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)");
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)");
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) ||
254 (isa<Argument>(Object) &&
255 (cast<Argument>(Object)->hasByValAttr() ||
256 cast<Argument>(Object)->hasNoAliasAttr())))) {
257 // Okay, the pointer is to a stack allocated (or effectively so, for
258 // for noalias parameters) object. If we can prove that
259 // the pointer never "escapes", then we know the call cannot clobber it,
260 // because it simply can't get its address.
261 if (!AddressMightEscape(Object))
264 // If this is a tail call and P points to a stack location, we know that
265 // the tail call cannot access or modify the local stack.
266 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
267 if (CI->isTailCall() && !isa<MallocInst>(Object))
272 // The AliasAnalysis base class has some smarts, lets use them.
273 return AliasAnalysis::getModRefInfo(CS, P, Size);
276 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
277 // as array references. Note that this function is heavily tail recursive.
278 // Hopefully we have a smart C++ compiler. :)
280 AliasAnalysis::AliasResult
281 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
282 const Value *V2, unsigned V2Size) {
283 // Strip off any constant expression casts if they exist
284 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
285 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
286 V1 = CE->getOperand(0);
287 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
288 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
289 V2 = CE->getOperand(0);
291 // Are we checking for alias of the same value?
292 if (V1 == V2) return MustAlias;
294 if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
295 V1->getType() != Type::Int64Ty && V2->getType() != Type::Int64Ty)
296 return NoAlias; // Scalars cannot alias each other
298 // Strip off cast instructions...
299 if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
300 return alias(I->getOperand(0), V1Size, V2, V2Size);
301 if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
302 return alias(V1, V1Size, I->getOperand(0), V2Size);
304 // Figure out what objects these things are pointing to if we can...
305 const Value *O1 = getUnderlyingObject(V1);
306 const Value *O2 = getUnderlyingObject(V2);
308 // Pointing at a discernible object?
311 if (const Argument *O1Arg = dyn_cast<Argument>(O1)) {
312 // Incoming argument cannot alias locally allocated object!
313 if (isa<AllocationInst>(O2)) return NoAlias;
315 // If they are two different objects, and one is a noalias argument
316 // then they do not alias.
317 if (O1 != O2 && O1Arg->hasNoAliasAttr())
320 // Byval arguments can't alias globals or other arguments.
321 if (O1 != O2 && O1Arg->hasByValAttr()) return NoAlias;
323 // Otherwise, nothing is known...
326 if (const Argument *O2Arg = dyn_cast<Argument>(O2)) {
327 // Incoming argument cannot alias locally allocated object!
328 if (isa<AllocationInst>(O1)) return NoAlias;
330 // If they are two different objects, and one is a noalias argument
331 // then they do not alias.
332 if (O1 != O2 && O2Arg->hasNoAliasAttr())
335 // Byval arguments can't alias globals or other arguments.
336 if (O1 != O2 && O2Arg->hasByValAttr()) return NoAlias;
338 // Otherwise, nothing is known...
340 } else if (O1 != O2 && !isa<Argument>(O1)) {
341 // If they are two different objects, and neither is an argument,
342 // we know that we have no alias.
346 // If they are the same object, they we can look at the indexes. If they
347 // index off of the object is the same for both pointers, they must alias.
348 // If they are provably different, they must not alias. Otherwise, we
349 // can't tell anything.
352 // Unique values don't alias null, except non-byval arguments.
353 if (isa<ConstantPointerNull>(V2)) {
354 if (const Argument *O1Arg = dyn_cast<Argument>(O1)) {
355 if (O1Arg->hasByValAttr())
362 if (isa<GlobalVariable>(O1) ||
363 (isa<AllocationInst>(O1) &&
364 !cast<AllocationInst>(O1)->isArrayAllocation()))
365 if (cast<PointerType>(O1->getType())->getElementType()->isSized()) {
366 // If the size of the other access is larger than the total size of the
367 // global/alloca/malloc, it cannot be accessing the global (it's
368 // undefined to load or store bytes before or after an object).
