-//===- 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/AliasAnalysis.h"
#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/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/Analysis/CaptureTracking.h"
-#include "llvm/Analysis/MemoryBuiltins.h"
-#include "llvm/Analysis/ValueTracking.h"
-#include "llvm/Target/TargetData.h"
-#include "llvm/ADT/SmallPtrSet.h"
-#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/GetElementPtrTypeIterator.h"
+#include "llvm/Target/TargetLibraryInfo.h"
#include <algorithm>
using namespace llvm;
// Useful predicates
//===----------------------------------------------------------------------===//
-/// 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) {
// 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;
+ 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;
}
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 AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
- if (!AI->isArrayAllocation())
- AccessTy = AI->getType()->getElementType();
- else
- return false;
- } else if (const CallInst* CI = extractMallocCall(V)) {
- if (!isArrayMalloc(V, &TD))
- // The size is the argument to the malloc call.
- if (const ConstantInt* C = dyn_cast<ConstantInt>(CI->getArgOperand(0)))
- return (C->getZExtValue() < Size);
- 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 NoAA : public ImmutablePass, public AliasAnalysis {
- static char ID; // Class identification, replacement for typeinfo
- NoAA() : ImmutablePass(&ID) {}
- explicit NoAA(void *PID) : ImmutablePass(PID) { }
-
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ 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 initializePass() {
- TD = getAnalysisIfAvailable<TargetData>();
+ bool operator!=(const VariableGEPIndex &Other) const {
+ return !operator==(Other);
}
+ };
+}
- virtual AliasResult alias(const Value *V1, unsigned V1Size,
- const Value *V2, unsigned V2Size) {
- return MayAlias;
+
+/// 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 bool pointsToConstantMemory(const Value *P) { return false; }
- virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
- const Value *P, unsigned Size) {
- return ModRef;
+/// 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;
}
- virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
- ImmutableCallSite CS2) {
- return ModRef;
+
+ if (Op->getOpcode() == Instruction::BitCast) {
+ V = Op->getOperand(0);
+ continue;
}
- virtual void deleteValue(Value *V) {}
- virtual void copyValue(Value *From, Value *To) {}
+ 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;
+ }
- /// 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 PassInfo *PI) {
- if (PI->isPassID(&AliasAnalysis::ID))
- return (AliasAnalysis*)this;
- return this;
+ return V;
}
- };
-} // End of anonymous namespace
+
+ // 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;
+}
-// Register this pass...
-char NoAA::ID = 0;
-INITIALIZE_AG_PASS(NoAA, AliasAnalysis, "no-aa",
- "No Alias Analysis (always returns 'may' alias)",
- true, true, false);
+/// 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;
-ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
+ 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
#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 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) {}
+ BasicAliasAnalysis() : ImmutablePass(ID) {
+ initializeBasicAliasAnalysisPass(*PassRegistry::getPassRegistry());
+ }
- AliasResult alias(const Value *V1, unsigned V1Size,
- const Value *V2, unsigned V2Size) {
- assert(Visited.empty() && "Visited must be cleared after use!");
- assert(notDifferentParent(V1, V2) &&
+ virtual void initializePass() {
+ InitializeAliasAnalysis(this);
+ }
+
+ virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ AU.addRequired<AliasAnalysis>();
+ AU.addRequired<TargetLibraryInfo>();
+ }
+
+ 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(V1, V1Size, V2, V2Size);
- Visited.clear();
+ 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;
}
- ModRefResult getModRefInfo(ImmutableCallSite CS,
- const Value *P, unsigned Size);
- ModRefResult getModRefInfo(ImmutableCallSite CS1,
- ImmutableCallSite CS2);
+ 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 PassInfo *PI) {
- if (PI->isPassID(&AliasAnalysis::ID))
+ /// 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:
- // Visited - Track instructions visited by a aliasPHI, aliasSelect(), and aliasGEP().
