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) || isa<AllocationInst>(O1))
311 if (cast<PointerType>(O1->getType())->getElementType()->isSized()) {
312 // If the size of the other access is larger than the total size of the
313 // global/alloca/malloc, it cannot be accessing the global (it's
314 // undefined to load or store bytes before or after an object).
315 const Type *ElTy = cast<PointerType>(O1->getType())->getElementType();
316 unsigned GlobalSize = getTargetData().getTypeSize(ElTy);
317 if (GlobalSize < V2Size && V2Size != ~0U)
323 if (!isa<Argument>(O2) && isa<ConstantPointerNull>(V1))
324 return NoAlias; // Unique values don't alias null
326 if (isa<GlobalVariable>(O2) || isa<AllocationInst>(O2))
327 if (cast<PointerType>(O2->getType())->getElementType()->isSized()) {
328 // If the size of the other access is larger than the total size of the
329 // global/alloca/malloc, it cannot be accessing the object (it's
330 // undefined to load or store bytes before or after an object).
331 const Type *ElTy = cast<PointerType>(O2->getType())->getElementType();
332 unsigned GlobalSize = getTargetData().getTypeSize(ElTy);
333 if (GlobalSize < V1Size && V1Size != ~0U)
338 // If we have two gep instructions with must-alias'ing base pointers, figure
339 // out if the indexes to the GEP tell us anything about the derived pointer.
340 // Note that we also handle chains of getelementptr instructions as well as
341 // constant expression getelementptrs here.
343 if (isGEP(V1) && isGEP(V2)) {
344 // Drill down into the first non-gep value, to test for must-aliasing of
345 // the base pointers.
346 const Value *BasePtr1 = V1, *BasePtr2 = V2;
348 BasePtr1 = cast<User>(BasePtr1)->getOperand(0);
349 } while (isGEP(BasePtr1) &&
350 cast<User>(BasePtr1)->getOperand(1) ==
351 Constant::getNullValue(cast<User>(BasePtr1)->getOperand(1)->getType()));
353 BasePtr2 = cast<User>(BasePtr2)->getOperand(0);
354 } while (isGEP(BasePtr2) &&
355 cast<User>(BasePtr2)->getOperand(1) ==
356 Constant::getNullValue(cast<User>(BasePtr2)->getOperand(1)->getType()));
358 // Do the base pointers alias?
359 AliasResult BaseAlias = alias(BasePtr1, V1Size, BasePtr2, V2Size);
360 if (BaseAlias == NoAlias) return NoAlias;
361 if (BaseAlias == MustAlias) {
362 // If the base pointers alias each other exactly, check to see if we can
363 // figure out anything about the resultant pointers, to try to prove
366 // Collect all of the chained GEP operands together into one simple place
367 std::vector<Value*> GEP1Ops, GEP2Ops;
368 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
369 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
371 // If GetGEPOperands were able to fold to the same must-aliased pointer,
372 // do the comparison.
373 if (BasePtr1 == BasePtr2) {
375 CheckGEPInstructions(BasePtr1->getType(), GEP1Ops, V1Size,
376 BasePtr2->getType(), GEP2Ops, V2Size);
377 if (GAlias != MayAlias)
383 // Check to see if these two pointers are related by a getelementptr
384 // instruction. If one pointer is a GEP with a non-zero index of the other
385 // pointer, we know they cannot alias.
389 std::swap(V1Size, V2Size);
392 if (V1Size != ~0U && V2Size != ~0U)
393 if (const User *GEP = isGEP(V1)) {
394 std::vector<Value*> GEPOperands;
395 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
397 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
398 if (R == MustAlias) {
399 // If there is at least one non-zero constant index, we know they cannot
401 bool ConstantFound = false;
402 bool AllZerosFound = true;
403 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
404 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
405 if (!C->isNullValue()) {
406 ConstantFound = true;
407 AllZerosFound = false;
411 AllZerosFound = false;
414 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
415 // the ptr, the end result is a must alias also.
420 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
423 // Otherwise we have to check to see that the distance is more than
424 // the size of the argument... build an index vector that is equal to
425 // the arguments provided, except substitute 0's for any variable
426 // indexes we find...
