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 /// NoAA - This class implements the -no-aa pass, which always returns "I
40 /// don't know" for alias queries. NoAA is unlike other alias analysis
41 /// implementations, in that it does not chain to a previous analysis. As
42 /// such it doesn't follow many of the rules that other alias analyses must.
44 struct NoAA : public ImmutablePass, public AliasAnalysis {
45 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
46 AU.addRequired<TargetData>();
49 virtual void initializePass() {
50 TD = &getAnalysis<TargetData>();
53 virtual AliasResult alias(const Value *V1, unsigned V1Size,
54 const Value *V2, unsigned V2Size) {
58 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
59 virtual bool pointsToConstantMemory(const Value *P) { return false; }
60 virtual bool doesNotAccessMemory(Function *F) { return false; }
61 virtual bool onlyReadsMemory(Function *F) { return false; }
62 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
65 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
68 virtual bool hasNoModRefInfoForCalls() const { return true; }
70 virtual void deleteValue(Value *V) {}
71 virtual void copyValue(Value *From, Value *To) {}
74 // Register this pass...
76 U("no-aa", "No Alias Analysis (always returns 'may' alias)");
78 // Declare that we implement the AliasAnalysis interface
79 RegisterAnalysisGroup<AliasAnalysis, NoAA> V;
80 } // End of anonymous namespace
84 /// BasicAliasAnalysis - This is the default alias analysis implementation.
85 /// Because it doesn't chain to a previous alias analysis (like -no-aa), it
86 /// derives from the NoAA class.
87 struct BasicAliasAnalysis : public NoAA {
88 AliasResult alias(const Value *V1, unsigned V1Size,
89 const Value *V2, unsigned V2Size);
91 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
93 /// hasNoModRefInfoForCalls - We have no way to test one call against
94 /// another, unless they are pure or const.
95 virtual bool hasNoModRefInfoForCalls() const { return true; }
97 /// pointsToConstantMemory - Chase pointers until we find a (constant
99 bool pointsToConstantMemory(const Value *P);
101 virtual bool doesNotAccessMemory(Function *F);
102 virtual bool onlyReadsMemory(Function *F);
105 // CheckGEPInstructions - Check two GEP instructions with known
106 // must-aliasing base pointers. This checks to see if the index expressions
107 // preclude the pointers from aliasing...
109 CheckGEPInstructions(const Type* BasePtr1Ty, std::vector<Value*> &GEP1Ops,
111 const Type *BasePtr2Ty, std::vector<Value*> &GEP2Ops,
115 // Register this pass...
116 RegisterOpt<BasicAliasAnalysis>
117 X("basicaa", "Basic Alias Analysis (default AA impl)");
119 // Declare that we implement the AliasAnalysis interface
120 RegisterAnalysisGroup<AliasAnalysis, BasicAliasAnalysis, true> Y;
121 } // End of anonymous namespace
123 // hasUniqueAddress - Return true if the specified value points to something
124 // with a unique, discernable, address.
125 static inline bool hasUniqueAddress(const Value *V) {
126 return isa<GlobalValue>(V) || isa<AllocationInst>(V);
129 // getUnderlyingObject - This traverses the use chain to figure out what object
130 // the specified value points to. If the value points to, or is derived from, a
131 // unique object or an argument, return it.
132 static const Value *getUnderlyingObject(const Value *V) {
133 if (!isa<PointerType>(V->getType())) return 0;
135 // If we are at some type of object... return it.
136 if (hasUniqueAddress(V) || isa<Argument>(V)) return V;
138 // Traverse through different addressing mechanisms...
