| //===- BasicAliasAnalysis.cpp - Local Alias Analysis Impl -----------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file defines the default implementation of the Alias Analysis interface |
| // that simply implements a few identities (two different globals cannot alias, |
| // etc), but otherwise does no analysis. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Analysis/AliasAnalysis.h" |
| #include "llvm/Analysis/Passes.h" |
| #include "llvm/Constants.h" |
| #include "llvm/DerivedTypes.h" |
| #include "llvm/Function.h" |
| #include "llvm/GlobalVariable.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/IntrinsicInst.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Target/TargetData.h" |
| #include "llvm/ADT/SmallVector.h" |
| #include "llvm/ADT/STLExtras.h" |
| #include "llvm/Support/Compiler.h" |
| #include "llvm/Support/GetElementPtrTypeIterator.h" |
| #include "llvm/Support/ManagedStatic.h" |
| #include <algorithm> |
| using namespace llvm; |
| |
| //===----------------------------------------------------------------------===// |
| // Useful predicates |
| //===----------------------------------------------------------------------===// |
| |
| // Determine if an AllocationInst instruction escapes from the function it is |
| // contained in. If it does not escape, there is no way for another function to |
| // mod/ref it. We do this by looking at its uses and determining if the uses |
| // can escape (recursively). |
| static bool AddressMightEscape(const Value *V) { |
| for (Value::use_const_iterator UI = V->use_begin(), E = V->use_end(); |
| UI != E; ++UI) { |
| const Instruction *I = cast<Instruction>(*UI); |
| switch (I->getOpcode()) { |
| case Instruction::Load: |
| break; //next use. |
| case Instruction::Store: |
| if (I->getOperand(0) == V) |
| return true; // Escapes if the pointer is stored. |
| break; // next use. |
| case Instruction::GetElementPtr: |
| if (AddressMightEscape(I)) |
| return true; |
| break; // next use. |
| case Instruction::BitCast: |
| if (AddressMightEscape(I)) |
| return true; |
| break; // next use |
| case Instruction::Ret: |
| // If returned, the address will escape to calling functions, but no |
| // callees could modify it. |
| break; // next use |
| case Instruction::Call: |
| // If the call is to a few known safe intrinsics, we know that it does |
| // not escape. |
| // TODO: Eventually just check the 'nocapture' attribute. |
| if (!isa<MemIntrinsic>(I)) |
| return true; |
| break; // next use |
| default: |
| return true; |
| } |
| } |
| return false; |
| } |
| |
| static const User *isGEP(const Value *V) { |
| if (isa<GetElementPtrInst>(V) || |
| (isa<ConstantExpr>(V) && |
| cast<ConstantExpr>(V)->getOpcode() == Instruction::GetElementPtr)) |
| return cast<User>(V); |
| return 0; |
| } |
| |
| static const Value *GetGEPOperands(const Value *V, |
| SmallVector<Value*, 16> &GEPOps){ |
| assert(GEPOps.empty() && "Expect empty list to populate!"); |
| GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1, |
| cast<User>(V)->op_end()); |
| |
| // Accumulate all of the chained indexes into the operand array |
| V = cast<User>(V)->getOperand(0); |
| |
| while (const User *G = isGEP(V)) { |
| if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) || |
| !cast<Constant>(GEPOps[0])->isNullValue()) |
| break; // Don't handle folding arbitrary pointer offsets yet... |
| GEPOps.erase(GEPOps.begin()); // Drop the zero index |
| GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end()); |
| V = G->getOperand(0); |
| } |
| return V; |
| } |
| |
| /// isIdentifiedObject - Return true if this pointer refers to a distinct and |
| /// identifiable object. This returns true for: |
| /// Global Variables and Functions |
| /// Allocas and Mallocs |
| /// ByVal and NoAlias Arguments |
| /// |
| static bool isIdentifiedObject(const Value *V) { |
| if (isa<GlobalValue>(V) || isa<AllocationInst>(V)) |
| return true; |
| if (const Argument *A = dyn_cast<Argument>(V)) |
