1119 lines
42 KiB
C++
1119 lines
42 KiB
C++
//===- BasicAliasAnalysis.cpp - Stateless Alias Analysis Impl -------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the primary stateless implementation of the
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// Alias Analysis interface that implements identities (two different
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// globals cannot alias, etc), but does no stateful analysis.
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/Passes.h"
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#include "llvm/Constants.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Function.h"
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#include "llvm/GlobalAlias.h"
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#include "llvm/GlobalVariable.h"
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#include "llvm/Instructions.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/LLVMContext.h"
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#include "llvm/Operator.h"
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#include "llvm/Pass.h"
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#include "llvm/Analysis/CaptureTracking.h"
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#include "llvm/Analysis/MemoryBuiltins.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/Target/TargetData.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/Support/ErrorHandling.h"
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#include "llvm/Support/GetElementPtrTypeIterator.h"
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#include <algorithm>
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using namespace llvm;
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//===----------------------------------------------------------------------===//
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// Useful predicates
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//===----------------------------------------------------------------------===//
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/// isKnownNonNull - Return true if we know that the specified value is never
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/// null.
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static bool isKnownNonNull(const Value *V) {
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// Alloca never returns null, malloc might.
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if (isa<AllocaInst>(V)) return true;
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// A byval argument is never null.
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if (const Argument *A = dyn_cast<Argument>(V))
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return A->hasByValAttr();
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// Global values are not null unless extern weak.
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if (const GlobalValue *GV = dyn_cast<GlobalValue>(V))
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return !GV->hasExternalWeakLinkage();
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return false;
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}
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/// isNonEscapingLocalObject - Return true if the pointer is to a function-local
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/// object that never escapes from the function.
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static bool isNonEscapingLocalObject(const Value *V) {
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// If this is a local allocation, check to see if it escapes.
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if (isa<AllocaInst>(V) || isNoAliasCall(V))
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// Set StoreCaptures to True so that we can assume in our callers that the
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// pointer is not the result of a load instruction. Currently
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// PointerMayBeCaptured doesn't have any special analysis for the
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// StoreCaptures=false case; if it did, our callers could be refined to be
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// more precise.
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return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
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// If this is an argument that corresponds to a byval or noalias argument,
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// then it has not escaped before entering the function. Check if it escapes
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// inside the function.
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if (const Argument *A = dyn_cast<Argument>(V))
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if (A->hasByValAttr() || A->hasNoAliasAttr()) {
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// Don't bother analyzing arguments already known not to escape.
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if (A->hasNoCaptureAttr())
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return true;
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return !PointerMayBeCaptured(V, false, /*StoreCaptures=*/true);
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}
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return false;
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}
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/// isEscapeSource - Return true if the pointer is one which would have
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/// been considered an escape by isNonEscapingLocalObject.
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static bool isEscapeSource(const Value *V) {
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if (isa<CallInst>(V) || isa<InvokeInst>(V) || isa<Argument>(V))
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return true;
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// The load case works because isNonEscapingLocalObject considers all
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// stores to be escapes (it passes true for the StoreCaptures argument
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// to PointerMayBeCaptured).
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if (isa<LoadInst>(V))
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return true;
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return false;
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}
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/// isObjectSmallerThan - Return true if we can prove that the object specified
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/// by V is smaller than Size.
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static bool isObjectSmallerThan(const Value *V, uint64_t Size,
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const TargetData &TD) {
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const Type *AccessTy;
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if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(V)) {
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AccessTy = GV->getType()->getElementType();
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} else if (const AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
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if (!AI->isArrayAllocation())
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AccessTy = AI->getType()->getElementType();
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else
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return false;
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} else if (const CallInst* CI = extractMallocCall(V)) {
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if (!isArrayMalloc(V, &TD))
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// The size is the argument to the malloc call.
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if (const ConstantInt* C = dyn_cast<ConstantInt>(CI->getArgOperand(0)))
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return (C->getZExtValue() < Size);
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return false;
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} else if (const Argument *A = dyn_cast<Argument>(V)) {
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if (A->hasByValAttr())
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AccessTy = cast<PointerType>(A->getType())->getElementType();
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else
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return false;
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} else {
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return false;
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}
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if (AccessTy->isSized())
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return TD.getTypeAllocSize(AccessTy) < Size;
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return false;
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}
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//===----------------------------------------------------------------------===//
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// GetElementPtr Instruction Decomposition and Analysis
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//===----------------------------------------------------------------------===//
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namespace {
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enum ExtensionKind {
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EK_NotExtended,
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EK_SignExt,
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EK_ZeroExt
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};
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struct VariableGEPIndex {
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const Value *V;
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ExtensionKind Extension;
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int64_t Scale;
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};
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}
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/// GetLinearExpression - Analyze the specified value as a linear expression:
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/// "A*V + B", where A and B are constant integers. Return the scale and offset
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/// values as APInts and return V as a Value*, and return whether we looked
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/// through any sign or zero extends. The incoming Value is known to have
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/// IntegerType and it may already be sign or zero extended.