139 if (const Instruction *I = dyn_cast<Instruction>(V)) {
140 if (isa<CastInst>(I) || isa<GetElementPtrInst>(I))
141 return getUnderlyingObject(I->getOperand(0));
142 } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
143 if (CE->getOpcode() == Instruction::Cast ||
144 CE->getOpcode() == Instruction::GetElementPtr)
145 return getUnderlyingObject(CE->getOperand(0));
146 } else if (const GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
152 static const User *isGEP(const Value *V) {
153 if (isa<GetElementPtrInst>(V) ||
154 (isa<ConstantExpr>(V) &&
155 cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
156 return cast<User>(V);
160 static const Value *GetGEPOperands(const Value *V, std::vector<Value*> &GEPOps){
161 assert(GEPOps.empty() && "Expect empty list to populate!");
162 GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
163 cast<User>(V)->op_end());
165 // Accumulate all of the chained indexes into the operand array
166 V = cast<User>(V)->getOperand(0);
168 while (const User *G = isGEP(V)) {
169 if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
170 !cast<Constant>(GEPOps[0])->isNullValue())
171 break; // Don't handle folding arbitrary pointer offsets yet...
172 GEPOps.erase(GEPOps.begin()); // Drop the zero index
173 GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
174 V = G->getOperand(0);
179 /// pointsToConstantMemory - Chase pointers until we find a (constant
181 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
182 if (const Value *V = getUnderlyingObject(P))
183 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
184 return GV->isConstant();
188 static bool AddressMightEscape(const Value *V) {
189 for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
191 const Instruction *I = cast<Instruction>(*UI);
192 switch (I->getOpcode()) {
193 case Instruction::Load: break;
194 case Instruction::Store:
195 if (I->getOperand(0) == V)
196 return true; // Escapes if the pointer is stored.
198 case Instruction::GetElementPtr:
199 if (AddressMightEscape(I)) return true;
201 case Instruction::Cast:
202 if (!isa<PointerType>(I->getType()))
204 if (AddressMightEscape(I)) return true;
213 // getModRefInfo - Check to see if the specified callsite can clobber the
214 // specified memory object. Since we only look at local properties of this
215 // function, we really can't say much about this query. We do, however, use
216 // simple "address taken" analysis on local objects.
218 AliasAnalysis::ModRefResult
219 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
220 if (!isa<Constant>(P))
221 if (const AllocationInst *AI =
222 dyn_cast_or_null<AllocationInst>(getUnderlyingObject(P))) {
223 // Okay, the pointer is to a stack allocated object. If we can prove that
224 // the pointer never "escapes", then we know the call cannot clobber it,
225 // because it simply can't get its address.
226 if (!AddressMightEscape(AI))
230 // The AliasAnalysis base class has some smarts, lets use them.
231 return AliasAnalysis::getModRefInfo(CS, P, Size);
234 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
235 // as array references. Note that this function is heavily tail recursive.
236 // Hopefully we have a smart C++ compiler. :)
238 AliasAnalysis::AliasResult
239 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
240 const Value *V2, unsigned V2Size) {
241 // Strip off any constant expression casts if they exist
242 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
243 if (CE->getOpcode() == Instruction::Cast &&
244 isa<PointerType>(CE->getOperand(0)->getType()))
245 V1 = CE->getOperand(0);
246 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
247 if (CE->getOpcode() == Instruction::Cast &&
248 isa<PointerType>(CE->getOperand(0)->getType()))
249 V2 = CE->getOperand(0);
251 // Are we checking for alias of the same value?
252 if (V1 == V2) return MustAlias;
254 if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
255 V1->getType() != Type::LongTy && V2->getType() != Type::LongTy)
256 return NoAlias; // Scalars cannot alias each other
258 // Strip off cast instructions...
259 if (const Instruction *I = dyn_cast<CastInst>(V1))
260 if (isa<PointerType>(I->getOperand(0)->getType()))
261 return alias(I->getOperand(0), V1Size, V2, V2Size);
262 if (const Instruction *I = dyn_cast<CastInst>(V2))
263 if (isa<PointerType>(I->getOperand(0)->getType()))
264 return alias(V1, V1Size, I->getOperand(0), V2Size);
266 // Figure out what objects these things are pointing to if we can...
267 const Value *O1 = getUnderlyingObject(V1);
268 const Value *O2 = getUnderlyingObject(V2);
270 // Pointing at a discernible object?
272 if (isa<Argument>(O1)) {
273 // Incoming argument cannot alias locally allocated object!
274 if (isa<AllocationInst>(O2)) return NoAlias;
275 // Otherwise, nothing is known...
276 } else if (isa<Argument>(O2)) {
277 // Incoming argument cannot alias locally allocated object!
