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Diffstat (limited to 'clang-r353983/include/llvm/Analysis/ObjCARCAnalysisUtils.h')
| -rw-r--r-- | clang-r353983/include/llvm/Analysis/ObjCARCAnalysisUtils.h | 300 |
1 files changed, 300 insertions, 0 deletions
diff --git a/clang-r353983/include/llvm/Analysis/ObjCARCAnalysisUtils.h b/clang-r353983/include/llvm/Analysis/ObjCARCAnalysisUtils.h new file mode 100644 index 00000000..522abd75 --- /dev/null +++ b/clang-r353983/include/llvm/Analysis/ObjCARCAnalysisUtils.h @@ -0,0 +1,300 @@ +//===- 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 |