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/ParameterAttributes.h"
22 #include "llvm/GlobalVariable.h"
23 #include "llvm/Instructions.h"
24 #include "llvm/Intrinsics.h"
25 #include "llvm/Pass.h"
26 #include "llvm/Target/TargetData.h"
27 #include "llvm/ADT/SmallVector.h"
28 #include "llvm/ADT/StringMap.h"
29 #include "llvm/ADT/BitVector.h"
30 #include "llvm/Support/Compiler.h"
31 #include "llvm/Support/GetElementPtrTypeIterator.h"
32 #include "llvm/Support/ManagedStatic.h"
37 /// NoAA - This class implements the -no-aa pass, which always returns "I
38 /// don't know" for alias queries. NoAA is unlike other alias analysis
39 /// implementations, in that it does not chain to a previous analysis. As
40 /// such it doesn't follow many of the rules that other alias analyses must.
42 struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
43 static char ID; // Class identification, replacement for typeinfo
44 NoAA() : ImmutablePass((intptr_t)&ID) {}
45 explicit NoAA(intptr_t PID) : ImmutablePass(PID) { }
47 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
48 AU.addRequired<TargetData>();
51 virtual void initializePass() {
52 TD = &getAnalysis<TargetData>();
55 virtual AliasResult alias(const Value *V1, unsigned V1Size,
56 const Value *V2, unsigned V2Size) {
60 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
61 std::vector<PointerAccessInfo> *Info) {
62 return UnknownModRefBehavior;
65 virtual void getArgumentAccesses(Function *F, CallSite CS,
66 std::vector<PointerAccessInfo> &Info) {
67 assert(0 && "This method may not be called on this function!");
70 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
71 virtual bool pointsToConstantMemory(const Value *P) { return false; }
72 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
75 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
78 virtual bool hasNoModRefInfoForCalls() const { return true; }
80 virtual void deleteValue(Value *V) {}
81 virtual void copyValue(Value *From, Value *To) {}
84 // Register this pass...
87 U("no-aa", "No Alias Analysis (always returns 'may' alias)");
89 // Declare that we implement the AliasAnalysis interface
90 RegisterAnalysisGroup<AliasAnalysis> V(U);
91 } // End of anonymous namespace
93 ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
96 /// BasicAliasAnalysis - This is the default alias analysis implementation.
97 /// Because it doesn't chain to a previous alias analysis (like -no-aa), it
98 /// derives from the NoAA class.
99 struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA {
100 static char ID; // Class identification, replacement for typeinfo
101 BasicAliasAnalysis() : NoAA((intptr_t)&ID) { }
102 AliasResult alias(const Value *V1, unsigned V1Size,
103 const Value *V2, unsigned V2Size);
105 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
106 ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
107 return NoAA::getModRefInfo(CS1,CS2);
110 /// hasNoModRefInfoForCalls - We can provide mod/ref information against
111 /// non-escaping allocations.
112 virtual bool hasNoModRefInfoForCalls() const { return false; }
114 /// pointsToConstantMemory - Chase pointers until we find a (constant
116 bool pointsToConstantMemory(const Value *P);
118 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
119 std::vector<PointerAccessInfo> *Info);
122 // CheckGEPInstructions - Check two GEP instructions with known
123 // must-aliasing base pointers. This checks to see if the index expressions
124 // preclude the pointers from aliasing...
126 CheckGEPInstructions(const Type* BasePtr1Ty,
127 Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size,
128 const Type *BasePtr2Ty,
129 Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size);
132 // Register this pass...
133 char BasicAliasAnalysis::ID = 0;
134 RegisterPass<BasicAliasAnalysis>
135 X("basicaa", "Basic Alias Analysis (default AA impl)");
137 // Declare that we implement the AliasAnalysis interface
138 RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
139 } // End of anonymous namespace
141 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
142 return new BasicAliasAnalysis();
145 // getUnderlyingObject - This traverses the use chain to figure out what object
146 // the specified value points to. If the value points to, or is derived from, a
147 // unique object or an argument, return it.
148 static const Value *getUnderlyingObject(const Value *V) {
149 if (!isa<PointerType>(V->getType())) return 0;
151 // If we are at some type of object, return it. GlobalValues and Allocations
152 // have unique addresses.
