-//===- BasicAliasAnalysis.cpp - Local Alias Analysis Impl -----------------===//
+//===- BasicAliasAnalysis.cpp - Stateless Alias Analysis Impl -------------===//
//
// The LLVM Compiler Infrastructure
//
//
//===----------------------------------------------------------------------===//
//
-// This file defines the default implementation of the Alias Analysis interface
-// that simply implements a few identities (two different globals cannot alias,
-// etc), but otherwise does no analysis.
+// 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/Passes.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/CaptureTracking.h"
-#include "llvm/Analysis/Passes.h"
+#include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Analysis/MemoryBuiltins.h"
+#include "llvm/Analysis/ValueTracking.h"
#include "llvm/Constants.h"
+#include "llvm/DataLayout.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/Target/TargetData.h"
-#include "llvm/ADT/SmallVector.h"
-#include "llvm/ADT/STLExtras.h"
-#include "llvm/Support/Compiler.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
+#include "llvm/Target/TargetLibraryInfo.h"
#include <algorithm>
using namespace llvm;
// Useful predicates
//===----------------------------------------------------------------------===//
-static const GEPOperator *isGEP(const Value *V) {
- return dyn_cast<GEPOperator>(V);
-}
-
-static const Value *GetGEPOperands(const Value *V,
- SmallVector<Value*, 16> &GEPOps) {
- assert(GEPOps.empty() && "Expect empty list to populate!");
- GEPOps.insert(GEPOps.end(), cast<User>(V)->op_begin()+1,
- cast<User>(V)->op_end());
-
- // Accumulate all of the chained indexes into the operand array
- V = cast<User>(V)->getOperand(0);
-
- while (const User *G = isGEP(V)) {
- if (!isa<Constant>(GEPOps[0]) || isa<GlobalValue>(GEPOps[0]) ||
- !cast<Constant>(GEPOps[0])->isNullValue())
- break; // Don't handle folding arbitrary pointer offsets yet...
- GEPOps.erase(GEPOps.begin()); // Drop the zero index
- GEPOps.insert(GEPOps.begin(), G->op_begin()+1, G->op_end());
- V = G->getOperand(0);
- }
- return V;
-}
-
-/// isKnownNonNull - Return true if we know that the specified value is never
-/// null.
-static bool isKnownNonNull(const Value *V) {
- // Alloca never returns null, malloc might.
- if (isa<AllocaInst>(V)) return true;
-
- // A byval argument is never null.
- if (const Argument *A = dyn_cast<Argument>(V))
- return A->hasByValAttr();
-
- // Global values are not null unless extern weak.
- if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
- return !GV->hasExternalWeakLinkage();
- return false;
-}
-
/// isNonEscapingLocalObject - Return true if the pointer is to a function-local
/// object that never escapes from the function.
static bool isNonEscapingLocalObject(const Value *V) {
// If this is a local allocation, check to see if it escapes.
- if (isa<AllocationInst>(V) || isNoAliasCall(V))
- return !PointerMayBeCaptured(V, false);
+ 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()) {
- // Don't bother analyzing arguments already known not to escape.
- if (A->hasNoCaptureAttr())
- return true;
- return !PointerMayBeCaptured(V, false);
- }
+ 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;
+}
+
+/// isEscapeSource - Return 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;
}
+/// getObjectSize - Return the size of the object specified by V, or
+/// UnknownSize if unknown.
+static uint64_t getObjectSize(const Value *V, const DataLayout &TD,
+ const TargetLibraryInfo &TLI,
+ bool RoundToAlign = false) {
+ uint64_t Size;
+ if (getObjectSize(V, Size, &TD, &TLI, RoundToAlign))
+ return Size;
+ return AliasAnalysis::UnknownSize;
+}
/// isObjectSmallerThan - Return true if we can prove that the object specified
/// by V is smaller than Size.
-static bool isObjectSmallerThan(const Value *V, unsigned Size,
- const TargetData &TD) {
- const Type *AccessTy;
- if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
- AccessTy = GV->getType()->getElementType();
- } else if (const AllocationInst *AI = dyn_cast<AllocationInst>(V)) {
- if (!AI->isArrayAllocation())
- AccessTy = AI->getType()->getElementType();
- else
- return false;
- } else if (const Argument *A = dyn_cast<Argument>(V)) {
- if (A->hasByValAttr())
- AccessTy = cast<PointerType>(A->getType())->getElementType();
- else
- return false;
- } else {
- return false;
- }
+static bool isObjectSmallerThan(const Value *V, uint64_t Size,
+ const DataLayout &TD,
+ const TargetLibraryInfo &TLI) {
+ // 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);
- if (AccessTy->isSized())
- return TD.getTypeAllocSize(AccessTy) < Size;
- return false;
+ 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 DataLayout &TD, const TargetLibraryInfo &TLI) {
+ uint64_t ObjectSize = getObjectSize(V, TD, TLI);
+ return ObjectSize != AliasAnalysis::UnknownSize && ObjectSize == Size;
}
//===----------------------------------------------------------------------===//
-// NoAA Pass
+// GetElementPtr Instruction Decomposition and Analysis
//===----------------------------------------------------------------------===//
namespace {
- /// NoAA - This class implements the -no-aa pass, which always returns "I
- /// don't know" for alias queries. NoAA is unlike other alias analysis
- /// implementations, in that it does not chain to a previous analysis. As
- /// such it doesn't follow many of the rules that other alias analyses must.
- ///
- struct VISIBILITY_HIDDEN NoAA : public ImmutablePass, public AliasAnalysis {
- static char ID; // Class identification, replacement for typeinfo
- NoAA() : ImmutablePass(&ID) {}
- explicit NoAA(void *PID) : ImmutablePass(PID) { }
+ enum ExtensionKind {
+ EK_NotExtended,
+ 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;
+ }
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- AU.addRequired<TargetData>();
+ bool operator!=(const VariableGEPIndex &Other) const {
+ return !operator==(Other);
}
+ };
+}
- virtual void initializePass() {
- TD = &getAnalysis<TargetData>();
+
+/// GetLinearExpression - Analyze the specified value as a linear expression:
+/// "A*V + B", where A and B are constant integers. Return 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 Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset,
+ ExtensionKind &Extension,
+ const DataLayout &TD, unsigned Depth) {
+ assert(V->getType()->isIntegerTy() && "Not an integer value");
+
+ // Limit our recursion depth.
+ if (Depth == 6) {
+ Scale = 1;
+ Offset = 0;
+ return V;
+ }
+
+ if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(V)) {
+ if (ConstantInt *RHSC = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
+ switch (BOp->getOpcode()) {
+ default: break;
+ 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))
+ break;
+ // FALL THROUGH.
+ case Instruction::Add:
+ V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
+ TD, Depth+1);
+ Offset += RHSC->getValue();
+ return V;
+ case Instruction::Mul:
+ V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
+ TD, Depth+1);
+ Offset *= RHSC->getValue();
+ Scale *= RHSC->getValue();
+ return V;
+ case Instruction::Shl:
+ V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
+ TD, Depth+1);
+ 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.
