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llvm / llvm / eaedc0223b81be365f4d2ee28b438765665fbdda / . / lib / Transforms / ObjCARC / ObjCARCOpts.cpp
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//===- ObjCARCOpts.cpp - ObjC ARC Optimization ----------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
/// \file
/// This file defines 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.
//
//===----------------------------------------------------------------------===//
#include "ARCRuntimeEntryPoints.h"
#include "BlotMapVector.h"
#include "DependencyAnalysis.h"
#include "ObjCARC.h"
#include "ProvenanceAnalysis.h"
#include "PtrState.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/None.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/EHPersonalities.h"
#include "llvm/Analysis/ObjCARCAliasAnalysis.h"
#include "llvm/Analysis/ObjCARCAnalysisUtils.h"
#include "llvm/Analysis/ObjCARCInstKind.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/Constant.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Metadata.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/Pass.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/raw_ostream.h"
#include <cassert>
#include <iterator>
#include <utility>
using namespace llvm;
using namespace llvm::objcarc;
#define DEBUG_TYPE "objc-arc-opts"
/// \defgroup ARCUtilities Utility declarations/definitions specific to ARC.
/// @{
/// This is similar to GetRCIdentityRoot but it stops as soon
/// as it finds a value with multiple uses.
static const Value *FindSingleUseIdentifiedObject(const Value *Arg) {
// ConstantData (like ConstantPointerNull and UndefValue) is used across
// modules. It's never a single-use value.
if (isa<ConstantData>(Arg))
return nullptr;
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(GetBasicARCInstKind(Arg)))
return FindSingleUseIdentifiedObject(
cast<CallInst>(Arg)->getArgOperand(0));
if (!IsObjCIdentifiedObject(Arg))
return nullptr;
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 (const User *U : Arg->users())
if (!U->use_empty() || GetRCIdentityRoot(U) != Arg)
return nullptr;
return Arg;
}
return nullptr;
}
/// @}
///
/// \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 {
/// Per-BasicBlock state.
class BBState {
/// The number of unique control paths from the entry which can reach this
/// block.
unsigned TopDownPathCount = 0;
/// The number of unique control paths to exits from this block.
unsigned BottomUpPathCount = 0;
/// The top-down traversal uses this to record information known about a
/// pointer at the bottom of each block.
BlotMapVector<const Value *, TopDownPtrState> PerPtrTopDown;
/// The bottom-up traversal uses this to record information known about a
/// pointer at the top of each block.
BlotMapVector<const Value *, BottomUpPtrState> 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:
static const unsigned OverflowOccurredValue;
BBState() = default;
using top_down_ptr_iterator = decltype(PerPtrTopDown)::iterator;
using const_top_down_ptr_iterator = decltype(PerPtrTopDown)::const_iterator;
top_down_ptr_iterator top_down_ptr_begin() { return PerPtrTopDown.begin(); }
top_down_ptr_iterator top_down_ptr_end() { return PerPtrTopDown.end(); }
const_top_down_ptr_iterator top_down_ptr_begin() const {
return PerPtrTopDown.begin();
}
const_top_down_ptr_iterator top_down_ptr_end() const {
return PerPtrTopDown.end();
}
bool hasTopDownPtrs() const {
return !PerPtrTopDown.empty();
}
using bottom_up_ptr_iterator = decltype(PerPtrBottomUp)::iterator;
using const_bottom_up_ptr_iterator =
decltype(PerPtrBottomUp)::const_iterator;
bottom_up_ptr_iterator bottom_up_ptr_begin() {
return PerPtrBottomUp.begin();
}
bottom_up_ptr_iterator bottom_up_ptr_end() { return PerPtrBottomUp.end(); }
const_bottom_up_ptr_iterator bottom_up_ptr_begin() const {
return PerPtrBottomUp.begin();
}
const_bottom_up_ptr_iterator bottom_up_ptr_end() const {
return PerPtrBottomUp.end();
}
bool hasBottomUpPtrs() const {
return !PerPtrBottomUp.empty();
}
/// 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.
TopDownPtrState &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.
BottomUpPtrState &getPtrBottomUpState(const Value *Arg) {
return PerPtrBottomUp[Arg];
}
/// Attempt to find the PtrState object describing the bottom up state for
/// pointer Arg.
bottom_up_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 occurred. Returns false if overflow did not
/// occur.
bool GetAllPathCountWithOverflow(unsigned &PathCount) const {
if (TopDownPathCount == OverflowOccurredValue ||
BottomUpPathCount == OverflowOccurredValue)
return true;
unsigned long long Product =
(unsigned long long)TopDownPathCount*BottomUpPathCount;
// Overflow occurred if any of the upper bits of Product are set or if all
// the lower bits of Product are all set.
return (Product >> 32) ||
((PathCount = Product) == OverflowOccurredValue);
}
// Specialized CFG utilities.
using edge_iterator = SmallVectorImpl<BasicBlock *>::const_iterator;
edge_iterator pred_begin() const { return Preds.begin(); }
edge_iterator pred_end() const { return Preds.end(); }
edge_iterator succ_begin() const { return Succs.begin(); }
edge_iterator succ_end() const { 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(); }
};
} // end anonymous namespace
const unsigned BBState::OverflowOccurredValue = 0xffffffff;
namespace llvm {
raw_ostream &operator<<(raw_ostream &OS,
BBState &BBState) LLVM_ATTRIBUTE_UNUSED;
} // end namespace llvm
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) {
if (TopDownPathCount == OverflowOccurredValue)
return;
// Other.TopDownPathCount can be 0, in which case it is either dead or a
// loop backedge. Loop backedges are special.