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///
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/// Note that this looks through extends, so the high bits may not be
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/// represented in the result.
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static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset,
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ExtensionKind &Extension,
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const TargetData &TD, unsigned Depth) {
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assert(V->getType()->isIntegerTy() && "Not an integer value");
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// Limit our recursion depth.
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if (Depth == 6) {
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Scale = 1;
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Offset = 0;
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return V;
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}
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if (BinaryOperator *BOp = dyn_cast<BinaryOperator>(V)) {
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if (ConstantInt *RHSC = dyn_cast<ConstantInt>(BOp->getOperand(1))) {
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switch (BOp->getOpcode()) {
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default: break;
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case Instruction::Or:
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// X|C == X+C if all the bits in C are unset in X. Otherwise we can't
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// analyze it.
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if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(), &TD))
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break;
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// FALL THROUGH.
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case Instruction::Add:
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V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
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TD, Depth+1);
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Offset += RHSC->getValue();
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return V;
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case Instruction::Mul:
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V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
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TD, Depth+1);
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Offset *= RHSC->getValue();
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Scale *= RHSC->getValue();
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return V;
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case Instruction::Shl:
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V = GetLinearExpression(BOp->getOperand(0), Scale, Offset, Extension,
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TD, Depth+1);
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Offset <<= RHSC->getValue().getLimitedValue();
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Scale <<= RHSC->getValue().getLimitedValue();
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return V;
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}
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}
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}
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// Since GEP indices are sign extended anyway, we don't care about the high
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// bits of a sign or zero extended value - just scales and offsets. The
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// extensions have to be consistent though.
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if ((isa<SExtInst>(V) && Extension != EK_ZeroExt) ||
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(isa<ZExtInst>(V) && Extension != EK_SignExt)) {
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Value *CastOp = cast<CastInst>(V)->getOperand(0);
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unsigned OldWidth = Scale.getBitWidth();
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unsigned SmallWidth = CastOp->getType()->getPrimitiveSizeInBits();
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Scale.trunc(SmallWidth);
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Offset.trunc(SmallWidth);
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Extension = isa<SExtInst>(V) ? EK_SignExt : EK_ZeroExt;
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Value *Result = GetLinearExpression(CastOp, Scale, Offset, Extension,
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TD, Depth+1);
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Scale.zext(OldWidth);
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Offset.zext(OldWidth);
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return Result;
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}
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Scale = 1;
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Offset = 0;
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return V;
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}
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/// DecomposeGEPExpression - If V is a symbolic pointer expression, decompose it
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/// into a base pointer with a constant offset and a number of scaled symbolic
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/// offsets.
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///
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/// The scaled symbolic offsets (represented by pairs of a Value* and a scale in
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/// the VarIndices vector) are Value*'s that are known to be scaled by the
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/// specified amount, but which may have other unrepresented high bits. As such,
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/// the gep cannot necessarily be reconstructed from its decomposed form.
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///
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/// When TargetData is around, this function is capable of analyzing everything
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/// that Value::getUnderlyingObject() can look through. When not, it just looks
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/// through pointer casts.
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///
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static const Value *
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DecomposeGEPExpression(const Value *V, int64_t &BaseOffs,
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SmallVectorImpl<VariableGEPIndex> &VarIndices,
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const TargetData *TD) {
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// Limit recursion depth to limit compile time in crazy cases.
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unsigned MaxLookup = 6;
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BaseOffs = 0;
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do {
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// See if this is a bitcast or GEP.
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const Operator *Op = dyn_cast<Operator>(V);
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if (Op == 0) {
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// The only non-operator case we can handle are GlobalAliases.
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if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
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if (!GA->mayBeOverridden()) {
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V = GA->getAliasee();
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continue;
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}
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}
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return V;
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}
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if (Op->getOpcode() == Instruction::BitCast) {
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V = Op->getOperand(0);
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continue;
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}
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const GEPOperator *GEPOp = dyn_cast<GEPOperator>(Op);
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if (GEPOp == 0)
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return V;
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// Don't attempt to analyze GEPs over unsized objects.
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if (!cast<PointerType>(GEPOp->getOperand(0)->getType())
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->getElementType()->isSized())
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return V;
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// If we are lacking TargetData information, we can't compute the offets of
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// elements computed by GEPs. However, we can handle bitcast equivalent
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// GEPs.