+ if ((isa<SExtInst>(V) && Extension != EK_ZeroExt) ||
+ (isa<ZExtInst>(V) && Extension != EK_SignExt)) {
+ Value *CastOp = cast<CastInst>(V)->getOperand(0);
+ unsigned OldWidth = Scale.getBitWidth();
+ unsigned SmallWidth = CastOp->getType()->getPrimitiveSizeInBits();
+ Scale = Scale.trunc(SmallWidth);
+ Offset = Offset.trunc(SmallWidth);
+ Extension = isa<SExtInst>(V) ? EK_SignExt : EK_ZeroExt;
+
+ Value *Result = GetLinearExpression(CastOp, Scale, Offset, Extension,
+ TD, Depth+1);
+ Scale = Scale.zext(OldWidth);
+ Offset = Offset.zext(OldWidth);
+
+ return Result;
+ }
+
+ Scale = 1;
+ Offset = 0;
+ return V;
+}
- virtual AliasResult alias(const Value *V1, unsigned V1Size,
- const Value *V2, unsigned V2Size) {
- return MayAlias;
+/// DecomposeGEPExpression - 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. When not, it just looks
+/// through pointer casts.
+///
+static const Value *
+DecomposeGEPExpression(const Value *V, int64_t &BaseOffs,
+ SmallVectorImpl<VariableGEPIndex> &VarIndices,
+ const DataLayout *TD) {
+ // Limit recursion depth to limit compile time in crazy cases.
+ unsigned MaxLookup = 6;
+
+ BaseOffs = 0;
+ do {
+ // See if this is a bitcast or GEP.
+ const Operator *Op = dyn_cast<Operator>(V);
+ if (Op == 0) {
+ // 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) {
+ V = Op->getOperand(0);
+ continue;
}
- virtual void getArgumentAccesses(Function *F, CallSite CS,
- std::vector<PointerAccessInfo> &Info) {
- llvm_unreachable("This method may not be called on this function!");
+ const GEPOperator *GEPOp = dyn_cast<GEPOperator>(Op);
+ if (GEPOp == 0) {
+ // 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 use it here.
+ if (const Value *Simplified =
+ SimplifyInstruction(const_cast<Instruction *>(I), TD)) {
+ V = Simplified;
+ continue;
+ }
+
+ return V;
}
+
+ // Don't attempt to analyze GEPs over unsized objects.
+ if (!cast<PointerType>(GEPOp->getOperand(0)->getType())
+ ->getElementType()->isSized())
+ return V;
+
+ // If we are lacking DataLayout 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;
+ }
+
+ // 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) {
+ 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 += TD->getStructLayout(STy)->getElementOffset(FieldNo);
+ continue;
+ }
+
+ // For an array/pointer, add the element offset, explicitly scaled.
+ if (ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) {
+ if (CIdx->isZero()) continue;
+ BaseOffs += TD->getTypeAllocSize(*GTI)*CIdx->getSExtValue();
+ continue;
+ }
+
+ uint64_t Scale = TD->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<IntegerType>(Index->getType())->getBitWidth();
+ if (TD->getPointerSizeInBits() > 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);
+
+ // 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].Extension == Extension) {
+ 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-TD->getPointerSizeInBits()) {
+ Scale <<= ShiftBits;
+ Scale = (int64_t)Scale >> ShiftBits;
+ }
+
+ if (Scale) {
+ VariableGEPIndex Entry = {Index, Extension,
+ 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.
+ return V;
+}
- virtual void getMustAliases(Value *P, std::vector<Value*> &RetVals) { }
- virtual bool pointsToConstantMemory(const Value *P) { return false; }
- virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
- return ModRef;
+/// 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<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;
+ 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;
}
- virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
- return ModRef;
+
+ // 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);
}
- virtual bool hasNoModRefInfoForCalls() const { return true; }
+ }
+}
- virtual void deleteValue(Value *V) {}
- virtual void copyValue(Value *From, Value *To) {}
- };
-} // End of anonymous namespace
+//===----------------------------------------------------------------------===//
+// BasicAliasAnalysis Pass
+//===----------------------------------------------------------------------===//
-// Register this pass...
-char NoAA::ID = 0;
-static RegisterPass<NoAA>
-U("no-aa", "No Alias Analysis (always returns 'may' alias)", true, true);
+#ifndef NDEBUG
+static const Function *getParent(const Value *V) {
+ if (const Instruction *inst = dyn_cast<Instruction>(V))
+ return inst->getParent()->getParent();
-// Declare that we implement the AliasAnalysis interface
-static RegisterAnalysisGroup<AliasAnalysis> V(U);
+ if (const Argument *arg = dyn_cast<Argument>(V))
+ return arg->getParent();
-ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
+ return NULL;
+}
-//===----------------------------------------------------------------------===//
-// BasicAA Pass
-//===----------------------------------------------------------------------===//
+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
namespace {
- /// BasicAliasAnalysis - This is the default alias analysis implementation.
- /// Because it doesn't chain to a previous alias analysis (like -no-aa), it
- /// derives from the NoAA class.
- struct VISIBILITY_HIDDEN BasicAliasAnalysis : public NoAA {
+ /// BasicAliasAnalysis - This is the primary alias analysis implementation.
+ struct BasicAliasAnalysis : public ImmutablePass, public AliasAnalysis {
static char ID; // Class identification, replacement for typeinfo
- BasicAliasAnalysis() : NoAA(&ID) {}
- AliasResult alias(const Value *V1, unsigned V1Size,
- const Value *V2, unsigned V2Size);
+ BasicAliasAnalysis() : ImmutablePass(ID) {
+ initializeBasicAliasAnalysisPass(*PassRegistry::getPassRegistry());
+ }
+
+ virtual void initializePass() {
+ InitializeAliasAnalysis(this);
+ }
- ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
- ModRefResult getModRefInfo(CallSite CS1, CallSite CS2);
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.addRequired<AliasAnalysis>();
+ AU.addRequired<TargetLibraryInfo>();
+ }
- /// hasNoModRefInfoForCalls - We can provide mod/ref information against
- /// non-escaping allocations.
- virtual bool hasNoModRefInfoForCalls() const { return false; }
+ virtual AliasResult alias(const Location &LocA,
+ const Location &LocB) {
+ 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 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();
+ return Alias;
+ }
+
+ virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
+ const Location &Loc);
+
+ virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
+ ImmutableCallSite CS2) {
+ // The AliasAnalysis base class has some smarts, lets use them.
+ return AliasAnalysis::getModRefInfo(CS1, CS2);
+ }
/// pointsToConstantMemory - Chase pointers until we find a (constant
/// global) or not.
- bool pointsToConstantMemory(const Value *P);
-
+ virtual bool pointsToConstantMemory(const Location &Loc, bool OrLocal);
+
+ /// getModRefBehavior - Return the behavior when calling the given
+ /// call site.
+ virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS);
+
+ /// getModRefBehavior - Return the behavior when calling the given function.
+ /// For use when the call site is not known.
+ virtual ModRefBehavior getModRefBehavior(const Function *F);
+
+ /// 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) {
+ if (ID == &AliasAnalysis::ID)
+ return (AliasAnalysis*)this;
+ return this;
+ }
+
private:
- // CheckGEPInstructions - Check two GEP instructions with known
- // must-aliasing base pointers. This checks to see if the index expressions
- // preclude the pointers from aliasing...