TopDownPathCount += Other.TopDownPathCount;
// In order to be consistent, we clear the top down pointers when by adding
// TopDownPathCount becomes OverflowOccurredValue even though "true" overflow
// has not occurred.
if (TopDownPathCount == OverflowOccurredValue) {
clearTopDownPointers();
return;
}
// Check for overflow. If we have overflow, fall back to conservative
// behavior.
if (TopDownPathCount < Other.TopDownPathCount) {
TopDownPathCount = OverflowOccurredValue;
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 (auto MI = Other.top_down_ptr_begin(), ME = Other.top_down_ptr_end();
MI != ME; ++MI) {
auto Pair = PerPtrTopDown.insert(*MI);
Pair.first->second.Merge(Pair.second ? TopDownPtrState() : 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 (auto 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(TopDownPtrState(), /*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) {
if (BottomUpPathCount == OverflowOccurredValue)
return;
// Other.BottomUpPathCount can be 0, in which case it is either dead or a
// loop backedge. Loop backedges are special.
BottomUpPathCount += Other.BottomUpPathCount;
// In order to be consistent, we clear the top down pointers when by adding
// BottomUpPathCount becomes OverflowOccurredValue even though "true" overflow
// has not occurred.
if (BottomUpPathCount == OverflowOccurredValue) {
clearBottomUpPointers();
return;
}
// Check for overflow. If we have overflow, fall back to conservative
// behavior.
if (BottomUpPathCount < Other.BottomUpPathCount) {
BottomUpPathCount = OverflowOccurredValue;
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 (auto MI = Other.bottom_up_ptr_begin(), ME = Other.bottom_up_ptr_end();
MI != ME; ++MI) {
auto Pair = PerPtrBottomUp.insert(*MI);
Pair.first->second.Merge(Pair.second ? BottomUpPtrState() : 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 (auto 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(BottomUpPtrState(), /*TopDown=*/false);
}
raw_ostream &llvm::operator<<(raw_ostream &OS, BBState &BBInfo) {
// Dump the pointers we are tracking.
OS << " TopDown State:\n";
if (!BBInfo.hasTopDownPtrs()) {
LLVM_DEBUG(dbgs() << " NONE!\n");
} else {
for (auto I = BBInfo.top_down_ptr_begin(), E = BBInfo.top_down_ptr_end();
I != E; ++I) {
const PtrState &P = I->second;
OS << " Ptr: " << *I->first
<< "\n KnownSafe: " << (P.IsKnownSafe()?"true":"false")
<< "\n ImpreciseRelease: "
<< (P.IsTrackingImpreciseReleases()?"true":"false") << "\n"
<< " HasCFGHazards: "
<< (P.IsCFGHazardAfflicted()?"true":"false") << "\n"
<< " KnownPositive: "
<< (P.HasKnownPositiveRefCount()?"true":"false") << "\n"
<< " Seq: "
<< P.GetSeq() << "\n";
}
}
OS << " BottomUp State:\n";
if (!BBInfo.hasBottomUpPtrs()) {
LLVM_DEBUG(dbgs() << " NONE!\n");
} else {
for (auto I = BBInfo.bottom_up_ptr_begin(), E = BBInfo.bottom_up_ptr_end();
I != E; ++I) {
const PtrState &P = I->second;
OS << " Ptr: " << *I->first
<< "\n KnownSafe: " << (P.IsKnownSafe()?"true":"false")
<< "\n ImpreciseRelease: "
<< (P.IsTrackingImpreciseReleases()?"true":"false") << "\n"
<< " HasCFGHazards: "
<< (P.IsCFGHazardAfflicted()?"true":"false") << "\n"
<< " KnownPositive: "
<< (P.HasKnownPositiveRefCount()?"true":"false") << "\n"
<< " Seq: "
<< P.GetSeq() << "\n";
}
}
return OS;
}
namespace {
/// The main ARC optimization pass.
class ObjCARCOpt : public FunctionPass {
bool Changed;
ProvenanceAnalysis PA;
/// A cache of references to runtime entry point constants.
ARCRuntimeEntryPoints EP;
/// A cache of MDKinds that can be passed into other functions to propagate
/// MDKind identifiers.
ARCMDKindCache MDKindCache;
/// A flag indicating whether this optimization pass should run.
bool Run;
/// Flags which determine whether each of the interesting runtime functions
/// is in fact used in the current function.
unsigned UsedInThisFunction;
bool OptimizeRetainRVCall(Function &F, Instruction *RetainRV);
void OptimizeAutoreleaseRVCall(Function &F, Instruction *AutoreleaseRV,
ARCInstKind &Class);
void OptimizeIndividualCalls(Function &F);
void CheckForCFGHazards(const BasicBlock *BB,
DenseMap<const BasicBlock *, BBState> &BBStates,
BBState &MyStates) const;
bool VisitInstructionBottomUp(Instruction *Inst, BasicBlock *BB,
BlotMapVector<Value *, RRInfo> &Retains,
BBState &MyStates);
bool VisitBottomUp(BasicBlock *BB,
DenseMap<const BasicBlock *, BBState> &BBStates,
BlotMapVector<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,
BlotMapVector<Value *, RRInfo> &Retains,
DenseMap<Value *, RRInfo> &Releases);
void MoveCalls(Value *Arg, RRInfo &RetainsToMove, RRInfo &ReleasesToMove,
BlotMapVector<Value *, RRInfo> &Retains,
DenseMap<Value *, RRInfo> &Releases,
SmallVectorImpl<Instruction *> &DeadInsts, Module *M);
bool
PairUpRetainsAndReleases(DenseMap<const BasicBlock *, BBState> &BBStates,
BlotMapVector<Value *, RRInfo> &Retains,
DenseMap<Value *, RRInfo> &Releases, Module *M,
Instruction * Retain,
SmallVectorImpl<Instruction *> &DeadInsts,
RRInfo &RetainsToMove, RRInfo &ReleasesToMove,
Value *Arg, bool KnownSafe,
bool &AnyPairsCompletelyEliminated);
bool PerformCodePlacement(DenseMap<const BasicBlock *, BBState> &BBStates,
BlotMapVector<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
void getAnalysisUsage(AnalysisUsage &AU) const override;
bool doInitialization(Module &M) override;
bool runOnFunction(Function &F) override;
void releaseMemory() override;
public:
static char ID;
ObjCARCOpt() : FunctionPass(ID) {
initializeObjCARCOptPass(*PassRegistry::getPassRegistry());
}
};
} // end anonymous namespace
char ObjCARCOpt::ID = 0;
INITIALIZE_PASS_BEGIN(ObjCARCOpt,
"objc-arc", "ObjC ARC optimization", false, false)
INITIALIZE_PASS_DEPENDENCY(ObjCARCAAWrapperPass)
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<ObjCARCAAWrapperPass>();
AU.addRequired<AAResultsWrapperPass>();
// ARC optimization doesn't currently split critical edges.
