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llvm-6502/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
Michael Gottesman 4ee7e47a87 Removed trailing whitespace. 
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//===- ObjCARCOpts.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, and numerous minor simplifications.
///
/// 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-opts"
#include "ObjCARC.h"
#include "ARCRuntimeEntryPoints.h"
#include "DependencyAnalysis.h"
#include "ObjCARCAliasAnalysis.h"
#include "ProvenanceAnalysis.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
using namespace llvm::objcarc;
/// \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);
}
iterator find(const KeyT &Key) {
typename MapTy::iterator It = Map.find(Key);
if (It == Map.end()) return Vector.end();
return Vector.begin() + It->second;
}
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.
/// @{
/// \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 whether the given retainable object pointer escapes.
///
/// This differs from regular escape analysis in that a use as an
/// argument to a call is not considered an escape.
///
static bool DoesRetainableObjPtrEscape(const User *Ptr) {
DEBUG(dbgs() << "DoesRetainableObjPtrEscape: Target: " << *Ptr << "\n");
// Walk the def-use chains.
SmallVector<const Value *, 4> Worklist;
Worklist.push_back(Ptr);
// If Ptr has any operands add them as well.
for (User::const_op_iterator I = Ptr->op_begin(), E = Ptr->op_end(); I != E;
++I) {
Worklist.push_back(*I);
}
// Ensure we do not visit any value twice.
SmallPtrSet<const Value *, 8> VisitedSet;
do {
const Value *V = Worklist.pop_back_val();
DEBUG(dbgs() << "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() << "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() << "User copies pointer arguments. Pointer Escapes!\n");
// These special functions make copies of their pointer arguments.
return true;
}
case IC_IntrinsicUser:
// Use by the use intrinsic is not an escape.
continue;
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.insert(UUser)) {
DEBUG(dbgs() << "User copies value. Ptr escapes if result escapes."
" Adding to list.\n");
Worklist.push_back(UUser);
} else {
DEBUG(dbgs() << "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() << "Assuming ptr escapes.\n");
return true;
}
} while (!Worklist.empty());
// No escapes found.
DEBUG(dbgs() << "Ptr does not escape.\n");
return false;
}
/// This is a wrapper around getUnderlyingObjCPtr along the lines of
/// GetUnderlyingObjects except that it returns early when it sees the first
/// alloca.
static inline bool AreAnyUnderlyingObjectsAnAlloca(const Value *V) {
SmallPtrSet<const Value *, 4> Visited;
SmallVector<const Value *, 4> Worklist;
Worklist.push_back(V);
do {
const Value *P = Worklist.pop_back_val();
P = GetUnderlyingObjCPtr(P);
if (isa<AllocaInst>(P))
return true;
if (!Visited.insert(P))
continue;
if (const SelectInst *SI = dyn_cast<const SelectInst>(P)) {
Worklist.push_back(SI->getTrueValue());
Worklist.push_back(SI->getFalseValue());
continue;
}
if (const PHINode *PN = dyn_cast<const PHINode>(P)) {
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
Worklist.push_back(PN->getIncomingValue(i));
continue;
}
} while (!Worklist.empty());
return false;
}
/// @}
///
/// \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).
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+autoreleases eliminated");
STATISTIC(NumRRs, "Number of retain+release paths eliminated");
STATISTIC(NumPeeps, "Number of calls peephole-optimized");
#ifndef NDEBUG
STATISTIC(NumRetainsBeforeOpt,
"Number of retains before optimization");
STATISTIC(NumReleasesBeforeOpt,
"Number of releases before optimization");
STATISTIC(NumRetainsAfterOpt,
"Number of retains after optimization");
STATISTIC(NumReleasesAfterOpt,
"Number of releases after optimization");
#endif
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.
};
raw_ostream &operator<<(raw_ostream &OS, const Sequence S)
LLVM_ATTRIBUTE_UNUSED;
raw_ostream &operator<<(raw_ostream &OS, const Sequence S) {
switch (S) {
case S_None:
return OS << "S_None";
case S_Retain:
return OS << "S_Retain";
case S_CanRelease:
return OS << "S_CanRelease";
case S_Use:
return OS << "S_Use";
case S_Release:
return OS << "S_Release";
case S_MovableRelease:
return OS << "S_MovableRelease";
case S_Stop:
return OS << "S_Stop";
}
llvm_unreachable("Unknown sequence type.");
}
}
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
/// reverse 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 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;
/// If this is true, we cannot perform code motion but can still remove
/// retain/release pairs.
bool CFGHazardAfflicted;
RRInfo() :
KnownSafe(false), IsTailCallRelease(false), ReleaseMetadata(0),
CFGHazardAfflicted(false) {}
void clear();
/// Conservatively merge the two RRInfo. Returns true if a partial merge has
/// occured, false otherwise.
bool Merge(const RRInfo &Other);
};
}
void RRInfo::clear() {
KnownSafe = false;
IsTailCallRelease = false;
ReleaseMetadata = 0;
Calls.clear();
ReverseInsertPts.clear();
CFGHazardAfflicted = false;
}
bool RRInfo::Merge(const RRInfo &Other) {
// Conservatively merge the ReleaseMetadata information.
if (ReleaseMetadata != Other.ReleaseMetadata)
ReleaseMetadata = 0;
// Conservatively merge the boolean state.
KnownSafe &= Other.KnownSafe;
IsTailCallRelease &= Other.IsTailCallRelease;
CFGHazardAfflicted |= Other.CFGHazardAfflicted;
// Merge the call sets.
Calls.insert(Other.Calls.begin(), Other.Calls.end());
// Merge the insert point sets. If there are any differences,
// that makes this a partial merge.
bool Partial = ReverseInsertPts.size() != Other.ReverseInsertPts.size();
for (SmallPtrSet<Instruction *, 2>::const_iterator
I = Other.ReverseInsertPts.begin(),
E = Other.ReverseInsertPts.end(); I != E; ++I)
Partial |= ReverseInsertPts.insert(*I);
return Partial;
}
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 if 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;
/// Unidirectional information about the current sequence.