153 if (isa<GlobalValue>(V) || isa<AllocationInst>(V) || isa<Argument>(V))
156 // Traverse through different addressing mechanisms...
157 if (const Instruction *I = dyn_cast<Instruction>(V)) {
158 if (isa<BitCastInst>(I) || isa<GetElementPtrInst>(I))
159 return getUnderlyingObject(I->getOperand(0));
160 } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
161 if (CE->getOpcode() == Instruction::BitCast ||
162 CE->getOpcode() == Instruction::GetElementPtr)
163 return getUnderlyingObject(CE->getOperand(0));
168 static const User *isGEP(const Value *V) {
169 if (isa<GetElementPtrInst>(V) ||
170 (isa<ConstantExpr>(V) &&
171 cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
172 return cast<User>(V);
176 static const Value *GetGEPOperands(const Value *V,
177 SmallVector<Value*, 16> &GEPOps){
178 assert(GEPOps.empty() && "Expect empty list to populate!");
179 GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
180 cast<User>(V)->op_end());
182 // Accumulate all of the chained indexes into the operand array
183 V = cast<User>(V)->getOperand(0);
185 while (const User *G = isGEP(V)) {
186 if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
187 !cast<Constant>(GEPOps[0])->isNullValue())
188 break; // Don't handle folding arbitrary pointer offsets yet...
189 GEPOps.erase(GEPOps.begin()); // Drop the zero index
190 GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
191 V = G->getOperand(0);
196 /// pointsToConstantMemory - Chase pointers until we find a (constant
198 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
199 if (const Value *V = getUnderlyingObject(P))
200 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
201 return GV->isConstant();
205 // Determine if an AllocationInst instruction escapes from the function it is
206 // contained in. If it does not escape, there is no way for another function to
207 // mod/ref it. We do this by looking at its uses and determining if the uses
208 // can escape (recursively).
209 static bool AddressMightEscape(const Value *V) {
210 for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
212 const Instruction *I = cast<Instruction>(*UI);
213 switch (I->getOpcode()) {
214 case Instruction::Load:
216 case Instruction::Store:
217 if (I->getOperand(0) == V)
218 return true; // Escapes if the pointer is stored.
220 case Instruction::GetElementPtr:
221 if (AddressMightEscape(I))
224 case Instruction::BitCast:
225 if (!isa<PointerType>(I->getType()))
227 if (AddressMightEscape(I))
230 case Instruction::Ret:
231 // If returned, the address will escape to calling functions, but no
232 // callees could modify it.
241 // getModRefInfo - Check to see if the specified callsite can clobber the
242 // specified memory object. Since we only look at local properties of this
243 // function, we really can't say much about this query. We do, however, use
244 // simple "address taken" analysis on local objects.
246 AliasAnalysis::ModRefResult
247 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
248 if (!isa<Constant>(P))
249 if (const AllocationInst *AI =
250 dyn_cast_or_null<AllocationInst>(getUnderlyingObject(P))) {
251 // Okay, the pointer is to a stack allocated object. If we can prove that
252 // the pointer never "escapes", then we know the call cannot clobber it,
253 // because it simply can't get its address.
254 if (!AddressMightEscape(AI))
257 // If this is a tail call and P points to a stack location, we know that
258 // the tail call cannot access or modify the local stack.
259 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
260 if (CI->isTailCall() && isa<AllocaInst>(AI))
264 // The AliasAnalysis base class has some smarts, lets use them.
265 return AliasAnalysis::getModRefInfo(CS, P, Size);
268 static bool isNoAliasArgument(const Argument *Arg) {
269 const Function *Func = Arg->getParent();
270 const ParamAttrsList *Attr = Func->getFunctionType()->getParamAttrs();
273 for (Function::const_arg_iterator I = Func->arg_begin(),
274 E = Func->arg_end(); I != E; ++I, ++Idx) {
276 Attr->paramHasAttr(Idx, ParamAttr::NoAlias))
283 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
284 // as array references. Note that this function is heavily tail recursive.
285 // Hopefully we have a smart C++ compiler. :)
287 AliasAnalysis::AliasResult
288 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
289 const Value *V2, unsigned V2Size) {
290 // Strip off any constant expression casts if they exist
291 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
292 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
293 V1 = CE->getOperand(0);
294 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
295 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
296 V2 = CE->getOperand(0);
298 // Are we checking for alias of the same value?
