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))
244 // The AliasAnalysis base class has some smarts, lets use them.
245 return AliasAnalysis::getModRefInfo(CS, P, Size);
248 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
249 // as array references. Note that this function is heavily tail recursive.
250 // Hopefully we have a smart C++ compiler. :)
252 AliasAnalysis::AliasResult
253 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
254 const Value *V2, unsigned V2Size) {
255 // Strip off any constant expression casts if they exist
256 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
257 if (CE->getOpcode() == Instruction::Cast &&
258 isa<PointerType>(CE->getOperand(0)->getType()))
259 V1 = CE->getOperand(0);
260 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
261 if (CE->getOpcode() == Instruction::Cast &&
262 isa<PointerType>(CE->getOperand(0)->getType()))
263 V2 = CE->getOperand(0);
265 // Are we checking for alias of the same value?
266 if (V1 == V2) return MustAlias;
268 if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
269 V1->getType() != Type::LongTy && V2->getType() != Type::LongTy)
270 return NoAlias; // Scalars cannot alias each other
272 // Strip off cast instructions...
273 if (const Instruction *I = dyn_cast<CastInst>(V1))
274 if (isa<PointerType>(I->getOperand(0)->getType()))
275 return alias(I->getOperand(0), V1Size, V2, V2Size);
276 if (const Instruction *I = dyn_cast<CastInst>(V2))
277 if (isa<PointerType>(I->getOperand(0)->getType()))
278 return alias(V1, V1Size, I->getOperand(0), V2Size);
280 // Figure out what objects these things are pointing to if we can...
281 const Value *O1 = getUnderlyingObject(V1);
282 const Value *O2 = getUnderlyingObject(V2);
284 // Pointing at a discernible object?
287 if (isa<Argument>(O1)) {
288 // Incoming argument cannot alias locally allocated object!
289 if (isa<AllocationInst>(O2)) return NoAlias;
290 // Otherwise, nothing is known...
291 } else if (isa<Argument>(O2)) {
292 // Incoming argument cannot alias locally allocated object!
293 if (isa<AllocationInst>(O1)) return NoAlias;
294 // Otherwise, nothing is known...
295 } else if (O1 != O2) {
296 // If they are two different objects, we know that we have no alias...
300 // If they are the same object, they we can look at the indexes. If they
301 // index off of the object is the same for both pointers, they must alias.
302 // If they are provably different, they must not alias. Otherwise, we
303 // can't tell anything.
307 if (!isa<Argument>(O1) && isa<ConstantPointerNull>(V2))
308 return NoAlias; // Unique values don't alias null
310 if (isa<GlobalVariable>(O1) ||
311 (isa<AllocationInst>(O1) &&
312 !cast<AllocationInst>(O1)->isArrayAllocation()))
313 if (cast<PointerType>(O1->getType())->getElementType()->isSized()) {
314 // If the size of the other access is larger than the total size of the
315 // global/alloca/malloc, it cannot be accessing the global (it's
316 // undefined to load or store bytes before or after an object).
317 const Type *ElTy = cast<PointerType>(O1->getType())->getElementType();
318 unsigned GlobalSize = getTargetData().getTypeSize(ElTy);
319 if (GlobalSize < V2Size && V2Size != ~0U)
325 if (!isa<Argument>(O2) && isa<ConstantPointerNull>(V1))
326 return NoAlias; // Unique values don't alias null
328 if (isa<GlobalVariable>(O2) ||
329 (isa<AllocationInst>(O2) &&
330 !cast<AllocationInst>(O2)->isArrayAllocation()))
331 if (cast<PointerType>(O2->getType())->getElementType()->isSized()) {
332 // If the size of the other access is larger than the total size of the
333 // global/alloca/malloc, it cannot be accessing the object (it's
334 // undefined to load or store bytes before or after an object).
335 const Type *ElTy = cast<PointerType>(O2->getType())->getElementType();
336 unsigned GlobalSize = getTargetData().getTypeSize(ElTy);
337 if (GlobalSize < V1Size && V1Size != ~0U)
342 // If we have two gep instructions with must-alias'ing base pointers, figure
343 // out if the indexes to the GEP tell us anything about the derived pointer.
344 // Note that we also handle chains of getelementptr instructions as well as
345 // constant expression getelementptrs here.
347 if (isGEP(V1) && isGEP(V2)) {
348 // Drill down into the first non-gep value, to test for must-aliasing of
349 // the base pointers.
350 const Value *BasePtr1 = V1, *BasePtr2 = V2;
352 BasePtr1 = cast<User>(BasePtr1)->getOperand(0);
353 } while (isGEP(BasePtr1) &&
354 cast<User>(BasePtr1)->getOperand(1) ==
355 Constant::getNullValue(cast<User>(BasePtr1)->getOperand(1)->getType()));
357 BasePtr2 = cast<User>(BasePtr2)->getOperand(0);
358 } while (isGEP(BasePtr2) &&
359 cast<User>(BasePtr2)->getOperand(1) ==
360 Constant::getNullValue(cast<User>(BasePtr2)->getOperand(1)->getType()));
362 // Do the base pointers alias?