AU.setPreservesCFG();
}
/// 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 = GetArgRCIdentityRoot(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;
}
}
}
// Track PHIs which are equivalent to our Arg.
SmallDenseSet<const Value*, 2> EquivalentArgs;
EquivalentArgs.insert(Arg);
// Add PHIs that are equivalent to Arg to ArgUsers.
if (const PHINode *PN = dyn_cast<PHINode>(Arg)) {
SmallVector<const Value *, 2> ArgUsers;
getEquivalentPHIs(*PN, ArgUsers);
EquivalentArgs.insert(ArgUsers.begin(), ArgUsers.end());
}
// Check for being preceded by an objc_autoreleaseReturnValue on the same
// pointer. In this case, we can delete the pair.
BasicBlock::iterator I = RetainRV->getIterator(),
Begin = RetainRV->getParent()->begin();
if (I != Begin) {
do
--I;
while (I != Begin && IsNoopInstruction(&*I));
if (GetBasicARCInstKind(&*I) == ARCInstKind::AutoreleaseRV &&
EquivalentArgs.count(GetArgRCIdentityRoot(&*I))) {
Changed = true;
++NumPeeps;
LLVM_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;
LLVM_DEBUG(dbgs() << "Transforming objc_retainAutoreleasedReturnValue => "
"objc_retain since the operand is not a return value.\n"
"Old = "
<< *RetainRV << "\n");
Function *NewDecl = EP.get(ARCRuntimeEntryPointKind::Retain);
cast<CallInst>(RetainRV)->setCalledFunction(NewDecl);
LLVM_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,
ARCInstKind &Class) {
// Check for a return of the pointer value.
const Value *Ptr = GetArgRCIdentityRoot(AutoreleaseRV);
// If the argument is ConstantPointerNull or UndefValue, its other users
// aren't actually interesting to look at.
if (isa<ConstantData>(Ptr))
return;
SmallVector<const Value *, 2> Users;
Users.push_back(Ptr);
// Add PHIs that are equivalent to Ptr to Users.
if (const PHINode *PN = dyn_cast<PHINode>(Ptr))
getEquivalentPHIs(*PN, Users);
do {
Ptr = Users.pop_back_val();
for (const User *U : Ptr->users()) {
if (isa<ReturnInst>(U) || GetBasicARCInstKind(U) == ARCInstKind::RetainRV)
return;
if (isa<BitCastInst>(U))
Users.push_back(U);
}
} while (!Users.empty());
Changed = true;
++NumPeeps;
LLVM_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);
Function *NewDecl = EP.get(ARCRuntimeEntryPointKind::Autorelease);
AutoreleaseRVCI->setCalledFunction(NewDecl);
AutoreleaseRVCI->setTailCall(false); // Never tail call objc_autorelease.
Class = ARCInstKind::Autorelease;
LLVM_DEBUG(dbgs() << "New: " << *AutoreleaseRV << "\n");
}
namespace {
Instruction *
CloneCallInstForBB(CallInst &CI, BasicBlock &BB,
const DenseMap<BasicBlock *, ColorVector> &BlockColors) {
SmallVector<OperandBundleDef, 1> OpBundles;
for (unsigned I = 0, E = CI.getNumOperandBundles(); I != E; ++I) {
auto Bundle = CI.getOperandBundleAt(I);
// Funclets will be reassociated in the future.
if (Bundle.getTagID() == LLVMContext::OB_funclet)
continue;
OpBundles.emplace_back(Bundle);
}
if (!BlockColors.empty()) {
const ColorVector &CV = BlockColors.find(&BB)->second;
assert(CV.size() == 1 && "non-unique color for block!");
Instruction *EHPad = CV.front()->getFirstNonPHI();
if (EHPad->isEHPad())
OpBundles.emplace_back("funclet", EHPad);
}
return CallInst::Create(&CI, OpBundles);
}
}
/// Visit each call, one at a time, and make simplifications without doing any
/// additional analysis.
void ObjCARCOpt::OptimizeIndividualCalls(Function &F) {
LLVM_DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeIndividualCalls ==\n");
// Reset all the flags in preparation for recomputing them.
UsedInThisFunction = 0;
DenseMap<BasicBlock *, ColorVector> BlockColors;
if (F.hasPersonalityFn() &&
isScopedEHPersonality(classifyEHPersonality(F.getPersonalityFn())))
BlockColors = colorEHFunclets(F);
// Visit all objc_* calls in F.
for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
Instruction *Inst = &*I++;
ARCInstKind Class = GetBasicARCInstKind(Inst);
LLVM_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 ARCInstKind::NoopCast:
Changed = true;
++NumNoops;
LLVM_DEBUG(dbgs() << "Erasing no-op cast: " << *Inst << "\n");
EraseInstruction(Inst);
continue;
// If the pointer-to-weak-pointer is null, it's undefined behavior.
case ARCInstKind::StoreWeak:
case ARCInstKind::LoadWeak:
case ARCInstKind::LoadWeakRetained:
case ARCInstKind::InitWeak:
case ARCInstKind::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);
Value *NewValue = UndefValue::get(CI->getType());
LLVM_DEBUG(
dbgs() << "A null pointer-to-weak-pointer is undefined behavior."
