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Diffstat (limited to 'lib/Analysis/BasicAliasAnalysis.cpp')
| -rw-r--r-- | lib/Analysis/BasicAliasAnalysis.cpp | 807 |
1 files changed, 807 insertions, 0 deletions
diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp new file mode 100644 index 0000000000..86cc5646be --- /dev/null +++ b/lib/Analysis/BasicAliasAnalysis.cpp @@ -0,0 +1,807 @@ +//===- BasicAliasAnalysis.cpp - Local Alias Analysis Impl -----------------===// +// +// The LLVM Compiler Infrastructure +// +// This file was developed by the LLVM research group and 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/Pass.h" +#include "llvm/Target/TargetData.h" +#include "llvm/Support/GetElementPtrTypeIterator.h" +#include <algorithm> +using namespace llvm; + +// Make sure that anything that uses AliasAnalysis pulls in this file... +void llvm::BasicAAStub() {} + +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 NoAA : public ImmutablePass, public AliasAnalysis { + 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) {} + }; + + // Register this pass... + RegisterOpt<NoAA> + U("no-aa", "No Alias Analysis (always returns 'may' alias)"); + + // Declare that we implement the AliasAnalysis interface + RegisterAnalysisGroup<AliasAnalysis, NoAA> V; +} // End of anonymous namespace + +ImmutablePass *llvm::createNoAAPass() { return new NoAA(); } + +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 BasicAliasAnalysis : public NoAA { + 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); + + virtual ModRefBehavior getModRefBehavior(Function *F, CallSite CS, + std::vector<PointerAccessInfo> *Info); + + 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, std::vector<Value*> &GEP1Ops, + unsigned G1Size, + const Type *BasePtr2Ty, std::vector<Value*> &GEP2Ops, + unsigned G2Size); + }; + + // Register this pass... + RegisterOpt<BasicAliasAnalysis> + X("basicaa", "Basic Alias Analysis (default AA impl)"); + + // Declare that we implement the AliasAnalysis interface + RegisterAnalysisGroup<AliasAnalysis, BasicAliasAnalysis, true> Y; +} // End of anonymous namespace + +ImmutablePass *llvm::createBasicAliasAnalysisPass() { + return new BasicAliasAnalysis(); +} + +// hasUniqueAddress - Return true if the specified value points to something +// with a unique, discernable, address. +static inline bool hasUniqueAddress(const Value *V) { + return isa<GlobalValue>(V) || isa<AllocationInst>(V); +} + +// getUnderlyingObject - This traverses the use chain to figure out what object +// the specified value points to. If the value points to, or is derived from, a +// unique object or an argument, return it. +static const Value *getUnderlyingObject(const Value *V) { + if (!isa<PointerType>(V->getType())) return 0; + + // If we are at some type of object... return it. + if (hasUniqueAddress(V) || isa<Argument>(V)) return V; + + // Traverse through different addressing mechanisms... + if (const Instruction *I = dyn_cast<Instruction>(V)) { + if (isa<CastInst>(I) || isa<GetElementPtrInst>(I)) + return getUnderlyingObject(I->getOperand(0)); + } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) { + if (CE->getOpcode() == Instruction::Cast || + CE->getOpcode() == Instruction::GetElementPtr) + return getUnderlyingObject(CE->getOperand(0)); + } else if (const GlobalValue *GV = dyn_cast<GlobalValue>(V)) { + return GV; + } + return 0; +} + +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, std::vector<Value*> &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; +} + +/// pointsToConstantMemory - Chase pointers until we find a (constant +/// global) or not. +bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) { + if (const Value *V = getUnderlyingObject(P)) + if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) + return GV->isConstant(); + return false; +} + +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; + case Instruction::Store: + if (I->getOperand(0) == V) + return true; // Escapes if the pointer is stored. + break; + case