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llvm/lib/Transforms/Scalar/ObjCARC.cpp

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//===- ObjCARC.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 ObjC ARC optimizations. ARC stands for Automatic
/// Reference Counting and is a system for managing reference counts for objects
/// in Objective C.
///
/// The optimizations performed include elimination of redundant, partially
/// redundant, and inconsequential reference count operations, elimination of
/// redundant weak pointer operations, pattern-matching and replacement of
/// low-level operations into higher-level operations, and numerous minor
/// simplifications.
///
/// This file also defines a simple ARC-aware AliasAnalysis.
///
/// 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"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
/// \brief A handy option to enable/disable all optimizations in this file.
static cl::opt<bool> EnableARCOpts("enable-objc-arc-opts", cl::init(true));
/// \defgroup MiscUtils Miscellaneous utilities that are not ARC specific.
/// @{
namespace {
/// \brief An associative container with fast insertion-order (deterministic)
/// iteration over its elements. Plus the special blot operation.
template<class KeyT, class ValueT>
class MapVector {
/// Map keys to indices in Vector.
typedef DenseMap<KeyT, size_t> MapTy;
MapTy Map;
typedef std::vector<std::pair<KeyT, ValueT> > VectorTy;
/// Keys and values.
VectorTy Vector;
public:
typedef typename VectorTy::iterator iterator;
typedef typename VectorTy::const_iterator const_iterator;
iterator begin() { return Vector.begin(); }
iterator end() { return Vector.end(); }
const_iterator begin() const { return Vector.begin(); }
const_iterator end() const { return Vector.end(); }
#ifdef XDEBUG
~MapVector() {
assert(Vector.size() >= Map.size()); // May differ due to blotting.
for (typename MapTy::const_iterator I = Map.begin(), E = Map.end();
I != E; ++I) {
assert(I->second < Vector.size());
assert(Vector[I->second].first == I->first);
}
for (typename VectorTy::const_iterator I = Vector.begin(),
E = Vector.end(); I != E; ++I)
assert(!I->first ||
(Map.count(I->first) &&
Map[I->first] == size_t(I - Vector.begin())));
}
#endif
ValueT &operator[](const KeyT &Arg) {
std::pair<typename MapTy::iterator, bool> Pair =
Map.insert(std::make_pair(Arg, size_t(0)));
if (Pair.second) {
size_t Num = Vector.size();
Pair.first->second = Num;
Vector.push_back(std::make_pair(Arg, ValueT()));
return Vector[Num].second;
}
return Vector[Pair.first->second].second;
}
std::pair<iterator, bool>
insert(const std::pair<KeyT, ValueT> &InsertPair) {
std::pair<typename MapTy::iterator, bool> Pair =
Map.insert(std::make_pair(InsertPair.first, size_t(0)));
if (Pair.second) {
size_t Num = Vector.size();
Pair.first->second = Num;
Vector.push_back(InsertPair);
return std::make_pair(Vector.begin() + Num, true);
}
return std::make_pair(Vector.begin() + Pair.first->second, false);
}
const_iterator find(const KeyT &Key) const {
typename MapTy::const_iterator It = Map.find(Key);
if (It == Map.end()) return Vector.end();
return Vector.begin() + It->second;
}
/// This is similar to erase, but instead of removing the element from the
/// vector, it just zeros out the key in the vector. This leaves iterators
/// intact, but clients must be prepared for zeroed-out keys when iterating.
void blot(const KeyT &Key) {
typename MapTy::iterator It = Map.find(Key);
if (It == Map.end()) return;
Vector[It->second].first = KeyT();
Map.erase(It);
}
void clear() {
Map.clear();
Vector.clear();
}
};
}
/// @}
///
/// \defgroup ARCUtilities Utility declarations/definitions specific to ARC.
/// @{
#include "llvm/ADT/StringSwitch.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Transforms/Utils/Local.h"
namespace {
/// \enum InstructionClass
/// \brief A simple classification for instructions.
enum InstructionClass {
IC_Retain, ///< objc_retain
IC_RetainRV, ///< objc_retainAutoreleasedReturnValue
IC_RetainBlock, ///< objc_retainBlock
IC_Release, ///< objc_release
IC_Autorelease, ///< objc_autorelease
IC_AutoreleaseRV, ///< objc_autoreleaseReturnValue
IC_AutoreleasepoolPush, ///< objc_autoreleasePoolPush
IC_AutoreleasepoolPop, ///< objc_autoreleasePoolPop
IC_NoopCast, ///< objc_retainedObject, etc.
IC_FusedRetainAutorelease, ///< objc_retainAutorelease
IC_FusedRetainAutoreleaseRV, ///< objc_retainAutoreleaseReturnValue
IC_LoadWeakRetained, ///< objc_loadWeakRetained (primitive)
IC_StoreWeak, ///< objc_storeWeak (primitive)
IC_InitWeak, ///< objc_initWeak (derived)
IC_LoadWeak, ///< objc_loadWeak (derived)
IC_MoveWeak, ///< objc_moveWeak (derived)
IC_CopyWeak, ///< objc_copyWeak (derived)
IC_DestroyWeak, ///< objc_destroyWeak (derived)
IC_StoreStrong, ///< objc_storeStrong (derived)
IC_CallOrUser, ///< could call objc_release and/or "use" pointers
IC_Call, ///< could call objc_release
IC_User, ///< could "use" a pointer
IC_None ///< anything else
};
}
/// \brief Test whether the given value is possible a reference-counted pointer.
static bool IsPotentialUse(const Value *Op) {
// Pointers to static or stack storage are not reference-counted pointers.
if (isa<Constant>(Op) || isa<AllocaInst>(Op))
return false;
// Special arguments are not reference-counted.
if (const Argument *Arg = dyn_cast<Argument>(Op))
if (Arg->hasByValAttr() ||
Arg->hasNestAttr() ||
Arg->hasStructRetAttr())
return false;
// Only consider values with pointer types.
// It seemes intuitive to exclude function pointer types as well, since
// functions are never reference-counted, however clang occasionally
// bitcasts reference-counted pointers to function-pointer type
// temporarily.
PointerType *Ty = dyn_cast<PointerType>(Op->getType());
if (!Ty)
return false;
// Conservatively assume anything else is a potential use.
return true;
}
/// \brief Helper for GetInstructionClass. Determines what kind of construct CS is.
static InstructionClass GetCallSiteClass(ImmutableCallSite CS) {
for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
I != E; ++I)
if (IsPotentialUse(*I))
return CS.onlyReadsMemory() ? IC_User : IC_CallOrUser;
return CS.onlyReadsMemory() ? IC_None : IC_Call;
}
/// \brief Determine if F is one of the special known Functions. If it isn't,
/// return IC_CallOrUser.
static InstructionClass GetFunctionClass(const Function *F) {
Function::const_arg_iterator AI = F->arg_begin(), AE = F->arg_end();
// No arguments.
if (AI == AE)
return StringSwitch<InstructionClass>(F->getName())
.Case("objc_autoreleasePoolPush", IC_AutoreleasepoolPush)
.Default(IC_CallOrUser);
// One argument.
const Argument *A0 = AI++;
if (AI == AE)
// Argument is a pointer.
if (PointerType *PTy = dyn_cast<PointerType>(A0->getType())) {
Type *ETy = PTy->getElementType();
// Argument is i8*.
if (ETy->isIntegerTy(8))
return StringSwitch<InstructionClass>(F->getName())
.Case("objc_retain", IC_Retain)
.Case("objc_retainAutoreleasedReturnValue", IC_RetainRV)
.Case("objc_retainBlock", IC_RetainBlock)
.Case("objc_release", IC_Release)
.Case("objc_autorelease", IC_Autorelease)
.Case("objc_autoreleaseReturnValue", IC_AutoreleaseRV)
.Case("objc_autoreleasePoolPop", IC_AutoreleasepoolPop)
.Case("objc_retainedObject", IC_NoopCast)
.Case("objc_unretainedObject", IC_NoopCast)
.Case("objc_unretainedPointer", IC_NoopCast)
.Case("objc_retain_autorelease", IC_FusedRetainAutorelease)
.Case("objc_retainAutorelease", IC_FusedRetainAutorelease)
.Case("objc_retainAutoreleaseReturnValue",IC_FusedRetainAutoreleaseRV)
.Default(IC_CallOrUser);
// Argument is i8**
if (PointerType *Pte = dyn_cast<PointerType>(ETy))
if (Pte->getElementType()->isIntegerTy(8))
return StringSwitch<InstructionClass>(F->getName())
.Case("objc_loadWeakRetained", IC_LoadWeakRetained)
.Case("objc_loadWeak", IC_LoadWeak)
.Case("objc_destroyWeak", IC_DestroyWeak)
.Default(IC_CallOrUser);
}
// Two arguments, first is i8**.
const Argument *A1 = AI++;
if (AI == AE)
if (PointerType *PTy = dyn_cast<PointerType>(A0->getType()))
if (PointerType *Pte = dyn_cast<PointerType>(PTy->getElementType()))
if (Pte->getElementType()->isIntegerTy(8))
if (PointerType *PTy1 = dyn_cast<PointerType>(A1->getType())) {
Type *ETy1 = PTy1->getElementType();
// Second argument is i8*
if (ETy1->isIntegerTy(8))
return StringSwitch<InstructionClass>(F->getName())
.Case("objc_storeWeak", IC_StoreWeak)
.Case("objc_initWeak", IC_InitWeak)
.Case("objc_storeStrong", IC_StoreStrong)
.Default(IC_CallOrUser);
// Second argument is i8**.
if (PointerType *Pte1 = dyn_cast<PointerType>(ETy1))
if (Pte1->getElementType()->isIntegerTy(8))
return StringSwitch<InstructionClass>(F->getName())
.Case("objc_moveWeak", IC_MoveWeak)
.Case("objc_copyWeak", IC_CopyWeak)
.Default(IC_CallOrUser);
}
// Anything else.
return IC_CallOrUser;
}
/// \brief Determine what kind of construct V is.
static InstructionClass GetInstructionClass(const Value *V) {
if (const Instruction *I = dyn_cast<Instruction>(V)) {
// Any instruction other than bitcast and gep with a pointer operand have a
// use of an objc pointer. Bitcasts, GEPs, Selects, PHIs transfer a pointer
// to a subsequent use, rather than using it themselves, in this sense.
// As a short cut, several other opcodes are known to have no pointer
// operands of interest. And ret is never followed by a release, so it's
// not interesting to examine.
switch (I->getOpcode()) {
case Instruction::Call: {
const CallInst *CI = cast<CallInst>(I);
// Check for calls to special functions.
if (const Function *F = CI->getCalledFunction()) {
InstructionClass Class = GetFunctionClass(F);
if (Class != IC_CallOrUser)
return Class;
// None of the intrinsic functions do objc_release. For intrinsics, the
// only question is whether or not they may be users.
switch (F->getIntrinsicID()) {
case Intrinsic::returnaddress: case Intrinsic::frameaddress:
case Intrinsic::stacksave: case Intrinsic::stackrestore:
case Intrinsic::vastart: case Intrinsic::vacopy: case Intrinsic::vaend:
case Intrinsic::objectsize: case Intrinsic::prefetch:
case Intrinsic::stackprotector:
case Intrinsic::eh_return_i32: case Intrinsic::eh_return_i64:
case Intrinsic::eh_typeid_for: case Intrinsic::eh_dwarf_cfa:
case Intrinsic::eh_sjlj_lsda: case Intrinsic::eh_sjlj_functioncontext:
case Intrinsic::init_trampoline: case Intrinsic::adjust_trampoline:
case Intrinsic::lifetime_start: case Intrinsic::lifetime_end:
case Intrinsic::invariant_start: case Intrinsic::invariant_end:
// Don't let dbg info affect our results.
case Intrinsic::dbg_declare: case Intrinsic::dbg_value:
// Short cut: Some intrinsics obviously don't use ObjC pointers.
return IC_None;
default:
break;
}
}
return GetCallSiteClass(CI);
}
case Instruction::Invoke:
return GetCallSiteClass(cast<InvokeInst>(I));
case Instruction::BitCast:
case Instruction::GetElementPtr:
case Instruction::Select: case Instruction::PHI:
case Instruction::Ret: case Instruction::Br:
case Instruction::Switch: case Instruction::IndirectBr:
case Instruction::Alloca: case Instruction::VAArg:
case Instruction::Add: case Instruction::FAdd:
case Instruction::Sub: case Instruction::FSub:
case Instruction::Mul: case Instruction::FMul:
case Instruction::SDiv: case Instruction::UDiv: case Instruction::FDiv:
case Instruction::SRem: case Instruction::URem: case Instruction::FRem:
case Instruction::Shl: case Instruction::LShr: case Instruction::AShr:
case Instruction::And: case Instruction::Or: case Instruction::Xor:
case Instruction::SExt: case Instruction::ZExt: case Instruction::Trunc:
case Instruction::IntToPtr: case Instruction::FCmp:
case Instruction::FPTrunc: case Instruction::FPExt:
case Instruction::FPToUI: case Instruction::FPToSI:
case Instruction::UIToFP: case Instruction::SIToFP:
case Instruction::InsertElement: case Instruction::ExtractElement:
case Instruction::ShuffleVector:
case Instruction::ExtractValue:
break;
case Instruction::ICmp:
// Comparing a pointer with null, or any other constant, isn't an
// interesting use, because we don't care what the pointer points to, or
// about the values of any other dynamic reference-counted pointers.
if (IsPotentialUse(I->getOperand(1)))
return IC_User;
break;
default:
// For anything else, check all the operands.
// Note that this includes both operands of a Store: while the first
// operand isn't actually being dereferenced, it is being stored to
// memory where we can no longer track who might read it and dereference
// it, so we have to consider it potentially used.
for (User::const_op_iterator OI = I->op_begin(), OE = I->op_end();
OI != OE; ++OI)
if (IsPotentialUse(*OI))
return IC_User;
}
}
// Otherwise, it's totally inert for ARC purposes.
return IC_None;
}
/// \brief Determine which objc runtime call instruction class V belongs to.
///
/// This is similar to GetInstructionClass except that it only detects objc
/// runtime calls. This allows it to be faster.
///
static InstructionClass GetBasicInstructionClass(const Value *V) {
if (const CallInst *CI = dyn_cast<CallInst>(V)) {
if (const Function *F = CI->getCalledFunction())
return GetFunctionClass(F);
// Otherwise, be conservative.
return IC_CallOrUser;
}
// Otherwise, be conservative.
return isa<InvokeInst>(V) ? IC_CallOrUser : IC_User;
}
/// \brief Test if the given class is objc_retain or equivalent.
static bool IsRetain(InstructionClass Class) {
return Class == IC_Retain ||
Class == IC_RetainRV;
}
/// \brief Test if the given class is objc_autorelease or equivalent.
static bool IsAutorelease(InstructionClass Class) {
return Class == IC_Autorelease ||
Class == IC_AutoreleaseRV;
}
/// \brief Test if the given class represents instructions which return their
/// argument verbatim.
static bool IsForwarding(InstructionClass Class) {
// objc_retainBlock technically doesn't always return its argument
// verbatim, but it doesn't matter for our purposes here.
return Class == IC_Retain ||
Class == IC_RetainRV ||
Class == IC_Autorelease ||
Class == IC_AutoreleaseRV ||
Class == IC_RetainBlock ||
Class == IC_NoopCast;
}
/// \brief Test if the given class represents instructions which do nothing if
/// passed a null pointer.
static bool IsNoopOnNull(InstructionClass Class) {
return Class == IC_Retain ||
Class == IC_RetainRV ||
Class == IC_Release ||
Class == IC_Autorelease ||
Class == IC_AutoreleaseRV ||
Class == IC_RetainBlock;
}
/// \brief Test if the given class represents instructions which are always safe to
/// mark with the "tail" keyword.
static bool IsAlwaysTail(InstructionClass Class) {
// IC_RetainBlock may be given a stack argument.
return Class == IC_Retain ||
Class == IC_RetainRV ||
Class == IC_AutoreleaseRV;
}
/// \brief Test if the given class represents instructions which are never safe
/// to mark with the "tail" keyword.
static bool IsNeverTail(InstructionClass Class) {
/// It is never safe to tail call objc_autorelease since by tail calling
/// objc_autorelease, we also tail call -[NSObject autorelease] which supports
/// fast autoreleasing causing our object to be potentially reclaimed from the
/// autorelease pool which violates the semantics of __autoreleasing types in
/// ARC.
return Class == IC_Autorelease;
}
/// \brief Test if the given class represents instructions which are always safe
/// to mark with the nounwind attribute.
static bool IsNoThrow(InstructionClass Class) {
// objc_retainBlock is not nounwind because it calls user copy constructors
// which could theoretically throw.
return Class == IC_Retain ||
Class == IC_RetainRV ||
Class == IC_Release ||
Class == IC_Autorelease ||
Class == IC_AutoreleaseRV ||
Class == IC_AutoreleasepoolPush ||
Class == IC_AutoreleasepoolPop;
}
/// \brief Erase the given instruction.
///
/// Many ObjC calls return their argument verbatim,
/// so if it's such a call and the return value has users, replace them with the
/// argument value.
///
static void EraseInstruction(Instruction *CI) {
Value *OldArg = cast<CallInst>(CI)->getArgOperand(0);
bool Unused = CI->use_empty();
if (!Unused) {
// Replace the return value with the argument.
assert(IsForwarding(GetBasicInstructionClass(CI)) &&
"Can't delete non-forwarding instruction with users!");
CI->replaceAllUsesWith(OldArg);
}
CI->eraseFromParent();
if (Unused)
RecursivelyDeleteTriviallyDeadInstructions(OldArg);
}
/// \brief This is a wrapper around getUnderlyingObject which also knows how to
/// look through objc_retain and objc_autorelease calls, which we know to return
/// their argument verbatim.
static const Value *GetUnderlyingObjCPtr(const Value *V) {
for (;;) {
V = GetUnderlyingObject(V);
if (!IsForwarding(GetBasicInstructionClass(V)))
break;
V = cast<CallInst>(V)->getArgOperand(0);
}
return V;
}
/// \brief This is a wrapper around Value::stripPointerCasts which also knows
/// how to look through objc_retain and objc_autorelease calls, which we know to
/// return their argument verbatim.
static const Value *StripPointerCastsAndObjCCalls(const Value *V) {
for (;;) {
V = V->stripPointerCasts();
if (!IsForwarding(GetBasicInstructionClass(V)))
break;
V = cast<CallInst>(V)->getArgOperand(0);
}
return V;
}
/// \brief This is a wrapper around Value::stripPointerCasts which also knows
/// how to look through objc_retain and objc_autorelease calls, which we know to
/// return their argument verbatim.
static Value *StripPointerCastsAndObjCCalls(Value *V) {
for (;;) {
V = V->stripPointerCasts();
if (!IsForwarding(GetBasicInstructionClass(V)))
break;
V = cast<CallInst>(V)->getArgOperand(0);
}
return V;
}
/// \brief Assuming the given instruction is one of the special calls such as
/// objc_retain or objc_release, return the argument value, stripped of no-op
/// casts and forwarding calls.
static Value *GetObjCArg(Value *Inst) {
return StripPointerCastsAndObjCCalls(cast<CallInst>(Inst)->getArgOperand(0));
}
/// \brief This is similar to AliasAnalysis's isObjCIdentifiedObject, except
/// that it uses special knowledge of ObjC conventions.
static bool IsObjCIdentifiedObject(const Value *V) {
// Assume that call results and arguments have their own "provenance".