+ // 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, unsigned V1Size,
- const Value *V2, unsigned V2Size,
+ 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, unsigned PNSize,
- const Value *V2, unsigned V2Size);
+ 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, unsigned SISize,
- const Value *V2, unsigned V2Size);
-
- AliasResult aliasCheck(const Value *V1, unsigned V1Size,
- const Value *V2, unsigned V2Size);
+ 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;
-INITIALIZE_AG_PASS(BasicAliasAnalysis, AliasAnalysis, "basicaa",
- "Basic Alias Analysis (default AA impl)",
- false, true, 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)
+
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);
+ }
+
+ // 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;
+ }
-/// 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()))
- // 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.
- return GV->isConstant();
- return false;
+ // If both select values point to local memory, then so does the select.
+ if (const SelectInst *SI = dyn_cast<SelectInst>(V)) {
+ Worklist.push_back(SI->getTrueValue());
+ Worklist.push_back(SI->getFalseValue());
+ continue;
+ }
+
+ // If all values incoming to a phi node point to local memory, then so does
+ // the phi.
+ if (const PHINode *PN = dyn_cast<PHINode>(V)) {
+ // Don't bother inspecting phi nodes with many operands.
+ if (PN->getNumIncomingValues() > MaxLookup) {
+ Visited.clear();
+ return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
+ }
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+ Worklist.push_back(PN->getIncomingValue(i));
+ continue;
+ }
+
+ // Otherwise be conservative.
+ Visited.clear();
+ return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
+
+ } while (!Worklist.empty() && --MaxLookup);
+
+ 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;
+
+ ModRefBehavior Min = UnknownModRefBehavior;
+
+ // If the callsite knows it only reads memory, don't return worse
+ // than that.
+ if (CS.onlyReadsMemory())
+ Min = OnlyReadsMemory;
+
+ // The AliasAnalysis base class has some smarts, lets use them.
+ return ModRefBehavior(AliasAnalysis::getModRefBehavior(CS) & Min);
+}
+
+/// 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
+ }
+
+ ModRefBehavior Min = UnknownModRefBehavior;
+
+ // If the function declares it only reads memory, go with that.
+ if (F->onlyReadsMemory())
+ Min = OnlyReadsMemory;
+
+ // 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
/// simple "address taken" analysis on local objects.
AliasAnalysis::ModRefResult
BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS,
- const Value *P, unsigned Size) {
- assert(notDifferentParent(CS.getInstruction(), P) &&
+ const Location &Loc) {
+ assert(notDifferentParent(CS.getInstruction(), Loc.Ptr) &&
"AliasAnalysis query involving multiple functions!");
- const Value *Object = P->getUnderlyingObject();
+ const Value *Object = GetUnderlyingObject(Loc.Ptr, TD);
- // If this is a tail call and P points to a stack location, we know that
+ // 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
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 pointer arguments.
+ // 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.paramHasAttr(ArgNo+1, Attribute::NoCapture))
+ (!CS.doesNotCapture(ArgNo) && !CS.isByValArgument(ArgNo)))
continue;
- // If this is a no-capture pointer argument, see if we can tell that it
+ // 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(cast<Value>(CI), UnknownSize, P, UnknownSize)) {
+ if (!isNoAlias(Location(*CI), Location(Object))) {
PassedAsArg = true;
break;
}
return NoModRef;
}
+ 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)
- return AliasAnalysis::getModRefInfo(CS, P, Size);
-
- switch (II->getIntrinsicID()) {
- default: break;
- case Intrinsic::memcpy:
- case Intrinsic::memmove: {
- unsigned 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 (isNoAlias(Dest, Len, P, Size)) {
- if (isNoAlias(Src, Len, P, Size))
+ 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;
- return Ref;
+ break;
}
- 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))) {
