-//===- 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/BasicAliasAnalysis.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
-#include "llvm/Analysis/Passes.h"
-#include "llvm/Constants.h"
-#include "llvm/DerivedTypes.h"
-#include "llvm/Function.h"
-#include "llvm/GlobalVariable.h"
-#include "llvm/Instructions.h"
-#include "llvm/IntrinsicInst.h"
-#include "llvm/Operator.h"
-#include "llvm/Pass.h"
+#include "llvm/Analysis/CFG.h"
#include "llvm/Analysis/CaptureTracking.h"
+#include "llvm/Analysis/InstructionSimplify.h"
+#include "llvm/Analysis/LoopInfo.h"
#include "llvm/Analysis/MemoryBuiltins.h"
#include "llvm/Analysis/ValueTracking.h"
-#include "llvm/Target/TargetData.h"
-#include "llvm/ADT/SmallPtrSet.h"
-#include "llvm/ADT/SmallVector.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/GlobalAlias.h"
+#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Operator.h"
+#include "llvm/Pass.h"
#include "llvm/Support/ErrorHandling.h"
#include <algorithm>
using namespace llvm;
+/// Enable analysis of recursive PHI nodes.
+static cl::opt<bool> EnableRecPhiAnalysis("basicaa-recphi", cl::Hidden,
+ cl::init(false));
+
+/// SearchLimitReached / SearchTimes shows how often the limit of
+/// to decompose GEPs is reached. It will affect the precision
+/// of basic alias analysis.
+#define DEBUG_TYPE "basicaa"
+STATISTIC(SearchLimitReached, "Number of times the limit to "
+ "decompose GEPs is reached");
+STATISTIC(SearchTimes, "Number of times a GEP is decomposed");
+
+/// Cutoff after which to stop analysing a set of phi nodes potentially involved
+/// in a cycle. Because we are analysing 'through' phi nodes we need to be
+/// careful with value equivalence. We use reachability to make sure a value
+/// cannot be involved in a cycle.
+const unsigned MaxNumPhiBBsValueReachabilityCheck = 20;
+
+// The max limit of the search depth in DecomposeGEPExpression() and
+// GetUnderlyingObject(), both functions need to use the same search
+// depth otherwise the algorithm in aliasGEP will assert.
+static const unsigned MaxLookupSearchDepth = 6;
+
//===----------------------------------------------------------------------===//
// Useful predicates
//===----------------------------------------------------------------------===//
-/// 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.
+/// Returns true if the pointer is to a function-local object that never
+/// escapes from the function.
static bool isNonEscapingLocalObject(const Value *V) {
// If this is a local allocation, check to see if it escapes.
if (isa<AllocaInst>(V) || isNoAliasCall(V))
// 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;
}
-/// isEscapeSource - Return true if the pointer is one which would have
-/// been considered an escape by isNonEscapingLocalObject.
+/// Returns true if the pointer is one which would have been considered an
+/// escape by isNonEscapingLocalObject.
static bool isEscapeSource(const Value *V) {
if (isa<CallInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V))
return true;
return false;
}
-/// 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 {
+/// Returns the size of the object specified by V, or UnknownSize if unknown.
+static uint64_t getObjectSize(const Value *V, const DataLayout &DL,
+ const TargetLibraryInfo &TLI,
+ bool RoundToAlign = false) {
+ uint64_t Size;
+ if (getObjectSize(V, Size, DL, &TLI, RoundToAlign))
+ return Size;
+ return MemoryLocation::UnknownSize;
+}
+
+/// Returns true if we can prove that the object specified by V is smaller than
+/// Size.
+static bool isObjectSmallerThan(const Value *V, uint64_t Size,
+ const DataLayout &DL,
+ const TargetLibraryInfo &TLI) {
+ // Note that the meanings of the "object" are slightly different in the
+ // following contexts:
+ // c1: llvm::getObjectSize()
+ // c2: llvm.objectsize() intrinsic
+ // c3: isObjectSmallerThan()
+ // c1 and c2 share the same meaning; however, the meaning of "object" in c3
+ // refers to the "entire object".
+ //
+ // Consider this example:
+ // char *p = (char*)malloc(100)
+ // char *q = p+80;
+ //
+ // In the context of c1 and c2, the "object" pointed by q refers to the
+ // stretch of memory of q[0:19]. So, getObjectSize(q) should return 20.
+ //
+ // However, in the context of c3, the "object" refers to the chunk of memory
+ // being allocated. So, the "object" has 100 bytes, and q points to the middle
+ // the "object". In case q is passed to isObjectSmallerThan() as the 1st
+ // parameter, before the llvm::getObjectSize() is called to get the size of
+ // entire object, we should:
+ // - either rewind the pointer q to the base-address of the object in
+ // question (in this case rewind to p), or
+ // - just give up. It is up to caller to make sure the pointer is pointing
+ // to the base address the object.
+ //
+ // We go for 2nd option for simplicity.
+ if (!isIdentifiedObject(V))
return false;
- }
-
- if (AccessTy->isSized())
- return TD.getTypeAllocSize(AccessTy) < Size;
- return false;
+
+ // This function needs to use the aligned object size because we allow
+ // reads a bit past the end given sufficient alignment.
+ uint64_t ObjectSize = getObjectSize(V, DL, TLI, /*RoundToAlign*/ true);
+
+ return ObjectSize != MemoryLocation::UnknownSize && ObjectSize < Size;
+}
+
+/// Returns true if we can prove that the object specified by V has size Size.
+static bool isObjectSize(const Value *V, uint64_t Size, const DataLayout &DL,
+ const TargetLibraryInfo &TLI) {
+ uint64_t ObjectSize = getObjectSize(V, DL, TLI);
+ return ObjectSize != MemoryLocation::UnknownSize && ObjectSize == Size;
}
//===----------------------------------------------------------------------===//
-// 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(char &PID) : ImmutablePass(PID) { }
-
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+/// Analyzes the specified value as a linear expression: "A*V + B", where A and
+/// B are constant integers.
+///
+/// Returns the scale and offset values as APInts and return V as a Value*, and
+/// return whether we looked through any sign or zero extends. The incoming
+/// Value is known to have IntegerType and it may already be sign or zero
+/// extended.
+///
+/// Note that this looks through extends, so the high bits may not be
+/// represented in the result.
+/*static*/ const Value *BasicAliasAnalysis::GetLinearExpression(
+ const Value *V, APInt &Scale, APInt &Offset, unsigned &ZExtBits,
+ unsigned &SExtBits, const DataLayout &DL, unsigned Depth,
+ AssumptionCache *AC, DominatorTree *DT, bool &NSW, bool &NUW) {
+ assert(V->getType()->isIntegerTy() && "Not an integer value");
+
+ // Limit our recursion depth.
+ if (Depth == 6) {
+ Scale = 1;
+ Offset = 0;
+ return V;
+ }
+
+ if (const ConstantInt *Const = dyn_cast<ConstantInt>(V)) {
+ // if it's a constant, just convert it to an offset and remove the variable.
+ // If we've been called recursively the Offset bit width will be greater
+ // than the constant's (the Offset's always as wide as the outermost call),
+ // so we'll zext here and process any extension in the isa<SExtInst> &
+ // isa<ZExtInst> cases below.
+ Offset += Const->getValue().zextOrSelf(Offset.getBitWidth());
+ assert(Scale == 0 && "Constant values don't have a scale");
+ return V;
+ }
+
+ if (const BinaryOperator *BOp = dyn_cast<BinaryOperator>(V)) {
+ if (ConstantInt *RHSC = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
+
+ // If we've been called recursively then Offset and Scale will be wider
+ // that the BOp operands. We'll always zext it here as we'll process sign
+ // extensions below (see the isa<SExtInst> / isa<ZExtInst> cases).
+ APInt RHS = RHSC->getValue().zextOrSelf(Offset.getBitWidth());
+
+ switch (BOp->getOpcode()) {
+ default:
+ // We don't understand this instruction, so we can't decompose it any
+ // further.
+ Scale = 1;
+ Offset = 0;
+ return V;
+ case Instruction::Or:
+ // X|C == X+C if all the bits in C are unset in X. Otherwise we can't
+ // analyze it.
+ if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(), DL, 0, AC,
+ BOp, DT)) {
+ Scale = 1;
+ Offset = 0;
+ return V;
+ }
+ // FALL THROUGH.
