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Diffstat (limited to 'contrib/llvm/lib/Analysis/BasicAliasAnalysis.cpp')
| -rw-r--r-- | contrib/llvm/lib/Analysis/BasicAliasAnalysis.cpp | 1616 |
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diff --git a/contrib/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/contrib/llvm/lib/Analysis/BasicAliasAnalysis.cpp new file mode 100644 index 0000000..00f346e --- /dev/null +++ b/contrib/llvm/lib/Analysis/BasicAliasAnalysis.cpp @@ -0,0 +1,1616 @@ +//===- BasicAliasAnalysis.cpp - Stateless 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 primary stateless implementation of the +// Alias Analysis interface that implements identities (two different +// globals cannot alias, etc), but does no stateful analysis. +// +//===----------------------------------------------------------------------===// + +#include "llvm/Analysis/BasicAliasAnalysis.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/Analysis/CFG.h" +#include "llvm/Analysis/CaptureTracking.h" +#include "llvm/Analysis/InstructionSimplify.h" +#include "llvm/Analysis/LoopInfo.h" +#include "llvm/Analysis/MemoryBuiltins.h" +#include "llvm/Analysis/ValueTracking.h" +#include "llvm/Analysis/AssumptionCache.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/DerivedTypes.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/GlobalAlias.h" +#include "llvm/IR/GlobalVariable.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/IntrinsicInst.h" +#include "llvm/IR/LLVMContext.h" +#include "llvm/IR/Operator.h" +#include "llvm/Pass.h" +#include "llvm/Support/ErrorHandling.h" +#include <algorithm> +using namespace llvm; + +/// Enable analysis of recursive PHI nodes. +static cl::opt<bool> EnableRecPhiAnalysis("basicaa-recphi", cl::Hidden, + cl::init(false)); + +/// SearchLimitReached / SearchTimes shows how often the limit of +/// to decompose GEPs is reached. It will affect the precision +/// of basic alias analysis. +#define DEBUG_TYPE "basicaa" +STATISTIC(SearchLimitReached, "Number of times the limit to " + "decompose GEPs is reached"); +STATISTIC(SearchTimes, "Number of times a GEP is decomposed"); + +/// Cutoff after which to stop analysing a set of phi nodes potentially involved +/// in a cycle. Because we are analysing 'through' phi nodes we need to be +/// careful with value equivalence. We use reachability to make sure a value +/// cannot be involved in a cycle. +const unsigned MaxNumPhiBBsValueReachabilityCheck = 20; + +// The max limit of the search depth in DecomposeGEPExpression() and +// GetUnderlyingObject(), both functions need to use the same search +// depth otherwise the algorithm in aliasGEP will assert. +static const unsigned MaxLookupSearchDepth = 6; + +//===----------------------------------------------------------------------===// +// Useful predicates +//===----------------------------------------------------------------------===// + +/// Returns 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<AllocaInst>(V) || isNoAliasCall(V)) + // Set StoreCaptures to True so that we can assume in our callers that the + // pointer is not the result of a load instruction. Currently + // PointerMayBeCaptured doesn't have any special analysis for the + // StoreCaptures=false case; if it did, our callers could be refined to be + // more precise. + return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true); + + // If this is an argument that corresponds to a byval or noalias argument, + // then it has not escaped before entering the function. Check if it escapes + // inside the function. + if (const Argument *A = dyn_cast<Argument>(V)) + if (A->hasByValAttr() || A->hasNoAliasAttr()) + // Note even if the argument is marked nocapture we still need to check + // for copies made inside the function. The nocapture attribute only + // specifies that there are no copies made that outlive the function. + return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true); + + return false; +} + +/// Returns true if the pointer is one which would have been considered an +/// escape by isNonEscapingLocalObject. +static bool isEscapeSource(const Value *V) { + if (isa<CallInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V)) + return true; + + // The load case works because isNonEscapingLocalObject considers all + // stores to be escapes (it passes true for the StoreCaptures argument + // to PointerMayBeCaptured). + if (isa<LoadInst>(V)) + return true; + + return false; +} + +/// Returns the size of the object specified by V, or UnknownSize if unknown. +static uint64_t getObjectSize(const Value *V, const DataLayout &DL, + const TargetLibraryInfo &TLI, + bool RoundToAlign = false) { + uint64_t Size; + if (getObjectSize(V, Size, DL, &TLI, RoundToAlign)) + return Size; + return MemoryLocation::UnknownSize; +} + +/// Returns true if we can prove that the object specified by V is smaller than +/// Size. +static bool isObjectSmallerThan(const Value *V, uint64_t Size, + const DataLayout &DL, + const TargetLibraryInfo &TLI) { + // Note that the meanings of the "object" are slightly different in the + // following contexts: + // c1: llvm::getObjectSize() + // c2: llvm.objectsize() intrinsic + // c3: isObjectSmallerThan() + // c1 and c2 share the same meaning; however, the meaning of "object" in c3 + // refers to the "entire object". + // + // Consider this example: + // char *p = (char*)malloc(100) + // char *q = p+80; + // + // In the context of c1 and c2, the "object" pointed by q refers to the + // stretch of memory of q[0:19]. So, getObjectSize(q) should return 20. + // + // However, in the context of c3, the "object" refers to the chunk of memory + // being allocated. So, the "object" has 100 bytes, and q points to the middle + // the "object". In case q is passed to isObjectSmallerThan() as the 1st + // parameter, before the llvm::getObjectSize() is called to get the size of + // entire object, we should: + // - either rewind the pointer q to the base-address of the object in + // question (in this case rewind to p), or + // - just give up. It is up to caller to make sure the pointer is pointing + // to the base address the object. + // + // We go for 2nd option for simplicity. + if (!isIdentifiedObject(V)) + return false; + + // This function needs to use the aligned object size because we allow + // reads a bit past the end given sufficient alignment. + uint64_t ObjectSize = getObjectSize(V, DL, TLI, /*RoundToAlign*/ true); + + return ObjectSize != MemoryLocation::UnknownSize && ObjectSize < Size; +} + +/// Returns true if we can prove that the object specified by V has size Size. +static bool isObjectSize(const Value *V, uint64_t Size, const DataLayout &DL, + const TargetLibraryInfo &TLI) { + uint64_t ObjectSize = getObjectSize(V, DL, TLI); + return ObjectSize != MemoryLocation::UnknownSize && ObjectSize == Size; +} + +//===----------------------------------------------------------------------===// +// GetElementPtr Instruction Decomposition and Analysis +//===----------------------------------------------------------------------===// + +/// Analyzes the specified value as a linear expression: "A*V + B", where A and +/// B are constant integers. +/// +/// Returns the scale and offset values as APInts and return V as a Value*, and +/// return whether we looked through any sign or zero extends. The incoming +/// Value is known to have IntegerType and it may already be sign or zero +/// extended. +/// +/// Note that this looks through extends, so the high bits may not be +/// represented in the