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if (TD == 0) {
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if (!GEPOp->hasAllZeroIndices())
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return V;
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V = GEPOp->getOperand(0);
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continue;
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}
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// Walk the indices of the GEP, accumulating them into BaseOff/VarIndices.
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gep_type_iterator GTI = gep_type_begin(GEPOp);
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for (User::const_op_iterator I = GEPOp->op_begin()+1,
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E = GEPOp->op_end(); I != E; ++I) {
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Value *Index = *I;
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// Compute the (potentially symbolic) offset in bytes for this index.
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if (const StructType *STy = dyn_cast<StructType>(*GTI++)) {
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// For a struct, add the member offset.
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unsigned FieldNo = cast<ConstantInt>(Index)->getZExtValue();
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if (FieldNo == 0) continue;
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BaseOffs += TD->getStructLayout(STy)->getElementOffset(FieldNo);
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continue;
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}
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// For an array/pointer, add the element offset, explicitly scaled.
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if (ConstantInt *CIdx = dyn_cast<ConstantInt>(Index)) {
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if (CIdx->isZero()) continue;
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BaseOffs += TD->getTypeAllocSize(*GTI)*CIdx->getSExtValue();
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continue;
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}
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uint64_t Scale = TD->getTypeAllocSize(*GTI);
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ExtensionKind Extension = EK_NotExtended;
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// If the integer type is smaller than the pointer size, it is implicitly
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// sign extended to pointer size.
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unsigned Width = cast<IntegerType>(Index->getType())->getBitWidth();
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if (TD->getPointerSizeInBits() > Width)
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Extension = EK_SignExt;
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// Use GetLinearExpression to decompose the index into a C1*V+C2 form.
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APInt IndexScale(Width, 0), IndexOffset(Width, 0);
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Index = GetLinearExpression(Index, IndexScale, IndexOffset, Extension,
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*TD, 0);
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// The GEP index scale ("Scale") scales C1*V+C2, yielding (C1*V+C2)*Scale.
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// This gives us an aggregate computation of (C1*Scale)*V + C2*Scale.
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BaseOffs += IndexOffset.getSExtValue()*Scale;
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Scale *= IndexScale.getSExtValue();
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// If we already had an occurrance of this index variable, merge this
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// scale into it. For example, we want to handle:
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// A[x][x] -> x*16 + x*4 -> x*20
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// This also ensures that 'x' only appears in the index list once.
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for (unsigned i = 0, e = VarIndices.size(); i != e; ++i) {
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if (VarIndices[i].V == Index &&
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VarIndices[i].Extension == Extension) {
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Scale += VarIndices[i].Scale;
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VarIndices.erase(VarIndices.begin()+i);
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break;
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}
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}
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// Make sure that we have a scale that makes sense for this target's
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// pointer size.
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if (unsigned ShiftBits = 64-TD->getPointerSizeInBits()) {
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Scale <<= ShiftBits;
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Scale = (int64_t)Scale >> ShiftBits;
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}
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if (Scale) {
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VariableGEPIndex Entry = {Index, Extension, Scale};
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VarIndices.push_back(Entry);
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}
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}
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// Analyze the base pointer next.
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V = GEPOp->getOperand(0);
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} while (--MaxLookup);
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// If the chain of expressions is too deep, just return early.
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return V;
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}
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/// GetIndexDifference - Dest and Src are the variable indices from two
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/// decomposed GetElementPtr instructions GEP1 and GEP2 which have common base
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/// pointers. Subtract the GEP2 indices from GEP1 to find the symbolic
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/// difference between the two pointers.
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static void GetIndexDifference(SmallVectorImpl<VariableGEPIndex> &Dest,
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const SmallVectorImpl<VariableGEPIndex> &Src) {
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if (Src.empty()) return;
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for (unsigned i = 0, e = Src.size(); i != e; ++i) {
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const Value *V = Src[i].V;
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ExtensionKind Extension = Src[i].Extension;
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int64_t Scale = Src[i].Scale;
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// Find V in Dest. This is N^2, but pointer indices almost never have more
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// than a few variable indexes.
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for (unsigned j = 0, e = Dest.size(); j != e; ++j) {
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if (Dest[j].V != V || Dest[j].Extension != Extension) continue;
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// If we found it, subtract off Scale V's from the entry in Dest. If it
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// goes to zero, remove the entry.
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if (Dest[j].Scale != Scale)
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Dest[j].Scale -= Scale;
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else
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Dest.erase(Dest.begin()+j);
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Scale = 0;
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break;
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}
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// If we didn't consume this entry, add it to the end of the Dest list.