278 if (isa<AllocationInst>(O1)) return NoAlias;
279 // Otherwise, nothing is known...
281 // If they are two different objects, we know that we have no alias...
282 if (O1 != O2) return NoAlias;
285 // If they are the same object, they we can look at the indexes. If they
286 // index off of the object is the same for both pointers, they must alias.
287 // If they are provably different, they must not alias. Otherwise, we can't
289 } else if (O1 && !isa<Argument>(O1) && isa<ConstantPointerNull>(V2)) {
290 return NoAlias; // Unique values don't alias null
291 } else if (O2 && !isa<Argument>(O2) && isa<ConstantPointerNull>(V1)) {
292 return NoAlias; // Unique values don't alias null
295 // If we have two gep instructions with must-alias'ing base pointers, figure
296 // out if the indexes to the GEP tell us anything about the derived pointer.
297 // Note that we also handle chains of getelementptr instructions as well as
298 // constant expression getelementptrs here.
300 if (isGEP(V1) && isGEP(V2)) {
301 // Drill down into the first non-gep value, to test for must-aliasing of
302 // the base pointers.
303 const Value *BasePtr1 = V1, *BasePtr2 = V2;
305 BasePtr1 = cast<User>(BasePtr1)->getOperand(0);
306 } while (isGEP(BasePtr1) &&
307 cast<User>(BasePtr1)->getOperand(1) ==
308 Constant::getNullValue(cast<User>(BasePtr1)->getOperand(1)->getType()));
310 BasePtr2 = cast<User>(BasePtr2)->getOperand(0);
311 } while (isGEP(BasePtr2) &&
312 cast<User>(BasePtr2)->getOperand(1) ==
313 Constant::getNullValue(cast<User>(BasePtr2)->getOperand(1)->getType()));
315 // Do the base pointers alias?
316 AliasResult BaseAlias = alias(BasePtr1, V1Size, BasePtr2, V2Size);
317 if (BaseAlias == NoAlias) return NoAlias;
318 if (BaseAlias == MustAlias) {
319 // If the base pointers alias each other exactly, check to see if we can
320 // figure out anything about the resultant pointers, to try to prove
323 // Collect all of the chained GEP operands together into one simple place
324 std::vector<Value*> GEP1Ops, GEP2Ops;
325 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
326 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
329 CheckGEPInstructions(BasePtr1->getType(), GEP1Ops, V1Size,
330 BasePtr2->getType(), GEP2Ops, V2Size);
331 if (GAlias != MayAlias)
336 // Check to see if these two pointers are related by a getelementptr
337 // instruction. If one pointer is a GEP with a non-zero index of the other
338 // pointer, we know they cannot alias.
342 std::swap(V1Size, V2Size);
345 if (V1Size != ~0U && V2Size != ~0U)
346 if (const User *GEP = isGEP(V1)) {
347 std::vector<Value*> GEPOperands;
348 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
350 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
351 if (R == MustAlias) {
352 // If there is at least one non-zero constant index, we know they cannot
354 bool ConstantFound = false;
355 bool AllZerosFound = true;
356 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
357 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
358 if (!C->isNullValue()) {
359 ConstantFound = true;
360 AllZerosFound = false;
364 AllZerosFound = false;
367 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
368 // the ptr, the end result is a must alias also.
373 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
376 // Otherwise we have to check to see that the distance is more than
377 // the size of the argument... build an index vector that is equal to
378 // the arguments provided, except substitute 0's for any variable
379 // indexes we find...
380 for (unsigned i = 0; i != GEPOperands.size(); ++i)
381 if (!isa<Constant>(GEPOperands[i]) || isa<GlobalValue>(GEPOperands[i]) ||
382 isa<ConstantExpr>(GEPOperands[i]))
383 GEPOperands[i] =Constant::getNullValue(GEPOperands[i]->getType());
384 int64_t Offset = getTargetData().getIndexedOffset(BasePtr->getType(),
386 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
395 static bool ValuesEqual(Value *V1, Value *V2) {
396 if (V1->getType() == V2->getType())
398 if (Constant *C1 = dyn_cast<Constant>(V1))
399 if (Constant *C2 = dyn_cast<Constant>(V2)) {
400 // Sign extend the constants to long types.