- unsigned Len = LenCI->getZExtValue();
- Value *Dest = II->getArgOperand(0);
- if (isNoAlias(Dest, Len, P, Size))
+ 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;
}
- break;
- case Intrinsic::atomic_cmp_swap:
- case Intrinsic::atomic_swap:
- case Intrinsic::atomic_load_add:
- case Intrinsic::atomic_load_sub:
- case Intrinsic::atomic_load_and:
- case Intrinsic::atomic_load_nand:
- case Intrinsic::atomic_load_or:
- case Intrinsic::atomic_load_xor:
- case Intrinsic::atomic_load_max:
- case Intrinsic::atomic_load_min:
- case Intrinsic::atomic_load_umax:
- case Intrinsic::atomic_load_umin:
- if (TD) {
- Value *Op1 = II->getArgOperand(0);
- unsigned Op1Size = TD->getTypeStoreSize(Op1->getType());
- if (isNoAlias(Op1, Op1Size, P, Size))
+ 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;
+ }
+ }
+
+ // 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;
+ }
}
- break;
- case Intrinsic::lifetime_start:
- case Intrinsic::lifetime_end:
- case Intrinsic::invariant_start: {
- unsigned PtrSize = cast<ConstantInt>(II->getArgOperand(0))->getZExtValue();
- if (isNoAlias(II->getArgOperand(1), PtrSize, P, Size))
- return NoModRef;
- break;
- }
- case Intrinsic::invariant_end: {
- unsigned PtrSize = cast<ConstantInt>(II->getArgOperand(1))->getZExtValue();
- if (isNoAlias(II->getArgOperand(2), PtrSize, P, Size))
- return NoModRef;
- break;
- }
}
// The AliasAnalysis base class has some smarts, lets use them.
- return AliasAnalysis::getModRefInfo(CS, P, Size);
+ return ModRefResult(AliasAnalysis::getModRefInfo(CS, Loc) & Min);
}
+static bool areVarIndicesEqual(SmallVector<VariableGEPIndex, 4> &Indices1,
+ SmallVector<VariableGEPIndex, 4> &Indices2) {
+ unsigned Size1 = Indices1.size();
+ unsigned Size2 = Indices2.size();
-AliasAnalysis::ModRefResult
-BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS1,
- ImmutableCallSite 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, there is no dependence.
- if (CS1B == OnlyReadsMemory && CS2B == OnlyReadsMemory)
- return NoModRef;
-
- // If CS1 only reads memory, the only dependence on CS2 can be
- // from CS1 reading memory written by CS2.
- if (CS1B == OnlyReadsMemory)
- return Ref;
-
- // Otherwise, fall back to NoAA (mod+ref).
- return NoAA::getModRefInfo(CS1, CS2);
-}
+ if (Size1 != Size2)
+ return false;
-/// 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<std::pair<const Value*, int64_t> > &Dest,
- const SmallVectorImpl<std::pair<const Value*, int64_t> > &Src) {
- if (Src.empty()) return;
+ for (unsigned I = 0; I != Size1; ++I)
+ if (Indices1[I] != Indices2[I])
+ return false;
- for (unsigned i = 0, e = Src.size(); i != e; ++i) {
- const Value *V = Src[i].first;
- int64_t Scale = Src[i].second;
-
- // 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].first != V) 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].second != Scale)
- Dest[j].second -= 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)
- Dest.push_back(std::make_pair(V, -Scale));
- }
+ 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 GEP1->getUnderlyingObject(),
+/// anything about V2. UnderlyingV1 is GetUnderlyingObject(GEP1, TD),
/// UnderlyingV2 is the same for V2.
///
AliasAnalysis::AliasResult
-BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, unsigned V1Size,
- const Value *V2, unsigned V2Size,
+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) {
- // If this GEP has been visited before, we're on a use-def cycle.
- // Such cycles are only valid when PHI nodes are involved or in unreachable
- // code. The visitPHI function catches cycles containing PHIs, but there
- // could still be a cycle without PHIs in unreachable code.
- if (!Visited.insert(GEP1))
- return MayAlias;
-
int64_t GEP1BaseOffset;
- SmallVector<std::pair<const Value*, int64_t>, 4> GEP1VariableIndices;
+ SmallVector<VariableGEPIndex, 4> 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.
+ // 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();
+ }
+ }
+
// Do the base pointers alias?
- AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize,
- UnderlyingV2, UnknownSize);
+ 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.
DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD);
int64_t GEP2BaseOffset;
- SmallVector<std::pair<const Value*, int64_t>, 4> GEP2VariableIndices;
+ SmallVector<VariableGEPIndex, 4> 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 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!");
+ "DecomposeGEPExpression and GetUnderlyingObject disagree!");
return MayAlias;
}
if (V1Size == UnknownSize && V2Size == UnknownSize)
return MayAlias;
- AliasResult R = aliasCheck(UnderlyingV1, UnknownSize, V2, V2Size);
+ 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
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 and GetUnderlyingObject should return the
+ // same result except when DecomposeGEPExpression has no DataLayout.
if (GEP1BasePtr != UnderlyingV1) {
assert(TD == 0 &&
- "DecomposeGEPExpression and getUnderlyingObject disagree!");
+ "DecomposeGEPExpression and GetUnderlyingObject disagree!");
return MayAlias;
}
}
if (GEP1BaseOffset == 0 && GEP1VariableIndices.empty())
return MustAlias;
- // If we have a known constant offset, see if this offset is larger than the
- // access size being queried. If so, and if no variable indices can remove
- // pieces of this constant, then we know we have a no-alias. For example,
- // &A[100] != &A.
-
- // In order to handle cases like &A[100][i] where i is an out of range
- // subscript, we have to ignore all constant offset pieces that are a multiple
- // of a scaled index. Do this by removing constant offsets that are a
- // multiple of any of our variable indices. This allows us to transform
- // things like &A[i][1] because i has a stride of (e.g.) 8 bytes but the 1
- // provides an offset of 4 bytes (assuming a <= 4 byte access).
- for (unsigned i = 0, e = GEP1VariableIndices.size();
- i != e && GEP1BaseOffset;++i)
- if (int64_t RemovedOffset = GEP1BaseOffset/GEP1VariableIndices[i].second)
- GEP1BaseOffset -= RemovedOffset*GEP1VariableIndices[i].second;
-
- // If our known offset is bigger than the access size, we know we don't have
- // an alias.
- if (GEP1BaseOffset) {
- if (GEP1BaseOffset >= (int64_t)V2Size ||
- GEP1BaseOffset <= -(int64_t)V1Size)
+ // 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;
+ }
+ } 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;
}
-
- return MayAlias;
+
+ // Statically, we can see that the base objects are the same, but the
+ // pointers have dynamic offsets which we can't resolve. And none of our
+ // little tricks above worked.
+ //
+ // TODO: Returning PartialAlias instead of MayAlias is a mild hack; the
+ // practical effect of this is protecting TBAA in the case of dynamic
+ // indices into arrays of unions or malloc'd memory.
+ return PartialAlias;
+}
+
+static 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, unsigned SISize,
- const Value *V2, unsigned V2Size) {
- // If this select has been visited before, we're on a use-def cycle.
- // Such cycles are only valid when PHI nodes are involved or in unreachable
- // code. The visitPHI function catches cycles containing PHIs, but there
- // could still be a cycle without PHIs in unreachable code.
- if (!Visited.insert(SI))
- return MayAlias;
-
+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,
- SI2->getTrueValue(), V2Size);
+ aliasCheck(SI->getTrueValue(), SISize, SITBAAInfo,
+ SI2->getTrueValue(), V2Size, V2TBAAInfo);
if (Alias == MayAlias)
return MayAlias;
AliasResult ThisAlias =
- aliasCheck(SI->getFalseValue(), SISize,
- SI2->getFalseValue(), V2Size);
- if (ThisAlias != Alias)
- return MayAlias;
- return Alias;
+ aliasCheck(SI->getFalseValue(), SISize, SITBAAInfo,
+ SI2->getFalseValue(), V2Size, V2TBAAInfo);
+ 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, SI->getTrueValue(), SISize);
+ aliasCheck(V2, V2Size, V2TBAAInfo, SI->getTrueValue(), SISize, SITBAAInfo);
if (Alias == MayAlias)
return MayAlias;
- // If V2 is visited, the recursive case will have been caught in the
- // above aliasCheck call, so these subsequent calls to aliasCheck
- // don't need to assume that V2 is being visited recursively.