// Constants (including GlobalVariables) and Allocas are never
// reference-counted.
if (isa<CallInst>(V) || isa<InvokeInst>(V) ||
isa<Argument>(V) || isa<Constant>(V) ||
isa<AllocaInst>(V))
return true;
if (const LoadInst *LI = dyn_cast<LoadInst>(V)) {
const Value *Pointer =
StripPointerCastsAndObjCCalls(LI->getPointerOperand());
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Pointer)) {
// A constant pointer can't be pointing to an object on the heap. It may
// be reference-counted, but it won't be deleted.
if (GV->isConstant())
return true;
StringRef Name = GV->getName();
// These special variables are known to hold values which are not
// reference-counted pointers.
if (Name.startswith("\01L_OBJC_SELECTOR_REFERENCES_") ||
Name.startswith("\01L_OBJC_CLASSLIST_REFERENCES_") ||
Name.startswith("\01L_OBJC_CLASSLIST_SUP_REFS_$_") ||
Name.startswith("\01L_OBJC_METH_VAR_NAME_") ||
Name.startswith("\01l_objc_msgSend_fixup_"))
return true;
}
}
return false;
}
/// \brief This is similar to StripPointerCastsAndObjCCalls but it stops as soon
/// as it finds a value with multiple uses.
static const Value *FindSingleUseIdentifiedObject(const Value *Arg) {
if (Arg->hasOneUse()) {
if (const BitCastInst *BC = dyn_cast<BitCastInst>(Arg))
return FindSingleUseIdentifiedObject(BC->getOperand(0));
if (const GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Arg))
if (GEP->hasAllZeroIndices())
return FindSingleUseIdentifiedObject(GEP->getPointerOperand());
if (IsForwarding(GetBasicInstructionClass(Arg)))
return FindSingleUseIdentifiedObject(
cast<CallInst>(Arg)->getArgOperand(0));
if (!IsObjCIdentifiedObject(Arg))
return 0;
return Arg;
}
// If we found an identifiable object but it has multiple uses, but they are
// trivial uses, we can still consider this to be a single-use value.
if (IsObjCIdentifiedObject(Arg)) {
for (Value::const_use_iterator UI = Arg->use_begin(), UE = Arg->use_end();
UI != UE; ++UI) {
const User *U = *UI;
if (!U->use_empty() || StripPointerCastsAndObjCCalls(U) != Arg)
return 0;
}
return Arg;
}
return 0;
}
/// \brief Test if the given module looks interesting to run ARC optimization
/// on.
static bool ModuleHasARC(const Module &M) {
return
M.getNamedValue("objc_retain") ||
M.getNamedValue("objc_release") ||
M.getNamedValue("objc_autorelease") ||
M.getNamedValue("objc_retainAutoreleasedReturnValue") ||
M.getNamedValue("objc_retainBlock") ||
M.getNamedValue("objc_autoreleaseReturnValue") ||
M.getNamedValue("objc_autoreleasePoolPush") ||
M.getNamedValue("objc_loadWeakRetained") ||
M.getNamedValue("objc_loadWeak") ||
M.getNamedValue("objc_destroyWeak") ||
M.getNamedValue("objc_storeWeak") ||
M.getNamedValue("objc_initWeak") ||
M.getNamedValue("objc_moveWeak") ||
M.getNamedValue("objc_copyWeak") ||
M.getNamedValue("objc_retainedObject") ||
M.getNamedValue("objc_unretainedObject") ||
M.getNamedValue("objc_unretainedPointer");
}
/// \brief Test whether the given pointer, which is an Objective C block pointer, does
/// not "escape".
///
/// This differs from regular escape analysis in that a use as an
/// argument to a call is not considered an escape.
///
static bool DoesObjCBlockEscape(const Value *BlockPtr) {
DEBUG(dbgs() << "DoesObjCBlockEscape: Target: " << *BlockPtr << "\n");
// Walk the def-use chains.
SmallVector<const Value *, 4> Worklist;
Worklist.push_back(BlockPtr);
// Ensure we do not visit any value twice.
SmallPtrSet<const Value *, 4> VisitedSet;
do {
const Value *V = Worklist.pop_back_val();
DEBUG(dbgs() << "DoesObjCBlockEscape: Visiting: " << *V << "\n");
for (Value::const_use_iterator UI = V->use_begin(), UE = V->use_end();
UI != UE; ++UI) {
const User *UUser = *UI;
DEBUG(dbgs() << "DoesObjCBlockEscape: User: " << *UUser << "\n");
// Special - Use by a call (callee or argument) is not considered
// to be an escape.
switch (GetBasicInstructionClass(UUser)) {
case IC_StoreWeak:
case IC_InitWeak:
case IC_StoreStrong:
case IC_Autorelease:
case IC_AutoreleaseRV: {
DEBUG(dbgs() << "DoesObjCBlockEscape: User copies pointer arguments. "
"Block Escapes!\n");
// These special functions make copies of their pointer arguments.
return true;
}
case IC_User:
case IC_None:
// Use by an instruction which copies the value is an escape if the
// result is an escape.
if (isa<BitCastInst>(UUser) || isa<GetElementPtrInst>(UUser) ||
isa<PHINode>(UUser) || isa<SelectInst>(UUser)) {
if (!VisitedSet.count(UUser)) {
DEBUG(dbgs() << "DoesObjCBlockEscape: User copies value. Escapes if "
"result escapes. Adding to list.\n");
VisitedSet.insert(V);
Worklist.push_back(UUser);
} else {
DEBUG(dbgs() << "DoesObjCBlockEscape: Already visited node.\n");
}
continue;
}
// Use by a load is not an escape.
if (isa<LoadInst>(UUser))
continue;
// Use by a store is not an escape if the use is the address.
if (const StoreInst *SI = dyn_cast<StoreInst>(UUser))
if (V != SI->getValueOperand())
continue;
break;
default:
// Regular calls and other stuff are not considered escapes.
continue;
}
// Otherwise, conservatively assume an escape.
DEBUG(dbgs() << "DoesObjCBlockEscape: Assuming block escapes.\n");
return true;
}
} while (!Worklist.empty());
// No escapes found.
DEBUG(dbgs() << "DoesObjCBlockEscape: Block does not escape.\n");
return false;
}
/// @}
///
/// \defgroup ARCAA An extension of alias analysis using ObjC specific knowledge.
/// @{
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/Passes.h"
#include "llvm/Pass.h"
namespace {
/// \brief This is a simple alias analysis implementation that uses knowledge
/// of ARC constructs to answer queries.
///
/// TODO: This class could be generalized to know about other ObjC-specific
/// tricks. Such as knowing that ivars in the non-fragile ABI are non-aliasing
/// even though their offsets are dynamic.
class ObjCARCAliasAnalysis : public ImmutablePass,
public AliasAnalysis {
public:
static char ID; // Class identification, replacement for typeinfo
ObjCARCAliasAnalysis() : ImmutablePass(ID) {
initializeObjCARCAliasAnalysisPass(*PassRegistry::getPassRegistry());
}
private:
virtual void initializePass() {
InitializeAliasAnalysis(this);
}
/// This method is used when a pass implements an analysis interface through
/// multiple inheritance. If needed, it should override this to adjust the
/// this pointer as needed for the specified pass info.
virtual void *getAdjustedAnalysisPointer(const void *PI) {
if (PI == &AliasAnalysis::ID)
return static_cast<AliasAnalysis *>(this);
return this;
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
virtual AliasResult alias(const Location &LocA, const Location &LocB);
virtual bool pointsToConstantMemory(const Location &Loc, bool OrLocal);
virtual ModRefBehavior getModRefBehavior(ImmutableCallSite CS);
virtual ModRefBehavior getModRefBehavior(const Function *F);
virtual ModRefResult getModRefInfo(ImmutableCallSite CS,
const Location &Loc);
virtual ModRefResult getModRefInfo(ImmutableCallSite CS1,
ImmutableCallSite CS2);
};
} // End of anonymous namespace
// 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);
}
/// @}
///
/// \defgroup ARCExpansion Early ARC Optimizations.
/// @{
#include "llvm/Support/InstIterator.h"
#include "llvm/Transforms/Scalar.h"
namespace {
/// \brief Early ARC transformations.
class ObjCARCExpand : public FunctionPass {
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
virtual bool doInitialization(Module &M);
virtual bool runOnFunction(Function &F);
/// A flag indicating whether this optimization pass should run.
bool Run;
public:
static char ID;
ObjCARCExpand() : FunctionPass(ID) {
initializeObjCARCExpandPass(*PassRegistry::getPassRegistry());
}
};
}
char ObjCARCExpand::ID = 0;
INITIALIZE_PASS(ObjCARCExpand,
"objc-arc-expand", "ObjC ARC expansion", false, false)
Pass *llvm::createObjCARCExpandPass() {
return new ObjCARCExpand();
}
void ObjCARCExpand::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
}
bool ObjCARCExpand::doInitialization(Module &M) {
Run = ModuleHasARC(M);
return false;
}
bool ObjCARCExpand::runOnFunction(Function &F) {
if (!EnableARCOpts)
return false;
// If nothing in the Module uses ARC, don't do anything.
if (!Run)
return false;
bool Changed = false;
DEBUG(dbgs() << "ObjCARCExpand: Visiting Function: " << F.getName() << "\n");
for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ++I) {
Instruction *Inst = &*I;
DEBUG(dbgs() << "ObjCARCExpand: Visiting: " << *Inst << "\n");
switch (GetBasicInstructionClass(Inst)) {
case IC_Retain:
case IC_RetainRV:
case IC_Autorelease:
case IC_AutoreleaseRV:
case IC_FusedRetainAutorelease:
case IC_FusedRetainAutoreleaseRV: {
// These calls return their argument verbatim, as a low-level
// optimization. However, this makes high-level optimizations
// harder. Undo any uses of this optimization that the front-end
// emitted here. We'll redo them in the contract pass.
Changed = true;
Value *Value = cast<CallInst>(Inst)->getArgOperand(0);
DEBUG(dbgs() << "ObjCARCExpand: Old = " << *Inst << "\n"
" New = " << *Value << "\n");
Inst->replaceAllUsesWith(Value);
break;
}
default:
break;
}
}
DEBUG(dbgs() << "ObjCARCExpand: Finished List.\n\n");
return Changed;
}
/// @}
///
/// \defgroup ARCAPElim ARC Autorelease Pool Elimination.
/// @{
#include "llvm/ADT/STLExtras.h"
#include "llvm/IR/Constants.h"
namespace {
/// \brief Autorelease pool elimination.
class ObjCARCAPElim : public ModulePass {
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
virtual bool runOnModule(Module &M);
static bool MayAutorelease(ImmutableCallSite CS, unsigned Depth = 0);
static bool OptimizeBB(BasicBlock *BB);
public:
static char ID;
ObjCARCAPElim() : ModulePass(ID) {
initializeObjCARCAPElimPass(*PassRegistry::getPassRegistry());
}
};
}
char ObjCARCAPElim::ID = 0;
INITIALIZE_PASS(ObjCARCAPElim,
"objc-arc-apelim",
"ObjC ARC autorelease pool elimination",
false, false)
Pass *llvm::createObjCARCAPElimPass() {
return new ObjCARCAPElim();
}
void ObjCARCAPElim::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
}
/// Interprocedurally determine if calls made by the given call site can
/// possibly produce autoreleases.
bool ObjCARCAPElim::MayAutorelease(ImmutableCallSite CS, unsigned Depth) {
if (const Function *Callee = CS.getCalledFunction()) {
if (Callee->isDeclaration() || Callee->mayBeOverridden())
return true;
for (Function::const_iterator I = Callee->begin(), E = Callee->end();
I != E; ++I) {
const BasicBlock *BB = I;
for (BasicBlock::const_iterator J = BB->begin(), F = BB->end();
J != F; ++J)
if (ImmutableCallSite JCS = ImmutableCallSite(J))
// This recursion depth limit is arbitrary. It's just great
// enough to cover known interesting testcases.
if (Depth < 3 &&
!JCS.onlyReadsMemory() &&
MayAutorelease(JCS, Depth + 1))
return true;
}
return false;
}
return true;
}
bool ObjCARCAPElim::OptimizeBB(BasicBlock *BB) {
bool Changed = false;
Instruction *Push = 0;
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
Instruction *Inst = I++;
switch (GetBasicInstructionClass(Inst)) {
case IC_AutoreleasepoolPush:
Push = Inst;
break;
case IC_AutoreleasepoolPop:
// If this pop matches a push and nothing in between can autorelease,
// zap the pair.
if (Push && cast<CallInst>(Inst)->getArgOperand(0) == Push) {
Changed = true;
DEBUG(dbgs() << "ObjCARCAPElim::OptimizeBB: Zapping push pop autorelease pair:\n"
<< " Pop: " << *Inst << "\n"
<< " Push: " << *Push << "\n");
Inst->eraseFromParent();
Push->eraseFromParent();
}
Push = 0;
break;
case IC_CallOrUser:
if (MayAutorelease(ImmutableCallSite(Inst)))
Push = 0;
break;
default:
break;
}
}
return Changed;
}
bool ObjCARCAPElim::runOnModule(Module &M) {
if (!EnableARCOpts)
return false;
// If nothing in the Module uses ARC, don't do anything.
if (!ModuleHasARC(M))
return false;
// Find the llvm.global_ctors variable, as the first step in
// identifying the global constructors. In theory, unnecessary autorelease
// pools could occur anywhere, but in practice it's pretty rare. Global
// ctors are a place where autorelease pools get inserted automatically,
// so it's pretty common for them to be unnecessary, and it's pretty
// profitable to eliminate them.
GlobalVariable *GV = M.getGlobalVariable("llvm.global_ctors");
if (!GV)
return false;
assert(GV->hasDefinitiveInitializer() &&
"llvm.global_ctors is uncooperative!");
bool Changed = false;
// Dig the constructor functions out of GV's initializer.
ConstantArray *Init = cast<ConstantArray>(GV->getInitializer());
for (User::op_iterator OI = Init->op_begin(), OE = Init->op_end();
OI != OE; ++OI) {
Value *Op = *OI;
// llvm.global_ctors is an array of pairs where the second members
// are constructor functions.
Function *F = dyn_cast<Function>(cast<ConstantStruct>(Op)->getOperand(1));
// If the user used a constructor function with the wrong signature and
// it got bitcasted or whatever, look the other way.
if (!F)
continue;
// Only look at function definitions.
if (F->isDeclaration())
continue;
// Only look at functions with one basic block.
if (llvm::next(F->begin()) != F->end())
continue;
// Ok, a single-block constructor function definition. Try to optimize it.
Changed |= OptimizeBB(F->begin());
}
return Changed;
}
/// @}
///
/// \defgroup ARCOpt ARC Optimization.
/// @{
// TODO: On code like this:
//
// objc_retain(%x)
// stuff_that_cannot_release()
// objc_autorelease(%x)
// stuff_that_cannot_release()
// objc_retain(%x)
// stuff_that_cannot_release()
// objc_autorelease(%x)
//
// The second retain and autorelease can be deleted.
// TODO: It should be possible to delete
// objc_autoreleasePoolPush and objc_autoreleasePoolPop
// pairs if nothing is actually autoreleased between them. Also, autorelease
// calls followed by objc_autoreleasePoolPop calls (perhaps in ObjC++ code
// after inlining) can be turned into plain release calls.
// TODO: Critical-edge splitting. If the optimial insertion point is
// a critical edge, the current algorithm has to fail, because it doesn't
// know how to split edges. It should be possible to make the optimizer
// think in terms of edges, rather than blocks, and then split critical
// edges on demand.
// TODO: OptimizeSequences could generalized to be Interprocedural.
// TODO: Recognize that a bunch of other objc runtime calls have
// non-escaping arguments and non-releasing arguments, and may be
// non-autoreleasing.
// TODO: Sink autorelease calls as far as possible. Unfortunately we
// usually can't sink them past other calls, which would be the main
// case where it would be useful.
// TODO: The pointer returned from objc_loadWeakRetained is retained.
// TODO: Delete release+retain pairs (rare).
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/Support/CFG.h"
STATISTIC(NumNoops, "Number of no-op objc calls eliminated");
STATISTIC(NumPartialNoops, "Number of partially no-op objc calls eliminated");
STATISTIC(NumAutoreleases,"Number of autoreleases converted to releases");
STATISTIC(NumRets, "Number of return value forwarding "
"retain+autoreleaes eliminated");
STATISTIC(NumRRs, "Number of retain+release paths eliminated");
STATISTIC(NumPeeps, "Number of calls peephole-optimized");
namespace {
/// \brief This is similar to BasicAliasAnalysis, and it uses many of the same
/// techniques, except it uses special ObjC-specific reasoning about pointer
/// relationships.
class ProvenanceAnalysis {
AliasAnalysis *AA;
typedef std::pair<const Value *, const Value *> ValuePairTy;
typedef DenseMap<ValuePairTy, bool> CachedResultsTy;
CachedResultsTy CachedResults;
bool relatedCheck(const Value *A, const Value *B);
bool relatedSelect(const SelectInst *A, const Value *B);
bool relatedPHI(const PHINode *A, const Value *B);
void operator=(const ProvenanceAnalysis &) LLVM_DELETED_FUNCTION;
ProvenanceAnalysis(const ProvenanceAnalysis &) LLVM_DELETED_FUNCTION;
public:
ProvenanceAnalysis() {}
void setAA(AliasAnalysis *aa) { AA = aa; }
AliasAnalysis *getAA() const { return AA; }
bool related(const Value *A, const Value *B);
void clear() {
CachedResults.clear();
}
};
}
bool ProvenanceAnalysis::relatedSelect(const SelectInst *A, const Value *B) {
// If the values are Selects with the same condition, we can do a more precise
// check: just check for relations between the values on corresponding arms.
if (const SelectInst *SB = dyn_cast<SelectInst>(B))
if (A->getCondition() == SB->getCondition())
return related(A->getTrueValue(), SB->getTrueValue()) ||
related(A->getFalseValue(), SB->getFalseValue());
// Check both arms of the Select node individually.
return related(A->getTrueValue(), B) ||
related(A->getFalseValue(), B);
}
bool ProvenanceAnalysis::relatedPHI(const PHINode *A, const Value *B) {
// If the values are PHIs in the same block, we can do a more precise as well
// as efficient check: just check for relations between the values on
// corresponding edges.
if (const PHINode *PNB = dyn_cast<PHINode>(B))
if (PNB->getParent() == A->getParent()) {
for (unsigned i = 0, e = A->getNumIncomingValues(); i != e; ++i)
if (related(A->getIncomingValue(i),
PNB->getIncomingValueForBlock(A->getIncomingBlock(i))))
return true;
return false;
}
// Check each unique source of the PHI node against B.