Instruction::GetElementPtr: + if (AddressMightEscape(I)) return true; + break; + case Instruction::Cast: + if (!isa<PointerType>(I->getType())) + return true; + if (AddressMightEscape(I)) return true; + break; + case Instruction::Ret: + // If returned, the address will escape to calling functions, but no + // callees could modify it. + break; + default: + return true; + } + } + 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)) + if (const AllocationInst *AI = + dyn_cast_or_null<AllocationInst>(getUnderlyingObject(P))) { + // Okay, the pointer is to a stack allocated object. If we can prove that + // the pointer never "escapes", then we know the call cannot clobber it, + // because it simply can't get its address. + if (!AddressMightEscape(AI)) + return NoModRef; + + // 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. + if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction())) + if (CI->isTailCall() && isa<AllocaInst>(AI)) + 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->getOpcode() == Instruction::Cast && + isa<PointerType>(CE->getOperand(0)->getType())) + V1 = CE->getOperand(0); + if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2)) + if (CE->getOpcode() == Instruction::Cast && + 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::LongTy && V2->getType() != Type::LongTy) + return NoAlias; // Scalars cannot alias each other + + // Strip off cast instructions... + if (const Instruction *I = dyn_cast<CastInst>(V1)) + if (isa<PointerType>(I->getOperand(0)->getType())) + return alias(I->getOperand(0), V1Size, V2, V2Size); + if (const Instruction *I = dyn_cast<CastInst>(V2)) + if (isa<PointerType>(I->getOperand(0)->getType())) + return alias(V1, V1Size, I->getOperand(0), V2Size); + + // Figure out what objects these things are pointing to if we can... + const Value *O1 = getUnderlyingObject(V1); + const Value *O2 = getUnderlyingObject(V2); + + // Pointing at a discernible object? + if (O1) { + if (O2) { + if (isa<Argument>(O1)) { + // Incoming argument cannot alias locally allocated object! + if (isa<AllocationInst>(O2)) return NoAlias; + // Otherwise, nothing is known... + } else if (isa<Argument>(O2)) { + // Incoming argument cannot alias locally allocated object! + if (isa<AllocationInst>(O1)) return NoAlias; + // Otherwise, nothing is known... + } else if (O1 != O2) { + // If they are two different objects, we know that we have no alias... + return NoAlias; + } + + // If they are the same object, they we can look at the indexes. If they + // index off of the object is the same for both pointers, they must alias. + // If they are provably different, they must not alias. Otherwise, we + // can't tell anything. + } + + + if (!isa<Argument>(O1) && isa<ConstantPointerNull>(V2)) + return NoAlias; // Unique values don't alias null + + if (isa<GlobalVariable>(O1) || + (isa<AllocationInst>(O1) && + !cast<AllocationInst>(O1)->isArrayAllocation())) + if (cast<PointerType>(O1->getType())->getElementType()->isSized()) { + // If the size of the other access is larger than the total size of the + // global/alloca/malloc, it cannot be accessing the global (it's + // undefined to load or store bytes before or after an object). + const Type *ElTy = cast<PointerType>(O1->getType())->getElementType(); + unsigned GlobalSize = getTargetData().getTypeSize(ElTy); + if (GlobalSize < V2Size && V2Size != ~0U) + return NoAlias; + } + } + + if (O2) { + if (!isa<Argument>(O2) && isa<ConstantPointerNull>(V1)) + return NoAlias; // Unique values don't alias null + + if (isa<GlobalVariable>(O2) || + (isa<AllocationInst>(O2) && + !cast<AllocationInst>(O2)->isArrayAllocation())) + if (cast<PointerType>(O2->getType())->getElementType()->isSized()) { + // If the size of the other access is larger than the total size of the + // global/alloca/malloc, it cannot be accessing the object (it's + // undefined to load or store bytes before or after an object). + const Type *ElTy = cast<PointerType>(O2->getType())->getElementType(); + unsigned