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and T->isPointerTy(). Convert most instances of the first form to the second form. Requested by Chris. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@96344 91177308-0d34-0410-b5e6-96231b3b80d8
754 lines
29 KiB
C++
754 lines
29 KiB
C++
//===- BasicAliasAnalysis.cpp - Local 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 default implementation of the Alias Analysis interface
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// that simply implements a few identities (two different globals cannot alias,
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// etc), but otherwise does no 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/GlobalVariable.h"
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#include "llvm/Instructions.h"
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#include "llvm/IntrinsicInst.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 <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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/// 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, unsigned 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->getOperand(1)))
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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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// NoAA Pass
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//===----------------------------------------------------------------------===//
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namespace {
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/// NoAA - This class implements the -no-aa pass, which always returns "I
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/// don't know" for alias queries. NoAA is unlike other alias analysis
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/// implementations, in that it does not chain to a previous analysis. As
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/// such it doesn't follow many of the rules that other alias analyses must.
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///
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struct NoAA : public ImmutablePass, public AliasAnalysis {
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static char ID; // Class identification, replacement for typeinfo
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NoAA() : ImmutablePass(&ID) {}
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explicit NoAA(void *PID) : ImmutablePass(PID) { }
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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}
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virtual void initializePass() {
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TD = getAnalysisIfAvailable<TargetData>();
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}
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virtual AliasResult alias(const Value *V1, unsigned V1Size,
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const Value *V2, unsigned V2Size) {
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return MayAlias;
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}
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virtual void getArgumentAccesses(Function *F, CallSite CS,
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std::vector<PointerAccessInfo> &Info) {
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llvm_unreachable("This method may not be called on this function!");
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}
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virtual bool pointsToConstantMemory(const Value *P) { return false; }
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virtual ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size) {
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return ModRef;
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}
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virtual ModRefResult getModRefInfo(CallSite CS1, CallSite CS2) {
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return ModRef;
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}
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virtual void deleteValue(Value *V) {}
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virtual void copyValue(Value *From, Value *To) {}
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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 should
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/// override this to adjust the this pointer as needed for the specified pass
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/// info.
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virtual void *getAdjustedAnalysisPointer(const PassInfo *PI) {
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if (PI->isPassID(&AliasAnalysis::ID))
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return (AliasAnalysis*)this;
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return this;
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}
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};
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} // End of anonymous namespace
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// Register this pass...
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char NoAA::ID = 0;
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static RegisterPass<NoAA>
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U("no-aa", "No Alias Analysis (always returns 'may' alias)", true, true);
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// Declare that we implement the AliasAnalysis interface
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static RegisterAnalysisGroup<AliasAnalysis> V(U);
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ImmutablePass *llvm::createNoAAPass() { return new NoAA(); }
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//===----------------------------------------------------------------------===//
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// BasicAA Pass
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//===----------------------------------------------------------------------===//
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namespace {
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/// BasicAliasAnalysis - This is the default alias analysis implementation.
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/// Because it doesn't chain to a previous alias analysis (like -no-aa), it
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/// derives from the NoAA class.
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struct BasicAliasAnalysis : public NoAA {
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static char ID; // Class identification, replacement for typeinfo
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BasicAliasAnalysis() : NoAA(&ID) {}
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AliasResult alias(const Value *V1, unsigned V1Size,
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const Value *V2, unsigned V2Size) {
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assert(VisitedPHIs.empty() && "VisitedPHIs must be cleared after use!");
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AliasResult Alias = aliasCheck(V1, V1Size, V2, V2Size);
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VisitedPHIs.clear();
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return Alias;
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}
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ModRefResult getModRefInfo(CallSite CS, Value *P, unsigned Size);
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ModRefResult getModRefInfo(CallSite CS1, CallSite CS2);
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/// pointsToConstantMemory - Chase pointers until we find a (constant
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/// global) or not.
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bool pointsToConstantMemory(const Value *P);
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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 should
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/// override this to adjust the this pointer as needed for the specified pass
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/// info.
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virtual void *getAdjustedAnalysisPointer(const PassInfo *PI) {
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if (PI->isPassID(&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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// VisitedPHIs - Track PHI nodes visited by a aliasCheck() call.
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SmallPtrSet<const Value*, 16> VisitedPHIs;
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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, unsigned V1Size,
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const Value *V2, unsigned V2Size,
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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, unsigned PNSize,
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const Value *V2, unsigned V2Size);
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/// aliasSelect - Disambiguate a Select instruction against another value.
