 // case, there may still be hope. Check this now.
570 if (FirstConstantOper == MinOperands) {
571 // Make GEP1Ops be the longer one if there is a longer one.
572 if (GEP1Ops.size() < GEP2Ops.size())
573 std::swap(GEP1Ops, GEP2Ops);
575 // Is there anything to check?
576 if (GEP1Ops.size() > MinOperands) {
577 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
578 if (isa<ConstantInt>(GEP1Ops[i]) &&
579 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
580 // Yup, there's a constant in the tail. Set all variables to
581 // constants in the GEP instruction to make it suiteable for
582 // TargetData::getIndexedOffset.
583 for (i = 0; i != MaxOperands; ++i)
584 if (!isa<ConstantInt>(GEP1Ops[i]))
585 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
586 // Okay, now get the offset. This is the relative offset for the full
588 const TargetData &TD = getTargetData();
589 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops);
591 // Now crop off any constants from the end...
592 GEP1Ops.resize(MinOperands);
593 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops);
595 // If the tail provided a bit enough offset, return noalias!
596 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
601 // Couldn't find anything useful.
605 // If there are non-equal constants arguments, then we can figure
606 // out a minimum known delta between the two index expressions... at
607 // this point we know that the first constant index of GEP1 is less
608 // than the first constant index of GEP2.
610 // Advance BasePtr[12]Ty over this first differing constant operand.
611 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(GEP2Ops[FirstConstantOper]);
612 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(GEP1Ops[FirstConstantOper]);
614 // We are going to be using TargetData::getIndexedOffset to determine the
615 // offset that each of the GEP's is reaching. To do this, we have to convert
616 // all variable references to constant references. To do this, we convert the
617 // initial equal sequence of variables into constant zeros to start with.
618 for (unsigned i = 0; i != FirstConstantOper; ++i)
619 if (!isa<ConstantInt>(GEP1Ops[i]) || !isa<ConstantInt>(GEP2Ops[i]))
620 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::UIntTy);
622 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
624 // Loop over the rest of the operands...
625 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
626 const Value *Op1 = i < GEP1Ops.size() ? GEP1Ops[i] : 0;
627 const Value *Op2 = i < GEP2Ops.size() ? GEP2Ops[i] : 0;
628 // If they are equal, use a zero index...
629 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
630 if (!isa<ConstantInt>(Op1))
631 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
632 // Otherwise, just keep the constants we have.
635 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
636 // If this is an array index, make sure the array element is in range.
637 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
638 if (Op1C->getRawValue() >= AT->getNumElements())
639 return MayAlias; // Be conservative with out-of-range accesses
642 // GEP1 is known to produce a value less than GEP2. To be
643 // conservatively correct, we must assume the largest possible
644 // constant is used in this position. This cannot be the initial
645 // index to the GEP instructions (because we know we have at least one
646 // element before this one with the different constant arguments), so
647 // we know that the current index must be into either a struct or
648 // array. Because we know it's not constant, this cannot be a
649 // structure index. Because of this, we can calculate the maximum
652 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
653 GEP1Ops[i] = ConstantSInt::get(Type::LongTy,AT->getNumElements()-1);
658 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
659 // If this is an array index, make sure the array element is in range.
660 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
661 if (Op2C->getRawValue() >= AT->getNumElements())
662 return MayAlias; // Be conservative with out-of-range accesses
663 } else { // Conservatively assume the minimum value for this index
664 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
669 if (BasePtr1Ty && Op1) {
670 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
671 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
676 if (BasePtr2Ty && Op2) {
677 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
678 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
684 if (GEPPointerTy->getElementType()->isSized()) {
685 int64_t Offset1 = getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops);
686 int64_t Offset2 = getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops);
687 assert(Offset1<Offset2 && "There is at least one different constant here!");
689 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
690 //std::cerr << "Determined that these two GEP's don't alias ["
691 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
699 struct StringCompare {
700 bool operator()(const char *LHS, const char *RHS) {
701 return strcmp(LHS, RHS) < 0;
706 // Note that this list cannot contain libm functions (such as acos and sqrt)
707 // that set errno on a domain or other error.