GlobalSize = getTargetData().getTypeSize(ElTy); + if (GlobalSize < V1Size && V1Size != ~0U) + 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 Value *BasePtr1 = V1, *BasePtr2 = V2; + do { + BasePtr1 = cast<User>(BasePtr1)->getOperand(0); + } while (isGEP(BasePtr1) && + cast<User>(BasePtr1)->getOperand(1) == + Constant::getNullValue(cast<User>(BasePtr1)->getOperand(1)->getType())); + do { + BasePtr2 = cast<User>(BasePtr2)->getOperand(0); + } while (isGEP(BasePtr2) && + cast<User>(BasePtr2)->getOperand(1) == + Constant::getNullValue(cast<User>(BasePtr2)->getOperand(1)->getType())); + + // Do the base pointers alias? + AliasResult BaseAlias = alias(BasePtr1, V1Size, BasePtr2, V2Size); + 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 + std::vector<Value*> 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, V1Size, + BasePtr2->getType(), GEP2Ops, 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 (const User *GEP = isGEP(V1)) { + std::vector<Value*> 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); + + if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size) + return NoAlias; + } + } + } + } + + return MayAlias; +} + +static bool ValuesEqual(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. + C1 = ConstantExpr::getSignExtend(C1, Type::LongTy); + C2 = ConstantExpr::getSignExtend(C2, Type::LongTy); + 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, std::vector<Value*> &GEP1Ops, + unsigned G1S, + const Type *BasePtr2Ty, std::vector<Value*> &GEP2Ops, + 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 = GEP1Ops.size(), NumGEP2Operands = GEP2Ops.size(); + unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands); + unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands); + unsigned UnequalOper = 0; + while (UnequalOper != MinOperands && + ValuesEqual(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 (GEP1Ops.size() < GEP2Ops.size()) std::swap(GEP1Ops, GEP2Ops); + + 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)) + // + 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. + G1OC = ConstantExpr::getSignExtend(G1OC, Type::LongTy); + G2OC = ConstantExpr::getSignExtend(G2OC, Type::LongTy); + GEP1Ops[FirstConstantOper] = G1OC; + GEP2Ops[FirstConstantOper] = G2OC; + } + + if (G1OC != G2OC) { + // Make sure they are comparable (ie, not constant expressions), and + // make sure the GEP with the smaller leading constant is GEP1. + Constant *Compare = ConstantExpr::getSetGT(G1OC, G2OC); + if (ConstantBool *CV = dyn_cast<ConstantBool>(Compare)) { + if (CV->getValue()) // If they are comparable and G2 > G1 + std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2 + 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 (GEP1Ops.size() < GEP2Ops.size()) + std::swap(GEP1Ops, GEP2Ops); + + // Is there anything to check? + if (GEP1Ops.size() > MinOperands) { + for (unsigned i = FirstConstantOper; i != MaxOperands; ++i) + if (isa<ConstantInt>(GEP1Ops[i]) && + !cast<Constant>(GEP1Ops[i])->isNullValue()) { + // Yup, there's a constant in the tail. Set all variables to + // constants in the GEP instruction to make it suiteable 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); + + // Now crop off any constants from the end... + GEP1Ops.resize(MinOperands); + int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops); + + // If the tail provided a bit enough offset, return noalias! + if ((uint64_t)(Offset2-Offset1) >= SizeMax) + return NoAlias; + } + } + + // 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 equal sequence of variables into constant zeros to start with. + for (unsigned i = 0; i != FirstConstantOper; ++i) + if (!isa<ConstantInt>(GEP1Ops[i]) || !isa<ConstantInt>(GEP2Ops[i])) + GEP1Ops[i] = GEP2Ops[i] = Constant::getNullValue(Type::UIntTy); + + // 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 < GEP1Ops.size() ? GEP1Ops[i] : 0; + const Value *Op2 = i < GEP2Ops.size() ? 