1 //===- BasicAliasAnalysis.cpp - Local Alias Analysis Impl -----------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // 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/IntrinsicInst.h"
25 #include "llvm/Pass.h"
26 #include "llvm/Target/TargetData.h"
27 #include "llvm/ADT/SmallVector.h"
28 #include "llvm/ADT/STLExtras.h"
29 #include "llvm/Support/Compiler.h"
30 #include "llvm/Support/GetElementPtrTypeIterator.h"
31 #include "llvm/Support/ManagedStatic.h"
36 /// NoAA - This class implements the -no-aa pass, which always returns "I
37 /// don't know" for alias queries. NoAA is unlike other alias analysis
38 /// implementations, in that it does not chain to a previous analysis. As
39 /// such it doesn't follow many of the rules that other alias analyses must.
41 struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
42 static char ID; // Class identification, replacement for typeinfo
43 NoAA() : ImmutablePass((intptr_t)&ID) {}
44 explicit NoAA(intptr_t PID) : ImmutablePass(PID) { }
46 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
47 AU.addRequired<TargetData>();
50 virtual void initializePass() {
51 TD = &getAnalysis<TargetData>();
54 virtual AliasResult alias(const Value *V1, unsigned V1Size,
55 const Value *V2, unsigned V2Size) {
59 virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS,
60 std::vector<PointerAccessInfo> *Info) {
61 return UnknownModRefBehavior;
64 virtual void getArgumentAccesses(Function *F, CallSite CS,
65 std::vector<PointerAccessInfo> &Info) {
66 assert(0 && "This method may not be called on this function!");
69 virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
70 virtual bool pointsToConstantMemory(const Value *P) { return false; }
71 virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
74 virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
77 virtual bool hasNoModRefInfoForCalls() const { return true; }
79 virtual void deleteValue(Value *V) {}
80 virtual void copyValue(Value *From, Value *To) {}
83 // Register this pass...
86 U("no-aa", "No Alias Analysis (always returns 'may' alias)", true, true);
88 // Declare that we implement the AliasAnalysis interface
89 RegisterAnalysisGroup<AliasAnalysis> V(U);
90 } // End of anonymous namespace
92 ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
95 /// BasicAliasAnalysis - This is the default alias analysis implementation.
96 /// Because it doesn't chain to a previous alias analysis (like -no-aa), it
97 /// derives from the NoAA class.
98 struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA {
99 static char ID; // Class identification, replacement for typeinfo
100 BasicAliasAnalysis() : NoAA((intptr_t)&ID) { }
101 AliasResult alias(const Value *V1, unsigned V1Size,
102 const Value *V2, unsigned V2Size);
104 ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
105 ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
106 return NoAA::getModRefInfo(CS1,CS2);
109 /// hasNoModRefInfoForCalls - We can provide mod/ref information against
110 /// non-escaping allocations.
111 virtual bool hasNoModRefInfoForCalls() const { return false; }
113 /// pointsToConstantMemory - Chase pointers until we find a (constant
115 bool pointsToConstantMemory(const Value *P);
118 // CheckGEPInstructions - Check two GEP instructions with known
119 // must-aliasing base pointers. This checks to see if the index expressions
120 // preclude the pointers from aliasing...
122 CheckGEPInstructions(const Type* BasePtr1Ty,
123 Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size,
124 const Type *BasePtr2Ty,
125 Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size);
128 // Register this pass...
129 char BasicAliasAnalysis::ID = 0;
130 RegisterPass<BasicAliasAnalysis>
131 X("basicaa", "Basic Alias Analysis (default AA impl)", false, true);
133 // Declare that we implement the AliasAnalysis interface
134 RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
135 } // End of anonymous namespace
137 ImmutablePass *llvm::createBasicAliasAnalysisPass() {
138 return new BasicAliasAnalysis();
141 /// getUnderlyingObject - This traverses the use chain to figure out what object
142 /// the specified value points to. If the value points to, or is derived from,
143 /// a unique object or an argument, return it. This returns:
144 /// Arguments, GlobalVariables, Functions, Allocas, Mallocs.