+ case Instruction::Add:
+ V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits,
+ SExtBits, DL, Depth + 1, AC, DT, NSW, NUW);
+ Offset += RHS;
+ break;
+ case Instruction::Sub:
+ V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits,
+ SExtBits, DL, Depth + 1, AC, DT, NSW, NUW);
+ Offset -= RHS;
+ break;
+ case Instruction::Mul:
+ V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits,
+ SExtBits, DL, Depth + 1, AC, DT, NSW, NUW);
+ Offset *= RHS;
+ Scale *= RHS;
+ break;
+ case Instruction::Shl:
+ V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, ZExtBits,
+ SExtBits, DL, Depth + 1, AC, DT, NSW, NUW);
+ Offset <<= RHS.getLimitedValue();
+ Scale <<= RHS.getLimitedValue();
+ // the semantics of nsw and nuw for left shifts don't match those of
+ // multiplications, so we won't propagate them.
+ NSW = NUW = false;
+ return V;
+ }
+
+ if (isa<OverflowingBinaryOperator>(BOp)) {
+ NUW &= BOp->hasNoUnsignedWrap();
+ NSW &= BOp->hasNoSignedWrap();
+ }
+ return V;
}
+ }
- virtual void initializePass() {
- TD = getAnalysisIfAvailable<TargetData>();
+ // Since GEP indices are sign extended anyway, we don't care about the high
+ // bits of a sign or zero extended value - just scales and offsets. The
+ // extensions have to be consistent though.
+ if (isa<SExtInst>(V) || isa<ZExtInst>(V)) {
+ Value *CastOp = cast<CastInst>(V)->getOperand(0);
+ unsigned NewWidth = V->getType()->getPrimitiveSizeInBits();
+ unsigned SmallWidth = CastOp->getType()->getPrimitiveSizeInBits();
+ unsigned OldZExtBits = ZExtBits, OldSExtBits = SExtBits;
+ const Value *Result =
+ GetLinearExpression(CastOp, Scale, Offset, ZExtBits, SExtBits, DL,
+ Depth + 1, AC, DT, NSW, NUW);
+
+ // zext(zext(%x)) == zext(%x), and similiarly for sext; we'll handle this
+ // by just incrementing the number of bits we've extended by.
+ unsigned ExtendedBy = NewWidth - SmallWidth;
+
+ if (isa<SExtInst>(V) && ZExtBits == 0) {
+ // sext(sext(%x, a), b) == sext(%x, a + b)
+
+ if (NSW) {
+ // We haven't sign-wrapped, so it's valid to decompose sext(%x + c)
+ // into sext(%x) + sext(c). We'll sext the Offset ourselves:
+ unsigned OldWidth = Offset.getBitWidth();
+ Offset = Offset.trunc(SmallWidth).sext(NewWidth).zextOrSelf(OldWidth);
+ } else {
+ // We may have signed-wrapped, so don't decompose sext(%x + c) into
+ // sext(%x) + sext(c)
+ Scale = 1;
+ Offset = 0;
+ Result = CastOp;
+ ZExtBits = OldZExtBits;
+ SExtBits = OldSExtBits;
+ }
+ SExtBits += ExtendedBy;
+ } else {
+ // sext(zext(%x, a), b) = zext(zext(%x, a), b) = zext(%x, a + b)
+
+ if (!NUW) {
+ // We may have unsigned-wrapped, so don't decompose zext(%x + c) into
+ // zext(%x) + zext(c)
+ Scale = 1;
+ Offset = 0;
+ Result = CastOp;
+ ZExtBits = OldZExtBits;
+ SExtBits = OldSExtBits;
+ }
+ ZExtBits += ExtendedBy;
}
- virtual AliasResult alias(const Value *V1, unsigned V1Size,
- const Value *V2, unsigned V2Size) {
- return MayAlias;
+ return Result;
+ }
+
+ Scale = 1;
+ Offset = 0;
+ return V;
+}
+
+/// If V is a symbolic pointer expression, decompose it into a base pointer
+/// with a constant offset and a number of scaled symbolic offsets.
+///
+/// The scaled symbolic offsets (represented by pairs of a Value* and a scale
+/// in the VarIndices vector) are Value*'s that are known to be scaled by the
+/// specified amount, but which may have other unrepresented high bits. As
+/// such, the gep cannot necessarily be reconstructed from its decomposed form.
+///
+/// When DataLayout is around, this function is capable of analyzing everything
+/// that GetUnderlyingObject can look through. To be able to do that
+/// GetUnderlyingObject and DecomposeGEPExpression must use the same search
+/// depth (MaxLookupSearchDepth). When DataLayout not is around, it just looks
+/// through pointer casts.
+/*static*/ const Value *BasicAliasAnalysis::DecomposeGEPExpression(
+ const Value *V, int64_t &BaseOffs,
+ SmallVectorImpl<VariableGEPIndex> &VarIndices, bool &MaxLookupReached,
+ const DataLayout &DL, AssumptionCache *AC, DominatorTree *DT) {
+ // Limit recursion depth to limit compile time in crazy cases.
+ unsigned MaxLookup = MaxLookupSearchDepth;
+ MaxLookupReached = false;
+ SearchTimes++;
+
+ BaseOffs = 0;
+ do {
+ // See if this is a bitcast or GEP.
+ const Operator *Op = dyn_cast<Operator>(V);
+ if (!Op) {
+ // The only non-operator case we can handle are GlobalAliases.
+ if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
+ if (!GA->mayBeOverridden()) {
+ V = GA->getAliasee();
+ continue;
+ }
+ }
+ return V;
}
- virtual bool pointsToConstantMemory(const Value *P) { return false; }
- virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
- const Value *P, unsigned Size) {
- return ModRef;
+ if (Op->getOpcode() == Instruction::BitCast ||
+ Op->getOpcode() == Instruction::AddrSpaceCast) {
+ V = Op->getOperand(0);
+ continue;
}
- virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
- ImmutableCallSite CS2) {
- return ModRef;
+
+ const GEPOperator *GEPOp = dyn_cast<GEPOperator>(Op);
+ if (!GEPOp) {
+ // If it's not a GEP, hand it off to SimplifyInstruction to see if it
+ // can come up with something. This matches what GetUnderlyingObject does.
+ if (const Instruction *I = dyn_cast<Instruction>(V))
+ // TODO: Get a DominatorTree and AssumptionCache and use them here
+ // (these are both now available in this function, but this should be
+ // updated when GetUnderlyingObject is updated). TLI should be
+ // provided also.
+ if (const Value *Simplified =
+ SimplifyInstruction(const_cast<Instruction *>(I), DL)) {
+ V = Simplified;
+ continue;
+ }
+
+ return V;
}
- virtual void deleteValue(Value *V) {}
- virtual void copyValue(Value *From, Value *To) {}
-
- /// 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(AnalysisID PI) {
- if (PI == &AliasAnalysis::ID)
- return (AliasAnalysis*)this;
- return this;
+ // Don't attempt to analyze GEPs over unsized objects.
+ if (!GEPOp->getOperand(0)->getType()->getPointerElementType()->isSized())
+ return V;
+
+ unsigned AS = GEPOp->getPointerAddressSpace();
+ // Walk the indices of the GEP, accumulating them into BaseOff/VarIndices.
+ gep_type_iterator GTI = gep_type_begin(GEPOp);
+ for (User::const_op_iterator I = GEPOp->op_begin() + 1, E = GEPOp->op_end();
+ I != E; ++I) {
+ const Value *Index = *I;
+ // Compute the (potentially symbolic) offset in bytes for this index.
+ if (StructType *STy = dyn_cast<StructType>(*GTI++)) {
+ // For a struct, add the member offset.
+ unsigned FieldNo = cast<ConstantInt>(Index)->getZExtValue();
+ if (FieldNo == 0)
+ continue;
+
+ BaseOffs += DL.getStructLayout(STy)->getElementOffset(FieldNo);
+ continue;
+ }
+
+ // For an array/pointer, add the element offset, explicitly scaled.
+ if (const ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) {
+ if (CIdx->isZero())
+ continue;
+ BaseOffs += DL.getTypeAllocSize(*GTI) * CIdx->getSExtValue();
+ continue;
+ }
+
+ uint64_t Scale = DL.getTypeAllocSize(*GTI);
+ unsigned ZExtBits = 0, SExtBits = 0;
+
+ // If the integer type is smaller than the pointer size, it is implicitly
+ // sign extended to pointer size.