- AliasResult
- CheckGEPInstructions(const Type* BasePtr1Ty,
- Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1Size,
- const Type *BasePtr2Ty,
- Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2Size);
+ // AliasCache - Track alias queries to guard against recursion.
+ typedef std::pair<Location, Location> LocPair;
+ typedef SmallDenseMap<LocPair, AliasResult, 8> AliasCacheTy;
+ AliasCacheTy AliasCache;
+
+ // Visited - Track instructions visited by pointsToConstantMemory.
+ SmallPtrSet<const Value*, 16> Visited;
+
+ // aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP
+ // instruction against another.
+ AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size,
+ const MDNode *V1TBAAInfo,
+ const Value *V2, uint64_t V2Size,
+ const MDNode *V2TBAAInfo,
+ 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 Value *V2, uint64_t V2Size,
+ const MDNode *V2TBAAInfo);
+
+ /// aliasSelect - Disambiguate a Select instruction against another value.
+ AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize,
+ const MDNode *SITBAAInfo,
+ const Value *V2, uint64_t V2Size,
+ const MDNode *V2TBAAInfo);
+
+ AliasResult aliasCheck(const Value *V1, uint64_t V1Size,
+ const MDNode *V1TBAATag,
+ const Value *V2, uint64_t V2Size,
+ const MDNode *V2TBAATag);
};
} // End of anonymous namespace
// Register this pass...
char BasicAliasAnalysis::ID = 0;
-static RegisterPass<BasicAliasAnalysis>
-X("basicaa", "Basic Alias Analysis (default AA impl)", false, true);
+INITIALIZE_AG_PASS_BEGIN(BasicAliasAnalysis, AliasAnalysis, "basicaa",
+ "Basic Alias Analysis (stateless AA impl)",
+ false, true, false)
+INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
+INITIALIZE_AG_PASS_END(BasicAliasAnalysis, AliasAnalysis, "basicaa",
+ "Basic Alias Analysis (stateless AA impl)",
+ false, true, false)
-// Declare that we implement the AliasAnalysis interface
-static RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
ImmutablePass *llvm::createBasicAliasAnalysisPass() {
return new BasicAliasAnalysis();
}
+/// pointsToConstantMemory - 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
+BasicAliasAnalysis::pointsToConstantMemory(const Location &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(), TD);
+ if (!Visited.insert(V)) {
+ Visited.clear();
+ return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
+ }
-/// pointsToConstantMemory - Chase pointers until we find a (constant
-/// global) or not.
-bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
- if (const GlobalVariable *GV =
- dyn_cast<GlobalVariable>(P->getUnderlyingObject()))
- return GV->isConstant();
- return false;
-}
+ // 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 AliasAnalysis::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;
+ }
-// getModRefInfo - Check to see if the specified callsite can clobber the
-// specified memory object. Since we only look at local properties of this
-// function, we really can't say much about this query. We do, however, use
-// simple "address taken" analysis on local objects.
-//
-AliasAnalysis::ModRefResult
-BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
- if (!isa<Constant>(P)) {
- const Value *Object = P->getUnderlyingObject();
-
- // If this is a tail call and P points to a stack location, we know that
- // the tail call cannot access or modify the local stack.
- // We cannot exclude byval arguments here; these belong to the caller of
- // the current function not to the current function, and a tail callee
- // may reference them.
- if (isa<AllocaInst>(Object))
- if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
- if (CI->isTailCall())
- return NoModRef;
-
- // If the pointer is to a locally allocated object that does not escape,
- // then the call can not mod/ref the pointer unless the call takes the
- // argument without capturing it.
- if (isNonEscapingLocalObject(Object) && CS.getInstruction() != Object) {
- bool passedAsArg = false;
- // TODO: Eventually only check 'nocapture' arguments.
- for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
- CI != CE; ++CI)
- if (isa<PointerType>((*CI)->getType()) &&
- alias(cast<Value>(CI), ~0U, P, ~0U) != NoAlias)
- passedAsArg = true;
-
- if (!passedAsArg)
- return NoModRef;
+ // 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 AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
+ }
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+ Worklist.push_back(PN->getIncomingValue(i));
+ continue;
}
- }
- // The AliasAnalysis base class has some smarts, lets use them.
- return AliasAnalysis::getModRefInfo(CS, P, Size);
-}
+ // Otherwise be conservative.
+ Visited.clear();
+ return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
+ } while (!Worklist.empty() && --MaxLookup);
-AliasAnalysis::ModRefResult
-BasicAliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) {
- // If CS1 or CS2 are readnone, they don't interact.
- ModRefBehavior CS1B = AliasAnalysis::getModRefBehavior(CS1);
- if (CS1B == DoesNotAccessMemory) return NoModRef;
-
- ModRefBehavior CS2B = AliasAnalysis::getModRefBehavior(CS2);
- if (CS2B == DoesNotAccessMemory) return NoModRef;
-
- // If they both only read from memory, just return ref.
- if (CS1B == OnlyReadsMemory && CS2B == OnlyReadsMemory)
- return Ref;
-
- // Otherwise, fall back to NoAA (mod+ref).
- return NoAA::getModRefInfo(CS1, CS2);
+ Visited.clear();
+ return Worklist.empty();
}
+/// getModRefBehavior - Return the behavior when calling the given call site.
+AliasAnalysis::ModRefBehavior
+BasicAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
+ if (CS.doesNotAccessMemory())
+ // Can't do better than this.
+ return DoesNotAccessMemory;
-// alias - Provide a bunch of ad-hoc rules to disambiguate in common cases, such
-// as array references.
-//
-AliasAnalysis::AliasResult
-BasicAliasAnalysis::alias(const Value *V1, unsigned V1Size,
- const Value *V2, unsigned V2Size) {
- Context = &V1->getType()->getContext();
-
- // Strip off any constant expression casts if they exist
- if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V1))
- if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
- V1 = CE->getOperand(0);
- if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(V2))
- if (CE->isCast() && isa<PointerType>(CE->getOperand(0)->getType()))
- V2 = CE->getOperand(0);
+ ModRefBehavior Min = UnknownModRefBehavior;
- // Are we checking for alias of the same value?
- if (V1 == V2) return MustAlias;
+ // If the callsite knows it only reads memory, don't return worse
+ // than that.
+ if (CS.onlyReadsMemory())
+ Min = OnlyReadsMemory;
- if (!isa<PointerType>(V1->getType()) || !isa<PointerType>(V2->getType()))
- return NoAlias; // Scalars cannot alias each other
+ // The AliasAnalysis base class has some smarts, lets use them.
+ return ModRefBehavior(AliasAnalysis::getModRefBehavior(CS) & Min);
+}
- // Strip off cast instructions. Since V1 and V2 are pointers, they must be
- // pointer<->pointer bitcasts.
- if (const BitCastInst *I = dyn_cast<BitCastInst>(V1))
- return alias(I->getOperand(0), V1Size, V2, V2Size);
- if (const BitCastInst *I = dyn_cast<BitCastInst>(V2))
- return alias(V1, V1Size, I->getOperand(0), V2Size);
+/// getModRefBehavior - Return the behavior when calling the given function.
+/// For use when the call site is not known.