145 static const Value *getUnderlyingObject(const Value *V) {
146 if (!isa<PointerType>(V->getType())) return 0;
148 // If we are at some type of object, return it. GlobalValues and Allocations
149 // have unique addresses.
150 if (isa<GlobalValue>(V) || isa<AllocationInst>(V) || isa<Argument>(V))
153 // Traverse through different addressing mechanisms...
154 if (const Instruction *I = dyn_cast<Instruction>(V)) {
155 if (isa<BitCastInst>(I) || isa<GetElementPtrInst>(I))
156 return getUnderlyingObject(I->getOperand(0));
157 } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
158 if (CE->getOpcode() == Instruction::BitCast ||
159 CE->getOpcode() == Instruction::GetElementPtr)
160 return getUnderlyingObject(CE->getOperand(0));
165 static const User *isGEP(const Value *V) {
166 if (isa<GetElementPtrInst>(V) ||
167 (isa<ConstantExpr>(V) &&
168 cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr))
169 return cast<User>(V);
173 static const Value *GetGEPOperands(const Value *V,
174 SmallVector<Value*, 16> &GEPOps){
175 assert(GEPOps.empty() && "Expect empty list to populate!");
176 GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
177 cast<User>(V)->op_end());
179 // Accumulate all of the chained indexes into the operand array
180 V = cast<User>(V)->getOperand(0);
182 while (const User *G = isGEP(V)) {
183 if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
184 !cast<Constant>(GEPOps[0])->isNullValue())
185 break; // Don't handle folding arbitrary pointer offsets yet...
186 GEPOps.erase(GEPOps.begin()); // Drop the zero index
187 GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
188 V = G->getOperand(0);
193 /// pointsToConstantMemory - Chase pointers until we find a (constant
195 bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
196 if (const Value *V = getUnderlyingObject(P))
197 if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
198 return GV->isConstant();
202 // Determine if an AllocationInst instruction escapes from the function it is
203 // contained in. If it does not escape, there is no way for another function to
204 // mod/ref it. We do this by looking at its uses and determining if the uses
205 // can escape (recursively).
206 static bool AddressMightEscape(const Value *V) {
207 for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end();
209 const Instruction *I = cast<Instruction>(*UI);
210 switch (I->getOpcode()) {
211 case Instruction::Load:
213 case Instruction::Store:
214 if (I->getOperand(0) == V)
215 return true; // Escapes if the pointer is stored.
217 case Instruction::GetElementPtr:
218 if (AddressMightEscape(I))
221 case Instruction::BitCast:
222 if (AddressMightEscape(I))
225 case Instruction::Ret:
226 // If returned, the address will escape to calling functions, but no
227 // callees could modify it.
229 case Instruction::Call:
230 // If the call is to a few known safe intrinsics, we know that it does
232 if (!isa<MemIntrinsic>(I))
242 // getModRefInfo - Check to see if the specified callsite can clobber the
243 // specified memory object. Since we only look at local properties of this
244 // function, we really can't say much about this query. We do, however, use
245 // simple "address taken" analysis on local objects.
247 AliasAnalysis::ModRefResult
248 BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
249 if (!isa<Constant>(P)) {
250 const Value *Object = getUnderlyingObject(P);
251 // Allocations and byval arguments are "new" objects.
253 (isa<AllocationInst>(Object) || isa<Argument>(Object))) {
254 // Okay, the pointer is to a stack allocated (or effectively so, for
255 // for noalias parameters) object. If the address of this object doesn't
256 // escape from this function body to a callee, then we know that no
257 // callees can mod/ref it unless they are actually passed it.
258 if (isa<AllocationInst>(Object) ||
259 cast<Argument>(Object)->hasByValAttr() ||
260 cast<Argument>(Object)->hasNoAliasAttr())
261 if (!AddressMightEscape(Object)) {
262 bool passedAsArg = false;
263 for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
265 if (isa<PointerType>((*CI)->getType()) &&
266 ( getUnderlyingObject(*CI) == P ||
267 alias(cast<Value>(CI), ~0U, P, ~0U) != NoAlias) )
274 // If this is a tail call and P points to a stack location, we know that
275 // the tail call cannot access or modify the local stack.