427 if (cast<PointerType>(
428 BasePtr->getType())->getElementType()->isSized()) {
429 for (unsigned i = 0; i != GEPOperands.size(); ++i)
430 if (!isa<ConstantInt>(GEPOperands[i]))
432 Constant::getNullValue(GEPOperands[i]->getType());
434 getTargetData().getIndexedOffset(BasePtr->getType(), GEPOperands);
436 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
446 static bool ValuesEqual(Value *V1, Value *V2) {
447 if (V1->getType() == V2->getType())
449 if (Constant *C1 = dyn_cast<Constant>(V1))
450 if (Constant *C2 = dyn_cast<Constant>(V2)) {
451 // Sign extend the constants to long types.
452 C1 = ConstantExpr::getSignExtend(C1, Type::LongTy);
453 C2 = ConstantExpr::getSignExtend(C2, Type::LongTy);
459 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
460 /// base pointers. This checks to see if the index expressions preclude the
461 /// pointers from aliasing...
462 AliasAnalysis::AliasResult BasicAliasAnalysis::
463 CheckGEPInstructions(const Type* BasePtr1Ty, std::vector<Value*> &GEP1Ops,
465 const Type *BasePtr2Ty, std::vector<Value*> &GEP2Ops,
467 // We currently can't handle the case when the base pointers have different
468 // primitive types. Since this is uncommon anyway, we are happy being
469 // extremely conservative.
470 if (BasePtr1Ty != BasePtr2Ty)
473 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
475 // Find the (possibly empty) initial sequence of equal values... which are not
476 // necessarily constants.
477 unsigned NumGEP1Operands = GEP1Ops.size(), NumGEP2Operands = GEP2Ops.size();
478 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
479 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
480 unsigned UnequalOper = 0;
481 while (UnequalOper != MinOperands &&
482 ValuesEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
483 // Advance through the type as we go...
485 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
486 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
488 // If all operands equal each other, then the derived pointers must
489 // alias each other...
491 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
492 "Ran out of type nesting, but not out of operands?");
497 // If we have seen all constant operands, and run out of indexes on one of the
498 // getelementptrs, check to see if the tail of the leftover one is all zeros.
499 // If so, return mustalias.
500 if (UnequalOper == MinOperands) {
501 if (GEP1Ops.size() < GEP2Ops.size()) std::swap(GEP1Ops, GEP2Ops);
503 bool AllAreZeros = true;
504 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
505 if (!isa<Constant>(GEP1Ops[i]) ||
506 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
510 if (AllAreZeros) return MustAlias;
514 // So now we know that the indexes derived from the base pointers,
515 // which are known to alias, are different. We can still determine a
516 // no-alias result if there are differing constant pairs in the index
517 // chain. For example:
518 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
520 unsigned SizeMax = std::max(G1S, G2S);
521 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
523 // Scan for the first operand that is constant and unequal in the
524 // two getelementptrs...
525 unsigned FirstConstantOper = UnequalOper;
526 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
527 const Value *G1Oper = GEP1Ops[FirstConstantOper];
528 const Value *G2Oper = GEP2Ops[FirstConstantOper];
530 if (G1Oper != G2Oper) // Found non-equal constant indexes...
531 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
532 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
533 if (G1OC->getType() != G2OC->getType()) {
534 // Sign extend both operands to long.
535 G1OC = ConstantExpr::getSignExtend(G1OC, Type::LongTy);
536 G2OC = ConstantExpr::getSignExtend(G2OC, Type::LongTy);
537 GEP1Ops[FirstConstantOper] = G1OC;
538 GEP2Ops[FirstConstantOper] = G2OC;
542 // Make sure they are comparable (ie, not constant expressions), and
543 // make sure the GEP with the smaller leading constant is GEP1.
544 Constant *Compare = ConstantExpr::getSetGT(G1OC, G2OC);
545 if (ConstantBool *CV = dyn_cast<ConstantBool>(Compare)) {
546 if (CV->getValue()) // If they are comparable and G2 > G1
547 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
552 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
555 // No shared constant operands, and we ran out of common operands. At this
556 // point, the GEP instructions have run through all of their operands, and we
557 // haven't found evidence that there are any deltas between the GEP's.