+ unsigned Width = Index->getType()->getIntegerBitWidth();
+ unsigned PointerSize = DL.getPointerSizeInBits(AS);
+ if (PointerSize > Width)
+ SExtBits += PointerSize - Width;
+
+ // Use GetLinearExpression to decompose the index into a C1*V+C2 form.
+ APInt IndexScale(Width, 0), IndexOffset(Width, 0);
+ bool NSW = true, NUW = true;
+ Index = GetLinearExpression(Index, IndexScale, IndexOffset, ZExtBits,
+ SExtBits, DL, 0, AC, DT, NSW, NUW);
+
+ // The GEP index scale ("Scale") scales C1*V+C2, yielding (C1*V+C2)*Scale.
+ // This gives us an aggregate computation of (C1*Scale)*V + C2*Scale.
+ BaseOffs += IndexOffset.getSExtValue() * Scale;
+ Scale *= IndexScale.getSExtValue();
+
+ // If we already had an occurrence of this index variable, merge this
+ // scale into it. For example, we want to handle:
+ // A[x][x] -> x*16 + x*4 -> x*20
+ // This also ensures that 'x' only appears in the index list once.
+ for (unsigned i = 0, e = VarIndices.size(); i != e; ++i) {
+ if (VarIndices[i].V == Index && VarIndices[i].ZExtBits == ZExtBits &&
+ VarIndices[i].SExtBits == SExtBits) {
+ Scale += VarIndices[i].Scale;
+ VarIndices.erase(VarIndices.begin() + i);
+ break;
+ }
+ }
+
+ // Make sure that we have a scale that makes sense for this target's
+ // pointer size.
+ if (unsigned ShiftBits = 64 - PointerSize) {
+ Scale <<= ShiftBits;
+ Scale = (int64_t)Scale >> ShiftBits;
+ }
+
+ if (Scale) {
+ VariableGEPIndex Entry = {Index, ZExtBits, SExtBits,
+ static_cast<int64_t>(Scale)};
+ VarIndices.push_back(Entry);
+ }
}
- };
-} // End of anonymous namespace
-// Register this pass...
-char NoAA::ID = 0;
-INITIALIZE_AG_PASS(NoAA, AliasAnalysis, "no-aa",
- "No Alias Analysis (always returns 'may' alias)",
- true, true, false);
+ // Analyze the base pointer next.
+ V = GEPOp->getOperand(0);
+ } while (--MaxLookup);
-ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
+ // If the chain of expressions is too deep, just return early.
+ MaxLookupReached = true;
+ SearchLimitReached++;
+ return V;
+}
//===----------------------------------------------------------------------===//
// BasicAliasAnalysis Pass
//===----------------------------------------------------------------------===//
-#ifndef NDEBUG
-static const Function *getParent(const Value *V) {
- if (const Instruction *inst = dyn_cast<Instruction>(V))
- return inst->getParent()->getParent();
+// Register the pass...
+char BasicAliasAnalysis::ID = 0;
+INITIALIZE_AG_PASS_BEGIN(BasicAliasAnalysis, AliasAnalysis, "basicaa",
+ "Basic Alias Analysis (stateless AA impl)", false,
+ true, false)
+INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
+INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
+INITIALIZE_AG_PASS_END(BasicAliasAnalysis, AliasAnalysis, "basicaa",
+ "Basic Alias Analysis (stateless AA impl)", false, true,
+ false)
- if (const Argument *arg = dyn_cast<Argument>(V))
- return arg->getParent();
+ImmutablePass *llvm::createBasicAliasAnalysisPass() {
+ return new BasicAliasAnalysis();
+}
- return NULL;
+/// 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 MemoryLocation &Loc,
+ bool OrLocal) {
+ assert(Visited.empty() && "Visited must be cleared after use!");
+
+ unsigned MaxLookup = 8;
+ SmallVector<const Value *, 16> Worklist;
+ Worklist.push_back(Loc.Ptr);
+ do {
+ const Value *V = GetUnderlyingObject(Worklist.pop_back_val(), *DL);
+ if (!Visited.insert(V).second) {
+ Visited.clear();
+ return 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;
+ }
+
+ // 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 (Value *IncValue : PN->incoming_values())
+ Worklist.push_back(IncValue);
+ continue;
+ }
+
+ // Otherwise be conservative.
+ Visited.clear();
+ return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
+
+ } while (!Worklist.empty() && --MaxLookup);
+
+ Visited.clear();
+ return Worklist.empty();
+}
+
+// FIXME: This code is duplicated with MemoryLocation and should be hoisted to
+// some common utility location.
+static bool isMemsetPattern16(const Function *MS,
+ const TargetLibraryInfo &TLI) {
+ if (TLI.has(LibFunc::memset_pattern16) &&
+ MS->getName() == "memset_pattern16") {
+ FunctionType *MemsetType = MS->getFunctionType();
+ if (!MemsetType->isVarArg() && MemsetType->getNumParams() == 3 &&
+ isa<PointerType>(MemsetType->getParamType(0)) &&
+ isa<PointerType>(MemsetType->getParamType(1)) &&
+ isa<IntegerType>(MemsetType->getParamType(2)))
+ return true;
+ }
+
+ return false;
}
-static bool notDifferentParent(const Value *O1, const Value *O2) {
+/// Returns the behavior when calling the given call site.
+FunctionModRefBehavior
+BasicAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
+ if (CS.doesNotAccessMemory())
+ // Can't do better than this.
+ return FMRB_DoesNotAccessMemory;
+
+ FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior;
+
+ // If the callsite knows it only reads memory, don't return worse
+ // than that.
+ if (CS.onlyReadsMemory())
+ Min = FMRB_OnlyReadsMemory;
- const Function *F1 = getParent(O1);
- const Function *F2 = getParent(O2);
+ if (CS.onlyAccessesArgMemory())
+ Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesArgumentPointees);
- return !F1 || !F2 || F1 == F2;
+ // The AliasAnalysis base class has some smarts, lets use them.
+ return FunctionModRefBehavior(AliasAnalysis::getModRefBehavior(CS) & Min);
}
-#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 {
- static char ID; // Class identification, replacement for typeinfo
- BasicAliasAnalysis() : NoAA(ID) {}
-
- 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) &&
- "BasicAliasAnalysis doesn't support interprocedural queries.");
- AliasResult Alias = aliasCheck(V1, V1Size, V2, V2Size);
- Visited.clear();
- return Alias;
- }
- ModRefResult getModRefInfo(ImmutableCallSite CS,
- const Value *P, unsigned Size);
- ModRefResult getModRefInfo(ImmutableCallSite CS1,
- ImmutableCallSite CS2);
-
- /// pointsToConstantMemory - Chase pointers until we find a (constant
- /// global) or not.
- bool pointsToConstantMemory(const Value *P);
-
- /// 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(AnalysisID PI) {
- if (PI == &AliasAnalysis::ID)
- return (AliasAnalysis*)this;
- return this;
+/// Returns the behavior when calling the given function. For use when the call
+/// site is not known.
+FunctionModRefBehavior
+BasicAliasAnalysis::getModRefBehavior(const Function *F) {
+ // If the function declares it doesn't access memory, we can't do better.
+ if (F->doesNotAccessMemory())
+ return FMRB_DoesNotAccessMemory;
+
+ FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior;
+
+ // If the function declares it only reads memory, go with that.
+ if (F->onlyReadsMemory())
+ Min = FMRB_OnlyReadsMemory;
+
+ if (F->onlyAccessesArgMemory())
+ Min = FunctionModRefBehavior(Min & FMRB_OnlyAccessesArgumentPointees);
+
+ const TargetLibraryInfo &TLI =
+ getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
+ if (isMemsetPattern16(F, TLI))
+ Min = FMRB_OnlyAccessesArgumentPointees;
+
+ // Otherwise be conservative.