299 if (V1 == V2) return MustAlias;
301 if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
302 V1->getType() != Type::Int64Ty && V2->getType() != Type::Int64Ty)
303 return NoAlias; // Scalars cannot alias each other
305 // Strip off cast instructions...
306 if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
307 return alias(I->getOperand(0), V1Size, V2, V2Size);
308 if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
309 return alias(V1, V1Size, I->getOperand(0), V2Size);
311 // Figure out what objects these things are pointing to if we can...
312 const Value *O1 = getUnderlyingObject(V1);
313 const Value *O2 = getUnderlyingObject(V2);
315 // Pointing at a discernible object?
318 if (const Argument *O1Arg = dyn_cast<Argument>(O1)) {
319 // Incoming argument cannot alias locally allocated object!
320 if (isa<AllocationInst>(O2)) return NoAlias;
322 // If they are two different objects, and one is a noalias argument
323 // then they do not alias.
324 if (O1 != O2 && isNoAliasArgument(O1Arg))
327 // Otherwise, nothing is known...
330 if (const Argument *O2Arg = dyn_cast<Argument>(O2)) {
331 // Incoming argument cannot alias locally allocated object!
332 if (isa<AllocationInst>(O1)) return NoAlias;
334 // If they are two different objects, and one is a noalias argument
335 // then they do not alias.
336 if (O1 != O2 && isNoAliasArgument(O2Arg))
339 // Otherwise, nothing is known...
340 } else if (O1 != O2) {
341 // If they are two different objects, we know that we have no alias...
345 // If they are the same object, they we can look at the indexes. If they
346 // index off of the object is the same for both pointers, they must alias.
347 // If they are provably different, they must not alias. Otherwise, we
348 // can't tell anything.
352 if (!isa<Argument>(O1) && isa<ConstantPointerNull>(V2))
353 return NoAlias; // Unique values don't alias null
355 if (isa<GlobalVariable>(O1) ||
356 (isa<AllocationInst>(O1) &&
357 !cast<AllocationInst>(O1)->isArrayAllocation()))
358 if (cast<PointerType>(O1->getType())->getElementType()->isSized()) {
359 // If the size of the other access is larger than the total size of the
360 // global/alloca/malloc, it cannot be accessing the global (it's
361 // undefined to load or store bytes before or after an object).
362 const Type *ElTy = cast<PointerType>(O1->getType())->getElementType();
363 unsigned GlobalSize = getTargetData().getTypeSize(ElTy);
364 if (GlobalSize < V2Size && V2Size != ~0U)
370 if (!isa<Argument>(O2) && isa<ConstantPointerNull>(V1))
371 return NoAlias; // Unique values don't alias null
373 if (isa<GlobalVariable>(O2) ||
374 (isa<AllocationInst>(O2) &&
375 !cast<AllocationInst>(O2)->isArrayAllocation()))
376 if (cast<PointerType>(O2->getType())->getElementType()->isSized()) {
377 // If the size of the other access is larger than the total size of the
378 // global/alloca/malloc, it cannot be accessing the object (it's
379 // undefined to load or store bytes before or after an object).
380 const Type *ElTy = cast<PointerType>(O2->getType())->getElementType();
381 unsigned GlobalSize = getTargetData().getTypeSize(ElTy);
382 if (GlobalSize < V1Size && V1Size != ~0U)
387 // If we have two gep instructions with must-alias'ing base pointers, figure
388 // out if the indexes to the GEP tell us anything about the derived pointer.
389 // Note that we also handle chains of getelementptr instructions as well as
390 // constant expression getelementptrs here.
392 if (isGEP(V1) && isGEP(V2)) {
393 // Drill down into the first non-gep value, to test for must-aliasing of
394 // the base pointers.
395 const Value *BasePtr1 = V1, *BasePtr2 = V2;
397 BasePtr1 = cast<User>(BasePtr1)->getOperand(0);
398 } while (isGEP(BasePtr1) &&
399 cast<User>(BasePtr1)->getOperand(1) ==
400 Constant::getNullValue(cast<User>(BasePtr1)->getOperand(1)->getType()));
402 BasePtr2 = cast<User>(BasePtr2)->getOperand(0);
403 } while (isGEP(BasePtr2) &&
404 cast<User>(BasePtr2)->getOperand(1) ==
405 Constant::getNullValue(cast<User>(BasePtr2)->getOperand(1)->getType()));
407 // Do the base pointers alias?