276 // We cannot exclude byval arguments here; these belong to the caller of
277 // the current function not to the current function, and a tail callee
278 // may reference them.
279 if (isa<AllocaInst>(Object))
280 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
281 if (CI->isTailCall())
286 // The AliasAnalysis base class has some smarts, lets use them.
287 return AliasAnalysis::getModRefInfo(CS, P, Size);
290 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
291 // as array references. Note that this function is heavily tail recursive.
292 // Hopefully we have a smart C++ compiler. :)
294 AliasAnalysis::AliasResult
295 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
296 const Value *V2, unsigned V2Size) {
297 // Strip off any constant expression casts if they exist
298 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
299 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
300 V1 = CE->getOperand(0);
301 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
302 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
303 V2 = CE->getOperand(0);
305 // Are we checking for alias of the same value?
306 if (V1 == V2) return MustAlias;
308 if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
309 V1->getType() != Type::Int64Ty && V2->getType() != Type::Int64Ty)
310 return NoAlias; // Scalars cannot alias each other
312 // Strip off cast instructions...
313 if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
314 return alias(I->getOperand(0), V1Size, V2, V2Size);
315 if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
316 return alias(V1, V1Size, I->getOperand(0), V2Size);
318 // Figure out what objects these things are pointing to if we can...
319 const Value *O1 = getUnderlyingObject(V1);
320 const Value *O2 = getUnderlyingObject(V2);
322 // Pointing at a discernible object?
325 if (const Argument *O1Arg = dyn_cast<Argument>(O1)) {
326 // Incoming argument cannot alias locally allocated object!
327 if (isa<AllocationInst>(O2)) return NoAlias;
329 // If they are two different objects, and one is a noalias argument
330 // then they do not alias.
331 if (O1 != O2 && O1Arg->hasNoAliasAttr())
334 // Byval arguments can't alias globals or other arguments.
335 if (O1 != O2 && O1Arg->hasByValAttr()) return NoAlias;
337 // Otherwise, nothing is known...
340 if (const Argument *O2Arg = dyn_cast<Argument>(O2)) {
341 // Incoming argument cannot alias locally allocated object!
342 if (isa<AllocationInst>(O1)) return NoAlias;
344 // If they are two different objects, and one is a noalias argument
345 // then they do not alias.
346 if (O1 != O2 && O2Arg->hasNoAliasAttr())
349 // Byval arguments can't alias globals or other arguments.
350 if (O1 != O2 && O2Arg->hasByValAttr()) return NoAlias;
352 // Otherwise, nothing is known...
354 } else if (O1 != O2 && !isa<Argument>(O1)) {
355 // If they are two different objects, and neither is an argument,
356 // we know that we have no alias.
360 // If they are the same object, they we can look at the indexes. If they
361 // index off of the object is the same for both pointers, they must alias.
362 // If they are provably different, they must not alias. Otherwise, we
363 // can't tell anything.
366 // Unique values don't alias null, except non-byval arguments.
367 if (isa<ConstantPointerNull>(V2)) {
368 if (const Argument *O1Arg = dyn_cast<Argument>(O1)) {
369 if (O1Arg->hasByValAttr())
376 if (isa<GlobalVariable>(O1) ||
377 (isa<AllocationInst>(O1) &&
378 !cast<AllocationInst>(O1)->isArrayAllocation()))
379 if (cast<PointerType>(O1->getType())->getElementType()->isSized()) {
380 // If the size of the other access is larger than the total size of the
381 // global/alloca/malloc, it cannot be accessing the global (it's
382 // undefined to load or store bytes before or after an object).
383 const Type *ElTy = cast<PointerType>(O1->getType())->getElementType();
384 unsigned GlobalSize = getTargetData().getABITypeSize(ElTy);
385 if (GlobalSize < V2Size && V2Size != ~0U)
391 if (!isa<Argument>(O2) && isa<ConstantPointerNull>(V1))
392 return NoAlias; // Unique values don't alias null
394 if (isa<GlobalVariable>(O2) ||
395 (isa<AllocationInst>(O2) &&
396 !cast<AllocationInst>(O2)->isArrayAllocation()))
397 if (cast<PointerType>(O2->getType())->getElementType()->isSized()) {
398 // If the size of the other access is larger than the total size of the
399 // global/alloca/malloc, it cannot be accessing the object (it's
400 // undefined to load or store bytes before or after an object).
