blob: e062b665554afaf2a66b89674b16c871a94aa9cf [file] [log] [blame]
//===- ObjCARC.h - ObjC ARC Optimization --------------*- mode: c++ -*-----===//
//
// 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 common definitions/declarations used by the ObjC ARC
/// Optimizer. ARC stands for Automatic Reference Counting and is a system for
/// managing reference counts for objects in Objective C.
///
/// 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.
///
//===----------------------------------------------------------------------===//
#ifndef LLVM_TRANSFORMS_SCALAR_OBJCARC_H
#define LLVM_TRANSFORMS_SCALAR_OBJCARC_H
#include "llvm/ADT/StringSwitch.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/Passes.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Module.h"
#include "llvm/Pass.h"
#include "llvm/Support/CallSite.h"
#include "llvm/Support/InstIterator.h"
#include "llvm/Transforms/ObjCARC.h"
#include "llvm/Transforms/Utils/Local.h"
namespace llvm {
class raw_ostream;
}
namespace llvm {
namespace objcarc {
/// \brief A handy option to enable/disable all ARC Optimizations.
extern bool EnableARCOpts;
/// \brief Test if the given module looks interesting to run ARC optimization
/// on.
static inline bool ModuleHasARC(const Module &M) {
return
M.getNamedValue("objc_retain") ||
M.getNamedValue("objc_release") ||
M.getNamedValue("objc_autorelease") ||
M.getNamedValue("objc_retainAutoreleasedReturnValue") ||
M.getNamedValue("objc_retainBlock") ||
M.getNamedValue("objc_autoreleaseReturnValue") ||
M.getNamedValue("objc_autoreleasePoolPush") ||
M.getNamedValue("objc_loadWeakRetained") ||
M.getNamedValue("objc_loadWeak") ||
M.getNamedValue("objc_destroyWeak") ||
M.getNamedValue("objc_storeWeak") ||
M.getNamedValue("objc_initWeak") ||
M.getNamedValue("objc_moveWeak") ||
M.getNamedValue("objc_copyWeak") ||
M.getNamedValue("objc_retainedObject") ||
M.getNamedValue("objc_unretainedObject") ||
M.getNamedValue("objc_unretainedPointer");
}
/// \enum InstructionClass
/// \brief A simple classification for instructions.
enum InstructionClass {
IC_Retain, ///< objc_retain
IC_RetainRV, ///< objc_retainAutoreleasedReturnValue
IC_RetainBlock, ///< objc_retainBlock
IC_Release, ///< objc_release
IC_Autorelease, ///< objc_autorelease
IC_AutoreleaseRV, ///< objc_autoreleaseReturnValue
IC_AutoreleasepoolPush, ///< objc_autoreleasePoolPush
IC_AutoreleasepoolPop, ///< objc_autoreleasePoolPop
IC_NoopCast, ///< objc_retainedObject, etc.
IC_FusedRetainAutorelease, ///< objc_retainAutorelease
IC_FusedRetainAutoreleaseRV, ///< objc_retainAutoreleaseReturnValue
IC_LoadWeakRetained, ///< objc_loadWeakRetained (primitive)
IC_StoreWeak, ///< objc_storeWeak (primitive)
IC_InitWeak, ///< objc_initWeak (derived)
IC_LoadWeak, ///< objc_loadWeak (derived)
IC_MoveWeak, ///< objc_moveWeak (derived)
IC_CopyWeak, ///< objc_copyWeak (derived)
IC_DestroyWeak, ///< objc_destroyWeak (derived)
IC_StoreStrong, ///< objc_storeStrong (derived)
IC_CallOrUser, ///< could call objc_release and/or "use" pointers
IC_Call, ///< could call objc_release
IC_User, ///< could "use" a pointer
IC_None ///< anything else
};
raw_ostream &operator<<(raw_ostream &OS, const InstructionClass Class);
/// \brief Test if the given class is objc_retain or equivalent.
static inline bool IsRetain(InstructionClass Class) {
return Class == IC_Retain ||
Class == IC_RetainRV;
}
/// \brief Test if the given class is objc_autorelease or equivalent.
static inline bool IsAutorelease(InstructionClass Class) {
return Class == IC_Autorelease ||
Class == IC_AutoreleaseRV;
}
/// \brief Test if the given class represents instructions which return their
/// argument verbatim.
static inline bool IsForwarding(InstructionClass Class) {
// objc_retainBlock technically doesn't always return its argument
// verbatim, but it doesn't matter for our purposes here.
return Class == IC_Retain ||
Class == IC_RetainRV ||
Class == IC_Autorelease ||
Class == IC_AutoreleaseRV ||
Class == IC_RetainBlock ||
Class == IC_NoopCast;
}
/// \brief Test if the given class represents instructions which do nothing if
/// passed a null pointer.