RRInfo RRI;
public:
PtrState() : KnownPositiveRefCount(false), Partial(false),
Seq(S_None) {}
bool IsKnownSafe() const {
return RRI.KnownSafe;
}
void SetKnownSafe(const bool NewValue) {
RRI.KnownSafe = NewValue;
}
bool IsTailCallRelease() const {
return RRI.IsTailCallRelease;
}
void SetTailCallRelease(const bool NewValue) {
RRI.IsTailCallRelease = NewValue;
}
bool IsTrackingImpreciseReleases() const {
return RRI.ReleaseMetadata != 0;
}
const MDNode *GetReleaseMetadata() const {
return RRI.ReleaseMetadata;
}
void SetReleaseMetadata(MDNode *NewValue) {
RRI.ReleaseMetadata = NewValue;
}
bool IsCFGHazardAfflicted() const {
return RRI.CFGHazardAfflicted;
}
void SetCFGHazardAfflicted(const bool NewValue) {
RRI.CFGHazardAfflicted = NewValue;
}
void SetKnownPositiveRefCount() {
DEBUG(dbgs() << "Setting Known Positive.\n");
KnownPositiveRefCount = true;
}
void ClearKnownPositiveRefCount() {
DEBUG(dbgs() << "Clearing Known Positive.\n");
KnownPositiveRefCount = false;
}
bool HasKnownPositiveRefCount() const {
return KnownPositiveRefCount;
}
void SetSeq(Sequence NewSeq) {
DEBUG(dbgs() << "Old: " << Seq << "; New: " << NewSeq << "\n");
Seq = NewSeq;
}
Sequence GetSeq() const {
return Seq;
}
void ClearSequenceProgress() {
ResetSequenceProgress(S_None);
}
void ResetSequenceProgress(Sequence NewSeq) {
DEBUG(dbgs() << "Resetting sequence progress.\n");
SetSeq(NewSeq);
Partial = false;
RRI.clear();
}
void Merge(const PtrState &Other, bool TopDown);
void InsertCall(Instruction *I) {
RRI.Calls.insert(I);
}
void InsertReverseInsertPt(Instruction *I) {
RRI.ReverseInsertPts.insert(I);
}
void ClearReverseInsertPts() {
RRI.ReverseInsertPts.clear();
}
bool HasReverseInsertPts() const {
return !RRI.ReverseInsertPts.empty();
}
const RRInfo &GetRRInfo() const {
return RRI;
}
};
}
void
PtrState::Merge(const PtrState &Other, bool TopDown) {
Seq = MergeSeqs(Seq, Other.Seq, TopDown);
KnownPositiveRefCount &= Other.KnownPositiveRefCount;
// 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 {
// Otherwise merge the other PtrState's RRInfo into our RRInfo. At this
// point, we know that currently we are not partial. Stash whether or not
// the merge operation caused us to undergo a partial merging of reverse
// insertion points.
Partial = RRI.Merge(Other.RRI);
}
}
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; }
/// Attempt to find the PtrState object describing the top down state for
/// pointer Arg. Return a new initialized PtrState describing the top down
/// state for Arg if we do not find one.
PtrState &getPtrTopDownState(const Value *Arg) {
return PerPtrTopDown[Arg];
}
/// Attempt to find the PtrState object describing the bottom up state for
/// pointer Arg. Return a new initialized PtrState describing the bottom up
/// state for Arg if we do not find one.
PtrState &getPtrBottomUpState(const Value *Arg) {
return PerPtrBottomUp[Arg];
}
/// Attempt to find the PtrState object describing the bottom up state for
/// pointer Arg.
ptr_iterator findPtrBottomUpState(const Value *Arg) {
return PerPtrBottomUp.find(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);
/// Compute 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.
///
/// Returns true if overflow occured. Returns false if overflow did not
/// occur.
bool GetAllPathCountWithOverflow(unsigned &PathCount) const {
assert(TopDownPathCount != 0);
assert(BottomUpPathCount != 0);
unsigned long long Product =
(unsigned long long)TopDownPathCount*BottomUpPathCount;
PathCount = Product;
// Overflow occured if any of the upper bits of Product are set.
return Product >> 32;
}
// 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);
}
// Only enable ARC Annotations if we are building a debug version of
// libObjCARCOpts.
#ifndef NDEBUG
#define ARC_ANNOTATIONS
#endif
// Define some macros along the lines of DEBUG and some helper functions to make
// it cleaner to create annotations in the source code and to no-op when not
// building in debug mode.
#ifdef ARC_ANNOTATIONS
#include "llvm/Support/CommandLine.h"
/// Enable/disable ARC sequence annotations.
static cl::opt<bool>
EnableARCAnnotations("enable-objc-arc-annotations", cl::init(false),
cl::desc("Enable emission of arc data flow analysis "
"annotations"));
static cl::opt<bool>
DisableCheckForCFGHazards("disable-objc-arc-checkforcfghazards", cl::init(false),
cl::desc("Disable check for cfg hazards when "
"annotating"));
static cl::opt<std::string>
ARCAnnotationTargetIdentifier("objc-arc-annotation-target-identifier",
cl::init(""),
cl::desc("filter out all data flow annotations "
"but those that apply to the given "
"target llvm identifier."));
/// This function appends a unique ARCAnnotationProvenanceSourceMDKind id to an
/// instruction so that we can track backwards when post processing via the llvm
/// arc annotation processor tool. If the function is an
static MDString *AppendMDNodeToSourcePtr(unsigned NodeId,
Value *Ptr) {
MDString *Hash = 0;
// If pointer is a result of an instruction and it does not have a source
// MDNode it, attach a new MDNode onto it. If pointer is a result of
// an instruction and does have a source MDNode attached to it, return a
// reference to said Node. Otherwise just return 0.
if (Instruction *Inst = dyn_cast<Instruction>(Ptr)) {
MDNode *Node;
if (!(Node = Inst->getMetadata(NodeId))) {
// We do not have any node. Generate and attatch the hash MDString to the
// instruction.
// We just use an MDString to ensure that this metadata gets written out
// of line at the module level and to provide a very simple format
// encoding the information herein. Both of these makes it simpler to
// parse the annotations by a simple external program.
std::string Str;
raw_string_ostream os(Str);
os << "(" << Inst->getParent()->getParent()->getName() << ",%"
<< Inst->getName() << ")";
Hash = MDString::get(Inst->getContext(), os.str());
Inst->setMetadata(NodeId, MDNode::get(Inst->getContext(),Hash));
} else {
// We have a node. Grab its hash and return it.
assert(Node->getNumOperands() == 1 &&
"An ARCAnnotationProvenanceSourceMDKind can only have 1 operand.");
Hash = cast<MDString>(Node->getOperand(0));
}
} else if (Argument *Arg = dyn_cast<Argument>(Ptr)) {
std::string str;
raw_string_ostream os(str);
os << "(" << Arg->getParent()->getName() << ",%" << Arg->getName()
<< ")";
Hash = MDString::get(Arg->getContext(), os.str());
}
return Hash;
}
static std::string SequenceToString(Sequence A) {
std::string str;
raw_string_ostream os(str);
os << A;
return os.str();
}
/// Helper function to change a Sequence into a String object using our overload
/// for raw_ostream so we only have printing code in one location.
static MDString *SequenceToMDString(LLVMContext &Context,
Sequence A) {
return MDString::get(Context, SequenceToString(A));
}
/// A simple function to generate a MDNode which describes the change in state
/// for Value *Ptr caused by Instruction *Inst.