401 const Type *ElTy = cast<PointerType>(O2->getType())->getElementType();
402 unsigned GlobalSize = getTargetData().getABITypeSize(ElTy);
403 if (GlobalSize < V1Size && V1Size != ~0U)
408 // If we have two gep instructions with must-alias'ing base pointers, figure
409 // out if the indexes to the GEP tell us anything about the derived pointer.
410 // Note that we also handle chains of getelementptr instructions as well as
411 // constant expression getelementptrs here.
413 if (isGEP(V1) && isGEP(V2)) {
414 // Drill down into the first non-gep value, to test for must-aliasing of
415 // the base pointers.
416 const User *G = cast<User>(V1);
417 while (isGEP(G->getOperand(0)) &&
419 Constant::getNullValue(G->getOperand(1)->getType()))
420 G = cast<User>(G->getOperand(0));
421 const Value *BasePtr1 = G->getOperand(0);
424 while (isGEP(G->getOperand(0)) &&
426 Constant::getNullValue(G->getOperand(1)->getType()))
427 G = cast<User>(G->getOperand(0));
428 const Value *BasePtr2 = G->getOperand(0);
430 // Do the base pointers alias?
431 AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
432 if (BaseAlias == NoAlias) return NoAlias;
433 if (BaseAlias == MustAlias) {
434 // If the base pointers alias each other exactly, check to see if we can
435 // figure out anything about the resultant pointers, to try to prove
438 // Collect all of the chained GEP operands together into one simple place
439 SmallVector<Value*, 16> GEP1Ops, GEP2Ops;
440 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
441 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
443 // If GetGEPOperands were able to fold to the same must-aliased pointer,
444 // do the comparison.
445 if (BasePtr1 == BasePtr2) {
447 CheckGEPInstructions(BasePtr1->getType(),
448 &GEP1Ops[0], GEP1Ops.size(), V1Size,
450 &GEP2Ops[0], GEP2Ops.size(), V2Size);
451 if (GAlias != MayAlias)
457 // Check to see if these two pointers are related by a getelementptr
458 // instruction. If one pointer is a GEP with a non-zero index of the other
459 // pointer, we know they cannot alias.
463 std::swap(V1Size, V2Size);
466 if (V1Size != ~0U && V2Size != ~0U)
468 SmallVector<Value*, 16> GEPOperands;
469 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
471 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
472 if (R == MustAlias) {
473 // If there is at least one non-zero constant index, we know they cannot
475 bool ConstantFound = false;
476 bool AllZerosFound = true;
477 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
478 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
479 if (!C->isNullValue()) {
480 ConstantFound = true;
481 AllZerosFound = false;
485 AllZerosFound = false;
488 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
489 // the ptr, the end result is a must alias also.
494 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
497 // Otherwise we have to check to see that the distance is more than
498 // the size of the argument... build an index vector that is equal to
499 // the arguments provided, except substitute 0's for any variable
500 // indexes we find...
501 if (cast<PointerType>(
502 BasePtr->getType())->getElementType()->isSized()) {
503 for (unsigned i = 0; i != GEPOperands.size(); ++i)
504 if (!isa<ConstantInt>(GEPOperands[i]))
506 Constant::getNullValue(GEPOperands[i]->getType());
508 getTargetData().getIndexedOffset(BasePtr->getType(),
512 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
522 // This function is used to determin if the indices of two GEP instructions are
523 // equal. V1 and V2 are the indices.
524 static bool IndexOperandsEqual(Value *V1, Value *V2) {
525 if (V1->getType() == V2->getType())
527 if (Constant *C1 = dyn_cast<Constant>(V1))
528 if (Constant *C2 = dyn_cast<Constant>(V2)) {
529 // Sign extend the constants to long types, if necessary
530 if (C1->getType() != Type::Int64Ty)
531 C1 = ConstantExpr::getSExt(C1, Type::Int64Ty);
532 if (C2->getType() != Type::Int64Ty)
533 C2 = ConstantExpr::getSExt(C2, Type::Int64Ty);
539 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
540 /// base pointers. This checks to see if the index expressions preclude the
541 /// pointers from aliasing...