| return A->hasNoAliasAttr() || A->hasByValAttr(); |
| return false; |
| } |
| |
| /// isKnownNonNull - Return true if we know that the specified value is never |
| /// null. |
| static bool isKnownNonNull(const Value *V) { |
| // Alloca never returns null, malloc might. |
| if (isa<AllocaInst>(V)) return true; |
| |
| // A byval argument is never null. |
| if (const Argument *A = dyn_cast<Argument>(V)) |
| return A->hasByValAttr(); |
| |
| // Global values are not null unless extern weak. |
| if (const GlobalValue *GV = dyn_cast<GlobalValue>(V)) |
| return !GV->hasExternalWeakLinkage(); |
| return false; |
| } |
| |
| /// isNonEscapingLocalObject - Return true if the pointer is to a function-local |
| /// object that never escapes from the function. |
| static bool isNonEscapingLocalObject(const Value *V) { |
| // If this is a local allocation, check to see if it escapes. |
| if (isa<AllocationInst>(V)) |
| return !AddressMightEscape(V); |
| |
| // If this is an argument that corresponds to a byval or noalias argument, |
| // it can't escape either. |
| if (const Argument *A = dyn_cast<Argument>(V)) |
| if (A->hasByValAttr() || A->hasNoAliasAttr()) |
| return !AddressMightEscape(V); |
| return false; |
| } |
| |
| |
| /// isObjectSmallerThan - Return true if we can prove that the object specified |
| /// by V is smaller than Size. |
| static bool isObjectSmallerThan(const Value *V, unsigned Size, |
| const TargetData &TD) { |
| const Type *AccessTy = 0; |
| if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) |
| AccessTy = GV->getType()->getElementType(); |
| |
| if (const AllocationInst *AI = dyn_cast<AllocationInst>(V)) |
| if (!AI->isArrayAllocation()) |
| AccessTy = AI->getType()->getElementType(); |
| |
| if (const Argument *A = dyn_cast<Argument>(V)) |
| if (A->hasByValAttr()) |
| AccessTy = cast<PointerType>(A->getType())->getElementType(); |
| |
| if (AccessTy && AccessTy->isSized()) |
| return TD.getABITypeSize(AccessTy) < Size; |
| return false; |
| } |
| |
| //===----------------------------------------------------------------------===// |
| // NoAA Pass |
| //===----------------------------------------------------------------------===// |
| |
| namespace { |
| /// NoAA - This class implements the -no-aa pass, which always returns "I |
| /// don't know" for alias queries. NoAA is unlike other alias analysis |
| /// implementations, in that it does not chain to a previous analysis. As |
| /// such it doesn't follow many of the rules that other alias analyses must. |
| /// |
| struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis { |
| static char ID; // Class identification, replacement for typeinfo |
| NoAA() : ImmutablePass(&ID) {} |
| explicit NoAA(void *PID) : ImmutablePass(PID) { } |
| |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.addRequired<TargetData>(); |
| } |
| |
| virtual void initializePass() { |
| TD = &getAnalysis<TargetData>(); |
| } |
| |
| virtual AliasResult alias(const Value *V1, unsigned V1Size, |
| const Value *V2, unsigned V2Size) { |
| return MayAlias; |
| } |
| |
| virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS, |
| std::vector<PointerAccessInfo> *Info) { |
| return UnknownModRefBehavior; |
| } |
| |
| virtual void getArgumentAccesses(Function *F, CallSite CS, |
| std::vector<PointerAccessInfo> &Info) { |
| assert(0 && "This method may not be called on this function!"); |
| } |
| |
| virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { } |
| virtual bool pointsToConstantMemory(const Value *P) { return false; } |
| virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) { |
| return ModRef; |
| } |
| virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) { |
| return ModRef; |
| } |
| virtual bool hasNoModRefInfoForCalls() const { return true; } |
| |
| virtual void deleteValue(Value *V) {} |
| virtual void copyValue(Value *From, Value *To) {} |
| }; |
| } // End of anonymous namespace |
| |
| // Register this pass... |
| char NoAA::ID = 0; |