"\nOld = "
<< *CI << "\nNew = " << *NewValue << "\n");
CI->replaceAllUsesWith(NewValue);
CI->eraseFromParent();
continue;
}
break;
}
case ARCInstKind::CopyWeak:
case ARCInstKind::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);
Value *NewValue = UndefValue::get(CI->getType());
LLVM_DEBUG(
dbgs() << "A null pointer-to-weak-pointer is undefined behavior."
"\nOld = "
<< *CI << "\nNew = " << *NewValue << "\n");
CI->replaceAllUsesWith(NewValue);
CI->eraseFromParent();
continue;
}
break;
}
case ARCInstKind::RetainRV:
if (OptimizeRetainRVCall(F, Inst))
continue;
break;
case ARCInstKind::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();
Function *Decl = EP.get(ARCRuntimeEntryPointKind::Release);
CallInst *NewCall = CallInst::Create(Decl, Call->getArgOperand(0), "",
Call);
NewCall->setMetadata(MDKindCache.get(ARCMDKindID::ImpreciseRelease),
MDNode::get(C, None));
LLVM_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 = ARCInstKind::Release;
}
}
// For functions which can never be passed stack arguments, add
// a tail keyword.
if (IsAlwaysTail(Class) && !cast<CallInst>(Inst)->isNoTailCall()) {
Changed = true;
LLVM_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;
LLVM_DEBUG(dbgs() << "Removing tail keyword from function: " << *Inst
<< "\n");
cast<CallInst>(Inst)->setTailCall(false);
}
// Set nounwind as needed.
if (IsNoThrow(Class)) {
Changed = true;
LLVM_DEBUG(dbgs() << "Found no throw class. Setting nounwind on: "
<< *Inst << "\n");
cast<CallInst>(Inst)->setDoesNotThrow();
}
if (!IsNoopOnNull(Class)) {
UsedInThisFunction |= 1 << unsigned(Class);
continue;
}
const Value *Arg = GetArgRCIdentityRoot(Inst);
// ARC calls with null are no-ops. Delete them.
if (IsNullOrUndef(Arg)) {
Changed = true;
++NumNoops;
LLVM_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 << unsigned(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, and the call
// is not a release that doesn't have the clang.imprecise_release tag, 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.
if (Class == ARCInstKind::Release &&
!Inst->getMetadata(MDKindCache.get(ARCMDKindID::ImpreciseRelease)))
continue;
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 =
GetRCIdentityRoot(PN->getIncomingValue(i));
if (IsNullOrUndef(Incoming))
HasNull = true;
else if (PN->getIncomingBlock(i)->getTerminator()->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 ARCInstKind::Retain:
case ARCInstKind::RetainBlock:
// These can always be moved up.
break;
case ARCInstKind::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 ARCInstKind::Autorelease:
// These can't be moved across autorelease pool scope boundaries.
FindDependencies(AutoreleasePoolBoundary, Arg,
Inst->getParent(), Inst,
DependingInstructions, Visited, PA);
break;
case ARCInstKind::ClaimRV:
case ARCInstKind::RetainRV:
case ARCInstKind::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 =
GetRCIdentityRoot(PN->getIncomingValue(i));
if (!IsNullOrUndef(Incoming)) {
Value *Op = PN->getIncomingValue(i);
Instruction *InsertPos = &PN->getIncomingBlock(i)->back();
CallInst *Clone = cast<CallInst>(CloneCallInstForBB(
*CInst, *InsertPos->getParent(), BlockColors));
if (Op->getType() != ParamTy)
Op = new BitCastInst(Op, ParamTy, "", InsertPos);
Clone->setArgOperand(0, Op);
Clone->insertBefore(InsertPos);
LLVM_DEBUG(dbgs() << "Cloning " << *CInst
<< "\n"
"And inserting clone at "
<< *InsertPos << "\n");
Worklist.push_back(std::make_pair(Clone, Incoming));
}
}
// Erase the original call.
LLVM_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,
TopDownPtrState &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,
TopDownPtrState &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 (auto I = MyStates.top_down_ptr_begin(), E = MyStates.top_down_ptr_end();
I != E; ++I) {
TopDownPtrState &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;
bool SomeSuccHasSame = false;
bool AllSuccsHaveSame = true;
bool NotAllSeqEqualButKnownSafe = false;
for (const BasicBlock *Succ : successors(BB)) {
// If VisitBottomUp has pointer information for this successor, take
// what we know about it.
const DenseMap<const BasicBlock *, BBState>::iterator BBI =
BBStates.find(Succ);
assert(BBI != BBStates.end());
const BottomUpPtrState &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, BlotMapVector<Value *, RRInfo> &Retains,
BBState &MyStates) {
bool NestingDetected = false;
ARCInstKind Class = GetARCInstKind(Inst);
const Value *Arg = nullptr;
LLVM_DEBUG(dbgs() << " Class: " << Class << "\n");
switch (Class) {
case ARCInstKind::Release: {
Arg = GetArgRCIdentityRoot(Inst);
BottomUpPtrState &S = MyStates.getPtrBottomUpState(Arg);
NestingDetected |= S.InitBottomUp(MDKindCache, Inst);
break;
}
case ARCInstKind::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 ARCInstKind::Retain:
case ARCInstKind::RetainRV: {
Arg = GetArgRCIdentityRoot(Inst);
BottomUpPtrState &S = MyStates.getPtrBottomUpState(Arg);
if (S.MatchWithRetain()) {
// Don't do retain+release tracking for ARCInstKind::RetainRV, because
// it's better to let it remain as the first instruction after a call.
if (Class != ARCInstKind::RetainRV) {
LLVM_DEBUG(dbgs() << " Matching with: " << *Inst << "\n");
Retains[Inst] = S.GetRRInfo();
}
S.ClearSequenceProgress();
}
// A retain moving bottom up can be a use.
break;
}
case ARCInstKind::AutoreleasepoolPop:
// Conservatively, clear MyStates for all known pointers.