542 AliasAnalysis::AliasResult
543 BasicAliasAnalysis::CheckGEPInstructions(
544 const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
545 const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
546 // We currently can't handle the case when the base pointers have different
547 // primitive types. Since this is uncommon anyway, we are happy being
548 // extremely conservative.
549 if (BasePtr1Ty != BasePtr2Ty)
552 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
554 // Find the (possibly empty) initial sequence of equal values... which are not
555 // necessarily constants.
556 unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
557 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
558 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
559 unsigned UnequalOper = 0;
560 while (UnequalOper != MinOperands &&
561 IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
562 // Advance through the type as we go...
564 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
565 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
567 // If all operands equal each other, then the derived pointers must
568 // alias each other...
570 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
571 "Ran out of type nesting, but not out of operands?");
576 // If we have seen all constant operands, and run out of indexes on one of the
577 // getelementptrs, check to see if the tail of the leftover one is all zeros.
578 // If so, return mustalias.
579 if (UnequalOper == MinOperands) {
580 if (NumGEP1Ops < NumGEP2Ops) {
581 std::swap(GEP1Ops, GEP2Ops);
582 std::swap(NumGEP1Ops, NumGEP2Ops);
585 bool AllAreZeros = true;
586 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
587 if (!isa<Constant>(GEP1Ops[i]) ||
588 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
592 if (AllAreZeros) return MustAlias;
596 // So now we know that the indexes derived from the base pointers,
597 // which are known to alias, are different. We can still determine a
598 // no-alias result if there are differing constant pairs in the index
599 // chain. For example:
600 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
602 // We have to be careful here about array accesses. In particular, consider:
603 // A[1][0] vs A[0][i]
604 // In this case, we don't *know* that the array will be accessed in bounds:
605 // the index could even be negative. Because of this, we have to
606 // conservatively *give up* and return may alias. We disregard differing
607 // array subscripts that are followed by a variable index without going
610 unsigned SizeMax = std::max(G1S, G2S);
611 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
613 // Scan for the first operand that is constant and unequal in the
614 // two getelementptrs...
615 unsigned FirstConstantOper = UnequalOper;
616 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
617 const Value *G1Oper = GEP1Ops[FirstConstantOper];
618 const Value *G2Oper = GEP2Ops[FirstConstantOper];
620 if (G1Oper != G2Oper) // Found non-equal constant indexes...
621 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
622 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
623 if (G1OC->getType() != G2OC->getType()) {
624 // Sign extend both operands to long.
625 if (G1OC->getType() != Type::Int64Ty)
626 G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty);
627 if (G2OC->getType() != Type::Int64Ty)
628 G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty);
629 GEP1Ops[FirstConstantOper] = G1OC;
630 GEP2Ops[FirstConstantOper] = G2OC;
634 // Handle the "be careful" case above: if this is an array/vector
635 // subscript, scan for a subsequent variable array index.
636 if (isa<SequentialType>(BasePtr1Ty)) {
638 cast<SequentialType>(BasePtr1Ty)->getElementType();
639 bool isBadCase = false;
641 for (unsigned Idx = FirstConstantOper+1;
642 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
643 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
644 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
648 NextTy = cast<SequentialType>(NextTy)->getElementType();
651 if (isBadCase) G1OC = 0;
654 // Make sure they are comparable (ie, not constant expressions), and
655 // make sure the GEP with the smaller leading constant is GEP1.
657 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
659 if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
660 if (CV->getZExtValue()) { // If they are comparable and G2 > G1
661 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
662 std::swap(NumGEP1Ops, NumGEP2Ops);
669 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
672 // No shared constant operands, and we ran out of common operands. At this
673 // point, the GEP instructions have run through all of their operands, and we
674 // haven't found evidence that there are any deltas between the GEP's.
675 // However, one GEP may have more operands than the other. If this is the
676 // case, there may still be hope. Check this now.