static void AppendMDNodeToInstForPtr(unsigned NodeId,
Instruction *Inst,
Value *Ptr,
MDString *PtrSourceMDNodeID,
Sequence OldSeq,
Sequence NewSeq) {
MDNode *Node = 0;
Value *tmp[3] = {PtrSourceMDNodeID,
SequenceToMDString(Inst->getContext(),
OldSeq),
SequenceToMDString(Inst->getContext(),
NewSeq)};
Node = MDNode::get(Inst->getContext(),
ArrayRef<Value*>(tmp, 3));
Inst->setMetadata(NodeId, Node);
}
/// Add to the beginning of the basic block llvm.ptr.annotations which show the
/// state of a pointer at the entrance to a basic block.
static void GenerateARCBBEntranceAnnotation(const char *Name, BasicBlock *BB,
Value *Ptr, Sequence Seq) {
// If we have a target identifier, make sure that we match it before
// continuing.
if(!ARCAnnotationTargetIdentifier.empty() &&
!Ptr->getName().equals(ARCAnnotationTargetIdentifier))
return;
Module *M = BB->getParent()->getParent();
LLVMContext &C = M->getContext();
Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
Type *I8XX = PointerType::getUnqual(I8X);
Type *Params[] = {I8XX, I8XX};
FunctionType *FTy = FunctionType::get(Type::getVoidTy(C),
ArrayRef<Type*>(Params, 2),
/*isVarArg=*/false);
Constant *Callee = M->getOrInsertFunction(Name, FTy);
IRBuilder<> Builder(BB, BB->getFirstInsertionPt());
Value *PtrName;
StringRef Tmp = Ptr->getName();
if (0 == (PtrName = M->getGlobalVariable(Tmp, true))) {
Value *ActualPtrName = Builder.CreateGlobalStringPtr(Tmp,
Tmp + "_STR");
PtrName = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
cast<Constant>(ActualPtrName), Tmp);
}
Value *S;
std::string SeqStr = SequenceToString(Seq);
if (0 == (S = M->getGlobalVariable(SeqStr, true))) {
Value *ActualPtrName = Builder.CreateGlobalStringPtr(SeqStr,
SeqStr + "_STR");
S = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
cast<Constant>(ActualPtrName), SeqStr);
}
Builder.CreateCall2(Callee, PtrName, S);
}
/// Add to the end of the basic block llvm.ptr.annotations which show the state
/// of the pointer at the bottom of the basic block.
static void GenerateARCBBTerminatorAnnotation(const char *Name, BasicBlock *BB,
Value *Ptr, Sequence Seq) {
// If we have a target identifier, make sure that we match it before emitting
// an annotation.
if(!ARCAnnotationTargetIdentifier.empty() &&
!Ptr->getName().equals(ARCAnnotationTargetIdentifier))
return;
Module *M = BB->getParent()->getParent();
LLVMContext &C = M->getContext();
Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
Type *I8XX = PointerType::getUnqual(I8X);
Type *Params[] = {I8XX, I8XX};
FunctionType *FTy = FunctionType::get(Type::getVoidTy(C),
ArrayRef<Type*>(Params, 2),
/*isVarArg=*/false);
Constant *Callee = M->getOrInsertFunction(Name, FTy);
IRBuilder<> Builder(BB, llvm::prior(BB->end()));
Value *PtrName;
StringRef Tmp = Ptr->getName();
if (0 == (PtrName = M->getGlobalVariable(Tmp, true))) {
Value *ActualPtrName = Builder.CreateGlobalStringPtr(Tmp,
Tmp + "_STR");
PtrName = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
cast<Constant>(ActualPtrName), Tmp);
}
Value *S;
std::string SeqStr = SequenceToString(Seq);
if (0 == (S = M->getGlobalVariable(SeqStr, true))) {
Value *ActualPtrName = Builder.CreateGlobalStringPtr(SeqStr,
SeqStr + "_STR");
S = new GlobalVariable(*M, I8X, true, GlobalVariable::InternalLinkage,
cast<Constant>(ActualPtrName), SeqStr);
}
Builder.CreateCall2(Callee, PtrName, S);
}
/// Adds a source annotation to pointer and a state change annotation to Inst
/// referencing the source annotation and the old/new state of pointer.
static void GenerateARCAnnotation(unsigned InstMDId,
unsigned PtrMDId,
Instruction *Inst,
Value *Ptr,
Sequence OldSeq,
Sequence NewSeq) {
if (EnableARCAnnotations) {
// If we have a target identifier, make sure that we match it before
// emitting an annotation.
if(!ARCAnnotationTargetIdentifier.empty() &&
!Ptr->getName().equals(ARCAnnotationTargetIdentifier))
return;
// First generate the source annotation on our pointer. This will return an
// MDString* if Ptr actually comes from an instruction implying we can put
// in a source annotation. If AppendMDNodeToSourcePtr returns 0 (i.e. NULL),
// then we know that our pointer is from an Argument so we put a reference
// to the argument number.
//
// The point of this is to make it easy for the
// llvm-arc-annotation-processor tool to cross reference where the source
// pointer is in the LLVM IR since the LLVM IR parser does not submit such
// information via debug info for backends to use (since why would anyone
// need such a thing from LLVM IR besides in non standard cases
// [i.e. this]).
MDString *SourcePtrMDNode =
AppendMDNodeToSourcePtr(PtrMDId, Ptr);
AppendMDNodeToInstForPtr(InstMDId, Inst, Ptr, SourcePtrMDNode, OldSeq,
NewSeq);
}
}
// The actual interface for accessing the above functionality is defined via
// some simple macros which are defined below. We do this so that the user does
// not need to pass in what metadata id is needed resulting in cleaner code and
// additionally since it provides an easy way to conditionally no-op all
// annotation support in a non-debug build.
/// Use this macro to annotate a sequence state change when processing
/// instructions bottom up,
#define ANNOTATE_BOTTOMUP(inst, ptr, old, new) \
GenerateARCAnnotation(ARCAnnotationBottomUpMDKind, \
ARCAnnotationProvenanceSourceMDKind, (inst), \
const_cast<Value*>(ptr), (old), (new))
/// Use this macro to annotate a sequence state change when processing
/// instructions top down.