401 C1 = ConstantExpr::getSignExtend(C1, Type::LongTy);
402 C2 = ConstantExpr::getSignExtend(C2, Type::LongTy);
408 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
409 /// base pointers. This checks to see if the index expressions preclude the
410 /// pointers from aliasing...
411 AliasAnalysis::AliasResult BasicAliasAnalysis::
412 CheckGEPInstructions(const Type* BasePtr1Ty, std::vector<Value*> &GEP1Ops,
414 const Type *BasePtr2Ty, std::vector<Value*> &GEP2Ops,
416 // We currently can't handle the case when the base pointers have different
417 // primitive types. Since this is uncommon anyway, we are happy being
418 // extremely conservative.
419 if (BasePtr1Ty != BasePtr2Ty)
422 const Type *GEPPointerTy = BasePtr1Ty;
424 // Find the (possibly empty) initial sequence of equal values... which are not
425 // necessarily constants.
426 unsigned NumGEP1Operands = GEP1Ops.size(), NumGEP2Operands = GEP2Ops.size();
427 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
428 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
429 unsigned UnequalOper = 0;
430 while (UnequalOper != MinOperands &&
431 ValuesEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
432 // Advance through the type as we go...
434 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
435 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
437 // If all operands equal each other, then the derived pointers must
438 // alias each other...
440 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
441 "Ran out of type nesting, but not out of operands?");
446 // If we have seen all constant operands, and run out of indexes on one of the
447 // getelementptrs, check to see if the tail of the leftover one is all zeros.
448 // If so, return mustalias.
449 if (UnequalOper == MinOperands) {
450 if (GEP1Ops.size() < GEP2Ops.size()) std::swap(GEP1Ops, GEP2Ops);
452 bool AllAreZeros = true;
453 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
454 if (!isa<Constant>(GEP1Ops[i]) ||
455 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
459 if (AllAreZeros) return MustAlias;
463 // So now we know that the indexes derived from the base pointers,
464 // which are known to alias, are different. We can still determine a
465 // no-alias result if there are differing constant pairs in the index
466 // chain. For example:
467 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
469 unsigned SizeMax = std::max(G1S, G2S);
470 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work...
472 // Scan for the first operand that is constant and unequal in the
473 // two getelementptrs...
474 unsigned FirstConstantOper = UnequalOper;
475 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
476 const Value *G1Oper = GEP1Ops[FirstConstantOper];
477 const Value *G2Oper = GEP2Ops[FirstConstantOper];
479 if (G1Oper != G2Oper) // Found non-equal constant indexes...
480 if (Constant *G1OC = dyn_cast<Constant>(const_cast<Value*>(G1Oper)))
481 if (Constant *G2OC = dyn_cast<Constant>(const_cast<Value*>(G2Oper))) {
482 if (G1OC->getType() != G2OC->getType()) {
483 // Sign extend both operands to long.
484 G1OC = ConstantExpr::getSignExtend(G1OC, Type::LongTy);
485 G2OC = ConstantExpr::getSignExtend(G2OC, Type::LongTy);
486 GEP1Ops[FirstConstantOper] = G1OC;
487 GEP2Ops[FirstConstantOper] = G2OC;
491 // Make sure they are comparable (ie, not constant expressions)...
492 // and make sure the GEP with the smaller leading constant is GEP1.
493 Constant *Compare = ConstantExpr::getSetGT(G1OC, G2OC);
494 if (ConstantBool *CV = dyn_cast<ConstantBool>(Compare)) {
495 if (CV->getValue()) // If they are comparable and G2 > G1
496 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
501 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
504 // No shared constant operands, and we ran out of common operands. At this
505 // point, the GEP instructions have run through all of their operands, and we
506 // haven't found evidence that there are any deltas between the GEP's.
507 // However, one GEP may have more operands than the other. If this is the
508 // case, there may still be hope. Check this now.
509 if (FirstConstantOper == MinOperands) {
510 // Make GEP1Ops be the longer one if there is a longer one.