static inline bool IsNoopOnNull(InstructionClass Class) {
return Class == IC_Retain ||
Class == IC_RetainRV ||
Class == IC_Release ||
Class == IC_Autorelease ||
Class == IC_AutoreleaseRV ||
Class == IC_RetainBlock;
}
/// \brief Test if the given class represents instructions which are always safe
/// to mark with the "tail" keyword.
static inline bool IsAlwaysTail(InstructionClass Class) {
// IC_RetainBlock may be given a stack argument.
return Class == IC_Retain ||
Class == IC_RetainRV ||
Class == IC_AutoreleaseRV;
}
/// \brief Test if the given class represents instructions which are never safe
/// to mark with the "tail" keyword.
static inline bool IsNeverTail(InstructionClass Class) {
/// It is never safe to tail call objc_autorelease since by tail calling
/// objc_autorelease, we also tail call -[NSObject autorelease] which supports
/// fast autoreleasing causing our object to be potentially reclaimed from the
/// autorelease pool which violates the semantics of __autoreleasing types in
/// ARC.
return Class == IC_Autorelease;
}
/// \brief Test if the given class represents instructions which are always safe
/// to mark with the nounwind attribute.
static inline bool IsNoThrow(InstructionClass Class) {
// objc_retainBlock is not nounwind because it calls user copy constructors
// which could theoretically throw.
return Class == IC_Retain ||
Class == IC_RetainRV ||
Class == IC_Release ||
Class == IC_Autorelease ||
Class == IC_AutoreleaseRV ||
Class == IC_AutoreleasepoolPush ||
Class == IC_AutoreleasepoolPop;
}
/// Test whether the given instruction can autorelease any pointer or cause an
/// autoreleasepool pop.
static inline bool
CanInterruptRV(InstructionClass Class) {
switch (Class) {
case IC_AutoreleasepoolPop:
case IC_CallOrUser:
case IC_Call:
case IC_Autorelease:
case IC_AutoreleaseRV:
case IC_FusedRetainAutorelease:
case IC_FusedRetainAutoreleaseRV:
return true;
default:
return false;
}
}
/// \brief Determine if F is one of the special known Functions. If it isn't,
/// return IC_CallOrUser.
InstructionClass GetFunctionClass(const Function *F);
/// \brief Determine which objc runtime call instruction class V belongs to.
///
/// This is similar to GetInstructionClass except that it only detects objc
/// runtime calls. This allows it to be faster.
///
static inline InstructionClass GetBasicInstructionClass(const Value *V) {
if (const CallInst *CI = dyn_cast<CallInst>(V)) {
if (const Function *F = CI->getCalledFunction())
return GetFunctionClass(F);
// Otherwise, be conservative.
return IC_CallOrUser;
}
// Otherwise, be conservative.
return isa<InvokeInst>(V) ? IC_CallOrUser : IC_User;
}
/// \brief Determine what kind of construct V is.
InstructionClass GetInstructionClass(const Value *V);
/// \brief This is a wrapper around getUnderlyingObject which also knows how to
/// look through objc_retain and objc_autorelease calls, which we know to return
/// their argument verbatim.
static inline const Value *GetUnderlyingObjCPtr(const Value *V) {
for (;;) {
V = GetUnderlyingObject(V);
if (!IsForwarding(GetBasicInstructionClass(V)))
break;
V = cast<CallInst>(V)->getArgOperand(0);
}
return V;
}
/// \brief This is a wrapper around Value::stripPointerCasts which also knows
/// how to look through objc_retain and objc_autorelease calls, which we know to
/// return their argument verbatim.
static inline const Value *StripPointerCastsAndObjCCalls(const Value *V) {
for (;;) {
V = V->stripPointerCasts();
if (!IsForwarding(GetBasicInstructionClass(V)))
break;
V = cast<CallInst>(V)->getArgOperand(0);
}
return V;
}
/// \brief This is a wrapper around Value::stripPointerCasts which also knows
/// how to look through objc_retain and objc_autorelease calls, which we know to
/// return their argument verbatim.
static inline Value *StripPointerCastsAndObjCCalls(Value *V) {
for (;;) {
V = V->stripPointerCasts();
if (!IsForwarding(GetBasicInstructionClass(V)))
break;
V = cast<CallInst>(V)->getArgOperand(0);
}
return V;
}
/// \brief Assuming the given instruction is one of the special calls such as
/// objc_retain or objc_release, return the argument value, stripped of no-op
/// casts and forwarding calls.
static inline Value *GetObjCArg(Value *Inst) {
return StripPointerCastsAndObjCCalls(cast<CallInst>(Inst)->getArgOperand(0));
}
static inline bool isNullOrUndef(const Value *V) {
return isa<ConstantPointerNull>(V) || isa<UndefValue>(V);
}
static inline bool isNoopInstruction(const Instruction *I) {
return isa<BitCastInst>(I) ||
(isa<GetElementPtrInst>(I) &&
cast<GetElementPtrInst>(I)->hasAllZeroIndices());
}
/// \brief Erase the given instruction.