+AliasAnalysis::ModRefBehavior
+BasicAliasAnalysis::getModRefBehavior(const Function *F) {
+ // If the function declares it doesn't access memory, we can't do better.
+ if (F->doesNotAccessMemory())
+ return DoesNotAccessMemory;
+
+ // For intrinsics, we can check the table.
+ if (unsigned iid = F->getIntrinsicID()) {
+#define GET_INTRINSIC_MODREF_BEHAVIOR
+#include "llvm/Intrinsics.gen"
+#undef GET_INTRINSIC_MODREF_BEHAVIOR
+ }
- // Figure out what objects these things are pointing to if we can.
- const Value *O1 = V1->getUnderlyingObject();
- const Value *O2 = V2->getUnderlyingObject();
+ ModRefBehavior Min = UnknownModRefBehavior;
- 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;
-
- // Arguments can't alias with local allocations or noalias calls.
- if ((isa<Argument>(O1) && (isa<AllocationInst>(O2) || isNoAliasCall(O2))) ||
- (isa<Argument>(O2) && (isa<AllocationInst>(O1) || isNoAliasCall(O1))))
- return NoAlias;
+ // If the function declares it only reads memory, go with that.
+ if (F->onlyReadsMemory())
+ Min = OnlyReadsMemory;
- // Most objects can't alias null.
- if ((isa<ConstantPointerNull>(V2) && isKnownNonNull(O1)) ||
- (isa<ConstantPointerNull>(V1) && isKnownNonNull(O2)))
- return NoAlias;
- }
-
- // If the size of one access is larger than the entire object on the other
- // side, then we know such behavior is undefined and can assume no alias.
- const TargetData &TD = getTargetData();
- if ((V1Size != ~0U && isObjectSmallerThan(O2, V1Size, TD)) ||
- (V2Size != ~0U && isObjectSmallerThan(O1, V2Size, TD)))
- return NoAlias;
+ // Otherwise be conservative.
+ return ModRefBehavior(AliasAnalysis::getModRefBehavior(F) & Min);
+}
+
+/// getModRefInfo - Check to see if the specified callsite can clobber the
+/// specified memory object. Since we only look at local properties of this
+/// function, we really can't say much about this query. We do, however, use
+/// simple "address taken" analysis on local objects.
+AliasAnalysis::ModRefResult
+BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS,
+ const Location &Loc) {
+ assert(notDifferentParent(CS.getInstruction(), Loc.Ptr) &&
+ "AliasAnalysis query involving multiple functions!");
+
+ const Value *Object = GetUnderlyingObject(Loc.Ptr, TD);
- // If one pointer is the result of a call/invoke and the other is a
- // non-escaping local object, then we know the object couldn't escape to a
- // point where the call could return it.
- if ((isa<CallInst>(O1) || isa<InvokeInst>(O1)) &&
- isNonEscapingLocalObject(O2) && O1 != O2)
- return NoAlias;
- if ((isa<CallInst>(O2) || isa<InvokeInst>(O2)) &&
- isNonEscapingLocalObject(O1) && O1 != O2)
- return NoAlias;
+ // 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 NoModRef;
- // If we have two gep instructions with must-alias'ing base pointers, figure
- // out if the indexes to the GEP tell us anything about the derived pointer.
- // Note that we also handle chains of getelementptr instructions as well as
- // constant expression getelementptrs here.
- //
- if (isGEP(V1) && isGEP(V2)) {
- const User *GEP1 = cast<User>(V1);
- const User *GEP2 = cast<User>(V2);
-
- // If V1 and V2 are identical GEPs, just recurse down on both of them.
- // This allows us to analyze things like:
- // P = gep A, 0, i, 1
- // Q = gep B, 0, i, 1
- // by just analyzing A and B. This is even safe for variable indices.
- if (GEP1->getType() == GEP2->getType() &&
- GEP1->getNumOperands() == GEP2->getNumOperands() &&
- GEP1->getOperand(0)->getType() == GEP2->getOperand(0)->getType() &&
- // All operands are the same, ignoring the base.
- std::equal(GEP1->op_begin()+1, GEP1->op_end(), GEP2->op_begin()+1))
- return alias(GEP1->getOperand(0), V1Size, GEP2->getOperand(0), V2Size);
-
-
- // Drill down into the first non-gep value, to test for must-aliasing of
- // the base pointers.
- while (isGEP(GEP1->getOperand(0)) &&
- GEP1->getOperand(1) ==
- Context->getNullValue(GEP1->getOperand(1)->getType()))
- GEP1 = cast<User>(GEP1->getOperand(0));
- const Value *BasePtr1 = GEP1->getOperand(0);
-
- while (isGEP(GEP2->getOperand(0)) &&
- GEP2->getOperand(1) ==
- Context->getNullValue(GEP2->getOperand(1)->getType()))
- GEP2 = cast<User>(GEP2->getOperand(0));
- const Value *BasePtr2 = GEP2->getOperand(0);
-
- // Do the base pointers alias?
- AliasResult BaseAlias = alias(BasePtr1, ~0U, BasePtr2, ~0U);
- if (BaseAlias == NoAlias) return NoAlias;
- if (BaseAlias == MustAlias) {
- // If the base pointers alias each other exactly, check to see if we can
- // figure out anything about the resultant pointers, to try to prove
- // non-aliasing.
-
- // Collect all of the chained GEP operands together into one simple place
- SmallVector<Value*, 16> GEP1Ops, GEP2Ops;
- BasePtr1 = GetGEPOperands(V1, GEP1Ops);
- BasePtr2 = GetGEPOperands(V2, GEP2Ops);
-
- // If GetGEPOperands were able to fold to the same must-aliased pointer,
- // do the comparison.
- if (BasePtr1 == BasePtr2) {
- AliasResult GAlias =
- CheckGEPInstructions(BasePtr1->getType(),
- &GEP1Ops[0], GEP1Ops.size(), V1Size,
- BasePtr2->getType(),
- &GEP2Ops[0], GEP2Ops.size(), V2Size);
- if (GAlias != MayAlias)
- return GAlias;
+ // 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.
+ if (!isNoAlias(Location(*CI), Location(Object))) {
+ PassedAsArg = true;
+ break;
}
}
+
+ if (!PassedAsArg)
+ return NoModRef;
}
- // Check to see if these two pointers are related by a getelementptr
- // instruction. If one pointer is a GEP with a non-zero index of the other
- // pointer, we know they cannot alias.
- //
- if (isGEP(V2)) {
- std::swap(V1, V2);
- std::swap(V1Size, V2Size);
- }
+ const TargetLibraryInfo &TLI = getAnalysis<TargetLibraryInfo>();
+ ModRefResult Min = ModRef;
+
+ // Finally, handle specific knowledge of intrinsics.
+ const IntrinsicInst *II = dyn_cast<IntrinsicInst>(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<ConstantInt>(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<ConstantInt>(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<ConstantInt>(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<ConstantInt>(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;
+ }
+ }
- if (V1Size != ~0U && V2Size != ~0U)
- if (isGEP(V1)) {
- SmallVector<Value*, 16> GEPOperands;
- const Value *BasePtr = GetGEPOperands(V1, GEPOperands);
-
- AliasResult R = alias(BasePtr, V1Size, V2, V2Size);
- if (R == MustAlias) {
- // If there is at least one non-zero constant index, we know they cannot
- // alias.
