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/Compiler.h"
26 #include "llvm/Support/GetElementPtrTypeIterator.h"
27 #include "llvm/Support/ManagedStatic.h"
32 /// NoAA - This class implements the -no-aa pass, which always returns "I
33 /// don't know" for alias queries. NoAA is unlike other alias analysis
34 /// implementations, in that it does not chain to a previous analysis. As
35 /// such it doesn't follow many of the rules that other alias analyses must.
37 struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
38 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
39 AU.addRequired<TargetData>();
42 virtual void initializePass() {
43 TD = &getAnalysis<TargetData>();
46 virtual AliasResult alias(const Value *V1, unsigned V1Size,
47 const Value *V2, unsigned V2Size) {
51 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
52 std::vector<PointerAccessInfo> *Info) {
53 return UnknownModRefBehavior;
56 virtual void getArgumentAccesses(Function *F, CallSite CS,
57 std::vector<PointerAccessInfo> &Info) {
58 assert(0 && "This method may not be called on this function!");
61 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
62 virtual bool pointsToConstantMemory(const Value *P) { return false; }
63 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
66 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
69 virtual bool hasNoModRefInfoForCalls() const { return true; }
71 virtual void deleteValue(Value *V) {}
72 virtual void copyValue(Value *From, Value *To) {}
75 // Register this pass...
77 U("no-aa", "No Alias Analysis (always returns 'may' alias)");
79 // Declare that we implement the AliasAnalysis interface
80 RegisterAnalysisGroup<AliasAnalysis> V(U);
81 } // End of anonymous namespace
83 ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
86 /// BasicAliasAnalysis - This is the default alias analysis implementation.
87 /// Because it doesn't chain to a previous alias analysis (like -no-aa), it
88 /// derives from the NoAA class.
89 struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA {
90 AliasResult alias(const Value *V1, unsigned V1Size,
91 const Value *V2, unsigned V2Size);
93 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
94 ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
95 return NoAA::getModRefInfo(CS1,CS2);
98 /// hasNoModRefInfoForCalls - We can provide mod/ref information against
99 /// non-escaping allocations.
100 virtual bool hasNoModRefInfoForCalls() const { return false; }
102 /// pointsToConstantMemory - Chase pointers until we find a (constant
104 bool pointsToConstantMemory(const Value *P);
106 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
107 std::vector<PointerAccessInfo> *Info);
110 // CheckGEPInstructions - Check two GEP instructions with known
111 // must-aliasing base pointers. This checks to see if the index expressions
112 // preclude the pointers from aliasing...
114 CheckGEPInstructions(const Type* BasePtr1Ty, std::vector<Value*> &GEP1Ops,
116 const Type *BasePtr2Ty, std::vector<Value*> &GEP2Ops,
120 // Register this pass...
121 RegisterPass<BasicAliasAnalysis>
122 X("basicaa", "Basic Alias Analysis (default AA impl)");
124 // Declare that we implement the AliasAnalysis interface
125 RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
126 } // End of anonymous namespace
128 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
129 return new BasicAliasAnalysis();
132 // getUnderlyingObject - This traverses the use chain to figure out what object
133 // the specified value points to. If the value points to, or is derived from, a
134 // unique object or an argument, return it.
135 static const Value *getUnderlyingObject(const Value *V) {
136 if (!isa<PointerType>(V->getType())) return 0;
138 // If we are at some type of object, return it. GlobalValues and Allocations
139 // have unique addresses.
140 if (isa<GlobalValue>(V) || isa<AllocationInst>(V) || isa<Argument>(V))
143 // Traverse through different addressing mechanisms...
144 if (const Instruction *I = dyn_cast<Instruction>(V)) {
145 if (isa<BitCastInst>(I) || isa<GetElementPtrInst>(I))
146 return getUnderlyingObject(I->getOperand(0));
147 } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
148 if (CE->getOpcode() == Instruction::BitCast ||
149 CE->getOpcode() == Instruction::GetElementPtr)
150 return getUnderlyingObject(CE->getOperand(0));
155 static const User *isGEP(const Value *V) {
156 if (isa<GetElementPtrInst>(V) ||
157 (isa<ConstantExpr>(V) &&
158 cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
159 return cast<User>(V);
163 static const Value *GetGEPOperands(const Value *V, std::vector<Value*> &GEPOps){
164 assert(GEPOps.empty() && "Expect empty list to populate!");
165 GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
166 cast<User>(V)->op_end());
168 // Accumulate all of the chained indexes into the operand array
169 V = cast<User>(V)->getOperand(0);
171 while (const User *G = isGEP(V)) {
172 if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
173 !cast<Constant>(GEPOps[0])->isNullValue())
174 break; // Don't handle folding arbitrary pointer offsets yet...