511 if (GEP1Ops.size() < GEP2Ops.size())
512 std::swap(GEP1Ops, GEP2Ops);
514 // Is there anything to check?
515 if (GEP1Ops.size() > MinOperands) {
516 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
517 if (isa<ConstantInt>(GEP1Ops[i]) &&
518 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
519 // Yup, there's a constant in the tail. Set all variables to
520 // constants in the GEP instruction to make it suiteable for
521 // TargetData::getIndexedOffset.
522 for (i = 0; i != MaxOperands; ++i)
523 if (!isa<ConstantInt>(GEP1Ops[i]))
524 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
525 // Okay, now get the offset. This is the relative offset for the full
527 const TargetData &TD = getTargetData();
528 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops);
530 // Now crop off any constants from the end...
531 GEP1Ops.resize(MinOperands);
532 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops);
534 // If the tail provided a bit enough offset, return noalias!
535 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
540 // Couldn't find anything useful.
544 // If there are non-equal constants arguments, then we can figure
545 // out a minimum known delta between the two index expressions... at
546 // this point we know that the first constant index of GEP1 is less
547 // than the first constant index of GEP2.
549 // Advance BasePtr[12]Ty over this first differing constant operand.
550 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(GEP2Ops[FirstConstantOper]);
551 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(GEP1Ops[FirstConstantOper]);
553 // We are going to be using TargetData::getIndexedOffset to determine the
554 // offset that each of the GEP's is reaching. To do this, we have to convert
555 // all variable references to constant references. To do this, we convert the
556 // initial equal sequence of variables into constant zeros to start with.
557 for (unsigned i = 0; i != FirstConstantOper; ++i) {
558 if (!isa<Constant>(GEP1Ops[i]) || isa<ConstantExpr>(GEP1Ops[i]) ||
559 !isa<Constant>(GEP2Ops[i]) || isa<ConstantExpr>(GEP2Ops[i]))
560 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::UIntTy);
563 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
565 // Loop over the rest of the operands...
566 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
567 const Value *Op1 = i < GEP1Ops.size() ? GEP1Ops[i] : 0;
568 const Value *Op2 = i < GEP2Ops.size() ? GEP2Ops[i] : 0;
569 // If they are equal, use a zero index...
570 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
571 if (!isa<Constant>(Op1) || isa<ConstantExpr>(Op1))
572 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
573 // Otherwise, just keep the constants we have.
576 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
577 // If this is an array index, make sure the array element is in range.
578 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
579 if (Op1C->getRawValue() >= AT->getNumElements())
580 return MayAlias; // Be conservative with out-of-range accesses
583 // GEP1 is known to produce a value less than GEP2. To be
584 // conservatively correct, we must assume the largest possible
585 // constant is used in this position. This cannot be the initial
586 // index to the GEP instructions (because we know we have at least one
587 // element before this one with the different constant arguments), so
588 // we know that the current index must be into either a struct or
589 // array. Because we know it's not constant, this cannot be a
590 // structure index. Because of this, we can calculate the maximum
593 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
594 GEP1Ops[i] = ConstantSInt::get(Type::LongTy,AT->getNumElements()-1);
599 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
600 // If this is an array index, make sure the array element is in range.
601 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
602 if (Op2C->getRawValue() >= AT->getNumElements())
603 return MayAlias; // Be conservative with out-of-range accesses
604 } else { // Conservatively assume the minimum value for this index
605 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
610 if (BasePtr1Ty && Op1) {
611 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
612 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
617 if (BasePtr2Ty && Op2) {
618 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
619 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
625 int64_t Offset1 = getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops);
626 int64_t Offset2 = getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops);
627 assert(Offset1 < Offset2 &&"There is at least one different constant here!");
629 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
630 //std::cerr << "Determined that these two GEP's don't alias ["
631 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
638 struct StringCompare {
639 bool operator()(const char *LHS, const char *RHS) {
640 return strcmp(LHS, RHS) < 0;
645 // Note that this list cannot contain libm functions (such as acos and sqrt)
646 // that set errno on a domain or other error.