- bool ConstantFound = false;
- bool AllZerosFound = true;
- for (unsigned i = 0, e = GEPOperands.size(); i != e; ++i)
- if (const Constant *C = dyn_cast<Constant>(GEPOperands[i])) {
- if (!C->isNullValue()) {
- ConstantFound = true;
- AllZerosFound = false;
- break;
- }
- } else {
- AllZerosFound = false;
- }
-
- // If we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2 must aliases
- // the ptr, the end result is a must alias also.
- if (AllZerosFound)
- return MustAlias;
-
- if (ConstantFound) {
- if (V2Size <= 1 && V1Size <= 1) // Just pointer check?
- return NoAlias;
-
- // Otherwise we have to check to see that the distance is more than
- // the size of the argument... build an index vector that is equal to
- // the arguments provided, except substitute 0's for any variable
- // indexes we find...
- if (cast<PointerType>(
- BasePtr->getType())->getElementType()->isSized()) {
- for (unsigned i = 0; i != GEPOperands.size(); ++i)
- if (!isa<ConstantInt>(GEPOperands[i]))
- GEPOperands[i] =
- Context->getNullValue(GEPOperands[i]->getType());
- int64_t Offset =
- getTargetData().getIndexedOffset(BasePtr->getType(),
- &GEPOperands[0],
- GEPOperands.size());
-
- if (Offset >= (int64_t)V2Size || Offset <= -(int64_t)V1Size)
- return NoAlias;
- }
- }
+ // 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<PointerType>(MemsetType->getParamType(0)) &&
+ isa<PointerType>(MemsetType->getParamType(1)) &&
+ isa<IntegerType>(MemsetType->getParamType(2))) {
+ uint64_t Len = UnknownSize;
+ if (const ConstantInt *LenCI = dyn_cast<ConstantInt>(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;
}
}
+ }
- return MayAlias;
+ // The AliasAnalysis base class has some smarts, lets use them.
+ return ModRefResult(AliasAnalysis::getModRefInfo(CS, Loc) & Min);
}
-// This function is used to determine if the indices of two GEP instructions are
-// equal. V1 and V2 are the indices.
-static bool IndexOperandsEqual(Value *V1, Value *V2, LLVMContext *Context) {
- if (V1->getType() == V2->getType())
- return V1 == V2;
- if (Constant *C1 = dyn_cast<Constant>(V1))
- if (Constant *C2 = dyn_cast<Constant>(V2)) {
- // Sign extend the constants to long types, if necessary
- if (C1->getType() != Type::Int64Ty)
- C1 = Context->getConstantExprSExt(C1, Type::Int64Ty);
- if (C2->getType() != Type::Int64Ty)
- C2 = Context->getConstantExprSExt(C2, Type::Int64Ty);
- return C1 == C2;
- }
- return false;
-}
+static bool areVarIndicesEqual(SmallVector<VariableGEPIndex, 4> &Indices1,
+ SmallVector<VariableGEPIndex, 4> &Indices2) {
+ unsigned Size1 = Indices1.size();
+ unsigned Size2 = Indices2.size();
-/// CheckGEPInstructions - Check two GEP instructions with known must-aliasing
-/// base pointers. This checks to see if the index expressions preclude the
-/// pointers from aliasing...
-AliasAnalysis::AliasResult
-BasicAliasAnalysis::CheckGEPInstructions(
- const Type* BasePtr1Ty, Value **GEP1Ops, unsigned NumGEP1Ops, unsigned G1S,
- const Type *BasePtr2Ty, Value **GEP2Ops, unsigned NumGEP2Ops, unsigned G2S) {
- // We currently can't handle the case when the base pointers have different
- // primitive types. Since this is uncommon anyway, we are happy being
- // extremely conservative.
- if (BasePtr1Ty != BasePtr2Ty)
- return MayAlias;
+ if (Size1 != Size2)
+ return false;
+
+ for (unsigned I = 0; I != Size1; ++I)
+ if (Indices1[I] != Indices2[I])
+ return false;
- const PointerType *GEPPointerTy = cast<PointerType>(BasePtr1Ty);
-
- Context = &GEPPointerTy->getContext();
-
- // Find the (possibly empty) initial sequence of equal values... which are not
- // necessarily constants.
- unsigned NumGEP1Operands = NumGEP1Ops, NumGEP2Operands = NumGEP2Ops;
- unsigned MinOperands = std::min(NumGEP1Operands, NumGEP2Operands);
- unsigned MaxOperands = std::max(NumGEP1Operands, NumGEP2Operands);
- unsigned UnequalOper = 0;
- while (UnequalOper != MinOperands &&
- IndexOperandsEqual(GEP1Ops[UnequalOper], GEP2Ops[UnequalOper],
- Context)) {
- // Advance through the type as we go...
- ++UnequalOper;
- if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
- BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[UnequalOper-1]);
- else {
- // If all operands equal each other, then the derived pointers must
- // alias each other...
- BasePtr1Ty = 0;
- assert(UnequalOper == NumGEP1Operands && UnequalOper == NumGEP2Operands &&
- "Ran out of type nesting, but not out of operands?");
- return MustAlias;
+ return true;
+}
+
+/// 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),
+/// UnderlyingV2 is the same for V2.
+///
+AliasAnalysis::AliasResult
+BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
+ const MDNode *V1TBAAInfo,
+ const Value *V2, uint64_t V2Size,
+ const MDNode *V2TBAAInfo,
+ const Value *UnderlyingV1,
+ const Value *UnderlyingV2) {
+ int64_t GEP1BaseOffset;
+ 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)) {
+ // Check for geps of non-aliasing underlying pointers where the offsets are
+ // identical.
+ if (V1Size == V2Size) {
+ // Do the base pointers alias assuming type and size.
+ AliasResult PreciseBaseAlias = aliasCheck(UnderlyingV1, V1Size,
+ V1TBAAInfo, UnderlyingV2,
+ V2Size, V2TBAAInfo);
+ if (PreciseBaseAlias == NoAlias) {
+ // See if the computed offset from the common pointer tells us about the
+ // relation of the resulting pointer.
+ int64_t GEP2BaseOffset;
+ SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
+ const Value *GEP2BasePtr =
+ DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD);
+ const Value *GEP1BasePtr =
+ DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD);
+ // DecomposeGEPExpression and GetUnderlyingObject should return the
+ // same result except when DecomposeGEPExpression has no DataLayout.
+ if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
+ assert(TD == 0 &&
+ "DecomposeGEPExpression and GetUnderlyingObject disagree!");
+ return MayAlias;
+ }
+ // Same offsets.
+ if (GEP1BaseOffset == GEP2BaseOffset &&
+ areVarIndicesEqual(GEP1VariableIndices, GEP2VariableIndices))
+ return NoAlias;
+ GEP1VariableIndices.clear();
+ }
}
- }
- // If we have seen all constant operands, and run out of indexes on one of the
- // getelementptrs, check to see if the tail of the leftover one is all zeros.
- // If so, return mustalias.