369 const Type *ElTy = cast<PointerType>(O1->getType())->getElementType();
370 unsigned GlobalSize = getTargetData().getABITypeSize(ElTy);
371 if (GlobalSize < V2Size && V2Size != ~0U)
377 if (!isa<Argument>(O2) && isa<ConstantPointerNull>(V1))
378 return NoAlias; // Unique values don't alias null
380 if (isa<GlobalVariable>(O2) ||
381 (isa<AllocationInst>(O2) &&
382 !cast<AllocationInst>(O2)->isArrayAllocation()))
383 if (cast<PointerType>(O2->getType())->getElementType()->isSized()) {
384 // If the size of the other access is larger than the total size of the
385 // global/alloca/malloc, it cannot be accessing the object (it's
386 // undefined to load or store bytes before or after an object).
387 const Type *ElTy = cast<PointerType>(O2->getType())->getElementType();
388 unsigned GlobalSize = getTargetData().getABITypeSize(ElTy);
389 if (GlobalSize < V1Size && V1Size != ~0U)
394 // If we have two gep instructions with must-alias'ing base pointers, figure
395 // out if the indexes to the GEP tell us anything about the derived pointer.
396 // Note that we also handle chains of getelementptr instructions as well as
397 // constant expression getelementptrs here.
399 if (isGEP(V1) && isGEP(V2)) {
400 // Drill down into the first non-gep value, to test for must-aliasing of
401 // the base pointers.
402 const User *G = cast<User>(V1);
403 while (isGEP(G->getOperand(0)) &&
405 Constant::getNullValue(G->getOperand(1)->getType()))
406 G = cast<User>(G->getOperand(0));
407 const Value *BasePtr1 = G->getOperand(0);
410 while (isGEP(G->getOperand(0)) &&
412 Constant::getNullValue(G->getOperand(1)->getType()))
413 G = cast<User>(G->getOperand(0));
414 const Value *BasePtr2 = G->getOperand(0);
416 // Do the base pointers alias?
417 AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
418 if (BaseAlias == NoAlias) return NoAlias;
419 if (BaseAlias == MustAlias) {
420 // If the base pointers alias each other exactly, check to see if we can
421 // figure out anything about the resultant pointers, to try to prove
424 // Collect all of the chained GEP operands together into one simple place
425 SmallVector<Value*, 16> GEP1Ops, GEP2Ops;
426 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
427 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
429 // If GetGEPOperands were able to fold to the same must-aliased pointer,
430 // do the comparison.
431 if (BasePtr1 == BasePtr2) {
433 CheckGEPInstructions(BasePtr1->getType(),
434 &GEP1Ops[0], GEP1Ops.size(), V1Size,
436 &GEP2Ops[0], GEP2Ops.size(), V2Size);
437 if (GAlias != MayAlias)
443 // Check to see if these two pointers are related by a getelementptr
444 // instruction. If one pointer is a GEP with a non-zero index of the other
445 // pointer, we know they cannot alias.
449 std::swap(V1Size, V2Size);
452 if (V1Size != ~0U && V2Size != ~0U)
454 SmallVector<Value*, 16> GEPOperands;
455 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
457 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
458 if (R == MustAlias) {
459 // If there is at least one non-zero constant index, we know they cannot
461 bool ConstantFound = false;
462 bool AllZerosFound = true;
463 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
464 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
465 if (!C->isNullValue()) {
466 ConstantFound = true;
467 AllZerosFound = false;
471 AllZerosFound = false;
474 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
475 // the ptr, the end result is a must alias also.
480 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
483 // Otherwise we have to check to see that the distance is more than
484 // the size of the argument... build an index vector that is equal to
485 // the arguments provided, except substitute 0's for any variable
486 // indexes we find...
487 if (cast<PointerType>(
488 BasePtr->getType())->getElementType()->isSized()) {
489 for (unsigned i = 0; i != GEPOperands.size(); ++i)
490 if (!isa<ConstantInt>(GEPOperands[i]))
492 Constant::getNullValue(GEPOperands[i]->getType());
494 getTargetData().getIndexedOffset(BasePtr->getType(),
498 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
508 // This function is used to determin if the indices of two GEP instructions are
509 // equal. V1 and V2 are the indices.