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if (Scale) {
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VariableGEPIndex Entry = { V, Extension, -Scale };
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Dest.push_back(Entry);
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}
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}
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}
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//===----------------------------------------------------------------------===//
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// BasicAliasAnalysis Pass
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//===----------------------------------------------------------------------===//
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#ifndef NDEBUG
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static const Function *getParent(const Value *V) {
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if (const Instruction *inst = dyn_cast<Instruction>(V))
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return inst->getParent()->getParent();
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if (const Argument *arg = dyn_cast<Argument>(V))
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return arg->getParent();
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return NULL;
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}
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static bool notDifferentParent(const Value *O1, const Value *O2) {
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const Function *F1 = getParent(O1);
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const Function *F2 = getParent(O2);
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return !F1 || !F2 || F1 == F2;
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}
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#endif
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namespace {
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/// BasicAliasAnalysis - This is the primary alias analysis implementation.
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struct BasicAliasAnalysis : public ImmutablePass, public AliasAnalysis {
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static char ID; // Class identification, replacement for typeinfo
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BasicAliasAnalysis() : ImmutablePass(ID) {
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initializeBasicAliasAnalysisPass(*PassRegistry::getPassRegistry());
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}
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virtual void initializePass() {
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InitializeAliasAnalysis(this);
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}
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.addRequired<AliasAnalysis>();
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}
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virtual AliasResult alias(const Location &LocA,
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const Location &LocB) {
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assert(Visited.empty() && "Visited must be cleared after use!");
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assert(notDifferentParent(LocA.Ptr, LocB.Ptr) &&
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"BasicAliasAnalysis doesn't support interprocedural queries.");
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AliasResult Alias = aliasCheck(LocA.Ptr, LocA.Size, LocA.TBAATag,
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LocB.Ptr, LocB.Size, LocB.TBAATag);
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Visited.clear();
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return Alias;
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}
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virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
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const Location &Loc);
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virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
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ImmutableCallSite CS2) {
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// The AliasAnalysis base class has some smarts, lets use them.
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return AliasAnalysis::getModRefInfo(CS1, CS2);
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}
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/// pointsToConstantMemory - Chase pointers until we find a (constant
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/// global) or not.
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virtual bool pointsToConstantMemory(const Location &Loc, bool OrLocal);
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/// getModRefBehavior - Return the behavior when calling the given
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/// call site.
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virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS);
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/// getModRefBehavior - Return the behavior when calling the given function.
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/// For use when the call site is not known.
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virtual ModRefBehavior getModRefBehavior(const Function *F);
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/// getAdjustedAnalysisPointer - This method is used when a pass implements
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/// an analysis interface through multiple inheritance. If needed, it
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/// should override this to adjust the this pointer as needed for the
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/// specified pass info.
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virtual void *getAdjustedAnalysisPointer(const void *ID) {
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if (ID == &AliasAnalysis::ID)
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return (AliasAnalysis*)this;
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return this;
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}
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private:
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// Visited - Track instructions visited by a aliasPHI, aliasSelect(), and aliasGEP().
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SmallPtrSet<const Value*, 16> Visited;
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// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP
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// instruction against another.
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AliasResult aliasGEP(const GEPOperator *V1, uint64_t V1Size,
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const Value *V2, uint64_t V2Size,
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const MDNode *V2TBAAInfo,
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const Value *UnderlyingV1, const Value *UnderlyingV2);
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// aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI
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// instruction against another.
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AliasResult aliasPHI(const PHINode *PN, uint64_t PNSize,
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const MDNode *PNTBAAInfo,
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const Value *V2, uint64_t V2Size,
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|
const MDNode *V2TBAAInfo);
|
|
|
|
/// aliasSelect - Disambiguate a Select instruction against another value.
|
|
AliasResult aliasSelect(const SelectInst *SI, uint64_t SISize,
|
|
const MDNode *SITBAAInfo,
|
|
const Value *V2, uint64_t V2Size,
|
|
const MDNode *V2TBAAInfo);
|
|
|
|
AliasResult aliasCheck(const Value *V1, uint64_t V1Size,
|
|
const MDNode *V1TBAATag,
|
|
const Value *V2, uint64_t V2Size,
|
|
const MDNode *V2TBAATag);
|
|
};
|
|
} // End of anonymous namespace
|
|
|
|
// Register this pass...
|
|
char BasicAliasAnalysis::ID = 0;
|
|
INITIALIZE_AG_PASS(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 = Worklist.pop_back_val()->getUnderlyingObject();
|
|
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;
|
|
}
|
|
|
|
// 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
|
|
/// function, we really can't say much about this query. We do, however, use
|
|
/// simple "address taken" analysis on local objects.
