X-Git-Url: http://plrg.eecs.uci.edu/git/?p=oota-llvm.git;a=blobdiff_plain;f=lib%2FAnalysis%2FBasicAliasAnalysis.cpp;h=1514e78010ebe85a138d68ba29810c21b405d790;hp=e3476ac537d0483653178ef6f40d31e14a6034a0;hb=529919ff310cbfce1ba55ea252ff738d5b56b93d;hpb=8e0d1c03ca7fd86e6879b4e37d0d7f0e982feef6 diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp index e3476ac537d..1514e78010e 100644 --- a/lib/Analysis/BasicAliasAnalysis.cpp +++ b/lib/Analysis/BasicAliasAnalysis.cpp @@ -13,31 +13,46 @@ // //===----------------------------------------------------------------------===// -#include "llvm/Analysis/AliasAnalysis.h" #include "llvm/Analysis/Passes.h" -#include "llvm/Constants.h" -#include "llvm/DerivedTypes.h" -#include "llvm/Function.h" -#include "llvm/GlobalAlias.h" -#include "llvm/GlobalVariable.h" -#include "llvm/Instructions.h" -#include "llvm/IntrinsicInst.h" -#include "llvm/LLVMContext.h" -#include "llvm/Operator.h" -#include "llvm/Pass.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/Analysis/AliasAnalysis.h" +#include "llvm/Analysis/AssumptionCache.h" +#include "llvm/Analysis/CFG.h" #include "llvm/Analysis/CaptureTracking.h" -#include "llvm/Analysis/MemoryBuiltins.h" #include "llvm/Analysis/InstructionSimplify.h" +#include "llvm/Analysis/LoopInfo.h" +#include "llvm/Analysis/MemoryBuiltins.h" +#include "llvm/Analysis/TargetLibraryInfo.h" #include "llvm/Analysis/ValueTracking.h" -#include "llvm/Target/TargetData.h" -#include "llvm/Target/TargetLibraryInfo.h" -#include "llvm/ADT/SmallPtrSet.h" -#include "llvm/ADT/SmallVector.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/DerivedTypes.h" +#include "llvm/IR/Dominators.h" +#include "llvm/IR/Function.h" +#include "llvm/IR/GetElementPtrTypeIterator.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 "llvm/Support/GetElementPtrTypeIterator.h" #include using namespace llvm; +/// 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 //===----------------------------------------------------------------------===// @@ -58,12 +73,12 @@ static bool isNonEscapingLocalObject(const Value *V) { // then it has not escaped before entering the function. Check if it escapes // inside the function. if (const Argument *A = dyn_cast(V)) - if (A->hasByValAttr() || A->hasNoAliasAttr()) { - // Don't bother analyzing arguments already known not to escape. - if (A->hasNoCaptureAttr()) - return true; + 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; } @@ -84,11 +99,11 @@ static bool isEscapeSource(const Value *V) { /// getObjectSize - Return the size of the object specified by V, or /// UnknownSize if unknown. -static uint64_t getObjectSize(const Value *V, const TargetData &TD, +static uint64_t getObjectSize(const Value *V, const DataLayout &DL, const TargetLibraryInfo &TLI, bool RoundToAlign = false) { uint64_t Size; - if (getObjectSize(V, Size, &TD, &TLI, RoundToAlign)) + if (getObjectSize(V, Size, DL, &TLI, RoundToAlign)) return Size; return AliasAnalysis::UnknownSize; } @@ -96,20 +111,49 @@ static uint64_t getObjectSize(const Value *V, const TargetData &TD, /// isObjectSmallerThan - Return 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 TargetData &TD, + 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, TD, TLI, /*RoundToAlign*/true); - + uint64_t ObjectSize = getObjectSize(V, DL, TLI, /*RoundToAlign*/true); + return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize < Size; } /// isObjectSize - Return true if we can prove that the object specified /// by V has size Size. static bool isObjectSize(const Value *V, uint64_t Size, - const TargetData &TD, const TargetLibraryInfo &TLI) { - uint64_t ObjectSize = getObjectSize(V, TD, TLI); + const DataLayout &DL, const TargetLibraryInfo &TLI) { + uint64_t ObjectSize = getObjectSize(V, DL, TLI); return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize == Size; } @@ -123,11 +167,20 @@ namespace { EK_SignExt, EK_ZeroExt }; - + struct VariableGEPIndex { const Value *V; ExtensionKind Extension; int64_t Scale; + + bool operator==(const VariableGEPIndex &Other) const { + return V == Other.V && Extension == Other.Extension && + Scale == Other.Scale; + } + + bool operator!=(const VariableGEPIndex &Other) const { + return !operator==(Other); + } }; } @@ -142,7 +195,8 @@ namespace { /// represented in the result. static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset, ExtensionKind &Extension, - const TargetData &TD, unsigned Depth) { + const DataLayout &DL, unsigned Depth, + AssumptionCache *AC, DominatorTree *DT) { assert(V->getType()->isIntegerTy() && "Not an integer value"); // Limit our recursion depth. @@ -151,7 +205,15 @@ static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset, Offset = 0; return V; } - + + if (ConstantInt *Const = dyn_cast(V)) { + // if it's a constant, just convert it to an offset + // and remove the variable. + Offset += Const->getValue(); + assert(Scale == 0 && "Constant values don't have a scale"); + return V; + } + if (BinaryOperator *BOp = dyn_cast(V)) { if (ConstantInt *RHSC = dyn_cast(BOp->getOperand(1))) { switch (BOp->getOpcode()) { @@ -159,30 +221,31 @@ static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset, 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(), &TD)) + if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(), DL, 0, AC, + BOp, DT)) break; // FALL THROUGH. case Instruction::Add: V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension, - TD, Depth+1); + DL, Depth + 1, AC, DT); Offset += RHSC->getValue(); return V; case Instruction::Mul: V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension, - TD, Depth+1); + DL, Depth + 1, AC, DT); Offset *= RHSC->getValue(); Scale *= RHSC->getValue(); return V; case Instruction::Shl: V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension, - TD, Depth+1); + DL, Depth + 1, AC, DT); Offset <<= RHSC->getValue().getLimitedValue(); Scale <<= RHSC->getValue().getLimitedValue(); 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. @@ -195,14 +258,17 @@ static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset, Offset = Offset.trunc(SmallWidth); Extension = isa(V) ? EK_SignExt : EK_ZeroExt; - Value *Result = GetLinearExpression(CastOp, Scale, Offset, Extension, - TD, Depth+1); + Value *Result = GetLinearExpression(CastOp, Scale, Offset, Extension, DL, + Depth + 1, AC, DT); Scale = Scale.zext(OldWidth); - Offset = Offset.zext(OldWidth); - + + // We have to sign-extend even if Extension == EK_ZeroExt as we can't + // decompose a sign extension (i.e. zext(x - 1) != zext(x) - zext(-1)). + Offset = Offset.sext(OldWidth); + return Result; } - + Scale = 1; Offset = 0; return V; @@ -217,22 +283,26 @@ static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset, /// specified amount, but which may have other unrepresented high bits. As such, /// the gep cannot necessarily be reconstructed from its decomposed form. /// -/// When TargetData is around, this function is capable of analyzing everything -/// that GetUnderlyingObject can look through. When not, it just looks -/// through pointer casts. +/// 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 * DecomposeGEPExpression(const Value *V, int64_t &BaseOffs, SmallVectorImpl &VarIndices, - const TargetData *TD) { + bool &MaxLookupReached, const DataLayout &DL, + AssumptionCache *AC, DominatorTree *DT) { // Limit recursion depth to limit compile time in crazy cases. - unsigned MaxLookup = 6; - + unsigned MaxLookup = MaxLookupSearchDepth; + MaxLookupReached = false; + BaseOffs = 0; do { // See if this is a bitcast or GEP. const Operator *Op = dyn_cast(V); - if (Op == 0) { + if (!Op) { // The only non-operator case we can handle are GlobalAliases. if (const GlobalAlias *GA = dyn_cast(V)) { if (!GA->mayBeOverridden()) { @@ -242,42 +312,36 @@ DecomposeGEPExpression(const Value *V, int64_t &BaseOffs, } return V; } - - if (Op->getOpcode() == Instruction::BitCast) { + + if (Op->getOpcode() == Instruction::BitCast || + Op->getOpcode() == Instruction::AddrSpaceCast) { V = Op->getOperand(0); continue; } const GEPOperator *GEPOp = dyn_cast(Op); - if (GEPOp == 0) { + 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(V)) - // TODO: Get a DominatorTree and use it here. + // 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(I), TD)) { + SimplifyInstruction(const_cast(I), DL)) { V = Simplified; continue; } - + return V; } - + // Don't attempt to analyze GEPs over unsized objects. - if (!cast(GEPOp->getOperand(0)->getType()) - ->getElementType()->isSized()) + if (!GEPOp->getOperand(0)->getType()->getPointerElementType()->isSized()) return V; - - // If we are lacking TargetData information, we can't compute the offets of - // elements computed by GEPs. However, we can handle bitcast equivalent - // GEPs. - if (TD == 0) { - if (!GEPOp->hasAllZeroIndices()) - return V; - V = GEPOp->getOperand(0); - continue; - } - + + 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, @@ -288,38 +352,37 @@ DecomposeGEPExpression(const Value *V, int64_t &BaseOffs, // For a struct, add the member offset. unsigned FieldNo = cast(Index)->getZExtValue(); if (FieldNo == 0) continue; - - BaseOffs += TD->getStructLayout(STy)->getElementOffset(FieldNo); + + BaseOffs += DL.getStructLayout(STy)->getElementOffset(FieldNo); continue; } - + // For an array/pointer, add the element offset, explicitly scaled. if (ConstantInt *CIdx = dyn_cast(Index)) { if (CIdx->isZero()) continue; - BaseOffs += TD->getTypeAllocSize(*GTI)*CIdx->getSExtValue(); + BaseOffs += DL.getTypeAllocSize(*GTI) * CIdx->getSExtValue(); continue; } - - uint64_t Scale = TD->getTypeAllocSize(*GTI); + + uint64_t Scale = DL.getTypeAllocSize(*GTI); ExtensionKind Extension = EK_NotExtended; - + // If the integer type is smaller than the pointer size, it is implicitly // sign extended to pointer size. - unsigned Width = cast(Index->getType())->getBitWidth(); - if (TD->getPointerSizeInBits() > Width) + unsigned Width = Index->getType()->getIntegerBitWidth(); + if (DL.getPointerSizeInBits(AS) > Width) Extension = EK_SignExt; - + // Use GetLinearExpression to decompose the index into a C1*V+C2 form. APInt IndexScale(Width, 0), IndexOffset(Width, 0); - Index = GetLinearExpression(Index, IndexScale, IndexOffset, Extension, - *TD, 0); - + Index = GetLinearExpression(Index, IndexScale, IndexOffset, Extension, DL, + 0, AC, DT); + // 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 @@ -332,65 +395,30 @@ DecomposeGEPExpression(const Value *V, int64_t &BaseOffs, break; } } - + // Make sure that we have a scale that makes sense for this target's // pointer size. - if (unsigned ShiftBits = 64-TD->getPointerSizeInBits()) { + if (unsigned ShiftBits = 64 - DL.getPointerSizeInBits(AS)) { Scale <<= ShiftBits; Scale = (int64_t)Scale >> ShiftBits; } - + if (Scale) { VariableGEPIndex Entry = {Index, Extension, static_cast(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; return