SmallPtrSet<const Value *, 4> UniqueSrc;
for (unsigned i = 0, e = A->getNumIncomingValues(); i != e; ++i) {
const Value *PV1 = A->getIncomingValue(i);
if (UniqueSrc.insert(PV1) && related(PV1, B))
return true;
}
// All of the arms checked out.
return false;
}
/// Test if the value of P, or any value covered by its provenance, is ever
/// stored within the function (not counting callees).
static bool isStoredObjCPointer(const Value *P) {
SmallPtrSet<const Value *, 8> Visited;
SmallVector<const Value *, 8> Worklist;
Worklist.push_back(P);
Visited.insert(P);
do {
P = Worklist.pop_back_val();
for (Value::const_use_iterator UI = P->use_begin(), UE = P->use_end();
UI != UE; ++UI) {
const User *Ur = *UI;
if (isa<StoreInst>(Ur)) {
if (UI.getOperandNo() == 0)
// The pointer is stored.
return true;
// The pointed is stored through.
continue;
}
if (isa<CallInst>(Ur))
// The pointer is passed as an argument, ignore this.
continue;
if (isa<PtrToIntInst>(P))
// Assume the worst.
return true;
if (Visited.insert(Ur))
Worklist.push_back(Ur);
}
} while (!Worklist.empty());
// Everything checked out.
return false;
}
bool ProvenanceAnalysis::relatedCheck(const Value *A, const Value *B) {
// Skip past provenance pass-throughs.
A = GetUnderlyingObjCPtr(A);
B = GetUnderlyingObjCPtr(B);
// Quick check.
if (A == B)
return true;
// Ask regular AliasAnalysis, for a first approximation.
switch (AA->alias(A, B)) {
case AliasAnalysis::NoAlias:
return false;
case AliasAnalysis::MustAlias:
case AliasAnalysis::PartialAlias:
return true;
case AliasAnalysis::MayAlias:
break;
}
bool AIsIdentified = IsObjCIdentifiedObject(A);
bool BIsIdentified = IsObjCIdentifiedObject(B);
// An ObjC-Identified object can't alias a load if it is never locally stored.
if (AIsIdentified) {
// Check for an obvious escape.
if (isa<LoadInst>(B))
return isStoredObjCPointer(A);
if (BIsIdentified) {
// Check for an obvious escape.
if (isa<LoadInst>(A))
return isStoredObjCPointer(B);
// Both pointers are identified and escapes aren't an evident problem.
return false;
}
} else if (BIsIdentified) {
// Check for an obvious escape.
if (isa<LoadInst>(A))
return isStoredObjCPointer(B);
}
// Special handling for PHI and Select.
if (const PHINode *PN = dyn_cast<PHINode>(A))
return relatedPHI(PN, B);
if (const PHINode *PN = dyn_cast<PHINode>(B))
return relatedPHI(PN, A);
if (const SelectInst *S = dyn_cast<SelectInst>(A))
return relatedSelect(S, B);
if (const SelectInst *S = dyn_cast<SelectInst>(B))
return relatedSelect(S, A);
// Conservative.
return true;
}
bool ProvenanceAnalysis::related(const Value *A, const Value *B) {
// Begin by inserting a conservative value into the map. If the insertion
// fails, we have the answer already. If it succeeds, leave it there until we
// compute the real answer to guard against recursive queries.
if (A > B) std::swap(A, B);
std::pair<CachedResultsTy::iterator, bool> Pair =
CachedResults.insert(std::make_pair(ValuePairTy(A, B), true));
if (!Pair.second)
return Pair.first->second;
bool Result = relatedCheck(A, B);
CachedResults[ValuePairTy(A, B)] = Result;
return Result;
}
namespace {
/// \enum Sequence
///
/// \brief A sequence of states that a pointer may go through in which an
/// objc_retain and objc_release are actually needed.
enum Sequence {
S_None,
S_Retain, ///< objc_retain(x)
S_CanRelease, ///< foo(x) -- x could possibly see a ref count decrement
S_Use, ///< any use of x
S_Stop, ///< like S_Release, but code motion is stopped
S_Release, ///< objc_release(x)
S_MovableRelease ///< objc_release(x), !clang.imprecise_release
};
}
static Sequence MergeSeqs(Sequence A, Sequence B, bool TopDown) {
// The easy cases.
if (A == B)
return A;
if (A == S_None || B == S_None)
return S_None;
if (A > B) std::swap(A, B);
if (TopDown) {
// Choose the side which is further along in the sequence.
if ((A == S_Retain || A == S_CanRelease) &&
(B == S_CanRelease || B == S_Use))
return B;
} else {
// Choose the side which is further along in the sequence.
if ((A == S_Use || A == S_CanRelease) &&
(B == S_Use || B == S_Release || B == S_Stop || B == S_MovableRelease))
return A;
// If both sides are releases, choose the more conservative one.
if (A == S_Stop && (B == S_Release || B == S_MovableRelease))
return A;
if (A == S_Release && B == S_MovableRelease)
return A;
}
return S_None;
}
namespace {
/// \brief Unidirectional information about either a
/// retain-decrement-use-release sequence or release-use-decrement-retain
/// reverese sequence.
struct RRInfo {
/// After an objc_retain, the reference count of the referenced
/// object is known to be positive. Similarly, before an objc_release, the
/// reference count of the referenced object is known to be positive. If
/// there are retain-release pairs in code regions where the retain count
/// is known to be positive, they can be eliminated, regardless of any side
/// effects between them.
///
/// Also, a retain+release pair nested within another retain+release
/// pair all on the known same pointer value can be eliminated, regardless
/// of any intervening side effects.
///
/// KnownSafe is true when either of these conditions is satisfied.
bool KnownSafe;
/// True if the Calls are objc_retainBlock calls (as opposed to objc_retain
/// calls).
bool IsRetainBlock;
/// True of the objc_release calls are all marked with the "tail" keyword.
bool IsTailCallRelease;
/// If the Calls are objc_release calls and they all have a
/// clang.imprecise_release tag, this is the metadata tag.
MDNode *ReleaseMetadata;
/// For a top-down sequence, the set of objc_retains or
/// objc_retainBlocks. For bottom-up, the set of objc_releases.
SmallPtrSet<Instruction *, 2> Calls;
/// The set of optimal insert positions for moving calls in the opposite
/// sequence.
SmallPtrSet<Instruction *, 2> ReverseInsertPts;
RRInfo() :
KnownSafe(false), IsRetainBlock(false),
IsTailCallRelease(false),
ReleaseMetadata(0) {}
void clear();
};
}
void RRInfo::clear() {
KnownSafe = false;
IsRetainBlock = false;
IsTailCallRelease = false;
ReleaseMetadata = 0;
Calls.clear();
ReverseInsertPts.clear();
}
namespace {
/// \brief This class summarizes several per-pointer runtime properties which
/// are propogated through the flow graph.
class PtrState {
/// True if the reference count is known to be incremented.
bool KnownPositiveRefCount;
/// True of we've seen an opportunity for partial RR elimination, such as
/// pushing calls into a CFG triangle or into one side of a CFG diamond.
bool Partial;
/// The current position in the sequence.
Sequence Seq : 8;
public:
/// Unidirectional information about the current sequence.
///
/// TODO: Encapsulate this better.
RRInfo RRI;
PtrState() : KnownPositiveRefCount(false), Partial(false),
Seq(S_None) {}
void SetKnownPositiveRefCount() {
KnownPositiveRefCount = true;
}
void ClearRefCount() {
KnownPositiveRefCount = false;
}
bool IsKnownIncremented() const {
return KnownPositiveRefCount;
}
void SetSeq(Sequence NewSeq) {
Seq = NewSeq;
}
Sequence GetSeq() const {
return Seq;
}
void ClearSequenceProgress() {
ResetSequenceProgress(S_None);
}
void ResetSequenceProgress(Sequence NewSeq) {
Seq = NewSeq;
Partial = false;
RRI.clear();
}
void Merge(const PtrState &Other, bool TopDown);
};
}
void
PtrState::Merge(const PtrState &Other, bool TopDown) {
Seq = MergeSeqs(Seq, Other.Seq, TopDown);
KnownPositiveRefCount = KnownPositiveRefCount && Other.KnownPositiveRefCount;
// We can't merge a plain objc_retain with an objc_retainBlock.
if (RRI.IsRetainBlock != Other.RRI.IsRetainBlock)
Seq = S_None;
// If we're not in a sequence (anymore), drop all associated state.
if (Seq == S_None) {
Partial = false;
RRI.clear();
} else if (Partial || Other.Partial) {
// If we're doing a merge on a path that's previously seen a partial
// merge, conservatively drop the sequence, to avoid doing partial
// RR elimination. If the branch predicates for the two merge differ,
// mixing them is unsafe.
ClearSequenceProgress();
} else {
// Conservatively merge the ReleaseMetadata information.
if (RRI.ReleaseMetadata != Other.RRI.ReleaseMetadata)
RRI.ReleaseMetadata = 0;
RRI.KnownSafe = RRI.KnownSafe && Other.RRI.KnownSafe;
RRI.IsTailCallRelease = RRI.IsTailCallRelease &&
Other.RRI.IsTailCallRelease;
RRI.Calls.insert(Other.RRI.Calls.begin(), Other.RRI.Calls.end());
// Merge the insert point sets. If there are any differences,
// that makes this a partial merge.
Partial = RRI.ReverseInsertPts.size() != Other.RRI.ReverseInsertPts.size();
for (SmallPtrSet<Instruction *, 2>::const_iterator
I = Other.RRI.ReverseInsertPts.begin(),
E = Other.RRI.ReverseInsertPts.end(); I != E; ++I)
Partial |= RRI.ReverseInsertPts.insert(*I);
}
}
namespace {
/// \brief Per-BasicBlock state.
class BBState {
/// The number of unique control paths from the entry which can reach this
/// block.
unsigned TopDownPathCount;
/// The number of unique control paths to exits from this block.
unsigned BottomUpPathCount;
/// A type for PerPtrTopDown and PerPtrBottomUp.
typedef MapVector<const Value *, PtrState> MapTy;
/// The top-down traversal uses this to record information known about a
/// pointer at the bottom of each block.
MapTy PerPtrTopDown;
/// The bottom-up traversal uses this to record information known about a
/// pointer at the top of each block.
MapTy PerPtrBottomUp;
/// Effective predecessors of the current block ignoring ignorable edges and
/// ignored backedges.
SmallVector<BasicBlock *, 2> Preds;
/// Effective successors of the current block ignoring ignorable edges and
/// ignored backedges.
SmallVector<BasicBlock *, 2> Succs;
public:
BBState() : TopDownPathCount(0), BottomUpPathCount(0) {}
typedef MapTy::iterator ptr_iterator;
typedef MapTy::const_iterator ptr_const_iterator;
ptr_iterator top_down_ptr_begin() { return PerPtrTopDown.begin(); }
ptr_iterator top_down_ptr_end() { return PerPtrTopDown.end(); }
ptr_const_iterator top_down_ptr_begin() const {
return PerPtrTopDown.begin();
}
ptr_const_iterator top_down_ptr_end() const {
return PerPtrTopDown.end();
}
ptr_iterator bottom_up_ptr_begin() { return PerPtrBottomUp.begin(); }
ptr_iterator bottom_up_ptr_end() { return PerPtrBottomUp.end(); }
ptr_const_iterator bottom_up_ptr_begin() const {
return PerPtrBottomUp.begin();
}
ptr_const_iterator bottom_up_ptr_end() const {
return PerPtrBottomUp.end();
}
/// Mark this block as being an entry block, which has one path from the
/// entry by definition.
void SetAsEntry() { TopDownPathCount = 1; }
/// Mark this block as being an exit block, which has one path to an exit by
/// definition.
void SetAsExit() { BottomUpPathCount = 1; }
PtrState &getPtrTopDownState(const Value *Arg) {
return PerPtrTopDown[Arg];
}
PtrState &getPtrBottomUpState(const Value *Arg) {
return PerPtrBottomUp[Arg];
}
void clearBottomUpPointers() {
PerPtrBottomUp.clear();
}
void clearTopDownPointers() {
PerPtrTopDown.clear();
}
void InitFromPred(const BBState &Other);
void InitFromSucc(const BBState &Other);
void MergePred(const BBState &Other);
void MergeSucc(const BBState &Other);
/// Return the number of possible unique paths from an entry to an exit
/// which pass through this block. This is only valid after both the
/// top-down and bottom-up traversals are complete.
unsigned GetAllPathCount() const {
assert(TopDownPathCount != 0);
assert(BottomUpPathCount != 0);
return TopDownPathCount * BottomUpPathCount;
}
// Specialized CFG utilities.
typedef SmallVectorImpl<BasicBlock *>::const_iterator edge_iterator;
edge_iterator pred_begin() { return Preds.begin(); }
edge_iterator pred_end() { return Preds.end(); }
edge_iterator succ_begin() { return Succs.begin(); }
edge_iterator succ_end() { return Succs.end(); }
void addSucc(BasicBlock *Succ) { Succs.push_back(Succ); }
void addPred(BasicBlock *Pred) { Preds.push_back(Pred); }
bool isExit() const { return Succs.empty(); }
};
}
void BBState::InitFromPred(const BBState &Other) {
PerPtrTopDown = Other.PerPtrTopDown;
TopDownPathCount = Other.TopDownPathCount;
}
void BBState::InitFromSucc(const BBState &Other) {
PerPtrBottomUp = Other.PerPtrBottomUp;
BottomUpPathCount = Other.BottomUpPathCount;
}
/// The top-down traversal uses this to merge information about predecessors to
/// form the initial state for a new block.
void BBState::MergePred(const BBState &Other) {
// Other.TopDownPathCount can be 0, in which case it is either dead or a
// loop backedge. Loop backedges are special.
TopDownPathCount += Other.TopDownPathCount;
// Check for overflow. If we have overflow, fall back to conservative behavior.
if (TopDownPathCount < Other.TopDownPathCount) {
clearTopDownPointers();
return;
}
// For each entry in the other set, if our set has an entry with the same key,
// merge the entries. Otherwise, copy the entry and merge it with an empty
// entry.
for (ptr_const_iterator MI = Other.top_down_ptr_begin(),
ME = Other.top_down_ptr_end(); MI != ME; ++MI) {
std::pair<ptr_iterator, bool> Pair = PerPtrTopDown.insert(*MI);
Pair.first->second.Merge(Pair.second ? PtrState() : MI->second,
/*TopDown=*/true);
}
// For each entry in our set, if the other set doesn't have an entry with the
// same key, force it to merge with an empty entry.
for (ptr_iterator MI = top_down_ptr_begin(),
ME = top_down_ptr_end(); MI != ME; ++MI)
if (Other.PerPtrTopDown.find(MI->first) == Other.PerPtrTopDown.end())
MI->second.Merge(PtrState(), /*TopDown=*/true);
}
/// The bottom-up traversal uses this to merge information about successors to
/// form the initial state for a new block.
void BBState::MergeSucc(const BBState &Other) {
// Other.BottomUpPathCount can be 0, in which case it is either dead or a
// loop backedge. Loop backedges are special.
BottomUpPathCount += Other.BottomUpPathCount;
// Check for overflow. If we have overflow, fall back to conservative behavior.
if (BottomUpPathCount < Other.BottomUpPathCount) {
clearBottomUpPointers();
return;
}
// For each entry in the other set, if our set has an entry with the
// same key, merge the entries. Otherwise, copy the entry and merge
// it with an empty entry.
for (ptr_const_iterator MI = Other.bottom_up_ptr_begin(),
ME = Other.bottom_up_ptr_end(); MI != ME; ++MI) {
std::pair<ptr_iterator, bool> Pair = PerPtrBottomUp.insert(*MI);
Pair.first->second.Merge(Pair.second ? PtrState() : MI->second,
/*TopDown=*/false);
}
// For each entry in our set, if the other set doesn't have an entry
// with the same key, force it to merge with an empty entry.
for (ptr_iterator MI = bottom_up_ptr_begin(),
ME = bottom_up_ptr_end(); MI != ME; ++MI)
if (Other.PerPtrBottomUp.find(MI->first) == Other.PerPtrBottomUp.end())
MI->second.Merge(PtrState(), /*TopDown=*/false);
}
namespace {
/// \brief The main ARC optimization pass.
class ObjCARCOpt : public FunctionPass {
bool Changed;
ProvenanceAnalysis PA;
/// A flag indicating whether this optimization pass should run.
bool Run;
/// Declarations for ObjC runtime functions, for use in creating calls to
/// them. These are initialized lazily to avoid cluttering up the Module
/// with unused declarations.
/// Declaration for ObjC runtime function
/// objc_retainAutoreleasedReturnValue.
Constant *RetainRVCallee;
/// Declaration for ObjC runtime function objc_autoreleaseReturnValue.
Constant *AutoreleaseRVCallee;
/// Declaration for ObjC runtime function objc_release.
Constant *ReleaseCallee;
/// Declaration for ObjC runtime function objc_retain.
Constant *RetainCallee;
/// Declaration for ObjC runtime function objc_retainBlock.
Constant *RetainBlockCallee;
/// Declaration for ObjC runtime function objc_autorelease.