558 // However, one GEP may have more operands than the other. If this is the
559 // case, there may still be hope. Check this now.
560 if (FirstConstantOper == MinOperands) {
561 // Make GEP1Ops be the longer one if there is a longer one.
562 if (GEP1Ops.size() < GEP2Ops.size())
563 std::swap(GEP1Ops, GEP2Ops);
565 // Is there anything to check?
566 if (GEP1Ops.size() > MinOperands) {
567 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
568 if (isa<ConstantInt>(GEP1Ops[i]) &&
569 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
570 // Yup, there's a constant in the tail. Set all variables to
571 // constants in the GEP instruction to make it suiteable for
572 // TargetData::getIndexedOffset.
573 for (i = 0; i != MaxOperands; ++i)
574 if (!isa<ConstantInt>(GEP1Ops[i]))
575 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
576 // Okay, now get the offset. This is the relative offset for the full
578 const TargetData &TD = getTargetData();
579 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops);
581 // Now crop off any constants from the end...
582 GEP1Ops.resize(MinOperands);
583 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops);
585 // If the tail provided a bit enough offset, return noalias!
586 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
591 // Couldn't find anything useful.
595 // If there are non-equal constants arguments, then we can figure
596 // out a minimum known delta between the two index expressions... at
597 // this point we know that the first constant index of GEP1 is less
598 // than the first constant index of GEP2.
600 // Advance BasePtr[12]Ty over this first differing constant operand.
601 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(GEP2Ops[FirstConstantOper]);
602 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(GEP1Ops[FirstConstantOper]);
604 // We are going to be using TargetData::getIndexedOffset to determine the
605 // offset that each of the GEP's is reaching. To do this, we have to convert
606 // all variable references to constant references. To do this, we convert the
607 // initial equal sequence of variables into constant zeros to start with.
608 for (unsigned i = 0; i != FirstConstantOper; ++i)
609 if (!isa<ConstantInt>(GEP1Ops[i]) || !isa<ConstantInt>(GEP2Ops[i]))
610 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::UIntTy);
612 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
614 // Loop over the rest of the operands...
615 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
616 const Value *Op1 = i < GEP1Ops.size() ? GEP1Ops[i] : 0;
617 const Value *Op2 = i < GEP2Ops.size() ? GEP2Ops[i] : 0;
618 // If they are equal, use a zero index...
619 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
620 if (!isa<ConstantInt>(Op1))
621 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
622 // Otherwise, just keep the constants we have.
625 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
626 // If this is an array index, make sure the array element is in range.
627 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
628 if (Op1C->getRawValue() >= AT->getNumElements())
629 return MayAlias; // Be conservative with out-of-range accesses
632 // GEP1 is known to produce a value less than GEP2. To be
633 // conservatively correct, we must assume the largest possible
634 // constant is used in this position. This cannot be the initial
635 // index to the GEP instructions (because we know we have at least one
636 // element before this one with the different constant arguments), so
637 // we know that the current index must be into either a struct or
638 // array. Because we know it's not constant, this cannot be a
639 // structure index. Because of this, we can calculate the maximum
642 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
643 GEP1Ops[i] = ConstantSInt::get(Type::LongTy,AT->getNumElements()-1);
648 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
649 // If this is an array index, make sure the array element is in range.
650 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
651 if (Op2C->getRawValue() >= AT->getNumElements())
652 return MayAlias; // Be conservative with out-of-range accesses
653 } else { // Conservatively assume the minimum value for this index
654 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
659 if (BasePtr1Ty && Op1) {
660 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
661 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
666 if (BasePtr2Ty && Op2) {
667 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
668 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
674 if (GEPPointerTy->getElementType()->isSized()) {
675 int64_t Offset1 = getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops);
676 int64_t Offset2 = getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops);
677 assert(Offset1<Offset2 && "There is at least one different constant here!");
679 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
680 //std::cerr << "Determined that these two GEP's don't alias ["
681 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
689 struct StringCompare {
690 bool operator()(const char *LHS, const char *RHS) {
691 return strcmp(LHS, RHS) < 0;
696 // Note that this list cannot contain libm functions (such as acos and sqrt)
697 // that set errno on a domain or other error.