363 AliasResult BaseAlias = alias(BasePtr1, V1Size, BasePtr2, V2Size);
364 if (BaseAlias == NoAlias) return NoAlias;
365 if (BaseAlias == MustAlias) {
366 // If the base pointers alias each other exactly, check to see if we can
367 // figure out anything about the resultant pointers, to try to prove
370 // Collect all of the chained GEP operands together into one simple place
371 std::vector<Value*> GEP1Ops, GEP2Ops;
372 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
373 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
375 // If GetGEPOperands were able to fold to the same must-aliased pointer,
376 // do the comparison.
377 if (BasePtr1 == BasePtr2) {
379 CheckGEPInstructions(BasePtr1->getType(), GEP1Ops, V1Size,
380 BasePtr2->getType(), GEP2Ops, V2Size);
381 if (GAlias != MayAlias)
387 // Check to see if these two pointers are related by a getelementptr
388 // instruction. If one pointer is a GEP with a non-zero index of the other
389 // pointer, we know they cannot alias.
393 std::swap(V1Size, V2Size);
396 if (V1Size != ~0U && V2Size != ~0U)
397 if (const User *GEP = isGEP(V1)) {
398 std::vector<Value*> GEPOperands;
399 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
401 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
402 if (R == MustAlias) {
403 // If there is at least one non-zero constant index, we know they cannot
405 bool ConstantFound = false;
406 bool AllZerosFound = true;
407 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
408 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
409 if (!C->isNullValue()) {
410 ConstantFound = true;
411 AllZerosFound = false;
415 AllZerosFound = false;
418 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
419 // the ptr, the end result is a must alias also.
424 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
427 // Otherwise we have to check to see that the distance is more than
428 // the size of the argument... build an index vector that is equal to
429 // the arguments provided, except substitute 0's for any variable
430 // indexes we find...
431 if (cast<PointerType>(
432 BasePtr->getType())->getElementType()->isSized()) {
433 for (unsigned i = 0; i != GEPOperands.size(); ++i)
434 if (!isa<ConstantInt>(GEPOperands[i]))
436 Constant::getNullValue(GEPOperands[i]->getType());
438 getTargetData().getIndexedOffset(BasePtr->getType(), GEPOperands);
440 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
450 static bool ValuesEqual(Value *V1, Value *V2) {
451 if (V1->getType() == V2->getType())
453 if (Constant *C1 = dyn_cast<Constant>(V1))
454 if (Constant *C2 = dyn_cast<Constant>(V2)) {
455 // Sign extend the constants to long types.
456 C1 = ConstantExpr::getSignExtend(C1, Type::LongTy);
457 C2 = ConstantExpr::getSignExtend(C2, Type::LongTy);
463 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
464 /// base pointers. This checks to see if the index expressions preclude the
465 /// pointers from aliasing...
466 AliasAnalysis::AliasResult BasicAliasAnalysis::
467 CheckGEPInstructions(const Type* BasePtr1Ty, std::vector<Value*> &GEP1Ops,
469 const Type *BasePtr2Ty, std::vector<Value*> &GEP2Ops,
471 // We currently can't handle the case when the base pointers have different
472 // primitive types. Since this is uncommon anyway, we are happy being
473 // extremely conservative.
474 if (BasePtr1Ty != BasePtr2Ty)
477 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
479 // Find the (possibly empty) initial sequence of equal values... which are not
480 // necessarily constants.
481 unsigned NumGEP1Operands = GEP1Ops.size(), NumGEP2Operands = GEP2Ops.size();
482 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
483 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
484 unsigned UnequalOper = 0;
485 while (UnequalOper != MinOperands &&
486 ValuesEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
487 // Advance through the type as we go...
489 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
490 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
492 // If all operands equal each other, then the derived pointers must
493 // alias each other...
495 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
496 "Ran out of type nesting, but not out of operands?");
501 // If we have seen all constant operands, and run out of indexes on one of the
502 // getelementptrs, check to see if the tail of the leftover one is all zeros.
503 // If so, return mustalias.
504 if (UnequalOper == MinOperands) {
505 if (GEP1Ops.size() < GEP2Ops.size()) std::swap(GEP1Ops, GEP2Ops);
507 bool AllAreZeros = true;
508 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
509 if (!isa<Constant>(GEP1Ops[i]) ||
510 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
514 if (AllAreZeros) return MustAlias;
518 // So now we know that the indexes derived from the base pointers,
519 // which are known to alias, are different. We can still determine a
520 // no-alias result if there are differing constant pairs in the index
521 // chain. For example:
522 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
524 unsigned SizeMax = std::max(G1S, G2S);
525 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
527 // Scan for the first operand that is constant and unequal in the
528 // two getelementptrs...