Constant *AutoreleaseCallee;
/// Flags which determine whether each of the interesting runtine functions
/// is in fact used in the current function.
unsigned UsedInThisFunction;
/// The Metadata Kind for clang.imprecise_release metadata.
unsigned ImpreciseReleaseMDKind;
/// The Metadata Kind for clang.arc.copy_on_escape metadata.
unsigned CopyOnEscapeMDKind;
/// The Metadata Kind for clang.arc.no_objc_arc_exceptions metadata.
unsigned NoObjCARCExceptionsMDKind;
Constant *getRetainRVCallee(Module *M);
Constant *getAutoreleaseRVCallee(Module *M);
Constant *getReleaseCallee(Module *M);
Constant *getRetainCallee(Module *M);
Constant *getRetainBlockCallee(Module *M);
Constant *getAutoreleaseCallee(Module *M);
bool IsRetainBlockOptimizable(const Instruction *Inst);
void OptimizeRetainCall(Function &F, Instruction *Retain);
bool OptimizeRetainRVCall(Function &F, Instruction *RetainRV);
void OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV,
InstructionClass &Class);
void OptimizeIndividualCalls(Function &F);
void CheckForCFGHazards(const BasicBlock *BB,
DenseMap<const BasicBlock *, BBState> &BBStates,
BBState &MyStates) const;
bool VisitInstructionBottomUp(Instruction *Inst,
BasicBlock *BB,
MapVector<Value *, RRInfo> &Retains,
BBState &MyStates);
bool VisitBottomUp(BasicBlock *BB,
DenseMap<const BasicBlock *, BBState> &BBStates,
MapVector<Value *, RRInfo> &Retains);
bool VisitInstructionTopDown(Instruction *Inst,
DenseMap<Value *, RRInfo> &Releases,
BBState &MyStates);
bool VisitTopDown(BasicBlock *BB,
DenseMap<const BasicBlock *, BBState> &BBStates,
DenseMap<Value *, RRInfo> &Releases);
bool Visit(Function &F,
DenseMap<const BasicBlock *, BBState> &BBStates,
MapVector<Value *, RRInfo> &Retains,
DenseMap<Value *, RRInfo> &Releases);
void MoveCalls(Value *Arg, RRInfo &RetainsToMove, RRInfo &ReleasesToMove,
MapVector<Value *, RRInfo> &Retains,
DenseMap<Value *, RRInfo> &Releases,
SmallVectorImpl<Instruction *> &DeadInsts,
Module *M);
bool PerformCodePlacement(DenseMap<const BasicBlock *, BBState> &BBStates,
MapVector<Value *, RRInfo> &Retains,
DenseMap<Value *, RRInfo> &Releases,
Module *M);
void OptimizeWeakCalls(Function &F);
bool OptimizeSequences(Function &F);
void OptimizeReturns(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
virtual bool doInitialization(Module &M);
virtual bool runOnFunction(Function &F);
virtual void releaseMemory();
public:
static char ID;
ObjCARCOpt() : FunctionPass(ID) {
initializeObjCARCOptPass(*PassRegistry::getPassRegistry());
}
};
}
char ObjCARCOpt::ID = 0;
INITIALIZE_PASS_BEGIN(ObjCARCOpt,
"objc-arc", "ObjC ARC optimization", false, false)
INITIALIZE_PASS_DEPENDENCY(ObjCARCAliasAnalysis)
INITIALIZE_PASS_END(ObjCARCOpt,
"objc-arc", "ObjC ARC optimization", false, false)
Pass *llvm::createObjCARCOptPass() {
return new ObjCARCOpt();
}
void ObjCARCOpt::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<ObjCARCAliasAnalysis>();
AU.addRequired<AliasAnalysis>();
// ARC optimization doesn't currently split critical edges.
AU.setPreservesCFG();
}
bool ObjCARCOpt::IsRetainBlockOptimizable(const Instruction *Inst) {
// Without the magic metadata tag, we have to assume this might be an
// objc_retainBlock call inserted to convert a block pointer to an id,
// in which case it really is needed.
if (!Inst->getMetadata(CopyOnEscapeMDKind))
return false;
// If the pointer "escapes" (not including being used in a call),
// the copy may be needed.
if (DoesObjCBlockEscape(Inst))
return false;
// Otherwise, it's not needed.
return true;
}
Constant *ObjCARCOpt::getRetainRVCallee(Module *M) {
if (!RetainRVCallee) {
LLVMContext &C = M->getContext();
Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
Type *Params[] = { I8X };
FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false);
AttributeSet Attribute =
AttributeSet().addAttr(M->getContext(), AttributeSet::FunctionIndex,
Attribute::get(C, Attribute::NoUnwind));
RetainRVCallee =
M->getOrInsertFunction("objc_retainAutoreleasedReturnValue", FTy,
Attribute);
}
return RetainRVCallee;
}
Constant *ObjCARCOpt::getAutoreleaseRVCallee(Module *M) {
if (!AutoreleaseRVCallee) {
LLVMContext &C = M->getContext();
Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
Type *Params[] = { I8X };
FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false);
AttributeSet Attribute =
AttributeSet().addAttr(M->getContext(), AttributeSet::FunctionIndex,
Attribute::get(C, Attribute::NoUnwind));
AutoreleaseRVCallee =
M->getOrInsertFunction("objc_autoreleaseReturnValue", FTy,
Attribute);
}
return AutoreleaseRVCallee;
}
Constant *ObjCARCOpt::getReleaseCallee(Module *M) {
if (!ReleaseCallee) {
LLVMContext &C = M->getContext();
Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
AttributeSet Attribute =
AttributeSet().addAttr(M->getContext(), AttributeSet::FunctionIndex,
Attribute::get(C, Attribute::NoUnwind));
ReleaseCallee =
M->getOrInsertFunction(
"objc_release",
FunctionType::get(Type::getVoidTy(C), Params, /*isVarArg=*/false),
Attribute);
}
return ReleaseCallee;
}
Constant *ObjCARCOpt::getRetainCallee(Module *M) {
if (!RetainCallee) {
LLVMContext &C = M->getContext();
Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
AttributeSet Attribute =
AttributeSet().addAttr(M->getContext(), AttributeSet::FunctionIndex,
Attribute::get(C, Attribute::NoUnwind));
RetainCallee =
M->getOrInsertFunction(
"objc_retain",
FunctionType::get(Params[0], Params, /*isVarArg=*/false),
Attribute);
}
return RetainCallee;
}
Constant *ObjCARCOpt::getRetainBlockCallee(Module *M) {
if (!RetainBlockCallee) {
LLVMContext &C = M->getContext();
Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
// objc_retainBlock is not nounwind because it calls user copy constructors
// which could theoretically throw.
RetainBlockCallee =
M->getOrInsertFunction(
"objc_retainBlock",
FunctionType::get(Params[0], Params, /*isVarArg=*/false),
AttributeSet());
}
return RetainBlockCallee;
}
Constant *ObjCARCOpt::getAutoreleaseCallee(Module *M) {
if (!AutoreleaseCallee) {
LLVMContext &C = M->getContext();
Type *Params[] = { PointerType::getUnqual(Type::getInt8Ty(C)) };
AttributeSet Attribute =
AttributeSet().addAttr(M->getContext(), AttributeSet::FunctionIndex,
Attribute::get(C, Attribute::NoUnwind));
AutoreleaseCallee =
M->getOrInsertFunction(
"objc_autorelease",
FunctionType::get(Params[0], Params, /*isVarArg=*/false),
Attribute);
}
return AutoreleaseCallee;
}
/// Test whether the given value is possible a reference-counted pointer,
/// including tests which utilize AliasAnalysis.
static bool IsPotentialUse(const Value *Op, AliasAnalysis &AA) {
// First make the rudimentary check.
if (!IsPotentialUse(Op))
return false;
// Objects in constant memory are not reference-counted.
if (AA.pointsToConstantMemory(Op))
return false;
// Pointers in constant memory are not pointing to reference-counted objects.
if (const LoadInst *LI = dyn_cast<LoadInst>(Op))
if (AA.pointsToConstantMemory(LI->getPointerOperand()))
return false;
// Otherwise assume the worst.
return true;
}
/// Test whether the given instruction can result in a reference count
/// modification (positive or negative) for the pointer's object.
static bool
CanAlterRefCount(const Instruction *Inst, const Value *Ptr,
ProvenanceAnalysis &PA, InstructionClass Class) {
switch (Class) {
case IC_Autorelease:
case IC_AutoreleaseRV:
case IC_User:
// These operations never directly modify a reference count.
return false;
default: break;
}
ImmutableCallSite CS = static_cast<const Value *>(Inst);
assert(CS && "Only calls can alter reference counts!");
// See if AliasAnalysis can help us with the call.
AliasAnalysis::ModRefBehavior MRB = PA.getAA()->getModRefBehavior(CS);
if (AliasAnalysis::onlyReadsMemory(MRB))
return false;
if (AliasAnalysis::onlyAccessesArgPointees(MRB)) {
for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
I != E; ++I) {
const Value *Op = *I;
if (IsPotentialUse(Op, *PA.getAA()) && PA.related(Ptr, Op))
return true;
}
return false;
}
// Assume the worst.
return true;
}
/// Test whether the given instruction can "use" the given pointer's object in a
/// way that requires the reference count to be positive.
static bool
CanUse(const Instruction *Inst, const Value *Ptr, ProvenanceAnalysis &PA,
InstructionClass Class) {
// IC_Call operations (as opposed to IC_CallOrUser) never "use" objc pointers.
if (Class == IC_Call)
return false;
// Consider various instructions which may have pointer arguments which are
// not "uses".
if (const ICmpInst *ICI = dyn_cast<ICmpInst>(Inst)) {
// Comparing a pointer with null, or any other constant, isn't really a use,
// because we don't care what the pointer points to, or about the values
// of any other dynamic reference-counted pointers.
if (!IsPotentialUse(ICI->getOperand(1), *PA.getAA()))
return false;
} else if (ImmutableCallSite CS = static_cast<const Value *>(Inst)) {
// For calls, just check the arguments (and not the callee operand).
for (ImmutableCallSite::arg_iterator OI = CS.arg_begin(),
OE = CS.arg_end(); OI != OE; ++OI) {
const Value *Op = *OI;
if (IsPotentialUse(Op, *PA.getAA()) && PA.related(Ptr, Op))
return true;
}
return false;
} else if (const StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
// Special-case stores, because we don't care about the stored value, just
// the store address.
const Value *Op = GetUnderlyingObjCPtr(SI->getPointerOperand());
// If we can't tell what the underlying object was, assume there is a
// dependence.
return IsPotentialUse(Op, *PA.getAA()) && PA.related(Op, Ptr);
}
// Check each operand for a match.
for (User::const_op_iterator OI = Inst->op_begin(), OE = Inst->op_end();
OI != OE; ++OI) {
const Value *Op = *OI;
if (IsPotentialUse(Op, *PA.getAA()) && PA.related(Ptr, Op))
return true;
}
return false;
}
/// Test whether the given instruction can autorelease any pointer or cause an
/// autoreleasepool pop.
static bool
CanInterruptRV(InstructionClass Class) {
switch (Class) {
case IC_AutoreleasepoolPop:
case IC_CallOrUser:
case IC_Call:
case IC_Autorelease:
case IC_AutoreleaseRV:
case IC_FusedRetainAutorelease:
case IC_FusedRetainAutoreleaseRV:
return true;
default:
return false;
}
}
namespace {
/// \enum DependenceKind
/// \brief Defines different dependence kinds among various ARC constructs.
///
/// There are several kinds of dependence-like concepts in use here.
///
enum DependenceKind {
NeedsPositiveRetainCount,
AutoreleasePoolBoundary,
CanChangeRetainCount,
RetainAutoreleaseDep, ///< Blocks objc_retainAutorelease.
RetainAutoreleaseRVDep, ///< Blocks objc_retainAutoreleaseReturnValue.
RetainRVDep ///< Blocks objc_retainAutoreleasedReturnValue.
};
}
/// Test if there can be dependencies on Inst through Arg. This function only
/// tests dependencies relevant for removing pairs of calls.
static bool
Depends(DependenceKind Flavor, Instruction *Inst, const Value *Arg,
ProvenanceAnalysis &PA) {
// If we've reached the definition of Arg, stop.
if (Inst == Arg)
return true;
switch (Flavor) {
case NeedsPositiveRetainCount: {
InstructionClass Class = GetInstructionClass(Inst);
switch (Class) {
case IC_AutoreleasepoolPop:
case IC_AutoreleasepoolPush:
case IC_None:
return false;
default:
return CanUse(Inst, Arg, PA, Class);
}
}
case AutoreleasePoolBoundary: {
InstructionClass Class = GetInstructionClass(Inst);
switch (Class) {
case IC_AutoreleasepoolPop:
case IC_AutoreleasepoolPush:
// These mark the end and begin of an autorelease pool scope.
return true;
default:
// Nothing else does this.
return false;
}
}
case CanChangeRetainCount: {
InstructionClass Class = GetInstructionClass(Inst);
switch (Class) {
case IC_AutoreleasepoolPop:
// Conservatively assume this can decrement any count.
return true;
case IC_AutoreleasepoolPush:
case IC_None:
return false;
default:
return CanAlterRefCount(Inst, Arg, PA, Class);
}
}
case RetainAutoreleaseDep:
switch (GetBasicInstructionClass(Inst)) {
case IC_AutoreleasepoolPop:
case IC_AutoreleasepoolPush:
// Don't merge an objc_autorelease with an objc_retain inside a different
// autoreleasepool scope.
return true;
case IC_Retain:
case IC_RetainRV:
// Check for a retain of the same pointer for merging.
return GetObjCArg(Inst) == Arg;
default:
// Nothing else matters for objc_retainAutorelease formation.
return false;
}
case RetainAutoreleaseRVDep: {
InstructionClass Class = GetBasicInstructionClass(Inst);
switch (Class) {
case IC_Retain:
case IC_RetainRV:
// Check for a retain of the same pointer for merging.
return GetObjCArg(Inst) == Arg;
default:
// Anything that can autorelease interrupts
// retainAutoreleaseReturnValue formation.
return CanInterruptRV(Class);
}
}
case RetainRVDep:
return CanInterruptRV(GetBasicInstructionClass(Inst));
}
llvm_unreachable("Invalid dependence flavor");
}
/// Walk up the CFG from StartPos (which is in StartBB) and find local and
/// non-local dependencies on Arg.
///
/// TODO: Cache results?
static void
FindDependencies(DependenceKind Flavor,
const Value *Arg,
BasicBlock *StartBB, Instruction *StartInst,
SmallPtrSet<Instruction *, 4> &DependingInstructions,
SmallPtrSet<const BasicBlock *, 4> &Visited,
ProvenanceAnalysis &PA) {
BasicBlock::iterator StartPos = StartInst;
SmallVector<std::pair<BasicBlock *, BasicBlock::iterator>, 4> Worklist;
Worklist.push_back(std::make_pair(StartBB, StartPos));
do {
std::pair<BasicBlock *, BasicBlock::iterator> Pair =
Worklist.pop_back_val();
BasicBlock *LocalStartBB = Pair.first;
BasicBlock::iterator LocalStartPos = Pair.second;
BasicBlock::iterator StartBBBegin = LocalStartBB->begin();
for (;;) {
if (LocalStartPos == StartBBBegin) {
pred_iterator PI(LocalStartBB), PE(LocalStartBB, false);
if (PI == PE)
// If we've reached the function entry, produce a null dependence.
DependingInstructions.insert(0);
else
// Add the predecessors to the worklist.
do {
BasicBlock *PredBB = *PI;
if (Visited.insert(PredBB))
Worklist.push_back(std::make_pair(PredBB, PredBB->end()));
} while (++PI != PE);
break;
}
Instruction *Inst = --LocalStartPos;
if (Depends(Flavor, Inst, Arg, PA)) {
DependingInstructions.insert(Inst);
break;
}
}
} while (!Worklist.empty());
// Determine whether the original StartBB post-dominates all of the blocks we
// visited. If not, insert a sentinal indicating that most optimizations are
// not safe.
for (SmallPtrSet<const BasicBlock *, 4>::const_iterator I = Visited.begin(),
E = Visited.end(); I != E; ++I) {
const BasicBlock *BB = *I;
if (BB == StartBB)
continue;
const TerminatorInst *TI = cast<TerminatorInst>(&BB->back());
for (succ_const_iterator SI(TI), SE(TI, false); SI != SE; ++SI) {
const BasicBlock *Succ = *SI;
if (Succ != StartBB && !Visited.count(Succ)) {
DependingInstructions.insert(reinterpret_cast<Instruction *>(-1));
return;
}
}
}
}
static bool isNullOrUndef(const Value *V) {
return isa<ConstantPointerNull>(V) || isa<UndefValue>(V);
}
static bool isNoopInstruction(const Instruction *I) {
return isa<BitCastInst>(I) ||
(isa<GetElementPtrInst>(I) &&
cast<GetElementPtrInst>(I)->hasAllZeroIndices());
}
/// Turn objc_retain into objc_retainAutoreleasedReturnValue if the operand is a
/// return value.
void
ObjCARCOpt::OptimizeRetainCall(Function &F, Instruction *Retain) {
ImmutableCallSite CS(GetObjCArg(Retain));
const Instruction *Call = CS.getInstruction();
if (!Call) return;
if (Call->getParent() != Retain->getParent()) return;
// Check that the call is next to the retain.
BasicBlock::const_iterator I = Call;
++I;
while (isNoopInstruction(I)) ++I;
if (&*I != Retain)
return;
// Turn it to an objc_retainAutoreleasedReturnValue..
Changed = true;
++NumPeeps;
DEBUG(dbgs() << "ObjCARCOpt::OptimizeRetainCall: Transforming "
"objc_retain => objc_retainAutoreleasedReturnValue"
" since the operand is a return value.\n"
" Old: "
<< *Retain << "\n");
cast<CallInst>(Retain)->setCalledFunction(getRetainRVCallee(F.getParent()));
DEBUG(dbgs() << " New: "
<< *Retain << "\n");
}
/// Turn objc_retainAutoreleasedReturnValue into objc_retain if the operand is
/// not a return value. Or, if it can be paired with an
/// objc_autoreleaseReturnValue, delete the pair and return true.
bool
ObjCARCOpt::OptimizeRetainRVCall(Function &F, Instruction *RetainRV) {
// Check for the argument being from an immediately preceding call or invoke.
const Value *Arg = GetObjCArg(RetainRV);
ImmutableCallSite CS(Arg);
if (const Instruction *Call = CS.getInstruction()) {
if (Call->getParent() == RetainRV->getParent()) {
BasicBlock::const_iterator I = Call;
++I;
while (isNoopInstruction(I)) ++I;
if (&*I == RetainRV)
return false;
} else if (const InvokeInst *II = dyn_cast<InvokeInst>(Call)) {
BasicBlock *RetainRVParent = RetainRV->getParent();
if (II->getNormalDest() == RetainRVParent) {
BasicBlock::const_iterator I = RetainRVParent->begin();
while (isNoopInstruction(I)) ++I;
if (&*I == RetainRV)
return false;
}
}
}
// Check for being preceded by an objc_autoreleaseReturnValue on the same
// pointer. In this case, we can delete the pair.
BasicBlock::iterator I = RetainRV, Begin = RetainRV->getParent()->begin();
if (I != Begin) {
do --I; while (I != Begin && isNoopInstruction(I));
if (GetBasicInstructionClass(I) == IC_AutoreleaseRV &&
GetObjCArg(I) == Arg) {
Changed = true;
++NumPeeps;
DEBUG(dbgs() << "ObjCARCOpt::OptimizeRetainRVCall: Erasing " << *I << "\n"
<< " Erasing " << *RetainRV
<< "\n");
EraseInstruction(I);
EraseInstruction(RetainRV);
return true;
}
}
// Turn it to a plain objc_retain.