+ return FunctionModRefBehavior(AliasAnalysis::getModRefBehavior(F) & Min);
+}
+
+ModRefInfo BasicAliasAnalysis::getArgModRefInfo(ImmutableCallSite CS,
+ unsigned ArgIdx) {
+ if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction()))
+ switch (II->getIntrinsicID()) {
+ default:
+ break;
+ case Intrinsic::memset:
+ case Intrinsic::memcpy:
+ case Intrinsic::memmove:
+ assert((ArgIdx == 0 || ArgIdx == 1) &&
+ "Invalid argument index for memory intrinsic");
+ return ArgIdx ? MRI_Ref : MRI_Mod;
}
-
- private:
- // Visited - Track instructions visited by a aliasPHI, aliasSelect(), and aliasGEP().
- 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,
- 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);
-
- /// 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);
- };
-} // 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);
+ // We can bound the aliasing properties of memset_pattern16 just as we can
+ // for memcpy/memset. This is particularly important because the
+ // LoopIdiomRecognizer likes to turn loops into calls to memset_pattern16
+ // whenever possible.
+ if (CS.getCalledFunction() &&
+ isMemsetPattern16(CS.getCalledFunction(), *TLI)) {
+ assert((ArgIdx == 0 || ArgIdx == 1) &&
+ "Invalid argument index for memset_pattern16");
+ return ArgIdx ? MRI_Ref : MRI_Mod;
+ }
+ // FIXME: Handle memset_pattern4 and memset_pattern8 also.
-ImmutablePass *llvm::createBasicAliasAnalysisPass() {
- return new BasicAliasAnalysis();
+ return AliasAnalysis::getArgModRefInfo(CS, ArgIdx);
}
+static bool isAssumeIntrinsic(ImmutableCallSite CS) {
+ const IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction());
+ if (II && II->getIntrinsicID() == Intrinsic::assume)
+ return true;
-/// 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;
}
+bool BasicAliasAnalysis::doInitialization(Module &M) {
+ InitializeAliasAnalysis(this, &M.getDataLayout());
+ return true;
+}
-/// getModRefInfo - Check to see if the specified callsite can clobber the
-/// specified memory object. Since we only look at local properties of this
-/// function, we really can't say much about this query. We do, however, use
-/// simple "address taken" analysis on local objects.
-AliasAnalysis::ModRefResult
-BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS,
- const Value *P, unsigned Size) {
- assert(notDifferentParent(CS.getInstruction(), P) &&
+/// Checks to see if the specified callsite can clobber the specified memory
+/// object.
+///
+/// Since we only look at local properties of this function, we really can't
+/// say much about this query. We do, however, use simple "address taken"
+/// analysis on local objects.
+ModRefInfo BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS,
+ const MemoryLocation &Loc) {
+ assert(notDifferentParent(CS.getInstruction(), Loc.Ptr) &&
"AliasAnalysis query involving multiple functions!");
- const Value *Object = P->getUnderlyingObject();
-
- // If this is a tail call and P points to a stack location, we know that
+ const Value *Object = GetUnderlyingObject(Loc.Ptr, *DL);
+
+ // If this is a tail call and Loc.Ptr points to a stack location, we know that
// the tail call cannot access or modify the local stack.
// We cannot exclude byval arguments here; these belong to the caller of
// the current function not to the current function, and a tail callee
if (isa<AllocaInst>(Object))
if (const CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
if (CI->isTailCall())
- return NoModRef;
-
+ return MRI_NoModRef;
+
// If the pointer is to a locally allocated object that does not escape,
// then the call can not mod/ref the pointer unless the call takes the pointer
// as an argument, and itself doesn't capture it.
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(MemoryLocation(*CI), MemoryLocation(Object))) {
PassedAsArg = true;
break;
}
}
-
+
if (!PassedAsArg)
- return NoModRef;
+ return MRI_NoModRef;
}
- // 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))
- return NoModRef;
- return Ref;
- }
- 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))
- return NoModRef;
- }
- 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))
- return NoModRef;
- }
- 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;
- }
- }
+ // While the assume intrinsic is marked as arbitrarily writing so that
+ // proper control dependencies will be maintained, it never aliases any
+ // particular memory location.
+ if (isAssumeIntrinsic(CS))
+ return MRI_NoModRef;
// The AliasAnalysis base class has some smarts, lets use them.
- return AliasAnalysis::getModRefInfo(CS, P, Size);
+ return AliasAnalysis::getModRefInfo(CS, Loc);
}
+ModRefInfo BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS1,
+ ImmutableCallSite CS2) {
+ // While the assume intrinsic is marked as arbitrarily writing so that
+ // proper control dependencies will be maintained, it never aliases any
+ // particular memory location.
+ if (isAssumeIntrinsic(CS1) || isAssumeIntrinsic(CS2))
+ return MRI_NoModRef;
-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;
-
- AliasAnalysis::ModRefResult Mask = ModRef;
-
- // If CS1 only reads memory, the only dependence on CS2 can be
- // from CS1 reading memory written by CS2.
- if (CS1B == OnlyReadsMemory)
- Mask = ModRefResult(Mask & Ref);
-
- // If CS2 only access memory through arguments, accumulate the mod/ref
- // information from CS1's references to the memory referenced by
- // CS2's arguments.
- if (CS2B == AccessesArguments) {
- AliasAnalysis::ModRefResult R = NoModRef;
- for (ImmutableCallSite::arg_iterator
- I = CS2.arg_begin(), E = CS2.arg_end(); I != E; ++I) {
- R = ModRefResult((R | getModRefInfo(CS1, *I, UnknownSize)) & Mask);
- if (R == Mask)
- break;
- }
- return R;
- }
+ // The AliasAnalysis base class has some smarts, lets use them.
+ return AliasAnalysis::getModRefInfo(CS1, CS2);
+}
- // If CS1 only accesses memory through arguments, check if CS2 references
- // any of the memory referenced by CS1's arguments. If not, return NoModRef.
- if (CS1B == AccessesArguments) {
- AliasAnalysis::ModRefResult R = NoModRef;
- for (ImmutableCallSite::arg_iterator
- I = CS1.arg_begin(), E = CS1.arg_end(); I != E; ++I)
- if (getModRefInfo(CS2, *I, UnknownSize) != NoModRef) {
- R = Mask;
- break;
- }
- if (R == NoModRef)
- return R;
- }
+/// Provide ad-hoc rules to disambiguate accesses through two GEP operators,
+/// both having the exact same pointer operand.
+static AliasResult aliasSameBasePointerGEPs(const GEPOperator *GEP1,
+ uint64_t V1Size,
+ const GEPOperator *GEP2,
+ uint64_t V2Size,
+ const DataLayout &DL) {
+
+ assert(GEP1->getPointerOperand() == GEP2->getPointerOperand() &&
+ "Expected GEPs with the same pointer operand");
+
+ // Try to determine whether GEP1 and GEP2 index through arrays, into structs,
+ // such that the struct field accesses provably cannot alias.
+ // We also need at least two indices (the pointer, and the struct field).
+ if (GEP1->getNumIndices() != GEP2->getNumIndices() ||
+ GEP1->getNumIndices() < 2)
+ return MayAlias;
- // Otherwise, fall back to NoAA (mod+ref).
- return ModRefResult(NoAA::getModRefInfo(CS1, CS2) & Mask);
-}
+ // If we don't know the size of the accesses through both GEPs, we can't
+ // determine whether the struct fields accessed can't alias.
+ if (V1Size == MemoryLocation::UnknownSize ||
+ V2Size == MemoryLocation::UnknownSize)
+ return MayAlias;
-/// 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;
+ ConstantInt *C1 =
+ dyn_cast<ConstantInt>(GEP1->getOperand(GEP1->getNumOperands() - 1));
+ ConstantInt *C2 =
+ dyn_cast<ConstantInt>(GEP2->getOperand(GEP2->getNumOperands() - 1));
- 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));
+ // If the last (struct) indices aren't constants, we can't say anything.
+ // If they're identical, the other indices might be also be dynamically
+ // equal, so the GEPs can alias.
+ if (!C1 || !C2 || C1 == C2)
+ return MayAlias;
+
+ // Find the last-indexed type of the GEP, i.e., the type you'd get if
+ // you stripped the last index.
+ // On the way, look at each indexed type. If there's something other
+ // than an array, different indices can lead to different final types.
+ SmallVector<Value *, 8> IntermediateIndices;
+
+ // Insert the first index; we don't need to check the type indexed
+ // through it as it only drops the pointer indirection.