MyStates.clearBottomUpPointers();
return NestingDetected;
case ARCInstKind::AutoreleasepoolPush:
case ARCInstKind::None:
// These are irrelevant.
return NestingDetected;
default:
break;
}
// Consider any other possible effects of this instruction on each
// pointer being tracked.
for (auto 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.
BottomUpPtrState &S = MI->second;
if (S.HandlePotentialAlterRefCount(Inst, Ptr, PA, Class))
continue;
S.HandlePotentialUse(BB, Inst, Ptr, PA, Class);
}
return NestingDetected;
}
bool ObjCARCOpt::VisitBottomUp(BasicBlock *BB,
DenseMap<const BasicBlock *, BBState> &BBStates,
BlotMapVector<Value *, RRInfo> &Retains) {
LLVM_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);
}
}
LLVM_DEBUG(dbgs() << "Before:\n"
<< BBStates[BB] << "\n"
<< "Performing Dataflow:\n");
// Visit all the instructions, bottom-up.
for (BasicBlock::iterator I = BB->end(), E = BB->begin(); I != E; --I) {
Instruction *Inst = &*std::prev(I);
// Invoke instructions are visited as part of their successors (below).
if (isa<InvokeInst>(Inst))
continue;
LLVM_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);
}
LLVM_DEBUG(dbgs() << "\nFinal State:\n" << BBStates[BB] << "\n");
return NestingDetected;
}
bool
ObjCARCOpt::VisitInstructionTopDown(Instruction *Inst,
DenseMap<Value *, RRInfo> &Releases,
BBState &MyStates) {
bool NestingDetected = false;
ARCInstKind Class = GetARCInstKind(Inst);
const Value *Arg = nullptr;
LLVM_DEBUG(dbgs() << " Class: " << Class << "\n");
switch (Class) {
case ARCInstKind::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. We need to break since
// a retain can be a potential use.
break;
case ARCInstKind::Retain:
case ARCInstKind::RetainRV: {
Arg = GetArgRCIdentityRoot(Inst);
TopDownPtrState &S = MyStates.getPtrTopDownState(Arg);
NestingDetected |= S.InitTopDown(Class, Inst);
// A retain can be a potential use; proceed to the generic checking
// code below.
break;
}
case ARCInstKind::Release: {
Arg = GetArgRCIdentityRoot(Inst);
TopDownPtrState &S = MyStates.getPtrTopDownState(Arg);
// Try to form a tentative pair in between this release instruction and the
// top down pointers that we are tracking.
if (S.MatchWithRelease(MDKindCache, Inst)) {
// If we succeed, copy S's RRInfo into the Release -> {Retain Set
// Map}. Then we clear S.
LLVM_DEBUG(dbgs() << " Matching with: " << *Inst << "\n");
Releases[Inst] = S.GetRRInfo();
S.ClearSequenceProgress();
}
break;
}
case ARCInstKind::AutoreleasepoolPop:
// Conservatively, clear MyStates for all known pointers.
MyStates.clearTopDownPointers();
return false;
case ARCInstKind::AutoreleasepoolPush:
case ARCInstKind::None:
// These can not be uses of
return false;
default:
break;
}
// Consider any other possible effects of this instruction on each
// pointer being tracked.
for (auto 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.
TopDownPtrState &S = MI->second;
if (S.HandlePotentialAlterRefCount(Inst, Ptr, PA, Class))
continue;
S.HandlePotentialUse(Inst, Ptr, PA, Class);
}
return NestingDetected;
}
bool
ObjCARCOpt::VisitTopDown(BasicBlock *BB,
DenseMap<const BasicBlock *, BBState> &BBStates,
DenseMap<Value *, RRInfo> &Releases) {
LLVM_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);
}
}
LLVM_DEBUG(dbgs() << "Before:\n"
<< BBStates[BB] << "\n"
<< "Performing Dataflow:\n");
// Visit all the instructions, top-down.
for (Instruction &Inst : *BB) {
LLVM_DEBUG(dbgs() << " Visiting " << Inst << "\n");
NestingDetected |= VisitInstructionTopDown(&Inst, Releases, MyStates);
}
LLVM_DEBUG(dbgs() << "\nState Before Checking for CFG Hazards:\n"
<< BBStates[BB] << "\n\n");
CheckForCFGHazards(BB, BBStates, MyStates);
LLVM_DEBUG(dbgs() << "Final State:\n" << BBStates[BB] << "\n");
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();
Instruction *EntryTI = EntryBB->getTerminator();
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;
succ_iterator SE(CurrBB->getTerminator(), false);
while (SuccStack.back().second != SE) {
BasicBlock *SuccBB = *SuccStack.back().second++;
if (Visited.insert(SuccBB).second) {
SuccStack.push_back(
std::make_pair(SuccBB, succ_iterator(SuccBB->getTerminator())));
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 (BasicBlock &ExitBB : F) {
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).second) {
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,
BlotMapVector<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,
MDKindCache.get(ARCMDKindID::NoObjCARCExceptions),
BBStates);
// Use reverse-postorder on the reverse CFG for bottom-up.
bool BottomUpNestingDetected = false;
for (BasicBlock *BB : llvm::reverse(ReverseCFGPostOrder))
BottomUpNestingDetected |= VisitBottomUp(BB, BBStates, Retains);
// Use reverse-postorder for top-down.