Changed = true;
++NumPeeps;
DEBUG(dbgs() << "ObjCARCOpt::OptimizeRetainRVCall: Transforming "
"objc_retainAutoreleasedReturnValue => "
"objc_retain since the operand is not a return value.\n"
" Old: "
<< *RetainRV << "\n");
cast<CallInst>(RetainRV)->setCalledFunction(getRetainCallee(F.getParent()));
DEBUG(dbgs() << " New: "
<< *RetainRV << "\n");
return false;
}
/// Turn objc_autoreleaseReturnValue into objc_autorelease if the result is not
/// used as a return value.
void
ObjCARCOpt::OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV,
InstructionClass &Class) {
// Check for a return of the pointer value.
const Value *Ptr = GetObjCArg(AutoreleaseRV);
SmallVector<const Value *, 2> Users;
Users.push_back(Ptr);
do {
Ptr = Users.pop_back_val();
for (Value::const_use_iterator UI = Ptr->use_begin(), UE = Ptr->use_end();
UI != UE; ++UI) {
const User *I = *UI;
if (isa<ReturnInst>(I) || GetBasicInstructionClass(I) == IC_RetainRV)
return;
if (isa<BitCastInst>(I))
Users.push_back(I);
}
} while (!Users.empty());
Changed = true;
++NumPeeps;
DEBUG(dbgs() << "ObjCARCOpt::OptimizeAutoreleaseRVCall: Transforming "
"objc_autoreleaseReturnValue => "
"objc_autorelease since its operand is not used as a return "
"value.\n"
" Old: "
<< *AutoreleaseRV << "\n");
CallInst *AutoreleaseRVCI = cast<CallInst>(AutoreleaseRV);
AutoreleaseRVCI->
setCalledFunction(getAutoreleaseCallee(F.getParent()));
AutoreleaseRVCI->setTailCall(false); // Never tail call objc_autorelease.
Class = IC_Autorelease;
DEBUG(dbgs() << " New: "
<< *AutoreleaseRV << "\n");
}
/// Visit each call, one at a time, and make simplifications without doing any
/// additional analysis.
void ObjCARCOpt::OptimizeIndividualCalls(Function &F) {
// Reset all the flags in preparation for recomputing them.
UsedInThisFunction = 0;
// Visit all objc_* calls in F.
for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
Instruction *Inst = &*I++;
DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Visiting: " <<
*Inst << "\n");
InstructionClass Class = GetBasicInstructionClass(Inst);
switch (Class) {
default: break;
// Delete no-op casts. These function calls have special semantics, but
// the semantics are entirely implemented via lowering in the front-end,
// so by the time they reach the optimizer, they are just no-op calls
// which return their argument.
//
// There are gray areas here, as the ability to cast reference-counted
// pointers to raw void* and back allows code to break ARC assumptions,
// however these are currently considered to be unimportant.
case IC_NoopCast:
Changed = true;
++NumNoops;
DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Erasing no-op cast:"
" " << *Inst << "\n");
EraseInstruction(Inst);
continue;
// If the pointer-to-weak-pointer is null, it's undefined behavior.
case IC_StoreWeak:
case IC_LoadWeak:
case IC_LoadWeakRetained:
case IC_InitWeak:
case IC_DestroyWeak: {
CallInst *CI = cast<CallInst>(Inst);
if (isNullOrUndef(CI->getArgOperand(0))) {
Changed = true;
Type *Ty = CI->getArgOperand(0)->getType();
new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()),
Constant::getNullValue(Ty),
CI);
llvm::Value *NewValue = UndefValue::get(CI->getType());
DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: A null "
"pointer-to-weak-pointer is undefined behavior.\n"
" Old = " << *CI <<
"\n New = " <<
*NewValue << "\n");
CI->replaceAllUsesWith(NewValue);
CI->eraseFromParent();
continue;
}
break;
}
case IC_CopyWeak:
case IC_MoveWeak: {
CallInst *CI = cast<CallInst>(Inst);
if (isNullOrUndef(CI->getArgOperand(0)) ||
isNullOrUndef(CI->getArgOperand(1))) {
Changed = true;
Type *Ty = CI->getArgOperand(0)->getType();
new StoreInst(UndefValue::get(cast<PointerType>(Ty)->getElementType()),
Constant::getNullValue(Ty),
CI);
llvm::Value *NewValue = UndefValue::get(CI->getType());
DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: A null "
"pointer-to-weak-pointer is undefined behavior.\n"
" Old = " << *CI <<
"\n New = " <<
*NewValue << "\n");
CI->replaceAllUsesWith(NewValue);
CI->eraseFromParent();
continue;
}
break;
}
case IC_Retain:
OptimizeRetainCall(F, Inst);
break;
case IC_RetainRV:
if (OptimizeRetainRVCall(F, Inst))
continue;
break;
case IC_AutoreleaseRV:
OptimizeAutoreleaseRVCall(F, Inst, Class);
break;
}
// objc_autorelease(x) -> objc_release(x) if x is otherwise unused.
if (IsAutorelease(Class) && Inst->use_empty()) {
CallInst *Call = cast<CallInst>(Inst);
const Value *Arg = Call->getArgOperand(0);
Arg = FindSingleUseIdentifiedObject(Arg);
if (Arg) {
Changed = true;
++NumAutoreleases;
// Create the declaration lazily.
LLVMContext &C = Inst->getContext();
CallInst *NewCall =
CallInst::Create(getReleaseCallee(F.getParent()),
Call->getArgOperand(0), "", Call);
NewCall->setMetadata(ImpreciseReleaseMDKind,
MDNode::get(C, ArrayRef<Value *>()));
DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Replacing "
"objc_autorelease(x) with objc_release(x) since x is "
"otherwise unused.\n"
" Old: " << *Call <<
"\n New: " <<
*NewCall << "\n");
EraseInstruction(Call);
Inst = NewCall;
Class = IC_Release;
}
}
// For functions which can never be passed stack arguments, add
// a tail keyword.
if (IsAlwaysTail(Class)) {
Changed = true;
DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Adding tail keyword"
" to function since it can never be passed stack args: " << *Inst <<
"\n");
cast<CallInst>(Inst)->setTailCall();
}
// Ensure that functions that can never have a "tail" keyword due to the
// semantics of ARC truly do not do so.
if (IsNeverTail(Class)) {
Changed = true;
DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Removing tail keyword"
" from function: " << *Inst <<
"\n");
cast<CallInst>(Inst)->setTailCall(false);
}
// Set nounwind as needed.
if (IsNoThrow(Class)) {
Changed = true;
DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Found no throw"
" class. Setting nounwind on: " << *Inst << "\n");
cast<CallInst>(Inst)->setDoesNotThrow();
}
if (!IsNoopOnNull(Class)) {
UsedInThisFunction |= 1 << Class;
continue;
}
const Value *Arg = GetObjCArg(Inst);
// ARC calls with null are no-ops. Delete them.
if (isNullOrUndef(Arg)) {
Changed = true;
++NumNoops;
DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: ARC calls with "
" null are no-ops. Erasing: " << *Inst << "\n");
EraseInstruction(Inst);
continue;
}
// Keep track of which of retain, release, autorelease, and retain_block
// are actually present in this function.
UsedInThisFunction |= 1 << Class;
// If Arg is a PHI, and one or more incoming values to the
// PHI are null, and the call is control-equivalent to the PHI, and there
// are no relevant side effects between the PHI and the call, the call
// could be pushed up to just those paths with non-null incoming values.
// For now, don't bother splitting critical edges for this.
SmallVector<std::pair<Instruction *, const Value *>, 4> Worklist;
Worklist.push_back(std::make_pair(Inst, Arg));
do {
std::pair<Instruction *, const Value *> Pair = Worklist.pop_back_val();
Inst = Pair.first;
Arg = Pair.second;
const PHINode *PN = dyn_cast<PHINode>(Arg);
if (!PN) continue;
// Determine if the PHI has any null operands, or any incoming
// critical edges.
bool HasNull = false;
bool HasCriticalEdges = false;
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
Value *Incoming =
StripPointerCastsAndObjCCalls(PN->getIncomingValue(i));
if (isNullOrUndef(Incoming))
HasNull = true;
else if (cast<TerminatorInst>(PN->getIncomingBlock(i)->back())
.getNumSuccessors() != 1) {
HasCriticalEdges = true;
break;
}
}
// If we have null operands and no critical edges, optimize.
if (!HasCriticalEdges && HasNull) {
SmallPtrSet<Instruction *, 4> DependingInstructions;
SmallPtrSet<const BasicBlock *, 4> Visited;
// Check that there is nothing that cares about the reference
// count between the call and the phi.
switch (Class) {
case IC_Retain:
case IC_RetainBlock:
// These can always be moved up.
break;
case IC_Release:
// These can't be moved across things that care about the retain
// count.
FindDependencies(NeedsPositiveRetainCount, Arg,
Inst->getParent(), Inst,
DependingInstructions, Visited, PA);
break;
case IC_Autorelease:
// These can't be moved across autorelease pool scope boundaries.
FindDependencies(AutoreleasePoolBoundary, Arg,
Inst->getParent(), Inst,
DependingInstructions, Visited, PA);
break;
case IC_RetainRV:
case IC_AutoreleaseRV:
// Don't move these; the RV optimization depends on the autoreleaseRV
// being tail called, and the retainRV being immediately after a call
// (which might still happen if we get lucky with codegen layout, but
// it's not worth taking the chance).
continue;
default:
llvm_unreachable("Invalid dependence flavor");
}
if (DependingInstructions.size() == 1 &&
*DependingInstructions.begin() == PN) {
Changed = true;
++NumPartialNoops;
// Clone the call into each predecessor that has a non-null value.
CallInst *CInst = cast<CallInst>(Inst);
Type *ParamTy = CInst->getArgOperand(0)->getType();
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
Value *Incoming =
StripPointerCastsAndObjCCalls(PN->getIncomingValue(i));
if (!isNullOrUndef(Incoming)) {
CallInst *Clone = cast<CallInst>(CInst->clone());
Value *Op = PN->getIncomingValue(i);
Instruction *InsertPos = &PN->getIncomingBlock(i)->back();
if (Op->getType() != ParamTy)
Op = new BitCastInst(Op, ParamTy, "", InsertPos);
Clone->setArgOperand(0, Op);
Clone->insertBefore(InsertPos);
DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Cloning "
<< *CInst << "\n"
" And inserting "
"clone at " << *InsertPos << "\n");
Worklist.push_back(std::make_pair(Clone, Incoming));
}
}
// Erase the original call.
DEBUG(dbgs() << "Erasing: " << *CInst << "\n");
EraseInstruction(CInst);
continue;
}
}
} while (!Worklist.empty());
}
DEBUG(dbgs() << "ObjCARCOpt::OptimizeIndividualCalls: Finished List.\n");
}
/// Check for critical edges, loop boundaries, irreducible control flow, or
/// other CFG structures where moving code across the edge would result in it
/// being executed more.
void
ObjCARCOpt::CheckForCFGHazards(const BasicBlock *BB,
DenseMap<const BasicBlock *, BBState> &BBStates,
BBState &MyStates) const {
// If any top-down local-use or possible-dec has a succ which is earlier in
// the sequence, forget it.
for (BBState::ptr_iterator I = MyStates.top_down_ptr_begin(),
E = MyStates.top_down_ptr_end(); I != E; ++I)
switch (I->second.GetSeq()) {
default: break;
case S_Use: {
const Value *Arg = I->first;
const TerminatorInst *TI = cast<TerminatorInst>(&BB->back());
bool SomeSuccHasSame = false;
bool AllSuccsHaveSame = true;
PtrState &S = I->second;
succ_const_iterator SI(TI), SE(TI, false);
// If the terminator is an invoke marked with the
// clang.arc.no_objc_arc_exceptions metadata, the unwind edge can be
// ignored, for ARC purposes.
if (isa<InvokeInst>(TI) && TI->getMetadata(NoObjCARCExceptionsMDKind)) {
DEBUG(dbgs() << "ObjCARCOpt::CheckForCFGHazards: Found an invoke "
"terminator marked with "
"clang.arc.no_objc_arc_exceptions. Ignoring unwind "
"edge.\n");
--SE;
}
for (; SI != SE; ++SI) {
Sequence SuccSSeq = S_None;
bool SuccSRRIKnownSafe = false;
// If VisitBottomUp has pointer information for this successor, take
// what we know about it.
DenseMap<const BasicBlock *, BBState>::iterator BBI =
BBStates.find(*SI);
assert(BBI != BBStates.end());
const PtrState &SuccS = BBI->second.getPtrBottomUpState(Arg);
SuccSSeq = SuccS.GetSeq();
SuccSRRIKnownSafe = SuccS.RRI.KnownSafe;
switch (SuccSSeq) {
case S_None:
case S_CanRelease: {
if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe) {
S.ClearSequenceProgress();
break;
}
continue;
}
case S_Use:
SomeSuccHasSame = true;
break;
case S_Stop:
case S_Release:
case S_MovableRelease:
if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe)
AllSuccsHaveSame = false;
break;
case S_Retain:
llvm_unreachable("bottom-up pointer in retain state!");
}
}
// If the state at the other end of any of the successor edges
// matches the current state, require all edges to match. This
// guards against loops in the middle of a sequence.
if (SomeSuccHasSame && !AllSuccsHaveSame)
S.ClearSequenceProgress();
break;
}
case S_CanRelease: {
const Value *Arg = I->first;
const TerminatorInst *TI = cast<TerminatorInst>(&BB->back());
bool SomeSuccHasSame = false;
bool AllSuccsHaveSame = true;
PtrState &S = I->second;
succ_const_iterator SI(TI), SE(TI, false);
// If the terminator is an invoke marked with the
// clang.arc.no_objc_arc_exceptions metadata, the unwind edge can be
// ignored, for ARC purposes.
if (isa<InvokeInst>(TI) && TI->getMetadata(NoObjCARCExceptionsMDKind)) {
DEBUG(dbgs() << "ObjCARCOpt::CheckForCFGHazards: Found an invoke "
"terminator marked with "
"clang.arc.no_objc_arc_exceptions. Ignoring unwind "
"edge.\n");
--SE;
}
for (; SI != SE; ++SI) {
Sequence SuccSSeq = S_None;
bool SuccSRRIKnownSafe = false;
// If VisitBottomUp has pointer information for this successor, take
// what we know about it.
DenseMap<const BasicBlock *, BBState>::iterator BBI =
BBStates.find(*SI);
assert(BBI != BBStates.end());
const PtrState &SuccS = BBI->second.getPtrBottomUpState(Arg);
SuccSSeq = SuccS.GetSeq();
SuccSRRIKnownSafe = SuccS.RRI.KnownSafe;
switch (SuccSSeq) {
case S_None: {
if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe) {
S.ClearSequenceProgress();
break;
}
continue;
}
case S_CanRelease:
SomeSuccHasSame = true;
break;
case S_Stop:
case S_Release:
case S_MovableRelease:
case S_Use:
if (!S.RRI.KnownSafe && !SuccSRRIKnownSafe)
AllSuccsHaveSame = false;
break;
case S_Retain:
llvm_unreachable("bottom-up pointer in retain state!");
}
}
// If the state at the other end of any of the successor edges
// matches the current state, require all edges to match. This
// guards against loops in the middle of a sequence.
if (SomeSuccHasSame && !AllSuccsHaveSame)
S.ClearSequenceProgress();
break;
}
}
}
bool
ObjCARCOpt::VisitInstructionBottomUp(Instruction *Inst,
BasicBlock *BB,
MapVector<Value *, RRInfo> &Retains,
BBState &MyStates) {
bool NestingDetected = false;
InstructionClass Class = GetInstructionClass(Inst);
const Value *Arg = 0;
switch (Class) {
case IC_Release: {
Arg = GetObjCArg(Inst);
PtrState &S = MyStates.getPtrBottomUpState(Arg);
// If we see two releases in a row on the same pointer. If so, make
// a note, and we'll cicle back to revisit it after we've
// hopefully eliminated the second release, which may allow us to
// eliminate the first release too.
// Theoretically we could implement removal of nested retain+release
// pairs by making PtrState hold a stack of states, but this is
// simple and avoids adding overhead for the non-nested case.
if (S.GetSeq() == S_Release || S.GetSeq() == S_MovableRelease) {
DEBUG(dbgs() << "ObjCARCOpt::VisitInstructionBottomUp: Found nested "
"releases (i.e. a release pair)\n");
NestingDetected = true;
}
MDNode *ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind);
S.ResetSequenceProgress(ReleaseMetadata ? S_MovableRelease : S_Release);
S.RRI.ReleaseMetadata = ReleaseMetadata;
S.RRI.KnownSafe = S.IsKnownIncremented();
S.RRI.IsTailCallRelease = cast<CallInst>(Inst)->isTailCall();
S.RRI.Calls.insert(Inst);
S.SetKnownPositiveRefCount();
break;
}
case IC_RetainBlock:
// An objc_retainBlock call with just a use may need to be kept,
// because it may be copying a block from the stack to the heap.
if (!IsRetainBlockOptimizable(Inst))
break;
// FALLTHROUGH
case IC_Retain:
case IC_RetainRV: {
Arg = GetObjCArg(Inst);
PtrState &S = MyStates.getPtrBottomUpState(Arg);
S.SetKnownPositiveRefCount();
switch (S.GetSeq()) {
case S_Stop:
case S_Release:
case S_MovableRelease:
case S_Use:
S.RRI.ReverseInsertPts.clear();
// FALL THROUGH
case S_CanRelease:
// Don't do retain+release tracking for IC_RetainRV, because it's
// better to let it remain as the first instruction after a call.
if (Class != IC_RetainRV) {
S.RRI.IsRetainBlock = Class == IC_RetainBlock;
Retains[Inst] = S.RRI;
}
S.ClearSequenceProgress();
break;
case S_None:
break;
case S_Retain:
llvm_unreachable("bottom-up pointer in retain state!");
}
return NestingDetected;
}
case IC_AutoreleasepoolPop:
// Conservatively, clear MyStates for all known pointers.
MyStates.clearBottomUpPointers();
return NestingDetected;
case IC_AutoreleasepoolPush:
case IC_None:
// These are irrelevant.
return NestingDetected;
default:
break;
}
// Consider any other possible effects of this instruction on each
// pointer being tracked.
for (BBState::ptr_iterator MI = MyStates.bottom_up_ptr_begin(),
ME = MyStates.bottom_up_ptr_end(); MI != ME; ++MI) {
const Value *Ptr = MI->first;
if (Ptr == Arg)
continue; // Handled above.