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AliasResult aliasSelect(const SelectInst *SI, unsigned SISize,
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const Value *V2, unsigned V2Size);
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AliasResult aliasCheck(const Value *V1, unsigned V1Size,
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const Value *V2, unsigned V2Size);
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};
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} // End of anonymous namespace
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// Register this pass...
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char BasicAliasAnalysis::ID = 0;
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static RegisterPass<BasicAliasAnalysis>
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X("basicaa", "Basic Alias Analysis (default AA impl)", false, true);
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// Declare that we implement the AliasAnalysis interface
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static RegisterAnalysisGroup<AliasAnalysis, true> Y(X);
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ImmutablePass *llvm::createBasicAliasAnalysisPass() {
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return new BasicAliasAnalysis();
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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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bool BasicAliasAnalysis::pointsToConstantMemory(const Value *P) {
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if (const GlobalVariable *GV =
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dyn_cast<GlobalVariable>(P->getUnderlyingObject()))
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// Note: this doesn't require GV to be "ODR" because it isn't legal for a
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// global to be marked constant in some modules and non-constant in others.
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// GV may even be a declaration, not a definition.
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return GV->isConstant();
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return false;
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}
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/// getModRefInfo - Check to see if the specified callsite can clobber the
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/// specified memory object. Since we only look at local properties of this
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/// function, we really can't say much about this query. We do, however, use
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/// simple "address taken" analysis on local objects.
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AliasAnalysis::ModRefResult
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BasicAliasAnalysis::getModRefInfo(CallSite CS, Value *P, unsigned Size) {
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const Value *Object = P->getUnderlyingObject();
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// If this is a tail call and P points to a stack location, we know that
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// the tail call cannot access or modify the local stack.
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// We cannot exclude byval arguments here; these belong to the caller of
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// the current function not to the current function, and a tail callee
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// may reference them.
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if (isa<AllocaInst>(Object))
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if (CallInst *CI = dyn_cast<CallInst>(CS.getInstruction()))
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if (CI->isTailCall())
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return NoModRef;
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// If the pointer is to a locally allocated object that does not escape,
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// then the call can not mod/ref the pointer unless the call takes the pointer
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// as an argument, and itself doesn't capture it.
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if (!isa<Constant>(Object) && CS.getInstruction() != Object &&
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isNonEscapingLocalObject(Object)) {
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bool PassedAsArg = false;
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unsigned ArgNo = 0;
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for (CallSite::arg_iterator CI = CS.arg_begin(), CE = CS.arg_end();
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CI != CE; ++CI, ++ArgNo) {
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// Only look at the no-capture pointer arguments.
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if (!(*CI)->getType()->isPointerTy() ||
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!CS.paramHasAttr(ArgNo+1, Attribute::NoCapture))
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continue;
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// If this is a no-capture pointer argument, see if we can tell that it
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// is impossible to alias the pointer we're checking. If not, we have to
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// assume that the call could touch the pointer, even though it doesn't
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// escape.
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if (!isNoAlias(cast<Value>(CI), ~0U, P, ~0U)) {
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PassedAsArg = true;
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break;
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}
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}
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if (!PassedAsArg)
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return NoModRef;
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}
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// Finally, handle specific knowledge of intrinsics.
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IntrinsicInst *II = dyn_cast<IntrinsicInst>(CS.getInstruction());
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if (II == 0)
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return AliasAnalysis::getModRefInfo(CS, P, Size);
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switch (II->getIntrinsicID()) {
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default: break;
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case Intrinsic::memcpy:
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case Intrinsic::memmove: {
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unsigned Len = ~0U;
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if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getOperand(3)))
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Len = LenCI->getZExtValue();
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Value *Dest = II->getOperand(1);
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Value *Src = II->getOperand(2);
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if (isNoAlias(Dest, Len, P, Size)) {
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if (isNoAlias(Src, Len, P, Size))
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return NoModRef;
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return Ref;
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}
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break;
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}
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case Intrinsic::memset:
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// Since memset is 'accesses arguments' only, the AliasAnalysis base class
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// will handle it for the variable length case.
