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) || 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 (getUnderlyingObject(CI->get()) == P)
272 // If this is a tail call and P points to a stack location, we know that
273 // the tail call cannot access or modify the local stack.
274 if (isa<AllocationInst>(Object) ||
275 cast<Argument>(Object)->hasByValAttr())
276 if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
277 if (CI->isTailCall() && !isa<MallocInst>(Object))
282 // The AliasAnalysis base class has some smarts, lets use them.
283 return AliasAnalysis::getModRefInfo(CS, P, Size);
286 // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
287 // as array references. Note that this function is heavily tail recursive.
288 // Hopefully we have a smart C++ compiler. :)
290 AliasAnalysis::AliasResult
291 BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
292 const Value *V2, unsigned V2Size) {
293 // Strip off any constant expression casts if they exist
294 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
295 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
296 V1 = CE->getOperand(0);
297 if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
298 if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
299 V2 = CE->getOperand(0);
301 // Are we checking for alias of the same value?
302 if (V1 == V2) return MustAlias;
304 if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) &&
305 V1->getType() != Type::Int64Ty && V2->getType() != Type::Int64Ty)
306 return NoAlias; // Scalars cannot alias each other
308 // Strip off cast instructions...
309 if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
310 return alias(I->getOperand(0), V1Size, V2, V2Size);
311 if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
312 return alias(V1, V1Size, I->getOperand(0), V2Size);
314 // Figure out what objects these things are pointing to if we can...
315 const Value *O1 = getUnderlyingObject(V1);
316 const Value *O2 = getUnderlyingObject(V2);
318 // Pointing at a discernible object?
321 if (const Argument *O1Arg = dyn_cast<Argument>(O1)) {
322 // Incoming argument cannot alias locally allocated object!
323 if (isa<AllocationInst>(O2)) return NoAlias;
325 // If they are two different objects, and one is a noalias argument
326 // then they do not alias.
327 if (O1 != O2 && O1Arg->hasNoAliasAttr())
330 // Byval arguments can't alias globals or other arguments.
331 if (O1 != O2 && O1Arg->hasByValAttr()) return NoAlias;
333 // Otherwise, nothing is known...
336 if (const Argument *O2Arg = dyn_cast<Argument>(O2)) {
337 // Incoming argument cannot alias locally allocated object!
338 if (isa<AllocationInst>(O1)) return NoAlias;
340 // If they are two different objects, and one is a noalias argument
341 // then they do not alias.
342 if (O1 != O2 && O2Arg->hasNoAliasAttr())
345 // Byval arguments can't alias globals or other arguments.
346 if (O1 != O2 && O2Arg->hasByValAttr()) return NoAlias;
348 // Otherwise, nothing is known...
350 } else if (O1 != O2 && !isa<Argument>(O1)) {
351 // If they are two different objects, and neither is an argument,
352 // we know that we have no alias.
356 // If they are the same object, they we can look at the indexes. If they
357 // index off of the object is the same for both pointers, they must alias.
358 // If they are provably different, they must not alias. Otherwise, we
359 // can't tell anything.
362 // Unique values don't alias null, except non-byval arguments.
363 if (isa<ConstantPointerNull>(V2)) {
364 if (const Argument *O1Arg = dyn_cast<Argument>(O1)) {
365 if (O1Arg->hasByValAttr())
372 if (isa<GlobalVariable>(O1) ||
373 (isa<AllocationInst>(O1) &&
374 !cast<AllocationInst>(O1)->isArrayAllocation()))
375 if (cast<PointerType>(O1->getType())->getElementType()->isSized()) {
376 // If the size of the other access is larger than the total size of the
377 // global/alloca/malloc, it cannot be accessing the global (it's
378 // undefined to load or store bytes before or after an object).
379 const Type *ElTy = cast<PointerType>(O1->getType())->getElementType();
380 unsigned GlobalSize = getTargetData().getABITypeSize(ElTy);
381 if (GlobalSize < V2Size && V2Size != ~0U)
387 if (!isa<Argument>(O2) && isa<ConstantPointerNull>(V1))
388 return NoAlias; // Unique values don't alias null
390 if (isa<GlobalVariable>(O2) ||
391 (isa<AllocationInst>(O2) &&
392 !cast<AllocationInst>(O2)->isArrayAllocation()))
393 if (cast<PointerType>(O2->getType())->getElementType()->isSized()) {
394 // If the size of the other access is larger than the total size of the
395 // global/alloca/malloc, it cannot be accessing the object (it's
396 // undefined to load or store bytes before or after an object).