| static RegisterPass<NoAA> |
| U("no-aa", "No Alias Analysis (always returns 'may' alias)", true, true); |
| |
| // Declare that we implement the AliasAnalysis interface |
| static RegisterAnalysisGroup<AliasAnalysis> V(U); |
| |
| ImmutablePass *llvm::createNoAAPass() { return new NoAA(); } |
| |
| //===----------------------------------------------------------------------===// |
| // BasicAA Pass |
| //===----------------------------------------------------------------------===// |
| |
| namespace { |
| /// BasicAliasAnalysis - This is the default alias analysis implementation. |
| /// Because it doesn't chain to a previous alias analysis (like -no-aa), it |
| /// derives from the NoAA class. |
| struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA { |
| static char ID; // Class identification, replacement for typeinfo |
| BasicAliasAnalysis() : NoAA(&ID) {} |
| AliasResult alias(const Value *V1, unsigned V1Size, |
| const Value *V2, unsigned V2Size); |
| |
| ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size); |
| ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) { |
| return NoAA::getModRefInfo(CS1,CS2); |
| } |
| |
| /// hasNoModRefInfoForCalls - We can provide mod/ref information against |
| /// non-escaping allocations. |
| virtual bool hasNoModRefInfoForCalls() const { return false; } |
| |
| /// pointsToConstantMemory - Chase pointers until we find a (constant |
| /// global) or not. |
| bool pointsToConstantMemory(const Value *P); |
| |
| private: |
| // CheckGEPInstructions - Check two GEP instructions with known |
| // must-aliasing base pointers. This checks to see if the index expressions |
| // preclude the pointers from aliasing... |
| AliasResult |
| CheckGEPInstructions(const Type* BasePtr1Ty, |
| Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size, |
| const Type *BasePtr2Ty, |
| Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size); |
| }; |
| } // End of anonymous namespace |
| |
| // Register this pass... |
| char BasicAliasAnalysis::ID = 0; |
| static RegisterPass<BasicAliasAnalysis> |
| X("basicaa", "Basic Alias Analysis (default AA impl)", false, true); |
| |
| // Declare that we implement the AliasAnalysis interface |
| static RegisterAnalysisGroup<AliasAnalysis, true> Y(X); |
| |
| ImmutablePass *llvm::createBasicAliasAnalysisPass() { |
| return new BasicAliasAnalysis(); |
| } |
| |
| |
| /// pointsToConstantMemory - Chase pointers until we find a (constant |
| /// global) or not. |
| bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) { |
| if (const GlobalVariable *GV = |
| dyn_cast<GlobalVariable>(P->getUnderlyingObject())) |
| return GV->isConstant(); |
| return false; |
| } |
| |
| // getModRefInfo - Check to see if the specified callsite can clobber the |
| // specified memory object. Since we only look at local properties of this |
| // function, we really can't say much about this query. We do, however, use |
| // simple "address taken" analysis on local objects. |
| // |
| AliasAnalysis::ModRefResult |
| BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) { |
| if (!isa<Constant>(P)) { |
| const Value *Object = P->getUnderlyingObject(); |
| |
| // If this is a tail call and P points to a stack location, we know that |
| // the tail call cannot access or modify the local stack. |
| // We cannot exclude byval arguments here; these belong to the caller of |
| // the current function not to the current function, and a tail callee |
| // may reference them. |
| if (isa<AllocaInst>(Object)) |
| if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction())) |
| if (CI->isTailCall()) |
| return NoModRef; |
| |
| // If the pointer is to a locally allocated object that does not escape, |
| // then the call can not mod/ref the pointer unless the call takes the |
| // argument without capturing it. |
| if (isNonEscapingLocalObject(Object)) { |
| bool passedAsArg = false; |
| // TODO: Eventually only check 'nocapture' arguments. |
| for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end(); |
