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/ADT/SmallVector.h"
26 #include "llvm/Support/Compiler.h"
27 #include "llvm/Support/GetElementPtrTypeIterator.h"
28 #include "llvm/Support/ManagedStatic.h"
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 VISIBILITY_HIDDEN 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> V(U);
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 VISIBILITY_HIDDEN 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,
116 Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size,
117 const Type *BasePtr2Ty,
118 Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size);
121 // Register this pass...
122 RegisterPass<BasicAliasAnalysis>
123 X("basicaa", "Basic Alias Analysis (default AA impl)");
125 // Declare that we implement the AliasAnalysis interface
126 RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
127 } // End of anonymous namespace
129 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
130 return new BasicAliasAnalysis();
133 // getUnderlyingObject - This traverses the use chain to figure out what object
134 // the specified value points to. If the value points to, or is derived from, a
135 // unique object or an argument, return it.
136 static const Value *getUnderlyingObject(const Value *V) {
137 if (!isa<PointerType>(V->getType())) return 0;
139 // If we are at some type of object, return it. GlobalValues and Allocations
140 // have unique addresses.
141 if (isa<GlobalValue>(V) || isa<AllocationInst>(V) || isa<Argument>(V))
144 // Traverse through different addressing mechanisms...
145 if (const Instruction *I = dyn_cast<Instruction>(V)) {
146 if (isa<BitCastInst>(I) || isa<GetElementPtrInst>(I))
147 return getUnderlyingObject(I->getOperand(0));
148 } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
149 if (CE->getOpcode() == Instruction::BitCast ||
150 CE->getOpcode() == Instruction::GetElementPtr)
151 return getUnderlyingObject(CE->getOperand(0));
156 static const User *isGEP(const Value *V) {
157 if (isa<GetElementPtrInst>(V) ||
158 (isa<ConstantExpr>(V) &&
159 cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
160 return cast<User>(V);
164 static const Value *GetGEPOperands(const Value *V,
165 SmallVector<Value*, 16> &GEPOps){
166 assert(GEPOps.empty() && "Expect empty list to populate!");
167 GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
168 cast<User>(V)->op_end());
170 // Accumulate all of the chained indexes into the operand array
171 V = cast<User>(V)->getOperand(0);
173 while (const User *G = isGEP(V)) {
174 if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
175 !cast<Constant>(GEPOps[0])->isNullValue())
176 break; // Don't handle folding arbitrary pointer offsets yet...
177 GEPOps.erase(GEPOps.begin()); // Drop the zero index
178 GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
179 V = G->getOperand(0);
184 /// pointsToConstantMemory - Chase pointers until we find a (constant
186 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
187 if (const Value *V = getUnderlyingObject(P))
188 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
189 return GV->isConstant();
193 // Determine if an AllocationInst instruction escapes from the function it is
194 // contained in. If it does not escape, there is no way for another function to
195 // mod/ref it. We do this by looking at its uses and determining if the uses
196 // can escape (recursively).
197 static bool AddressMightEscape(const Value *V) {
198 for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
200 const Instruction *I = cast<Instruction>(*UI);
201 switch (I->getOpcode()) {
202 case Instruction::Load:
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))
211 case Instruction::BitCast:
212 if (!isa<PointerType>(I->getType()))
214 if (AddressMightEscape(I))
217 case Instruction::Ret:
218 // If returned, the address will escape to calling functions, but no
219 // callees could modify it.
228 // getModRefInfo - Check to see if the specified callsite can clobber the
229 // specified memory object. Since we only look at local properties of this
230 // function, we really can't say much about this query. We do, however, use
231 // simple "address taken" analysis on local objects.
233 AliasAnalysis::ModRefResult
234 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
235 if (!isa<Constant>(P))
236 if (const AllocationInst *AI =
237 dyn_cast_or_null<AllocationInst>(getUnderlyingObject(P))) {
238 // Okay, the pointer is to a stack allocated object. If we can prove that
239 // the pointer never "escapes", then we know the call cannot clobber it,
240 // because it simply can't get its address.