397 const Type *ElTy = cast<PointerType>(O2->getType())->getElementType();
398 unsigned GlobalSize = getTargetData().getABITypeSize(ElTy);
399 if (GlobalSize < V1Size && V1Size != ~0U)
404 // If we have two gep instructions with must-alias'ing base pointers, figure
405 // out if the indexes to the GEP tell us anything about the derived pointer.
406 // Note that we also handle chains of getelementptr instructions as well as
407 // constant expression getelementptrs here.
409 if (isGEP(V1) && isGEP(V2)) {
410 // Drill down into the first non-gep value, to test for must-aliasing of
411 // the base pointers.
412 const User *G = cast<User>(V1);
413 while (isGEP(G->getOperand(0)) &&
415 Constant::getNullValue(G->getOperand(1)->getType()))
416 G = cast<User>(G->getOperand(0));
417 const Value *BasePtr1 = G->getOperand(0);
420 while (isGEP(G->getOperand(0)) &&
422 Constant::getNullValue(G->getOperand(1)->getType()))
423 G = cast<User>(G->getOperand(0));
424 const Value *BasePtr2 = G->getOperand(0);
426 // Do the base pointers alias?
427 AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
428 if (BaseAlias == NoAlias) return NoAlias;
429 if (BaseAlias == MustAlias) {
430 // If the base pointers alias each other exactly, check to see if we can
431 // figure out anything about the resultant pointers, to try to prove
434 // Collect all of the chained GEP operands together into one simple place
435 SmallVector<Value*, 16> GEP1Ops, GEP2Ops;
436 BasePtr1 = GetGEPOperands(V1, GEP1Ops);
437 BasePtr2 = GetGEPOperands(V2, GEP2Ops);
439 // If GetGEPOperands were able to fold to the same must-aliased pointer,
440 // do the comparison.
441 if (BasePtr1 == BasePtr2) {
443 CheckGEPInstructions(BasePtr1->getType(),
444 &GEP1Ops[0], GEP1Ops.size(), V1Size,
446 &GEP2Ops[0], GEP2Ops.size(), V2Size);
447 if (GAlias != MayAlias)
453 // Check to see if these two pointers are related by a getelementptr
454 // instruction. If one pointer is a GEP with a non-zero index of the other
455 // pointer, we know they cannot alias.
459 std::swap(V1Size, V2Size);
462 if (V1Size != ~0U && V2Size != ~0U)
464 SmallVector<Value*, 16> GEPOperands;
465 const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
467 AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
468 if (R == MustAlias) {
469 // If there is at least one non-zero constant index, we know they cannot
471 bool ConstantFound = false;
472 bool AllZerosFound = true;
473 for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
474 if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
475 if (!C->isNullValue()) {
476 ConstantFound = true;
477 AllZerosFound = false;
481 AllZerosFound = false;
484 // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
485 // the ptr, the end result is a must alias also.
490 if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
493 // Otherwise we have to check to see that the distance is more than
494 // the size of the argument... build an index vector that is equal to
495 // the arguments provided, except substitute 0's for any variable
496 // indexes we find...
497 if (cast<PointerType>(
498 BasePtr->getType())->getElementType()->isSized()) {
499 for (unsigned i = 0; i != GEPOperands.size(); ++i)
500 if (!isa<ConstantInt>(GEPOperands[i]))
502 Constant::getNullValue(GEPOperands[i]->getType());
504 getTargetData().getIndexedOffset(BasePtr->getType(),
508 if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
518 // This function is used to determin if the indices of two GEP instructions are
519 // equal. V1 and V2 are the indices.
520 static bool IndexOperandsEqual(Value *V1, Value *V2) {
521 if (V1->getType() == V2->getType())
523 if (Constant *C1 = dyn_cast<Constant>(V1))
524 if (Constant *C2 = dyn_cast<Constant>(V2)) {
525 // Sign extend the constants to long types, if necessary
526 if (C1->getType() != Type::Int64Ty)
527 C1 = ConstantExpr::getSExt(C1, Type::Int64Ty);
528 if (C2->getType() != Type::Int64Ty)
529 C2 = ConstantExpr::getSExt(C2, Type::Int64Ty);
535 /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
536 /// base pointers. This checks to see if the index expressions preclude the
537 /// pointers from aliasing...