| CI != CE; ++CI) |
| if (isa<PointerType>((*CI)->getType()) && |
| alias(cast<Value>(CI), ~0U, P, ~0U) != NoAlias) |
| passedAsArg = true; |
| |
| if (!passedAsArg) |
| return NoModRef; |
| } |
| } |
| |
| // The AliasAnalysis base class has some smarts, lets use them. |
| return AliasAnalysis::getModRefInfo(CS, P, Size); |
| } |
| |
| |
| // alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such |
| // as array references. Note that this function is heavily tail recursive. |
| // Hopefully we have a smart C++ compiler. :) |
| // |
| AliasAnalysis::AliasResult |
| BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size, |
| const Value *V2, unsigned V2Size) { |
| // Strip off any constant expression casts if they exist |
| if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1)) |
| if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType())) |
| V1 = CE->getOperand(0); |
| if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2)) |
| if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType())) |
| V2 = CE->getOperand(0); |
| |
| // Are we checking for alias of the same value? |
| if (V1 == V2) return MustAlias; |
| |
| if ((!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType())) && |
| V1->getType() != Type::Int64Ty && V2->getType() != Type::Int64Ty) |
| return NoAlias; // Scalars cannot alias each other |
| |
| // Strip off cast instructions... |
| if (const BitCastInst *I = dyn_cast<BitCastInst>(V1)) |
| return alias(I->getOperand(0), V1Size, V2, V2Size); |
| if (const BitCastInst *I = dyn_cast<BitCastInst>(V2)) |
| return alias(V1, V1Size, I->getOperand(0), V2Size); |
| |
| // Figure out what objects these things are pointing to if we can... |
| const Value *O1 = V1->getUnderlyingObject(); |
| const Value *O2 = V2->getUnderlyingObject(); |
| |
| if (O1 != O2) { |
| // If V1/V2 point to two different objects we know that we have no alias. |
| if (isIdentifiedObject(O1) && isIdentifiedObject(O2)) |
| return NoAlias; |
| |
| // Incoming argument cannot alias locally allocated object! |
| if ((isa<Argument>(O1) && isa<AllocationInst>(O2)) || |
| (isa<Argument>(O2) && isa<AllocationInst>(O1))) |
| return NoAlias; |
| |
| // Most objects can't alias null. |
| if ((isa<ConstantPointerNull>(V2) && isKnownNonNull(O1)) || |
| (isa<ConstantPointerNull>(V1) && isKnownNonNull(O2))) |
| return NoAlias; |
| } |
| |
| // If the size of one access is larger than the entire object on the other |
| // side, then we know such behavior is undefined and can assume no alias. |
| const TargetData &TD = getTargetData(); |
| if ((V1Size != ~0U && isObjectSmallerThan(O2, V1Size, TD)) || |
| (V2Size != ~0U && isObjectSmallerThan(O1, V2Size, TD))) |
| return NoAlias; |
| |
| // If one pointer is the result of a call/invoke and the other is a |
| // non-escaping local object, then we know the object couldn't escape to a |
| // point where the call could return it. |
| if ((isa<CallInst>(O1) || isa<InvokeInst>(O1)) && |
| isNonEscapingLocalObject(O2)) |
| return NoAlias; |
| if ((isa<CallInst>(O2) || isa<InvokeInst>(O2)) && |
| isNonEscapingLocalObject(O1)) |
| return NoAlias; |
| |
| // If we have two gep instructions with must-alias'ing base pointers, figure |
| // out if the indexes to the GEP tell us anything about the derived pointer. |
| // Note that we also handle chains of getelementptr instructions as well as |
| // constant expression getelementptrs here. |
| // |
| if (isGEP(V1) && isGEP(V2)) { |
| // Drill down into the first non-gep value, to test for must-aliasing of |
| // the base pointers. |
| const User *G = cast<User>(V1); |
| while (isGEP(G->getOperand(0)) && |
| G->getOperand(1) == |
| Constant::getNullValue(G->getOperand(1)->getType())) |
| G = cast<User>(G->getOperand(0)); |
| const Value *BasePtr1 = G->getOperand(0); |
| |
| G = cast<User>(V2); |
| while (isGEP(G->getOperand(0)) && |
| G->getOperand(1) == |
| Constant::getNullValue(G->getOperand(1)->getType())) |
