| //===- ObjCARCAnalysisUtils.h - ObjC ARC Analysis Utilities -----*- C++ -*-===// |
| // |
| // 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 common analysis utilities 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_LIB_ANALYSIS_OBJCARCANALYSISUTILS_H |
| #define LLVM_LIB_ANALYSIS_OBJCARCANALYSISUTILS_H |
| |
| #include "llvm/ADT/Optional.h" |
| #include "llvm/ADT/StringSwitch.h" |
| #include "llvm/Analysis/AliasAnalysis.h" |
| #include "llvm/Analysis/ObjCARCInstKind.h" |
| #include "llvm/Analysis/Passes.h" |
| #include "llvm/Analysis/ValueTracking.h" |
| #include "llvm/IR/CallSite.h" |
| #include "llvm/IR/Constants.h" |
| #include "llvm/IR/InstIterator.h" |
| #include "llvm/IR/LLVMContext.h" |
| #include "llvm/IR/Module.h" |
| #include "llvm/IR/ValueHandle.h" |
| #include "llvm/Pass.h" |
| |
| namespace llvm { |
| class raw_ostream; |
| } |
| |
| namespace llvm { |
| namespace objcarc { |
| |
| /// A handy option to enable/disable all ARC Optimizations. |
| extern bool EnableARCOpts; |
| |
| /// Test if the given module looks interesting to run ARC optimization |
| /// on. |
| inline bool ModuleHasARC(const Module &M) { |
| return |
| M.getNamedValue("llvm.objc.retain") || |
| M.getNamedValue("llvm.objc.release") || |
| M.getNamedValue("llvm.objc.autorelease") || |
| M.getNamedValue("llvm.objc.retainAutoreleasedReturnValue") || |
| M.getNamedValue("llvm.objc.unsafeClaimAutoreleasedReturnValue") || |
| M.getNamedValue("llvm.objc.retainBlock") || |
| M.getNamedValue("llvm.objc.autoreleaseReturnValue") || |
| M.getNamedValue("llvm.objc.autoreleasePoolPush") || |
| M.getNamedValue("llvm.objc.loadWeakRetained") || |
| M.getNamedValue("llvm.objc.loadWeak") || |
| M.getNamedValue("llvm.objc.destroyWeak") || |
| M.getNamedValue("llvm.objc.storeWeak") || |
| M.getNamedValue("llvm.objc.initWeak") || |
| M.getNamedValue("llvm.objc.moveWeak") || |
| M.getNamedValue("llvm.objc.copyWeak") || |
| M.getNamedValue("llvm.objc.retainedObject") || |
| M.getNamedValue("llvm.objc.unretainedObject") || |
| M.getNamedValue("llvm.objc.unretainedPointer") || |
| M.getNamedValue("llvm.objc.clang.arc.use"); |
| } |
| |
| /// 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. |
| inline const Value *GetUnderlyingObjCPtr(const Value *V, |
| const DataLayout &DL) { |
| for (;;) { |
| V = GetUnderlyingObject(V, DL); |
| if (!IsForwarding(GetBasicARCInstKind(V))) |
| break; |
| V = cast<CallInst>(V)->getArgOperand(0); |
| } |
| |
| return V; |
| } |
| |
| /// A wrapper for GetUnderlyingObjCPtr used for results memoization. |
| inline const Value * |
| GetUnderlyingObjCPtrCached(const Value *V, const DataLayout &DL, |
| DenseMap<const Value *, WeakTrackingVH> &Cache) { |
| if (auto InCache = Cache.lookup(V)) |
| return InCache; |
| |
| const Value *Computed = GetUnderlyingObjCPtr(V, DL); |
| Cache[V] = const_cast<Value *>(Computed); |
| return Computed; |
| } |
| |
| /// The RCIdentity root of a value \p V is a dominating value U for which |
| /// retaining or releasing U is equivalent to retaining or releasing V. In other |
| /// words, ARC operations on \p V are equivalent to ARC operations on \p U. |
| /// |
| /// We use this in the ARC optimizer to make it easier to match up ARC |
| /// operations by always mapping ARC operations to RCIdentityRoots instead of |
| /// pointers themselves. |
| /// |
| /// The two ways that we see RCIdentical values in ObjC are via: |
| /// |
| /// 1. PointerCasts |
| /// 2. Forwarding Calls that return their argument verbatim. |
| /// |
| /// Thus this function strips off pointer casts and forwarding calls. *NOTE* |
| /// This implies that two RCIdentical values must alias. |
| inline const Value *GetRCIdentityRoot(const Value *V) { |
| for (;;) { |
| V = V->stripPointerCasts(); |
| if (!IsForwarding(GetBasicARCInstKind(V))) |
| break; |
| V = cast<CallInst>(V)->getArgOperand(0); |
| } |
| return V; |
| } |
| |
