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162 lines
5.6 KiB
C++
162 lines
5.6 KiB
C++
//===- ObjCARCAliasAnalysis.cpp - ObjC ARC Optimization -------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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/// \file
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/// This file defines a simple ARC-aware AliasAnalysis using special knowledge
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/// of Objective C to enhance other optimization passes which rely on the Alias
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/// Analysis infrastructure.
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///
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/// WARNING: This file knows about certain library functions. It recognizes them
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/// by name, and hardwires knowledge of their semantics.
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///
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/// WARNING: This file knows about how certain Objective-C library functions are
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/// used. Naive LLVM IR transformations which would otherwise be
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/// behavior-preserving may break these assumptions.
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///
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/// TODO: Theoretically we could check for dependencies between objc_* calls
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/// and FMRB_OnlyAccessesArgumentPointees calls or other well-behaved calls.
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///
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//===----------------------------------------------------------------------===//
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#include "llvm/Analysis/ObjCARCAliasAnalysis.h"
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#include "llvm/Analysis/ObjCARCAnalysisUtils.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/Instruction.h"
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#include "llvm/IR/Value.h"
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#include "llvm/InitializePasses.h"
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#include "llvm/PassAnalysisSupport.h"
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#include "llvm/PassSupport.h"
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#define DEBUG_TYPE "objc-arc-aa"
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using namespace llvm;
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using namespace llvm::objcarc;
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AliasResult ObjCARCAAResult::alias(const MemoryLocation &LocA,
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const MemoryLocation &LocB) {
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if (!EnableARCOpts)
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return AAResultBase::alias(LocA, LocB);
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// First, strip off no-ops, including ObjC-specific no-ops, and try making a
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// precise alias query.
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const Value *SA = GetRCIdentityRoot(LocA.Ptr);
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const Value *SB = GetRCIdentityRoot(LocB.Ptr);
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AliasResult Result =
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AAResultBase::alias(MemoryLocation(SA, LocA.Size, LocA.AATags),
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MemoryLocation(SB, LocB.Size, LocB.AATags));
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if (Result != MayAlias)
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return Result;
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// If that failed, climb to the underlying object, including climbing through
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// ObjC-specific no-ops, and try making an imprecise alias query.
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const Value *UA = GetUnderlyingObjCPtr(SA, DL);
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const Value *UB = GetUnderlyingObjCPtr(SB, DL);
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if (UA != SA || UB != SB) {
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Result = AAResultBase::alias(MemoryLocation(UA), MemoryLocation(UB));
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// We can't use MustAlias or PartialAlias results here because
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// GetUnderlyingObjCPtr may return an offsetted pointer value.
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if (Result == NoAlias)
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return NoAlias;
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}
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// If that failed, fail. We don't need to chain here, since that's covered
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// by the earlier precise query.
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return MayAlias;
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}
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bool ObjCARCAAResult::pointsToConstantMemory(const MemoryLocation &Loc,
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bool OrLocal) {
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if (!EnableARCOpts)
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return AAResultBase::pointsToConstantMemory(Loc, OrLocal);
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// First, strip off no-ops, including ObjC-specific no-ops, and try making
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// a precise alias query.
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const Value *S = GetRCIdentityRoot(Loc.Ptr);
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if (AAResultBase::pointsToConstantMemory(
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MemoryLocation(S, Loc.Size, Loc.AATags), OrLocal))
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return true;
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// If that failed, climb to the underlying object, including climbing through
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// ObjC-specific no-ops, and try making an imprecise alias query.
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const Value *U = GetUnderlyingObjCPtr(S, DL);
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if (U != S)
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return AAResultBase::pointsToConstantMemory(MemoryLocation(U), OrLocal);
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// If that failed, fail. We don't need to chain here, since that's covered
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// by the earlier precise query.
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return false;
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}
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FunctionModRefBehavior ObjCARCAAResult::getModRefBehavior(const Function *F) {
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if (!EnableARCOpts)
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return AAResultBase::getModRefBehavior(F);
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switch (GetFunctionClass(F)) {
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case ARCInstKind::NoopCast:
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return FMRB_DoesNotAccessMemory;
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default:
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break;
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}
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return AAResultBase::getModRefBehavior(F);
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}
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ModRefInfo ObjCARCAAResult::getModRefInfo(const CallBase *Call,
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const MemoryLocation &Loc) {
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if (!EnableARCOpts)
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return AAResultBase::getModRefInfo(Call, Loc);
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switch (GetBasicARCInstKind(Call)) {
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case ARCInstKind::Retain:
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case ARCInstKind::RetainRV:
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case ARCInstKind::Autorelease:
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case ARCInstKind::AutoreleaseRV:
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case ARCInstKind::NoopCast:
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case ARCInstKind::AutoreleasepoolPush:
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case ARCInstKind::FusedRetainAutorelease:
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case ARCInstKind::FusedRetainAutoreleaseRV:
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// These functions don't access any memory visible to the compiler.
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// Note that this doesn't include objc_retainBlock, because it updates
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// pointers when it copies block data.
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return ModRefInfo::NoModRef;
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default:
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break;
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}
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return AAResultBase::getModRefInfo(Call, Loc);
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}
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ObjCARCAAResult ObjCARCAA::run(Function &F, FunctionAnalysisManager &AM) {
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return ObjCARCAAResult(F.getParent()->getDataLayout());
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}
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char ObjCARCAAWrapperPass::ID = 0;
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INITIALIZE_PASS(ObjCARCAAWrapperPass, "objc-arc-aa",
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"ObjC-ARC-Based Alias Analysis", false, true)
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ImmutablePass *llvm::createObjCARCAAWrapperPass() {
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return new ObjCARCAAWrapperPass();
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}
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ObjCARCAAWrapperPass::ObjCARCAAWrapperPass() : ImmutablePass(ID) {
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initializeObjCARCAAWrapperPassPass(*PassRegistry::getPassRegistry());
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}
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bool ObjCARCAAWrapperPass::doInitialization(Module &M) {
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Result.reset(new ObjCARCAAResult(M.getDataLayout()));
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return false;
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}
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bool ObjCARCAAWrapperPass::doFinalization(Module &M) {
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Result.reset();
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return false;
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}
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void ObjCARCAAWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesAll();
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}
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