175 GEPOps.erase(GEPOps.begin()); // Drop the zero index
176 GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
177 V = G->getOperand(0);
182 /// pointsToConstantMemory - Chase pointers until we find a (constant
184 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
185 if (const Value *V = getUnderlyingObject(P))
186 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
187 return GV->isConstant();
191 // Determine if an AllocationInst instruction escapes from the function it is
192 // contained in. If it does not escape, there is no way for another function to
193 // mod/ref it. We do this by looking at its uses and determining if the uses
194 // can escape (recursively).
195 static bool AddressMightEscape(const Value *V) {
196 for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
198 const Instruction *I = cast<Instruction>(*UI);
199 switch (I->getOpcode()) {
200 case Instruction::Load:
202 case Instruction::Store:
203 if (I->getOperand(0) == V)
204 return true; // Escapes if the pointer is stored.
206 case Instruction::GetElementPtr:
207 if (AddressMightEscape(I))
209 case Instruction::BitCast:
210 if (!isa<PointerType>(I->getType()))
212 if (AddressMightEscape(I))
215 case Instruction::Ret:
216 // If returned, the address will escape to calling functions, but no
217 // callees could modify it.
226 // getModRefInfo - Check to see if the specified callsite can clobber the
227 // specified memory object. Since we only look at local properties of this
228 // function, we really can't say much about this query. We do, however, use
229 // simple "address taken" analysis on local objects.
231 AliasAnalysis::ModRefResult
232 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
233 if (!isa<Constant>(P))
234 if (const AllocationInst *AI =
235 dyn_cast_or_null<AllocationInst>(getUnderlyingObject(P))) {
236 // Okay, the pointer is to a stack allocated object. If we can prove that
237 // the pointer never "escapes", then we know the call cannot clobber it,
238 // because it simply can't get its address.
239 if (!AddressMightEscape(AI))
242 // If this is a tail call and P points to a stack location, we know that
243 // the tail call cannot access or modify the local stack.
244 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
245 if (CI->isTailCall() && isa<AllocaInst>(AI))
249 // The AliasAnalysis base class has some smarts, lets use them.
250 return AliasAnalysis::getModRefInfo(CS, P, Size);
253 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
254 // as array references. Note that this function is heavily tail recursive.
255 // Hopefully we have a smart C++ compiler. :)
257 AliasAnalysis::AliasResult
258 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
259 const Value *V2, unsigned V2Size) {
260 // Strip off any constant expression casts if they exist
261 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
262 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
263 V1 = CE->getOperand(0);
264 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
265 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
266 V2 = CE->getOperand(0);
268 // Are we checking for alias of the same value?
269 if (V1 == V2) return MustAlias;
271 if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
272 V1->getType() != Type::LongTy && V2->getType() != Type::LongTy)
273 return NoAlias; // Scalars cannot alias each other
275 // Strip off cast instructions...
276 if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
277 if (isa<PointerType>(I->getOperand(0)->getType()))
278 return alias(I->getOperand(0), V1Size, V2, V2Size);
279 if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
280 if (isa<PointerType>(I->getOperand(0)->getType()))
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, V1Size, BasePtr2, V2Size);
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 std::vector<Value*> 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(), GEP1Ops, V1Size,
383 BasePtr2->getType(), GEP2Ops, V2Size);
384 if (GAlias != MayAlias)
390 // Check to see if these two pointers are related by a getelementptr
391 // instruction. If one pointer is a GEP with a non-zero index of the other
392 // pointer, we know they cannot alias.
396 std::swap(V1Size, V2Size);
399 if (V1Size != ~0U && V2Size != ~0U)
401 std::vector<Value*> GEPOperands;
402 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
404 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
405 if (R == MustAlias) {
406 // If there is at least one non-zero constant index, we know they cannot
408 bool ConstantFound = false;
409 bool AllZerosFound = true;
410 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
411 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
412 if (!C->isNullValue()) {
413 ConstantFound = true;
414 AllZerosFound = false;
418 AllZerosFound = false;
421 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
422 // the ptr, the end result is a must alias also.
427 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
430 // Otherwise we have to check to see that the distance is more than
431 // the size of the argument... build an index vector that is equal to
432 // the arguments provided, except substitute 0's for any variable
433 // indexes we find...