#define ANNOTATE_TOPDOWN(inst, ptr, old, new) \
GenerateARCAnnotation(ARCAnnotationTopDownMDKind, \
ARCAnnotationProvenanceSourceMDKind, (inst), \
const_cast<Value*>(ptr), (old), (new))
#define ANNOTATE_BB(_states, _bb, _name, _type, _direction) \
do { \
if (EnableARCAnnotations) { \
for(BBState::ptr_const_iterator I = (_states)._direction##_ptr_begin(), \
E = (_states)._direction##_ptr_end(); I != E; ++I) { \
Value *Ptr = const_cast<Value*>(I->first); \
Sequence Seq = I->second.GetSeq(); \
GenerateARCBB ## _type ## Annotation(_name, (_bb), Ptr, Seq); \
} \
} \
} while (0)
#define ANNOTATE_BOTTOMUP_BBSTART(_states, _basicblock) \
ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.bottomup.bbstart", \
Entrance, bottom_up)
#define ANNOTATE_BOTTOMUP_BBEND(_states, _basicblock) \
ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.bottomup.bbend", \
Terminator, bottom_up)
#define ANNOTATE_TOPDOWN_BBSTART(_states, _basicblock) \
ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.topdown.bbstart", \
Entrance, top_down)
#define ANNOTATE_TOPDOWN_BBEND(_states, _basicblock) \
ANNOTATE_BB(_states, _basicblock, "llvm.arc.annotation.topdown.bbend", \
Terminator, top_down)
#else // !ARC_ANNOTATION
// If annotations are off, noop.
#define ANNOTATE_BOTTOMUP(inst, ptr, old, new)
#define ANNOTATE_TOPDOWN(inst, ptr, old, new)
#define ANNOTATE_BOTTOMUP_BBSTART(states, basicblock)
#define ANNOTATE_BOTTOMUP_BBEND(states, basicblock)
#define ANNOTATE_TOPDOWN_BBSTART(states, basicblock)
#define ANNOTATE_TOPDOWN_BBEND(states, basicblock)
#endif // !ARC_ANNOTATION
namespace {
/// \brief The main ARC optimization pass.
class ObjCARCOpt : public FunctionPass {
bool Changed;
ProvenanceAnalysis PA;
ARCRuntimeEntryPoints EP;
// This is used to track if a pointer is stored into an alloca.
DenseSet<const Value *> MultiOwnersSet;
/// A flag indicating whether this optimization pass should run.
bool Run;
/// 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;
#ifdef ARC_ANNOTATIONS
/// The Metadata Kind for llvm.arc.annotation.bottomup metadata.
unsigned ARCAnnotationBottomUpMDKind;
/// The Metadata Kind for llvm.arc.annotation.topdown metadata.
unsigned ARCAnnotationTopDownMDKind;
/// The Metadata Kind for llvm.arc.annotation.provenancesource metadata.
unsigned ARCAnnotationProvenanceSourceMDKind;
#endif // ARC_ANNOATIONS
bool IsRetainBlockOptimizable(const Instruction *Inst);
bool OptimizeRetainRVCall(Function &F, Instruction *RetainRV);
void OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV,
InstructionClass &Class);
bool OptimizeRetainBlockCall(Function &F, Instruction *RetainBlock,
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 ConnectTDBUTraversals(DenseMap<const BasicBlock *, BBState> &BBStates,
MapVector<Value *, RRInfo> &Retains,
DenseMap<Value *, RRInfo> &Releases,
Module *M,
SmallVector<Instruction *, 4> &NewRetains,
SmallVector<Instruction *, 4> &NewReleases,
SmallVector<Instruction *, 8> &DeadInsts,
RRInfo &RetainsToMove,
RRInfo &ReleasesToMove,
Value *Arg,
bool KnownSafe,
bool &AnyPairsCompletelyEliminated);
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);
#ifndef NDEBUG
void GatherStatistics(Function &F, bool AfterOptimization = false);
#endif
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 (DoesRetainableObjPtrEscape(Inst))
return false;
// Otherwise, it's not needed.
return true;
}
/// 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() << "Erasing autoreleaseRV,retainRV pair: " << *I << "\n"
<< "Erasing " << *RetainRV << "\n");
EraseInstruction(I);
EraseInstruction(RetainRV);
return true;
}
}
// Turn it to a plain objc_retain.
Changed = true;
++NumPeeps;
DEBUG(dbgs() << "Transforming objc_retainAutoreleasedReturnValue => "
"objc_retain since the operand is not a return value.\n"
"Old = " << *RetainRV << "\n");
Constant *NewDecl = EP.get(ARCRuntimeEntryPoints::EPT_Retain);
cast<CallInst>(RetainRV)->setCalledFunction(NewDecl);
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() << "Transforming objc_autoreleaseReturnValue => "
"objc_autorelease since its operand is not used as a return "
"value.\n"
"Old = " << *AutoreleaseRV << "\n");
CallInst *AutoreleaseRVCI = cast<CallInst>(AutoreleaseRV);
Constant *NewDecl = EP.get(ARCRuntimeEntryPoints::EPT_Autorelease);
AutoreleaseRVCI->setCalledFunction(NewDecl);
AutoreleaseRVCI->setTailCall(false); // Never tail call objc_autorelease.
Class = IC_Autorelease;
DEBUG(dbgs() << "New: " << *AutoreleaseRV << "\n");
}
// \brief Attempt to strength reduce objc_retainBlock calls to objc_retain
// calls.
//
// Specifically: If an objc_retainBlock call has the copy_on_escape metadata and
// does not escape (following the rules of block escaping), strength reduce the
// objc_retainBlock to an objc_retain.
//
// TODO: If an objc_retainBlock call is dominated period by a previous
// objc_retainBlock call, strength reduce the objc_retainBlock to an
// objc_retain.
bool
ObjCARCOpt::OptimizeRetainBlockCall(Function &F, Instruction *Inst,
InstructionClass &Class) {
assert(GetBasicInstructionClass(Inst) == Class);
assert(IC_RetainBlock == Class);
// If we can not optimize Inst, return false.
if (!IsRetainBlockOptimizable(Inst))
return false;
Changed = true;
++NumPeeps;
DEBUG(dbgs() << "Strength reduced retainBlock => retain.\n");
DEBUG(dbgs() << "Old: " << *Inst << "\n");
CallInst *RetainBlock = cast<CallInst>(Inst);
Constant *NewDecl = EP.get(ARCRuntimeEntryPoints::EPT_Retain);
RetainBlock->setCalledFunction(NewDecl);
// Remove copy_on_escape metadata.
RetainBlock->setMetadata(CopyOnEscapeMDKind, 0);
Class = IC_Retain;
DEBUG(dbgs() << "New: " << *Inst << "\n");
return true;
}
/// Visit each call, one at a time, and make simplifications without doing any
/// additional analysis.
void ObjCARCOpt::OptimizeIndividualCalls(Function &F) {
DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeIndividualCalls ==\n");
// 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++;
InstructionClass Class = GetBasicInstructionClass(Inst);
DEBUG(dbgs() << "Visiting: Class: " << Class << "; " << *Inst << "\n");
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() << "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() << "A null pointer-to-weak-pointer is undefined behavior."