|
|
AliasAnalysis::ModRefResult
|
|
BasicAliasAnalysis::getModRefInfo(ImmutableCallSite CS,
|
|
const Location &Loc) {
|
|
assert(notDifferentParent(CS.getInstruction(), Loc.Ptr) &&
|
|
"AliasAnalysis query involving multiple functions!");
|
|
|
|
const Value *Object = Loc.Ptr->getUnderlyingObject();
|
|
|
|
// If this is a tail call and Loc.Ptr points to a stack location, we know that
|
|
// the tail call cannot access or modify the local stack.
|
|
// We cannot exclude byval arguments here; these belong to the caller of
|
|
// the current function not to the current function, and a tail callee
|
|
// may reference them.
|
|
if (isa<AllocaInst>(Object))
|
|
if (const CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
|
|
if (CI->isTailCall())
|
|
return NoModRef;
|
|
|
|
// If the pointer is to a locally allocated object that does not escape,
|
|
// then the call can not mod/ref the pointer unless the call takes the pointer
|
|
// as an argument, and itself doesn't capture it.
|
|
if (!isa<Constant>(Object) && CS.getInstruction() != Object &&
|
|
isNonEscapingLocalObject(Object)) {
|
|
bool PassedAsArg = false;
|
|
unsigned ArgNo = 0;
|
|
for (ImmutableCallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
|
|
CI != CE; ++CI, ++ArgNo) {
|
|
// Only look at the no-capture pointer arguments.
|
|
if (!(*CI)->getType()->isPointerTy() ||
|
|
!CS.paramHasAttr(ArgNo+1, Attribute::NoCapture))
|
|
continue;
|
|
|
|
// If this is a no-capture pointer argument, see if we can tell that it
|
|
// is impossible to alias the pointer we're checking. If not, we have to
|
|
// assume that the call could touch the pointer, even though it doesn't
|
|
// escape.
|
|
if (!isNoAlias(Location(cast<Value>(CI)), Loc)) {
|
|
PassedAsArg = true;
|
|
break;
|
|
}
|
|
}
|
|
|
|
if (!PassedAsArg)
|
|
return NoModRef;
|
|
}
|
|
|
|
ModRefResult Min = ModRef;
|
|
|
|
// Finally, handle specific knowledge of intrinsics.
|
|
const IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction());
|
|
if (II != 0)
|
|
switch (II->getIntrinsicID()) {
|
|
default: break;
|
|
case Intrinsic::memcpy:
|
|
case Intrinsic::memmove: {
|
|
uint64_t Len = UnknownSize;
|
|
if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getArgOperand(2)))
|
|
Len = LenCI->getZExtValue();
|
|
Value *Dest = II->getArgOperand(0);
|
|
Value *Src = II->getArgOperand(1);
|
|
if (isNoAlias(Location(Dest, Len), Loc)) {
|
|
if (isNoAlias(Location(Src, Len), Loc))
|
|
return NoModRef;
|
|
Min = 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))) {
|
|
uint64_t Len = LenCI->getZExtValue();
|
|
Value *Dest = II->getArgOperand(0);
|
|
if (isNoAlias(Location(Dest, Len), Loc))
|
|
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);
|
|
uint64_t Op1Size = TD->getTypeStoreSize(Op1->getType());
|
|
MDNode *Tag = II->getMetadata(LLVMContext::MD_tbaa);
|
|
if (isNoAlias(Location(Op1, Op1Size, Tag), Loc))
|
|
return NoModRef;
|
|
}
|
|
break;
|
|
case Intrinsic::lifetime_start:
|
|
case Intrinsic::lifetime_end:
|
|
case Intrinsic::invariant_start: {
|
|
uint64_t PtrSize =
|
|
cast<ConstantInt>(II->getArgOperand(0))->getZExtValue();
|
|
if (isNoAlias(Location(II->getArgOperand(1),
|
|
PtrSize,
|
|
II->getMetadata(LLVMContext::MD_tbaa)),
|
|
Loc))
|
|
return NoModRef;
|
|
break;
|
|
}
|
|
case Intrinsic::invariant_end: {
|
|
uint64_t PtrSize =
|
|
cast<ConstantInt>(II->getArgOperand(1))->getZExtValue();
|
|
if (isNoAlias(Location(II->getArgOperand(2),
|
|
PtrSize,
|
|
II->getMetadata(LLVMContext::MD_tbaa)),
|
|
Loc))
|
|
return NoModRef;
|
|
break;
|
|
}
|
|
}
|
|
|
|
// The AliasAnalysis base class has some smarts, lets use them.
|
|
return ModRefResult(AliasAnalysis::getModRefInfo(CS, Loc) & Min);
|
|
}
|
|
|
|
/// 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, uint64_t V1Size,
|
|
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<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 (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) {
|
|
// Do the base pointers alias?