- if (UnequalOper == MinOperands) {
- if (NumGEP1Ops < NumGEP2Ops) {
- std::swap(GEP1Ops, GEP2Ops);
- std::swap(NumGEP1Ops, NumGEP2Ops);
+ // Do the base pointers alias?
+ AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, 0,
+ UnderlyingV2, UnknownSize, 0);
+
+ // 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);
+
+ int64_t GEP2BaseOffset;
+ SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
+ const Value *GEP2BasePtr =
+ DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD);
+
+ // DecomposeGEPExpression and GetUnderlyingObject should return the
+ // same result except when DecomposeGEPExpression has no DataLayout.
+ if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
+ assert(TD == 0 &&
+ "DecomposeGEPExpression and GetUnderlyingObject disagree!");
+ 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.
- bool AllAreZeros = true;
- for (unsigned i = UnequalOper; i != MaxOperands; ++i)
- if (!isa<Constant>(GEP1Ops[i]) ||
- !cast<Constant>(GEP1Ops[i])->isNullValue()) {
- AllAreZeros = false;
- break;
+ // If both accesses are unknown size, we can't do anything useful here.
+ if (V1Size == UnknownSize && V2Size == UnknownSize)
+ return MayAlias;
+
+ AliasResult R = aliasCheck(UnderlyingV1, UnknownSize, 0,
+ V2, V2Size, V2TBAAInfo);
+ 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, TD);
+
+ // DecomposeGEPExpression and GetUnderlyingObject should return the
+ // same result except when DecomposeGEPExpression has no DataLayout.
+ if (GEP1BasePtr != UnderlyingV1) {
+ assert(TD == 0 &&
+ "DecomposeGEPExpression and GetUnderlyingObject disagree!");
+ 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 != UnknownSize) {
+ if ((uint64_t)GEP1BaseOffset < V2Size)
+ return PartialAlias;
+ return NoAlias;
}
- if (AllAreZeros) return MustAlias;
+ } else {
+ if (V1Size != UnknownSize) {
+ if (-(uint64_t)GEP1BaseOffset < V1Size)
+ return PartialAlias;
+ return NoAlias;
+ }
+ }
}
+ // 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;
+ 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 != UnknownSize && V2Size != UnknownSize &&
+ ModOffset >= V2Size && V1Size <= Modulo - ModOffset)
+ return NoAlias;
+ }
- // So now we know that the indexes derived from the base pointers,
- // which are known to alias, are different. We can still determine a
- // no-alias result if there are differing constant pairs in the index
- // chain. For example:
- // A[i][0] != A[j][1] iff (&A[0][1]-&A[0][0] >= std::max(G1S, G2S))
- //
- // We have to be careful here about array accesses. In particular, consider:
- // A[1][0] vs A[0][i]
- // In this case, we don't *know* that the array will be accessed in bounds:
- // the index could even be negative. Because of this, we have to
- // conservatively *give up* and return may alias. We disregard differing
- // array subscripts that are followed by a variable index without going
- // through a struct.
+ // 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.
//
- unsigned SizeMax = std::max(G1S, G2S);
- if (SizeMax == ~0U) return MayAlias; // Avoid frivolous work.
-
- // Scan for the first operand that is constant and unequal in the
- // two getelementptrs...
- unsigned FirstConstantOper = UnequalOper;
- for (; FirstConstantOper != MinOperands; ++FirstConstantOper) {
- const Value *G1Oper = GEP1Ops[FirstConstantOper];
- const Value *G2Oper = GEP2Ops[FirstConstantOper];
-
- if (G1Oper != G2Oper) // Found non-equal constant indexes...
- if (Constant *G1OC = dyn_cast<ConstantInt>(const_cast<Value*>(G1Oper)))
- if (Constant *G2OC = dyn_cast<ConstantInt>(const_cast<Value*>(G2Oper))){
- if (G1OC->getType() != G2OC->getType()) {
- // Sign extend both operands to long.
- if (G1OC->getType() != Type::Int64Ty)
- G1OC = Context->getConstantExprSExt(G1OC, Type::Int64Ty);
- if (G2OC->getType() != Type::Int64Ty)
- G2OC = Context->getConstantExprSExt(G2OC, Type::Int64Ty);
- GEP1Ops[FirstConstantOper] = G1OC;
- GEP2Ops[FirstConstantOper] = G2OC;
- }
-
- if (G1OC != G2OC) {
- // Handle the "be careful" case above: if this is an array/vector
- // subscript, scan for a subsequent variable array index.
- if (const SequentialType *STy =
- dyn_cast<SequentialType>(BasePtr1Ty)) {
- const Type *NextTy = STy;
- bool isBadCase = false;
-
- for (unsigned Idx = FirstConstantOper;
- Idx != MinOperands && isa<SequentialType>(NextTy); ++Idx) {
- const Value *V1 = GEP1Ops[Idx], *V2 = GEP2Ops[Idx];
- if (!isa<Constant>(V1) || !isa<Constant>(V2)) {
- isBadCase = true;
- break;
- }
- // If the array is indexed beyond the bounds of the static type
- // at this level, it will also fall into the "be careful" case.
- // It would theoretically be possible to analyze these cases,
- // but for now just be conservatively correct.
- if (const ArrayType *ATy = dyn_cast<ArrayType>(STy))
- if (cast<ConstantInt>(G1OC)->getZExtValue() >=
- ATy->getNumElements() ||
- cast<ConstantInt>(G2OC)->getZExtValue() >=
- ATy->getNumElements()) {
- isBadCase = true;
- break;
- }
- if (const VectorType *VTy = dyn_cast<VectorType>(STy))
- if (cast<ConstantInt>(G1OC)->getZExtValue() >=
- VTy->getNumElements() ||
- cast<ConstantInt>(G2OC)->getZExtValue() >=
- VTy->getNumElements()) {
- isBadCase = true;
- break;
- }
- STy = cast<SequentialType>(NextTy);
- NextTy = cast<SequentialType>(NextTy)->getElementType();
- }
-
- if (isBadCase) G1OC = 0;
- }
-
- // Make sure they are comparable (ie, not constant expressions), and
- // make sure the GEP with the smaller leading constant is GEP1.
- if (G1OC) {
- Constant *Compare = ConstantExpr::getICmp(ICmpInst::ICMP_SGT,
- G1OC, G2OC);
- if (ConstantInt *CV = dyn_cast<ConstantInt>(Compare)) {
- if (CV->getZExtValue()) { // If they are comparable and G2 > G1
- std::swap(GEP1Ops, GEP2Ops); // Make GEP1 < GEP2
- std::swap(NumGEP1Ops, NumGEP2Ops);
- }
- break;
- }
- }
- }
- }
- BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->getTypeAtIndex(G1Oper);
- }
+ // 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;
+}
- // No shared constant operands, and we ran out of common operands. At this
- // point, the GEP instructions have run through all of their operands, and we
- // haven't found evidence that there are any deltas between the GEP's.
- // However, one GEP may have more operands than the other. If this is the
- // case, there may still be hope. Check this now.
- if (FirstConstantOper == MinOperands) {
- // Make GEP1Ops be the longer one if there is a longer one.
- if (NumGEP1Ops < NumGEP2Ops) {
- std::swap(GEP1Ops, GEP2Ops);
- std::swap(NumGEP1Ops, NumGEP2Ops);
- }
-
- // Is there anything to check?