434 if (cast<PointerType>(
435 BasePtr->getType())->getElementType()->isSized()) {
436 for (unsigned i = 0; i != GEPOperands.size(); ++i)
437 if (!isa<ConstantInt>(GEPOperands[i]))
439 Constant::getNullValue(GEPOperands[i]->getType());
441 getTargetData().getIndexedOffset(BasePtr->getType(), GEPOperands);
443 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
453 // This function is used to determin if the indices of two GEP instructions are
454 // equal. V1 and V2 are the indices.
455 static bool IndexOperandsEqual(Value *V1, Value *V2) {
456 if (V1->getType() == V2->getType())
458 if (Constant *C1 = dyn_cast<Constant>(V1))
459 if (Constant *C2 = dyn_cast<Constant>(V2)) {
460 // Sign extend the constants to long types, if necessary
461 if (C1->getType()->getPrimitiveSizeInBits() < 64)
462 C1 = ConstantExpr::getSExt(C1, Type::LongTy);
463 else if (C1->getType() == Type::ULongTy)
464 C1 = ConstantExpr::getBitCast(C1, Type::LongTy);
465 if (C2->getType()->getPrimitiveSizeInBits() < 64)
466 C2 = ConstantExpr::getSExt(C2, Type::LongTy);
467 else if (C2->getType() == Type::ULongTy)
468 C2 = ConstantExpr::getBitCast(C2, Type::LongTy);
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, std::vector<Value*> &GEP1Ops, unsigned G1S,
480 const Type *BasePtr2Ty, std::vector<Value*> &GEP2Ops, 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 = GEP1Ops.size(), NumGEP2Operands = GEP2Ops.size();
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 (GEP1Ops.size() < GEP2Ops.size()) std::swap(GEP1Ops, GEP2Ops);
517 bool AllAreZeros = true;
518 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
519 if (!isa<Constant>(GEP1Ops[i]) ||
520 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
524 if (AllAreZeros) return MustAlias;
528 // So now we know that the indexes derived from the base pointers,
529 // which are known to alias, are different. We can still determine a
530 // no-alias result if there are differing constant pairs in the index
531 // chain. For example:
532 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
534 // We have to be careful here about array accesses. In particular, consider:
535 // A[1][0] vs A[0][i]
536 // In this case, we don't *know* that the array will be accessed in bounds:
537 // the index could even be negative. Because of this, we have to
538 // conservatively *give up* and return may alias. We disregard differing
539 // array subscripts that are followed by a variable index without going
542 unsigned SizeMax = std::max(G1S, G2S);
543 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
545 // Scan for the first operand that is constant and unequal in the
546 // two getelementptrs...
547 unsigned FirstConstantOper = UnequalOper;
548 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
549 const Value *G1Oper = GEP1Ops[FirstConstantOper];
550 const Value *G2Oper = GEP2Ops[FirstConstantOper];
552 if (G1Oper != G2Oper) // Found non-equal constant indexes...
553 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
554 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
555 if (G1OC->getType() != G2OC->getType()) {
556 // Sign extend both operands to long.
557 if (G1OC->getType()->getPrimitiveSizeInBits() < 64)
558 G1OC = ConstantExpr::getSExt(G1OC, Type::LongTy);
559 else if (G1OC->getType() == Type::ULongTy)
560 G1OC = ConstantExpr::getBitCast(G1OC, Type::LongTy);
561 if (G2OC->getType()->getPrimitiveSizeInBits() < 64)
562 G2OC = ConstantExpr::getSExt(G2OC, Type::LongTy);
563 else if (G2OC->getType() == Type::ULongTy)
564 G2OC = ConstantExpr::getBitCast(G2OC, Type::LongTy);
565 GEP1Ops[FirstConstantOper] = G1OC;
566 GEP2Ops[FirstConstantOper] = G2OC;
570 // Handle the "be careful" case above: if this is an array/packed
571 // subscript, scan for a subsequent variable array index.
572 if (isa<SequentialType>(BasePtr1Ty)) {
574 cast<SequentialType>(BasePtr1Ty)->getElementType();
575 bool isBadCase = false;
577 for (unsigned Idx = FirstConstantOper+1;
578 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
579 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
580 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
584 NextTy = cast<SequentialType>(NextTy)->getElementType();
587 if (isBadCase) G1OC = 0;
590 // Make sure they are comparable (ie, not constant expressions), and
591 // make sure the GEP with the smaller leading constant is GEP1.
593 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
595 if (ConstantBool *CV = dyn_cast<ConstantBool>(Compare)) {
596 if (CV->getValue()) // If they are comparable and G2 > G1
597 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
603 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
606 // No shared constant operands, and we ran out of common operands. At this
607 // point, the GEP instructions have run through all of their operands, and we
608 // haven't found evidence that there are any deltas between the GEP's.