"\nOld = " << *CI << "\nNew = " << *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() << "A null pointer-to-weak-pointer is undefined behavior."
"\nOld = " << *CI << "\nNew = " << *NewValue << "\n");
CI->replaceAllUsesWith(NewValue);
CI->eraseFromParent();
continue;
}
break;
}
case IC_RetainBlock:
// If we strength reduce an objc_retainBlock to an objc_retain, continue
// onto the objc_retain peephole optimizations. Otherwise break.
OptimizeRetainBlockCall(F, Inst, Class);
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();
Constant *Decl = EP.get(ARCRuntimeEntryPoints::EPT_Release);
CallInst *NewCall = CallInst::Create(Decl, Call->getArgOperand(0), "",
Call);
NewCall->setMetadata(ImpreciseReleaseMDKind, MDNode::get(C, None));
DEBUG(dbgs() << "Replacing autorelease{,RV}(x) with objc_release(x) "
"since x is otherwise unused.\nOld: " << *Call << "\nNew: "
<< *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() << "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() << "Removing tail keyword from function: " << *Inst <<
"\n");
cast<CallInst>(Inst)->setTailCall(false);
}
// Set nounwind as needed.
if (IsNoThrow(Class)) {
Changed = true;
DEBUG(dbgs() << "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() << "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() << "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());
}
}
/// If we have a top down pointer in the S_Use state, make sure that there are
/// no CFG hazards by checking the states of various bottom up pointers.
static void CheckForUseCFGHazard(const Sequence SuccSSeq,
const bool SuccSRRIKnownSafe,
PtrState &S,
bool &SomeSuccHasSame,
bool &AllSuccsHaveSame,
bool &NotAllSeqEqualButKnownSafe,
bool &ShouldContinue) {
switch (SuccSSeq) {
case S_CanRelease: {
if (!S.IsKnownSafe() && !SuccSRRIKnownSafe) {
S.ClearSequenceProgress();
break;
}
S.SetCFGHazardAfflicted(true);
ShouldContinue = true;
break;
}
case S_Use:
SomeSuccHasSame = true;
break;
case S_Stop:
case S_Release:
case S_MovableRelease:
if (!S.IsKnownSafe() && !SuccSRRIKnownSafe)
AllSuccsHaveSame = false;
else
NotAllSeqEqualButKnownSafe = true;
break;
case S_Retain:
llvm_unreachable("bottom-up pointer in retain state!");
case S_None:
llvm_unreachable("This should have been handled earlier.");
}
}
/// If we have a Top Down pointer in the S_CanRelease state, make sure that
/// there are no CFG hazards by checking the states of various bottom up
/// pointers.
static void CheckForCanReleaseCFGHazard(const Sequence SuccSSeq,
const bool SuccSRRIKnownSafe,
PtrState &S,
bool &SomeSuccHasSame,
bool &AllSuccsHaveSame,
bool &NotAllSeqEqualButKnownSafe) {
switch (SuccSSeq) {
case S_CanRelease:
SomeSuccHasSame = true;
break;
case S_Stop:
case S_Release:
case S_MovableRelease:
case S_Use:
if (!S.IsKnownSafe() && !SuccSRRIKnownSafe)
AllSuccsHaveSame = false;
else
NotAllSeqEqualButKnownSafe = true;
break;
case S_Retain:
llvm_unreachable("bottom-up pointer in retain state!");
case S_None:
llvm_unreachable("This should have been handled earlier.");
}
}
/// 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) {
PtrState &S = I->second;
const Sequence Seq = I->second.GetSeq();
// We only care about S_Retain, S_CanRelease, and S_Use.
if (Seq == S_None)
continue;
// Make sure that if extra top down states are added in the future that this
// code is updated to handle it.
assert((Seq == S_Retain || Seq == S_CanRelease || Seq == S_Use) &&
"Unknown top down sequence state.");
const Value *Arg = I->first;
const TerminatorInst *TI = cast<TerminatorInst>(&BB->back());
bool SomeSuccHasSame = false;
bool AllSuccsHaveSame = true;
bool NotAllSeqEqualButKnownSafe = false;
succ_const_iterator SI(TI), SE(TI, false);
for (; SI != SE; ++SI) {
// If VisitBottomUp has pointer information for this successor, take
// what we know about it.
const DenseMap<const BasicBlock *, BBState>::iterator BBI =
BBStates.find(*SI);
assert(BBI != BBStates.end());
const PtrState &SuccS = BBI->second.getPtrBottomUpState(Arg);
const Sequence SuccSSeq = SuccS.GetSeq();
// If bottom up, the pointer is in an S_None state, clear the sequence
// progress since the sequence in the bottom up state finished
// suggesting a mismatch in between retains/releases. This is true for
// all three cases that we are handling here: S_Retain, S_Use, and
// S_CanRelease.
if (SuccSSeq == S_None) {
S.ClearSequenceProgress();
continue;
}
// If we have S_Use or S_CanRelease, perform our check for cfg hazard
// checks.
const bool SuccSRRIKnownSafe = SuccS.IsKnownSafe();
// *NOTE* We do not use Seq from above here since we are allowing for
// S.GetSeq() to change while we are visiting basic blocks.
switch(S.GetSeq()) {
case S_Use: {
bool ShouldContinue = false;
CheckForUseCFGHazard(SuccSSeq, SuccSRRIKnownSafe, S, SomeSuccHasSame,
AllSuccsHaveSame, NotAllSeqEqualButKnownSafe,
ShouldContinue);
if (ShouldContinue)
continue;
break;
}
case S_CanRelease: {
CheckForCanReleaseCFGHazard(SuccSSeq, SuccSRRIKnownSafe, S,
SomeSuccHasSame, AllSuccsHaveSame,
NotAllSeqEqualButKnownSafe);
break;
}
case S_Retain:
case S_None:
case S_Stop:
case S_Release:
case S_MovableRelease:
break;
}
}
// 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();
} else if (NotAllSeqEqualButKnownSafe) {
// If we would have cleared the state foregoing the fact that we are known
// safe, stop code motion. This is because whether or not it is safe to
// remove RR pairs via KnownSafe is an orthogonal concept to whether we
// are allowed to perform code motion.