- if (NumGEP1Ops > MinOperands) {
- for (unsigned i = FirstConstantOper; i != MaxOperands; ++i)
- if (isa<ConstantInt>(GEP1Ops[i]) &&
- !cast<ConstantInt>(GEP1Ops[i])->isZero()) {
- // Yup, there's a constant in the tail. Set all variables to
- // constants in the GEP instruction to make it suitable for
- // TargetData::getIndexedOffset.
- for (i = 0; i != MaxOperands; ++i)
- if (!isa<ConstantInt>(GEP1Ops[i]))
- GEP1Ops[i] = Context->getNullValue(GEP1Ops[i]->getType());
- // Okay, now get the offset. This is the relative offset for the full
- // instruction.
- const TargetData &TD = getTargetData();
- int64_t Offset1 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
- NumGEP1Ops);
-
- // Now check without any constants at the end.
- int64_t Offset2 = TD.getIndexedOffset(GEPPointerTy, GEP1Ops,
- MinOperands);
-
- // Make sure we compare the absolute difference.
- if (Offset1 > Offset2)
- std::swap(Offset1, Offset2);
-
- // If the tail provided a bit enough offset, return noalias!
- if ((uint64_t)(Offset2-Offset1) >= SizeMax)
- return NoAlias;
- // Otherwise break - we don't look for another constant in the tail.
- break;
- }
+static AliasAnalysis::AliasResult
+MergeAliasResults(AliasAnalysis::AliasResult A, AliasAnalysis::AliasResult B) {
+ // If the results agree, take it.
+ if (A == B)
+ return A;
+ // A mix of PartialAlias and MustAlias is PartialAlias.
+ if ((A == AliasAnalysis::PartialAlias && B == AliasAnalysis::MustAlias) ||
+ (B == AliasAnalysis::PartialAlias && A == AliasAnalysis::MustAlias))
+ return AliasAnalysis::PartialAlias;
+ // Otherwise, we don't know anything.
+ return AliasAnalysis::MayAlias;
+}
+
+/// aliasSelect - Provide a bunch of ad-hoc rules to disambiguate a Select
+/// instruction against another.
+AliasAnalysis::AliasResult
+BasicAliasAnalysis::aliasSelect(const SelectInst *SI, uint64_t SISize,
+ const MDNode *SITBAAInfo,
+ const Value *V2, uint64_t V2Size,
+ const MDNode *V2TBAAInfo) {
+ // 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, SITBAAInfo,
+ SI2->getTrueValue(), V2Size, V2TBAAInfo);
+ if (Alias == MayAlias)
+ return MayAlias;
+ AliasResult ThisAlias =
+ aliasCheck(SI->getFalseValue(), SISize, SITBAAInfo,
+ SI2->getFalseValue(), V2Size, V2TBAAInfo);
+ return MergeAliasResults(ThisAlias, Alias);
}
- // Couldn't find anything useful.
+ // 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);
+ if (Alias == MayAlias)
return MayAlias;
- }
- // If there are non-equal constants arguments, then we can figure
- // out a minimum known delta between the two index expressions... at
- // this point we know that the first constant index of GEP1 is less
- // than the first constant index of GEP2.
-
- // Advance BasePtr[12]Ty over this first differing constant operand.
- BasePtr2Ty = cast<CompositeType>(BasePtr1Ty)->
- getTypeAtIndex(GEP2Ops[FirstConstantOper]);
- BasePtr1Ty = cast<CompositeType>(BasePtr1Ty)->
- getTypeAtIndex(GEP1Ops[FirstConstantOper]);
-
- // We are going to be using TargetData::getIndexedOffset to determine the
- // offset that each of the GEP's is reaching. To do this, we have to convert
- // all variable references to constant references. To do this, we convert the
- // initial sequence of array subscripts into constant zeros to start with.
- const Type *ZeroIdxTy = GEPPointerTy;
- for (unsigned i = 0; i != FirstConstantOper; ++i) {
- if (!isa<StructType>(ZeroIdxTy))
- GEP1Ops[i] = GEP2Ops[i] = Context->getNullValue(Type::Int32Ty);
-
- if (const CompositeType *CT = dyn_cast<CompositeType>(ZeroIdxTy))
- ZeroIdxTy = CT->getTypeAtIndex(GEP1Ops[i]);
- }
+ AliasResult ThisAlias =
+ aliasCheck(V2, V2Size, V2TBAAInfo, SI->getFalseValue(), SISize, SITBAAInfo);
+ return MergeAliasResults(ThisAlias, Alias);
+}
- // We know that GEP1Ops[FirstConstantOper] & GEP2Ops[FirstConstantOper] are ok
-
- // Loop over the rest of the operands...
- for (unsigned i = FirstConstantOper+1; i != MaxOperands; ++i) {
- const Value *Op1 = i < NumGEP1Ops ? GEP1Ops[i] : 0;
- const Value *Op2 = i < NumGEP2Ops ? GEP2Ops[i] : 0;
- // If they are equal, use a zero index...
- if (Op1 == Op2 && BasePtr1Ty == BasePtr2Ty) {
- if (!isa<ConstantInt>(Op1))
- GEP1Ops[i] = GEP2Ops[i] = Context->getNullValue(Op1->getType());
- // Otherwise, just keep the constants we have.
- } else {
- if (Op1) {
- if (const ConstantInt *Op1C = dyn_cast<ConstantInt>(Op1)) {
- // If this is an array index, make sure the array element is in range.
- if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty)) {
- if (Op1C->getZExtValue() >= AT->getNumElements())
- return MayAlias; // Be conservative with out-of-range accesses
- } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty)) {
- if (Op1C->getZExtValue() >= VT->getNumElements())
- return MayAlias; // Be conservative with out-of-range accesses
- }
-
- } else {
- // GEP1 is known to produce a value less than GEP2. To be
- // conservatively correct, we must assume the largest possible
- // constant is used in this position. This cannot be the initial
- // index to the GEP instructions (because we know we have at least one
- // element before this one with the different constant arguments), so
- // we know that the current index must be into either a struct or
- // array. Because we know it's not constant, this cannot be a
- // structure index. Because of this, we can calculate the maximum
- // value possible.
- //
- if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr1Ty))
- GEP1Ops[i] =
- Context->getConstantInt(Type::Int64Ty,AT->getNumElements()-1);
- else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr1Ty))
- GEP1Ops[i] =
- Context->getConstantInt(Type::Int64Ty,VT->getNumElements()-1);
- }
+// aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI instruction
+// against another.
+AliasAnalysis::AliasResult
+BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize,
+ const MDNode *PNTBAAInfo,
+ const Value *V2, uint64_t V2Size,
+ const MDNode *V2TBAAInfo) {
+ // 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(Location(PN, PNSize, PNTBAAInfo),
+ Location(V2, V2Size, V2TBAAInfo));
+ if (PN > V2)
+ std::swap(Locs.first, Locs.second);
+
+ // Find the first incoming phi value not from its parent.