bool TopDownNestingDetected = false;
for (BasicBlock *BB : llvm::reverse(PostOrder))
TopDownNestingDetected |= VisitTopDown(BB, BBStates, Releases);
return TopDownNestingDetected && BottomUpNestingDetected;
}
/// Move the calls in RetainsToMove and ReleasesToMove.
void ObjCARCOpt::MoveCalls(Value *Arg, RRInfo &RetainsToMove,
RRInfo &ReleasesToMove,
BlotMapVector<Value *, RRInfo> &Retains,
DenseMap<Value *, RRInfo> &Releases,
SmallVectorImpl<Instruction *> &DeadInsts,
Module *M) {
Type *ArgTy = Arg->getType();
Type *ParamTy = PointerType::getUnqual(Type::getInt8Ty(ArgTy->getContext()));
LLVM_DEBUG(dbgs() << "== ObjCARCOpt::MoveCalls ==\n");
// Insert the new retain and release calls.
for (Instruction *InsertPt : ReleasesToMove.ReverseInsertPts) {
Value *MyArg = ArgTy == ParamTy ? Arg :
new BitCastInst(Arg, ParamTy, "", InsertPt);
Function *Decl = EP.get(ARCRuntimeEntryPointKind::Retain);
CallInst *Call = CallInst::Create(Decl, MyArg, "", InsertPt);
Call->setDoesNotThrow();
Call->setTailCall();
LLVM_DEBUG(dbgs() << "Inserting new Retain: " << *Call
<< "\n"
"At insertion point: "
<< *InsertPt << "\n");
}
for (Instruction *InsertPt : RetainsToMove.ReverseInsertPts) {
Value *MyArg = ArgTy == ParamTy ? Arg :
new BitCastInst(Arg, ParamTy, "", InsertPt);
Function *Decl = EP.get(ARCRuntimeEntryPointKind::Release);
CallInst *Call = CallInst::Create(Decl, MyArg, "", InsertPt);
// Attach a clang.imprecise_release metadata tag, if appropriate.
if (MDNode *M = ReleasesToMove.ReleaseMetadata)
Call->setMetadata(MDKindCache.get(ARCMDKindID::ImpreciseRelease), M);
Call->setDoesNotThrow();
if (ReleasesToMove.IsTailCallRelease)
Call->setTailCall();
LLVM_DEBUG(dbgs() << "Inserting new Release: " << *Call
<< "\n"
"At insertion point: "
<< *InsertPt << "\n");
}
// Delete the original retain and release calls.
for (Instruction *OrigRetain : RetainsToMove.Calls) {
Retains.blot(OrigRetain);
DeadInsts.push_back(OrigRetain);
LLVM_DEBUG(dbgs() << "Deleting retain: " << *OrigRetain << "\n");
}
for (Instruction *OrigRelease : ReleasesToMove.Calls) {
Releases.erase(OrigRelease);
DeadInsts.push_back(OrigRelease);
LLVM_DEBUG(dbgs() << "Deleting release: " << *OrigRelease << "\n");
}
}
bool ObjCARCOpt::PairUpRetainsAndReleases(
DenseMap<const BasicBlock *, BBState> &BBStates,
BlotMapVector<Value *, RRInfo> &Retains,
DenseMap<Value *, RRInfo> &Releases, Module *M,
Instruction *Retain,
SmallVectorImpl<Instruction *> &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 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 (SmallVector<Instruction *, 4> NewRetains{Retain};;) {
SmallVector<Instruction *, 4> NewReleases;
for (Instruction *NewRetain : NewRetains) {
auto It = Retains.find(NewRetain);
assert(It != Retains.end());
const RRInfo &NewRetainRRI = It->second;
KnownSafeTD &= NewRetainRRI.KnownSafe;
CFGHazardAfflicted |= NewRetainRRI.CFGHazardAfflicted;
for (Instruction *NewRetainRelease : NewRetainRRI.Calls) {
auto Jt = Releases.find(NewRetainRelease);
if (Jt == Releases.end())
return false;
const RRInfo &NewRetainReleaseRRI = Jt->second;
// If the release does not have a reference to the retain as well,
// something happened which is unaccounted for. Do not do anything.
//
// This can happen if we catch an additive overflow during path count
// merging.
if (!NewRetainReleaseRRI.Calls.count(NewRetain))
return false;
if (ReleasesToMove.Calls.insert(NewRetainRelease).second) {
// If we overflow when we compute the path count, don't remove/move
// anything.
const BBState &NRRBBState = BBStates[NewRetainRelease->getParent()];
unsigned PathCount = BBState::OverflowOccurredValue;
if (NRRBBState.GetAllPathCountWithOverflow(PathCount))
return false;
assert(PathCount != BBState::OverflowOccurredValue &&
"PathCount at this point can not be "
"OverflowOccurredValue.");
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 = nullptr;
if (ReleasesToMove.IsTailCallRelease !=
NewRetainReleaseRRI.IsTailCallRelease)
ReleasesToMove.IsTailCallRelease = false;
}
// Collect the optimal insertion points.
if (!KnownSafe)
for (Instruction *RIP : NewRetainReleaseRRI.ReverseInsertPts) {
if (ReleasesToMove.ReverseInsertPts.insert(RIP).second) {
// If we overflow when we compute the path count, don't
// remove/move anything.
const BBState &RIPBBState = BBStates[RIP->getParent()];
PathCount = BBState::OverflowOccurredValue;
if (RIPBBState.GetAllPathCountWithOverflow(PathCount))
return false;
assert(PathCount != BBState::OverflowOccurredValue &&
"PathCount at this point can not be "
"OverflowOccurredValue.");
NewDelta -= PathCount;
}
}
NewReleases.push_back(NewRetainRelease);
}
}
}
NewRetains.clear();
if (NewReleases.empty()) break;
// Back the other way.
for (Instruction *NewRelease : NewReleases) {
auto It = Releases.find(NewRelease);
assert(It != Releases.end());
const RRInfo &NewReleaseRRI = It->second;
KnownSafeBU &= NewReleaseRRI.KnownSafe;
CFGHazardAfflicted |= NewReleaseRRI.CFGHazardAfflicted;
for (Instruction *NewReleaseRetain : NewReleaseRRI.Calls) {
auto Jt = Retains.find(NewReleaseRetain);
if (Jt == Retains.end())
return false;
const RRInfo &NewReleaseRetainRRI = Jt->second;
// If the retain does not have a reference to the release as well,
// something happened which is unaccounted for. Do not do anything.