609 // However, one GEP may have more operands than the other. If this is the
610 // case, there may still be hope. Check this now.
611 if (FirstConstantOper == MinOperands) {
612 // Make GEP1Ops be the longer one if there is a longer one.
613 if (GEP1Ops.size() < GEP2Ops.size())
614 std::swap(GEP1Ops, GEP2Ops);
616 // Is there anything to check?
617 if (GEP1Ops.size() > MinOperands) {
618 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
619 if (isa<ConstantInt>(GEP1Ops[i]) &&
620 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
621 // Yup, there's a constant in the tail. Set all variables to
622 // constants in the GEP instruction to make it suiteable for
623 // TargetData::getIndexedOffset.
624 for (i = 0; i != MaxOperands; ++i)
625 if (!isa<ConstantInt>(GEP1Ops[i]))
626 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
627 // Okay, now get the offset. This is the relative offset for the full
629 const TargetData &TD = getTargetData();
630 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops);
632 // Now crop off any constants from the end...
633 GEP1Ops.resize(MinOperands);
634 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops);
636 // If the tail provided a bit enough offset, return noalias!
637 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
642 // Couldn't find anything useful.
646 // If there are non-equal constants arguments, then we can figure
647 // out a minimum known delta between the two index expressions... at
648 // this point we know that the first constant index of GEP1 is less
649 // than the first constant index of GEP2.
651 // Advance BasePtr[12]Ty over this first differing constant operand.
652 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
653 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
654 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
655 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
657 // We are going to be using TargetData::getIndexedOffset to determine the
658 // offset that each of the GEP's is reaching. To do this, we have to convert
659 // all variable references to constant references. To do this, we convert the
660 // initial sequence of array subscripts into constant zeros to start with.
661 const Type *ZeroIdxTy = GEPPointerTy;
662 for (unsigned i = 0; i != FirstConstantOper; ++i) {
663 if (!isa<StructType>(ZeroIdxTy))
664 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::UIntTy);
666 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
667 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
670 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
672 // Loop over the rest of the operands...
673 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
674 const Value *Op1 = i < GEP1Ops.size() ? GEP1Ops[i] : 0;
675 const Value *Op2 = i < GEP2Ops.size() ? GEP2Ops[i] : 0;
676 // If they are equal, use a zero index...
677 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
678 if (!isa<ConstantInt>(Op1))
679 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
680 // Otherwise, just keep the constants we have.
683 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
684 // If this is an array index, make sure the array element is in range.
685 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
686 if (Op1C->getZExtValue() >= AT->getNumElements())
687 return MayAlias; // Be conservative with out-of-range accesses
688 } else if (const PackedType *PT = dyn_cast<PackedType>(BasePtr1Ty)) {
689 if (Op1C->getZExtValue() >= PT->getNumElements())
690 return MayAlias; // Be conservative with out-of-range accesses
694 // GEP1 is known to produce a value less than GEP2. To be
695 // conservatively correct, we must assume the largest possible
696 // constant is used in this position. This cannot be the initial
697 // index to the GEP instructions (because we know we have at least one
698 // element before this one with the different constant arguments), so
699 // we know that the current index must be into either a struct or
700 // array. Because we know it's not constant, this cannot be a
701 // structure index. Because of this, we can calculate the maximum
704 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
705 GEP1Ops[i] = ConstantInt::get(Type::LongTy, AT->getNumElements()-1);
706 else if (const PackedType *PT = dyn_cast<PackedType>(BasePtr1Ty))
707 GEP1Ops[i] = ConstantInt::get(Type::LongTy, PT->getNumElements()-1);
713 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
714 // If this is an array index, make sure the array element is in range.
715 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
716 if (Op2C->getZExtValue() >= AT->getNumElements())
717 return MayAlias; // Be conservative with out-of-range accesses
718 } else if (const PackedType *PT = dyn_cast<PackedType>(BasePtr1Ty)) {
719 if (Op2C->getZExtValue() >= PT->getNumElements())
720 return MayAlias; // Be conservative with out-of-range accesses
722 } else { // Conservatively assume the minimum value for this index
723 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
728 if (BasePtr1Ty && Op1) {
729 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
730 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
735 if (BasePtr2Ty && Op2) {
736 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
737 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
743 if (GEPPointerTy->getElementType()->isSized()) {
744 int64_t Offset1 = getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops);
745 int64_t Offset2 = getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops);
746 assert(Offset1<Offset2 && "There is at least one different constant here!");
748 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
749 //cerr << "Determined that these two GEP's don't alias ["
750 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
758 struct StringCompare {
759 bool operator()(const char *LHS, const char *RHS) {
760 return strcmp(LHS, RHS) < 0;
765 // Note that this list cannot contain libm functions (such as acos and sqrt)
766 // that set errno on a domain or other error.