| G = cast<User>(G->getOperand(0)); |
| const Value *BasePtr2 = G->getOperand(0); |
| |
| // Do the base pointers alias? |
| AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U); |
| if (BaseAlias == NoAlias) return NoAlias; |
| if (BaseAlias == MustAlias) { |
| // If the base pointers alias each other exactly, check to see if we can |
| // figure out anything about the resultant pointers, to try to prove |
| // non-aliasing. |
| |
| // Collect all of the chained GEP operands together into one simple place |
| SmallVector<Value*, 16> GEP1Ops, GEP2Ops; |
| BasePtr1 = GetGEPOperands(V1, GEP1Ops); |
| BasePtr2 = GetGEPOperands(V2, GEP2Ops); |
| |
| // If GetGEPOperands were able to fold to the same must-aliased pointer, |
| // do the comparison. |
| if (BasePtr1 == BasePtr2) { |
| AliasResult GAlias = |
| CheckGEPInstructions(BasePtr1->getType(), |
| &GEP1Ops[0], GEP1Ops.size(), V1Size, |
| BasePtr2->getType(), |
| &GEP2Ops[0], GEP2Ops.size(), V2Size); |
| if (GAlias != MayAlias) |
| return GAlias; |
| } |
| } |
| } |
| |
| // Check to see if these two pointers are related by a getelementptr |
| // instruction. If one pointer is a GEP with a non-zero index of the other |
| // pointer, we know they cannot alias. |
| // |
| if (isGEP(V2)) { |
| std::swap(V1, V2); |
| std::swap(V1Size, V2Size); |
| } |
| |
| if (V1Size != ~0U && V2Size != ~0U) |
| if (isGEP(V1)) { |
| SmallVector<Value*, 16> GEPOperands; |
| const Value *BasePtr = GetGEPOperands(V1, GEPOperands); |
| |
| AliasResult R = alias(BasePtr, V1Size, V2, V2Size); |
| if (R == MustAlias) { |
| // If there is at least one non-zero constant index, we know they cannot |
| // alias. |
| bool ConstantFound = false; |
| bool AllZerosFound = true; |
| for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i) |
| if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) { |
| if (!C->isNullValue()) { |
| ConstantFound = true; |
| AllZerosFound = false; |
| break; |
| } |
| } else { |
| AllZerosFound = false; |
| } |
| |
| // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases |
| // the ptr, the end result is a must alias also. |
| if (AllZerosFound) |
| return MustAlias; |
| |
| if (ConstantFound) { |
| if (V2Size <= 1 && V1Size <= 1) // Just pointer check? |
| return NoAlias; |
| |
| // Otherwise we have to check to see that the distance is more than |
| // the size of the argument... build an index vector that is equal to |
| // the arguments provided, except substitute 0's for any variable |
| // indexes we find... |
| if (cast<PointerType>( |
| BasePtr->getType())->getElementType()->isSized()) { |
| for (unsigned i = 0; i != GEPOperands.size(); ++i) |
| if (!isa<ConstantInt>(GEPOperands[i])) |
| GEPOperands[i] = |
| Constant::getNullValue(GEPOperands[i]->getType()); |
| int64_t Offset = |
| getTargetData().getIndexedOffset(BasePtr->getType(), |
| &GEPOperands[0], |
| GEPOperands.size()); |
| |
| if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size) |
| return NoAlias; |
| } |
| } |
| } |
| } |
| |
| return MayAlias; |
| } |
| |
| // This function is used to determin if the indices of two GEP instructions are |
| // equal. V1 and V2 are the indices. |
| static bool IndexOperandsEqual(Value *V1, Value *V2) { |
| if (V1->getType() == V2->getType()) |
| return V1 == V2; |
| if (Constant *C1 = dyn_cast<Constant>(V1)) |
| if (Constant *C2 = dyn_cast<Constant>(V2)) { |
| // Sign extend the constants to long types, if necessary |
| if (C1->getType() != Type::Int64Ty) |
| C1 = ConstantExpr::getSExt(C1, Type::Int64Ty); |
| if (C2->getType() != Type::Int64Ty) |
| C2 = ConstantExpr::getSExt(C2, Type::Int64Ty); |
| return C1 == C2; |
| } |
| return false; |
| } |
| |
| /// CheckGEPInstructions - Check two GEP instructions with known must-aliasing |
| /// base pointers. This checks to see if the index expressions preclude the |
| /// pointers from aliasing... |
| AliasAnalysis::AliasResult |
| BasicAliasAnalysis::CheckGEPInstructions( |
| const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S, |