241 if (!AddressMightEscape(AI))
244 // If this is a tail call and P points to a stack location, we know that
245 // the tail call cannot access or modify the local stack.
246 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
247 if (CI->isTailCall() && isa<AllocaInst>(AI))
251 // The AliasAnalysis base class has some smarts, lets use them.
252 return AliasAnalysis::getModRefInfo(CS, P, Size);
255 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
256 // as array references. Note that this function is heavily tail recursive.
257 // Hopefully we have a smart C++ compiler. :)
259 AliasAnalysis::AliasResult
260 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
261 const Value *V2, unsigned V2Size) {
262 // Strip off any constant expression casts if they exist
263 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
264 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
265 V1 = CE->getOperand(0);
266 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
267 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
268 V2 = CE->getOperand(0);
270 // Are we checking for alias of the same value?
271 if (V1 == V2) return MustAlias;
273 if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
274 V1->getType() != Type::Int64Ty && V2->getType() != Type::Int64Ty)
275 return NoAlias; // Scalars cannot alias each other
277 // Strip off cast instructions...
278 if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
279 return alias(I->getOperand(0), V1Size, V2, V2Size);
280 if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
281 return alias(V1, V1Size, I->getOperand(0), V2Size);
283 // Figure out what objects these things are pointing to if we can...
284 const Value *O1 = getUnderlyingObject(V1);
285 const Value *O2 = getUnderlyingObject(V2);
287 // Pointing at a discernible object?
290 if (isa<Argument>(O1)) {
291 // Incoming argument cannot alias locally allocated object!
292 if (isa<AllocationInst>(O2)) return NoAlias;
293 // Otherwise, nothing is known...
294 } else if (isa<Argument>(O2)) {
295 // Incoming argument cannot alias locally allocated object!
296 if (isa<AllocationInst>(O1)) return NoAlias;
297 // Otherwise, nothing is known...
298 } else if (O1 != O2) {
299 // If they are two different objects, we know that we have no alias...
303 // If they are the same object, they we can look at the indexes. If they
304 // index off of the object is the same for both pointers, they must alias.
305 // If they are provably different, they must not alias. Otherwise, we
306 // can't tell anything.
310 if (!isa<Argument>(O1) && isa<ConstantPointerNull>(V2))
311 return NoAlias; // Unique values don't alias null
313 if (isa<GlobalVariable>(O1) ||
314 (isa<AllocationInst>(O1) &&
315 !cast<AllocationInst>(O1)->isArrayAllocation()))
316 if (cast<PointerType>(O1->getType())->getElementType()->isSized()) {
317 // If the size of the other access is larger than the total size of the
318 // global/alloca/malloc, it cannot be accessing the global (it's
319 // undefined to load or store bytes before or after an object).
320 const Type *ElTy = cast<PointerType>(O1->getType())->getElementType();
321 unsigned GlobalSize = getTargetData().getTypeSize(ElTy);
322 if (GlobalSize < V2Size && V2Size != ~0U)
328 if (!isa<Argument>(O2) && isa<ConstantPointerNull>(V1))
329 return NoAlias; // Unique values don't alias null
331 if (isa<GlobalVariable>(O2) ||
332 (isa<AllocationInst>(O2) &&
333 !cast<AllocationInst>(O2)->isArrayAllocation()))
334 if (cast<PointerType>(O2->getType())->getElementType()->isSized()) {
335 // If the size of the other access is larger than the total size of the
336 // global/alloca/malloc, it cannot be accessing the object (it's
337 // undefined to load or store bytes before or after an object).
338 const Type *ElTy = cast<PointerType>(O2->getType())->getElementType();
339 unsigned GlobalSize = getTargetData().getTypeSize(ElTy);
340 if (GlobalSize < V1Size && V1Size != ~0U)
345 // If we have two gep instructions with must-alias'ing base pointers, figure
346 // out if the indexes to the GEP tell us anything about the derived pointer.
347 // Note that we also handle chains of getelementptr instructions as well as
348 // constant expression getelementptrs here.
350 if (isGEP(V1) && isGEP(V2)) {
351 // Drill down into the first non-gep value, to test for must-aliasing of
352 // the base pointers.