677 if (FirstConstantOper == MinOperands) {
678 // Make GEP1Ops be the longer one if there is a longer one.
679 if (NumGEP1Ops < NumGEP2Ops) {
680 std::swap(GEP1Ops, GEP2Ops);
681 std::swap(NumGEP1Ops, NumGEP2Ops);
684 // Is there anything to check?
685 if (NumGEP1Ops > MinOperands) {
686 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
687 if (isa<ConstantInt>(GEP1Ops[i]) &&
688 !cast<ConstantInt>(GEP1Ops[i])->isZero()) {
689 // Yup, there's a constant in the tail. Set all variables to
690 // constants in the GEP instruction to make it suiteable for
691 // TargetData::getIndexedOffset.
692 for (i = 0; i != MaxOperands; ++i)
693 if (!isa<ConstantInt>(GEP1Ops[i]))
694 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
695 // Okay, now get the offset. This is the relative offset for the full
697 const TargetData &TD = getTargetData();
698 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
701 // Now check without any constants at the end.
702 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
705 // If the tail provided a bit enough offset, return noalias!
706 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
711 // Couldn't find anything useful.
715 // If there are non-equal constants arguments, then we can figure
716 // out a minimum known delta between the two index expressions... at
717 // this point we know that the first constant index of GEP1 is less
718 // than the first constant index of GEP2.
720 // Advance BasePtr[12]Ty over this first differing constant operand.
721 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
722 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
723 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
724 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
726 // We are going to be using TargetData::getIndexedOffset to determine the
727 // offset that each of the GEP's is reaching. To do this, we have to convert
728 // all variable references to constant references. To do this, we convert the
729 // initial sequence of array subscripts into constant zeros to start with.
730 const Type *ZeroIdxTy = GEPPointerTy;
731 for (unsigned i = 0; i != FirstConstantOper; ++i) {
732 if (!isa<StructType>(ZeroIdxTy))
733 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty);
735 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
736 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
739 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
741 // Loop over the rest of the operands...
742 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
743 const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
744 const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
745 // If they are equal, use a zero index...
746 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
747 if (!isa<ConstantInt>(Op1))
748 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
749 // Otherwise, just keep the constants we have.
752 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
753 // If this is an array index, make sure the array element is in range.
754 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
755 if (Op1C->getZExtValue() >= AT->getNumElements())
756 return MayAlias; // Be conservative with out-of-range accesses
757 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) {
758 if (Op1C->getZExtValue() >= VT->getNumElements())
759 return MayAlias; // Be conservative with out-of-range accesses
763 // GEP1 is known to produce a value less than GEP2. To be
764 // conservatively correct, we must assume the largest possible
765 // constant is used in this position. This cannot be the initial
766 // index to the GEP instructions (because we know we have at least one
767 // element before this one with the different constant arguments), so
768 // we know that the current index must be into either a struct or
769 // array. Because we know it's not constant, this cannot be a
770 // structure index. Because of this, we can calculate the maximum
773 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
774 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1);
775 else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty))
776 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,VT->getNumElements()-1);
781 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
782 // If this is an array index, make sure the array element is in range.
783 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr2Ty)) {
784 if (Op2C->getZExtValue() >= AT->getNumElements())
785 return MayAlias; // Be conservative with out-of-range accesses
786 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr2Ty)) {
787 if (Op2C->getZExtValue() >= VT->getNumElements())
788 return MayAlias; // Be conservative with out-of-range accesses
790 } else { // Conservatively assume the minimum value for this index
791 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
796 if (BasePtr1Ty && Op1) {
797 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
798 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
803 if (BasePtr2Ty && Op2) {
804 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
805 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
811 if (GEPPointerTy->getElementType()->isSized()) {
813 getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
815 getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
816 assert(Offset1 != Offset2 &&
817 "There is at least one different constant here!");
819 // Make sure we compare the absolute difference.
820 if (Offset1 > Offset2)
821 std::swap(Offset1, Offset2);
823 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
824 //cerr << "Determined that these two GEP's don't alias ["
825 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
832 // Make sure that anything that uses AliasAnalysis pulls in this file...
833 DEFINING_FILE_FOR(BasicAliasAnalysis)