| const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) { |
| // We currently can't handle the case when the base pointers have different |
| // primitive types. Since this is uncommon anyway, we are happy being |
| // extremely conservative. |
| if (BasePtr1Ty != BasePtr2Ty) |
| return MayAlias; |
| |
| const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty); |
| |
| // Find the (possibly empty) initial sequence of equal values... which are not |
| // necessarily constants. |
| unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops; |
| unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands); |
| unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands); |
| unsigned UnequalOper = 0; |
| while (UnequalOper != MinOperands && |
| IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper])) { |
| // Advance through the type as we go... |
| ++UnequalOper; |
| if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty)) |
| BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]); |
| else { |
| // If all operands equal each other, then the derived pointers must |
| // alias each other... |
| BasePtr1Ty = 0; |
| assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands && |
| "Ran out of type nesting, but not out of operands?"); |
| return MustAlias; |
| } |
| } |
| |
| // If we have seen all constant operands, and run out of indexes on one of the |
| // getelementptrs, check to see if the tail of the leftover one is all zeros. |
| // If so, return mustalias. |
| if (UnequalOper == MinOperands) { |
| if (NumGEP1Ops < NumGEP2Ops) { |
| std::swap(GEP1Ops, GEP2Ops); |
| std::swap(NumGEP1Ops, NumGEP2Ops); |
| } |
| |
| bool AllAreZeros = true; |
| for (unsigned i = UnequalOper; i != MaxOperands; ++i) |
| if (!isa<Constant>(GEP1Ops[i]) || |
| !cast<Constant>(GEP1Ops[i])->isNullValue()) { |
| AllAreZeros = false; |
| break; |
| } |
| if (AllAreZeros) return MustAlias; |
| } |
| |
| |
| // So now we know that the indexes derived from the base pointers, |
| // which are known to alias, are different. We can still determine a |
| // no-alias result if there are differing constant pairs in the index |
| // chain. For example: |
| // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S)) |
| // |
| // We have to be careful here about array accesses. In particular, consider: |
| // A[1][0] vs A[0][i] |
| // In this case, we don't *know* that the array will be accessed in bounds: |
| // the index could even be negative. Because of this, we have to |
| // conservatively *give up* and return may alias. We disregard differing |
| // array subscripts that are followed by a variable index without going |
| // through a struct. |
| // |
| unsigned SizeMax = std::max(G1S, G2S); |
| if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work. |
| |
| // Scan for the first operand that is constant and unequal in the |
| // two getelementptrs... |
| unsigned FirstConstantOper = UnequalOper; |
| for (; FirstConstantOper != MinOperands; ++FirstConstantOper) { |
| const Value *G1Oper = GEP1Ops[FirstConstantOper]; |
| const Value *G2Oper = GEP2Ops[FirstConstantOper]; |
| |
| if (G1Oper != G2Oper) // Found non-equal constant indexes... |
| if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper))) |
| if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){ |
| if (G1OC->getType() != G2OC->getType()) { |
| // Sign extend both operands to long. |
| if (G1OC->getType() != Type::Int64Ty) |
| G1OC = ConstantExpr::getSExt(G1OC, Type::Int64Ty); |
| if (G2OC->getType() != Type::Int64Ty) |
| G2OC = ConstantExpr::getSExt(G2OC, Type::Int64Ty); |
| GEP1Ops[FirstConstantOper] = G1OC; |
| GEP2Ops[FirstConstantOper] = G2OC; |
| } |
| |
| if (G1OC != G2OC) { |
| // Handle the "be careful" case above: if this is an array/vector |
| // subscript, scan for a subsequent variable array index. |
| if (isa<SequentialType>(BasePtr1Ty)) { |
| const Type *NextTy = |
| cast<SequentialType>(BasePtr1Ty)->getElementType(); |