353 const Value *BasePtr1 = V1, *BasePtr2 = V2;
355 BasePtr1 = cast<User>(BasePtr1)->getOperand(0);
356 } while (isGEP(BasePtr1) &&
357 cast<User>(BasePtr1)->getOperand(1) ==
358 Constant::getNullValue(cast<User>(BasePtr1)->getOperand(1)->getType()));
360 BasePtr2 = cast<User>(BasePtr2)->getOperand(0);
361 } while (isGEP(BasePtr2) &&
362 cast<User>(BasePtr2)->getOperand(1) ==
363 Constant::getNullValue(cast<User>(BasePtr2)->getOperand(1)->getType()));
365 // Do the base pointers alias?
366 AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
367 if (BaseAlias == NoAlias) return NoAlias;
368 if (BaseAlias == MustAlias) {
369 // If the base pointers alias each other exactly, check to see if we can
370 // figure out anything about the resultant pointers, to try to prove
373 // Collect all of the chained GEP operands together into one simple place
374 SmallVector<Value*, 16> GEP1Ops, GEP2Ops;
375 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
376 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
378 // If GetGEPOperands were able to fold to the same must-aliased pointer,
379 // do the comparison.
380 if (BasePtr1 == BasePtr2) {
382 CheckGEPInstructions(BasePtr1->getType(),
383 &GEP1Ops[0], GEP1Ops.size(), V1Size,
385 &GEP2Ops[0], GEP2Ops.size(), V2Size);
386 if (GAlias != MayAlias)
392 // Check to see if these two pointers are related by a getelementptr
393 // instruction. If one pointer is a GEP with a non-zero index of the other
394 // pointer, we know they cannot alias.
398 std::swap(V1Size, V2Size);
401 if (V1Size != ~0U && V2Size != ~0U)
403 SmallVector<Value*, 16> GEPOperands;
404 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
406 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
407 if (R == MustAlias) {
408 // If there is at least one non-zero constant index, we know they cannot
410 bool ConstantFound = false;
411 bool AllZerosFound = true;
412 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
413 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
414 if (!C->isNullValue()) {
415 ConstantFound = true;
416 AllZerosFound = false;
420 AllZerosFound = false;
423 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
424 // the ptr, the end result is a must alias also.
429 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
432 // Otherwise we have to check to see that the distance is more than
433 // the size of the argument... build an index vector that is equal to
434 // the arguments provided, except substitute 0's for any variable
435 // indexes we find...
436 if (cast<PointerType>(
437 BasePtr->getType())->getElementType()->isSized()) {
438 for (unsigned i = 0; i != GEPOperands.size(); ++i)
439 if (!isa<ConstantInt>(GEPOperands[i]))
441 Constant::getNullValue(GEPOperands[i]->getType());
443 getTargetData().getIndexedOffset(BasePtr->getType(),
447 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
457 // This function is used to determin if the indices of two GEP instructions are
458 // equal. V1 and V2 are the indices.
459 static bool IndexOperandsEqual(Value *V1, Value *V2) {
460 if (V1->getType() == V2->getType())
462 if (Constant *C1 = dyn_cast<Constant>(V1))
463 if (Constant *C2 = dyn_cast<Constant>(V2)) {
464 // Sign extend the constants to long types, if necessary
465 if (C1->getType() != Type::Int64Ty)
466 C1 = ConstantExpr::getSExt(C1, Type::Int64Ty);
467 if (C2->getType() != Type::Int64Ty)
468 C2 = ConstantExpr::getSExt(C2, Type::Int64Ty);
474 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
475 /// base pointers. This checks to see if the index expressions preclude the
476 /// pointers from aliasing...
477 AliasAnalysis::AliasResult
478 BasicAliasAnalysis::CheckGEPInstructions(
479 const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
480 const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
481 // We currently can't handle the case when the base pointers have different
482 // primitive types. Since this is uncommon anyway, we are happy being
483 // extremely conservative.
484 if (BasePtr1Ty != BasePtr2Ty)
487 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
489 // Find the (possibly empty) initial sequence of equal values... which are not
490 // necessarily constants.