510 static bool IndexOperandsEqual(Value *V1, Value *V2) {
511 if (V1->getType() == V2->getType())
513 if (Constant *C1 = dyn_cast<Constant>(V1))
514 if (Constant *C2 = dyn_cast<Constant>(V2)) {
515 // Sign extend the constants to long types, if necessary
516 if (C1->getType() != Type::Int64Ty)
517 C1 = ConstantExpr::getSExt(C1, Type::Int64Ty);
518 if (C2->getType() != Type::Int64Ty)
519 C2 = ConstantExpr::getSExt(C2, Type::Int64Ty);
525 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
526 /// base pointers. This checks to see if the index expressions preclude the
527 /// pointers from aliasing...
528 AliasAnalysis::AliasResult
529 BasicAliasAnalysis::CheckGEPInstructions(
530 const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
531 const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
532 // We currently can't handle the case when the base pointers have different
533 // primitive types. Since this is uncommon anyway, we are happy being
534 // extremely conservative.
535 if (BasePtr1Ty != BasePtr2Ty)
538 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
540 // Find the (possibly empty) initial sequence of equal values... which are not
541 // necessarily constants.
542 unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
543 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
544 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
545 unsigned UnequalOper = 0;
546 while (UnequalOper != MinOperands &&
547 IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
548 // Advance through the type as we go...
550 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
551 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
553 // If all operands equal each other, then the derived pointers must
554 // alias each other...
556 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
557 "Ran out of type nesting, but not out of operands?");
562 // If we have seen all constant operands, and run out of indexes on one of the
563 // getelementptrs, check to see if the tail of the leftover one is all zeros.
564 // If so, return mustalias.
565 if (UnequalOper == MinOperands) {
566 if (NumGEP1Ops < NumGEP2Ops) {
567 std::swap(GEP1Ops, GEP2Ops);
568 std::swap(NumGEP1Ops, NumGEP2Ops);
571 bool AllAreZeros = true;
572 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
573 if (!isa<Constant>(GEP1Ops[i]) ||
574 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
578 if (AllAreZeros) return MustAlias;
582 // So now we know that the indexes derived from the base pointers,
583 // which are known to alias, are different. We can still determine a
584 // no-alias result if there are differing constant pairs in the index
585 // chain. For example:
586 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
588 // We have to be careful here about array accesses. In particular, consider:
589 // A[1][0] vs A[0][i]
590 // In this case, we don't *know* that the array will be accessed in bounds:
591 // the index could even be negative. Because of this, we have to
592 // conservatively *give up* and return may alias. We disregard differing
593 // array subscripts that are followed by a variable index without going
596 unsigned SizeMax = std::max(G1S, G2S);
597 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
599 // Scan for the first operand that is constant and unequal in the
600 // two getelementptrs...
601 unsigned FirstConstantOper = UnequalOper;
602 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
603 const Value *G1Oper = GEP1Ops[FirstConstantOper];
604 const Value *G2Oper = GEP2Ops[FirstConstantOper];
606 if (G1Oper != G2Oper) // Found non-equal constant indexes...
607 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
608 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
609 if (G1OC->getType() != G2OC->getType()) {
610 // Sign extend both operands to long.
611 if (G1OC->getType() != Type::Int64Ty)
612 G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty);
613 if (G2OC->getType() != Type::Int64Ty)
614 G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty);
615 GEP1Ops[FirstConstantOper] = G1OC;
616 GEP2Ops[FirstConstantOper] = G2OC;
620 // Handle the "be careful" case above: if this is an array/vector
621 // subscript, scan for a subsequent variable array index.
622 if (isa<SequentialType>(BasePtr1Ty)) {
624 cast<SequentialType>(BasePtr1Ty)->getElementType();
625 bool isBadCase = false;
627 for (unsigned Idx = FirstConstantOper+1;
628 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
629 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
630 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
634 NextTy = cast<SequentialType>(NextTy)->getElementType();
637 if (isBadCase) G1OC = 0;
640 // Make sure they are comparable (ie, not constant expressions), and
641 // make sure the GEP with the smaller leading constant is GEP1.
643 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
645 if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
646 if (CV->getZExtValue()) { // If they are comparable and G2 > G1
647 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
648 std::swap(NumGEP1Ops, NumGEP2Ops);
655 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
658 // No shared constant operands, and we ran out of common operands. At this
659 // point, the GEP instructions have run through all of their operands, and we
660 // haven't found evidence that there are any deltas between the GEP's.
