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//===- ObjCARCAliasAnalysis.cpp - ObjC ARC Optimization -------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
/// \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.
///
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "objc-arc-aa"
#include "ObjCARC.h"
#include "ObjCARCAliasAnalysis.h"
#include "llvm/IR/Instruction.h"
#include "llvm/InitializePasses.h"
#include "llvm/PassAnalysisSupport.h"
#include "llvm/PassSupport.h"
namespace llvm {
class Function;
class Value;
}
using namespace llvm;
using namespace llvm::objcarc;
// Register this pass...
char ObjCARCAliasAnalysis::ID = 0;
INITIALIZE_AG_PASS(ObjCARCAliasAnalysis, AliasAnalysis, "objc-arc-aa",
"ObjC-ARC-Based Alias Analysis", false, true, false)
ImmutablePass *llvm::createObjCARCAliasAnalysisPass() {
return new ObjCARCAliasAnalysis();
}
void
ObjCARCAliasAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
AliasAnalysis::getAnalysisUsage(AU);
}
AliasAnalysis::AliasResult
ObjCARCAliasAnalysis::alias(const Location &LocA, const Location &LocB) {
if (!EnableARCOpts)
return AliasAnalysis::alias(LocA, LocB);
// First, strip off no-ops, including ObjC-specific no-ops, and try making a
// precise alias query.
const Value *SA = StripPointerCastsAndObjCCalls(LocA.Ptr);
const Value *SB = StripPointerCastsAndObjCCalls(LocB.Ptr);
AliasResult Result =
AliasAnalysis::alias(Location(SA, LocA.Size, LocA.TBAATag),
Location(SB, LocB.Size, LocB.TBAATag));
if (Result != 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 = AliasAnalysis::alias(Location(UA), Location(UB));
// We can't use MustAlias or PartialAlias results here because
// GetUnderlyingObjCPtr may return an offsetted pointer value.
if (Result == NoAlias)
return NoAlias;
}
// If that failed, fail. We don't need to chain here, since that's covered
// by the earlier precise query.
return MayAlias;
}
bool
ObjCARCAliasAnalysis::pointsToConstantMemory(const Location &Loc,
bool OrLocal) {
if (!EnableARCOpts)
return AliasAnalysis::pointsToConstantMemory(Loc, OrLocal);
// First, strip off no-ops, including ObjC-specific no-ops, and try making
// a precise alias query.
const Value *S = StripPointerCastsAndObjCCalls(Loc.Ptr);
if (AliasAnalysis::pointsToConstantMemory(Location(S, Loc.Size, Loc.TBAATag),
OrLocal))
return true;
// 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 AliasAnalysis::pointsToConstantMemory(Location(U), OrLocal);
// If that failed, fail. We don't need to chain here, since that's covered
// by the earlier precise query.
return false;
}
AliasAnalysis::ModRefBehavior
ObjCARCAliasAnalysis::getModRefBehavior(ImmutableCallSite CS) {
// We have nothing to do. Just chain to the next AliasAnalysis.
return AliasAnalysis::getModRefBehavior(CS);
}
AliasAnalysis::ModRefBehavior
ObjCARCAliasAnalysis::getModRefBehavior(const Function *F) {
if (!EnableARCOpts)
return AliasAnalysis::getModRefBehavior(F);
switch (GetFunctionClass(F)) {
case IC_NoopCast:
return DoesNotAccessMemory;
default:
break;
}
return AliasAnalysis::getModRefBehavior(F);
}
AliasAnalysis::ModRefResult
ObjCARCAliasAnalysis::getModRefInfo(ImmutableCallSite CS, const Location &Loc) {
if (!EnableARCOpts)
return AliasAnalysis::getModRefInfo(CS, Loc);
switch (GetBasicInstructionClass(CS.getInstruction())) {
case IC_Retain:
case IC_RetainRV:
case IC_Autorelease:
case IC_AutoreleaseRV:
case IC_NoopCast:
case IC_AutoreleasepoolPush:
case IC_FusedRetainAutorelease:
case IC_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 NoModRef;
default:
break;
}
return AliasAnalysis::getModRefInfo(CS, Loc);
}
AliasAnalysis::ModRefResult
ObjCARCAliasAnalysis::getModRefInfo(ImmutableCallSite CS1,
ImmutableCallSite CS2) {
// TODO: Theoretically we could check for dependencies between objc_* calls
// and OnlyAccessesArgumentPointees calls or other well-behaved calls.
return AliasAnalysis::getModRefInfo(CS1, CS2);
}
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