|
|
AliasResult BaseAlias = aliasCheck(UnderlyingV1, UnknownSize, 0,
|
|
UnderlyingV2, UnknownSize, 0);
|
|
|
|
// If we get a No or May, then return it immediately, no amount of analysis
|
|
// will improve this situation.
|
|
if (BaseAlias != MustAlias) return BaseAlias;
|
|
|
|
// Otherwise, we have a MustAlias. Since the base pointers alias each other
|
|
// exactly, see if the computed offset from the common pointer tells us
|
|
// about the relation of the resulting pointer.
|
|
const Value *GEP1BasePtr =
|
|
DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD);
|
|
|
|
int64_t GEP2BaseOffset;
|
|
SmallVector<VariableGEPIndex, 4> GEP2VariableIndices;
|
|
const Value *GEP2BasePtr =
|
|
DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD);
|
|
|
|
// 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.
|
|
if (GEP1BasePtr != UnderlyingV1 || GEP2BasePtr != UnderlyingV2) {
|
|
assert(TD == 0 &&
|
|
"DecomposeGEPExpression and getUnderlyingObject disagree!");
|
|
return MayAlias;
|
|
}
|
|
|
|
// Subtract the GEP2 pointer from the GEP1 pointer to find out their
|
|
// symbolic difference.
|
|
GEP1BaseOffset -= GEP2BaseOffset;
|
|
GetIndexDifference(GEP1VariableIndices, GEP2VariableIndices);
|
|
|
|
} else {
|
|
// Check to see if these two pointers are related by the getelementptr
|
|
// instruction. If one pointer is a GEP with a non-zero index of the other
|
|
// pointer, we know they cannot alias.
|
|
|
|
// If both accesses are unknown size, we can't do anything useful here.
|
|
if (V1Size == UnknownSize && V2Size == UnknownSize)
|
|
return MayAlias;
|
|
|
|
AliasResult R = aliasCheck(UnderlyingV1, UnknownSize, 0,
|
|
V2, V2Size, V2TBAAInfo);
|
|
if (R != MustAlias)
|
|
// If V2 may alias GEP base pointer, conservatively returns MayAlias.
|
|
// If V2 is known not to alias GEP base pointer, then the two values
|
|
// cannot alias per GEP semantics: "A pointer value formed from a
|
|
// getelementptr instruction is associated with the addresses associated
|
|
// with the first operand of the getelementptr".
|
|
return R;
|
|
|
|
const Value *GEP1BasePtr =
|
|
DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD);
|
|
|
|
// 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.
|
|
if (GEP1BasePtr != UnderlyingV1) {
|
|
assert(TD == 0 &&
|
|
"DecomposeGEPExpression and getUnderlyingObject disagree!");
|
|
return MayAlias;
|
|
}
|
|
}
|
|
|
|
// In the two GEP Case, if there is no difference in the offsets of the
|
|
// computed pointers, the resultant pointers are a must alias. This
|
|
// hapens when we have two lexically identical GEP's (for example).
|
|
//
|
|
// In the other case, if we have getelementptr <ptr>, 0, 0, 0, 0, ... and V2
|
|
// must aliases the GEP, the end result is a must alias also.
|
|
if (GEP1BaseOffset == 0 && GEP1VariableIndices.empty())
|
|
return MustAlias;
|
|
|
|
// If 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].Scale)
|
|
GEP1BaseOffset -= RemovedOffset*GEP1VariableIndices[i].Scale;
|
|
|
|
// If our known offset is bigger than the access size, we know we don't have
|
|
// an alias.
|
|
if (GEP1BaseOffset) {
|
|
if (GEP1BaseOffset >= 0 ?
|
|
(V2Size != UnknownSize && (uint64_t)GEP1BaseOffset >= V2Size) :
|
|
(V1Size != UnknownSize && -(uint64_t)GEP1BaseOffset >= V1Size &&
|
|
GEP1BaseOffset != INT64_MIN))
|
|
return NoAlias;
|
|
}
|
|
|
|
return MayAlias;
|
|
}
|
|
|
|
/// aliasSelect - Provide a bunch of ad-hoc rules to disambiguate a Select
|
|
/// instruction against another.
|
|
AliasAnalysis::AliasResult
|
|
BasicAliasAnalysis::aliasSelect(const SelectInst *SI, uint64_t SISize,
|
|
const MDNode *SITBAAInfo,
|
|
const Value *V2, uint64_t V2Size,
|
|
const MDNode *V2TBAAInfo) {
|
|
// If 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;
|
|
|
|
// If the values are Selects with the same condition, we can do a more precise
|
|
// check: just check for aliases between the values on corresponding arms.