V; } -/// GetIndexDifference - Dest and Src are the variable indices from two -/// decomposed GetElementPtr instructions GEP1 and GEP2 which have common base -/// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic -/// difference between the two pointers. -static void GetIndexDifference(SmallVectorImpl &Dest, - const SmallVectorImpl &Src) { - if (Src.empty()) return; - - for (unsigned i = 0, e = Src.size(); i != e; ++i) { - const Value *V = Src[i].V; - ExtensionKind Extension = Src[i].Extension; - 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 (Dest[j].V != V || Dest[j].Extension != Extension) 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, Extension, -Scale }; - Dest.push_back(Entry); - } - } -} - //===----------------------------------------------------------------------===// // BasicAliasAnalysis Pass //===----------------------------------------------------------------------===// @@ -403,7 +431,7 @@ static const Function *getParent(const Value *V) { if (const Argument *arg = dyn_cast(V)) return arg->getParent(); - return NULL; + return nullptr; } static bool notDifferentParent(const Value *O1, const Value *O2) { @@ -419,100 +447,129 @@ namespace { /// BasicAliasAnalysis - This is the primary alias analysis implementation. struct BasicAliasAnalysis : public ImmutablePass, public AliasAnalysis { static char ID; // Class identification, replacement for typeinfo - BasicAliasAnalysis() : ImmutablePass(ID), - // AliasCache rarely has more than 1 or 2 elements, - // so start it off fairly small so that clear() - // doesn't have to tromp through 64 (the default) - // elements on each alias query. This really wants - // something like a SmallDenseMap. - AliasCache(8) { + BasicAliasAnalysis() : ImmutablePass(ID) { initializeBasicAliasAnalysisPass(*PassRegistry::getPassRegistry()); } - virtual void initializePass() { - InitializeAliasAnalysis(this); - } + bool doInitialization(Module &M) override; - virtual void getAnalysisUsage(AnalysisUsage &AU) const { + void getAnalysisUsage(AnalysisUsage &AU) const override { AU.addRequired(); - AU.addRequired(); + AU.addRequired(); + AU.addRequired(); } - virtual AliasResult alias(const Location &LocA, - const Location &LocB) { + AliasResult alias(const Location &LocA, const Location &LocB) override { assert(AliasCache.empty() && "AliasCache must be cleared after use!"); assert(notDifferentParent(LocA.Ptr, LocB.Ptr) && "BasicAliasAnalysis doesn't support interprocedural queries."); - AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.TBAATag, - LocB.Ptr, LocB.Size, LocB.TBAATag); - AliasCache.clear(); + 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; } - virtual ModRefResult getModRefInfo(ImmutableCallSite CS, - const Location &Loc); + ModRefResult getModRefInfo(ImmutableCallSite CS, + const Location &Loc) override; - virtual ModRefResult getModRefInfo(ImmutableCallSite CS1, - ImmutableCallSite CS2) { - // The AliasAnalysis base class has some smarts, lets use them. - return AliasAnalysis::getModRefInfo(CS1, CS2); - } + ModRefResult getModRefInfo(ImmutableCallSite CS1, + ImmutableCallSite CS2) override; /// pointsToConstantMemory - Chase pointers until we find a (constant /// global) or not. - virtual bool pointsToConstantMemory(const Location &Loc, bool OrLocal); + bool pointsToConstantMemory(const Location &Loc, bool OrLocal) override; + + /// Get the location associated with a pointer argument of a callsite. + Location getArgLocation(ImmutableCallSite CS, unsigned ArgIdx, + ModRefResult &Mask) override; /// getModRefBehavior - Return the behavior when calling the given /// call site. - virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS); + ModRefBehavior getModRefBehavior(ImmutableCallSite CS) override; /// getModRefBehavior - Return the behavior when calling the given function. /// For use when the call site is not known. - virtual ModRefBehavior getModRefBehavior(const Function *F); + ModRefBehavior getModRefBehavior(const Function *F) override; /// getAdjustedAnalysisPointer - This method is used when a pass implements /// an analysis interface through multiple inheritance. If needed, it /// should override this to adjust the this pointer as needed for the /// specified pass info. - virtual void *getAdjustedAnalysisPointer(const void *ID) { + void *getAdjustedAnalysisPointer(const void *ID) override { if (ID == &AliasAnalysis::ID) return (AliasAnalysis*)this; return this; } - + private: // AliasCache - Track alias queries to guard against recursion. typedef std::pair LocPair; - typedef DenseMap AliasCacheTy; + typedef SmallDenseMap AliasCacheTy; AliasCacheTy AliasCache; + /// \brief Track phi nodes we have visited. When interpret "Value" pointer + /// equality as value equality we need to make sure that the "Value" is not + /// part of a cycle. Otherwise, two uses could come from different + /// "iterations" of a cycle and see different values for the same "Value" + /// pointer. + /// The following example shows the problem: + /// %p = phi(%alloca1, %addr2) + /// %l = load %ptr + /// %addr1 = gep, %alloca2, 0, %l + /// %addr2 = gep %alloca2, 0, (%l + 1) + /// alias(%p, %addr1) -> MayAlias ! + /// store %l, ... + SmallPtrSet VisitedPhiBBs; + // Visited - Track instructions visited by pointsToConstantMemory. SmallPtrSet Visited; + /// \brief 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 isValueEqualInPotentialCycles(const