PtrState &S = MI->second;
Sequence Seq = S.GetSeq();
// Check for possible releases.
if (CanAlterRefCount(Inst, Ptr, PA, Class)) {
S.ClearRefCount();
switch (Seq) {
case S_Use:
S.SetSeq(S_CanRelease);
continue;
case S_CanRelease:
case S_Release:
case S_MovableRelease:
case S_Stop:
case S_None:
break;
case S_Retain:
llvm_unreachable("bottom-up pointer in retain state!");
}
}
// Check for possible direct uses.
switch (Seq) {
case S_Release:
case S_MovableRelease:
if (CanUse(Inst, Ptr, PA, Class)) {
assert(S.RRI.ReverseInsertPts.empty());
// If this is an invoke instruction, we're scanning it as part of
// one of its successor blocks, since we can't insert code after it
// in its own block, and we don't want to split critical edges.
if (isa<InvokeInst>(Inst))
S.RRI.ReverseInsertPts.insert(BB->getFirstInsertionPt());
else
S.RRI.ReverseInsertPts.insert(llvm::next(BasicBlock::iterator(Inst)));
S.SetSeq(S_Use);
} else if (Seq == S_Release &&
(Class == IC_User || Class == IC_CallOrUser)) {
// Non-movable releases depend on any possible objc pointer use.
S.SetSeq(S_Stop);
assert(S.RRI.ReverseInsertPts.empty());
// As above; handle invoke specially.
if (isa<InvokeInst>(Inst))
S.RRI.ReverseInsertPts.insert(BB->getFirstInsertionPt());
else
S.RRI.ReverseInsertPts.insert(llvm::next(BasicBlock::iterator(Inst)));
}
break;
case S_Stop:
if (CanUse(Inst, Ptr, PA, Class))
S.SetSeq(S_Use);
break;
case S_CanRelease:
case S_Use:
case S_None:
break;
case S_Retain:
llvm_unreachable("bottom-up pointer in retain state!");
}
}
return NestingDetected;
}
bool
ObjCARCOpt::VisitBottomUp(BasicBlock *BB,
DenseMap<const BasicBlock *, BBState> &BBStates,
MapVector<Value *, RRInfo> &Retains) {
bool NestingDetected = false;
BBState &MyStates = BBStates[BB];
// Merge the states from each successor to compute the initial state
// for the current block.
BBState::edge_iterator SI(MyStates.succ_begin()),
SE(MyStates.succ_end());
if (SI != SE) {
const BasicBlock *Succ = *SI;
DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Succ);
assert(I != BBStates.end());
MyStates.InitFromSucc(I->second);
++SI;
for (; SI != SE; ++SI) {
Succ = *SI;
I = BBStates.find(Succ);
assert(I != BBStates.end());
MyStates.MergeSucc(I->second);
}
}
// Visit all the instructions, bottom-up.
for (BasicBlock::iterator I = BB->end(), E = BB->begin(); I != E; --I) {
Instruction *Inst = llvm::prior(I);
// Invoke instructions are visited as part of their successors (below).
if (isa<InvokeInst>(Inst))
continue;
DEBUG(dbgs() << "ObjCARCOpt::VisitButtonUp: Visiting " << *Inst << "\n");
NestingDetected |= VisitInstructionBottomUp(Inst, BB, Retains, MyStates);
}
// If there's a predecessor with an invoke, visit the invoke as if it were
// part of this block, since we can't insert code after an invoke in its own
// block, and we don't want to split critical edges.
for (BBState::edge_iterator PI(MyStates.pred_begin()),
PE(MyStates.pred_end()); PI != PE; ++PI) {
BasicBlock *Pred = *PI;
if (InvokeInst *II = dyn_cast<InvokeInst>(&Pred->back()))
NestingDetected |= VisitInstructionBottomUp(II, BB, Retains, MyStates);
}
return NestingDetected;
}
bool
ObjCARCOpt::VisitInstructionTopDown(Instruction *Inst,
DenseMap<Value *, RRInfo> &Releases,
BBState &MyStates) {
bool NestingDetected = false;
InstructionClass Class = GetInstructionClass(Inst);
const Value *Arg = 0;
switch (Class) {
case IC_RetainBlock:
// An objc_retainBlock call with just a use may need to be kept,
// because it may be copying a block from the stack to the heap.
if (!IsRetainBlockOptimizable(Inst))
break;
// FALLTHROUGH
case IC_Retain:
case IC_RetainRV: {
Arg = GetObjCArg(Inst);
PtrState &S = MyStates.getPtrTopDownState(Arg);
// Don't do retain+release tracking for IC_RetainRV, because it's
// better to let it remain as the first instruction after a call.
if (Class != IC_RetainRV) {
// If we see two retains in a row on the same pointer. If so, make
// a note, and we'll cicle back to revisit it after we've
// hopefully eliminated the second retain, which may allow us to
// eliminate the first retain too.
// Theoretically we could implement removal of nested retain+release
// pairs by making PtrState hold a stack of states, but this is
// simple and avoids adding overhead for the non-nested case.
if (S.GetSeq() == S_Retain)
NestingDetected = true;
S.ResetSequenceProgress(S_Retain);
S.RRI.IsRetainBlock = Class == IC_RetainBlock;
S.RRI.KnownSafe = S.IsKnownIncremented();
S.RRI.Calls.insert(Inst);
}
S.SetKnownPositiveRefCount();
// A retain can be a potential use; procede to the generic checking
// code below.
break;
}
case IC_Release: {
Arg = GetObjCArg(Inst);
PtrState &S = MyStates.getPtrTopDownState(Arg);
S.ClearRefCount();
switch (S.GetSeq()) {
case S_Retain:
case S_CanRelease:
S.RRI.ReverseInsertPts.clear();
// FALL THROUGH
case S_Use:
S.RRI.ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind);
S.RRI.IsTailCallRelease = cast<CallInst>(Inst)->isTailCall();
Releases[Inst] = S.RRI;
S.ClearSequenceProgress();
break;
case S_None:
break;
case S_Stop:
case S_Release:
case S_MovableRelease:
llvm_unreachable("top-down pointer in release state!");
}
break;
}
case IC_AutoreleasepoolPop:
// Conservatively, clear MyStates for all known pointers.
MyStates.clearTopDownPointers();
return NestingDetected;
case IC_AutoreleasepoolPush:
case IC_None:
// These are irrelevant.
return NestingDetected;
default:
break;
}
// Consider any other possible effects of this instruction on each
// pointer being tracked.
for (BBState::ptr_iterator MI = MyStates.top_down_ptr_begin(),
ME = MyStates.top_down_ptr_end(); MI != ME; ++MI) {
const Value *Ptr = MI->first;
if (Ptr == Arg)
continue; // Handled above.
PtrState &S = MI->second;
Sequence Seq = S.GetSeq();
// Check for possible releases.
if (CanAlterRefCount(Inst, Ptr, PA, Class)) {
S.ClearRefCount();
switch (Seq) {
case S_Retain:
S.SetSeq(S_CanRelease);
assert(S.RRI.ReverseInsertPts.empty());
S.RRI.ReverseInsertPts.insert(Inst);
// One call can't cause a transition from S_Retain to S_CanRelease
// and S_CanRelease to S_Use. If we've made the first transition,
// we're done.
continue;
case S_Use:
case S_CanRelease:
case S_None:
break;
case S_Stop:
case S_Release:
case S_MovableRelease:
llvm_unreachable("top-down pointer in release state!");
}
}
// Check for possible direct uses.
switch (Seq) {
case S_CanRelease:
if (CanUse(Inst, Ptr, PA, Class))
S.SetSeq(S_Use);
break;
case S_Retain:
case S_Use:
case S_None:
break;
case S_Stop:
case S_Release:
case S_MovableRelease:
llvm_unreachable("top-down pointer in release state!");
}
}
return NestingDetected;
}
bool
ObjCARCOpt::VisitTopDown(BasicBlock *BB,
DenseMap<const BasicBlock *, BBState> &BBStates,
DenseMap<Value *, RRInfo> &Releases) {
bool NestingDetected = false;
BBState &MyStates = BBStates[BB];
// Merge the states from each predecessor to compute the initial state
// for the current block.
BBState::edge_iterator PI(MyStates.pred_begin()),
PE(MyStates.pred_end());
if (PI != PE) {
const BasicBlock *Pred = *PI;
DenseMap<const BasicBlock *, BBState>::iterator I = BBStates.find(Pred);
assert(I != BBStates.end());
MyStates.InitFromPred(I->second);
++PI;
for (; PI != PE; ++PI) {
Pred = *PI;
I = BBStates.find(Pred);
assert(I != BBStates.end());
MyStates.MergePred(I->second);
}
}
// Visit all the instructions, top-down.
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
Instruction *Inst = I;
DEBUG(dbgs() << "ObjCARCOpt::VisitTopDown: Visiting " << *Inst << "\n");
NestingDetected |= VisitInstructionTopDown(Inst, Releases, MyStates);
}
CheckForCFGHazards(BB, BBStates, MyStates);
return NestingDetected;
}
static void
ComputePostOrders(Function &F,
SmallVectorImpl<BasicBlock *> &PostOrder,
SmallVectorImpl<BasicBlock *> &ReverseCFGPostOrder,
unsigned NoObjCARCExceptionsMDKind,
DenseMap<const BasicBlock *, BBState> &BBStates) {
/// The visited set, for doing DFS walks.
SmallPtrSet<BasicBlock *, 16> Visited;
// Do DFS, computing the PostOrder.
SmallPtrSet<BasicBlock *, 16> OnStack;
SmallVector<std::pair<BasicBlock *, succ_iterator>, 16> SuccStack;
// Functions always have exactly one entry block, and we don't have
// any other block that we treat like an entry block.
BasicBlock *EntryBB = &F.getEntryBlock();
BBState &MyStates = BBStates[EntryBB];
MyStates.SetAsEntry();
TerminatorInst *EntryTI = cast<TerminatorInst>(&EntryBB->back());
SuccStack.push_back(std::make_pair(EntryBB, succ_iterator(EntryTI)));
Visited.insert(EntryBB);
OnStack.insert(EntryBB);
do {
dfs_next_succ:
BasicBlock *CurrBB = SuccStack.back().first;
TerminatorInst *TI = cast<TerminatorInst>(&CurrBB->back());
succ_iterator SE(TI, false);
// If the terminator is an invoke marked with the
// clang.arc.no_objc_arc_exceptions metadata, the unwind edge can be
// ignored, for ARC purposes.
if (isa<InvokeInst>(TI) && TI->getMetadata(NoObjCARCExceptionsMDKind)) {
DEBUG(dbgs() << "ObjCARCOpt::ComputePostOrders: Found an invoke "
"terminator marked with "
"clang.arc.no_objc_arc_exceptions. Ignoring unwind "
"edge.\n");
--SE;
}
while (SuccStack.back().second != SE) {
BasicBlock *SuccBB = *SuccStack.back().second++;
if (Visited.insert(SuccBB)) {
TerminatorInst *TI = cast<TerminatorInst>(&SuccBB->back());
SuccStack.push_back(std::make_pair(SuccBB, succ_iterator(TI)));
BBStates[CurrBB].addSucc(SuccBB);
BBState &SuccStates = BBStates[SuccBB];
SuccStates.addPred(CurrBB);
OnStack.insert(SuccBB);
goto dfs_next_succ;
}
if (!OnStack.count(SuccBB)) {
BBStates[CurrBB].addSucc(SuccBB);
BBStates[SuccBB].addPred(CurrBB);
}
}
OnStack.erase(CurrBB);
PostOrder.push_back(CurrBB);
SuccStack.pop_back();
} while (!SuccStack.empty());
Visited.clear();
// Do reverse-CFG DFS, computing the reverse-CFG PostOrder.
// Functions may have many exits, and there also blocks which we treat
// as exits due to ignored edges.
SmallVector<std::pair<BasicBlock *, BBState::edge_iterator>, 16> PredStack;
for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
BasicBlock *ExitBB = I;
BBState &MyStates = BBStates[ExitBB];
if (!MyStates.isExit())
continue;
MyStates.SetAsExit();
PredStack.push_back(std::make_pair(ExitBB, MyStates.pred_begin()));
Visited.insert(ExitBB);
while (!PredStack.empty()) {
reverse_dfs_next_succ:
BBState::edge_iterator PE = BBStates[PredStack.back().first].pred_end();
while (PredStack.back().second != PE) {
BasicBlock *BB = *PredStack.back().second++;
if (Visited.insert(BB)) {
PredStack.push_back(std::make_pair(BB, BBStates[BB].pred_begin()));
goto reverse_dfs_next_succ;
}
}
ReverseCFGPostOrder.push_back(PredStack.pop_back_val().first);
}
}
}
// Visit the function both top-down and bottom-up.
bool
ObjCARCOpt::Visit(Function &F,
DenseMap<const BasicBlock *, BBState> &BBStates,
MapVector<Value *, RRInfo> &Retains,
DenseMap<Value *, RRInfo> &Releases) {
// Use reverse-postorder traversals, because we magically know that loops
// will be well behaved, i.e. they won't repeatedly call retain on a single
// pointer without doing a release. We can't use the ReversePostOrderTraversal
// class here because we want the reverse-CFG postorder to consider each
// function exit point, and we want to ignore selected cycle edges.
SmallVector<BasicBlock *, 16> PostOrder;
SmallVector<BasicBlock *, 16> ReverseCFGPostOrder;
ComputePostOrders(F, PostOrder, ReverseCFGPostOrder,
NoObjCARCExceptionsMDKind,
BBStates);
// Use reverse-postorder on the reverse CFG for bottom-up.
bool BottomUpNestingDetected = false;
for (SmallVectorImpl<BasicBlock *>::const_reverse_iterator I =
ReverseCFGPostOrder.rbegin(), E = ReverseCFGPostOrder.rend();
I != E; ++I)
BottomUpNestingDetected |= VisitBottomUp(*I, BBStates, Retains);
// Use reverse-postorder for top-down.
bool TopDownNestingDetected = false;
for (SmallVectorImpl<BasicBlock *>::const_reverse_iterator I =
PostOrder.rbegin(), E = PostOrder.rend();
I != E; ++I)
TopDownNestingDetected |= VisitTopDown(*I, BBStates, Releases);
return TopDownNestingDetected && BottomUpNestingDetected;
}
/// Move the calls in RetainsToMove and ReleasesToMove.
void ObjCARCOpt::MoveCalls(Value *Arg,
RRInfo &RetainsToMove,
RRInfo &ReleasesToMove,
MapVector<Value *, RRInfo> &Retains,
DenseMap<Value *, RRInfo> &Releases,
SmallVectorImpl<Instruction *> &DeadInsts,
Module *M) {
Type *ArgTy = Arg->getType();
Type *ParamTy = PointerType::getUnqual(Type::getInt8Ty(ArgTy->getContext()));
// Insert the new retain and release calls.
for (SmallPtrSet<Instruction *, 2>::const_iterator
PI = ReleasesToMove.ReverseInsertPts.begin(),
PE = ReleasesToMove.ReverseInsertPts.end(); PI != PE; ++PI) {
Instruction *InsertPt = *PI;
Value *MyArg = ArgTy == ParamTy ? Arg :
new BitCastInst(Arg, ParamTy, "", InsertPt);
CallInst *Call =
CallInst::Create(RetainsToMove.IsRetainBlock ?
getRetainBlockCallee(M) : getRetainCallee(M),
MyArg, "", InsertPt);
Call->setDoesNotThrow();
if (RetainsToMove.IsRetainBlock)
Call->setMetadata(CopyOnEscapeMDKind,
MDNode::get(M->getContext(), ArrayRef<Value *>()));
else
Call->setTailCall();
DEBUG(dbgs() << "ObjCARCOpt::MoveCalls: Inserting new Release: " << *Call
<< "\n"
" At insertion point: " << *InsertPt
<< "\n");
}
for (SmallPtrSet<Instruction *, 2>::const_iterator
PI = RetainsToMove.ReverseInsertPts.begin(),
PE = RetainsToMove.ReverseInsertPts.end(); PI != PE; ++PI) {
Instruction *InsertPt = *PI;
Value *MyArg = ArgTy == ParamTy ? Arg :
new BitCastInst(Arg, ParamTy, "", InsertPt);
CallInst *Call = CallInst::Create(getReleaseCallee(M), MyArg,
"", InsertPt);
// Attach a clang.imprecise_release metadata tag, if appropriate.
if (MDNode *M = ReleasesToMove.ReleaseMetadata)
Call->setMetadata(ImpreciseReleaseMDKind, M);
Call->setDoesNotThrow();
if (ReleasesToMove.IsTailCallRelease)
Call->setTailCall();
DEBUG(dbgs() << "ObjCARCOpt::MoveCalls: Inserting new Retain: " << *Call
<< "\n"
" At insertion point: " << *InsertPt
<< "\n");
}
// Delete the original retain and release calls.
for (SmallPtrSet<Instruction *, 2>::const_iterator
AI = RetainsToMove.Calls.begin(),
AE = RetainsToMove.Calls.end(); AI != AE; ++AI) {
Instruction *OrigRetain = *AI;
Retains.blot(OrigRetain);
DeadInsts.push_back(OrigRetain);
DEBUG(dbgs() << "ObjCARCOpt::MoveCalls: Deleting retain: " << *OrigRetain <<
"\n");
}
for (SmallPtrSet<Instruction *, 2>::const_iterator
AI = ReleasesToMove.Calls.begin(),
AE = ReleasesToMove.Calls.end(); AI != AE; ++AI) {
Instruction *OrigRelease = *AI;
Releases.erase(OrigRelease);
DeadInsts.push_back(OrigRelease);
DEBUG(dbgs() << "ObjCARCOpt::MoveCalls: Deleting release: " << *OrigRelease
<< "\n");
}
}
/// Identify pairings between the retains and releases, and delete and/or move
/// them.
bool
ObjCARCOpt::PerformCodePlacement(DenseMap<const BasicBlock *, BBState>
&BBStates,
MapVector<Value *, RRInfo> &Retains,
DenseMap<Value *, RRInfo> &Releases,
Module *M) {
bool AnyPairsCompletelyEliminated = false;
RRInfo RetainsToMove;
RRInfo ReleasesToMove;
SmallVector<Instruction *, 4> NewRetains;
SmallVector<Instruction *, 4> NewReleases;
SmallVector<Instruction *, 8> DeadInsts;
// Visit each retain.
for (MapVector<Value *, RRInfo>::const_iterator I = Retains.begin(),
E = Retains.end(); I != E; ++I) {
Value *V = I->first;
if (!V) continue; // blotted
Instruction *Retain = cast<Instruction>(V);
DEBUG(dbgs() << "ObjCARCOpt::PerformCodePlacement: Visiting: " << *Retain
<< "\n");
Value *Arg = GetObjCArg(Retain);
// If the object being released is in static or stack storage, we know it's
// not being managed by ObjC reference counting, so we can delete pairs
// regardless of what possible decrements or uses lie between them.
bool KnownSafe = isa<Constant>(Arg) || isa<AllocaInst>(Arg);
// A constant pointer can't be pointing to an object on the heap. It may
// be reference-counted, but it won't be deleted.
if (const LoadInst *LI = dyn_cast<LoadInst>(Arg))
if (const GlobalVariable *GV =
dyn_cast<GlobalVariable>(
StripPointerCastsAndObjCCalls(LI->getPointerOperand())))
if (GV->isConstant())
KnownSafe = true;
// If a pair happens in a region where it is known that the reference count
// is already incremented, we can similarly ignore possible decrements.
bool KnownSafeTD = true, KnownSafeBU = true;
// Connect the dots between the top-down-collected RetainsToMove and
// bottom-up-collected ReleasesToMove to form sets of related calls.