698 static const char *DoesntAccessMemoryTable[] = {
700 "llvm.frameaddress", "llvm.returnaddress", "llvm.readport",
703 "abs", "labs", "llabs", "imaxabs", "fabs", "fabsf", "fabsl",
704 "trunc", "truncf", "truncl", "ldexp",
706 "atan", "atanf", "atanl", "atan2", "atan2f", "atan2l",
708 "cos", "cosf", "cosl", "cosh", "coshf", "coshl",
709 "exp", "expf", "expl",
711 "sin", "sinf", "sinl", "sinh", "sinhf", "sinhl",
712 "tan", "tanf", "tanl", "tanh", "tanhf", "tanhl",
715 "isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower", "isprint"
716 "ispunct", "isspace", "isupper", "isxdigit", "tolower", "toupper",
719 "iswalnum", "iswalpha", "iswcntrl", "iswdigit", "iswgraph", "iswlower",
720 "iswprint", "iswpunct", "iswspace", "iswupper", "iswxdigit",
722 "iswctype", "towctrans", "towlower", "towupper",
726 "isinf", "isnan", "finite",
728 // C99 math functions
729 "copysign", "copysignf", "copysignd",
730 "nexttoward", "nexttowardf", "nexttowardd",
731 "nextafter", "nextafterf", "nextafterd",
734 "__fpclassify", "__fpclassifyf", "__fpclassifyl",
735 "__signbit", "__signbitf", "__signbitl",
738 static const unsigned DAMTableSize =
739 sizeof(DoesntAccessMemoryTable)/sizeof(DoesntAccessMemoryTable[0]);
741 static const char *OnlyReadsMemoryTable[] = {
742 "atoi", "atol", "atof", "atoll", "atoq", "a64l",
743 "bcmp", "memcmp", "memchr", "memrchr", "wmemcmp", "wmemchr",
746 "strcmp", "strcasecmp", "strcoll", "strncmp", "strncasecmp",
747 "strchr", "strcspn", "strlen", "strpbrk", "strrchr", "strspn", "strstr",
751 "wcschr", "wcscmp", "wcscoll", "wcscspn", "wcslen", "wcsncmp", "wcspbrk",
752 "wcsrchr", "wcsspn", "wcsstr",
755 "alphasort", "alphasort64", "versionsort", "versionsort64",
758 "nan", "nanf", "nand",
761 "feof", "ferror", "fileno",
762 "feof_unlocked", "ferror_unlocked", "fileno_unlocked"
765 static const unsigned ORMTableSize =
766 sizeof(OnlyReadsMemoryTable)/sizeof(OnlyReadsMemoryTable[0]);
768 AliasAnalysis::ModRefBehavior
769 BasicAliasAnalysis::getModRefBehavior(Function *F, CallSite CS,
770 std::vector<PointerAccessInfo> *Info) {
771 if (!F->isExternal()) return UnknownModRefBehavior;
773 static bool Initialized = false;
775 // Sort the table the first time through.
776 std::sort(DoesntAccessMemoryTable, DoesntAccessMemoryTable+DAMTableSize,
778 std::sort(OnlyReadsMemoryTable, OnlyReadsMemoryTable+ORMTableSize,
783 const char **Ptr = std::lower_bound(DoesntAccessMemoryTable,
784 DoesntAccessMemoryTable+DAMTableSize,
785 F->getName().c_str(), StringCompare());
786 if (Ptr != DoesntAccessMemoryTable+DAMTableSize && *Ptr == F->getName())
787 return DoesNotAccessMemory;
789 Ptr = std::lower_bound(OnlyReadsMemoryTable,
790 OnlyReadsMemoryTable+ORMTableSize,
791 F->getName().c_str(), StringCompare());
792 if (Ptr != OnlyReadsMemoryTable+ORMTableSize && *Ptr == F->getName())
793 return OnlyReadsMemory;
795 return UnknownModRefBehavior;