Value *V1, const Value *V2); + + /// \brief Dest and Src are the variable indices from two decomposed + /// GetElementPtr instructions GEP1 and GEP2 which have common base + /// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic + /// difference between the two pointers. + void GetIndexDifference(SmallVectorImpl &Dest, + const SmallVectorImpl &Src); + // aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP // instruction against another. AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size, + const AAMDNodes &V1AAInfo, const Value *V2, uint64_t V2Size, - const MDNode *V2TBAAInfo, + const AAMDNodes &V2AAInfo, const Value *UnderlyingV1, const Value *UnderlyingV2); // aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI // instruction against another. AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize, - const MDNode *PNTBAAInfo, + const AAMDNodes &PNAAInfo, const Value *V2, uint64_t V2Size, - const MDNode *V2TBAAInfo); + const AAMDNodes &V2AAInfo); /// aliasSelect - Disambiguate a Select instruction against another value. AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize, - const MDNode *SITBAAInfo, + const AAMDNodes &SIAAInfo, const Value *V2, uint64_t V2Size, - const MDNode *V2TBAAInfo); + const AAMDNodes &V2AAInfo); AliasResult aliasCheck(const Value *V1, uint64_t V1Size, - const MDNode *V1TBAATag, + AAMDNodes V1AATag, const Value *V2, uint64_t V2Size, - const MDNode *V2TBAATag); + AAMDNodes V2AATag); }; } // End of anonymous namespace @@ -521,7 +578,8 @@ char BasicAliasAnalysis::ID = 0; INITIALIZE_AG_PASS_BEGIN(BasicAliasAnalysis, AliasAnalysis, "basicaa", "Basic Alias Analysis (stateless AA impl)", false, true, false) -INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo) +INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker) +INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass) INITIALIZE_AG_PASS_END(BasicAliasAnalysis, AliasAnalysis, "basicaa", "Basic Alias Analysis (stateless AA impl)", false, true, false) @@ -542,8 +600,8 @@ BasicAliasAnalysis::pointsToConstantMemory(const Location &Loc, bool OrLocal) { SmallVector Worklist; Worklist.push_back(Loc.Ptr); do { - const Value *V = GetUnderlyingObject(Worklist.pop_back_val(), TD); - if (!Visited.insert(V)) { + const Value *V = GetUnderlyingObject(Worklist.pop_back_val(), *DL); + if (!Visited.insert(V).second) { Visited.clear(); return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal); } @@ -594,6 +652,21 @@ BasicAliasAnalysis::pointsToConstantMemory(const Location &Loc, bool OrLocal) { return Worklist.empty(); } +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(MemsetType->getParamType(0)) && + isa(MemsetType->getParamType(1)) && + isa(MemsetType->getParamType(2))) + return true; + } + + return false; +} + /// getModRefBehavior - Return the behavior when calling the given call site. AliasAnalysis::ModRefBehavior BasicAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) { @@ -623,7 +696,7 @@ BasicAliasAnalysis::getModRefBehavior(const Function *F) { // For intrinsics, we can check the table. if (unsigned iid = F->getIntrinsicID()) { #define GET_INTRINSIC_MODREF_BEHAVIOR -#include "llvm/Intrinsics.gen" +#include "llvm/IR/Intrinsics.gen" #undef GET_INTRINSIC_MODREF_BEHAVIOR } @@ -633,10 +706,108 @@ BasicAliasAnalysis::getModRefBehavior(const Function *F) { if (F->onlyReadsMemory()) Min = OnlyReadsMemory; + const TargetLibraryInfo &TLI = + getAnalysis().getTLI(); + if (isMemsetPattern16(F, TLI)) + Min = OnlyAccessesArgumentPointees; + // Otherwise be conservative. return ModRefBehavior(AliasAnalysis::getModRefBehavior(F) & Min); } +AliasAnalysis::Location +BasicAliasAnalysis::getArgLocation(ImmutableCallSite CS, unsigned ArgIdx, + ModRefResult &Mask) { + Location Loc = AliasAnalysis::getArgLocation(CS, ArgIdx, Mask); + const TargetLibraryInfo &TLI = + getAnalysis().getTLI(); + const IntrinsicInst *II = dyn_cast(CS.getInstruction()); + if (II != nullptr) + 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"); + if (ConstantInt *LenCI = dyn_cast(II->getArgOperand(2))) + Loc.Size = LenCI->getZExtValue(); + assert(Loc.Ptr == II->getArgOperand(ArgIdx) && + "Memory intrinsic location pointer not argument?"); + Mask = ArgIdx ? Ref : Mod; + break; + } + case Intrinsic::lifetime_start: + case Intrinsic::lifetime_end: + case Intrinsic::invariant_start: { + assert(ArgIdx == 1 && "Invalid argument index"); + assert(Loc.Ptr == II->getArgOperand(ArgIdx) && + "Intrinsic location pointer not argument?"); + Loc.Size = cast(II->getArgOperand(0))->getZExtValue(); + break; + } + case Intrinsic::invariant_end: { + assert(ArgIdx == 2 && "Invalid argument index"); + assert(Loc.Ptr == II->getArgOperand(ArgIdx) && + "Intrinsic location pointer not argument?"); + Loc.Size = cast(II->getArgOperand(1))->getZExtValue(); + break; + } + case Intrinsic::arm_neon_vld1: { + assert(ArgIdx == 0 && "Invalid argument index"); + assert(Loc.Ptr == II->getArgOperand(ArgIdx) && + "Intrinsic location pointer not argument?"); + // LLVM's vld1 and vst1 intrinsics currently only support a single + // vector register. + if (DL) + Loc.Size = DL->getTypeStoreSize(II->getType()); + break; + } + case Intrinsic::arm_neon_vst1: { + assert(ArgIdx == 0 && "Invalid argument index"); + assert(Loc.Ptr == II->getArgOperand(ArgIdx) && + "Intrinsic location pointer not argument?"); + if (DL) + Loc.Size = DL->getTypeStoreSize(II->getArgOperand(1)->getType()); + break; + } + } + + // 