| bool isBadCase = false; |
| |
| for (unsigned Idx = FirstConstantOper+1; |
| Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) { |
| const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx]; |
| if (!isa<Constant>(V1) || !isa<Constant>(V2)) { |
| isBadCase = true; |
| break; |
| } |
| NextTy = cast<SequentialType>(NextTy)->getElementType(); |
| } |
| |
| if (isBadCase) G1OC = 0; |
| } |
| |
| // Make sure they are comparable (ie, not constant expressions), and |
| // make sure the GEP with the smaller leading constant is GEP1. |
| if (G1OC) { |
| Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT, |
| G1OC, G2OC); |
| if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) { |
| if (CV->getZExtValue()) { // If they are comparable and G2 > G1 |
| std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2 |
| std::swap(NumGEP1Ops, NumGEP2Ops); |
| } |
| break; |
| } |
| } |
| } |
| } |
| BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper); |
| } |
| |
| // No shared constant operands, and we ran out of common operands. At this |
| // point, the GEP instructions have run through all of their operands, and we |
| // haven't found evidence that there are any deltas between the GEP's. |
| // However, one GEP may have more operands than the other. If this is the |
| // case, there may still be hope. Check this now. |
| if (FirstConstantOper == MinOperands) { |
| // Make GEP1Ops be the longer one if there is a longer one. |
| if (NumGEP1Ops < NumGEP2Ops) { |
| std::swap(GEP1Ops, GEP2Ops); |
| std::swap(NumGEP1Ops, NumGEP2Ops); |
| } |
| |
| // Is there anything to check? |
| if (NumGEP1Ops > MinOperands) { |
| for (unsigned i = FirstConstantOper; i != MaxOperands; ++i) |
| if (isa<ConstantInt>(GEP1Ops[i]) && |
| !cast<ConstantInt>(GEP1Ops[i])->isZero()) { |
| // Yup, there's a constant in the tail. Set all variables to |
| // constants in the GEP instruction to make it suitable for |
| // TargetData::getIndexedOffset. |
| for (i = 0; i != MaxOperands; ++i) |
| if (!isa<ConstantInt>(GEP1Ops[i])) |
| GEP1Ops[i] = Constant::getNullValue(GEP1Ops[i]->getType()); |
| // Okay, now get the offset. This is the relative offset for the full |
| // instruction. |
| const TargetData &TD = getTargetData(); |
| int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops, |
| NumGEP1Ops); |
| |
| // Now check without any constants at the end. |
| int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops, |
| MinOperands); |
| |
| // Make sure we compare the absolute difference. |
| if (Offset1 > Offset2) |
| std::swap(Offset1, Offset2); |
| |
| // If the tail provided a bit enough offset, return noalias! |
| if ((uint64_t)(Offset2-Offset1) >= SizeMax) |
| return NoAlias; |
| // Otherwise break - we don't look for another constant in the tail. |
| break; |
| } |
| } |
| |
| // Couldn't find anything useful. |
| return MayAlias; |
| } |
| |
| // If there are non-equal constants arguments, then we can figure |
| // out a minimum known delta between the two index expressions... at |
| // this point we know that the first constant index of GEP1 is less |
| // than the first constant index of GEP2. |
| |
| // Advance BasePtr[12]Ty over this first differing constant operand. |
| BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)-> |
| getTypeAtIndex(GEP2Ops[FirstConstantOper]); |
| BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)-> |
| getTypeAtIndex(GEP1Ops[FirstConstantOper]); |
| |
| // We are going to be using TargetData::getIndexedOffset to determine the |
| // offset that each of the GEP's is reaching. To do this, we have to convert |
| // all variable references to constant references. To do this, we convert the |
| // initial sequence of array subscripts into constant zeros to start with. |
| const Type *ZeroIdxTy = GEPPointerTy; |
| for (unsigned i = 0; i != FirstConstantOper; ++i) { |
| if (!isa<StructType>(ZeroIdxTy)) |
| GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::Int32Ty); |
| |