408 AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
409 if (BaseAlias == NoAlias) return NoAlias;
410 if (BaseAlias == MustAlias) {
411 // If the base pointers alias each other exactly, check to see if we can
412 // figure out anything about the resultant pointers, to try to prove
415 // Collect all of the chained GEP operands together into one simple place
416 SmallVector<Value*, 16> GEP1Ops, GEP2Ops;
417 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
418 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
420 // If GetGEPOperands were able to fold to the same must-aliased pointer,
421 // do the comparison.
422 if (BasePtr1 == BasePtr2) {
424 CheckGEPInstructions(BasePtr1->getType(),
425 &GEP1Ops[0], GEP1Ops.size(), V1Size,
427 &GEP2Ops[0], GEP2Ops.size(), V2Size);
428 if (GAlias != MayAlias)
434 // Check to see if these two pointers are related by a getelementptr
435 // instruction. If one pointer is a GEP with a non-zero index of the other
436 // pointer, we know they cannot alias.
440 std::swap(V1Size, V2Size);
443 if (V1Size != ~0U && V2Size != ~0U)
445 SmallVector<Value*, 16> GEPOperands;
446 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
448 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
449 if (R == MustAlias) {
450 // If there is at least one non-zero constant index, we know they cannot
452 bool ConstantFound = false;
453 bool AllZerosFound = true;
454 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
455 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
456 if (!C->isNullValue()) {
457 ConstantFound = true;
458 AllZerosFound = false;
462 AllZerosFound = false;
465 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
466 // the ptr, the end result is a must alias also.
471 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
474 // Otherwise we have to check to see that the distance is more than
475 // the size of the argument... build an index vector that is equal to
476 // the arguments provided, except substitute 0's for any variable
477 // indexes we find...
478 if (cast<PointerType>(
479 BasePtr->getType())->getElementType()->isSized()) {
480 for (unsigned i = 0; i != GEPOperands.size(); ++i)
481 if (!isa<ConstantInt>(GEPOperands[i]))
483 Constant::getNullValue(GEPOperands[i]->getType());
485 getTargetData().getIndexedOffset(BasePtr->getType(),
489 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
499 // This function is used to determin if the indices of two GEP instructions are
500 // equal. V1 and V2 are the indices.
501 static bool IndexOperandsEqual(Value *V1, Value *V2) {
502 if (V1->getType() == V2->getType())
504 if (Constant *C1 = dyn_cast<Constant>(V1))
505 if (Constant *C2 = dyn_cast<Constant>(V2)) {
506 // Sign extend the constants to long types, if necessary
507 if (C1->getType() != Type::Int64Ty)
508 C1 = ConstantExpr::getSExt(C1, Type::Int64Ty);
509 if (C2->getType() != Type::Int64Ty)
510 C2 = ConstantExpr::getSExt(C2, Type::Int64Ty);
516 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
517 /// base pointers. This checks to see if the index expressions preclude the
518 /// pointers from aliasing...
519 AliasAnalysis::AliasResult
520 BasicAliasAnalysis::CheckGEPInstructions(
521 const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
522 const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
523 // We currently can't handle the case when the base pointers have different
524 // primitive types. Since this is uncommon anyway, we are happy being
525 // extremely conservative.
526 if (BasePtr1Ty != BasePtr2Ty)
529 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
531 // Find the (possibly empty) initial sequence of equal values... which are not
532 // necessarily constants.
533 unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
534 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
535 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
536 unsigned UnequalOper = 0;
537 while (UnequalOper != MinOperands &&
538 IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
539 // Advance through the type as we go...
541 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
542 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
544 // If all operands equal each other, then the derived pointers must
545 // alias each other...
547 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
548 "Ran out of type nesting, but not out of operands?");
553 // If we have seen all constant operands, and run out of indexes on one of the
554 // getelementptrs, check to see if the tail of the leftover one is all zeros.
555 // If so, return mustalias.