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->getRawValue() >= AT->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] = ConstantSInt::get(Type::LongTy,AT->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>(BasePtr1Ty)) + if (Op2C->getRawValue() >= AT->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); + int64_t Offset2 = getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops); + assert(Offset1<Offset2 && "There is at least one different constant here!"); + + if ((uint64_t)(Offset2-Offset1) >= SizeMax) { + //std::cerr << "Determined that these two GEP's don't alias [" + // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2; + return NoAlias; + } + } + return MayAlias; +} + +namespace { + struct StringCompare { + bool operator()(const char *LHS, const char *RHS) { + return strcmp(LHS, RHS) < 0; + } + }; +} + +// Note that this list cannot contain libm functions (such as acos and sqrt) +// that set errno on a domain or other error. +static const char *DoesntAccessMemoryTable[] = { + // LLVM intrinsics: + "llvm.frameaddress", "llvm.returnaddress", "llvm.readport", + "llvm.isunordered", "llvm.sqrt", "llvm.ctpop", "llvm.ctlz", "llvm.cttz", + + "abs", "labs", "llabs", "imaxabs", "fabs", "fabsf", "fabsl", + "trunc", "truncf", "truncl", "ldexp", + + "atan", "atanf", "atanl", "atan2", "atan2f", "atan2l", + "cbrt", + "cos", "cosf", "cosl", + "exp", "expf", "expl", + "hypot", + "sin", "sinf", "sinl", + "tan", "tanf", "tanl", "tanh", "tanhf", "tanhl", + + "floor", "floorf", "floorl", "ceil", "ceilf", "ceill", + + // ctype.h + "isalnum", "isalpha", "iscntrl", "isdigit", "isgraph", "islower", "isprint" + "ispunct", "isspace", "isupper", "isxdigit", "tolower", "toupper", + + // wctype.h" + "iswalnum", "iswalpha", "iswcntrl", "iswdigit", "iswgraph", "iswlower", + "iswprint", "iswpunct", "iswspace", "iswupper", "iswxdigit", + + "iswctype", "towctrans", "towlower", "towupper", + + "btowc", "wctob", + + "isinf", "isnan", "finite", + + // C99 math functions + "copysign", "copysignf", "copysignd", + "nexttoward", "nexttowardf", "nexttowardd", + "nextafter", "nextafterf", "nextafterd", + + // ISO C99: + "__signbit", "__signbitf", "__signbitl", +}; + +static const unsigned DAMTableSize = + sizeof(DoesntAccessMemoryTable)/sizeof(DoesntAccessMemoryTable[0]); + +static const char *OnlyReadsMemoryTable[] = { + "atoi", "atol", "atof", "atoll", "atoq", "a64l", + "bcmp", "memcmp", "memchr", "memrchr", "wmemcmp", "wmemchr", + + // Strings + "strcmp", "strcasecmp", "strcoll", "strncmp", "strncasecmp", + "strchr", "strcspn", "strlen", "strpbrk", "strrchr", "strspn", "strstr", + "index", "rindex", + + // Wide char strings + "wcschr", "wcscmp", "wcscoll", "wcscspn", "wcslen", "wcsncmp", "wcspbrk", + "wcsrchr", "wcsspn", "wcsstr", + + // glibc + "alphasort", "alphasort64", "versionsort", "versionsort64", + + // C99 + "nan", "nanf", "nand", + + // File I/O + "feof", "ferror", "fileno", + "feof_unlocked", "ferror_unlocked", "fileno_unlocked" +}; + +static const unsigned ORMTableSize = + sizeof(OnlyReadsMemoryTable)/sizeof(OnlyReadsMemoryTable[0]); + +AliasAnalysis::ModRefBehavior +BasicAliasAnalysis::getModRefBehavior(Function *F, CallSite CS, + std::vector<PointerAccessInfo> *Info) { + if (!F->isExternal()) return UnknownModRefBehavior; + + static bool Initialized = false; + if (!Initialized) { + // Sort the table the first time through. + std::sort(DoesntAccessMemoryTable, DoesntAccessMemoryTable+DAMTableSize, + StringCompare()); + std::sort(OnlyReadsMemoryTable, OnlyReadsMemoryTable+ORMTableSize, + StringCompare()); + Initialized = true; + } + + const char **Ptr = std::lower_bound(DoesntAccessMemoryTable, + DoesntAccessMemoryTable+DAMTableSize, + F->getName().c_str(), StringCompare()); + if (Ptr != DoesntAccessMemoryTable+DAMTableSize && *Ptr == F->getName()) + return DoesNotAccessMemory; + + Ptr = std::lower_bound(OnlyReadsMemoryTable, + OnlyReadsMemoryTable+ORMTableSize, + F->getName().c_str(), StringCompare()); + if (Ptr != OnlyReadsMemoryTable+ORMTableSize && *Ptr == F->getName()) + return OnlyReadsMemory; + + return UnknownModRefBehavior; +} |