result. +/*static*/ const Value *BasicAAResult::GetLinearExpression( + const Value *V, APInt &Scale, APInt &Offset, unsigned &ZExtBits, + unsigned &SExtBits, const DataLayout &DL, unsigned Depth, + AssumptionCache *AC, DominatorTree *DT, bool &NSW, bool &NUW) { + assert(V->getType()->isIntegerTy() && "Not an integer value"); + + // Limit our recursion depth. + if (Depth == 6) { + Scale = 1; + Offset = 0; + return V; + } + + if (const ConstantInt *Const = dyn_cast<ConstantInt>(V)) { + // if it's a constant, just convert it to an offset and remove the variable. + // If we've been called recursively the Offset bit width will be greater + // than the constant's (the Offset's always as wide as the outermost call), + // so we'll zext here and process any extension in the isa<SExtInst> & + // isa<ZExtInst> cases below. + Offset += Const->getValue().zextOrSelf(Offset.getBitWidth()); + assert(Scale == 0 && "Constant values don't have a scale"); + return V; + } + + if (const BinaryOperator *BOp = dyn_cast<BinaryOperator>(V)) { + if (ConstantInt *RHSC = dyn_cast<ConstantInt>(BOp->getOperand(1))) { + + // If we've been called recursively then Offset and Scale will be wider + // that the BOp operands. We'll always zext it here as we'll process sign + // extensions below (see the isa<SExtInst> / isa<ZExtInst> cases). + APInt RHS = RHSC->getValue().zextOrSelf(Offset.getBitWidth()); + + switch (BOp->getOpcode()) { + default: + // We don't understand this instruction, so we can't decompose it any + // further. + Scale = 1; + Offset = 0; + return V; + case Instruction::Or: + // X|C == X+C if all the bits in C are unset in X. Otherwise we can't + // analyze it. + if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(), DL, 0, AC, + BOp, DT)) { + Scale = 1; + Offset = 0; + return V; + } + // FALL THROUGH. + case Instruction::Add: + V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits, + SExtBits, DL, Depth + 1, AC, DT, NSW, NUW); + Offset += RHS; + break; + case Instruction::Sub: + V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits, + SExtBits, DL, Depth + 1, AC, DT, NSW, NUW); + Offset -= RHS; + break; + case Instruction::Mul: + V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits, + SExtBits, DL, Depth + 1, AC, DT, NSW, NUW); + Offset *= RHS; + Scale *= RHS; + break; + case Instruction::Shl: + V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits, + SExtBits, DL, Depth + 1, AC, DT, NSW, NUW); + Offset <<= RHS.getLimitedValue(); + Scale <<= RHS.getLimitedValue(); + // the semantics of nsw and nuw for left shifts don't match those of + // multiplications, so we won't propagate them. + NSW = NUW = false; + return V; + } + + if (isa<OverflowingBinaryOperator>(BOp)) { + NUW &= BOp->hasNoUnsignedWrap(); + NSW &= BOp->hasNoSignedWrap(); + } + return V; + } + } + + // Since GEP indices are sign extended anyway, we don't care about the high + // bits of a sign or zero extended value - just scales and offsets. The + // extensions have to be consistent though. + if (isa<SExtInst>(V) || isa<ZExtInst>(V)) { + Value *CastOp = cast<CastInst>(V)->getOperand(0); + unsigned NewWidth = V->getType()->getPrimitiveSizeInBits(); + unsigned SmallWidth = CastOp->getType()->getPrimitiveSizeInBits(); + unsigned OldZExtBits = ZExtBits, OldSExtBits = SExtBits; + const Value *Result = + GetLinearExpression(CastOp, Scale, Offset, ZExtBits, SExtBits, DL, + Depth + 1, AC, DT, NSW, NUW); + + // zext(zext(%x)) == zext(%x), and similiarly for sext; we'll handle this + // by just incrementing the number of bits we've extended by. + unsigned ExtendedBy = NewWidth - SmallWidth; + + if (isa<SExtInst>(V) && ZExtBits == 0) { + // sext(sext(%x, a), b) == sext(%x, a + b) + + if (NSW) { + // We haven't sign-wrapped, so it's valid to decompose sext(%x + c) + // into sext(%x) + sext(c). We'll sext the Offset ourselves: + unsigned OldWidth = Offset.getBitWidth(); + Offset = Offset.trunc(SmallWidth).sext(NewWidth).zextOrSelf(OldWidth); + } else { + // We may have signed-wrapped, so don't decompose sext(%x + c) into + // sext(%x) + sext(c) + Scale = 1; + Offset = 0; + Result = CastOp; + ZExtBits = OldZExtBits; + SExtBits = OldSExtBits; + } + SExtBits += ExtendedBy; + } else { + // sext(zext(%x, a), b) = zext(zext(%x, a), b) = zext(%x, a + b) + + if (!NUW) { + // We may have unsigned-wrapped, so don't decompose zext(%x + c) into + // zext(%x) + zext(c) + Scale = 1; + Offset = 0; + Result = CastOp; + ZExtBits = OldZExtBits; + SExtBits = OldSExtBits; + } + ZExtBits += ExtendedBy; + } + + return Result; + } + + Scale = 1; + Offset = 0; + return V; +} + +/// If V is a symbolic pointer expression, decompose it into a base pointer +/// with a constant offset and a number of scaled symbolic offsets. +/// +/// The scaled symbolic offsets (represented by pairs of a Value* and a scale +/// in the VarIndices vector) are Value*'s that are known to be scaled by the +/// specified amount, but which may have other unrepresented high bits. As +/// such, the gep cannot necessarily be reconstructed from its decomposed form. +/// +/// When DataLayout is around, this function is capable of analyzing everything +/// that GetUnderlyingObject can look through. To be able to do that +/// GetUnderlyingObject and DecomposeGEPExpression must use the same search +/// depth (MaxLookupSearchDepth). When DataLayout not is around, it just looks +/// through pointer casts. +/*static*/ const Value *BasicAAResult::DecomposeGEPExpression( + const Value *V, int64_t &BaseOffs, + SmallVectorImpl<VariableGEPIndex> &VarIndices, bool &MaxLookupReached, + const DataLayout &DL, AssumptionCache *AC, DominatorTree *DT) { + // Limit recursion depth to limit compile time in crazy cases. + unsigned MaxLookup = MaxLookupSearchDepth; + MaxLookupReached = false; + SearchTimes++; + + BaseOffs = 0; + do { + // See if this is a bitcast or GEP. + const Operator *Op = dyn_cast<Operator>(V); + if (!Op) { + // The only non-operator case we can handle are GlobalAliases. + if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) { + if (!GA->mayBeOverridden()) { + V = GA->getAliasee(); + continue; + } + } + return V; + } + + if (Op->getOpcode() == Instruction::BitCast || + Op->getOpcode() == Instruction::AddrSpaceCast) { + V = Op->getOperand(0); + continue; + } + + const GEPOperator *GEPOp = dyn_cast<GEPOperator>(Op); + if (!GEPOp) { + // If it's not a GEP, hand it off to SimplifyInstruction to see if it + // can come up with something. This matches what GetUnderlyingObject does. + if (const Instruction *I = dyn_cast<Instruction>(V)) + // TODO: Get a DominatorTree and AssumptionCache and use them here + // (these are both now available in this function, but this should be + // updated when GetUnderlyingObject is updated). TLI should be + // provided also. + if (const Value *Simplified = + SimplifyInstruction(const_cast<Instruction *>(I), DL)) { + V = Simplified; + continue; + } + + return V; + } + + // Don't attempt to analyze GEPs over unsized objects. + if (!GEPOp->getOperand(0)->getType()->getPointerElementType()->isSized()) + return V; + + unsigned AS = GEPOp->getPointerAddressSpace(); + // Walk the indices of the GEP, accumulating them into BaseOff/VarIndices. + gep_type_iterator GTI = gep_type_begin(GEPOp); + for (User::const_op_iterator I = GEPOp->op_begin() + 1, E = GEPOp->op_end(); + I != E; ++I) { + const Value *Index = *I; + // Compute the (potentially symbolic) offset in bytes for this index. + if (StructType *STy = dyn_cast<StructType>(*GTI++)) { + // For a struct, add the member offset. + unsigned FieldNo = cast<ConstantInt>(Index)->getZExtValue(); + if (FieldNo == 0) + continue; + + BaseOffs += DL.getStructLayout(STy)->getElementOffset(FieldNo); + continue; + } + + // For an array/pointer, add the element offset, explicitly scaled. + if (const ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) { + if (CIdx->isZero()) + continue; + BaseOffs += DL.getTypeAllocSize(*GTI) * CIdx->getSExtValue(); + continue; + } + + uint64_t Scale = DL.getTypeAllocSize(*GTI); + unsigned ZExtBits = 0, SExtBits = 0; + + // If the integer type is smaller than the pointer size, it is implicitly + // sign extended to pointer size. + unsigned Width = Index->getType()->getIntegerBitWidth(); + unsigned PointerSize = DL.getPointerSizeInBits(AS); + if (PointerSize > Width) + SExtBits += PointerSize - Width; + + // Use GetLinearExpression to decompose the index into a C1*V+C2 form. + APInt IndexScale(Width, 0), IndexOffset(Width, 0); + bool NSW = true, NUW = true; + Index = GetLinearExpression(Index, IndexScale, IndexOffset, ZExtBits, + SExtBits, DL, 0, AC, DT, NSW, NUW); + + // The GEP index scale ("Scale") scales C1*V+C2, yielding (C1*V+C2)*Scale. + // This gives us an aggregate computation of (C1*Scale)*V + C2*Scale. + BaseOffs += IndexOffset.getSExtValue() * Scale; + Scale *= IndexScale.getSExtValue(); + + // If we already had an occurrence of this index variable, merge this + // scale into it. For example, we want to handle: + // A[x][x] -> x*16 + x*4 -> x*20 + // This also ensures that 'x' only appears in the index list once. + for (unsigned i = 0, e = VarIndices.size(); i != e; ++i) { + if (VarIndices[i].V == Index && VarIndices[i].ZExtBits == ZExtBits && + VarIndices[i].SExtBits == SExtBits) { + Scale += VarIndices[i].Scale; + VarIndices.erase(VarIndices.begin() + i); + break; + } + } + + // Make sure that we have a scale that makes sense for this target's + // pointer size. + if (unsigned ShiftBits = 64 - PointerSize) { + Scale <<= ShiftBits; + Scale = (int64_t)Scale >> ShiftBits; + } + + if (Scale) { + VariableGEPIndex Entry = {Index, ZExtBits, SExtBits, + static_cast<int64_t>(Scale)}; + VarIndices.push_back(Entry); + } + } + + // Analyze the base pointer next. + V = GEPOp->getOperand(0); + } while (--MaxLookup); + + // If the chain of expressions is too deep, just return early. + MaxLookupReached = true; + SearchLimitReached++; + return V; +} + +/// Returns whether the given pointer value points to memory that is local to +/// the function, with global constants being considered local to all +/// functions. +bool BasicAAResult::pointsToConstantMemory(const MemoryLocation &Loc, + bool OrLocal) { + assert(Visited.empty() && "Visited must be cleared after use!"); + + unsigned MaxLookup = 8; + SmallVector<const Value *, 16> Worklist; + Worklist.push_back(Loc.Ptr); + do { + const Value *V = GetUnderlyingObject(Worklist.pop_back_val(), DL); + if (!Visited.insert(V).second) { + Visited.clear(); + return AAResultBase::pointsToConstantMemory(Loc, OrLocal); + } + + // An alloca instruction defines local memory. + if (OrLocal && isa<AllocaInst>(V)) + continue; + + // A global constant counts as local memory for our purposes. + if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) { + // Note: this doesn't require GV to be "ODR" because it isn't legal for a + // global to be marked constant in some modules and non-constant in + // others. GV may even be a declaration, not a definition. + if (!GV->isConstant()) { + Visited.clear(); + return AAResultBase::pointsToConstantMemory(Loc, OrLocal); + } + continue; + } + + // If both select values point to local memory, then so does the select. + if (const SelectInst *SI = dyn_cast<SelectInst>(V)) { + Worklist.push_back(SI->getTrueValue()); + Worklist.push_back(SI->getFalseValue()); + continue; + } + + // If all values incoming to a phi node point to local memory, then so does + // the phi. + if (const PHINode *PN = dyn_cast<PHINode>(V)) { + // Don't bother inspecting phi nodes with many operands. + if (PN->getNumIncomingValues() > MaxLookup) { + Visited.clear(); + return AAResultBase::pointsToConstantMemory(Loc, OrLocal); + } + for (Value *IncValue : PN->incoming_values()) + Worklist.push_back(IncValue); + continue; + } + + // Otherwise be conservative. + Visited.clear(); + return AAResultBase::pointsToConstantMemory(Loc, OrLocal); + + } while (!Worklist.empty() && --MaxLookup); + + Visited.clear(); + return Worklist.empty(); +} + +// FIXME: This code is duplicated with MemoryLocation and should be hoisted to +// some common utility location. +static bool isMemsetPattern16(const Function *MS, + const TargetLibraryInfo &TLI) { + if (TLI.has(LibFunc::memset_pattern16) && + MS->getName() == "memset_pattern16") { + FunctionType *MemsetType = MS->getFunctionType(); + if (!MemsetType->isVarArg() && MemsetType->getNumParams() == 3 && + isa<PointerType>(MemsetType->getParamType(0)) && + isa<PointerType>(MemsetType->getParamType(1)) && + isa<IntegerType>(MemsetType->getParamType(2))) + return true; + } + + return false; +} + +/// Returns the behavior when calling the given call site. +FunctionModRefBehavior BasicAAResult::getModRefBehavior(ImmutableCallSite CS) { + if (CS.doesNotAccessMemory()) + // Can't do better than this. + return FMRB_DoesNotAccessMemory; + + FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior; + + // If the callsite knows it only reads memory, don't return worse + // than that. + if (CS.onlyReadsMemory()) + Min = FMRB_OnlyReadsMemory; + + if (CS.onlyAccessesArgMemory()) + Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesArgumentPointees); + + // The AAResultBase base class has some smarts, lets use them. + return FunctionModRefBehavior(AAResultBase::getModRefBehavior(CS) & Min); +} + +/// Returns the behavior when calling the given function. For use when the call +/// site is not known. +FunctionModRefBehavior BasicAAResult::getModRefBehavior(const Function *F) { + // If the function declares it doesn't access memory, we can't do better. + if (F->doesNotAccessMemory()) + return FMRB_DoesNotAccessMemory; + + FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior; + + // If the function declares it only reads memory, go with that. + if (F->onlyReadsMemory()) + Min = FMRB_OnlyReadsMemory; + + if (F->onlyAccessesArgMemory()) + Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesArgumentPointees); + + if (isMemsetPattern16(F, TLI)) + Min = FMRB_OnlyAccessesArgumentPointees; + + // Otherwise be conservative. + return FunctionModRefBehavior(AAResultBase::getModRefBehavior(F) & Min); +} + +ModRefInfo BasicAAResult::getArgModRefInfo(ImmutableCallSite CS, + unsigned ArgIdx) { + if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction())) + switch (II->getIntrinsicID()) { + default: + break; + case Intrinsic::memset: + case Intrinsic::memcpy: + case Intrinsic::memmove: + assert((ArgIdx == 0 || ArgIdx == 1) && + "Invalid argument index for memory intrinsic"); + return ArgIdx ? MRI_Ref : MRI_Mod; + } + + // We can bound the aliasing properties of memset_pattern16 just as we can + // for memcpy/memset. This is particularly important because the + // LoopIdiomRecognizer likes to turn loops into calls to memset_pattern16 + // whenever possible. + if (CS.getCalledFunction() && + isMemsetPattern16(CS.getCalledFunction(), TLI)) { + assert((ArgIdx == 0 || ArgIdx == 1) && + "Invalid argument index for memset_pattern16"); + return ArgIdx ? MRI_Ref : MRI_Mod; + } + // FIXME: Handle memset_pattern4 and memset_pattern8 also. + + if (CS.paramHasAttr(ArgIdx + 1, Attribute::ReadOnly)) + return