491 unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
492 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
493 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
494 unsigned UnequalOper = 0;
495 while (UnequalOper != MinOperands &&
496 IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
497 // Advance through the type as we go...
499 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
500 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
502 // If all operands equal each other, then the derived pointers must
503 // alias each other...
505 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
506 "Ran out of type nesting, but not out of operands?");
511 // If we have seen all constant operands, and run out of indexes on one of the
512 // getelementptrs, check to see if the tail of the leftover one is all zeros.
513 // If so, return mustalias.
514 if (UnequalOper == MinOperands) {
515 if (NumGEP1Ops < NumGEP2Ops) {
516 std::swap(GEP1Ops, GEP2Ops);
517 std::swap(NumGEP1Ops, NumGEP2Ops);
520 bool AllAreZeros = true;
521 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
522 if (!isa<Constant>(GEP1Ops[i]) ||
523 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
527 if (AllAreZeros) return MustAlias;
531 // So now we know that the indexes derived from the base pointers,
532 // which are known to alias, are different. We can still determine a
533 // no-alias result if there are differing constant pairs in the index
534 // chain. For example:
535 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
537 // We have to be careful here about array accesses. In particular, consider:
538 // A[1][0] vs A[0][i]
539 // In this case, we don't *know* that the array will be accessed in bounds:
540 // the index could even be negative. Because of this, we have to
541 // conservatively *give up* and return may alias. We disregard differing
542 // array subscripts that are followed by a variable index without going
545 unsigned SizeMax = std::max(G1S, G2S);
546 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
548 // Scan for the first operand that is constant and unequal in the
549 // two getelementptrs...
550 unsigned FirstConstantOper = UnequalOper;
551 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
552 const Value *G1Oper = GEP1Ops[FirstConstantOper];
553 const Value *G2Oper = GEP2Ops[FirstConstantOper];
555 if (G1Oper != G2Oper) // Found non-equal constant indexes...
556 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
557 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
558 if (G1OC->getType() != G2OC->getType()) {
559 // Sign extend both operands to long.
560 if (G1OC->getType() != Type::Int64Ty)
561 G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty);
562 if (G2OC->getType() != Type::Int64Ty)
563 G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty);
564 GEP1Ops[FirstConstantOper] = G1OC;
565 GEP2Ops[FirstConstantOper] = G2OC;
569 // Handle the "be careful" case above: if this is an array/packed
570 // subscript, scan for a subsequent variable array index.
571 if (isa<SequentialType>(BasePtr1Ty)) {
573 cast<SequentialType>(BasePtr1Ty)->getElementType();
574 bool isBadCase = false;
576 for (unsigned Idx = FirstConstantOper+1;
577 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
578 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
579 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
583 NextTy = cast<SequentialType>(NextTy)->getElementType();
586 if (isBadCase) G1OC = 0;
589 // Make sure they are comparable (ie, not constant expressions), and
590 // make sure the GEP with the smaller leading constant is GEP1.
592 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
594 if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
595 if (CV->getZExtValue()) { // If they are comparable and G2 > G1
596 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
597 std::swap(NumGEP1Ops, NumGEP2Ops);
604 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
607 // No shared constant operands, and we ran out of common operands. At this
608 // point, the GEP instructions have run through all of their operands, and we
609 // haven't found evidence that there are any deltas between the GEP's.
610 // However, one GEP may have more operands than the other. If this is the
611 // case, there may still be hope. Check this now.
612 if (FirstConstantOper == MinOperands) {
613 // Make GEP1Ops be the longer one if there is a longer one.
614 if (NumGEP1Ops < NumGEP2Ops) {
615 std::swap(GEP1Ops, GEP2Ops);
616 std::swap(NumGEP1Ops, NumGEP2Ops);
619 // Is there anything to check?
620 if (NumGEP1Ops > MinOperands) {
621 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
622 if (isa<ConstantInt>(GEP1Ops[i]) &&
623 !cast<ConstantInt>(GEP1Ops[i])->isZero()) {
624 // Yup, there's a constant in the tail. Set all variables to
625 // constants in the GEP instruction to make it suiteable for
626 // TargetData::getIndexedOffset.