+ assert(GEP1->getNumIndices() > 1 && "Not enough GEP indices to examine");
+ IntermediateIndices.push_back(GEP1->getOperand(1));
+
+ // Insert all the remaining indices but the last one.
+ // Also, check that they all index through arrays.
+ for (unsigned i = 1, e = GEP1->getNumIndices() - 1; i != e; ++i) {
+ if (!isa<ArrayType>(GetElementPtrInst::getIndexedType(
+ GEP1->getSourceElementType(), IntermediateIndices)))
+ return MayAlias;
+ IntermediateIndices.push_back(GEP1->getOperand(i + 1));
}
-}
-/// 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(),
-/// UnderlyingV2 is the same for V2.
-///
-AliasAnalysis::AliasResult
-BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, unsigned V1Size,
- const Value *V2, unsigned V2Size,
- 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))
+ StructType *LastIndexedStruct =
+ dyn_cast<StructType>(GetElementPtrInst::getIndexedType(
+ GEP1->getSourceElementType(), IntermediateIndices));
+
+ if (!LastIndexedStruct)
return MayAlias;
- int64_t GEP1BaseOffset;
- SmallVector<std::pair<const Value*, int64_t>, 4> GEP1VariableIndices;
+ // We know that:
+ // - both GEPs begin indexing from the exact same pointer;
+ // - the last indices in both GEPs are constants, indexing into a struct;
+ // - said indices are different, hence, the pointed-to fields are different;
+ // - both GEPs only index through arrays prior to that.
+ //
+ // This lets us determine that the struct that GEP1 indexes into and the
+ // struct that GEP2 indexes into must either precisely overlap or be
+ // completely disjoint. Because they cannot partially overlap, indexing into
+ // different non-overlapping fields of the struct will never alias.
+
+ // Therefore, the only remaining thing needed to show that both GEPs can't
+ // alias is that the fields are not overlapping.
+ const StructLayout *SL = DL.getStructLayout(LastIndexedStruct);
+ const uint64_t StructSize = SL->getSizeInBytes();
+ const uint64_t V1Off = SL->getElementOffset(C1->getZExtValue());
+ const uint64_t V2Off = SL->getElementOffset(C2->getZExtValue());
+
+ auto EltsDontOverlap = [StructSize](uint64_t V1Off, uint64_t V1Size,
+ uint64_t V2Off, uint64_t V2Size) {
+ return V1Off < V2Off && V1Off + V1Size <= V2Off &&
+ ((V2Off + V2Size <= StructSize) ||
+ (V2Off + V2Size - StructSize <= V1Off));
+ };
- // If 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 (EltsDontOverlap(V1Off, V1Size, V2Off, V2Size) ||
+ EltsDontOverlap(V2Off, V2Size, V1Off, V1Size))
+ return NoAlias;
+
+ return MayAlias;
+}
+
+/// Provides a bunch of ad-hoc rules to disambiguate a GEP instruction against
+/// another pointer.
+///
+/// We know that V1 is a GEP, but we don't know anything about V2.
+/// UnderlyingV1 is GetUnderlyingObject(GEP1, DL), UnderlyingV2 is the same for
+/// V2.
+AliasResult BasicAliasAnalysis::aliasGEP(
+ const GEPOperator *GEP1, uint64_t V1Size, const AAMDNodes &V1AAInfo,
+ const Value *V2, uint64_t V2Size, const AAMDNodes &V2AAInfo,
+ const Value *UnderlyingV1, const Value *UnderlyingV2) {
+ int64_t GEP1BaseOffset;
+ bool GEP1MaxLookupReached;
+ SmallVector<VariableGEPIndex, 4> GEP1VariableIndices;
+
+ // We have to get two AssumptionCaches here because GEP1 and V2 may be from
+ // different functions.
+ // FIXME: This really doesn't make any sense. We get a dominator tree below
+ // that can only refer to a single function. But this function (aliasGEP) is
+ // a method on an immutable pass that can be called when there *isn't*
+ // a single function. The old pass management layer makes this "work", but
+ // this isn't really a clean solution.
+ AssumptionCacheTracker &ACT = getAnalysis<AssumptionCacheTracker>();
+ AssumptionCache *AC1 = nullptr, *AC2 = nullptr;
+ if (auto *GEP1I = dyn_cast<Instruction>(GEP1))
+ AC1 = &ACT.getAssumptionCache(
+ const_cast<Function &>(*GEP1I->getParent()->getParent()));
+ if (auto *I2 = dyn_cast<Instruction>(V2))
+ AC2 = &ACT.getAssumptionCache(
+ const_cast<Function &>(*I2->getParent()->getParent()));
+
+ DominatorTreeWrapperPass *DTWP =
+ getAnalysisIfAvailable<DominatorTreeWrapperPass>();
+ DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr;
+
+ // If we have two gep instructions with must-alias or not-alias'ing base
+ // pointers, figure out if the indexes to the GEP tell us anything about the
+ // derived pointer.
if (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) {
// Do the base pointers alias?
- AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize,
- UnderlyingV2, UnknownSize);
-
+ AliasResult BaseAlias =
+ aliasCheck(UnderlyingV1, MemoryLocation::UnknownSize, AAMDNodes(),
+ UnderlyingV2, MemoryLocation::UnknownSize, AAMDNodes());
+
+ // Check for geps of non-aliasing underlying pointers where the offsets are
+ // identical.
+ if ((BaseAlias == MayAlias) && V1Size == V2Size) {
+ // Do the base pointers alias assuming type and size.
+ AliasResult PreciseBaseAlias = aliasCheck(UnderlyingV1, V1Size, V1AAInfo,
+ UnderlyingV2, V2Size, V2AAInfo);
+ if (PreciseBaseAlias == NoAlias) {
+ // See if the computed offset from the common pointer tells us about the
+ // relation of the resulting pointer.
+ int64_t GEP2BaseOffset;
+ bool GEP2MaxLookupReached;
+ SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
+ const Value *GEP2BasePtr =
+ DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices,
+ GEP2MaxLookupReached, *DL, AC2, DT);
+ const Value *GEP1BasePtr =
+ DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices,
+ GEP1MaxLookupReached, *DL, AC1, DT);
+ // DecomposeGEPExpression and GetUnderlyingObject should return the
+ // same result except when DecomposeGEPExpression has no DataLayout.
+ if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
+ assert(!DL &&
+ "DecomposeGEPExpression and GetUnderlyingObject disagree!");
+ return MayAlias;
+ }
+ // If the max search depth is reached the result is undefined
+ if (GEP2MaxLookupReached || GEP1MaxLookupReached)
+ return MayAlias;
+
+ // Same offsets.
+ if (GEP1BaseOffset == GEP2BaseOffset &&
+ GEP1VariableIndices == GEP2VariableIndices)
+ return NoAlias;
+ GEP1VariableIndices.clear();
+ }
+ }
+
// If we get a No or May, then return it immediately, no amount of analysis
// will improve this situation.
- if (BaseAlias != MustAlias) return BaseAlias;
-
+ if (BaseAlias != MustAlias)
+ return BaseAlias;
+
// Otherwise, we have a MustAlias. Since the base pointers alias each other
// exactly, see if the computed offset from the common pointer tells us
// about the relation of the resulting pointer.
const Value *GEP1BasePtr =
- DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD);
-
+ DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices,
+ GEP1MaxLookupReached, *DL, AC1, DT);
+
int64_t GEP2BaseOffset;
- SmallVector<std::pair<const Value*, int64_t>, 4> GEP2VariableIndices;
+ bool GEP2MaxLookupReached;
+ 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(GEP2, GEP2BaseOffset, GEP2VariableIndices,
+ GEP2MaxLookupReached, *DL, AC2, DT);
+
+ // DecomposeGEPExpression and GetUnderlyingObject should return the
+ // same result except when DecomposeGEPExpression has no DataLayout.
if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
- assert(TD == 0 &&
- "DecomposeGEPExpression and getUnderlyingObject disagree!");
+ assert(!DL && "DecomposeGEPExpression and GetUnderlyingObject disagree!");
return MayAlias;
}
-
+
+ // If we know the two GEPs are based off of the exact same pointer (and not
+ // just the same underlying object), see if that tells us anything about
+ // the resulting pointers.
+ if (DL && GEP1->getPointerOperand() == GEP2->getPointerOperand()) {
+ AliasResult R = aliasSameBasePointerGEPs(GEP1, V1Size, GEP2, V2Size, *DL);
+ // If we couldn't find anything interesting, don't abandon just yet.