538 AliasAnalysis::AliasResult
539 BasicAliasAnalysis::CheckGEPInstructions(
540 const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
541 const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
542 // We currently can't handle the case when the base pointers have different
543 // primitive types. Since this is uncommon anyway, we are happy being
544 // extremely conservative.
545 if (BasePtr1Ty != BasePtr2Ty)
548 const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
550 // Find the (possibly empty) initial sequence of equal values... which are not
551 // necessarily constants.
552 unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
553 unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
554 unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
555 unsigned UnequalOper = 0;
556 while (UnequalOper != MinOperands &&
557 IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) {
558 // Advance through the type as we go...
560 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
561 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
563 // If all operands equal each other, then the derived pointers must
564 // alias each other...
566 assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
567 "Ran out of type nesting, but not out of operands?");
572 // If we have seen all constant operands, and run out of indexes on one of the
573 // getelementptrs, check to see if the tail of the leftover one is all zeros.
574 // If so, return mustalias.
575 if (UnequalOper == MinOperands) {
576 if (NumGEP1Ops < NumGEP2Ops) {
577 std::swap(GEP1Ops, GEP2Ops);
578 std::swap(NumGEP1Ops, NumGEP2Ops);
581 bool AllAreZeros = true;
582 for (unsigned i = UnequalOper; i != MaxOperands; ++i)
583 if (!isa<Constant>(GEP1Ops[i]) ||
584 !cast<Constant>(GEP1Ops[i])->isNullValue()) {
588 if (AllAreZeros) return MustAlias;
592 // So now we know that the indexes derived from the base pointers,
593 // which are known to alias, are different. We can still determine a
594 // no-alias result if there are differing constant pairs in the index
595 // chain. For example:
596 // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
598 // We have to be careful here about array accesses. In particular, consider:
599 // A[1][0] vs A[0][i]
600 // In this case, we don't *know* that the array will be accessed in bounds:
601 // the index could even be negative. Because of this, we have to
602 // conservatively *give up* and return may alias. We disregard differing
603 // array subscripts that are followed by a variable index without going
606 unsigned SizeMax = std::max(G1S, G2S);
607 if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
609 // Scan for the first operand that is constant and unequal in the
610 // two getelementptrs...
611 unsigned FirstConstantOper = UnequalOper;
612 for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
613 const Value *G1Oper = GEP1Ops[FirstConstantOper];
614 const Value *G2Oper = GEP2Ops[FirstConstantOper];
616 if (G1Oper != G2Oper) // Found non-equal constant indexes...
617 if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
618 if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
619 if (G1OC->getType() != G2OC->getType()) {
620 // Sign extend both operands to long.
621 if (G1OC->getType() != Type::Int64Ty)
622 G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty);
623 if (G2OC->getType() != Type::Int64Ty)
624 G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty);
625 GEP1Ops[FirstConstantOper] = G1OC;
626 GEP2Ops[FirstConstantOper] = G2OC;
630 // Handle the "be careful" case above: if this is an array/vector
631 // subscript, scan for a subsequent variable array index.
632 if (isa<SequentialType>(BasePtr1Ty)) {
634 cast<SequentialType>(BasePtr1Ty)->getElementType();
635 bool isBadCase = false;
637 for (unsigned Idx = FirstConstantOper+1;
638 Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
639 const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
640 if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
644 NextTy = cast<SequentialType>(NextTy)->getElementType();
647 if (isBadCase) G1OC = 0;
650 // Make sure they are comparable (ie, not constant expressions), and
651 // make sure the GEP with the smaller leading constant is GEP1.
653 Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
655 if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
656 if (CV->getZExtValue()) { // If they are comparable and G2 > G1
657 std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
658 std::swap(NumGEP1Ops, NumGEP2Ops);
665 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
668 // No shared constant operands, and we ran out of common operands. At this
669 // point, the GEP instructions have run through all of their operands, and we
670 // haven't found evidence that there are any deltas between the GEP's.
671 // However, one GEP may have more operands than the other. If this is the
672 // case, there may still be hope. Check this now.
673 if (FirstConstantOper == MinOperands) {
674 // Make GEP1Ops be the longer one if there is a longer one.