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. + else if (CS.getCalledFunction() && + isMemsetPattern16(CS.getCalledFunction(), TLI)) { + assert((ArgIdx == 0 || ArgIdx == 1) && + "Invalid argument index for memset_pattern16"); + if (ArgIdx == 1) + Loc.Size = 16; + else if (const ConstantInt *LenCI = + dyn_cast(CS.getArgument(2))) + Loc.Size = LenCI->getZExtValue(); + assert(Loc.Ptr == CS.getArgument(ArgIdx) && + "memset_pattern16 location pointer not argument?"); + Mask = ArgIdx ? Ref : Mod; + } + // FIXME: Handle memset_pattern4 and memset_pattern8 also. + + return Loc; +} + +static bool isAssumeIntrinsic(ImmutableCallSite CS) { + const IntrinsicInst *II = dyn_cast(CS.getInstruction()); + if (II && II->getIntrinsicID() == Intrinsic::assume) + return true; + + return false; +} + +bool BasicAliasAnalysis::doInitialization(Module &M) { + InitializeAliasAnalysis(this, &M.getDataLayout()); + return true; +} + /// 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 @@ -647,8 +818,8 @@ BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS, assert(notDifferentParent(CS.getInstruction(), Loc.Ptr) && "AliasAnalysis query involving multiple functions!"); - const Value *Object = GetUnderlyingObject(Loc.Ptr, TD); - + 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 @@ -658,7 +829,7 @@ BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS, if (const CallInst *CI = dyn_cast(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 pointer // as an argument, and itself doesn't capture it. @@ -674,7 +845,7 @@ BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS, 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 @@ -684,181 +855,254 @@ BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS, break; } } - + if (!PassedAsArg) return NoModRef; } - const TargetLibraryInfo &TLI = getAnalysis(); - ModRefResult Min = ModRef; + // 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 NoModRef; - // Finally, handle specific knowledge of intrinsics. - const IntrinsicInst *II = dyn_cast(CS.getInstruction()); - if (II != 0) - switch (II->getIntrinsicID()) { - default: break; - case Intrinsic::memcpy: - case Intrinsic::memmove: { - uint64_t Len = UnknownSize; - if (ConstantInt *LenCI = dyn_cast(II->getArgOperand(2))) - Len = LenCI->getZExtValue(); - Value *Dest = II->getArgOperand(0); - Value *Src = II->getArgOperand(1); - // If it can't overlap the source dest, then it doesn't modref the loc. - if (isNoAlias(Location(Dest, Len), Loc)) { - if (isNoAlias(Location(Src, Len), Loc)) - return NoModRef; - // If it can't overlap the dest, then worst case it reads the loc. - Min = Ref; - } else if (isNoAlias(Location(Src, Len), Loc)) { - // If it can't overlap the source, then worst case it mutates the loc. - Min = Mod; - } - break; - } - case Intrinsic::memset: - // Since memset is 'accesses arguments' only, the AliasAnalysis base class - // will handle it for the variable length case. - if (ConstantInt *LenCI = dyn_cast(II->getArgOperand(2))) { - uint64_t Len = LenCI->getZExtValue(); - Value *Dest = II->getArgOperand(0); - if (isNoAlias(Location(Dest, Len), Loc)) - return NoModRef; - } - // We know that memset doesn't load anything. - Min = Mod; - break; - case Intrinsic::lifetime_start: - case Intrinsic::lifetime_end: - case Intrinsic::invariant_start: { - uint64_t PtrSize = - cast(II->getArgOperand(0))->getZExtValue(); - if (isNoAlias(Location(II->getArgOperand(1), - PtrSize, - II->getMetadata(LLVMContext::MD_tbaa)), - Loc)) - return NoModRef; - break; - } - case Intrinsic::invariant_end: { - uint64_t PtrSize = - cast(II->getArgOperand(1))->getZExtValue(); - if (isNoAlias(Location(II->getArgOperand(2), - PtrSize, - II->getMetadata(LLVMContext::MD_tbaa)), - Loc)) - return NoModRef; - break; - } - case Intrinsic::arm_neon_vld1: { - // LLVM's vld1 and vst1 intrinsics currently only support a single - // vector register. - uint64_t Size = - TD ? TD->getTypeStoreSize(II->getType()) : UnknownSize; - if (isNoAlias(Location(II->getArgOperand(0), Size, - II->getMetadata(LLVMContext::MD_tbaa)), - Loc)) - return NoModRef; - break; - } - case Intrinsic::arm_neon_vst1: { - uint64_t Size = - TD ? TD->getTypeStoreSize(II->getArgOperand(1)->getType()) : UnknownSize; - if (isNoAlias(Location(II->getArgOperand(0), Size, - II->getMetadata(LLVMContext::MD_tbaa)), - Loc)) - return NoModRef; - break; - } - } + // The AliasAnalysis base class has some smarts, lets use them. + return AliasAnalysis::getModRefInfo(CS, Loc); +} - // 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. - else if (TLI.has(LibFunc::memset_pattern16) && - CS.getCalledFunction() && - CS.getCalledFunction()->getName() == "memset_pattern16") { - const Function *MS = CS.getCalledFunction(); - FunctionType *MemsetType = MS->getFunctionType(); - if (!MemsetType->isVarArg() && MemsetType->getNumParams() == 3 && - isa(MemsetType->getParamType(0)) && - isa(MemsetType->getParamType(1)) && - isa(MemsetType->getParamType(2))) { - uint64_t Len = UnknownSize; - if (const ConstantInt *LenCI = dyn_cast(CS.getArgument(2))) - Len = LenCI->getZExtValue(); - const Value *Dest = CS.getArgument(0); - const Value *Src = CS.getArgument(1); - // If it can't overlap the source dest, then it doesn't modref the loc. - if (isNoAlias(Location(Dest, Len), Loc)) { - // Always reads 16 bytes of the source. - if (isNoAlias(Location(Src, 16), Loc)) - return NoModRef; - // If it can't overlap the