556 if (UnequalOper == MinOperands) {
557 if (NumGEP1Ops < NumGEP2Ops) {
558 std::swap(GEP1Ops, GEP2Ops);
559 std::swap(NumGEP1Ops, NumGEP2Ops);
562 bool AllAreZeros = true;
563 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
564 if (!isa<Constant>(GEP1Ops[i]) ||
565 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
569 if (AllAreZeros) return MustAlias;
573 // So now we know that the indexes derived from the base pointers,
574 // which are known to alias, are different. We can still determine a
575 // no-alias result if there are differing constant pairs in the index
576 // chain. For example:
577 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
579 // We have to be careful here about array accesses. In particular, consider:
580 // A[1][0] vs A[0][i]
581 // In this case, we don't *know* that the array will be accessed in bounds:
582 // the index could even be negative. Because of this, we have to
583 // conservatively *give up* and return may alias. We disregard differing
584 // array subscripts that are followed by a variable index without going
587 unsigned SizeMax = std::max(G1S, G2S);
588 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
590 // Scan for the first operand that is constant and unequal in the
591 // two getelementptrs...
592 unsigned FirstConstantOper = UnequalOper;
593 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
594 const Value *G1Oper = GEP1Ops[FirstConstantOper];
595 const Value *G2Oper = GEP2Ops[FirstConstantOper];
597 if (G1Oper != G2Oper) // Found non-equal constant indexes...
598 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
599 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
600 if (G1OC->getType() != G2OC->getType()) {
601 // Sign extend both operands to long.
602 if (G1OC->getType() != Type::Int64Ty)
603 G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty);
604 if (G2OC->getType() != Type::Int64Ty)
605 G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty);
606 GEP1Ops[FirstConstantOper] = G1OC;
607 GEP2Ops[FirstConstantOper] = G2OC;
611 // Handle the "be careful" case above: if this is an array/vector
612 // subscript, scan for a subsequent variable array index.
613 if (isa<SequentialType>(BasePtr1Ty)) {
615 cast<SequentialType>(BasePtr1Ty)->getElementType();
616 bool isBadCase = false;
618 for (unsigned Idx = FirstConstantOper+1;
619 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
620 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
621 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
625 NextTy = cast<SequentialType>(NextTy)->getElementType();
628 if (isBadCase) G1OC = 0;
631 // Make sure they are comparable (ie, not constant expressions), and
632 // make sure the GEP with the smaller leading constant is GEP1.
634 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
636 if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
637 if (CV->getZExtValue()) { // If they are comparable and G2 > G1
638 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
639 std::swap(NumGEP1Ops, NumGEP2Ops);
646 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
649 // No shared constant operands, and we ran out of common operands. At this
650 // point, the GEP instructions have run through all of their operands, and we
651 // haven't found evidence that there are any deltas between the GEP's.
652 // However, one GEP may have more operands than the other. If this is the
653 // case, there may still be hope. Check this now.
654 if (FirstConstantOper == MinOperands) {
655 // Make GEP1Ops be the longer one if there is a longer one.
656 if (NumGEP1Ops < NumGEP2Ops) {
657 std::swap(GEP1Ops, GEP2Ops);
658 std::swap(NumGEP1Ops, NumGEP2Ops);
661 // Is there anything to check?
662 if (NumGEP1Ops > MinOperands) {
663 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
664 if (isa<ConstantInt>(GEP1Ops[i]) &&
665 !cast<ConstantInt>(GEP1Ops[i])->isZero()) {
666 // Yup, there's a constant in the tail. Set all variables to
667 // constants in the GEP instruction to make it suiteable for
668 // TargetData::getIndexedOffset.
669 for (i = 0; i != MaxOperands; ++i)
670 if (!isa<ConstantInt>(GEP1Ops[i]))
671 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
672 // Okay, now get the offset. This is the relative offset for the full
674 const TargetData &TD = getTargetData();
675 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
678 // Now check without any constants at the end.
679 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
682 // If the tail provided a bit enough offset, return noalias!
683 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
688 // Couldn't find anything useful.
692 // If there are non-equal constants arguments, then we can figure
693 // out a minimum known delta between the two index expressions... at
694 // this point we know that the first constant index of GEP1 is less
695 // than the first constant index of GEP2.