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if (ConstantInt *LenCI = dyn_cast<ConstantInt>(II->getOperand(3))) {
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unsigned Len = LenCI->getZExtValue();
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Value *Dest = II->getOperand(1);
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if (isNoAlias(Dest, Len, P, Size))
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return NoModRef;
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}
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break;
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case Intrinsic::atomic_cmp_swap:
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case Intrinsic::atomic_swap:
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case Intrinsic::atomic_load_add:
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case Intrinsic::atomic_load_sub:
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case Intrinsic::atomic_load_and:
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case Intrinsic::atomic_load_nand:
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case Intrinsic::atomic_load_or:
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case Intrinsic::atomic_load_xor:
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case Intrinsic::atomic_load_max:
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case Intrinsic::atomic_load_min:
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case Intrinsic::atomic_load_umax:
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case Intrinsic::atomic_load_umin:
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if (TD) {
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Value *Op1 = II->getOperand(1);
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unsigned Op1Size = TD->getTypeStoreSize(Op1->getType());
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if (isNoAlias(Op1, Op1Size, P, Size))
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return NoModRef;
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}
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break;
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case Intrinsic::lifetime_start:
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case Intrinsic::lifetime_end:
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case Intrinsic::invariant_start: {
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unsigned PtrSize = cast<ConstantInt>(II->getOperand(1))->getZExtValue();
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if (isNoAlias(II->getOperand(2), PtrSize, P, Size))
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return NoModRef;
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break;
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}
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case Intrinsic::invariant_end: {
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unsigned PtrSize = cast<ConstantInt>(II->getOperand(2))->getZExtValue();
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if (isNoAlias(II->getOperand(3), PtrSize, P, Size))
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return NoModRef;
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break;
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}
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}
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// The AliasAnalysis base class has some smarts, lets use them.
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return AliasAnalysis::getModRefInfo(CS, P, Size);
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}
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AliasAnalysis::ModRefResult
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BasicAliasAnalysis::getModRefInfo(CallSite CS1, CallSite CS2) {
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// If CS1 or CS2 are readnone, they don't interact.
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ModRefBehavior CS1B = AliasAnalysis::getModRefBehavior(CS1);
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if (CS1B == DoesNotAccessMemory) return NoModRef;
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ModRefBehavior CS2B = AliasAnalysis::getModRefBehavior(CS2);
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if (CS2B == DoesNotAccessMemory) return NoModRef;
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// If they both only read from memory, just return ref.
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if (CS1B == OnlyReadsMemory && CS2B == OnlyReadsMemory)
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return Ref;
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// Otherwise, fall back to NoAA (mod+ref).
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return NoAA::getModRefInfo(CS1, CS2);
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}
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/// GetIndiceDifference - 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 GetIndiceDifference(
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SmallVectorImpl<std::pair<const Value*, int64_t> > &Dest,
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const SmallVectorImpl<std::pair<const Value*, int64_t> > &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].first;
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int64_t Scale = Src[i].second;
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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].first != V) 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].second != Scale)
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Dest[j].second -= 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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Dest.push_back(std::make_pair(V, -Scale));
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}
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}
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/// aliasGEP - Provide a bunch of ad-hoc rules to disambiguate a GEP instruction
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/// against another pointer. We know that V1 is a GEP, but we don't know
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/// anything about V2. UnderlyingV1 is GEP1->getUnderlyingObject(),
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/// UnderlyingV2 is the same for V2.
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///
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AliasAnalysis::AliasResult
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BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, unsigned V1Size,
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const Value *V2, unsigned V2Size,
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const Value *UnderlyingV1,
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const Value *UnderlyingV2) {
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int64_t GEP1BaseOffset;
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SmallVector<std::pair<const Value*, int64_t>, 4> GEP1VariableIndices;
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// If we have two gep instructions with must-alias'ing base pointers, figure
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// out if the indexes to the GEP tell us anything about the derived pointer.
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if (const GEPOperator *GEP2 = dyn_cast<GEPOperator>(V2)) {
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// Do the base pointers alias?
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AliasResult BaseAlias = aliasCheck(UnderlyingV1, ~0U, UnderlyingV2, ~0U);
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// If we get a No or May, then return it immediately, no amount of analysis
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// will improve this situation.
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if (BaseAlias != MustAlias) return BaseAlias;
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// Otherwise, we have a MustAlias. Since the base pointers alias each other
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// exactly, see if the computed offset from the common pointer tells us
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// about the relation of the resulting pointer.