647 static const char *DoesntAccessMemoryTable[] = {
649 "llvm.frameaddress", "llvm.returnaddress", "llvm.readport", "llvm.isunordered",
651 "abs", "labs", "llabs", "imaxabs", "fabs", "fabsf", "fabsl",
652 "trunc", "truncf", "truncl", "ldexp",
654 "atan", "atanf", "atanl", "atan2", "atan2f", "atan2l",
656 "cos", "cosf", "cosl", "cosh", "coshf", "coshl",
657 "exp", "expf", "expl",
659 "sin", "sinf", "sinl", "sinh", "sinhf", "sinhl",
660 "tan", "tanf", "tanl", "tanh", "tanhf", "tanhl",
663 "isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower", "isprint"
664 "ispunct", "isspace", "isupper", "isxdigit", "tolower", "toupper",
667 "iswalnum", "iswalpha", "iswcntrl", "iswdigit", "iswgraph", "iswlower",
668 "iswprint", "iswpunct", "iswspace", "iswupper", "iswxdigit",
670 "iswctype", "towctrans", "towlower", "towupper",
674 "isinf", "isnan", "finite",
676 // C99 math functions
677 "copysign", "copysignf", "copysignd",
678 "nexttoward", "nexttowardf", "nexttowardd",
679 "nextafter", "nextafterf", "nextafterd",
682 "__fpclassify", "__fpclassifyf", "__fpclassifyl",
683 "__signbit", "__signbitf", "__signbitl",
686 static const unsigned DAMTableSize =
687 sizeof(DoesntAccessMemoryTable)/sizeof(DoesntAccessMemoryTable[0]);
689 /// doesNotAccessMemory - Return true if we know that the function does not
690 /// access memory at all. Since basicaa does no analysis, we can only do simple
691 /// things here. In particular, if we have an external function with the name
692 /// of a standard C library function, we are allowed to assume it will be
693 /// resolved by libc, so we can hardcode some entries in here.
694 bool BasicAliasAnalysis::doesNotAccessMemory(Function *F) {
695 if (!F->isExternal()) return false;
697 static bool Initialized = false;
699 // Sort the table the first time through.
700 std::sort(DoesntAccessMemoryTable, DoesntAccessMemoryTable+DAMTableSize,
705 const char **Ptr = std::lower_bound(DoesntAccessMemoryTable,
706 DoesntAccessMemoryTable+DAMTableSize,
707 F->getName().c_str(), StringCompare());
708 return Ptr != DoesntAccessMemoryTable+DAMTableSize && *Ptr == F->getName();
712 static const char *OnlyReadsMemoryTable[] = {
713 "atoi", "atol", "atof", "atoll", "atoq", "a64l",
714 "bcmp", "memcmp", "memchr", "memrchr", "wmemcmp", "wmemchr",
717 "strcmp", "strcasecmp", "strcoll", "strncmp", "strncasecmp",
718 "strchr", "strcspn", "strlen", "strpbrk", "strrchr", "strspn", "strstr",
722 "wcschr", "wcscmp", "wcscoll", "wcscspn", "wcslen", "wcsncmp", "wcspbrk",
723 "wcsrchr", "wcsspn", "wcsstr",
726 "alphasort", "alphasort64", "versionsort", "versionsort64",
729 "nan", "nanf", "nand",
732 "feof", "ferror", "fileno",
733 "feof_unlocked", "ferror_unlocked", "fileno_unlocked"
736 static const unsigned ORMTableSize =
737 sizeof(OnlyReadsMemoryTable)/sizeof(OnlyReadsMemoryTable[0]);
739 bool BasicAliasAnalysis::onlyReadsMemory(Function *F) {
740 if (doesNotAccessMemory(F)) return true;
741 if (!F->isExternal()) return false;
743 static bool Initialized = false;
745 // Sort the table the first time through.
746 std::sort(OnlyReadsMemoryTable, OnlyReadsMemoryTable+ORMTableSize,
751 const char **Ptr = std::lower_bound(OnlyReadsMemoryTable,
752 OnlyReadsMemoryTable+ORMTableSize,
753 F->getName().c_str(), StringCompare());
754 return Ptr != OnlyReadsMemoryTable+ORMTableSize && *Ptr == F->getName();