- Visited.erase(V2);
-
AliasResult ThisAlias =
- aliasCheck(V2, V2Size, SI->getFalseValue(), SISize);
- if (ThisAlias != Alias)
- return MayAlias;
- return Alias;
+ aliasCheck(V2, V2Size, V2TBAAInfo, SI->getFalseValue(), SISize, SITBAAInfo);
+ return MergeAliasResults(ThisAlias, Alias);
}
// aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI instruction
// against another.
AliasAnalysis::AliasResult
-BasicAliasAnalysis::aliasPHI(const PHINode *PN, unsigned PNSize,
- const Value *V2, unsigned V2Size) {
- // The PHI node has already been visited, avoid recursion any further.
- if (!Visited.insert(PN))
- return MayAlias;
-
+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(0), PNSize,
- PN2->getIncomingValueForBlock(PN->getIncomingBlock(0)),
- V2Size);
+ aliasCheck(PN->getIncomingValue(f), PNSize, PNTBAAInfo,
+ PN2->getIncomingValueForBlock(PN->getIncomingBlock(f)),
+ V2Size, V2TBAAInfo);
if (Alias == MayAlias)
return MayAlias;
- for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) {
+
+ // 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;
+ }
+
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+ if (i == f)
+ continue;
+
AliasResult ThisAlias =
- aliasCheck(PN->getIncomingValue(i), PNSize,
+ aliasCheck(PN->getIncomingValue(i), PNSize, PNTBAAInfo,
PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
- V2Size);
- if (ThisAlias != Alias)
- return MayAlias;
+ V2Size, V2TBAAInfo);
+ Alias = MergeAliasResults(ThisAlias, Alias);
+ if (Alias == MayAlias)
+ break;
}
+
+ // Reset if speculation failed.
+ if (ArePhisAssumedNoAlias && Alias != NoAlias)
+ AliasCache[Locs] = OrigAliasResult;
+
return Alias;
}
V1Srcs.push_back(PV1);
}
- AliasResult Alias = aliasCheck(V2, V2Size, V1Srcs[0], PNSize);
+ 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)
for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) {
Value *V = V1Srcs[i];
- // If V2 is visited, the recursive case will have been caught in the
- // above aliasCheck call, so these subsequent calls to aliasCheck
- // don't need to assume that V2 is being visited recursively.
- Visited.erase(V2);
-
- AliasResult ThisAlias = aliasCheck(V2, V2Size, V, PNSize);
- if (ThisAlias != Alias || ThisAlias == MayAlias)
- return MayAlias;
+ AliasResult ThisAlias = aliasCheck(V2, V2Size, V2TBAAInfo,
+ V, PNSize, PNTBAAInfo);
+ Alias = MergeAliasResults(ThisAlias, Alias);
+ if (Alias == MayAlias)
+ break;
}
return Alias;
// such as array references.
//
AliasAnalysis::AliasResult
-BasicAliasAnalysis::aliasCheck(const Value *V1, unsigned V1Size,
- const Value *V2, unsigned V2Size) {
+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; // Scalars cannot alias each other
// Figure out what objects these things are pointing to if we can.
- const Value *O1 = V1->getUnderlyingObject();
- const Value *O2 = V2->getUnderlyingObject();
+ 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 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)) ||
- (V2Size != UnknownSize && isObjectSmallerThan(O1, V2Size, *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 (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1))
- return aliasGEP(GV1, V1Size, V2, V2Size, O1, O2);
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 (const PHINode *PN = dyn_cast<PHINode>(V1))
- return aliasPHI(PN, V1Size, V2, V2Size);
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 (const SelectInst *S1 = dyn_cast<SelectInst>(V1))
- return aliasSelect(S1, V1Size, V2, V2Size);
- return MayAlias;
+ // 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;
}
-
-// Make sure that anything that uses AliasAnalysis pulls in this file.
-DEFINING_FILE_FOR(BasicAliasAnalysis)
projects / oota-llvm.git / blobdiff