708 static const char *DoesntAccessMemoryTable[] = {
710 "llvm.frameaddress", "llvm.returnaddress", "llvm.readport",
711 "llvm.isunordered", "llvm.sqrt", "llvm.ctpop", "llvm.ctlz", "llvm.cttz",
713 "abs", "labs", "llabs", "imaxabs", "fabs", "fabsf", "fabsl",
714 "trunc", "truncf", "truncl", "ldexp",
716 "atan", "atanf", "atanl", "atan2", "atan2f", "atan2l",
718 "cos", "cosf", "cosl",
719 "exp", "expf", "expl",
721 "sin", "sinf", "sinl",
722 "tan", "tanf", "tanl", "tanh", "tanhf", "tanhl",
725 "isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower", "isprint"
726 "ispunct", "isspace", "isupper", "isxdigit", "tolower", "toupper",
729 "iswalnum", "iswalpha", "iswcntrl", "iswdigit", "iswgraph", "iswlower",
730 "iswprint", "iswpunct", "iswspace", "iswupper", "iswxdigit",
732 "iswctype", "towctrans", "towlower", "towupper",
736 "isinf", "isnan", "finite",
738 // C99 math functions
739 "copysign", "copysignf", "copysignd",
740 "nexttoward", "nexttowardf", "nexttowardd",
741 "nextafter", "nextafterf", "nextafterd",
744 "__signbit", "__signbitf", "__signbitl",
747 static const unsigned DAMTableSize =
748 sizeof(DoesntAccessMemoryTable)/sizeof(DoesntAccessMemoryTable[0]);
750 static const char *OnlyReadsMemoryTable[] = {
751 "atoi", "atol", "atof", "atoll", "atoq", "a64l",
752 "bcmp", "memcmp", "memchr", "memrchr", "wmemcmp", "wmemchr",
755 "strcmp", "strcasecmp", "strcoll", "strncmp", "strncasecmp",
756 "strchr", "strcspn", "strlen", "strpbrk", "strrchr", "strspn", "strstr",
760 "wcschr", "wcscmp", "wcscoll", "wcscspn", "wcslen", "wcsncmp", "wcspbrk",
761 "wcsrchr", "wcsspn", "wcsstr",
764 "alphasort", "alphasort64", "versionsort", "versionsort64",
767 "nan", "nanf", "nand",
770 "feof", "ferror", "fileno",
771 "feof_unlocked", "ferror_unlocked", "fileno_unlocked"
774 static const unsigned ORMTableSize =
775 sizeof(OnlyReadsMemoryTable)/sizeof(OnlyReadsMemoryTable[0]);
777 AliasAnalysis::ModRefBehavior
778 BasicAliasAnalysis::getModRefBehavior(Function *F, CallSite CS,
779 std::vector<PointerAccessInfo> *Info) {
780 if (!F->isExternal()) return UnknownModRefBehavior;
782 static bool Initialized = false;
784 // Sort the table the first time through.
785 std::sort(DoesntAccessMemoryTable, DoesntAccessMemoryTable+DAMTableSize,
787 std::sort(OnlyReadsMemoryTable, OnlyReadsMemoryTable+ORMTableSize,
792 const char **Ptr = std::lower_bound(DoesntAccessMemoryTable,
793 DoesntAccessMemoryTable+DAMTableSize,
794 F->getName().c_str(), StringCompare());
795 if (Ptr != DoesntAccessMemoryTable+DAMTableSize && *Ptr == F->getName())
796 return DoesNotAccessMemory;
798 Ptr = std::lower_bound(OnlyReadsMemoryTable,
799 OnlyReadsMemoryTable+ORMTableSize,
800 F->getName().c_str(), StringCompare());
801 if (Ptr != OnlyReadsMemoryTable+ORMTableSize && *Ptr == F->getName())
802 return OnlyReadsMemory;
804 return UnknownModRefBehavior;