627 for (i = 0; i != MaxOperands; ++i)
628 if (!isa<ConstantInt>(GEP1Ops[i]))
629 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
630 // Okay, now get the offset. This is the relative offset for the full
632 const TargetData &TD = getTargetData();
633 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
636 // Now check without any constants at the end.
637 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
640 // If the tail provided a bit enough offset, return noalias!
641 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
646 // Couldn't find anything useful.
650 // If there are non-equal constants arguments, then we can figure
651 // out a minimum known delta between the two index expressions... at
652 // this point we know that the first constant index of GEP1 is less
653 // than the first constant index of GEP2.
655 // Advance BasePtr[12]Ty over this first differing constant operand.
656 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
657 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
658 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
659 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
661 // We are going to be using TargetData::getIndexedOffset to determine the
662 // offset that each of the GEP's is reaching. To do this, we have to convert
663 // all variable references to constant references. To do this, we convert the
664 // initial sequence of array subscripts into constant zeros to start with.
665 const Type *ZeroIdxTy = GEPPointerTy;
666 for (unsigned i = 0; i != FirstConstantOper; ++i) {
667 if (!isa<StructType>(ZeroIdxTy))
668 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty);
670 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
671 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
674 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
676 // Loop over the rest of the operands...
677 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
678 const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
679 const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
680 // If they are equal, use a zero index...
681 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
682 if (!isa<ConstantInt>(Op1))
683 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
684 // Otherwise, just keep the constants we have.
687 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
688 // If this is an array index, make sure the array element is in range.
689 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
690 if (Op1C->getZExtValue() >= AT->getNumElements())
691 return MayAlias; // Be conservative with out-of-range accesses
692 } else if (const VectorType *PT = dyn_cast<VectorType>(BasePtr1Ty)) {
693 if (Op1C->getZExtValue() >= PT->getNumElements())
694 return MayAlias; // Be conservative with out-of-range accesses
698 // GEP1 is known to produce a value less than GEP2. To be
699 // conservatively correct, we must assume the largest possible
700 // constant is used in this position. This cannot be the initial
701 // index to the GEP instructions (because we know we have at least one
702 // element before this one with the different constant arguments), so
703 // we know that the current index must be into either a struct or
704 // array. Because we know it's not constant, this cannot be a
705 // structure index. Because of this, we can calculate the maximum
708 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
709 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1);
710 else if (const VectorType *PT = dyn_cast<VectorType>(BasePtr1Ty))
711 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,PT->getNumElements()-1);
717 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
718 // If this is an array index, make sure the array element is in range.
719 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
720 if (Op2C->getZExtValue() >= AT->getNumElements())
721 return MayAlias; // Be conservative with out-of-range accesses
722 } else if (const VectorType *PT = dyn_cast<VectorType>(BasePtr1Ty)) {
723 if (Op2C->getZExtValue() >= PT->getNumElements())
724 return MayAlias; // Be conservative with out-of-range accesses
726 } else { // Conservatively assume the minimum value for this index
727 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
732 if (BasePtr1Ty && Op1) {
733 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
734 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
739 if (BasePtr2Ty && Op2) {
740 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
741 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
747 if (GEPPointerTy->getElementType()->isSized()) {
749 getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
751 getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
752 assert(Offset1<Offset2 && "There is at least one different constant here!");
754 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
755 //cerr << "Determined that these two GEP's don't alias ["
756 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
764 struct VISIBILITY_HIDDEN StringCompare {
765 bool operator()(const char *LHS, const char *RHS) {
766 return strcmp(LHS, RHS) < 0;
771 // Note that this list cannot contain libm functions (such as acos and sqrt)
772 // that set errno on a domain or other error.