//
// This can happen if we catch an additive overflow during path count
// merging.
if (!NewReleaseRetainRRI.Calls.count(NewRelease))
return false;
if (RetainsToMove.Calls.insert(NewReleaseRetain).second) {
// If we overflow when we compute the path count, don't remove/move
// anything.
const BBState &NRRBBState = BBStates[NewReleaseRetain->getParent()];
unsigned PathCount = BBState::OverflowOccurredValue;
if (NRRBBState.GetAllPathCountWithOverflow(PathCount))
return false;
assert(PathCount != BBState::OverflowOccurredValue &&
"PathCount at this point can not be "
"OverflowOccurredValue.");
OldDelta += PathCount;
OldCount += PathCount;
// Collect the optimal insertion points.
if (!KnownSafe)
for (Instruction *RIP : NewReleaseRetainRRI.ReverseInsertPts) {
if (RetainsToMove.ReverseInsertPts.insert(RIP).second) {
// If we overflow when we compute the path count, don't
// remove/move anything.
const BBState &RIPBBState = BBStates[RIP->getParent()];
PathCount = BBState::OverflowOccurredValue;
if (RIPBBState.GetAllPathCountWithOverflow(PathCount))
return false;
assert(PathCount != BBState::OverflowOccurredValue &&
"PathCount at this point can not be "
"OverflowOccurredValue.");
NewDelta += PathCount;
NewCount += PathCount;
}
}
NewRetains.push_back(NewReleaseRetain);
}
}
}
if (NewRetains.empty()) break;
}
// We can only remove pointers if we are known safe in both directions.
bool UnconditionallySafe = KnownSafeTD && KnownSafeBU;
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.empty() ||
!ReleasesToMove.ReverseInsertPts.empty();
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;
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,
BlotMapVector<Value *, RRInfo> &Retains,
DenseMap<Value *, RRInfo> &Releases, Module *M) {
LLVM_DEBUG(dbgs() << "\n== ObjCARCOpt::PerformCodePlacement ==\n");
bool AnyPairsCompletelyEliminated = false;
SmallVector<Instruction *, 8> DeadInsts;
// Visit each retain.
for (BlotMapVector<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);
LLVM_DEBUG(dbgs() << "Visiting: " << *Retain << "\n");
Value *Arg = GetArgRCIdentityRoot(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>(
GetRCIdentityRoot(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.
RRInfo RetainsToMove, ReleasesToMove;
bool PerformMoveCalls = PairUpRetainsAndReleases(
BBStates, Retains, Releases, M, Retain, 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);
}
}
// 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) {
LLVM_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++;
LLVM_DEBUG(dbgs() << "Visiting: " << *Inst << "\n");
ARCInstKind Class = GetBasicARCInstKind(Inst);
if (Class != ARCInstKind::LoadWeak &&
Class != ARCInstKind::LoadWeakRetained)
continue;
// Delete objc_loadWeak calls with no users.
if (Class == ARCInstKind::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 = std::prev(I);
BasicBlock *CurrentBB = &*Current.getBasicBlockIterator();
for (BasicBlock::iterator B = CurrentBB->begin(),
J = Current.getInstructionIterator();
J != B; --J) {
Instruction *EarlierInst = &*std::prev(J);
ARCInstKind EarlierClass = GetARCInstKind(EarlierInst);
switch (EarlierClass) {
case ARCInstKind::LoadWeak:
case ARCInstKind::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 MustAlias:
Changed = true;
// If the load has a builtin retain, insert a plain retain for it.
if (Class == ARCInstKind::LoadWeakRetained) {
Function *Decl = EP.get(ARCRuntimeEntryPointKind::Retain);
CallInst *CI = CallInst::Create(Decl, EarlierCall, "", Call);
CI->setTailCall();
}
// Zap the fully redundant load.
Call->replaceAllUsesWith(EarlierCall);
Call->eraseFromParent();
goto clobbered;
case MayAlias:
case PartialAlias:
goto clobbered;
case NoAlias:
break;
}
break;
}
case ARCInstKind::StoreWeak:
case ARCInstKind::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 MustAlias:
Changed = true;
// If the load has a builtin retain, insert a plain retain for it.
if (Class == ARCInstKind::LoadWeakRetained) {
Function *Decl = EP.get(ARCRuntimeEntryPointKind::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 MayAlias:
case PartialAlias:
goto clobbered;
case NoAlias:
break;
}
break;
}
case ARCInstKind::MoveWeak:
case ARCInstKind::CopyWeak:
// TOOD: Grab the copied value.
goto clobbered;
case ARCInstKind::AutoreleasepoolPush:
case ARCInstKind::None:
case ARCInstKind::IntrinsicUser:
case ARCInstKind::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++;
ARCInstKind Class = GetBasicARCInstKind(Inst);
if (Class != ARCInstKind::DestroyWeak)
continue;
CallInst *Call = cast<CallInst>(Inst);
Value *Arg = Call->getArgOperand(0);
if (AllocaInst *Alloca = dyn_cast<AllocaInst>(Arg)) {
for (User *U : Alloca->users()) {
const Instruction *UserInst = cast<Instruction>(U);
switch (GetBasicARCInstKind(UserInst)) {
case ARCInstKind::InitWeak:
case ARCInstKind::StoreWeak:
case ARCInstKind::DestroyWeak:
continue;
default:
goto done;
}
}
Changed = true;
for (auto UI = Alloca->user_begin(), UE = Alloca->user_end(); UI != UE;) {
CallInst *UserInst = cast<CallInst>(*UI++);
switch (GetBasicARCInstKind(UserInst)) {
case ARCInstKind::InitWeak:
case ARCInstKind::StoreWeak:
// These functions return their second argument.