S.SetCFGHazardAfflicted(true);
}
}
}
bool
ObjCARCOpt::VisitInstructionBottomUp(Instruction *Inst,
BasicBlock *BB,
MapVector<Value *, RRInfo> &Retains,
BBState &MyStates) {
bool NestingDetected = false;
InstructionClass Class = GetInstructionClass(Inst);
const Value *Arg = 0;
DEBUG(dbgs() << "Class: " << Class << "\n");
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() << "Found nested releases (i.e. a release pair)\n");
NestingDetected = true;
}
MDNode *ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind);
Sequence NewSeq = ReleaseMetadata ? S_MovableRelease : S_Release;
ANNOTATE_BOTTOMUP(Inst, Arg, S.GetSeq(), NewSeq);
S.ResetSequenceProgress(NewSeq);
S.SetReleaseMetadata(ReleaseMetadata);
S.SetKnownSafe(S.HasKnownPositiveRefCount());
S.SetTailCallRelease(cast<CallInst>(Inst)->isTailCall());
S.InsertCall(Inst);
S.SetKnownPositiveRefCount();
break;
}
case IC_RetainBlock:
// In OptimizeIndividualCalls, we have strength reduced all optimizable
// objc_retainBlocks to objc_retains. Thus at this point any
// objc_retainBlocks that we see are not optimizable.
break;
case IC_Retain:
case IC_RetainRV: {
Arg = GetObjCArg(Inst);
PtrState &S = MyStates.getPtrBottomUpState(Arg);
S.SetKnownPositiveRefCount();
Sequence OldSeq = S.GetSeq();
switch (OldSeq) {
case S_Stop:
case S_Release:
case S_MovableRelease:
case S_Use:
// If OldSeq is not S_Use or OldSeq is S_Use and we are tracking an
// imprecise release, clear our reverse insertion points.
if (OldSeq != S_Use || S.IsTrackingImpreciseReleases())
S.ClearReverseInsertPts();
// 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)
Retains[Inst] = S.GetRRInfo();
S.ClearSequenceProgress();
break;
case S_None:
break;
case S_Retain:
llvm_unreachable("bottom-up pointer in retain state!");
}
ANNOTATE_BOTTOMUP(Inst, Arg, OldSeq, S.GetSeq());
// A retain moving bottom up can be a use.
break;
}
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;
case IC_User:
// If we have a store into an alloca of a pointer we are tracking, the
// pointer has multiple owners implying that we must be more conservative.
//
// This comes up in the context of a pointer being ``KnownSafe''. In the
// presense of a block being initialized, the frontend will emit the
// objc_retain on the original pointer and the release on the pointer loaded
// from the alloca. The optimizer will through the provenance analysis
// realize that the two are related, but since we only require KnownSafe in
// one direction, will match the inner retain on the original pointer with
// the guard release on the original pointer. This is fixed by ensuring that
// in the presense of allocas we only unconditionally remove pointers if
// both our retain and our release are KnownSafe.
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
if (AreAnyUnderlyingObjectsAnAlloca(SI->getPointerOperand())) {
BBState::ptr_iterator I = MyStates.findPtrBottomUpState(
StripPointerCastsAndObjCCalls(SI->getValueOperand()));
if (I != MyStates.bottom_up_ptr_end())
MultiOwnersSet.insert(I->first);
}
}
break;
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)) {
DEBUG(dbgs() << "CanAlterRefCount: Seq: " << Seq << "; " << *Ptr
<< "\n");
S.ClearKnownPositiveRefCount();
switch (Seq) {
case S_Use:
S.SetSeq(S_CanRelease);
ANNOTATE_BOTTOMUP(Inst, Ptr, Seq, S.GetSeq());
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)) {
DEBUG(dbgs() << "CanUse: Seq: " << Seq << "; " << *Ptr
<< "\n");
assert(!S.HasReverseInsertPts());
// 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.InsertReverseInsertPt(BB->getFirstInsertionPt());
else
S.InsertReverseInsertPt(llvm::next(BasicBlock::iterator(Inst)));
S.SetSeq(S_Use);
ANNOTATE_BOTTOMUP(Inst, Ptr, Seq, S_Use);
} else if (Seq == S_Release && IsUser(Class)) {
DEBUG(dbgs() << "PreciseReleaseUse: Seq: " << Seq << "; " << *Ptr
<< "\n");
// Non-movable releases depend on any possible objc pointer use.
S.SetSeq(S_Stop);
ANNOTATE_BOTTOMUP(Inst, Ptr, S_Release, S_Stop);
assert(!S.HasReverseInsertPts());
// As above; handle invoke specially.
if (isa<InvokeInst>(Inst))
S.InsertReverseInsertPt(BB->getFirstInsertionPt());
else
S.InsertReverseInsertPt(llvm::next(BasicBlock::iterator(Inst)));
}
break;
case S_Stop:
if (CanUse(Inst, Ptr, PA, Class)) {
DEBUG(dbgs() << "PreciseStopUse: Seq: " << Seq << "; " << *Ptr
<< "\n");
S.SetSeq(S_Use);
ANNOTATE_BOTTOMUP(Inst, Ptr, Seq, 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) {
DEBUG(dbgs() << "\n== ObjCARCOpt::VisitBottomUp ==\n");
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);
}
}
// If ARC Annotations are enabled, output the current state of pointers at the
// bottom of the basic block.
ANNOTATE_BOTTOMUP_BBEND(MyStates, BB);
// 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() << "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);
}
// If ARC Annotations are enabled, output the current state of pointers at the
// top of the basic block.
ANNOTATE_BOTTOMUP_BBSTART(MyStates, BB);
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:
// In OptimizeIndividualCalls, we have strength reduced all optimizable
// objc_retainBlocks to objc_retains. Thus at this point any
// objc_retainBlocks that we see are not optimizable.
break;
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;
ANNOTATE_TOPDOWN(Inst, Arg, S.GetSeq(), S_Retain);
S.ResetSequenceProgress(S_Retain);
S.SetKnownSafe(S.HasKnownPositiveRefCount());
S.InsertCall(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.ClearKnownPositiveRefCount();
Sequence OldSeq = S.GetSeq();
MDNode *ReleaseMetadata = Inst->getMetadata(ImpreciseReleaseMDKind);
switch (OldSeq) {
case S_Retain:
case S_CanRelease:
if (OldSeq == S_Retain || ReleaseMetadata != 0)
S.ClearReverseInsertPts();
// FALL THROUGH
case S_Use:
S.SetReleaseMetadata(ReleaseMetadata);
S.SetTailCallRelease(cast<CallInst>(Inst)->isTailCall());
Releases[Inst] = S.GetRRInfo();
ANNOTATE_TOPDOWN(Inst, Arg, S.GetSeq(), S_None);
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)) {
DEBUG(dbgs() << "CanAlterRefCount: Seq: " << Seq << "; " << *Ptr
<< "\n");
S.ClearKnownPositiveRefCount();
switch (Seq) {
case S_Retain:
S.SetSeq(S_CanRelease);
ANNOTATE_TOPDOWN(Inst, Ptr, Seq, S_CanRelease);
assert(!S.HasReverseInsertPts());
S.InsertReverseInsertPt(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)) {
DEBUG(dbgs() << "CanUse: Seq: " << Seq << "; " << *Ptr
<< "\n");
S.SetSeq(S_Use);
ANNOTATE_TOPDOWN(Inst, Ptr, Seq, 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) {
DEBUG(dbgs() << "\n== ObjCARCOpt::VisitTopDown ==\n");
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);
}
}
// If ARC Annotations are enabled, output the current state of pointers at the
// top of the basic block.