| if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy)) |
| ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]); |
| } |
| |
| // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok |
| |
| // Loop over the rest of the operands... |
| for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) { |
| const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0; |
| const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0; |
| // If they are equal, use a zero index... |
| if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) { |
| if (!isa<ConstantInt>(Op1)) |
| GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Op1->getType()); |
| // Otherwise, just keep the constants we have. |
| } else { |
| if (Op1) { |
| if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) { |
| // If this is an array index, make sure the array element is in range. |
| if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) { |
| if (Op1C->getZExtValue() >= AT->getNumElements()) |
| return MayAlias; // Be conservative with out-of-range accesses |
| } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) { |
| if (Op1C->getZExtValue() >= VT->getNumElements()) |
| return MayAlias; // Be conservative with out-of-range accesses |
| } |
| |
| } else { |
| // GEP1 is known to produce a value less than GEP2. To be |
| // conservatively correct, we must assume the largest possible |
| // constant is used in this position. This cannot be the initial |
| // index to the GEP instructions (because we know we have at least one |
| // element before this one with the different constant arguments), so |
| // we know that the current index must be into either a struct or |
| // array. Because we know it's not constant, this cannot be a |
| // structure index. Because of this, we can calculate the maximum |
| // value possible. |
| // |
| if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) |
| GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,AT->getNumElements()-1); |
| else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) |
| GEP1Ops[i] = ConstantInt::get(Type::Int64Ty,VT->getNumElements()-1); |
| } |
| } |
| |
| if (Op2) { |
| if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) { |
| // If this is an array index, make sure the array element is in range. |
| if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr2Ty)) { |
| if (Op2C->getZExtValue() >= AT->getNumElements()) |
| return MayAlias; // Be conservative with out-of-range accesses |
| } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr2Ty)) { |
| if (Op2C->getZExtValue() >= VT->getNumElements()) |
| return MayAlias; // Be conservative with out-of-range accesses |
| } |
| } else { // Conservatively assume the minimum value for this index |
| GEP2Ops[i] = Constant::getNullValue(Op2->getType()); |
| } |
| } |
| } |
| |
| if (BasePtr1Ty && Op1) { |
| if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty)) |
| BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]); |
| else |
| BasePtr1Ty = 0; |
| } |
| |
| if (BasePtr2Ty && Op2) { |
| if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty)) |
| BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]); |
| else |
| BasePtr2Ty = 0; |
| } |
| } |
| |
| if (GEPPointerTy->getElementType()->isSized()) { |
| int64_t Offset1 = |
| getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops); |
| int64_t Offset2 = |
| getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops); |
| assert(Offset1 != Offset2 && |
| "There is at least one different constant here!"); |
| |
| // Make sure we compare the absolute difference. |
| if (Offset1 > Offset2) |
| std::swap(Offset1, Offset2); |
| |
| if ((uint64_t)(Offset2-Offset1) >= SizeMax) { |
| //cerr << "Determined that these two GEP's don't alias [" |
| // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2; |
| return NoAlias; |
| } |
| } |
| return MayAlias; |
| } |
| |
| // Make sure that anything that uses AliasAnalysis pulls in this file... |
| DEFINING_FILE_FOR(BasicAliasAnalysis) |