MRI_Ref; + + if (CS.paramHasAttr(ArgIdx + 1, Attribute::ReadNone)) + return MRI_NoModRef; + + return AAResultBase::getArgModRefInfo(CS, ArgIdx); +} + +static bool isAssumeIntrinsic(ImmutableCallSite CS) { + const IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction()); + return II && II->getIntrinsicID() == Intrinsic::assume; +} + +#ifndef NDEBUG +static const Function *getParent(const Value *V) { + if (const Instruction *inst = dyn_cast<Instruction>(V)) + return inst->getParent()->getParent(); + + if (const Argument *arg = dyn_cast<Argument>(V)) + return arg->getParent(); + + return nullptr; +} + +static bool notDifferentParent(const Value *O1, const Value *O2) { + + const Function *F1 = getParent(O1); + const Function *F2 = getParent(O2); + + return !F1 || !F2 || F1 == F2; +} +#endif + +AliasResult BasicAAResult::alias(const MemoryLocation &LocA, + const MemoryLocation &LocB) { + assert(notDifferentParent(LocA.Ptr, LocB.Ptr) && + "BasicAliasAnalysis doesn't support interprocedural queries."); + + // If we have a directly cached entry for these locations, we have recursed + // through this once, so just return the cached results. Notably, when this + // happens, we don't clear the cache. + auto CacheIt = AliasCache.find(LocPair(LocA, LocB)); + if (CacheIt != AliasCache.end()) + return CacheIt->second; + + AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.AATags, LocB.Ptr, + LocB.Size, LocB.AATags); + // AliasCache rarely has more than 1 or 2 elements, always use + // shrink_and_clear so it quickly returns to the inline capacity of the + // SmallDenseMap if it ever grows larger. + // FIXME: This should really be shrink_to_inline_capacity_and_clear(). + AliasCache.shrink_and_clear(); + VisitedPhiBBs.clear(); + return Alias; +} + +/// Checks 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. +ModRefInfo BasicAAResult::getModRefInfo(ImmutableCallSite CS, + const MemoryLocation &Loc) { + assert(notDifferentParent(CS.getInstruction(), Loc.Ptr) && + "AliasAnalysis query involving multiple functions!"); + + const Value *Object = GetUnderlyingObject(Loc.Ptr, DL); + + // If this is a tail call and Loc.Ptr 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 (const CallInst *CI = dyn_cast<CallInst>(CS.getInstruction())) + if (CI->isTailCall()) + return MRI_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 pointer + // as an argument, and itself doesn't capture it. + if (!isa<Constant>(Object) && CS.getInstruction() != Object && + isNonEscapingLocalObject(Object)) { + bool PassedAsArg = false; + unsigned ArgNo = 0; + for (ImmutableCallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end(); + CI != CE; ++CI, ++ArgNo) { + // Only look at the no-capture or byval pointer arguments. If this + // pointer were passed to arguments that were neither of these, then it + // couldn't be no-capture. + if (!(*CI)->getType()->isPointerTy() || + (!CS.doesNotCapture(ArgNo) && !CS.isByValArgument(ArgNo))) + continue; + + // If this is a no-capture pointer argument, see if we can tell that it + // is impossible to alias the pointer we're checking. If not, we have to + // assume that the call could touch the pointer, even though it doesn't + // escape. + AliasResult AR = + getBestAAResults().alias(MemoryLocation(*CI), MemoryLocation(Object)); + if (AR) { + PassedAsArg = true; + break; + } + } + + if (!PassedAsArg) + return MRI_NoModRef; + } + + // While the assume intrinsic is marked as arbitrarily writing so that + // proper control dependencies will be maintained, it never aliases any + // particular memory location. + if (isAssumeIntrinsic(CS)) + return MRI_NoModRef; + + // The AAResultBase base class has some smarts, lets use them. + return AAResultBase::getModRefInfo(CS, Loc); +} + +ModRefInfo BasicAAResult::getModRefInfo(ImmutableCallSite CS1, + ImmutableCallSite CS2) { + // While the assume intrinsic is marked as arbitrarily writing so that + // proper control dependencies will be maintained, it never aliases any + // particular memory location. + if (isAssumeIntrinsic(CS1) || isAssumeIntrinsic(CS2)) + return MRI_NoModRef; + + // The AAResultBase base class has some smarts, lets use them. + return AAResultBase::getModRefInfo(CS1, CS2); +} + +/// Provide ad-hoc rules to disambiguate accesses through two GEP operators, +/// both having the exact same pointer operand. +static AliasResult aliasSameBasePointerGEPs(const GEPOperator *GEP1, + uint64_t V1Size, + const GEPOperator *GEP2, + uint64_t V2Size, + const DataLayout &DL) { + + assert(GEP1->getPointerOperand() == GEP2->getPointerOperand() && + "Expected GEPs with the same pointer operand"); + + // Try to determine whether GEP1 and GEP2 index through arrays, into structs, + // such that the struct field accesses provably cannot alias. + // We also need at least two indices (the pointer, and the struct field). + if (GEP1->getNumIndices() != GEP2->getNumIndices() || + GEP1->getNumIndices() < 2) + return MayAlias; + + // If we don't know the size of the accesses through both GEPs, we can't + // determine whether the struct fields accessed can't alias. + if (V1Size == MemoryLocation::UnknownSize || + V2Size == MemoryLocation::UnknownSize) + return MayAlias; + + ConstantInt *C1 = + dyn_cast<ConstantInt>(GEP1->getOperand(GEP1->getNumOperands() - 1)); + ConstantInt *C2 = + dyn_cast<ConstantInt>(GEP2->getOperand(GEP2->getNumOperands() - 1)); + + // If the last (struct) indices are constants and are equal, the other indices + // might be also be dynamically equal, so the GEPs can alias. + if (C1 && C2 && C1 == C2) + return MayAlias; + + // Find the last-indexed type of the GEP, i.e., the type you'd get if + // you stripped the last index. + // On the way, look at each indexed type. If there's something other + // than an array, different indices can lead to different final types. + SmallVector<Value *, 8> IntermediateIndices; + + // Insert the first index; we don't need to check the type indexed + // through it as it only drops the pointer indirection. + assert(GEP1->getNumIndices() > 1 && "Not enough GEP indices to examine"); + IntermediateIndices.push_back(GEP1->getOperand(1)); + + // Insert all the remaining indices but the last one. + // Also, check that they all index through arrays. + for (unsigned i = 1, e = GEP1->getNumIndices() - 1; i != e; ++i) { + if (!isa<ArrayType>(GetElementPtrInst::getIndexedType( + GEP1->getSourceElementType(), IntermediateIndices))) + return MayAlias; + IntermediateIndices.push_back(GEP1->getOperand(i + 1)); + } + + auto *Ty = GetElementPtrInst::getIndexedType( + GEP1->getSourceElementType(), IntermediateIndices); + StructType *LastIndexedStruct = dyn_cast<StructType>(Ty); + + if (isa<SequentialType>(Ty)) { + // We know that: + // - both GEPs begin indexing from the exact same pointer; + // - the last indices in both GEPs are constants, indexing into a sequential + // type (array or pointer); + // - both GEPs only index through arrays prior to that. + // + // Because array indices greater than the number of elements are valid in + // GEPs, unless we know the intermediate indices are identical between + // GEP1 and GEP2 we cannot guarantee that the last indexed arrays don't + // partially overlap. We also need to check that the loaded size matches + // the element size, otherwise we could still have overlap. + const uint64_t ElementSize = + DL.getTypeStoreSize(cast<SequentialType>(Ty)->getElementType()); + if (V1Size != ElementSize || V2Size != ElementSize) + return MayAlias; + + for (unsigned i = 0, e = GEP1->getNumIndices() - 