// This is an iterative process so that we connect multiple releases
// to multiple retains if needed.
unsigned OldDelta = 0;
unsigned NewDelta = 0;
unsigned OldCount = 0;
unsigned NewCount = 0;
bool FirstRelease = true;
bool FirstRetain = true;
NewRetains.push_back(Retain);
for (;;) {
for (SmallVectorImpl<Instruction *>::const_iterator
NI = NewRetains.begin(), NE = NewRetains.end(); NI != NE; ++NI) {
Instruction *NewRetain = *NI;
MapVector<Value *, RRInfo>::const_iterator It = Retains.find(NewRetain);
assert(It != Retains.end());
const RRInfo &NewRetainRRI = It->second;
KnownSafeTD &= NewRetainRRI.KnownSafe;
for (SmallPtrSet<Instruction *, 2>::const_iterator
LI = NewRetainRRI.Calls.begin(),
LE = NewRetainRRI.Calls.end(); LI != LE; ++LI) {
Instruction *NewRetainRelease = *LI;
DenseMap<Value *, RRInfo>::const_iterator Jt =
Releases.find(NewRetainRelease);
if (Jt == Releases.end())
goto next_retain;
const RRInfo &NewRetainReleaseRRI = Jt->second;
assert(NewRetainReleaseRRI.Calls.count(NewRetain));
if (ReleasesToMove.Calls.insert(NewRetainRelease)) {
OldDelta -=
BBStates[NewRetainRelease->getParent()].GetAllPathCount();
// Merge the ReleaseMetadata and IsTailCallRelease values.
if (FirstRelease) {
ReleasesToMove.ReleaseMetadata =
NewRetainReleaseRRI.ReleaseMetadata;
ReleasesToMove.IsTailCallRelease =
NewRetainReleaseRRI.IsTailCallRelease;
FirstRelease = false;
} else {
if (ReleasesToMove.ReleaseMetadata !=
NewRetainReleaseRRI.ReleaseMetadata)
ReleasesToMove.ReleaseMetadata = 0;
if (ReleasesToMove.IsTailCallRelease !=
NewRetainReleaseRRI.IsTailCallRelease)
ReleasesToMove.IsTailCallRelease = false;
}
// Collect the optimal insertion points.
if (!KnownSafe)
for (SmallPtrSet<Instruction *, 2>::const_iterator
RI = NewRetainReleaseRRI.ReverseInsertPts.begin(),
RE = NewRetainReleaseRRI.ReverseInsertPts.end();
RI != RE; ++RI) {
Instruction *RIP = *RI;
if (ReleasesToMove.ReverseInsertPts.insert(RIP))
NewDelta -= BBStates[RIP->getParent()].GetAllPathCount();
}
NewReleases.push_back(NewRetainRelease);
}
}
}
NewRetains.clear();
if (NewReleases.empty()) break;
// Back the other way.
for (SmallVectorImpl<Instruction *>::const_iterator
NI = NewReleases.begin(), NE = NewReleases.end(); NI != NE; ++NI) {
Instruction *NewRelease = *NI;
DenseMap<Value *, RRInfo>::const_iterator It =
Releases.find(NewRelease);
assert(It != Releases.end());
const RRInfo &NewReleaseRRI = It->second;
KnownSafeBU &= NewReleaseRRI.KnownSafe;
for (SmallPtrSet<Instruction *, 2>::const_iterator
LI = NewReleaseRRI.Calls.begin(),
LE = NewReleaseRRI.Calls.end(); LI != LE; ++LI) {
Instruction *NewReleaseRetain = *LI;
MapVector<Value *, RRInfo>::const_iterator Jt =
Retains.find(NewReleaseRetain);
if (Jt == Retains.end())
goto next_retain;
const RRInfo &NewReleaseRetainRRI = Jt->second;
assert(NewReleaseRetainRRI.Calls.count(NewRelease));
if (RetainsToMove.Calls.insert(NewReleaseRetain)) {
unsigned PathCount =
BBStates[NewReleaseRetain->getParent()].GetAllPathCount();
OldDelta += PathCount;
OldCount += PathCount;
// Merge the IsRetainBlock values.
if (FirstRetain) {
RetainsToMove.IsRetainBlock = NewReleaseRetainRRI.IsRetainBlock;
FirstRetain = false;
} else if (ReleasesToMove.IsRetainBlock !=
NewReleaseRetainRRI.IsRetainBlock)
// It's not possible to merge the sequences if one uses
// objc_retain and the other uses objc_retainBlock.
goto next_retain;
// Collect the optimal insertion points.
if (!KnownSafe)
for (SmallPtrSet<Instruction *, 2>::const_iterator
RI = NewReleaseRetainRRI.ReverseInsertPts.begin(),
RE = NewReleaseRetainRRI.ReverseInsertPts.end();
RI != RE; ++RI) {
Instruction *RIP = *RI;
if (RetainsToMove.ReverseInsertPts.insert(RIP)) {
PathCount = BBStates[RIP->getParent()].GetAllPathCount();
NewDelta += PathCount;
NewCount += PathCount;
}
}
NewRetains.push_back(NewReleaseRetain);
}
}
}
NewReleases.clear();
if (NewRetains.empty()) break;
}
// If the pointer is known incremented or nested, we can safely delete the
// pair regardless of what's between them.
if (KnownSafeTD || KnownSafeBU) {
RetainsToMove.ReverseInsertPts.clear();
ReleasesToMove.ReverseInsertPts.clear();
NewCount = 0;
} else {
// Determine whether the new insertion points we computed preserve the
// balance of retain and release calls through the program.
// TODO: If the fully aggressive solution isn't valid, try to find a
// less aggressive solution which is.
if (NewDelta != 0)
goto next_retain;
}
// Determine whether the original call points are balanced in the retain and
// release calls through the program. If not, conservatively don't touch
// them.
// TODO: It's theoretically possible to do code motion in this case, as
// long as the existing imbalances are maintained.
if (OldDelta != 0)
goto next_retain;
// Ok, everything checks out and we're all set. Let's move some code!
Changed = true;
assert(OldCount != 0 && "Unreachable code?");
AnyPairsCompletelyEliminated = NewCount == 0;
NumRRs += OldCount - NewCount;
MoveCalls(Arg, RetainsToMove, ReleasesToMove,
Retains, Releases, DeadInsts, M);
next_retain:
NewReleases.clear();
NewRetains.clear();
RetainsToMove.clear();
ReleasesToMove.clear();
}
// Now that we're done moving everything, we can delete the newly dead
// instructions, as we no longer need them as insert points.
while (!DeadInsts.empty())
EraseInstruction(DeadInsts.pop_back_val());
return AnyPairsCompletelyEliminated;
}
/// Weak pointer optimizations.
void ObjCARCOpt::OptimizeWeakCalls(Function &F) {
// First, do memdep-style RLE and S2L optimizations. We can't use memdep
// itself because it uses AliasAnalysis and we need to do provenance
// queries instead.
for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
Instruction *Inst = &*I++;
DEBUG(dbgs() << "ObjCARCOpt::OptimizeWeakCalls: Visiting: " << *Inst <<
"\n");
InstructionClass Class = GetBasicInstructionClass(Inst);
if (Class != IC_LoadWeak && Class != IC_LoadWeakRetained)
continue;
// Delete objc_loadWeak calls with no users.
if (Class == IC_LoadWeak && Inst->use_empty()) {
Inst->eraseFromParent();
continue;
}
// TODO: For now, just look for an earlier available version of this value
// within the same block. Theoretically, we could do memdep-style non-local
// analysis too, but that would want caching. A better approach would be to
// use the technique that EarlyCSE uses.
inst_iterator Current = llvm::prior(I);
BasicBlock *CurrentBB = Current.getBasicBlockIterator();
for (BasicBlock::iterator B = CurrentBB->begin(),
J = Current.getInstructionIterator();
J != B; --J) {
Instruction *EarlierInst = &*llvm::prior(J);
InstructionClass EarlierClass = GetInstructionClass(EarlierInst);
switch (EarlierClass) {
case IC_LoadWeak:
case IC_LoadWeakRetained: {
// If this is loading from the same pointer, replace this load's value
// with that one.
CallInst *Call = cast<CallInst>(Inst);
CallInst *EarlierCall = cast<CallInst>(EarlierInst);
Value *Arg = Call->getArgOperand(0);
Value *EarlierArg = EarlierCall->getArgOperand(0);
switch (PA.getAA()->alias(Arg, EarlierArg)) {
case AliasAnalysis::MustAlias:
Changed = true;
// If the load has a builtin retain, insert a plain retain for it.
if (Class == IC_LoadWeakRetained) {
CallInst *CI =
CallInst::Create(getRetainCallee(F.getParent()), EarlierCall,
"", Call);
CI->setTailCall();
}
// Zap the fully redundant load.
Call->replaceAllUsesWith(EarlierCall);
Call->eraseFromParent();
goto clobbered;
case AliasAnalysis::MayAlias:
case AliasAnalysis::PartialAlias:
goto clobbered;
case AliasAnalysis::NoAlias:
break;
}
break;
}
case IC_StoreWeak:
case IC_InitWeak: {
// If this is storing to the same pointer and has the same size etc.
// replace this load's value with the stored value.
CallInst *Call = cast<CallInst>(Inst);
CallInst *EarlierCall = cast<CallInst>(EarlierInst);
Value *Arg = Call->getArgOperand(0);
Value *EarlierArg = EarlierCall->getArgOperand(0);
switch (PA.getAA()->alias(Arg, EarlierArg)) {
case AliasAnalysis::MustAlias:
Changed = true;
// If the load has a builtin retain, insert a plain retain for it.
if (Class == IC_LoadWeakRetained) {
CallInst *CI =
CallInst::Create(getRetainCallee(F.getParent()), EarlierCall,
"", Call);
CI->setTailCall();
}
// Zap the fully redundant load.
Call->replaceAllUsesWith(EarlierCall->getArgOperand(1));
Call->eraseFromParent();
goto clobbered;
case AliasAnalysis::MayAlias:
case AliasAnalysis::PartialAlias:
goto clobbered;
case AliasAnalysis::NoAlias:
break;
}
break;
}
case IC_MoveWeak:
case IC_CopyWeak:
// TOOD: Grab the copied value.
goto clobbered;
case IC_AutoreleasepoolPush:
case IC_None:
case IC_User:
// Weak pointers are only modified through the weak entry points
// (and arbitrary calls, which could call the weak entry points).
break;
default:
// Anything else could modify the weak pointer.
goto clobbered;
}
}
clobbered:;
}
// Then, for each destroyWeak with an alloca operand, check to see if
// the alloca and all its users can be zapped.
for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
Instruction *Inst = &*I++;
InstructionClass Class = GetBasicInstructionClass(Inst);
if (Class != IC_DestroyWeak)
continue;
CallInst *Call = cast<CallInst>(Inst);
Value *Arg = Call->getArgOperand(0);
if (AllocaInst *Alloca = dyn_cast<AllocaInst>(Arg)) {
for (Value::use_iterator UI = Alloca->use_begin(),
UE = Alloca->use_end(); UI != UE; ++UI) {
const Instruction *UserInst = cast<Instruction>(*UI);
switch (GetBasicInstructionClass(UserInst)) {
case IC_InitWeak:
case IC_StoreWeak:
case IC_DestroyWeak:
continue;
default:
goto done;
}
}
Changed = true;
for (Value::use_iterator UI = Alloca->use_begin(),
UE = Alloca->use_end(); UI != UE; ) {
CallInst *UserInst = cast<CallInst>(*UI++);
switch (GetBasicInstructionClass(UserInst)) {
case IC_InitWeak:
case IC_StoreWeak:
// These functions return their second argument.
UserInst->replaceAllUsesWith(UserInst->getArgOperand(1));
break;
case IC_DestroyWeak:
// No return value.
break;
default:
llvm_unreachable("alloca really is used!");
}
UserInst->eraseFromParent();
}
Alloca->eraseFromParent();
done:;
}
}
DEBUG(dbgs() << "ObjCARCOpt::OptimizeWeakCalls: Finished List.\n\n");
}
/// Identify program paths which execute sequences of retains and releases which
/// can be eliminated.
bool ObjCARCOpt::OptimizeSequences(Function &F) {
/// Releases, Retains - These are used to store the results of the main flow
/// analysis. These use Value* as the key instead of Instruction* so that the
/// map stays valid when we get around to rewriting code and calls get
/// replaced by arguments.
DenseMap<Value *, RRInfo> Releases;
MapVector<Value *, RRInfo> Retains;
/// This is used during the traversal of the function to track the
/// states for each identified object at each block.
DenseMap<const BasicBlock *, BBState> BBStates;
// Analyze the CFG of the function, and all instructions.
bool NestingDetected = Visit(F, BBStates, Retains, Releases);
// Transform.
return PerformCodePlacement(BBStates, Retains, Releases, F.getParent()) &&
NestingDetected;
}
/// Look for this pattern:
/// \code
/// %call = call i8* @something(...)
/// %2 = call i8* @objc_retain(i8* %call)
/// %3 = call i8* @objc_autorelease(i8* %2)
/// ret i8* %3
/// \endcode
/// And delete the retain and autorelease.
///
/// Otherwise if it's just this:
/// \code
/// %3 = call i8* @objc_autorelease(i8* %2)
/// ret i8* %3
/// \endcode
/// convert the autorelease to autoreleaseRV.
void ObjCARCOpt::OptimizeReturns(Function &F) {
if (!F.getReturnType()->isPointerTy())
return;
SmallPtrSet<Instruction *, 4> DependingInstructions;
SmallPtrSet<const BasicBlock *, 4> Visited;
for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI) {
BasicBlock *BB = FI;
ReturnInst *Ret = dyn_cast<ReturnInst>(&BB->back());
DEBUG(dbgs() << "ObjCARCOpt::OptimizeReturns: Visiting: " << *Ret << "\n");
if (!Ret) continue;
const Value *Arg = StripPointerCastsAndObjCCalls(Ret->getOperand(0));
FindDependencies(NeedsPositiveRetainCount, Arg,
BB, Ret, DependingInstructions, Visited, PA);
if (DependingInstructions.size() != 1)
goto next_block;
{
CallInst *Autorelease =
dyn_cast_or_null<CallInst>(*DependingInstructions.begin());
if (!Autorelease)
goto next_block;
InstructionClass AutoreleaseClass = GetBasicInstructionClass(Autorelease);
if (!IsAutorelease(AutoreleaseClass))
goto next_block;
if (GetObjCArg(Autorelease) != Arg)
goto next_block;
DependingInstructions.clear();
Visited.clear();
// Check that there is nothing that can affect the reference
// count between the autorelease and the retain.
FindDependencies(CanChangeRetainCount, Arg,
BB, Autorelease, DependingInstructions, Visited, PA);
if (DependingInstructions.size() != 1)
goto next_block;
{
CallInst *Retain =
dyn_cast_or_null<CallInst>(*DependingInstructions.begin());
// Check that we found a retain with the same argument.
if (!Retain ||
!IsRetain(GetBasicInstructionClass(Retain)) ||
GetObjCArg(Retain) != Arg)
goto next_block;
DependingInstructions.clear();
Visited.clear();
// Convert the autorelease to an autoreleaseRV, since it's
// returning the value.
if (AutoreleaseClass == IC_Autorelease) {
DEBUG(dbgs() << "ObjCARCOpt::OptimizeReturns: Converting autorelease "
"=> autoreleaseRV since it's returning a value.\n"
" In: " << *Autorelease
<< "\n");
Autorelease->setCalledFunction(getAutoreleaseRVCallee(F.getParent()));
DEBUG(dbgs() << " Out: " << *Autorelease
<< "\n");
Autorelease->setTailCall(); // Always tail call autoreleaseRV.
AutoreleaseClass = IC_AutoreleaseRV;
}
// Check that there is nothing that can affect the reference
// count between the retain and the call.
// Note that Retain need not be in BB.
FindDependencies(CanChangeRetainCount, Arg, Retain->getParent(), Retain,
DependingInstructions, Visited, PA);
if (DependingInstructions.size() != 1)
goto next_block;
{
CallInst *Call =
dyn_cast_or_null<CallInst>(*DependingInstructions.begin());
// Check that the pointer is the return value of the call.
if (!Call || Arg != Call)
goto next_block;
// Check that the call is a regular call.
InstructionClass Class = GetBasicInstructionClass(Call);
if (Class != IC_CallOrUser && Class != IC_Call)
goto next_block;
// If so, we can zap the retain and autorelease.
Changed = true;
++NumRets;
DEBUG(dbgs() << "ObjCARCOpt::OptimizeReturns: Erasing: " << *Retain
<< "\n Erasing: "
<< *Autorelease << "\n");
EraseInstruction(Retain);
EraseInstruction(Autorelease);
}
}
}
next_block:
DependingInstructions.clear();
Visited.clear();
}
DEBUG(dbgs() << "ObjCARCOpt::OptimizeReturns: Finished List.\n\n");
}
bool ObjCARCOpt::doInitialization(Module &M) {
if (!EnableARCOpts)
return false;
// If nothing in the Module uses ARC, don't do anything.
Run = ModuleHasARC(M);
if (!Run)
return false;
// Identify the imprecise release metadata kind.
ImpreciseReleaseMDKind =
M.getContext().getMDKindID("clang.imprecise_release");
CopyOnEscapeMDKind =
M.getContext().getMDKindID("clang.arc.copy_on_escape");
NoObjCARCExceptionsMDKind =
M.getContext().getMDKindID("clang.arc.no_objc_arc_exceptions");
// Intuitively, objc_retain and others are nocapture, however in practice
// they are not, because they return their argument value. And objc_release
// calls finalizers which can have arbitrary side effects.
// These are initialized lazily.
RetainRVCallee = 0;
AutoreleaseRVCallee = 0;
ReleaseCallee = 0;
RetainCallee = 0;
RetainBlockCallee = 0;
AutoreleaseCallee = 0;
return false;
}
bool ObjCARCOpt::runOnFunction(Function &F) {
if (!EnableARCOpts)
return false;
// If nothing in the Module uses ARC, don't do anything.
if (!Run)
return false;
Changed = false;
DEBUG(dbgs() << "ObjCARCOpt: Visiting Function: " << F.getName() << "\n");
PA.setAA(&getAnalysis<AliasAnalysis>());
// This pass performs several distinct transformations. As a compile-time aid
// when compiling code that isn't ObjC, skip these if the relevant ObjC
// library functions aren't declared.