ANNOTATE_TOPDOWN_BBSTART(MyStates, BB);
// Visit all the instructions, top-down.
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) {
Instruction *Inst = I;
DEBUG(dbgs() << "Visiting " << *Inst << "\n");
NestingDetected |= VisitInstructionTopDown(Inst, Releases, MyStates);
}
// If ARC Annotations are enabled, output the current state of pointers at the
// bottom of the basic block.
ANNOTATE_TOPDOWN_BBEND(MyStates, BB);
#ifdef ARC_ANNOTATIONS
if (!(EnableARCAnnotations && DisableCheckForCFGHazards))
#endif
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);
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()));
DEBUG(dbgs() << "== ObjCARCOpt::MoveCalls ==\n");
// 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);
Constant *Decl = EP.get(ARCRuntimeEntryPoints::EPT_Retain);
CallInst *Call = CallInst::Create(Decl, MyArg, "", InsertPt);
Call->setDoesNotThrow();
Call->setTailCall();
DEBUG(dbgs() << "Inserting new Retain: " << *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);
Constant *Decl = EP.get(ARCRuntimeEntryPoints::EPT_Release);
CallInst *Call = CallInst::Create(Decl, 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() << "Inserting new Release: " << *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() << "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() << "Deleting release: " << *OrigRelease << "\n");
}
}
bool
ObjCARCOpt::ConnectTDBUTraversals(DenseMap<const BasicBlock *, BBState>
&BBStates,
MapVector<Value *, RRInfo> &Retains,
DenseMap<Value *, RRInfo> &Releases,
Module *M,
SmallVector<Instruction *, 4> &NewRetains,
SmallVector<Instruction *, 4> &NewReleases,
SmallVector<Instruction *, 8> &DeadInsts,
RRInfo &RetainsToMove,
RRInfo &ReleasesToMove,
Value *Arg,
bool KnownSafe,
bool &AnyPairsCompletelyEliminated) {
// If a pair happens in a region where it is known that the reference count
// is already incremented, we can similarly ignore possible decrements unless
// we are dealing with a retainable object with multiple provenance sources.
bool KnownSafeTD = true, KnownSafeBU = true;
bool MultipleOwners = false;
bool CFGHazardAfflicted = false;
// 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;
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;
MultipleOwners =
MultipleOwners || MultiOwnersSet.count(GetObjCArg(NewRetain));
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())
return false;
const RRInfo &NewRetainReleaseRRI = Jt->second;
assert(NewRetainReleaseRRI.Calls.count(NewRetain));
if (ReleasesToMove.Calls.insert(NewRetainRelease)) {
// If we overflow when we compute the path count, don't remove/move
// anything.
const BBState &NRRBBState = BBStates[NewRetainRelease->getParent()];
unsigned PathCount;
if (NRRBBState.GetAllPathCountWithOverflow(PathCount))
return false;
OldDelta -= PathCount;
// 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)) {
// If we overflow when we compute the path count, don't
// remove/move anything.
const BBState &RIPBBState = BBStates[RIP->getParent()];
if (RIPBBState.GetAllPathCountWithOverflow(PathCount))
return false;
NewDelta -= PathCount;
}
}
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;
CFGHazardAfflicted |= NewReleaseRRI.CFGHazardAfflicted;
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())
return false;
const RRInfo &NewReleaseRetainRRI = Jt->second;
assert(NewReleaseRetainRRI.Calls.count(NewRelease));
if (RetainsToMove.Calls.insert(NewReleaseRetain)) {
// If we overflow when we compute the path count, don't remove/move
// anything.
const BBState &NRRBBState = BBStates[NewReleaseRetain->getParent()];
unsigned PathCount;
if (NRRBBState.GetAllPathCountWithOverflow(PathCount))
return false;
OldDelta += PathCount;
OldCount += PathCount;
// 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)) {
// If we overflow when we compute the path count, don't
// remove/move anything.
const BBState &RIPBBState = BBStates[RIP->getParent()];
if (RIPBBState.GetAllPathCountWithOverflow(PathCount))
return false;
NewDelta += PathCount;
NewCount += PathCount;
}
}
NewRetains.push_back(NewReleaseRetain);
}
}
}
NewReleases.clear();
if (NewRetains.empty()) break;
}
// If the pointer is known incremented in 1 direction and we do not have
// MultipleOwners, we can safely remove the retain/releases. Otherwise we need
// to be known safe in both directions.
bool UnconditionallySafe = (KnownSafeTD && KnownSafeBU) ||
((KnownSafeTD || KnownSafeBU) && !MultipleOwners);
if (UnconditionallySafe) {
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)
return false;
// At this point, we are not going to remove any RR pairs, but we still are
// able to move RR pairs. If one of our pointers is afflicted with
// CFGHazards, we cannot perform such code motion so exit early.
const bool WillPerformCodeMotion = RetainsToMove.ReverseInsertPts.size() ||
ReleasesToMove.ReverseInsertPts.size();
if (CFGHazardAfflicted && WillPerformCodeMotion)
return false;
}
// 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)
return false;
#ifdef ARC_ANNOTATIONS
// Do not move calls if ARC annotations are requested.
if (EnableARCAnnotations)
return false;
#endif // ARC_ANNOTATIONS
Changed = true;
assert(OldCount != 0 && "Unreachable code?");
NumRRs += OldCount - NewCount;
// Set to true if we completely removed any RR pairs.
AnyPairsCompletelyEliminated = NewCount == 0;
// We can move calls!
return true;
}
/// 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) {
DEBUG(dbgs() << "\n== ObjCARCOpt::PerformCodePlacement ==\n");
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() << "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;
// Connect the dots between the top-down-collected RetainsToMove and
// bottom-up-collected ReleasesToMove to form sets of related calls.
NewRetains.push_back(Retain);
bool PerformMoveCalls =
ConnectTDBUTraversals(BBStates, Retains, Releases, M, NewRetains,
NewReleases, DeadInsts, RetainsToMove,
ReleasesToMove, Arg, KnownSafe,
AnyPairsCompletelyEliminated);
if (PerformMoveCalls) {
// Ok, everything checks out and we're all set. Let's move/delete some
// code!