UserInst->replaceAllUsesWith(UserInst->getArgOperand(1));
break;
case ARCInstKind::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;
BlotMapVector<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());
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,
SmallPtrSetImpl<Instruction *> &DepInsts,
SmallPtrSetImpl<const BasicBlock *> &Visited,
ProvenanceAnalysis &PA) {
FindDependencies(CanChangeRetainCount, Arg, Retain->getParent(), Retain,
DepInsts, Visited, PA);
if (DepInsts.size() != 1)
return false;
auto *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.
ARCInstKind Class = GetBasicARCInstKind(Call);
return Class == ARCInstKind::CallOrUser || Class == ARCInstKind::Call;
}
/// 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,
SmallPtrSetImpl<Instruction *> &DepInsts,
SmallPtrSetImpl<const BasicBlock *> &Visited,
ProvenanceAnalysis &PA) {
FindDependencies(CanChangeRetainCount, Arg,
BB, Autorelease, DepInsts, Visited, PA);
if (DepInsts.size() != 1)
return nullptr;
auto *Retain = dyn_cast_or_null<CallInst>(*DepInsts.begin());
// Check that we found a retain with the same argument.
if (!Retain || !IsRetain(GetBasicARCInstKind(Retain)) ||
GetArgRCIdentityRoot(Retain) != Arg) {
return nullptr;
}
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,
SmallPtrSetImpl<Instruction *> &DepInsts,
SmallPtrSetImpl<const BasicBlock *> &V,
ProvenanceAnalysis &PA) {
FindDependencies(NeedsPositiveRetainCount, Arg,
BB, Ret, DepInsts, V, PA);
if (DepInsts.size() != 1)
return nullptr;
auto *Autorelease = dyn_cast_or_null<CallInst>(*DepInsts.begin());
if (!Autorelease)
return nullptr;
ARCInstKind AutoreleaseClass = GetBasicARCInstKind(Autorelease);
if (!IsAutorelease(AutoreleaseClass))
return nullptr;
if (GetArgRCIdentityRoot(Autorelease) != Arg)
return nullptr;
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;
LLVM_DEBUG(dbgs() << "\n== ObjCARCOpt::OptimizeReturns ==\n");
SmallPtrSet<Instruction *, 4> DependingInstructions;
SmallPtrSet<const BasicBlock *, 4> Visited;
for (BasicBlock &BB: F) {
ReturnInst *Ret = dyn_cast<ReturnInst>(&BB.back());
if (!Ret)
continue;
LLVM_DEBUG(dbgs() << "Visiting: " << *Ret << "\n");
const Value *Arg = GetRCIdentityRoot(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, Autorelease->getParent(), 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;
LLVM_DEBUG(dbgs() << "Erasing: " << *Retain << "\nErasing: " << *Autorelease
<< "\n");
EraseInstruction(Retain);
EraseInstruction(Autorelease);
}
}
#ifndef NDEBUG
void
ObjCARCOpt::GatherStatistics(Function &F, bool AfterOptimization) {
Statistic &NumRetains =
AfterOptimization ? NumRetainsAfterOpt : NumRetainsBeforeOpt;
Statistic &NumReleases =
AfterOptimization ? NumReleasesAfterOpt : NumReleasesBeforeOpt;
for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ) {
Instruction *Inst = &*I++;
switch (GetBasicARCInstKind(Inst)) {
default:
break;
case ARCInstKind::Retain:
++NumRetains;
break;
case ARCInstKind::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;
// 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.
MDKindCache.init(&M);
// Initialize our runtime entry point cache.
EP.init(&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;
LLVM_DEBUG(dbgs() << "<<< ObjCARCOpt: Visiting Function: " << F.getName()
<< " >>>"
"\n");
PA.setAA(&getAnalysis<AAResultsWrapperPass>().getAAResults());
#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 << unsigned(ARCInstKind::LoadWeak)) |
(1 << unsigned(ARCInstKind::LoadWeakRetained)) |
(1 << unsigned(ARCInstKind::StoreWeak)) |
(1 << unsigned(ARCInstKind::InitWeak)) |
(1 << unsigned(ARCInstKind::CopyWeak)) |
(1 << unsigned(ARCInstKind::MoveWeak)) |
(1 << unsigned(ARCInstKind::DestroyWeak))))
OptimizeWeakCalls(F);
// Optimizations for retain+release pairs.
if (UsedInThisFunction & ((1 << unsigned(ARCInstKind::Retain)) |
(1 << unsigned(ARCInstKind::RetainRV)) |
(1 << unsigned(ARCInstKind::RetainBlock))))
if (UsedInThisFunction & (1 << unsigned(ARCInstKind::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 << unsigned(ARCInstKind::Autorelease)) |
(1 << unsigned(ARCInstKind::AutoreleaseRV))))
OptimizeReturns(F);
// Gather statistics after optimization.
#ifndef NDEBUG
if (AreStatisticsEnabled()) {
GatherStatistics(F, true);
}
#endif
LLVM_DEBUG(dbgs() << "\n");
return Changed;
}
void ObjCARCOpt::releaseMemory() {
PA.clear();
}
/// @}
///