dest, then worst case it reads the loc. - Min = Ref; - // Always reads 16 bytes of the source. - } else if (isNoAlias(Location(Src, 16), Loc)) { - // If it can't overlap the source, then worst case it mutates the loc. - Min = Mod; - } - } - } +AliasAnalysis::ModRefResult +BasicAliasAnalysis::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 NoModRef; // The AliasAnalysis base class has some smarts, lets use them. - return ModRefResult(AliasAnalysis::getModRefInfo(CS, Loc) & Min); + return AliasAnalysis::getModRefInfo(CS1, CS2); +} + +/// \brief Provide ad-hoc rules to disambiguate accesses through two GEP +/// operators, both having the exact same pointer operand. +static AliasAnalysis::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 AliasAnalysis::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 == AliasAnalysis::UnknownSize || + V2Size == AliasAnalysis::UnknownSize) + return AliasAnalysis::MayAlias; + + ConstantInt *C1 = + dyn_cast(GEP1->getOperand(GEP1->getNumOperands() - 1)); + ConstantInt *C2 = + dyn_cast(GEP2->getOperand(GEP2->getNumOperands() - 1)); + + // If the last (struct) indices aren't constants, we can't say anything. + // If they're identical, the other indices might be also be dynamically + // equal, so the GEPs can alias. + if (!C1 || !C2 || C1 == C2) + return AliasAnalysis::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 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(GetElementPtrInst::getIndexedType( + GEP1->getPointerOperandType(), IntermediateIndices))) + return AliasAnalysis::MayAlias; + IntermediateIndices.push_back(GEP1->getOperand(i + 1)); + } + + StructType *LastIndexedStruct = + dyn_cast(GetElementPtrInst::getIndexedType( + GEP1->getPointerOperandType(), IntermediateIndices)); + + if (!LastIndexedStruct) + return AliasAnalysis::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 AliasAnalysis::NoAlias; + + return AliasAnalysis::MayAlias; } /// aliasGEP - Provide 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, TD), +/// anything about V2. UnderlyingV1 is GetUnderlyingObject(GEP1, DL), /// UnderlyingV2 is the same for V2. /// AliasAnalysis::AliasResult BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size, + const AAMDNodes &V1AAInfo, const Value *V2, uint64_t V2Size, - const MDNode *V2TBAAInfo, + const AAMDNodes &V2AAInfo, const Value *UnderlyingV1, const Value *UnderlyingV2) { int64_t GEP1BaseOffset; + bool GEP1MaxLookupReached; SmallVector GEP1VariableIndices; - // 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. + // We have to get two AssumptionCaches here because GEP1 and V2 may be from + // different functions. + // FIXME: This really doesn't make any sense. We get a dominator tree below + // that can only refer to a single function. But this function (aliasGEP) is + // a method on an immutable pass that can be called when there *isn't* + // a single function. The old pass management layer makes this "work", but + // this isn't really a clean solution. + AssumptionCacheTracker &ACT = getAnalysis(); + AssumptionCache *AC1 = nullptr, *AC2 = nullptr; + if (auto *GEP1I = dyn_cast(GEP1)) + AC1 = &ACT.getAssumptionCache( + const_cast(*GEP1I->getParent()->getParent())); + if (auto *I2 = dyn_cast(V2)) + AC2 = &ACT.getAssumptionCache( + const_cast(*I2->getParent()->getParent())); + + DominatorTreeWrapperPass *DTWP = + getAnalysisIfAvailable(); + DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr; + + // 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(V2)) { // Do the base pointers alias? - AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, 0, - UnderlyingV2, UnknownSize, 0); - + AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, AAMDNodes(), + UnderlyingV2, 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 GEP2VariableIndices; + const Value *GEP2BasePtr = + DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, + GEP2MaxLookupReached, *DL, AC2, DT); + const Value *GEP1BasePtr = + DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, + GEP1MaxLookupReached, *DL, AC1, DT); + // DecomposeGEPExpression and GetUnderlyingObject should return the + // same result except when DecomposeGEPExpression has no DataLayout. + if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) { + assert(!DL && + "DecomposeGEPExpression and GetUnderlyingObject disagree!"); + 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, TD); - + DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, + GEP1MaxLookupReached, *DL, AC1, DT); + int64_t GEP2BaseOffset; + bool GEP2MaxLookupReached; SmallVector GEP2VariableIndices; const Value *GEP2BasePtr = - DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD); - - // If DecomposeGEPExpression isn't able to look all the way through the - // addressing operation, we must not have TD and this is too complex for us - // to handle without it. + DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, + GEP2MaxLookupReached, *DL, AC2, DT); + + // DecomposeGEPExpression and GetUnderlyingObject should return the + // same result except when DecomposeGEPExpression has no DataLayout. if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) { - assert(TD == 0 && + assert(!DL && "DecomposeGEPExpression and GetUnderlyingObject disagree!"); 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 (DL && 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 @@ -868,8 +1112,8 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size, if (V1Size == UnknownSize && V2Size == UnknownSize) return MayAlias; - AliasResult R = aliasCheck(UnderlyingV1, UnknownSize, 0, - V2, V2Size, V2TBAAInfo); + AliasResult R = aliasCheck(UnderlyingV1, 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 @@ -879,18 +1123,21 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size, return R; const Value *GEP1BasePtr = - DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD); - - // If DecomposeGEPExpression isn't able to look all the way through the - // addressing operation, we must not have TD and this is too complex for us - // to handle without it. + DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, + GEP1MaxLookupReached, *DL, AC1, DT); + + // DecomposeGEPExpression and GetUnderlyingObject should return the + // same result except when DecomposeGEPExpression has no DataLayout. if (GEP1BasePtr != UnderlyingV1) { - assert(TD == 0 && + assert(!DL && "DecomposeGEPExpression and GetUnderlyingObject disagree!"); 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). @@ -912,7 +1159,15 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size, return NoAlias; } } else { - if (V1Size != UnknownSize) { + // 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 , -1, ...). + if (V1Size != UnknownSize && V2Size != UnknownSize) { if (-(uint64_t)GEP1BaseOffset < V1Size) return PartialAlias; return NoAlias; @@ -920,12 +1175,43 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size, } } - // Try to distinguish something like &A[i][1] against &A[42][0]. - // Grab the least significant bit set in any of the scales. if (!GEP1VariableIndices.empty()) { uint64_t Modulo = 0; - for (unsigned i = 0, e = GEP1VariableIndices.size(); i != e; ++i) - Modulo |= (uint64_t)GEP1VariableIndices[i].Scale; + 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(V), SignKnownZero, SignKnownOne, *DL, + 0, AC1, nullptr, DT); + + // Zero-extension widens the variable, and so forces the sign + // bit to zero. + bool IsZExt = GEP1VariableIndices[i].Extension == EK_ZeroExt; + 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 @@ -935,6 +1221,12 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size, if (V1Size != UnknownSize && V2Size != 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; } // Statically, we can see that the base objects are the same, but the @@ -964,33 +1256,33 @@ MergeAliasResults(AliasAnalysis::AliasResult A, AliasAnalysis::AliasResult B) { /// instruction against another. AliasAnalysis::AliasResult BasicAliasAnalysis::aliasSelect(const SelectInst *SI, uint64_t SISize, - const MDNode *SITBAAInfo, + const AAMDNodes &SIAAInfo, const Value *V2, uint64_t V2Size, - const MDNode *V2TBAAInfo) { + 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(V2)) if (SI->getCondition() == SI2->getCondition()) { AliasResult Alias = - aliasCheck(SI->getTrueValue(), SISize, SITBAAInfo, - SI2->getTrueValue(), V2Size, V2TBAAInfo); + aliasCheck(SI->getTrueValue(), SISize, SIAAInfo, + SI2->getTrueValue(), V2Size, V2AAInfo); if (Alias == MayAlias) return MayAlias; AliasResult ThisAlias = - aliasCheck(SI->getFalseValue(), SISize, SITBAAInfo, - SI2->getFalseValue(), V2Size, V2TBAAInfo); + 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, V2TBAAInfo, SI->getTrueValue(), SISize, SITBAAInfo); + aliasCheck(V2, V2Size, V2AAInfo, SI->getTrueValue(), SISize, SIAAInfo); if (Alias == MayAlias) return MayAlias; AliasResult ThisAlias = - aliasCheck(V2, V2Size, V2TBAAInfo, SI->getFalseValue(), SISize, SITBAAInfo); + aliasCheck(V2, V2Size, V2AAInfo, SI->getFalseValue(), SISize, SIAAInfo); return MergeAliasResults(ThisAlias, Alias); } @@ -998,29 +1290,49 @@ BasicAliasAnalysis::aliasSelect(const SelectInst *SI, uint64_t SISize, // against another. AliasAnalysis::AliasResult BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize, - const MDNode *PNTBAAInfo, + const AAMDNodes &PNAAInfo, const Value *V2, uint64_t V2Size, - const MDNode *V2TBAAInfo) { + 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(V2)) if (PN2->getParent() == PN->getParent()) { - AliasResult Alias = - aliasCheck(PN->getIncomingValue(0), PNSize, PNTBAAInfo, - PN2->getIncomingValueForBlock(PN->getIncomingBlock(0)), - V2Size, V2TBAAInfo); - if (Alias == MayAlias) - return MayAlias; - for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) { + LocPair Locs(Location(PN, PNSize, PNAAInfo), + Location(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, PNTBAAInfo, + aliasCheck(PN->getIncomingValue(i), PNSize, PNAAInfo, PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)), - V2Size, V2TBAAInfo); + V2Size, V2AAInfo); Alias = MergeAliasResults(ThisAlias, Alias); if (Alias == MayAlias) break; } + + // Reset if speculation failed. + if (Alias != NoAlias) + AliasCache[Locs] = OrigAliasResult; + return Alias; } @@ -1034,12 +1346,12 @@ BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize, // 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 (UniqueSrc.insert(PV1)) + if (UniqueSrc.insert(PV1).second) V1Srcs.push_back(PV1); } - AliasResult Alias = aliasCheck(V2, V2Size, V2TBAAInfo, - V1Srcs[0], PNSize, PNTBAAInfo); + 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) @@ -1050,8 +1362,8 @@ BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize, for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) { Value *V = V1Srcs[i]; - AliasResult ThisAlias = aliasCheck(V2, V2Size, V2TBAAInfo, - V, PNSize, PNTBAAInfo); + AliasResult