773 static const char *DoesntAccessMemoryFns[] = {
774 "abs", "labs", "llabs", "imaxabs", "fabs", "fabsf", "fabsl",
775 "trunc", "truncf", "truncl", "ldexp",
777 "atan", "atanf", "atanl", "atan2", "atan2f", "atan2l",
779 "cos", "cosf", "cosl",
780 "exp", "expf", "expl",
782 "sin", "sinf", "sinl",
783 "tan", "tanf", "tanl", "tanh", "tanhf", "tanhl",
785 "floor", "floorf", "floorl", "ceil", "ceilf", "ceill",
788 "isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower", "isprint"
789 "ispunct", "isspace", "isupper", "isxdigit", "tolower", "toupper",
792 "iswalnum", "iswalpha", "iswcntrl", "iswdigit", "iswgraph", "iswlower",
793 "iswprint", "iswpunct", "iswspace", "iswupper", "iswxdigit",
795 "iswctype", "towctrans", "towlower", "towupper",
799 "isinf", "isnan", "finite",
801 // C99 math functions
802 "copysign", "copysignf", "copysignd",
803 "nexttoward", "nexttowardf", "nexttowardd",
804 "nextafter", "nextafterf", "nextafterd",
807 "__signbit", "__signbitf", "__signbitl",
811 static const char *OnlyReadsMemoryFns[] = {
812 "atoi", "atol", "atof", "atoll", "atoq", "a64l",
813 "bcmp", "memcmp", "memchr", "memrchr", "wmemcmp", "wmemchr",
816 "strcmp", "strcasecmp", "strcoll", "strncmp", "strncasecmp",
817 "strchr", "strcspn", "strlen", "strpbrk", "strrchr", "strspn", "strstr",
821 "wcschr", "wcscmp", "wcscoll", "wcscspn", "wcslen", "wcsncmp", "wcspbrk",
822 "wcsrchr", "wcsspn", "wcsstr",
825 "alphasort", "alphasort64", "versionsort", "versionsort64",
828 "nan", "nanf", "nand",
831 "feof", "ferror", "fileno",
832 "feof_unlocked", "ferror_unlocked", "fileno_unlocked"
835 static ManagedStatic<std::vector<const char*> > NoMemoryTable;
836 static ManagedStatic<std::vector<const char*> > OnlyReadsMemoryTable;
839 AliasAnalysis::ModRefBehavior
840 BasicAliasAnalysis::getModRefBehavior(Function *F, CallSite CS,
841 std::vector<PointerAccessInfo> *Info) {
842 if (!F->isDeclaration()) return UnknownModRefBehavior;
844 static bool Initialized = false;
846 NoMemoryTable->insert(NoMemoryTable->end(),
847 DoesntAccessMemoryFns,
848 DoesntAccessMemoryFns+
849 sizeof(DoesntAccessMemoryFns)/sizeof(DoesntAccessMemoryFns[0]));
851 OnlyReadsMemoryTable->insert(OnlyReadsMemoryTable->end(),
854 sizeof(OnlyReadsMemoryFns)/sizeof(OnlyReadsMemoryFns[0]));
855 #define GET_MODREF_BEHAVIOR
856 #include "llvm/Intrinsics.gen"
857 #undef GET_MODREF_BEHAVIOR
859 // Sort the table the first time through.
860 std::sort(NoMemoryTable->begin(), NoMemoryTable->end(), StringCompare());
861 std::sort(OnlyReadsMemoryTable->begin(), OnlyReadsMemoryTable->end(),
866 std::vector<const char*>::iterator Ptr =
867 std::lower_bound(NoMemoryTable->begin(), NoMemoryTable->end(),
868 F->getName().c_str(), StringCompare());
869 if (Ptr != NoMemoryTable->end() && *Ptr == F->getName())
870 return DoesNotAccessMemory;
872 Ptr = std::lower_bound(OnlyReadsMemoryTable->begin(),
873 OnlyReadsMemoryTable->end(),
874 F->getName().c_str(), StringCompare());
875 if (Ptr != OnlyReadsMemoryTable->end() && *Ptr == F->getName())
876 return OnlyReadsMemory;
878 return UnknownModRefBehavior;
881 // Make sure that anything that uses AliasAnalysis pulls in this file...
882 DEFINING_FILE_FOR(BasicAliasAnalysis)