| /// Helper which calls const Value *GetRCIdentityRoot(const Value *V) and just |
| /// casts away the const of the result. For documentation about what an |
| /// RCIdentityRoot (and by extension GetRCIdentityRoot is) look at that |
| /// function. |
| inline Value *GetRCIdentityRoot(Value *V) { |
| return const_cast<Value *>(GetRCIdentityRoot((const Value *)V)); |
| } |
| |
| /// Assuming the given instruction is one of the special calls such as |
| /// objc_retain or objc_release, return the RCIdentity root of the argument of |
| /// the call. |
| inline Value *GetArgRCIdentityRoot(Value *Inst) { |
| return GetRCIdentityRoot(cast<CallInst>(Inst)->getArgOperand(0)); |
| } |
| |
| inline bool IsNullOrUndef(const Value *V) { |
| return isa<ConstantPointerNull>(V) || isa<UndefValue>(V); |
| } |
| |
| inline bool IsNoopInstruction(const Instruction *I) { |
| return isa<BitCastInst>(I) || |
| (isa<GetElementPtrInst>(I) && |
| cast<GetElementPtrInst>(I)->hasAllZeroIndices()); |
| } |
| |
| /// Test whether the given value is possible a retainable object pointer. |
| 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->hasInAllocaAttr() || |
| 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; |
| } |
| |
| 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; |
| } |
| |
| /// Helper for GetARCInstKind. Determines what kind of construct CS |
| /// is. |
| inline ARCInstKind GetCallSiteClass(ImmutableCallSite CS) { |
| for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end(); |
| I != E; ++I) |
| if (IsPotentialRetainableObjPtr(*I)) |
| return CS.onlyReadsMemory() ? ARCInstKind::User : ARCInstKind::CallOrUser; |
| |
| return CS.onlyReadsMemory() ? ARCInstKind::None : ARCInstKind::Call; |
| } |
| |
| /// 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. |
| 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 = |
| GetRCIdentityRoot(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_msgSend_fixup_")) |
| return true; |
| |
| StringRef Section = GV->getSection(); |
| if (Section.find("__message_refs") != StringRef::npos || |
| Section.find("__objc_classrefs") != StringRef::npos || |
| Section.find("__objc_superrefs") != StringRef::npos || |
| Section.find("__objc_methname") != StringRef::npos || |
| Section.find("__cstring") != StringRef::npos) |
| return true; |
| } |
| } |
| |
| return false; |
| } |
| |
| enum class ARCMDKindID { |
| ImpreciseRelease, |
| CopyOnEscape, |
| NoObjCARCExceptions, |
| }; |
| |
| /// A cache of MDKinds used by various ARC optimizations. |
| class ARCMDKindCache { |
| Module *M; |
| |
| /// The Metadata Kind for clang.imprecise_release metadata. |
| llvm::Optional<unsigned> ImpreciseReleaseMDKind; |
| |
| /// The Metadata Kind for clang.arc.copy_on_escape metadata. |
| llvm::Optional<unsigned> CopyOnEscapeMDKind; |
| |
| /// The Metadata Kind for clang.arc.no_objc_arc_exceptions metadata. |
| llvm::Optional<unsigned> NoObjCARCExceptionsMDKind; |
| |
| public: |
| void init(Module *Mod) { |
| M = Mod; |
| ImpreciseReleaseMDKind = NoneType::None; |
| CopyOnEscapeMDKind = NoneType::None; |
| NoObjCARCExceptionsMDKind = NoneType::None; |
| } |
| |
| unsigned get(ARCMDKindID ID) { |
| switch (ID) { |
| case ARCMDKindID::ImpreciseRelease: |
| if (!ImpreciseReleaseMDKind) |
| ImpreciseReleaseMDKind = |
| M->getContext().getMDKindID("clang.imprecise_release"); |
| return *ImpreciseReleaseMDKind; |
| case ARCMDKindID::CopyOnEscape: |
| if (!CopyOnEscapeMDKind) |
| CopyOnEscapeMDKind = |
| M->getContext().getMDKindID("clang.arc.copy_on_escape"); |
| return *CopyOnEscapeMDKind; |
| case ARCMDKindID::NoObjCARCExceptions: |
| if (!NoObjCARCExceptionsMDKind) |
| NoObjCARCExceptionsMDKind = |
| M->getContext().getMDKindID("clang.arc.no_objc_arc_exceptions"); |
| return *NoObjCARCExceptionsMDKind; |
| } |
| llvm_unreachable("Covered switch isn't covered?!"); |
| } |
| }; |
| |
| } // end namespace objcarc |
| } // end namespace llvm |
| |
| #endif |