697 // Advance BasePtr[12]Ty over this first differing constant operand.
698 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
699 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
700 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
701 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
703 // We are going to be using TargetData::getIndexedOffset to determine the
704 // offset that each of the GEP's is reaching. To do this, we have to convert
705 // all variable references to constant references. To do this, we convert the
706 // initial sequence of array subscripts into constant zeros to start with.
707 const Type *ZeroIdxTy = GEPPointerTy;
708 for (unsigned i = 0; i != FirstConstantOper; ++i) {
709 if (!isa<StructType>(ZeroIdxTy))
710 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty);
712 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
713 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
716 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
718 // Loop over the rest of the operands...
719 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
720 const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
721 const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
722 // If they are equal, use a zero index...
723 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
724 if (!isa<ConstantInt>(Op1))
725 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
726 // Otherwise, just keep the constants we have.
729 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
730 // If this is an array index, make sure the array element is in range.
731 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
732 if (Op1C->getZExtValue() >= AT->getNumElements())
733 return MayAlias; // Be conservative with out-of-range accesses
734 } else if (const VectorType *PT = dyn_cast<VectorType>(BasePtr1Ty)) {
735 if (Op1C->getZExtValue() >= PT->getNumElements())
736 return MayAlias; // Be conservative with out-of-range accesses
740 // GEP1 is known to produce a value less than GEP2. To be
741 // conservatively correct, we must assume the largest possible
742 // constant is used in this position. This cannot be the initial
743 // index to the GEP instructions (because we know we have at least one
744 // element before this one with the different constant arguments), so
745 // we know that the current index must be into either a struct or
746 // array. Because we know it's not constant, this cannot be a
747 // structure index. Because of this, we can calculate the maximum
750 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
751 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1);
752 else if (const VectorType *PT = dyn_cast<VectorType>(BasePtr1Ty))
753 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,PT->getNumElements()-1);
759 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
760 // If this is an array index, make sure the array element is in range.
761 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
762 if (Op2C->getZExtValue() >= AT->getNumElements())
763 return MayAlias; // Be conservative with out-of-range accesses
764 } else if (const VectorType *PT = dyn_cast<VectorType>(BasePtr1Ty)) {
765 if (Op2C->getZExtValue() >= PT->getNumElements())
766 return MayAlias; // Be conservative with out-of-range accesses
768 } else { // Conservatively assume the minimum value for this index
769 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
774 if (BasePtr1Ty && Op1) {
775 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
776 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
781 if (BasePtr2Ty && Op2) {
782 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
783 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
789 if (GEPPointerTy->getElementType()->isSized()) {
791 getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
793 getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
794 assert(Offset1<Offset2 && "There is at least one different constant here!");
796 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
797 //cerr << "Determined that these two GEP's don't alias ["
798 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
806 struct VISIBILITY_HIDDEN StringCompare {
807 bool operator()(const char *LHS, const char *RHS) {
808 return strcmp(LHS, RHS) < 0;
813 // Note that this list cannot contain libm functions (such as acos and sqrt)
814 // that set errno on a domain or other error.