1; i != e; ++i) + if (GEP1->getOperand(i + 1) != GEP2->getOperand(i + 1)) + return MayAlias; + + // Now we know that the array/pointer that GEP1 indexes into and that + // that GEP2 indexes into must either precisely overlap or be disjoint. + // Because they cannot partially overlap and because fields in an array + // cannot overlap, if we can prove the final indices are different between + // GEP1 and GEP2, we can conclude GEP1 and GEP2 don't alias. + + // If the last indices are constants, we've already checked they don't + // equal each other so we can exit early. + if (C1 && C2) + return NoAlias; + if (isKnownNonEqual(GEP1->getOperand(GEP1->getNumOperands() - 1), + GEP2->getOperand(GEP2->getNumOperands() - 1), + DL)) + return NoAlias; + return MayAlias; + } else if (!LastIndexedStruct || !C1 || !C2) { + return MayAlias; + } + + // We know that: + // - both GEPs begin indexing from the exact same pointer; + // - the last indices in both GEPs are constants, indexing into a struct; + // - said indices are different, hence, the pointed-to fields are different; + // - both GEPs only index through arrays prior to that. + // + // This lets us determine that the struct that GEP1 indexes into and the + // struct that GEP2 indexes into must either precisely overlap or be + // completely disjoint. Because they cannot partially overlap, indexing into + // different non-overlapping fields of the struct will never alias. + + // Therefore, the only remaining thing needed to show that both GEPs can't + // alias is that the fields are not overlapping. + const StructLayout *SL = DL.getStructLayout(LastIndexedStruct); + const uint64_t StructSize = SL->getSizeInBytes(); + const uint64_t V1Off = SL->getElementOffset(C1->getZExtValue()); + const uint64_t V2Off = SL->getElementOffset(C2->getZExtValue()); + + auto EltsDontOverlap = [StructSize](uint64_t V1Off, uint64_t V1Size, + uint64_t V2Off, uint64_t V2Size) { + return V1Off < V2Off && V1Off + V1Size <= V2Off && + ((V2Off + V2Size <= StructSize) || + (V2Off + V2Size - StructSize <= V1Off)); + }; + + if (EltsDontOverlap(V1Off, V1Size, V2Off, V2Size) || + EltsDontOverlap(V2Off, V2Size, V1Off, V1Size)) + return NoAlias; + + return MayAlias; +} + +/// Provides a bunch of ad-hoc rules to disambiguate a GEP instruction against +/// another pointer. +/// +/// We know that V1 is a GEP, but we don't know anything about V2. +/// UnderlyingV1 is GetUnderlyingObject(GEP1, DL), UnderlyingV2 is the same for +/// V2. +AliasResult BasicAAResult::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size, + const AAMDNodes &V1AAInfo, const Value *V2, + uint64_t V2Size, const AAMDNodes &V2AAInfo, + const Value *UnderlyingV1, + const Value *UnderlyingV2) { + int64_t GEP1BaseOffset; + bool GEP1MaxLookupReached; + SmallVector<VariableGEPIndex, 4> GEP1VariableIndices; + + // If we have two gep instructions with must-alias or not-alias'ing base + // pointers, figure out if the indexes to the GEP tell us anything about the + // derived pointer. + if (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) { + // Do the base pointers alias? + AliasResult BaseAlias = + aliasCheck(UnderlyingV1, MemoryLocation::UnknownSize, AAMDNodes(), + UnderlyingV2, MemoryLocation::UnknownSize, AAMDNodes()); + + // Check for geps of non-aliasing underlying pointers where the offsets are + // identical. + if ((BaseAlias == MayAlias) && V1Size == V2Size) { + // Do the base pointers alias assuming type and size. + AliasResult PreciseBaseAlias = aliasCheck(UnderlyingV1, V1Size, V1AAInfo, + UnderlyingV2, V2Size, V2AAInfo); + if (PreciseBaseAlias == NoAlias) { + // See if the computed offset from the common pointer tells us about the + // relation of the resulting pointer. + int64_t GEP2BaseOffset; + bool GEP2MaxLookupReached; + SmallVector<VariableGEPIndex, 4> GEP2VariableIndices; + const Value *GEP2BasePtr = + DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, + GEP2MaxLookupReached, DL, &AC, DT); + const Value *GEP1BasePtr = + DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, + GEP1MaxLookupReached, DL, &AC, DT); + // DecomposeGEPExpression and GetUnderlyingObject should return the + // same result except when DecomposeGEPExpression has no DataLayout. + // FIXME: They always have a DataLayout so this should become an + // assert. + if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) { + return MayAlias; + } + // If the max search depth is reached the result is undefined + if (GEP2MaxLookupReached || GEP1MaxLookupReached) + return MayAlias; + + // Same offsets. + if (GEP1BaseOffset == GEP2BaseOffset && + GEP1VariableIndices == GEP2VariableIndices) + return NoAlias; + GEP1VariableIndices.clear(); + } + } + + // If we get a No or May, then return it immediately, no amount of analysis + // will improve this situation. + if (BaseAlias != MustAlias) + return BaseAlias; + + // Otherwise, we have a MustAlias. Since the base pointers alias each other + // exactly, see if the computed offset from the common pointer tells us + // about the relation of the resulting pointer. + const Value *GEP1BasePtr = + DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, + GEP1MaxLookupReached, DL, &AC, DT); + + int64_t GEP2BaseOffset; + bool GEP2MaxLookupReached; + SmallVector<VariableGEPIndex, 4> GEP2VariableIndices; + const Value *GEP2BasePtr = + DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, + GEP2MaxLookupReached, DL, &AC, DT); + + // DecomposeGEPExpression and GetUnderlyingObject should return the + // same result except when DecomposeGEPExpression has no DataLayout. + // FIXME: They always have a DataLayout so this should become an assert. + if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) { + return MayAlias; + } + + // If we know the two GEPs are based off of the exact same pointer (and not + // just the same underlying object), see if that tells us anything about + // the resulting pointers. + if (GEP1->getPointerOperand() == GEP2->getPointerOperand()) { + AliasResult R = aliasSameBasePointerGEPs(GEP1, V1Size, GEP2, V2Size, DL); + // If we couldn't find anything interesting, don't abandon just yet. + if (R != MayAlias) + return R; + } + + // If the max search depth is reached the result is undefined + if (GEP2MaxLookupReached || GEP1MaxLookupReached) + return MayAlias; + + // Subtract the GEP2 pointer from the GEP1 pointer to find out their + // symbolic difference. + GEP1BaseOffset -= GEP2BaseOffset; + GetIndexDifference(GEP1VariableIndices, GEP2VariableIndices); + + } else { + // Check to see if these two pointers are related by the getelementptr + // instruction. If one pointer is a GEP with a non-zero index of the other + // pointer, we know they cannot alias. + + // If both accesses are unknown size, we can't do anything useful here. + if (V1Size == MemoryLocation::UnknownSize && + V2Size == MemoryLocation::UnknownSize) + return MayAlias; + + AliasResult R = aliasCheck(UnderlyingV1, MemoryLocation::UnknownSize, + AAMDNodes(), V2, V2Size, V2AAInfo); + if (R != MustAlias) + // If V2 may alias GEP base pointer, conservatively returns MayAlias. + // If V2 is known not to alias GEP base pointer, then the two values + // cannot alias per GEP semantics: "A pointer value formed from a + // getelementptr instruction is associated with the addresses associated + // with the first operand of the getelementptr". + return R; + + const Value *GEP1BasePtr = + DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, + GEP1MaxLookupReached, DL, &AC, DT); + + // DecomposeGEPExpression and GetUnderlyingObject should