// Preliminary optimizations. This also computs UsedInThisFunction.
OptimizeIndividualCalls(F);
// Optimizations for weak pointers.
if (UsedInThisFunction & ((1 << IC_LoadWeak) |
(1 << IC_LoadWeakRetained) |
(1 << IC_StoreWeak) |
(1 << IC_InitWeak) |
(1 << IC_CopyWeak) |
(1 << IC_MoveWeak) |
(1 << IC_DestroyWeak)))
OptimizeWeakCalls(F);
// Optimizations for retain+release pairs.
if (UsedInThisFunction & ((1 << IC_Retain) |
(1 << IC_RetainRV) |
(1 << IC_RetainBlock)))
if (UsedInThisFunction & (1 << IC_Release))
// Run OptimizeSequences until it either stops making changes or
// no retain+release pair nesting is detected.
while (OptimizeSequences(F)) {}
// Optimizations if objc_autorelease is used.
if (UsedInThisFunction & ((1 << IC_Autorelease) |
(1 << IC_AutoreleaseRV)))
OptimizeReturns(F);
DEBUG(dbgs() << "\n");
return Changed;
}
void ObjCARCOpt::releaseMemory() {
PA.clear();
}
/// @}
///
/// \defgroup ARCContract ARC Contraction.
/// @{
// TODO: ObjCARCContract could insert PHI nodes when uses aren't
// dominated by single calls.
#include "llvm/Analysis/Dominators.h"
#include "llvm/IR/InlineAsm.h"
#include "llvm/IR/Operator.h"
STATISTIC(NumStoreStrongs, "Number objc_storeStrong calls formed");
namespace {
/// \brief Late ARC optimizations
///
/// These change the IR in a way that makes it difficult to be analyzed by
/// ObjCARCOpt, so it's run late.
class ObjCARCContract : public FunctionPass {
bool Changed;
AliasAnalysis *AA;
DominatorTree *DT;
ProvenanceAnalysis PA;
/// A flag indicating whether this optimization pass should run.
bool Run;
/// Declarations for ObjC runtime functions, for use in creating calls to
/// them. These are initialized lazily to avoid cluttering up the Module
/// with unused declarations.
/// Declaration for objc_storeStrong().
Constant *StoreStrongCallee;
/// Declaration for objc_retainAutorelease().
Constant *RetainAutoreleaseCallee;
/// Declaration for objc_retainAutoreleaseReturnValue().
Constant *RetainAutoreleaseRVCallee;
/// The inline asm string to insert between calls and RetainRV calls to make
/// the optimization work on targets which need it.
const MDString *RetainRVMarker;
/// The set of inserted objc_storeStrong calls. If at the end of walking the
/// function we have found no alloca instructions, these calls can be marked
/// "tail".
SmallPtrSet<CallInst *, 8> StoreStrongCalls;
Constant *getStoreStrongCallee(Module *M);
Constant *getRetainAutoreleaseCallee(Module *M);
Constant *getRetainAutoreleaseRVCallee(Module *M);
bool ContractAutorelease(Function &F, Instruction *Autorelease,
InstructionClass Class,
SmallPtrSet<Instruction *, 4>
&DependingInstructions,
SmallPtrSet<const BasicBlock *, 4>
&Visited);
void ContractRelease(Instruction *Release,
inst_iterator &Iter);
virtual void getAnalysisUsage(AnalysisUsage &AU) const;
virtual bool doInitialization(Module &M);
virtual bool runOnFunction(Function &F);
public:
static char ID;
ObjCARCContract() : FunctionPass(ID) {
initializeObjCARCContractPass(*PassRegistry::getPassRegistry());
}
};
}
char ObjCARCContract::ID = 0;
INITIALIZE_PASS_BEGIN(ObjCARCContract,
"objc-arc-contract", "ObjC ARC contraction", false, false)
INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
INITIALIZE_PASS_DEPENDENCY(DominatorTree)
INITIALIZE_PASS_END(ObjCARCContract,
"objc-arc-contract", "ObjC ARC contraction", false, false)
Pass *llvm::createObjCARCContractPass() {
return new ObjCARCContract();
}
void ObjCARCContract::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<AliasAnalysis>();
AU.addRequired<DominatorTree>();
AU.setPreservesCFG();
}
Constant *ObjCARCContract::getStoreStrongCallee(Module *M) {
if (!StoreStrongCallee) {
LLVMContext &C = M->getContext();
Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
Type *I8XX = PointerType::getUnqual(I8X);
Type *Params[] = { I8XX, I8X };
AttributeSet Attribute = AttributeSet()
.addAttr(M->getContext(), AttributeSet::FunctionIndex,
Attribute::get(C, Attribute::NoUnwind))
.addAttr(M->getContext(), 1, Attribute::get(C, Attribute::NoCapture));
StoreStrongCallee =
M->getOrInsertFunction(
"objc_storeStrong",
FunctionType::get(Type::getVoidTy(C), Params, /*isVarArg=*/false),
Attribute);
}
return StoreStrongCallee;
}
Constant *ObjCARCContract::getRetainAutoreleaseCallee(Module *M) {
if (!RetainAutoreleaseCallee) {
LLVMContext &C = M->getContext();
Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
Type *Params[] = { I8X };
FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false);
AttributeSet Attribute =
AttributeSet().addAttr(M->getContext(), AttributeSet::FunctionIndex,
Attribute::get(C, Attribute::NoUnwind));
RetainAutoreleaseCallee =
M->getOrInsertFunction("objc_retainAutorelease", FTy, Attribute);
}
return RetainAutoreleaseCallee;
}
Constant *ObjCARCContract::getRetainAutoreleaseRVCallee(Module *M) {
if (!RetainAutoreleaseRVCallee) {
LLVMContext &C = M->getContext();
Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
Type *Params[] = { I8X };
FunctionType *FTy = FunctionType::get(I8X, Params, /*isVarArg=*/false);
AttributeSet Attribute =
AttributeSet().addAttr(M->getContext(), AttributeSet::FunctionIndex,
Attribute::get(C, Attribute::NoUnwind));
RetainAutoreleaseRVCallee =
M->getOrInsertFunction("objc_retainAutoreleaseReturnValue", FTy,
Attribute);
}
return RetainAutoreleaseRVCallee;
}
/// Merge an autorelease with a retain into a fused call.
bool
ObjCARCContract::ContractAutorelease(Function &F, Instruction *Autorelease,
InstructionClass Class,
SmallPtrSet<Instruction *, 4>
&DependingInstructions,
SmallPtrSet<const BasicBlock *, 4>
&Visited) {
const Value *Arg = GetObjCArg(Autorelease);
// Check that there are no instructions between the retain and the autorelease
// (such as an autorelease_pop) which may change the count.
CallInst *Retain = 0;
if (Class == IC_AutoreleaseRV)
FindDependencies(RetainAutoreleaseRVDep, Arg,
Autorelease->getParent(), Autorelease,
DependingInstructions, Visited, PA);
else
FindDependencies(RetainAutoreleaseDep, Arg,
Autorelease->getParent(), Autorelease,
DependingInstructions, Visited, PA);
Visited.clear();
if (DependingInstructions.size() != 1) {
DependingInstructions.clear();
return false;
}
Retain = dyn_cast_or_null<CallInst>(*DependingInstructions.begin());
DependingInstructions.clear();
if (!Retain ||
GetBasicInstructionClass(Retain) != IC_Retain ||
GetObjCArg(Retain) != Arg)
return false;
Changed = true;
++NumPeeps;
DEBUG(dbgs() << "ObjCARCContract::ContractAutorelease: Fusing "
"retain/autorelease. Erasing: " << *Autorelease << "\n"
" Old Retain: "
<< *Retain << "\n");
if (Class == IC_AutoreleaseRV)
Retain->setCalledFunction(getRetainAutoreleaseRVCallee(F.getParent()));
else
Retain->setCalledFunction(getRetainAutoreleaseCallee(F.getParent()));
DEBUG(dbgs() << " New Retain: "
<< *Retain << "\n");
EraseInstruction(Autorelease);
return true;
}
/// Attempt to merge an objc_release with a store, load, and objc_retain to form
/// an objc_storeStrong. This can be a little tricky because the instructions
/// don't always appear in order, and there may be unrelated intervening
/// instructions.
void ObjCARCContract::ContractRelease(Instruction *Release,
inst_iterator &Iter) {
LoadInst *Load = dyn_cast<LoadInst>(GetObjCArg(Release));
if (!Load || !Load->isSimple()) return;
// For now, require everything to be in one basic block.
BasicBlock *BB = Release->getParent();
if (Load->getParent() != BB) return;
// Walk down to find the store and the release, which may be in either order.
BasicBlock::iterator I = Load, End = BB->end();
++I;
AliasAnalysis::Location Loc = AA->getLocation(Load);
StoreInst *Store = 0;
bool SawRelease = false;
for (; !Store || !SawRelease; ++I) {
if (I == End)
return;
Instruction *Inst = I;
if (Inst == Release) {
SawRelease = true;
continue;
}
InstructionClass Class = GetBasicInstructionClass(Inst);
// Unrelated retains are harmless.
if (IsRetain(Class))
continue;
if (Store) {
// The store is the point where we're going to put the objc_storeStrong,
// so make sure there are no uses after it.
if (CanUse(Inst, Load, PA, Class))
return;
} else if (AA->getModRefInfo(Inst, Loc) & AliasAnalysis::Mod) {
// We are moving the load down to the store, so check for anything
// else which writes to the memory between the load and the store.
Store = dyn_cast<StoreInst>(Inst);
if (!Store || !Store->isSimple()) return;
if (Store->getPointerOperand() != Loc.Ptr) return;
}
}
Value *New = StripPointerCastsAndObjCCalls(Store->getValueOperand());
// Walk up to find the retain.
I = Store;
BasicBlock::iterator Begin = BB->begin();
while (I != Begin && GetBasicInstructionClass(I) != IC_Retain)
--I;
Instruction *Retain = I;
if (GetBasicInstructionClass(Retain) != IC_Retain) return;
if (GetObjCArg(Retain) != New) return;
Changed = true;
++NumStoreStrongs;
LLVMContext &C = Release->getContext();
Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
Type *I8XX = PointerType::getUnqual(I8X);
Value *Args[] = { Load->getPointerOperand(), New };
if (Args[0]->getType() != I8XX)
Args[0] = new BitCastInst(Args[0], I8XX, "", Store);
if (Args[1]->getType() != I8X)
Args[1] = new BitCastInst(Args[1], I8X, "", Store);
CallInst *StoreStrong =
CallInst::Create(getStoreStrongCallee(BB->getParent()->getParent()),
Args, "", Store);
StoreStrong->setDoesNotThrow();
StoreStrong->setDebugLoc(Store->getDebugLoc());
// We can't set the tail flag yet, because we haven't yet determined
// whether there are any escaping allocas. Remember this call, so that
// we can set the tail flag once we know it's safe.
StoreStrongCalls.insert(StoreStrong);
if (&*Iter == Store) ++Iter;
Store->eraseFromParent();
Release->eraseFromParent();
EraseInstruction(Retain);
if (Load->use_empty())
Load->eraseFromParent();
}
bool ObjCARCContract::doInitialization(Module &M) {
// If nothing in the Module uses ARC, don't do anything.
Run = ModuleHasARC(M);
if (!Run)
return false;
// These are initialized lazily.
StoreStrongCallee = 0;
RetainAutoreleaseCallee = 0;
RetainAutoreleaseRVCallee = 0;
// Initialize RetainRVMarker.
RetainRVMarker = 0;
if (NamedMDNode *NMD =
M.getNamedMetadata("clang.arc.retainAutoreleasedReturnValueMarker"))
if (NMD->getNumOperands() == 1) {
const MDNode *N = NMD->getOperand(0);
if (N->getNumOperands() == 1)
if (const MDString *S = dyn_cast<MDString>(N->getOperand(0)))
RetainRVMarker = S;
}
return false;
}
bool ObjCARCContract::runOnFunction(Function &F) {
if (!EnableARCOpts)
return false;
// If nothing in the Module uses ARC, don't do anything.
if (!Run)
return false;
Changed = false;
AA = &getAnalysis<AliasAnalysis>();
DT = &getAnalysis<DominatorTree>();
PA.setAA(&getAnalysis<AliasAnalysis>());
// Track whether it's ok to mark objc_storeStrong calls with the "tail"
// keyword. Be conservative if the function has variadic arguments.
// It seems that functions which "return twice" are also unsafe for the
// "tail" argument, because they are setjmp, which could need to
// return to an earlier stack state.
bool TailOkForStoreStrongs = !F.isVarArg() &&
!F.callsFunctionThatReturnsTwice();
// For ObjC library calls which return their argument, replace uses of the
// argument with uses of the call return value, if it dominates the use. This
// reduces register pressure.
SmallPtrSet<Instruction *, 4> DependingInstructions;
SmallPtrSet<const BasicBlock *, 4> Visited;
for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
Instruction *Inst = &*I++;
DEBUG(dbgs() << "ObjCARCContract: Visiting: " << *Inst << "\n");
// Only these library routines return their argument. In particular,
// objc_retainBlock does not necessarily return its argument.
InstructionClass Class = GetBasicInstructionClass(Inst);
switch (Class) {
case IC_Retain:
case IC_FusedRetainAutorelease:
case IC_FusedRetainAutoreleaseRV:
break;
case IC_Autorelease:
case IC_AutoreleaseRV:
if (ContractAutorelease(F, Inst, Class, DependingInstructions, Visited))
continue;
break;
case IC_RetainRV: {
// If we're compiling for a target which needs a special inline-asm
// marker to do the retainAutoreleasedReturnValue optimization,
// insert it now.
if (!RetainRVMarker)
break;
BasicBlock::iterator BBI = Inst;
BasicBlock *InstParent = Inst->getParent();
// Step up to see if the call immediately precedes the RetainRV call.
// If it's an invoke, we have to cross a block boundary. And we have
// to carefully dodge no-op instructions.
do {
if (&*BBI == InstParent->begin()) {
BasicBlock *Pred = InstParent->getSinglePredecessor();
if (!Pred)
goto decline_rv_optimization;
BBI = Pred->getTerminator();
break;
}
--BBI;
} while (isNoopInstruction(BBI));
if (&*BBI == GetObjCArg(Inst)) {
DEBUG(dbgs() << "ObjCARCContract: Adding inline asm marker for "
"retainAutoreleasedReturnValue optimization.\n");
Changed = true;
InlineAsm *IA =
InlineAsm::get(FunctionType::get(Type::getVoidTy(Inst->getContext()),
/*isVarArg=*/false),
RetainRVMarker->getString(),
/*Constraints=*/"", /*hasSideEffects=*/true);
CallInst::Create(IA, "", Inst);
}
decline_rv_optimization:
break;
}
case IC_InitWeak: {
// objc_initWeak(p, null) => *p = null
CallInst *CI = cast<CallInst>(Inst);
if (isNullOrUndef(CI->getArgOperand(1))) {
Value *Null =
ConstantPointerNull::get(cast<PointerType>(CI->getType()));
Changed = true;
new StoreInst(Null, CI->getArgOperand(0), CI);
DEBUG(dbgs() << "OBJCARCContract: Old = " << *CI << "\n"
<< " New = " << *Null << "\n");
CI->replaceAllUsesWith(Null);
CI->eraseFromParent();
}
continue;
}
case IC_Release:
ContractRelease(Inst, I);
continue;
case IC_User:
// Be conservative if the function has any alloca instructions.
// Technically we only care about escaping alloca instructions,
// but this is sufficient to handle some interesting cases.
if (isa<AllocaInst>(Inst))
TailOkForStoreStrongs = false;
continue;
default:
continue;
}
DEBUG(dbgs() << "ObjCARCContract: Finished List.\n\n");
// Don't use GetObjCArg because we don't want to look through bitcasts
// and such; to do the replacement, the argument must have type i8*.
const Value *Arg = cast<CallInst>(Inst)->getArgOperand(0);
for (;;) {
// If we're compiling bugpointed code, don't get in trouble.
if (!isa<Instruction>(Arg) && !isa<Argument>(Arg))
break;
// Look through the uses of the pointer.
for (Value::const_use_iterator UI = Arg->use_begin(), UE = Arg->use_end();
UI != UE; ) {
Use &U = UI.getUse();
unsigned OperandNo = UI.getOperandNo();
++UI; // Increment UI now, because we may unlink its element.
// If the call's return value dominates a use of the call's argument
// value, rewrite the use to use the return value. We check for
// reachability here because an unreachable call is considered to
// trivially dominate itself, which would lead us to rewriting its
// argument in terms of its return value, which would lead to
// infinite loops in GetObjCArg.
if (DT->isReachableFromEntry(U) && DT->dominates(Inst, U)) {
Changed = true;
Instruction *Replacement = Inst;
Type *UseTy = U.get()->getType();
if (PHINode *PHI = dyn_cast<PHINode>(U.getUser())) {
// For PHI nodes, insert the bitcast in the predecessor block.
unsigned ValNo = PHINode::getIncomingValueNumForOperand(OperandNo);
BasicBlock *BB = PHI->getIncomingBlock(ValNo);
if (Replacement->getType() != UseTy)
Replacement = new BitCastInst(Replacement, UseTy, "",
&BB->back());
// While we're here, rewrite all edges for this PHI, rather
// than just one use at a time, to minimize the number of
// bitcasts we emit.
for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
if (PHI->getIncomingBlock(i) == BB) {
// Keep the UI iterator valid.
if (&PHI->getOperandUse(
PHINode::getOperandNumForIncomingValue(i)) ==
&UI.getUse())
++UI;
PHI->setIncomingValue(i, Replacement);
}
} else {
if (Replacement->getType() != UseTy)
Replacement = new BitCastInst(Replacement, UseTy, "",
cast<Instruction>(U.getUser()));
U.set(Replacement);
}
}
}
// If Arg is a no-op casted pointer, strip one level of casts and iterate.
if (const BitCastInst *BI = dyn_cast<BitCastInst>(Arg))
Arg = BI->getOperand(0);
else if (isa<GEPOperator>(Arg) &&
cast<GEPOperator>(Arg)->hasAllZeroIndices())
Arg = cast<GEPOperator>(Arg)->getPointerOperand();
else if (isa<GlobalAlias>(Arg) &&
!cast<GlobalAlias>(Arg)->mayBeOverridden())
Arg = cast<GlobalAlias>(Arg)->getAliasee();
else
break;
}
}
// If this function has no escaping allocas or suspicious vararg usage,
// objc_storeStrong calls can be marked with the "tail" keyword.
if (TailOkForStoreStrongs)
for (SmallPtrSet<CallInst *, 8>::iterator I = StoreStrongCalls.begin(),
E = StoreStrongCalls.end(); I != E; ++I)
(*I)->setTailCall();
StoreStrongCalls.clear();
return Changed;
}
/// @}
///
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