675 if (NumGEP1Ops < NumGEP2Ops) {
676 std::swap(GEP1Ops, GEP2Ops);
677 std::swap(NumGEP1Ops, NumGEP2Ops);
680 // Is there anything to check?
681 if (NumGEP1Ops > MinOperands) {
682 for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
683 if (isa<ConstantInt>(GEP1Ops[i]) &&
684 !cast<ConstantInt>(GEP1Ops[i])->isZero()) {
685 // Yup, there's a constant in the tail. Set all variables to
686 // constants in the GEP instruction to make it suiteable for
687 // TargetData::getIndexedOffset.
688 for (i = 0; i != MaxOperands; ++i)
689 if (!isa<ConstantInt>(GEP1Ops[i]))
690 GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType());
691 // Okay, now get the offset. This is the relative offset for the full
693 const TargetData &TD = getTargetData();
694 int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
697 // Now check without any constants at the end.
698 int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
701 // If the tail provided a bit enough offset, return noalias!
702 if ((uint64_t)(Offset2-Offset1) >= SizeMax)
707 // Couldn't find anything useful.
711 // If there are non-equal constants arguments, then we can figure
712 // out a minimum known delta between the two index expressions... at
713 // this point we know that the first constant index of GEP1 is less
714 // than the first constant index of GEP2.
716 // Advance BasePtr[12]Ty over this first differing constant operand.
717 BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
718 getTypeAtIndex(GEP2Ops[FirstConstantOper]);
719 BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
720 getTypeAtIndex(GEP1Ops[FirstConstantOper]);
722 // We are going to be using TargetData::getIndexedOffset to determine the
723 // offset that each of the GEP's is reaching. To do this, we have to convert
724 // all variable references to constant references. To do this, we convert the
725 // initial sequence of array subscripts into constant zeros to start with.
726 const Type *ZeroIdxTy = GEPPointerTy;
727 for (unsigned i = 0; i != FirstConstantOper; ++i) {
728 if (!isa<StructType>(ZeroIdxTy))
729 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty);
731 if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
732 ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
735 // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
737 // Loop over the rest of the operands...
738 for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
739 const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
740 const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
741 // If they are equal, use a zero index...
742 if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
743 if (!isa<ConstantInt>(Op1))
744 GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType());
745 // Otherwise, just keep the constants we have.
748 if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
749 // If this is an array index, make sure the array element is in range.
750 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
751 if (Op1C->getZExtValue() >= AT->getNumElements())
752 return MayAlias; // Be conservative with out-of-range accesses
753 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) {
754 if (Op1C->getZExtValue() >= VT->getNumElements())
755 return MayAlias; // Be conservative with out-of-range accesses
759 // GEP1 is known to produce a value less than GEP2. To be
760 // conservatively correct, we must assume the largest possible
761 // constant is used in this position. This cannot be the initial
762 // index to the GEP instructions (because we know we have at least one
763 // element before this one with the different constant arguments), so
764 // we know that the current index must be into either a struct or
765 // array. Because we know it's not constant, this cannot be a
766 // structure index. Because of this, we can calculate the maximum
769 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
770 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1);
771 else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty))
772 GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,VT->getNumElements()-1);
777 if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
778 // If this is an array index, make sure the array element is in range.
779 if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr2Ty)) {
780 if (Op2C->getZExtValue() >= AT->getNumElements())
781 return MayAlias; // Be conservative with out-of-range accesses
782 } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr2Ty)) {
783 if (Op2C->getZExtValue() >= VT->getNumElements())
784 return MayAlias; // Be conservative with out-of-range accesses
786 } else { // Conservatively assume the minimum value for this index
787 GEP2Ops[i] = Constant::getNullValue(Op2->getType());
792 if (BasePtr1Ty && Op1) {
793 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
794 BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
799 if (BasePtr2Ty && Op2) {
800 if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
801 BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
807 if (GEPPointerTy->getElementType()->isSized()) {
809 getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
811 getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
812 assert(Offset1 != Offset2 &&
813 "There is at least one different constant here!");
815 // Make sure we compare the absolute difference.
816 if (Offset1 > Offset2)
817 std::swap(Offset1, Offset2);
819 if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
820 //cerr << "Determined that these two GEP's don't alias ["
821 // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
828 // Make sure that anything that uses AliasAnalysis pulls in this file...
829 DEFINING_FILE_FOR(BasicAliasAnalysis)