815 static const char *DoesntAccessMemoryFns[] = {
816 "abs", "labs", "llabs", "imaxabs", "fabs", "fabsf", "fabsl",
817 "trunc", "truncf", "truncl", "ldexp",
819 "atan", "atanf", "atanl", "atan2", "atan2f", "atan2l",
821 "cos", "cosf", "cosl",
822 "exp", "expf", "expl",
824 "sin", "sinf", "sinl",
825 "tan", "tanf", "tanl", "tanh", "tanhf", "tanhl",
827 "floor", "floorf", "floorl", "ceil", "ceilf", "ceill",
830 "isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower", "isprint"
831 "ispunct", "isspace", "isupper", "isxdigit", "tolower", "toupper",
834 "iswalnum", "iswalpha", "iswcntrl", "iswdigit", "iswgraph", "iswlower",
835 "iswprint", "iswpunct", "iswspace", "iswupper", "iswxdigit",
837 "iswctype", "towctrans", "towlower", "towupper",
841 "isinf", "isnan", "finite",
843 // C99 math functions
844 "copysign", "copysignf", "copysignd",
845 "nexttoward", "nexttowardf", "nexttowardd",
846 "nextafter", "nextafterf", "nextafterd",
849 "__signbit", "__signbitf", "__signbitl",
853 static const char *OnlyReadsMemoryFns[] = {
854 "atoi", "atol", "atof", "atoll", "atoq", "a64l",
855 "bcmp", "memcmp", "memchr", "memrchr", "wmemcmp", "wmemchr",
858 "strcmp", "strcasecmp", "strcoll", "strncmp", "strncasecmp",
859 "strchr", "strcspn", "strlen", "strpbrk", "strrchr", "strspn", "strstr",
863 "wcschr", "wcscmp", "wcscoll", "wcscspn", "wcslen", "wcsncmp", "wcspbrk",
864 "wcsrchr", "wcsspn", "wcsstr",
867 "alphasort", "alphasort64", "versionsort", "versionsort64",
870 "nan", "nanf", "nand",
873 "feof", "ferror", "fileno",
874 "feof_unlocked", "ferror_unlocked", "fileno_unlocked"
877 static ManagedStatic<std::vector<const char*> > NoMemoryTable;
878 static ManagedStatic<std::vector<const char*> > OnlyReadsMemoryTable;
880 static ManagedStatic<BitVector> NoMemoryIntrinsics;
881 static ManagedStatic<BitVector> OnlyReadsMemoryIntrinsics;
884 AliasAnalysis::ModRefBehavior
885 BasicAliasAnalysis::getModRefBehavior(Function *F, CallSite CS,
886 std::vector<PointerAccessInfo> *Info) {
887 if (!F->isDeclaration()) return UnknownModRefBehavior;
889 static bool Initialized = false;
891 NoMemoryTable->insert(NoMemoryTable->end(),
892 DoesntAccessMemoryFns,
893 DoesntAccessMemoryFns+
894 sizeof(DoesntAccessMemoryFns)/sizeof(DoesntAccessMemoryFns[0]));
896 OnlyReadsMemoryTable->insert(OnlyReadsMemoryTable->end(),
899 sizeof(OnlyReadsMemoryFns)/sizeof(OnlyReadsMemoryFns[0]));
901 // Sort the table the first time through.
902 std::sort(NoMemoryTable->begin(), NoMemoryTable->end(), StringCompare());
903 std::sort(OnlyReadsMemoryTable->begin(), OnlyReadsMemoryTable->end(),
906 NoMemoryIntrinsics->resize(Intrinsic::num_intrinsics);
907 OnlyReadsMemoryIntrinsics->resize(Intrinsic::num_intrinsics);
908 #define GET_MODREF_BEHAVIOR
909 #include "llvm/Intrinsics.gen"
910 #undef GET_MODREF_BEHAVIOR
915 // If this is an intrinsic, we can use lookup tables
916 if (unsigned id = F->getIntrinsicID()) {
917 if (NoMemoryIntrinsics->test(id))
918 return DoesNotAccessMemory;
919 if (OnlyReadsMemoryIntrinsics->test(id))
920 return OnlyReadsMemory;
922 return UnknownModRefBehavior;
925 ValueName *Name = F->getValueName();
926 unsigned NameLen = Name->getKeyLength();
927 const char *NamePtr = Name->getKeyData();
929 // If there is an embedded nul character in the function name, we can never
931 if (strlen(NamePtr) != NameLen)
932 return UnknownModRefBehavior;
934 std::vector<const char*>::iterator Ptr =
935 std::lower_bound(NoMemoryTable->begin(), NoMemoryTable->end(),
936 NamePtr, StringCompare());
937 if (Ptr != NoMemoryTable->end() && strcmp(*Ptr, NamePtr) == 0)
938 return DoesNotAccessMemory;
940 Ptr = std::lower_bound(OnlyReadsMemoryTable->begin(),
941 OnlyReadsMemoryTable->end(),
942 NamePtr, StringCompare());
943 if (Ptr != OnlyReadsMemoryTable->end() && strcmp(*Ptr, NamePtr) == 0)
944 return OnlyReadsMemory;
946 return UnknownModRefBehavior;
949 // Make sure that anything that uses AliasAnalysis pulls in this file...
950 DEFINING_FILE_FOR(BasicAliasAnalysis)