+ if (R != MayAlias)
+ return R;
+ }
+
+ // If the max search depth is reached the result is undefined
+ if (GEP2MaxLookupReached || GEP1MaxLookupReached)
+ return MayAlias;
+
// Subtract the GEP2 pointer from the GEP1 pointer to find out their
// symbolic difference.
GEP1BaseOffset -= GEP2BaseOffset;
GetIndexDifference(GEP1VariableIndices, GEP2VariableIndices);
-
+
} else {
// Check to see if these two pointers are related by the getelementptr
// instruction. If one pointer is a GEP with a non-zero index of the other
// pointer, we know they cannot alias.
// If both accesses are unknown size, we can't do anything useful here.
- if (V1Size == UnknownSize && V2Size == UnknownSize)
+ if (V1Size == MemoryLocation::UnknownSize &&
+ V2Size == MemoryLocation::UnknownSize)
return MayAlias;
- AliasResult R = aliasCheck(UnderlyingV1, UnknownSize, V2, V2Size);
+ AliasResult R = aliasCheck(UnderlyingV1, MemoryLocation::UnknownSize,
+ AAMDNodes(), V2, V2Size, V2AAInfo);
if (R != MustAlias)
// If V2 may alias GEP base pointer, conservatively returns MayAlias.
// If V2 is known not to alias GEP base pointer, then the two values
return R;
const Value *GEP1BasePtr =
- DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD);
-
- // If DecomposeGEPExpression isn't able to look all the way through the
- // addressing operation, we must not have TD and this is too complex for us
- // to handle without it.
+ DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices,
+ GEP1MaxLookupReached, *DL, AC1, DT);
+
+ // DecomposeGEPExpression and GetUnderlyingObject should return the
+ // same result except when DecomposeGEPExpression has no DataLayout.
if (GEP1BasePtr != UnderlyingV1) {
- assert(TD == 0 &&
- "DecomposeGEPExpression and getUnderlyingObject disagree!");
+ assert(!DL && "DecomposeGEPExpression and GetUnderlyingObject disagree!");
return MayAlias;
}
+ // If the max search depth is reached the result is undefined
+ if (GEP1MaxLookupReached)
+ return MayAlias;
}
-
+
// In the two GEP Case, if there is no difference in the offsets of the
// computed pointers, the resultant pointers are a must alias. This
// hapens when we have two lexically identical GEP's (for example).
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 != MemoryLocation::UnknownSize) {
+ if ((uint64_t)GEP1BaseOffset < V2Size)
+ return PartialAlias;
+ return NoAlias;
+ }
+ } else {
+ // We have the situation where:
+ // + +
+ // | BaseOffset |
+ // ---------------->|
+ // |-->V1Size |-------> V2Size
+ // GEP1 V2
+ // We need to know that V2Size is not unknown, otherwise we might have
+ // stripped a gep with negative index ('gep <ptr>, -1, ...).
+ if (V1Size != MemoryLocation::UnknownSize &&
+ V2Size != MemoryLocation::UnknownSize) {
+ if (-(uint64_t)GEP1BaseOffset < V1Size)
+ return PartialAlias;
+ return NoAlias;
+ }
+ }
+ }
+
+ if (!GEP1VariableIndices.empty()) {
+ uint64_t Modulo = 0;
+ bool AllPositive = true;
+ for (unsigned i = 0, e = GEP1VariableIndices.size(); i != e; ++i) {
+
+ // Try to distinguish something like &A[i][1] against &A[42][0].
+ // Grab the least significant bit set in any of the scales. We
+ // don't need std::abs here (even if the scale's negative) as we'll
+ // be ^'ing Modulo with itself later.
+ Modulo |= (uint64_t)GEP1VariableIndices[i].Scale;
+
+ if (AllPositive) {
+ // If the Value could change between cycles, then any reasoning about
+ // the Value this cycle may not hold in the next cycle. We'll just
+ // give up if we can't determine conditions that hold for every cycle:
+ const Value *V = GEP1VariableIndices[i].V;
+
+ bool SignKnownZero, SignKnownOne;
+ ComputeSignBit(const_cast<Value *>(V), SignKnownZero, SignKnownOne, *DL,
+ 0, AC1, nullptr, DT);
+
+ // Zero-extension widens the variable, and so forces the sign
+ // bit to zero.
+ bool IsZExt = GEP1VariableIndices[i].ZExtBits > 0 || isa<ZExtInst>(V);
+ SignKnownZero |= IsZExt;
+ SignKnownOne &= !IsZExt;
+
+ // If the variable begins with a zero then we know it's
+ // positive, regardless of whether the value is signed or
+ // unsigned.
+ int64_t Scale = GEP1VariableIndices[i].Scale;
+ AllPositive =
+ (SignKnownZero && Scale >= 0) || (SignKnownOne && Scale < 0);
+ }
+ }
+
+ Modulo = Modulo ^ (Modulo & (Modulo - 1));
+
+ // We can compute the difference between the two addresses
+ // mod Modulo. Check whether that difference guarantees that the
+ // two locations do not alias.
+ uint64_t ModOffset = (uint64_t)GEP1BaseOffset & (Modulo - 1);
+ if (V1Size != MemoryLocation::UnknownSize &&
+ V2Size != MemoryLocation::UnknownSize && ModOffset >= V2Size &&
+ V1Size <= Modulo - ModOffset)
+ return NoAlias;
+
+ // If we know all the variables are positive, then GEP1 >= GEP1BasePtr.
+ // If GEP1BasePtr > V2 (GEP1BaseOffset > 0) then we know the pointers
+ // don't alias if V2Size can fit in the gap between V2 and GEP1BasePtr.
+ if (AllPositive && GEP1BaseOffset > 0 && V2Size <= (uint64_t)GEP1BaseOffset)
+ return NoAlias;
+
+ if (constantOffsetHeuristic(GEP1VariableIndices, V1Size, V2Size,
+ GEP1BaseOffset, DL, AC1, DT))
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;
}
-/// 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;
+static AliasResult MergeAliasResults(AliasResult A, AliasResult B) {
+ // If the results agree, take it.
+ if (A == B)
+ return A;
+ // A mix of PartialAlias and MustAlias is PartialAlias.
+ if ((A == PartialAlias && B == MustAlias) ||
+ (B == PartialAlias && A == MustAlias))
+ return PartialAlias;
+ // Otherwise, we don't know anything.
+ return MayAlias;
+}
+/// Provides a bunch of ad-hoc rules to disambiguate a Select instruction
+/// against another.
+AliasResult BasicAliasAnalysis::aliasSelect(const SelectInst *SI,
+ uint64_t SISize,
+ const AAMDNodes &SIAAInfo,
+ const Value *V2, uint64_t V2Size,
+ const AAMDNodes &V2AAInfo) {
// If the values are Selects with the same condition, we can do a more precise
// check: just check for aliases between the values on corresponding arms.
if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2))
if (SI->getCondition() == SI2->getCondition()) {
- AliasResult Alias =
- aliasCheck(SI->getTrueValue(), SISize,
- SI2->getTrueValue(), V2Size);
+ AliasResult Alias = aliasCheck(SI->getTrueValue(), SISize, SIAAInfo,
+ SI2->getTrueValue(), V2Size, V2AAInfo);
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, SIAAInfo,
+ SI2->getFalseValue(), V2Size, V2AAInfo);
+ return MergeAliasResults(ThisAlias, Alias);
}
// If both arms of the Select node NoAlias or MustAlias V2, then returns
// NoAlias / MustAlias. Otherwise, returns MayAlias.
AliasResult Alias =
- aliasCheck(V2, V2Size, SI->getTrueValue(), SISize);
+ aliasCheck(V2, V2Size, V2AAInfo, SI->getTrueValue(), SISize, SIAAInfo);
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, V2AAInfo, SI->getFalseValue(), SISize, SIAAInfo);
+ 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;
+/// Provide a bunch of ad-hoc rules to disambiguate a PHI instruction against
+/// another.
+AliasResult BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize,
+ const AAMDNodes &PNAAInfo,
+ const Value *V2, uint64_t V2Size,
+ const AAMDNodes &V2AAInfo) {
+ // Track phi nodes we have visited. We use this information when we determine
+ // value equivalence.