529 unsigned FirstConstantOper = UnequalOper;
530 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
531 const Value *G1Oper = GEP1Ops[FirstConstantOper];
532 const Value *G2Oper = GEP2Ops[FirstConstantOper];
534 if (G1Oper != G2Oper) // Found non-equal constant indexes...
535 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
536 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
537 if (G1OC->getType() != G2OC->getType()) {
538 // Sign extend both operands to long.
539 G1OC = ConstantExpr::getSignExtend(G1OC, Type::LongTy);
540 G2OC = ConstantExpr::getSignExtend(G2OC, Type::LongTy);
541 GEP1Ops[FirstConstantOper] = G1OC;
542 GEP2Ops[FirstConstantOper] = G2OC;
546 // Make sure they are comparable (ie, not constant expressions), and
547 // make sure the GEP with the smaller leading constant is GEP1.
548 Constant *Compare = ConstantExpr::getSetGT(G1OC, G2OC);
549 if (ConstantBool *CV = dyn_cast<ConstantBool>(Compare)) {
550 if (CV->getValue()) // If they are comparable and G2 > G1
551 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
556 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
559 // No shared constant operands, and we ran out of common operands. At this
560 // point, the GEP instructions have run through all of their operands, and we
561 // haven't found evidence that there are any deltas between the GEP's.
562 // However, one GEP may have more operands than the other. If this is the
563 // case, there may still be hope. Check this now.
564 if (FirstConstantOper == MinOperands) {
565 // Make GEP1Ops be the longer one if there is a longer one.
566 if (GEP1Ops.size() < GEP2Ops.size())
567 std::swap(GEP1Ops, GEP2Ops);
569 // Is there anything to check?
570 if (GEP1Ops.size() > MinOperands) {
571 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
572 if (isa<ConstantInt>(GEP1Ops[i]) &&
573 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
574 // Yup, there's a constant in the tail. Set all variables to
575 // constants in the GEP instruction to make it suiteable for
576 // TargetData::getIndexedOffset.
577 for (i = 0; i != MaxOperands; ++i)
578 if (!isa<ConstantInt>(GEP1Ops[i]))
579 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
580 // Okay, now get the offset. This is the relative offset for the full
582 const TargetData &TD = getTargetData();
583 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops);
585 // Now crop off any constants from the end...
586 GEP1Ops.resize(MinOperands);
587 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops);
589 // If the tail provided a bit enough offset, return noalias!
590 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
595 // Couldn't find anything useful.
599 // If there are non-equal constants arguments, then we can figure
600 // out a minimum known delta between the two index expressions... at
601 // this point we know that the first constant index of GEP1 is less
602 // than the first constant index of GEP2.
604 // Advance BasePtr[12]Ty over this first differing constant operand.
605 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(GEP2Ops[FirstConstantOper]);
606 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(GEP1Ops[FirstConstantOper]);
608 // We are going to be using TargetData::getIndexedOffset to determine the
609 // offset that each of the GEP's is reaching. To do this, we have to convert
610 // all variable references to constant references. To do this, we convert the
611 // initial equal sequence of variables into constant zeros to start with.
612 for (unsigned i = 0; i != FirstConstantOper; ++i)
613 if (!isa<ConstantInt>(GEP1Ops[i]) || !isa<ConstantInt>(GEP2Ops[i]))
614 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::UIntTy);
616 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
618 // Loop over the rest of the operands...
619 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
620 const Value *Op1 = i < GEP1Ops.size() ? GEP1Ops[i] : 0;
621 const Value *Op2 = i < GEP2Ops.size() ? GEP2Ops[i] : 0;
622 // If they are equal, use a zero index...
623 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
624 if (!isa<ConstantInt>(Op1))
625 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
626 // Otherwise, just keep the constants we have.
629 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
630 // If this is an array index, make sure the array element is in range.
631 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
632 if (Op1C->getRawValue() >= AT->getNumElements())
633 return MayAlias; // Be conservative with out-of-range accesses
636 // GEP1 is known to produce a value less than GEP2. To be
637 // conservatively correct, we must assume the largest possible
638 // constant is used in this position. This cannot be the initial
639 // index to the GEP instructions (because we know we have at least one
640 // element before this one with the different constant arguments), so
641 // we know that the current index must be into either a struct or
642 // array. Because we know it's not constant, this cannot be a
643 // structure index. Because of this, we can calculate the maximum
646 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
647 GEP1Ops[i] = ConstantSInt::get(Type::LongTy,AT->getNumElements()-1);
652 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
653 // If this is an array index, make sure the array element is in range.