///
/// Many ObjC calls return their argument verbatim,
/// so if it's such a call and the return value has users, replace them with the
/// argument value.
///
static inline void EraseInstruction(Instruction *CI) {
Value *OldArg = cast<CallInst>(CI)->getArgOperand(0);
bool Unused = CI->use_empty();
if (!Unused) {
// Replace the return value with the argument.
assert(IsForwarding(GetBasicInstructionClass(CI)) &&
"Can't delete non-forwarding instruction with users!");
CI->replaceAllUsesWith(OldArg);
}
CI->eraseFromParent();
if (Unused)
RecursivelyDeleteTriviallyDeadInstructions(OldArg);
}
/// \brief Test whether the given value is possible a retainable object pointer.
static inline bool IsPotentialRetainableObjPtr(const Value *Op) {
// Pointers to static or stack storage are not valid retainable object
// pointers.
if (isa<Constant>(Op) || isa<AllocaInst>(Op))
return false;
// Special arguments can not be a valid retainable object pointer.
if (const Argument *Arg = dyn_cast<Argument>(Op))
if (Arg->hasByValAttr() ||
Arg->hasNestAttr() ||
Arg->hasStructRetAttr())
return false;
// Only consider values with pointer types.
//
// It seemes intuitive to exclude function pointer types as well, since
// functions are never retainable object pointers, however clang occasionally
// bitcasts retainable object pointers to function-pointer type temporarily.
PointerType *Ty = dyn_cast<PointerType>(Op->getType());
if (!Ty)
return false;
// Conservatively assume anything else is a potential retainable object
// pointer.
return true;
}
static inline bool IsPotentialRetainableObjPtr(const Value *Op,
AliasAnalysis &AA) {
// First make the rudimentary check.
if (!IsPotentialRetainableObjPtr(Op))
return false;
// Objects in constant memory are not reference-counted.
if (AA.pointsToConstantMemory(Op))
return false;
// Pointers in constant memory are not pointing to reference-counted objects.
if (const LoadInst *LI = dyn_cast<LoadInst>(Op))
if (AA.pointsToConstantMemory(LI->getPointerOperand()))
return false;
// Otherwise assume the worst.
return true;
}
/// \brief Helper for GetInstructionClass. Determines what kind of construct CS
/// is.
static inline InstructionClass GetCallSiteClass(ImmutableCallSite CS) {
for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
I != E; ++I)
if (IsPotentialRetainableObjPtr(*I))
return CS.onlyReadsMemory() ? IC_User : IC_CallOrUser;
return CS.onlyReadsMemory() ? IC_None : IC_Call;
}
/// \brief Return true if this value refers to a distinct and identifiable
/// object.
///
/// This is similar to AliasAnalysis's isIdentifiedObject, except that it uses
/// special knowledge of ObjC conventions.
static inline bool IsObjCIdentifiedObject(const Value *V) {
// Assume that call results and arguments have their own "provenance".
// Constants (including GlobalVariables) and Allocas are never
// reference-counted.
if (isa<CallInst>(V) || isa<InvokeInst>(V) ||
isa<Argument>(V) || isa<Constant>(V) ||
isa<AllocaInst>(V))
return true;
if (const LoadInst *LI = dyn_cast<LoadInst>(V)) {
const Value *Pointer =
StripPointerCastsAndObjCCalls(LI->getPointerOperand());
if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Pointer)) {
// A constant pointer can't be pointing to an object on the heap. It may
// be reference-counted, but it won't be deleted.
if (GV->isConstant())
return true;
StringRef Name = GV->getName();
// These special variables are known to hold values which are not
// reference-counted pointers.
if (Name.startswith("\01L_OBJC_SELECTOR_REFERENCES_") ||
Name.startswith("\01L_OBJC_CLASSLIST_REFERENCES_") ||
Name.startswith("\01L_OBJC_CLASSLIST_SUP_REFS_$_") ||
Name.startswith("\01L_OBJC_METH_VAR_NAME_") ||
Name.startswith("\01l_objc_msgSend_fixup_"))
return true;
}
}
return false;
}
} // end namespace objcarc
} // end namespace llvm
#endif // LLVM_TRANSFORMS_SCALAR_OBJCARC_H