+ unsigned f = 0;
+ while (PN->getIncomingBlock(f) == PN->getParent() &&
+ f < PN->getNumIncomingValues()-1)
+ ++f;
+
+ AliasResult Alias =
+ aliasCheck(PN->getIncomingValue(f), PNSize, PNTBAAInfo,
+ PN2->getIncomingValueForBlock(PN->getIncomingBlock(f)),
+ V2Size, V2TBAAInfo);
+ if (Alias == MayAlias)
+ return MayAlias;
+
+ // If the first source of the PHI nodes NoAlias and the other inputs are
+ // the PHI node itself through some amount of recursion this does not add
+ // any new information so just return NoAlias.
+ // bb:
+ // ptr = ptr2 + 1
+ // loop:
+ // ptr_phi = phi [bb, ptr], [loop, ptr_plus_one]
+ // ptr2_phi = phi [bb, ptr2], [loop, ptr2_plus_one]
+ // ...
+ // ptr_plus_one = gep ptr_phi, 1
+ // ptr2_plus_one = gep ptr2_phi, 1
+ // We assume for the recursion that the the phis (ptr_phi, ptr2_phi) do
+ // not alias each other.
+ bool ArePhisAssumedNoAlias = false;
+ AliasResult OrigAliasResult = NoAlias;
+ if (Alias == NoAlias) {
+ // Pretend the phis do not alias.
+ assert(AliasCache.count(Locs) &&
+ "There must exist an entry for the phi node");
+ OrigAliasResult = AliasCache[Locs];
+ AliasCache[Locs] = NoAlias;
+ ArePhisAssumedNoAlias = true;
}
- if (Op2) {
- if (const ConstantInt *Op2C = dyn_cast<ConstantInt>(Op2)) {
- // If this is an array index, make sure the array element is in range.
- if (const ArrayType *AT = dyn_cast<ArrayType>(BasePtr2Ty)) {
- if (Op2C->getZExtValue() >= AT->getNumElements())
- return MayAlias; // Be conservative with out-of-range accesses
- } else if (const VectorType *VT = dyn_cast<VectorType>(BasePtr2Ty)) {
- if (Op2C->getZExtValue() >= VT->getNumElements())
- return MayAlias; // Be conservative with out-of-range accesses
- }
- } else { // Conservatively assume the minimum value for this index
- GEP2Ops[i] = Context->getNullValue(Op2->getType());
- }
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+ if (i == f)
+ continue;
+
+ AliasResult ThisAlias =
+ aliasCheck(PN->getIncomingValue(i), PNSize, PNTBAAInfo,
+ PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
+ V2Size, V2TBAAInfo);
+ Alias = MergeAliasResults(ThisAlias, Alias);
+ if (Alias == MayAlias)
+ break;
}
- }
- if (BasePtr1Ty && Op1) {
- if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr1Ty))
- BasePtr1Ty = CT->getTypeAtIndex(GEP1Ops[i]);
- else
- BasePtr1Ty = 0;
- }
+ // Reset if speculation failed.
+ if (ArePhisAssumedNoAlias && Alias != NoAlias)
+ AliasCache[Locs] = OrigAliasResult;
- if (BasePtr2Ty && Op2) {
- if (const CompositeType *CT = dyn_cast<CompositeType>(BasePtr2Ty))
- BasePtr2Ty = CT->getTypeAtIndex(GEP2Ops[i]);
- else
- BasePtr2Ty = 0;
+ return Alias;
}
+
+ SmallPtrSet<Value*, 4> UniqueSrc;
+ SmallVector<Value*, 4> V1Srcs;
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+ Value *PV1 = PN->getIncomingValue(i);
+ 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 (UniqueSrc.insert(PV1))
+ V1Srcs.push_back(PV1);
}
- if (GEPPointerTy->getElementType()->isSized()) {
- int64_t Offset1 =
- getTargetData().getIndexedOffset(GEPPointerTy, GEP1Ops, NumGEP1Ops);
- int64_t Offset2 =
- getTargetData().getIndexedOffset(GEPPointerTy, GEP2Ops, NumGEP2Ops);
- assert(Offset1 != Offset2 &&
- "There is at least one different constant here!");
-
- // Make sure we compare the absolute difference.
- if (Offset1 > Offset2)
- std::swap(Offset1, Offset2);
-
- if ((uint64_t)(Offset2-Offset1) >= SizeMax) {
- //cerr << "Determined that these two GEP's don't alias ["
- // << SizeMax << " bytes]: \n" << *GEP1 << *GEP2;
- return NoAlias;
- }
+ AliasResult Alias = aliasCheck(V2, V2Size, V2TBAAInfo,
+ V1Srcs[0], PNSize, PNTBAAInfo);
+ // 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, V2TBAAInfo,
+ V, PNSize, PNTBAAInfo);
+ Alias = MergeAliasResults(ThisAlias, Alias);
+ if (Alias == MayAlias)
+ break;
}
- return MayAlias;
+
+ return Alias;
}
-// Make sure that anything that uses AliasAnalysis pulls in this file...
-DEFINING_FILE_FOR(BasicAliasAnalysis)
+// aliasCheck - Provide a bunch of ad-hoc rules to disambiguate in common cases,
+// such as array references.
+//
+AliasAnalysis::AliasResult
+BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size,
+ const MDNode *V1TBAAInfo,
+ const Value *V2, uint64_t V2Size,
+ const MDNode *V2TBAAInfo) {
+ // 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();
+
+ // Are we checking for alias of the same value?
+ if (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);
+
+ // 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;
+
+ // Arguments can't alias with local allocations or noalias calls
+ // in the same function.
+ if (((isa<Argument>(O1) && (isa<AllocaInst>(O2) || isNoAliasCall(O2))) ||
+ (isa<Argument>(O2) && (isa<AllocaInst>(O1) || isNoAliasCall(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 (TD)
+ if ((V1Size != UnknownSize && isObjectSmallerThan(O2, V1Size, *TD, *TLI)) ||
+ (V2Size != UnknownSize && isObjectSmallerThan(O1, V2Size, *TD, *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));
+ 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(V1TBAAInfo, V2TBAAInfo);
+ }
+ if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) {
+ AliasResult Result = aliasGEP(GV1, V1Size, V1TBAAInfo, V2, V2Size, V2TBAAInfo, 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(V1TBAAInfo, V2TBAAInfo);
+ }
+ if (const PHINode *PN = dyn_cast<PHINode>(V1)) {
+ AliasResult Result = aliasPHI(PN, V1Size, V1TBAAInfo,
+ V2, V2Size, V2TBAAInfo);
+ if (Result != MayAlias) return AliasCache[Locs] = Result;
+ }
+
+ if (isa<SelectInst>(V2) && !isa<SelectInst>(V1)) {
+ std::swap(V1, V2);
+ std::swap(V1Size, V2Size);
+ std::swap(V1TBAAInfo, V2TBAAInfo);
+ }
+ if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) {
+ AliasResult Result = aliasSelect(S1, V1Size, V1TBAAInfo,
+ V2, V2Size, V2TBAAInfo);
+ 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)))
+ return AliasCache[Locs] = PartialAlias;
+
+ AliasResult Result =
+ AliasAnalysis::alias(Location(V1, V1Size, V1TBAAInfo),
+ Location(V2, V2Size, V2TBAAInfo));
+ return AliasCache[Locs] = Result;
+}
projects / oota-llvm.git / blobdiff