654 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
655 if (Op2C->getRawValue() >= AT->getNumElements())
656 return MayAlias; // Be conservative with out-of-range accesses
657 } else { // Conservatively assume the minimum value for this index
658 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
663 if (BasePtr1Ty && Op1) {
664 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
665 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
670 if (BasePtr2Ty && Op2) {
671 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
672 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
678 if (GEPPointerTy->getElementType()->isSized()) {
679 int64_t Offset1 = getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops);
680 int64_t Offset2 = getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops);
681 assert(Offset1<Offset2 && "There is at least one different constant here!");
683 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
684 //std::cerr << "Determined that these two GEP's don't alias ["
685 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
693 struct StringCompare {
694 bool operator()(const char *LHS, const char *RHS) {
695 return strcmp(LHS, RHS) < 0;
700 // Note that this list cannot contain libm functions (such as acos and sqrt)
701 // that set errno on a domain or other error.
702 static const char *DoesntAccessMemoryTable[] = {
704 "llvm.frameaddress", "llvm.returnaddress", "llvm.readport",
707 "abs", "labs", "llabs", "imaxabs", "fabs", "fabsf", "fabsl",
708 "trunc", "truncf", "truncl", "ldexp",
710 "atan", "atanf", "atanl", "atan2", "atan2f", "atan2l",
712 "cos", "cosf", "cosl",
713 "exp", "expf", "expl",
715 "sin", "sinf", "sinl",
716 "tan", "tanf", "tanl", "tanh", "tanhf", "tanhl",
719 "isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower", "isprint"
720 "ispunct", "isspace", "isupper", "isxdigit", "tolower", "toupper",
723 "iswalnum", "iswalpha", "iswcntrl", "iswdigit", "iswgraph", "iswlower",
724 "iswprint", "iswpunct", "iswspace", "iswupper", "iswxdigit",
726 "iswctype", "towctrans", "towlower", "towupper",
730 "isinf", "isnan", "finite",
732 // C99 math functions
733 "copysign", "copysignf", "copysignd",
734 "nexttoward", "nexttowardf", "nexttowardd",
735 "nextafter", "nextafterf", "nextafterd",
738 "__fpclassify", "__fpclassifyf", "__fpclassifyl",
739 "__signbit", "__signbitf", "__signbitl",
742 static const unsigned DAMTableSize =
743 sizeof(DoesntAccessMemoryTable)/sizeof(DoesntAccessMemoryTable[0]);
745 static const char *OnlyReadsMemoryTable[] = {
746 "atoi", "atol", "atof", "atoll", "atoq", "a64l",
747 "bcmp", "memcmp", "memchr", "memrchr", "wmemcmp", "wmemchr",
750 "strcmp", "strcasecmp", "strcoll", "strncmp", "strncasecmp",
751 "strchr", "strcspn", "strlen", "strpbrk", "strrchr", "strspn", "strstr",
755 "wcschr", "wcscmp", "wcscoll", "wcscspn", "wcslen", "wcsncmp", "wcspbrk",
756 "wcsrchr", "wcsspn", "wcsstr",
759 "alphasort", "alphasort64", "versionsort", "versionsort64",
762 "nan", "nanf", "nand",
765 "feof", "ferror", "fileno",
766 "feof_unlocked", "ferror_unlocked", "fileno_unlocked"
769 static const unsigned ORMTableSize =
770 sizeof(OnlyReadsMemoryTable)/sizeof(OnlyReadsMemoryTable[0]);
772 AliasAnalysis::ModRefBehavior
773 BasicAliasAnalysis::getModRefBehavior(Function *F, CallSite CS,
774 std::vector<PointerAccessInfo> *Info) {
775 if (!F->isExternal()) return UnknownModRefBehavior;
777 static bool Initialized = false;
779 // Sort the table the first time through.
780 std::sort(DoesntAccessMemoryTable, DoesntAccessMemoryTable+DAMTableSize,
782 std::sort(OnlyReadsMemoryTable, OnlyReadsMemoryTable+ORMTableSize,
787 const char **Ptr = std::lower_bound(DoesntAccessMemoryTable,
788 DoesntAccessMemoryTable+DAMTableSize,
789 F->getName().c_str(), StringCompare());
790 if (Ptr != DoesntAccessMemoryTable+DAMTableSize && *Ptr == F->getName())
791 return DoesNotAccessMemory;
793 Ptr = std::lower_bound(OnlyReadsMemoryTable,
794 OnlyReadsMemoryTable+ORMTableSize,
795 F->getName().c_str(), StringCompare());
796 if (Ptr != OnlyReadsMemoryTable+ORMTableSize && *Ptr == F->getName())
797 return OnlyReadsMemory;
799 return UnknownModRefBehavior;