MoveCalls(Arg, RetainsToMove, ReleasesToMove,
Retains, Releases, DeadInsts, M);
}
// Clean up state for 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) {
DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeWeakCalls ==\n");
// 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() << "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) {
Constant *Decl = EP.get(ARCRuntimeEntryPoints::EPT_Retain);
CallInst *CI = CallInst::Create(Decl, 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) {
Constant *Decl = EP.get(ARCRuntimeEntryPoints::EPT_Retain);
CallInst *CI = CallInst::Create(Decl, 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_IntrinsicUser:
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:;
}
}
}
/// 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.
bool AnyPairsCompletelyEliminated = PerformCodePlacement(BBStates, Retains,
Releases,
F.getParent());
// Cleanup.
MultiOwnersSet.clear();
return AnyPairsCompletelyEliminated && NestingDetected;
}
/// Check if there is a dependent call earlier that does not have anything in
/// between the Retain and the call that can affect the reference count of their
/// shared pointer argument. Note that Retain need not be in BB.
static bool
HasSafePathToPredecessorCall(const Value *Arg, Instruction *Retain,
SmallPtrSet<Instruction *, 4> &DepInsts,
SmallPtrSet<const BasicBlock *, 4> &Visited,
ProvenanceAnalysis &PA) {
FindDependencies(CanChangeRetainCount, Arg, Retain->getParent(), Retain,
DepInsts, Visited, PA);
if (DepInsts.size() != 1)
return false;
CallInst *Call =
dyn_cast_or_null<CallInst>(*DepInsts.begin());
// Check that the pointer is the return value of the call.
if (!Call || Arg != Call)
return false;
// Check that the call is a regular call.
InstructionClass Class = GetBasicInstructionClass(Call);
if (Class != IC_CallOrUser && Class != IC_Call)
return false;
return true;
}
/// Find a dependent retain that precedes the given autorelease for which there
/// is nothing in between the two instructions that can affect the ref count of
/// Arg.
static CallInst *
FindPredecessorRetainWithSafePath(const Value *Arg, BasicBlock *BB,
Instruction *Autorelease,
SmallPtrSet<Instruction *, 4> &DepInsts,
SmallPtrSet<const BasicBlock *, 4> &Visited,
ProvenanceAnalysis &PA) {
FindDependencies(CanChangeRetainCount, Arg,
BB, Autorelease, DepInsts, Visited, PA);
if (DepInsts.size() != 1)
return 0;
CallInst *Retain =
dyn_cast_or_null<CallInst>(*DepInsts.begin());
// Check that we found a retain with the same argument.
if (!Retain ||
!IsRetain(GetBasicInstructionClass(Retain)) ||
GetObjCArg(Retain) != Arg) {
return 0;
}
return Retain;
}
/// Look for an ``autorelease'' instruction dependent on Arg such that there are
/// no instructions dependent on Arg that need a positive ref count in between
/// the autorelease and the ret.
static CallInst *
FindPredecessorAutoreleaseWithSafePath(const Value *Arg, BasicBlock *BB,
ReturnInst *Ret,
SmallPtrSet<Instruction *, 4> &DepInsts,
SmallPtrSet<const BasicBlock *, 4> &V,
ProvenanceAnalysis &PA) {
FindDependencies(NeedsPositiveRetainCount, Arg,
BB, Ret, DepInsts, V, PA);
if (DepInsts.size() != 1)
return 0;
CallInst *Autorelease =
dyn_cast_or_null<CallInst>(*DepInsts.begin());
if (!Autorelease)
return 0;
InstructionClass AutoreleaseClass = GetBasicInstructionClass(Autorelease);
if (!IsAutorelease(AutoreleaseClass))
return 0;
if (GetObjCArg(Autorelease) != Arg)
return 0;
return Autorelease;
}
/// 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.
void ObjCARCOpt::OptimizeReturns(Function &F) {
if (!F.getReturnType()->isPointerTy())
return;
DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeReturns ==\n");
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() << "Visiting: " << *Ret << "\n");
if (!Ret)
continue;
const Value *Arg = StripPointerCastsAndObjCCalls(Ret->getOperand(0));
// Look for an ``autorelease'' instruction that is a predecessor of Ret and
// dependent on Arg such that there are no instructions dependent on Arg
// that need a positive ref count in between the autorelease and Ret.
CallInst *Autorelease =
FindPredecessorAutoreleaseWithSafePath(Arg, BB, Ret,
DependingInstructions, Visited,
PA);
DependingInstructions.clear();
Visited.clear();
if (!Autorelease)
continue;
CallInst *Retain =
FindPredecessorRetainWithSafePath(Arg, BB, Autorelease,
DependingInstructions, Visited, PA);
DependingInstructions.clear();
Visited.clear();
if (!Retain)
continue;
// 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.
bool HasSafePathToCall = HasSafePathToPredecessorCall(Arg, Retain,
DependingInstructions,
Visited, PA);
DependingInstructions.clear();
Visited.clear();
if (!HasSafePathToCall)
continue;
// If so, we can zap the retain and autorelease.
Changed = true;
++NumRets;
DEBUG(dbgs() << "Erasing: " << *Retain << "\nErasing: "
<< *Autorelease << "\n");
EraseInstruction(Retain);
EraseInstruction(Autorelease);
}
}
#ifndef NDEBUG
void
ObjCARCOpt::GatherStatistics(Function &F, bool AfterOptimization) {
llvm::Statistic &NumRetains =
AfterOptimization? NumRetainsAfterOpt : NumRetainsBeforeOpt;
llvm::Statistic &NumReleases =
AfterOptimization? NumReleasesAfterOpt : NumReleasesBeforeOpt;
for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
Instruction *Inst = &*I++;
switch (GetBasicInstructionClass(Inst)) {
default:
break;
case IC_Retain:
++NumRetains;
break;
case IC_Release:
++NumReleases;
break;
}
}
}
#endif
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");
#ifdef ARC_ANNOTATIONS
ARCAnnotationBottomUpMDKind =
M.getContext().getMDKindID("llvm.arc.annotation.bottomup");
ARCAnnotationTopDownMDKind =
M.getContext().getMDKindID("llvm.arc.annotation.topdown");
ARCAnnotationProvenanceSourceMDKind =
M.getContext().getMDKindID("llvm.arc.annotation.provenancesource");
#endif // ARC_ANNOTATIONS
// 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.
// Initialize our runtime entry point cache.
EP.Initialize(&M);
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>());
#ifndef NDEBUG
if (AreStatisticsEnabled()) {
GatherStatistics(F, false);
}
#endif
// 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 computes 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);
// Gather statistics after optimization.
#ifndef NDEBUG
if (AreStatisticsEnabled()) {
GatherStatistics(F, true);
}
#endif
DEBUG(dbgs() << "\n");
return Changed;
}
void ObjCARCOpt::releaseMemory() {
PA.clear();
}
/// @}
///
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