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//===- ObjCARCAliasAnalysis.cpp - ObjC ARC Optimization -------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
/// \file
/// This file defines a simple ARC-aware AliasAnalysis using special knowledge
/// of Objective C to enhance other optimization passes which rely on the Alias
/// Analysis infrastructure.
///
/// WARNING: This file knows about certain library functions. It recognizes them
/// by name, and hardwires knowledge of their semantics.
///
/// WARNING: This file knows about how certain Objective-C library functions are
/// used. Naive LLVM IR transformations which would otherwise be
/// behavior-preserving may break these assumptions.
///
/// TODO: Theoretically we could check for dependencies between objc_* calls
/// and FMRB_OnlyAccessesArgumentPointees calls or other well-behaved calls.
///
/// TODO: The calls here to AAResultBase member functions are all effectively
/// no-ops that just return a conservative result. The original intent was to
/// chain to another analysis for a recursive query, but this was lost in a
/// refactor. These should instead be rephrased in terms of queries to AAQI.AAR.
///
//===----------------------------------------------------------------------===//
#include "llvm/Analysis/ObjCARCAliasAnalysis.h"
#include "llvm/Analysis/ObjCARCAnalysisUtils.h"
#include "llvm/Analysis/Passes.h"
#include "llvm/IR/Function.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#define DEBUG_TYPE "objc-arc-aa"
using namespace llvm;
using namespace llvm::objcarc;
AliasResult ObjCARCAAResult::alias(const MemoryLocation &LocA,
const MemoryLocation &LocB,
AAQueryInfo &AAQI, const Instruction *) {
if (!EnableARCOpts)
return AAResultBase::alias(LocA, LocB, AAQI, nullptr);
// First, strip off no-ops, including ObjC-specific no-ops, and try making a
// precise alias query.
const Value *SA = GetRCIdentityRoot(LocA.Ptr);
const Value *SB = GetRCIdentityRoot(LocB.Ptr);
AliasResult Result = AAResultBase::alias(
MemoryLocation(SA, LocA.Size, LocA.AATags),
MemoryLocation(SB, LocB.Size, LocB.AATags), AAQI, nullptr);
if (Result != AliasResult::MayAlias)
return Result;
// If that failed, climb to the underlying object, including climbing through
// ObjC-specific no-ops, and try making an imprecise alias query.
const Value *UA = GetUnderlyingObjCPtr(SA);
const Value *UB = GetUnderlyingObjCPtr(SB);
if (UA != SA || UB != SB) {
Result = AAResultBase::alias(MemoryLocation::getBeforeOrAfter(UA),
MemoryLocation::getBeforeOrAfter(UB), AAQI,
nullptr);
// We can't use MustAlias or PartialAlias results here because
// GetUnderlyingObjCPtr may return an offsetted pointer value.
if (Result == AliasResult::NoAlias)
return AliasResult::NoAlias;
}
// If that failed, fail. We don't need to chain here, since that's covered
// by the earlier precise query.
return AliasResult::MayAlias;
}
ModRefInfo ObjCARCAAResult::getModRefInfoMask(const MemoryLocation &Loc,
AAQueryInfo &AAQI,
bool IgnoreLocals) {
if (!EnableARCOpts)
return AAResultBase::getModRefInfoMask(Loc, AAQI, IgnoreLocals);
// First, strip off no-ops, including ObjC-specific no-ops, and try making
// a precise alias query.
const Value *S = GetRCIdentityRoot(Loc.Ptr);
if (isNoModRef(AAResultBase::getModRefInfoMask(
MemoryLocation(S, Loc.Size, Loc.AATags), AAQI, IgnoreLocals)))
return ModRefInfo::NoModRef;
// If that failed, climb to the underlying object, including climbing through
// ObjC-specific no-ops, and try making an imprecise alias query.
const Value *U = GetUnderlyingObjCPtr(S);
if (U != S)
return AAResultBase::getModRefInfoMask(MemoryLocation::getBeforeOrAfter(U),
AAQI, IgnoreLocals);
// If that failed, fail. We don't need to chain here, since that's covered
// by the earlier precise query.
return ModRefInfo::ModRef;
}
MemoryEffects ObjCARCAAResult::getMemoryEffects(const Function *F) {
if (!EnableARCOpts)
return AAResultBase::getMemoryEffects(F);
switch (GetFunctionClass(F)) {
case ARCInstKind::NoopCast:
return MemoryEffects::none();
default:
break;
}
return AAResultBase::getMemoryEffects(F);
}
ModRefInfo ObjCARCAAResult::getModRefInfo(const CallBase *Call,
const MemoryLocation &Loc,
AAQueryInfo &AAQI) {
if (!EnableARCOpts)
return AAResultBase::getModRefInfo(Call, Loc, AAQI);
switch (GetBasicARCInstKind(Call)) {
case ARCInstKind::Retain:
case ARCInstKind::RetainRV:
case ARCInstKind::Autorelease:
case ARCInstKind::AutoreleaseRV:
case ARCInstKind::NoopCast:
case ARCInstKind::AutoreleasepoolPush:
case ARCInstKind::FusedRetainAutorelease:
case ARCInstKind::FusedRetainAutoreleaseRV:
// These functions don't access any memory visible to the compiler.
// Note that this doesn't include objc_retainBlock, because it updates
// pointers when it copies block data.
return ModRefInfo::NoModRef;
default:
break;
}
return AAResultBase::getModRefInfo(Call, Loc, AAQI);
}
AnalysisKey ObjCARCAA::Key;
ObjCARCAAResult ObjCARCAA::run(Function &F, FunctionAnalysisManager &AM) {
return ObjCARCAAResult(F.getDataLayout());
}
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