+ VisitedPhiBBs.insert(PN->getParent());
// If the values are PHIs in the same block, we can do a more precise
// as well as efficient check: just check for aliases between the values
// on corresponding edges.
if (const PHINode *PN2 = dyn_cast<PHINode>(V2))
if (PN2->getParent() == PN->getParent()) {
- AliasResult Alias =
- aliasCheck(PN->getIncomingValue(0), PNSize,
- PN2->getIncomingValueForBlock(PN->getIncomingBlock(0)),
- V2Size);
- if (Alias == MayAlias)
- return MayAlias;
- for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) {
+ LocPair Locs(MemoryLocation(PN, PNSize, PNAAInfo),
+ MemoryLocation(V2, V2Size, V2AAInfo));
+ if (PN > V2)
+ std::swap(Locs.first, Locs.second);
+ // Analyse the PHIs' inputs under the assumption that the PHIs are
+ // NoAlias.
+ // If the PHIs are May/MustAlias there must be (recursively) an input
+ // operand from outside the PHIs' cycle that is MayAlias/MustAlias or
+ // there must be an operation on the PHIs within the PHIs' value cycle
+ // that causes a MayAlias.
+ // Pretend the phis do not alias.
+ AliasResult Alias = NoAlias;
+ assert(AliasCache.count(Locs) &&
+ "There must exist an entry for the phi node");
+ AliasResult OrigAliasResult = AliasCache[Locs];
+ AliasCache[Locs] = NoAlias;
+
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
AliasResult ThisAlias =
- aliasCheck(PN->getIncomingValue(i), PNSize,
- PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
- V2Size);
- if (ThisAlias != Alias)
- return MayAlias;
+ aliasCheck(PN->getIncomingValue(i), PNSize, PNAAInfo,
+ PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
+ V2Size, V2AAInfo);
+ Alias = MergeAliasResults(ThisAlias, Alias);
+ if (Alias == MayAlias)
+ break;
}
+
+ // Reset if speculation failed.
+ if (Alias != NoAlias)
+ AliasCache[Locs] = OrigAliasResult;
+
return Alias;
}
- SmallPtrSet<Value*, 4> UniqueSrc;
- SmallVector<Value*, 4> V1Srcs;
- for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
- Value *PV1 = PN->getIncomingValue(i);
+ SmallPtrSet<Value *, 4> UniqueSrc;
+ SmallVector<Value *, 4> V1Srcs;
+ bool isRecursive = false;
+ for (Value *PV1 : PN->incoming_values()) {
if (isa<PHINode>(PV1))
// If any of the source itself is a PHI, return MayAlias conservatively
// to avoid compile time explosion. The worst possible case is if both
// sides are PHI nodes. In which case, this is O(m x n) time where 'm'
// and 'n' are the number of PHI sources.
return MayAlias;
- if (UniqueSrc.insert(PV1))
+
+ if (EnableRecPhiAnalysis)
+ if (GEPOperator *PV1GEP = dyn_cast<GEPOperator>(PV1)) {
+ // Check whether the incoming value is a GEP that advances the pointer
+ // result of this PHI node (e.g. in a loop). If this is the case, we
+ // would recurse and always get a MayAlias. Handle this case specially
+ // below.
+ if (PV1GEP->getPointerOperand() == PN && PV1GEP->getNumIndices() == 1 &&
+ isa<ConstantInt>(PV1GEP->idx_begin())) {
+ isRecursive = true;
+ continue;
+ }
+ }
+
+ if (UniqueSrc.insert(PV1).second)
V1Srcs.push_back(PV1);
}
- AliasResult Alias = aliasCheck(V2, V2Size, V1Srcs[0], PNSize);
+ // If this PHI node is recursive, set the size of the accessed memory to
+ // unknown to represent all the possible values the GEP could advance the
+ // pointer to.
+ if (isRecursive)
+ PNSize = MemoryLocation::UnknownSize;
+
+ AliasResult Alias =
+ aliasCheck(V2, V2Size, V2AAInfo, V1Srcs[0], PNSize, PNAAInfo);
+
// Early exit if the check of the first PHI source against V2 is MayAlias.
// Other results are not possible.
if (Alias == MayAlias)
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, V2AAInfo, V, PNSize, PNAAInfo);
+ Alias = MergeAliasResults(ThisAlias, Alias);
+ if (Alias == MayAlias)
+ break;
}
return Alias;
}
-// aliasCheck - Provide a bunch of ad-hoc rules to disambiguate in common cases,
-// such as array references.
-//
-AliasAnalysis::AliasResult
-BasicAliasAnalysis::aliasCheck(const Value *V1, unsigned V1Size,
- const Value *V2, unsigned V2Size) {
+/// Provideis a bunch of ad-hoc rules to disambiguate in common cases, such as
+/// array references.
+AliasResult BasicAliasAnalysis::aliasCheck(const Value *V1, uint64_t V1Size,
+ AAMDNodes V1AAInfo, const Value *V2,
+ uint64_t V2Size,
+ AAMDNodes V2AAInfo) {
// If either of the memory references is empty, it doesn't matter what the
// pointer values are.
if (V1Size == 0 || V2Size == 0)
V1 = V1->stripPointerCasts();
V2 = V2->stripPointerCasts();
+ // If V1 or V2 is undef, the result is NoAlias because we can always pick a
+ // value for undef that aliases nothing in the program.
+ if (isa<UndefValue>(V1) || isa<UndefValue>(V2))
+ return NoAlias;
+
// Are we checking for alias of the same value?
- if (V1 == V2) return MustAlias;
+ // Because we look 'through' phi nodes we could look at "Value" pointers from
+ // different iterations. We must therefore make sure that this is not the
+ // case. The function isValueEqualInPotentialCycles ensures that this cannot
+ // happen by looking at the visited phi nodes and making sure they cannot
+ // reach the value.
+ if (isValueEqualInPotentialCycles(V1, V2))
+ return MustAlias;
if (!V1->getType()->isPointerTy() || !V2->getType()->isPointerTy())
- return NoAlias; // Scalars cannot alias each other
+ 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, *DL, MaxLookupSearchDepth);
+ const Value *O2 = GetUnderlyingObject(V2, *DL, MaxLookupSearchDepth);
// Null values in the default address space don't point to any object, so they
// don't alias any other pointer.
(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)))))
+ // Function arguments can't alias with things that are known to be
+ // unambigously identified at the function level.
+ if ((isa<Argument>(O1) && isIdentifiedFunctionLocal(O2)) ||
+ (isa<Argument>(O2) && isIdentifiedFunctionLocal(O1)))
return NoAlias;
// Most objects can't alias null.
if ((isa<ConstantPointerNull>(O2) && isKnownNonNull(O1)) ||
(isa<ConstantPointerNull>(O1) && isKnownNonNull(O2)))
return NoAlias;
-
+
// If one pointer is the result of a call/invoke or load and the other is a
// non-escaping local object within the same function, then we know the
// object couldn't escape to a point where the call could return it.
// 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 (DL)
+ if ((V1Size != MemoryLocation::UnknownSize &&
+ isObjectSmallerThan(O2, V1Size, *DL, *TLI)) ||
+ (V2Size != MemoryLocation::UnknownSize &&
+ isObjectSmallerThan(O1, V2Size, *DL, *TLI)))
return NoAlias;
-
+
+ // Check the cache before climbing up use-def chains. This also terminates
+ // otherwise infinitely recursive queries.