661 // However, one GEP may have more operands than the other. If this is the
662 // case, there may still be hope. Check this now.
663 if (FirstConstantOper == MinOperands) {
664 // Make GEP1Ops be the longer one if there is a longer one.
665 if (NumGEP1Ops < NumGEP2Ops) {
666 std::swap(GEP1Ops, GEP2Ops);
667 std::swap(NumGEP1Ops, NumGEP2Ops);
670 // Is there anything to check?
671 if (NumGEP1Ops > MinOperands) {
672 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
673 if (isa<ConstantInt>(GEP1Ops[i]) &&
674 !cast<ConstantInt>(GEP1Ops[i])->isZero()) {
675 // Yup, there's a constant in the tail. Set all variables to
676 // constants in the GEP instruction to make it suiteable for
677 // TargetData::getIndexedOffset.
678 for (i = 0; i != MaxOperands; ++i)
679 if (!isa<ConstantInt>(GEP1Ops[i]))
680 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
681 // Okay, now get the offset. This is the relative offset for the full
683 const TargetData &TD = getTargetData();
684 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
687 // Now check without any constants at the end.
688 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
691 // If the tail provided a bit enough offset, return noalias!
692 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
697 // Couldn't find anything useful.
701 // If there are non-equal constants arguments, then we can figure
702 // out a minimum known delta between the two index expressions... at
703 // this point we know that the first constant index of GEP1 is less
704 // than the first constant index of GEP2.
706 // Advance BasePtr[12]Ty over this first differing constant operand.
707 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
708 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
709 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
710 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
712 // We are going to be using TargetData::getIndexedOffset to determine the
713 // offset that each of the GEP's is reaching. To do this, we have to convert
714 // all variable references to constant references. To do this, we convert the
715 // initial sequence of array subscripts into constant zeros to start with.
716 const Type *ZeroIdxTy = GEPPointerTy;
717 for (unsigned i = 0; i != FirstConstantOper; ++i) {
718 if (!isa<StructType>(ZeroIdxTy))
719 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty);
721 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
722 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
725 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
727 // Loop over the rest of the operands...
728 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
729 const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
730 const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
731 // If they are equal, use a zero index...
732 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
733 if (!isa<ConstantInt>(Op1))
734 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
735 // Otherwise, just keep the constants we have.
738 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
739 // If this is an array index, make sure the array element is in range.
740 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
741 if (Op1C->getZExtValue() >= AT->getNumElements())
742 return MayAlias; // Be conservative with out-of-range accesses
743 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) {
744 if (Op1C->getZExtValue() >= VT->getNumElements())
745 return MayAlias; // Be conservative with out-of-range accesses
749 // GEP1 is known to produce a value less than GEP2. To be
750 // conservatively correct, we must assume the largest possible
751 // constant is used in this position. This cannot be the initial
752 // index to the GEP instructions (because we know we have at least one
753 // element before this one with the different constant arguments), so
754 // we know that the current index must be into either a struct or
755 // array. Because we know it's not constant, this cannot be a
756 // structure index. Because of this, we can calculate the maximum
759 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
760 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1);
761 else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty))
762 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,VT->getNumElements()-1);
767 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
768 // If this is an array index, make sure the array element is in range.
769 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr2Ty)) {
770 if (Op2C->getZExtValue() >= AT->getNumElements())
771 return MayAlias; // Be conservative with out-of-range accesses
772 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr2Ty)) {
773 if (Op2C->getZExtValue() >= VT->getNumElements())
774 return MayAlias; // Be conservative with out-of-range accesses
776 } else { // Conservatively assume the minimum value for this index
777 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
782 if (BasePtr1Ty && Op1) {
783 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
784 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
789 if (BasePtr2Ty && Op2) {
790 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
791 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
797 if (GEPPointerTy->getElementType()->isSized()) {
799 getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
801 getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
802 assert(Offset1 != Offset2 &&
803 "There is at least one different constant here!");
805 // Make sure we compare the absolute difference.
806 if (Offset1 > Offset2)
807 std::swap(Offset1, Offset2);
809 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
810 //cerr << "Determined that these two GEP's don't alias ["
811 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
818 // Make sure that anything that uses AliasAnalysis pulls in this file...
819 DEFINING_FILE_FOR(BasicAliasAnalysis)