return the + // same result except when DecomposeGEPExpression has no DataLayout. + // FIXME: They always have a DataLayout so this should become an assert. + if (GEP1BasePtr != UnderlyingV1) { + return MayAlias; + } + // If the max search depth is reached the result is undefined + if (GEP1MaxLookupReached) + return MayAlias; + } + + // In the two GEP Case, if there is no difference in the offsets of the + // computed pointers, the resultant pointers are a must alias. This + // hapens when we have two lexically identical GEP's (for example). + // + // In the other case, if we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 + // must aliases the GEP, the end result is a must alias also. + if (GEP1BaseOffset == 0 && GEP1VariableIndices.empty()) + return MustAlias; + + // If there is a constant difference between the pointers, but the difference + // is less than the size of the associated memory object, then we know + // that the objects are partially overlapping. If the difference is + // greater, we know they do not overlap. + if (GEP1BaseOffset != 0 && GEP1VariableIndices.empty()) { + if (GEP1BaseOffset >= 0) { + if (V2Size != MemoryLocation::UnknownSize) { + if ((uint64_t)GEP1BaseOffset < V2Size) + return PartialAlias; + return NoAlias; + } + } else { + // We have the situation where: + // + + + // | BaseOffset | + // ---------------->| + // |-->V1Size |-------> V2Size + // GEP1 V2 + // We need to know that V2Size is not unknown, otherwise we might have + // stripped a gep with negative index ('gep <ptr>, -1, ...). + if (V1Size != MemoryLocation::UnknownSize && + V2Size != MemoryLocation::UnknownSize) { + if (-(uint64_t)GEP1BaseOffset < V1Size) + return PartialAlias; + return NoAlias; + } + } + } + + if (!GEP1VariableIndices.empty()) { + uint64_t Modulo = 0; + bool AllPositive = true; + for (unsigned i = 0, e = GEP1VariableIndices.size(); i != e; ++i) { + + // Try to distinguish something like &A[i][1] against &A[42][0]. + // Grab the least significant bit set in any of the scales. We + // don't need std::abs here (even if the scale's negative) as we'll + // be ^'ing Modulo with itself later. + Modulo |= (uint64_t)GEP1VariableIndices[i].Scale; + + if (AllPositive) { + // If the Value could change between cycles, then any reasoning about + // the Value this cycle may not hold in the next cycle. We'll just + // give up if we can't determine conditions that hold for every cycle: + const Value *V = GEP1VariableIndices[i].V; + + bool SignKnownZero, SignKnownOne; + ComputeSignBit(const_cast<Value *>(V), SignKnownZero, SignKnownOne, DL, + 0, &AC, nullptr, DT); + + // Zero-extension widens the variable, and so forces the sign + // bit to zero. + bool IsZExt = GEP1VariableIndices[i].ZExtBits > 0 || isa<ZExtInst>(V); + SignKnownZero |= IsZExt; + SignKnownOne &= !IsZExt; + + // If the variable begins with a zero then we know it's + // positive, regardless of whether the value is signed or + // unsigned. + int64_t Scale = GEP1VariableIndices[i].Scale; + AllPositive = + (SignKnownZero && Scale >= 0) || (SignKnownOne && Scale < 0); + } + } + + Modulo = Modulo ^ (Modulo & (Modulo - 1)); + + // We can compute the difference between the two addresses + // mod Modulo. Check whether that difference guarantees that the + // two locations do not alias. + uint64_t ModOffset = (uint64_t)GEP1BaseOffset & (Modulo - 1); + if (V1Size != MemoryLocation::UnknownSize && + V2Size != MemoryLocation::UnknownSize && ModOffset >= V2Size && + V1Size <= Modulo - ModOffset) + return NoAlias; + + // If we know all the variables are positive, then GEP1 >= GEP1BasePtr. + // If GEP1BasePtr > V2 (GEP1BaseOffset > 0) then we know the pointers + // don't alias if V2Size can fit in the gap between V2 and GEP1BasePtr. + if (AllPositive && GEP1BaseOffset > 0 && V2Size <= (uint64_t)GEP1BaseOffset) + return NoAlias; + + if (constantOffsetHeuristic(GEP1VariableIndices, V1Size, V2Size, + GEP1BaseOffset, &AC, DT)) + return NoAlias; + } + + // Statically, we can see that the base objects are the same, but the + // pointers have dynamic offsets which we can't resolve. And none of our + // little tricks above worked. + // + // TODO: Returning PartialAlias instead of MayAlias is a mild hack; the + // practical effect of this is protecting TBAA in the case of dynamic + // indices into arrays of unions or malloc'd memory. + return PartialAlias; +} + +static AliasResult MergeAliasResults(AliasResult A, AliasResult B) { + // If the results agree, take it. + if (A == B) + return A; + // A mix of PartialAlias and MustAlias is PartialAlias. + if ((A == PartialAlias && B == MustAlias) || + (B == PartialAlias && A == MustAlias)) + return PartialAlias; + // Otherwise, we don't know anything. + return MayAlias; +} + +/// Provides a bunch of ad-hoc rules to disambiguate a Select instruction +/// against another. +AliasResult BasicAAResult::aliasSelect(const SelectInst *SI, uint64_t SISize, + const AAMDNodes &SIAAInfo, + const Value *V2, uint64_t V2Size, + const AAMDNodes &V2AAInfo) { + // If the values are Selects with the same condition, we can do a more precise + // check: just check for aliases between the values on corresponding arms. + if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2)) + if (SI->getCondition() == SI2->getCondition()) { + AliasResult Alias = aliasCheck(SI->getTrueValue(), SISize, SIAAInfo, + SI2->getTrueValue(), V2Size, V2AAInfo); + if (Alias == MayAlias) + return MayAlias; + AliasResult ThisAlias = + aliasCheck(SI->getFalseValue(), SISize, SIAAInfo, + SI2->getFalseValue(), V2Size, V2AAInfo); + return MergeAliasResults(ThisAlias, Alias); + } + + // If both arms of the Select node NoAlias or MustAlias V2, then returns + // NoAlias / MustAlias. Otherwise, returns MayAlias. + AliasResult Alias = + aliasCheck(V2, V2Size, V2AAInfo, SI->getTrueValue(), SISize, SIAAInfo); + if (Alias == MayAlias) + return MayAlias; + + AliasResult ThisAlias = + aliasCheck(V2, V2Size, V2AAInfo, SI->getFalseValue(), SISize, SIAAInfo); + return MergeAliasResults(ThisAlias, Alias); +} + +/// Provide a bunch of ad-hoc rules to disambiguate a PHI instruction against +/// another. +AliasResult BasicAAResult::aliasPHI(const PHINode *PN, uint64_t PNSize, + const AAMDNodes &PNAAInfo, const Value *V2, + uint64_t V2Size, + const AAMDNodes &V2AAInfo) { + // Track phi nodes we have visited. We use this information when we determine + // value equivalence. + VisitedPhiBBs.insert(PN->getParent()); + + // If the values are PHIs in the same block, we can do a more precise + // as well as efficient check: just check for aliases between the values + // on corresponding edges. + if (const PHINode *PN2 = dyn_cast<PHINode>(V2)) + if (PN2->getParent() == PN->getParent()) { + LocPair Locs(MemoryLocation(PN, PNSize, PNAAInfo), + MemoryLocation(V2, V2Size, V2AAInfo)); + if (PN > V2) + std::swap(Locs.first, Locs.second); + // Analyse the PHIs' inputs under the assumption that the PHIs are + // NoAlias. + // If the PHIs are May/MustAlias there must be (recursively) an input + // operand from outside the PHIs' cycle that is MayAlias/MustAlias or + // there must be an operation on the PHIs within the PHIs' value cycle + // that causes a MayAlias. + // Pretend the phis do not alias. + AliasResult Alias = NoAlias; + assert(AliasCache.count(Locs) && + "There must exist an entry for the phi node"); + AliasResult OrigAliasResult = AliasCache[Locs]; + AliasCache[Locs] = NoAlias; + + for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { + AliasResult ThisAlias = + aliasCheck(PN->getIncomingValue(i), PNSize, PNAAInfo, + PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)), + V2Size, V2AAInfo); + Alias = MergeAliasResults(ThisAlias, Alias); + if (Alias == MayAlias) + break; + } + + // Reset if speculation failed. + if (Alias != NoAlias) + AliasCache[Locs] = OrigAliasResult; + + return Alias; + } + + SmallPtrSet<Value *, 4> UniqueSrc; + SmallVector<Value *, 4> V1Srcs; + bool isRecursive = false; + for (Value *PV1 : PN->incoming_values()) { + if (isa<PHINode>(PV1)) + // If any of the source itself is a PHI, return MayAlias conservatively + // to avoid compile time explosion. The worst possible case is if both + // sides are PHI nodes. In which case, this is O(m x n) time where 'm' + // and 'n' are the number of PHI sources. + return MayAlias; + + if (EnableRecPhiAnalysis) + if (GEPOperator *PV1GEP = dyn_cast<GEPOperator>(PV1)) { + // Check whether the incoming value is a GEP that advances the pointer + // result of this PHI node (e.g. in a loop). If this is the case, we + // would recurse and always get a MayAlias. Handle this case specially + // below. + if (PV1GEP->getPointerOperand() == PN && PV1GEP->getNumIndices() == 1 && + isa<ConstantInt>(PV1GEP->idx_begin())) { + isRecursive = true; + continue; + } + } + + if (UniqueSrc.insert(PV1).second) + V1Srcs.push_back(PV1); + } + + // If this PHI node is recursive, set the size of the accessed memory to + // unknown to represent all the possible values the GEP could advance the + // pointer to. + if (isRecursive) + PNSize = MemoryLocation::UnknownSize; + + AliasResult Alias = + aliasCheck(V2, V2Size, V2AAInfo, V1Srcs[0], PNSize, PNAAInfo); + + // Early exit if the check of the first PHI source against V2 is MayAlias. + // Other results are not possible. + if (Alias == MayAlias) + return MayAlias; + + // If all sources of the PHI node NoAlias or MustAlias V2, then returns + // NoAlias / MustAlias. Otherwise, returns MayAlias. + for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) { + Value *V = V1Srcs[i]; + + AliasResult ThisAlias = + aliasCheck(V2, V2Size, V2AAInfo, V, PNSize, PNAAInfo); + Alias = MergeAliasResults(ThisAlias, Alias); + if (Alias == MayAlias) + break; + } + + return Alias; +} + +/// Provides a bunch of ad-hoc rules to disambiguate in common cases, such as +/// array references. +AliasResult BasicAAResult::aliasCheck(const Value *V1, uint64_t V1Size, + AAMDNodes V1AAInfo, const Value *V2, + uint64_t V2Size, AAMDNodes V2AAInfo) { + // If either of the memory references is empty, it doesn't matter what the + // pointer values are. + if (V1Size == 0 || V2Size == 0) + return NoAlias; + + // Strip off any casts if they exist. + V1 = V1->stripPointerCasts(); + V2 = V2->stripPointerCasts(); + + // If V1 or V2 is undef, the result is NoAlias because we can always pick a + // value for undef that aliases nothing in the program. + if (isa<UndefValue>(V1) || isa<UndefValue>(V2)) + return NoAlias; + + // Are we checking for alias of the same value? + // Because we look 'through' phi nodes we could look at "Value" pointers from + // different iterations. We must therefore make sure that this is not the + // case. The function isValueEqualInPotentialCycles ensures that this cannot + // happen by looking at the visited phi nodes and making sure they cannot + // reach the value. + if (isValueEqualInPotentialCycles(V1, V2)) + return MustAlias; + + if (!V1->getType()->isPointerTy() || !V2->getType()->isPointerTy()) + return NoAlias; // Scalars cannot alias each other + + // Figure out what objects these things are pointing to if we can. + const Value *O1 = GetUnderlyingObject(V1, DL, MaxLookupSearchDepth); + const Value *O2 = GetUnderlyingObject(V2, DL, MaxLookupSearchDepth); + + // Null values in the default address space don't point to any object, so they + // don't alias any other pointer. + if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O1)) + if (CPN->getType()->getAddressSpace() == 0) + return NoAlias; + if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2)) + if (CPN->getType()->getAddressSpace() == 0) + return NoAlias; + + 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; + + // Constant pointers can't alias with non-const isIdentifiedObject objects. + if ((isa<Constant>(O1) && isIdentifiedObject(O2) && !isa<Constant>(O2)) || + (isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1))) + return NoAlias; + + // Function arguments can't alias with things that are known to be + // unambigously identified at the function level. + if ((isa<Argument>(O1) && isIdentifiedFunctionLocal(O2)) || + (isa<Argument>(O2) && isIdentifiedFunctionLocal(O1))) + return NoAlias; + + // Most objects can't alias null. + if ((isa<ConstantPointerNull>(O2) && isKnownNonNull(O1)) || + (isa<ConstantPointerNull>(O1) && isKnownNonNull(O2))) + return NoAlias; + + // If one pointer is the result of a call/invoke or load and the other is a + // non-escaping local object within the same function, then we know the + // object couldn't escape to a point where the call could return it. + // + // Note that if the pointers are in different functions, there are a + // variety of complications. A call with a nocapture argument may still + // temporary store the nocapture argument's value in a temporary memory + // location if that memory location doesn't escape. Or it may pass a + // nocapture value to other functions as long as they don't capture it. + if (isEscapeSource(O1) && isNonEscapingLocalObject(O2)) + return NoAlias; + if (isEscapeSource(O2) && isNonEscapingLocalObject(O1)) + 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. + if ((V1Size != MemoryLocation::UnknownSize && + isObjectSmallerThan(O2, V1Size, DL, TLI)) || + (V2Size != MemoryLocation::UnknownSize && + isObjectSmallerThan(O1, V2Size, DL, TLI))) + return NoAlias; + + // Check the cache before climbing up use-def chains. This also terminates + // otherwise infinitely recursive queries. + LocPair Locs(MemoryLocation(V1, V1Size, V1AAInfo), + MemoryLocation(V2, V2Size, V2AAInfo)); + if (V1 > V2) + std::swap(Locs.first, Locs.second); + std::pair<AliasCacheTy::iterator, bool> Pair = + AliasCache.insert(std::make_pair(Locs, MayAlias)); + if (!Pair.second) + return Pair.first->second; + + // FIXME: This isn't aggressively handling alias(GEP, PHI) for example: if the + // GEP can't simplify, we don't even look at the PHI cases. + if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) { + std::swap(V1, V2); + std::swap(V1Size, V2Size); + std::swap(O1, O2); + std::swap(V1AAInfo, V2AAInfo); + } + if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) { + AliasResult Result = + aliasGEP(GV1, V1Size, V1AAInfo, V2, V2Size, V2AAInfo, O1, O2); + if (Result != MayAlias) + return AliasCache[Locs] = Result; + } + + if (isa<PHINode>(V2) && !isa<PHINode>(V1)) { + std::swap(V1, V2); + std::swap(V1Size, V2Size); + std::swap(V1AAInfo, V2AAInfo); + } + if (const PHINode *PN = dyn_cast<PHINode>(V1)) { + AliasResult Result = aliasPHI(PN, V1Size, V1AAInfo, V2, V2Size, V2AAInfo); + if (Result != MayAlias) + return AliasCache[Locs] = Result; + } + + if (isa<SelectInst>(V2) && !isa<SelectInst>(V1)) { + std::swap(V1, V2); + std::swap(V1Size, V2Size); + std::swap(V1AAInfo, V2AAInfo); + } + if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) { + AliasResult Result = + aliasSelect(S1, V1Size, V1AAInfo, V2, V2Size, V2AAInfo); + if (Result != MayAlias) + return AliasCache[Locs] = Result; + } + + // If both pointers are pointing into the same object and one of them + // accesses is accessing the entire object, then the accesses