767 static const char *DoesntAccessMemoryFns[] = {
768 "abs", "labs", "llabs", "imaxabs", "fabs", "fabsf", "fabsl",
769 "trunc", "truncf", "truncl", "ldexp",
771 "atan", "atanf", "atanl", "atan2", "atan2f", "atan2l",
773 "cos", "cosf", "cosl",
774 "exp", "expf", "expl",
776 "sin", "sinf", "sinl",
777 "tan", "tanf", "tanl", "tanh", "tanhf", "tanhl",
779 "floor", "floorf", "floorl", "ceil", "ceilf", "ceill",
782 "isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower", "isprint"
783 "ispunct", "isspace", "isupper", "isxdigit", "tolower", "toupper",
786 "iswalnum", "iswalpha", "iswcntrl", "iswdigit", "iswgraph", "iswlower",
787 "iswprint", "iswpunct", "iswspace", "iswupper", "iswxdigit",
789 "iswctype", "towctrans", "towlower", "towupper",
793 "isinf", "isnan", "finite",
795 // C99 math functions
796 "copysign", "copysignf", "copysignd",
797 "nexttoward", "nexttowardf", "nexttowardd",
798 "nextafter", "nextafterf", "nextafterd",
801 "__signbit", "__signbitf", "__signbitl",
805 static const char *OnlyReadsMemoryFns[] = {
806 "atoi", "atol", "atof", "atoll", "atoq", "a64l",
807 "bcmp", "memcmp", "memchr", "memrchr", "wmemcmp", "wmemchr",
810 "strcmp", "strcasecmp", "strcoll", "strncmp", "strncasecmp",
811 "strchr", "strcspn", "strlen", "strpbrk", "strrchr", "strspn", "strstr",
815 "wcschr", "wcscmp", "wcscoll", "wcscspn", "wcslen", "wcsncmp", "wcspbrk",
816 "wcsrchr", "wcsspn", "wcsstr",
819 "alphasort", "alphasort64", "versionsort", "versionsort64",
822 "nan", "nanf", "nand",
825 "feof", "ferror", "fileno",
826 "feof_unlocked", "ferror_unlocked", "fileno_unlocked"
829 static ManagedStatic<std::vector<const char*> > NoMemoryTable;
830 static ManagedStatic<std::vector<const char*> > OnlyReadsMemoryTable;
833 AliasAnalysis::ModRefBehavior
834 BasicAliasAnalysis::getModRefBehavior(Function *F, CallSite CS,
835 std::vector<PointerAccessInfo> *Info) {
836 if (!F->isExternal()) return UnknownModRefBehavior;
838 static bool Initialized = false;
840 NoMemoryTable->insert(NoMemoryTable->end(),
841 DoesntAccessMemoryFns,
842 DoesntAccessMemoryFns+
843 sizeof(DoesntAccessMemoryFns)/sizeof(DoesntAccessMemoryFns[0]));
845 OnlyReadsMemoryTable->insert(OnlyReadsMemoryTable->end(),
848 sizeof(OnlyReadsMemoryFns)/sizeof(OnlyReadsMemoryFns[0]));
849 #define GET_MODREF_BEHAVIOR
850 #include "llvm/Intrinsics.gen"
851 #undef GET_MODREF_BEHAVIOR
853 // Sort the table the first time through.
854 std::sort(NoMemoryTable->begin(), NoMemoryTable->end(), StringCompare());
855 std::sort(OnlyReadsMemoryTable->begin(), OnlyReadsMemoryTable->end(),
860 std::vector<const char*>::iterator Ptr =
861 std::lower_bound(NoMemoryTable->begin(), NoMemoryTable->end(),
862 F->getName().c_str(), StringCompare());
863 if (Ptr != NoMemoryTable->end() && *Ptr == F->getName())
864 return DoesNotAccessMemory;
866 Ptr = std::lower_bound(OnlyReadsMemoryTable->begin(),
867 OnlyReadsMemoryTable->end(),
868 F->getName().c_str(), StringCompare());
869 if (Ptr != OnlyReadsMemoryTable->end() && *Ptr == F->getName())
870 return OnlyReadsMemory;
872 return UnknownModRefBehavior;
875 // Make sure that anything that uses AliasAnalysis pulls in this file...
876 DEFINING_FILE_FOR(BasicAliasAnalysis)