ThisAlias = aliasCheck(V2, V2Size, V2AAInfo, + V, PNSize, PNAAInfo); Alias = MergeAliasResults(ThisAlias, Alias); if (Alias == MayAlias) break; @@ -1065,9 +1377,9 @@ BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize, // AliasAnalysis::AliasResult BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size, - const MDNode *V1TBAAInfo, + AAMDNodes V1AAInfo, const Value *V2, uint64_t V2Size, - const MDNode *V2TBAAInfo) { + AAMDNodes V2AAInfo) { // If either of the memory references is empty, it doesn't matter what the // pointer values are. if (V1Size == 0 || V2Size == 0) @@ -1078,14 +1390,20 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size, V2 = V2->stripPointerCasts(); // Are we checking for alias of the same value? - if (V1 == V2) return MustAlias; + // 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, TD); - const Value *O2 = GetUnderlyingObject(V2, TD); + 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. @@ -1106,17 +1424,17 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size, (isa(O2) && isIdentifiedObject(O1) && !isa(O1))) return NoAlias; - // Arguments can't alias with local allocations or noalias calls - // in the same function. - if (((isa(O1) && (isa(O2) || isNoAliasCall(O2))) || - (isa(O2) && (isa(O1) || isNoAliasCall(O1))))) + // Function arguments can't alias with things that are known to be + // unambigously identified at the function level. + if ((isa(O1) && isIdentifiedFunctionLocal(O2)) || + (isa(O2) && isIdentifiedFunctionLocal(O1))) return NoAlias; // Most objects can't alias null. if ((isa(O2) && isKnownNonNull(O1)) || (isa(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. @@ -1134,15 +1452,15 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size, // 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 (TD) - if ((V1Size != UnknownSize && isObjectSmallerThan(O2, V1Size, *TD, *TLI)) || - (V2Size != UnknownSize && isObjectSmallerThan(O1, V2Size, *TD, *TLI))) + if (DL) + if ((V1Size != UnknownSize && isObjectSmallerThan(O2, V1Size, *DL, *TLI)) || + (V2Size != 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(Location(V1, V1Size, V1TBAAInfo), - Location(V2, V2Size, V2TBAAInfo)); + LocPair Locs(Location(V1, V1Size, V1AAInfo), + Location(V2, V2Size, V2AAInfo)); if (V1 > V2) std::swap(Locs.first, Locs.second); std::pair Pair = @@ -1156,42 +1474,114 @@ BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size, std::swap(V1, V2); std::swap(V1Size, V2Size); std::swap(O1, O2); + std::swap(V1AAInfo, V2AAInfo); } if (const GEPOperator *GV1 = dyn_cast(V1)) { - AliasResult Result = aliasGEP(GV1, V1Size, V2, V2Size, V2TBAAInfo, O1, O2); + AliasResult Result = aliasGEP(GV1, V1Size, V1AAInfo, V2, V2Size, V2AAInfo, O1, O2); if (Result != MayAlias) return AliasCache[Locs] = Result; } if (isa(V2) && !isa(V1)) { std::swap(V1, V2); std::swap(V1Size, V2Size); + std::swap(V1AAInfo, V2AAInfo); } if (const PHINode *PN = dyn_cast(V1)) { - AliasResult Result = aliasPHI(PN, V1Size, V1TBAAInfo, - V2, V2Size, V2TBAAInfo); + AliasResult Result = aliasPHI(PN, V1Size, V1AAInfo, + V2, V2Size, V2AAInfo); if (Result != MayAlias) return AliasCache[Locs] = Result; } if (isa(V2) && !isa(V1)) { std::swap(V1, V2); std::swap(V1Size, V2Size); + std::swap(V1AAInfo, V2AAInfo); } if (const SelectInst *S1 = dyn_cast(V1)) { - AliasResult Result = aliasSelect(S1, V1Size, V1TBAAInfo, - V2, V2Size, V2TBAAInfo); + 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 (TD && O1 == O2) - if ((V1Size != UnknownSize && isObjectSize(O1, V1Size, *TD, *TLI)) || - (V2Size != UnknownSize && isObjectSize(O2, V2Size, *TD, *TLI))) + if (DL && O1 == O2) + if ((V1Size != UnknownSize && isObjectSize(O1, V1Size, *DL, *TLI)) || + (V2Size != UnknownSize && isObjectSize(O2, V2Size, *DL, *TLI))) return AliasCache[Locs] = PartialAlias; AliasResult Result = - AliasAnalysis::alias(Location(V1, V1Size, V1TBAAInfo), - Location(V2, V2Size, V2TBAAInfo)); + AliasAnalysis::alias(Location(V1, V1Size, V1AAInfo), + Location(V2, V2Size, V2AAInfo)); return AliasCache[Locs] = Result; } + +bool BasicAliasAnalysis::isValueEqualInPotentialCycles(const Value *V, + const Value *V2) { + if (V != V2) + return false; + + const Instruction *Inst = dyn_cast(V); + if (!Inst) + return true; + + if (VisitedPhiBBs.size() > MaxNumPhiBBsValueReachabilityCheck) + return false; + + // Use dominance or loop info if available. + DominatorTreeWrapperPass *DTWP = + getAnalysisIfAvailable(); + DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr; + auto *LIWP = getAnalysisIfAvailable(); + LoopInfo *LI = LIWP ? &LIWP->getLoopInfo() : nullptr; + + // 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->begin(), Inst, DT, LI)) + return false; + + return true; +} + +/// GetIndexDifference - Dest and Src are the variable indices from two +/// decomposed GetElementPtr instructions GEP1 and GEP2 which have common base +/// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic +/// difference between the two pointers. +void BasicAliasAnalysis::GetIndexDifference( + SmallVectorImpl &Dest, + const SmallVectorImpl &Src) { + if (Src.empty()) + return; + + for (unsigned i = 0, e = Src.size(); i != e; ++i) { + const Value *V = Src[i].V; + ExtensionKind Extension = Src[i].Extension; + 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].Extension != Extension) + 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, Extension, -Scale }; + Dest.push_back(Entry); + } + } +}