|
|
if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2))
|
|
if (SI->getCondition() == SI2->getCondition()) {
|
|
AliasResult Alias =
|
|
aliasCheck(SI->getTrueValue(), SISize, SITBAAInfo,
|
|
SI2->getTrueValue(), V2Size, V2TBAAInfo);
|
|
if (Alias == MayAlias)
|
|
return MayAlias;
|
|
AliasResult ThisAlias =
|
|
aliasCheck(SI->getFalseValue(), SISize, SITBAAInfo,
|
|
SI2->getFalseValue(), V2Size, V2TBAAInfo);
|
|
if (ThisAlias != Alias)
|
|
return MayAlias;
|
|
return Alias;
|
|
}
|
|
|
|
// If both arms of the Select node NoAlias or MustAlias V2, then returns
|
|
// NoAlias / MustAlias. Otherwise, returns MayAlias.
|
|
AliasResult Alias =
|
|
aliasCheck(V2, V2Size, V2TBAAInfo, SI->getTrueValue(), SISize, SITBAAInfo);
|
|
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, V2TBAAInfo, SI->getFalseValue(), SISize, SITBAAInfo);
|
|
if (ThisAlias != Alias)
|
|
return MayAlias;
|
|
return Alias;
|
|
}
|
|
|
|
// aliasPHI - Provide a bunch of ad-hoc rules to disambiguate a PHI instruction
|
|
// against another.
|
|
AliasAnalysis::AliasResult
|
|
BasicAliasAnalysis::aliasPHI(const PHINode *PN, uint64_t PNSize,
|
|
const MDNode *PNTBAAInfo,
|
|
const Value *V2, uint64_t V2Size,
|
|
const MDNode *V2TBAAInfo) {
|
|
// The PHI node has already been visited, avoid recursion any further.
|
|
if (!Visited.insert(PN))
|
|
return MayAlias;
|
|
|
|
// 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, PNTBAAInfo,
|
|
PN2->getIncomingValueForBlock(PN->getIncomingBlock(0)),
|
|
V2Size, V2TBAAInfo);
|
|
if (Alias == MayAlias)
|
|
return MayAlias;
|
|
for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
AliasResult ThisAlias =
|
|
aliasCheck(PN->getIncomingValue(i), PNSize, PNTBAAInfo,
|
|
PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
|
|
V2Size, V2TBAAInfo);
|
|
if (ThisAlias != Alias)
|
|
return MayAlias;
|
|
}
|
|
return Alias;
|
|
}
|
|
|
|
SmallPtrSet<Value*, 4> UniqueSrc;
|
|
SmallVector<Value*, 4> V1Srcs;
|
|
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
Value *PV1 = PN->getIncomingValue(i);
|
|
if (isa<PHINode>(PV1))
|
|
// If any of the source itself is a PHI, return MayAlias conservatively
|
|
// to avoid compile time explosion. The worst possible case is if both
|
|
// sides are PHI nodes. In which case, this is O(m x n) time where 'm'
|
|
// and 'n' are the number of PHI sources.
|
|
return MayAlias;
|
|
if (UniqueSrc.insert(PV1))
|
|
V1Srcs.push_back(PV1);
|
|
}
|
|
|
|
AliasResult Alias = aliasCheck(V2, V2Size, V2TBAAInfo,
|
|
V1Srcs[0], PNSize, PNTBAAInfo);
|
|
// Early exit if the check of the first PHI source against V2 is MayAlias.
|
|
// Other results are not possible.
|
|
if (Alias == MayAlias)
|
|
return MayAlias;
|
|
|
|
// If all sources of the PHI node NoAlias or MustAlias V2, then returns
|
|
// NoAlias / MustAlias. Otherwise, returns MayAlias.
|
|
for (unsigned i = 1, e = V1Srcs.size(); i != e; ++i) {
|
|
Value *V = V1Srcs[i];
|
|
|
|
// 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, V2TBAAInfo,
|
|
V, PNSize, PNTBAAInfo);
|
|
if (ThisAlias != Alias || ThisAlias == MayAlias)
|
|
return MayAlias;
|
|
}
|
|
|
|
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, uint64_t V1Size,
|
|
const MDNode *V1TBAAInfo,
|
|
const Value *V2, uint64_t V2Size,
|
|
const MDNode *V2TBAAInfo) {
|
|
// If either of the memory references is empty, it doesn't matter what the
|
|
// pointer values are.
|
|
if (V1Size == 0 || V2Size == 0)
|
|
return NoAlias;
|
|
|
|
// Strip off any casts if they exist.
|
|
V1 = V1->stripPointerCasts();
|
|
V2 = V2->stripPointerCasts();
|
|
|
|
// Are we checking for alias of the same value?
|
|
if (V1 == V2) return MustAlias;
|
|
|
|
if (!V1->getType()->isPointerTy() || !V2->getType()->isPointerTy())
|
|
return NoAlias; // Scalars cannot alias each other
|
|
|
|
// Figure out what objects these things are pointing to if we can.