must + // overlap in some way. + if (O1 == O2) + if ((V1Size != MemoryLocation::UnknownSize && + isObjectSize(O1, V1Size, DL, TLI)) || + (V2Size != MemoryLocation::UnknownSize && + isObjectSize(O2, V2Size, DL, TLI))) + return AliasCache[Locs] = PartialAlias; + + // Recurse back into the best AA results we have, potentially with refined + // memory locations. We have already ensured that BasicAA has a MayAlias + // cache result for these, so any recursion back into BasicAA won't loop. + AliasResult Result = getBestAAResults().alias(Locs.first, Locs.second); + return AliasCache[Locs] = Result; +} + +/// Check whether two Values can be considered equivalent. +/// +/// In addition to pointer equivalence of \p V1 and \p V2 this checks whether +/// they can not be part of a cycle in the value graph by looking at all +/// visited phi nodes an making sure that the phis cannot reach the value. We +/// have to do this because we are looking through phi nodes (That is we say +/// noalias(V, phi(VA, VB)) if noalias(V, VA) and noalias(V, VB). +bool BasicAAResult::isValueEqualInPotentialCycles(const Value *V, + const Value *V2) { + if (V != V2) + return false; + + const Instruction *Inst = dyn_cast<Instruction>(V); + if (!Inst) + return true; + + if (VisitedPhiBBs.empty()) + return true; + + if (VisitedPhiBBs.size() > MaxNumPhiBBsValueReachabilityCheck) + return false; + + // Make sure that the visited phis cannot reach the Value. This ensures that + // the Values cannot come from different iterations of a potential cycle the + // phi nodes could be involved in. + for (auto *P : VisitedPhiBBs) + if (isPotentiallyReachable(&P->front(), Inst, DT, LI)) + return false; + + return true; +} + +/// Computes the symbolic difference between two de-composed GEPs. +/// +/// Dest and Src are the variable indices from two decomposed GetElementPtr +/// instructions GEP1 and GEP2 which have common base pointers. +void BasicAAResult::GetIndexDifference( + SmallVectorImpl<VariableGEPIndex> &Dest, + const SmallVectorImpl<VariableGEPIndex> &Src) { + if (Src.empty()) + return; + + for (unsigned i = 0, e = Src.size(); i != e; ++i) { + const Value *V = Src[i].V; + unsigned ZExtBits = Src[i].ZExtBits, SExtBits = Src[i].SExtBits; + int64_t Scale = Src[i].Scale; + + // Find V in Dest. This is N^2, but pointer indices almost never have more + // than a few variable indexes. + for (unsigned j = 0, e = Dest.size(); j != e; ++j) { + if (!isValueEqualInPotentialCycles(Dest[j].V, V) || + Dest[j].ZExtBits != ZExtBits || Dest[j].SExtBits != SExtBits) + continue; + + // If we found it, subtract off Scale V's from the entry in Dest. If it + // goes to zero, remove the entry. + if (Dest[j].Scale != Scale) + Dest[j].Scale -= Scale; + else + Dest.erase(Dest.begin() + j); + Scale = 0; + break; + } + + // If we didn't consume this entry, add it to the end of the Dest list. + if (Scale) { + VariableGEPIndex Entry = {V, ZExtBits, SExtBits, -Scale}; + Dest.push_back(Entry); + } + } +} + +bool BasicAAResult::constantOffsetHeuristic( + const SmallVectorImpl<VariableGEPIndex> &VarIndices, uint64_t V1Size, + uint64_t V2Size, int64_t BaseOffset, AssumptionCache *AC, + DominatorTree *DT) { + if (VarIndices.size() != 2 || V1Size == MemoryLocation::UnknownSize || + V2Size == MemoryLocation::UnknownSize) + return false; + + const VariableGEPIndex &Var0 = VarIndices[0], &Var1 = VarIndices[1]; + + if (Var0.ZExtBits != Var1.ZExtBits || Var0.SExtBits != Var1.SExtBits || + Var0.Scale != -Var1.Scale) + return false; + + unsigned Width = Var1.V->getType()->getIntegerBitWidth(); + + // We'll strip off the Extensions of Var0 and Var1 and do another round + // of GetLinearExpression decomposition. In the example above, if Var0 + // is zext(%x + 1) we should get V1 == %x and V1Offset == 1. + + APInt V0Scale(Width, 0), V0Offset(Width, 0), V1Scale(Width, 0), + V1Offset(Width, 0); + bool NSW = true, NUW = true; + unsigned V0ZExtBits = 0, V0SExtBits = 0, V1ZExtBits = 0, V1SExtBits = 0; + const Value *V0 = GetLinearExpression(Var0.V, V0Scale, V0Offset, V0ZExtBits, + V0SExtBits, DL, 0, AC, DT, NSW, NUW); + NSW = true, NUW = true; + const Value *V1 = GetLinearExpression(Var1.V, V1Scale, V1Offset, V1ZExtBits, + V1SExtBits, DL, 0, AC, DT, NSW, NUW); + + if (V0Scale != V1Scale || V0ZExtBits != V1ZExtBits || + V0SExtBits != V1SExtBits || !isValueEqualInPotentialCycles(V0, V1)) + return false; + + // We have a hit - Var0 and Var1 only differ by a constant offset! + + // If we've been sext'ed then zext'd the maximum difference between Var0 and + // Var1 is possible to calculate, but we're just interested in the absolute + // minimum difference between the two. The minimum distance may occur due to + // wrapping; consider "add i3 %i, 5": if %i == 7 then 7 + 5 mod 8 == 4, and so + // the minimum distance between %i and %i + 5 is 3. + APInt MinDiff = V0Offset - V1Offset, Wrapped = -MinDiff; + MinDiff = APIntOps::umin(MinDiff, Wrapped); + uint64_t MinDiffBytes = MinDiff.getZExtValue() * std::abs(Var0.Scale); + + // We can't definitely say whether GEP1 is before or after V2 due to wrapping + // arithmetic (i.e. for some values of GEP1 and V2 GEP1 < V2, and for other + // values GEP1 > V2). We'll therefore only declare NoAlias if both V1Size and + // V2Size can fit in the MinDiffBytes gap. + return V1Size + std::abs(BaseOffset) <= MinDiffBytes && + V2Size + std::abs(BaseOffset) <= MinDiffBytes; +} + +//===----------------------------------------------------------------------===// +// BasicAliasAnalysis Pass +//===----------------------------------------------------------------------===// + +char BasicAA::PassID; + +BasicAAResult BasicAA::run(Function &F, AnalysisManager<Function> *AM) { + return BasicAAResult(F.getParent()->getDataLayout(), + AM->getResult<TargetLibraryAnalysis>(F), + AM->getResult<AssumptionAnalysis>(F), + AM->getCachedResult<DominatorTreeAnalysis>(F), + AM->getCachedResult<LoopAnalysis>(F)); +} + +BasicAAWrapperPass::BasicAAWrapperPass() : FunctionPass(ID) { + initializeBasicAAWrapperPassPass(*PassRegistry::getPassRegistry()); +} + +char BasicAAWrapperPass::ID = 0; +void BasicAAWrapperPass::anchor() {} + +INITIALIZE_PASS_BEGIN(BasicAAWrapperPass, "basicaa", + "Basic Alias Analysis (stateless AA impl)", true, true) +INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) +INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) +INITIALIZE_PASS_END(BasicAAWrapperPass, "basicaa", + "Basic Alias Analysis (stateless AA impl)", true, true) + +FunctionPass *llvm::createBasicAAWrapperPass() { + return new BasicAAWrapperPass(); +} + +bool BasicAAWrapperPass::runOnFunction(Function &F) { + auto &ACT = getAnalysis<AssumptionCacheTracker>(); + auto &TLIWP = getAnalysis<TargetLibraryInfoWrapperPass>(); + auto *DTWP = getAnalysisIfAvailable<DominatorTreeWrapperPass>(); + auto *LIWP = getAnalysisIfAvailable<LoopInfoWrapperPass>(); + + Result.reset(new BasicAAResult(F.getParent()->getDataLayout(), TLIWP.getTLI(), + ACT.getAssumptionCache(F), + DTWP ? &DTWP->getDomTree() : nullptr, + LIWP ? &LIWP->getLoopInfo() : nullptr)); + + return false; +} + +void BasicAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const { + AU.setPreservesAll(); + AU.addRequired<AssumptionCacheTracker>(); + AU.addRequired<TargetLibraryInfoWrapperPass>(); +} + +BasicAAResult llvm::createLegacyPMBasicAAResult(Pass &P, Function &F) { + return BasicAAResult( + F.getParent()->getDataLayout(), + P.getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(), + P.getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F)); +} |