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const Value *GEP1BasePtr =
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DecomposeGEPExpression(GEP1, GEP1BaseOffset, GEP1VariableIndices, TD);
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int64_t GEP2BaseOffset;
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SmallVector<std::pair<const Value*, int64_t>, 4> GEP2VariableIndices;
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const Value *GEP2BasePtr =
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DecomposeGEPExpression(GEP2, GEP2BaseOffset, GEP2VariableIndices, TD);
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// If DecomposeGEPExpression isn't able to look all the way through the
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// addressing operation, we must not have TD and this is too complex for us
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// to handle without it.
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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;
|
|
GetIndiceDifference(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 == ~0U && V2Size == ~0U)
|
|
return MayAlias;
|
|
|
|
AliasResult R = aliasCheck(UnderlyingV1, ~0U, V2, V2Size);
|
|
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].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)
|
|
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, unsigned SISize,
|
|
const Value *V2, unsigned V2Size) {
|
|
// 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);
|
|
if (Alias == MayAlias)
|
|
return MayAlias;
|
|
AliasResult ThisAlias =
|
|
aliasCheck(SI->getFalseValue(), SISize,
|
|
SI2->getFalseValue(), V2Size);
|
|
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(SI->getTrueValue(), SISize, V2, V2Size);
|
|
if (Alias == MayAlias)
|
|
return MayAlias;
|
|
AliasResult ThisAlias =
|
|
aliasCheck(SI->getFalseValue(), SISize, V2, V2Size);
|
|
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, unsigned PNSize,
|
|
const Value *V2, unsigned V2Size) {
|
|
// The PHI node has already been visited, avoid recursion any further.
|
|
if (!VisitedPHIs.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,
|
|
PN2->getIncomingValueForBlock(PN->getIncomingBlock(0)),
|
|
V2Size);
|
|
if (Alias == MayAlias)
|
|
return MayAlias;
|
|
for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) {
|
|
AliasResult ThisAlias =
|
|
aliasCheck(PN->getIncomingValue(i), PNSize,
|
|
PN2->getIncomingValueForBlock(PN->getIncomingBlock(i)),
|
|
V2Size);
|
|
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, V1Srcs[0], PNSize);
|
|
// 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 a PHI, 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.
|
|
VisitedPHIs.erase(V2);
|
|
|
|
AliasResult ThisAlias = aliasCheck(V2, V2Size, V, PNSize);
|
|
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, unsigned V1Size,
|
|
const Value *V2, unsigned V2Size) {
|
|
// 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.
|
|
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>(V2) && isKnownNonNull(O1)) ||
|
|
(isa<ConstantPointerNull>(V1) && isKnownNonNull(O2)))
|
|
return NoAlias;
|
|
}
|
|
|
|
// If the size of one access is larger than the entire object on the other
|
|
// side, then we know such behavior is undefined and can assume no alias.
|
|
if (TD)
|
|
if ((V1Size != ~0U && isObjectSmallerThan(O2, V1Size, *TD)) ||
|
|
(V2Size != ~0U && isObjectSmallerThan(O1, V2Size, *TD)))
|
|
return NoAlias;
|
|
|
|
// If one pointer is the result of a call/invoke or load and the other is a
|
|
// non-escaping local object, then we know the object couldn't escape to a
|
|
// point where the call could return it. The load case works because
|
|
// isNonEscapingLocalObject considers all stores to be escapes (it
|
|
// passes true for the StoreCaptures argument to PointerMayBeCaptured).
|
|
if (O1 != O2) {
|
|
if ((isa<CallInst>(O1) || isa<InvokeInst>(O1) || isa<LoadInst>(O1) ||
|
|
isa<Argument>(O1)) &&
|
|
isNonEscapingLocalObject(O2))
|
|
return NoAlias;
|
|
if ((isa<CallInst>(O2) || isa<InvokeInst>(O2) || isa<LoadInst>(O2) ||
|
|
isa<Argument>(O2)) &&
|
|
isNonEscapingLocalObject(O1))
|
|
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))
|
|
return aliasGEP(GV1, V1Size, V2, V2Size, O1, O2);
|
|
|
|
if (isa<PHINode>(V2) && !isa<PHINode>(V1)) {
|
|
std::swap(V1, V2);
|
|
std::swap(V1Size, V2Size);
|
|
}
|
|
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);
|
|
}
|
|
if (const SelectInst *S1 = dyn_cast<SelectInst>(V1))
|
|
return aliasSelect(S1, V1Size, V2, V2Size);
|
|
|
|
return MayAlias;
|
|
}
|
|
|
|
// Make sure that anything that uses AliasAnalysis pulls in this file.
|
|
DEFINING_FILE_FOR(BasicAliasAnalysis)
|