|
|
const Value *O1 = V1->getUnderlyingObject();
|
|
const Value *O2 = V2->getUnderlyingObject();
|
|
|
|
// Null values in the default address space don't point to any object, so they
|
|
// don't alias any other pointer.
|
|
if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O1))
|
|
if (CPN->getType()->getAddressSpace() == 0)
|
|
return NoAlias;
|
|
if (const ConstantPointerNull *CPN = dyn_cast<ConstantPointerNull>(O2))
|
|
if (CPN->getType()->getAddressSpace() == 0)
|
|
return NoAlias;
|
|
|
|
if (O1 != O2) {
|
|
// If V1/V2 point to two different objects we know that we have no alias.
|
|
if (isIdentifiedObject(O1) && isIdentifiedObject(O2))
|
|
return NoAlias;
|
|
|
|
// Constant pointers can't alias with non-const isIdentifiedObject objects.
|
|
if ((isa<Constant>(O1) && isIdentifiedObject(O2) && !isa<Constant>(O2)) ||
|
|
(isa<Constant>(O2) && isIdentifiedObject(O1) && !isa<Constant>(O1)))
|
|
return NoAlias;
|
|
|
|
// Arguments can't alias with local allocations or noalias calls
|
|
// in the same function.
|
|
if (((isa<Argument>(O1) && (isa<AllocaInst>(O2) || isNoAliasCall(O2))) ||
|
|
(isa<Argument>(O2) && (isa<AllocaInst>(O1) || isNoAliasCall(O1)))))
|
|
return NoAlias;
|
|
|
|
// Most objects can't alias null.
|
|
if ((isa<ConstantPointerNull>(O2) && isKnownNonNull(O1)) ||
|
|
(isa<ConstantPointerNull>(O1) && isKnownNonNull(O2)))
|
|
return NoAlias;
|
|
|
|
// If one pointer is the result of a call/invoke or load and the other is a
|
|
// non-escaping local object within the same function, then we know the
|
|
// object couldn't escape to a point where the call could return it.
|
|
//
|
|
// Note that if the pointers are in different functions, there are a
|
|
// variety of complications. A call with a nocapture argument may still
|
|
// temporary store the nocapture argument's value in a temporary memory
|
|
// location if that memory location doesn't escape. Or it may pass a
|
|
// nocapture value to other functions as long as they don't capture it.
|
|
if (isEscapeSource(O1) && isNonEscapingLocalObject(O2))
|
|
return NoAlias;
|
|
if (isEscapeSource(O2) && isNonEscapingLocalObject(O1))
|
|
return NoAlias;
|
|
}
|
|
|
|
// If the size of one access is larger than the entire object on the other
|
|
// side, then we know such behavior is undefined and can assume no alias.
|
|
if (TD)
|
|
if ((V1Size != UnknownSize && isObjectSmallerThan(O2, V1Size, *TD)) ||
|
|
(V2Size != UnknownSize && isObjectSmallerThan(O1, V2Size, *TD)))
|
|
return NoAlias;
|
|
|
|
// 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);
|
|
}
|
|
if (const GEPOperator *GV1 = dyn_cast<GEPOperator>(V1)) {
|
|
AliasResult Result = aliasGEP(GV1, V1Size, V2, V2Size, V2TBAAInfo, O1, O2);
|
|
if (Result != MayAlias) return Result;
|
|
}
|
|
|
|
if (isa<PHINode>(V2) && !isa<PHINode>(V1)) {
|
|
std::swap(V1, V2);
|
|
std::swap(V1Size, V2Size);
|
|
}
|
|
if (const PHINode *PN = dyn_cast<PHINode>(V1)) {
|
|
AliasResult Result = aliasPHI(PN, V1Size, V1TBAAInfo,
|
|
V2, V2Size, V2TBAAInfo);
|
|
if (Result != MayAlias) return Result;
|
|
}
|
|
|
|
if (isa<SelectInst>(V2) && !isa<SelectInst>(V1)) {
|
|
std::swap(V1, V2);
|
|
std::swap(V1Size, V2Size);
|
|
}
|
|
if (const SelectInst *S1 = dyn_cast<SelectInst>(V1)) {
|
|
AliasResult Result = aliasSelect(S1, V1Size, V1TBAAInfo,
|
|
V2, V2Size, V2TBAAInfo);
|
|
if (Result != MayAlias) return Result;
|
|
}
|
|
|
|
return AliasAnalysis::alias(Location(V1, V1Size, V1TBAAInfo),
|
|
Location(V2, V2Size, V2TBAAInfo));
|
|
}
|