+ LocPair Locs(MemoryLocation(V1, V1Size, V1AAInfo),
+ MemoryLocation(V2, V2Size, V2AAInfo));
+ if (V1 > V2)
+ std::swap(Locs.first, Locs.second);
+ std::pair<AliasCacheTy::iterator, bool> Pair =
+ AliasCache.insert(std::make_pair(Locs, MayAlias));
+ if (!Pair.second)
+ return Pair.first->second;
+
// FIXME: This isn't aggressively handling alias(GEP, PHI) for example: if the
// GEP can't simplify, we don't even look at the PHI cases.
if (!isa<GEPOperator>(V1) && isa<GEPOperator>(V2)) {
std::swap(V1, V2);
std::swap(V1Size, V2Size);
std::swap(O1, O2);
+ std::swap(V1AAInfo, V2AAInfo);
+ }
+ if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) {
+ AliasResult Result =
+ aliasGEP(GV1, V1Size, V1AAInfo, V2, V2Size, V2AAInfo, O1, O2);
+ if (Result != MayAlias)
+ return AliasCache[Locs] = Result;
}
- if (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(V1AAInfo, V2AAInfo);
+ }
+ if (const PHINode *PN = dyn_cast<PHINode>(V1)) {
+ AliasResult Result = aliasPHI(PN, V1Size, V1AAInfo, V2, V2Size, V2AAInfo);
+ if (Result != MayAlias)
+ return AliasCache[Locs] = Result;
}
- if (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(V1AAInfo, V2AAInfo);
+ }
+ if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) {
+ AliasResult Result =
+ aliasSelect(S1, V1Size, V1AAInfo, V2, V2Size, V2AAInfo);
+ if (Result != MayAlias)
+ return AliasCache[Locs] = Result;
}
- if (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 (DL && O1 == O2)
+ if ((V1Size != MemoryLocation::UnknownSize &&
+ isObjectSize(O1, V1Size, *DL, *TLI)) ||
+ (V2Size != MemoryLocation::UnknownSize &&
+ isObjectSize(O2, V2Size, *DL, *TLI)))
+ return AliasCache[Locs] = PartialAlias;
+
+ AliasResult Result =
+ AliasAnalysis::alias(MemoryLocation(V1, V1Size, V1AAInfo),
+ MemoryLocation(V2, V2Size, V2AAInfo));
+ return AliasCache[Locs] = Result;
+}
+
+/// Check whether two Values can be considered equivalent.
+///
+/// In addition to pointer equivalence of \p V1 and \p V2 this checks whether
+/// they can not be part of a cycle in the value graph by looking at all
+/// visited phi nodes an making sure that the phis cannot reach the value. We
+/// have to do this because we are looking through phi nodes (That is we say
+/// noalias(V, phi(VA, VB)) if noalias(V, VA) and noalias(V, VB).
+bool BasicAliasAnalysis::isValueEqualInPotentialCycles(const Value *V,
+ const Value *V2) {
+ if (V != V2)
+ return false;
+
+ const Instruction *Inst = dyn_cast<Instruction>(V);
+ if (!Inst)
+ return true;
+
+ if (VisitedPhiBBs.empty())
+ return true;
+
+ if (VisitedPhiBBs.size() > MaxNumPhiBBsValueReachabilityCheck)
+ return false;
+
+ // Use dominance or loop info if available.
+ DominatorTreeWrapperPass *DTWP =
+ getAnalysisIfAvailable<DominatorTreeWrapperPass>();
+ DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr;
+ auto *LIWP = getAnalysisIfAvailable<LoopInfoWrapperPass>();
+ LoopInfo *LI = LIWP ? &LIWP->getLoopInfo() : nullptr;
+
+ // Make sure that the visited phis cannot reach the Value. This ensures that
+ // the Values cannot come from different iterations of a potential cycle the
+ // phi nodes could be involved in.
+ for (auto *P : VisitedPhiBBs)
+ if (isPotentiallyReachable(P->begin(), Inst, DT, LI))
+ return false;
+
+ return true;
+}
+
+/// Computes the symbolic difference between two de-composed GEPs.
+///
+/// Dest and Src are the variable indices from two decomposed GetElementPtr
+/// instructions GEP1 and GEP2 which have common base pointers.
+void BasicAliasAnalysis::GetIndexDifference(
+ SmallVectorImpl<VariableGEPIndex> &Dest,
+ const SmallVectorImpl<VariableGEPIndex> &Src) {
+ if (Src.empty())
+ return;
+
+ for (unsigned i = 0, e = Src.size(); i != e; ++i) {
+ const Value *V = Src[i].V;
+ unsigned ZExtBits = Src[i].ZExtBits, SExtBits = Src[i].SExtBits;
+ int64_t Scale = Src[i].Scale;
+
+ // Find V in Dest. This is N^2, but pointer indices almost never have more
+ // than a few variable indexes.
+ for (unsigned j = 0, e = Dest.size(); j != e; ++j) {
+ if (!isValueEqualInPotentialCycles(Dest[j].V, V) ||
+ Dest[j].ZExtBits != ZExtBits || Dest[j].SExtBits != SExtBits)
+ continue;
+
+ // If we found it, subtract off Scale V's from the entry in Dest. If it
+ // goes to zero, remove the entry.
+ if (Dest[j].Scale != Scale)
+ Dest[j].Scale -= Scale;
+ else
+ Dest.erase(Dest.begin() + j);
+ Scale = 0;
+ break;
+ }
+
+ // If we didn't consume this entry, add it to the end of the Dest list.
+ if (Scale) {
+ VariableGEPIndex Entry = {V, ZExtBits, SExtBits, -Scale};
+ Dest.push_back(Entry);
+ }
+ }
}
-// Make sure that anything that uses AliasAnalysis pulls in this file.
-DEFINING_FILE_FOR(BasicAliasAnalysis)
+bool BasicAliasAnalysis::constantOffsetHeuristic(
+ const SmallVectorImpl<VariableGEPIndex> &VarIndices, uint64_t V1Size,
+ uint64_t V2Size, int64_t BaseOffset, const DataLayout *DL,
+ AssumptionCache *AC, DominatorTree *DT) {
+ if (VarIndices.size() != 2 || V1Size == MemoryLocation::UnknownSize ||
+ V2Size == MemoryLocation::UnknownSize || !DL)
+ return false;
+
+ const VariableGEPIndex &Var0 = VarIndices[0], &Var1 = VarIndices[1];
+
+ if (Var0.ZExtBits != Var1.ZExtBits || Var0.SExtBits != Var1.SExtBits ||
+ Var0.Scale != -Var1.Scale)
+ return false;
+
+ unsigned Width = Var1.V->getType()->getIntegerBitWidth();
+
+ // We'll strip off the Extensions of Var0 and Var1 and do another round
+ // of GetLinearExpression decomposition. In the example above, if Var0
+ // is zext(%x + 1) we should get V1 == %x and V1Offset == 1.
+
+ APInt V0Scale(Width, 0), V0Offset(Width, 0), V1Scale(Width, 0),
+ V1Offset(Width, 0);
+ bool NSW = true, NUW = true;
+ unsigned V0ZExtBits = 0, V0SExtBits = 0, V1ZExtBits = 0, V1SExtBits = 0;
+ const Value *V0 = GetLinearExpression(Var0.V, V0Scale, V0Offset, V0ZExtBits,
+ V0SExtBits, *DL, 0, AC, DT, NSW, NUW);
+ NSW = true, NUW = true;
+ const Value *V1 = GetLinearExpression(Var1.V, V1Scale, V1Offset, V1ZExtBits,
+ V1SExtBits, *DL, 0, AC, DT, NSW, NUW);
+
+ if (V0Scale != V1Scale || V0ZExtBits != V1ZExtBits ||
+ V0SExtBits != V1SExtBits || !isValueEqualInPotentialCycles(V0, V1))
+ return false;
+
+ // We have a hit - Var0 and Var1 only differ by a constant offset!
+
+ // If we've been sext'ed then zext'd the maximum difference between Var0 and
+ // Var1 is possible to calculate, but we're just interested in the absolute
+ // minumum difference between the two. The minimum distance may occur due to
+ // wrapping; consider "add i3 %i, 5": if %i == 7 then 7 + 5 mod 8 == 4, and so
+ // the minimum distance between %i and %i + 5 is 3.
+ APInt MinDiff = V0Offset - V1Offset,
+ Wrapped = APInt::getMaxValue(Width) - MinDiff + APInt(Width, 1);
+ MinDiff = APIntOps::umin(MinDiff, Wrapped);
+ uint64_t MinDiffBytes = MinDiff.getZExtValue() * std::abs(Var0.Scale);
+
+ // We can't definitely say whether GEP1 is before or after V2 due to wrapping
+ // arithmetic (i.e. for some values of GEP1 and V2 GEP1 < V2, and for other
+ // values GEP1 > V2). We'll therefore only declare NoAlias if both V1Size and
+ // V2Size can fit in the MinDiffBytes gap.
+ return V1Size + std::abs(BaseOffset) <= MinDiffBytes &&
+ V2Size + std::abs(BaseOffset) <= MinDiffBytes;
+}
projects / oota-llvm.git / blobdiff