LCOV - code coverage report
Current view: top level - include/llvm/Analysis - ObjCARCAnalysisUtils.h (source / functions) Hit Total Coverage
Test: llvm-toolchain.info Lines: 89 96 92.7 %
Date: 2017-09-14 15:23:50 Functions: 8 8 100.0 %
Legend: Lines: hit not hit

          Line data    Source code
       1             : //===- ObjCARCAnalysisUtils.h - ObjC ARC Analysis Utilities -----*- C++ -*-===//
       2             : //
       3             : //                     The LLVM Compiler Infrastructure
       4             : //
       5             : // This file is distributed under the University of Illinois Open Source
       6             : // License. See LICENSE.TXT for details.
       7             : //
       8             : //===----------------------------------------------------------------------===//
       9             : /// \file
      10             : /// This file defines common analysis utilities used by the ObjC ARC Optimizer.
      11             : /// ARC stands for Automatic Reference Counting and is a system for managing
      12             : /// reference counts for objects in Objective C.
      13             : ///
      14             : /// WARNING: This file knows about certain library functions. It recognizes them
      15             : /// by name, and hardwires knowledge of their semantics.
      16             : ///
      17             : /// WARNING: This file knows about how certain Objective-C library functions are
      18             : /// used. Naive LLVM IR transformations which would otherwise be
      19             : /// behavior-preserving may break these assumptions.
      20             : ///
      21             : //===----------------------------------------------------------------------===//
      22             : 
      23             : #ifndef LLVM_LIB_ANALYSIS_OBJCARCANALYSISUTILS_H
      24             : #define LLVM_LIB_ANALYSIS_OBJCARCANALYSISUTILS_H
      25             : 
      26             : #include "llvm/ADT/Optional.h"
      27             : #include "llvm/ADT/StringSwitch.h"
      28             : #include "llvm/Analysis/AliasAnalysis.h"
      29             : #include "llvm/Analysis/ObjCARCInstKind.h"
      30             : #include "llvm/Analysis/Passes.h"
      31             : #include "llvm/Analysis/ValueTracking.h"
      32             : #include "llvm/IR/CallSite.h"
      33             : #include "llvm/IR/Constants.h"
      34             : #include "llvm/IR/InstIterator.h"
      35             : #include "llvm/IR/LLVMContext.h"
      36             : #include "llvm/IR/Module.h"
      37             : #include "llvm/Pass.h"
      38             : 
      39             : namespace llvm {
      40             : class raw_ostream;
      41             : }
      42             : 
      43             : namespace llvm {
      44             : namespace objcarc {
      45             : 
      46             : /// \brief A handy option to enable/disable all ARC Optimizations.
      47             : extern bool EnableARCOpts;
      48             : 
      49             : /// \brief Test if the given module looks interesting to run ARC optimization
      50             : /// on.
      51         243 : inline bool ModuleHasARC(const Module &M) {
      52             :   return
      53         698 :     M.getNamedValue("objc_retain") ||
      54         655 :     M.getNamedValue("objc_release") ||
      55         643 :     M.getNamedValue("objc_autorelease") ||
      56         642 :     M.getNamedValue("objc_retainAutoreleasedReturnValue") ||
      57         641 :     M.getNamedValue("objc_unsafeClaimAutoreleasedReturnValue") ||
      58         641 :     M.getNamedValue("objc_retainBlock") ||
      59         640 :     M.getNamedValue("objc_autoreleaseReturnValue") ||
      60         637 :     M.getNamedValue("objc_autoreleasePoolPush") ||
      61         632 :     M.getNamedValue("objc_loadWeakRetained") ||
      62         629 :     M.getNamedValue("objc_loadWeak") ||
      63         629 :     M.getNamedValue("objc_destroyWeak") ||
      64         629 :     M.getNamedValue("objc_storeWeak") ||
      65         628 :     M.getNamedValue("objc_initWeak") ||
      66         627 :     M.getNamedValue("objc_moveWeak") ||
      67         627 :     M.getNamedValue("objc_copyWeak") ||
      68         627 :     M.getNamedValue("objc_retainedObject") ||
      69         627 :     M.getNamedValue("objc_unretainedObject") ||
      70         870 :     M.getNamedValue("objc_unretainedPointer") ||
      71         678 :     M.getNamedValue("clang.arc.use");
      72             : }
      73             : 
      74             : /// \brief This is a wrapper around getUnderlyingObject which also knows how to
      75             : /// look through objc_retain and objc_autorelease calls, which we know to return
      76             : /// their argument verbatim.
      77        5958 : inline const Value *GetUnderlyingObjCPtr(const Value *V,
      78             :                                                 const DataLayout &DL) {
      79             :   for (;;) {
      80        6041 :     V = GetUnderlyingObject(V, DL);
      81        6041 :     if (!IsForwarding(GetBasicARCInstKind(V)))
      82             :       break;
      83          83 :     V = cast<CallInst>(V)->getArgOperand(0);
      84             :   }
      85             : 
      86        5958 :   return V;
      87             : }
      88             : 
      89             : /// The RCIdentity root of a value \p V is a dominating value U for which
      90             : /// retaining or releasing U is equivalent to retaining or releasing V. In other
      91             : /// words, ARC operations on \p V are equivalent to ARC operations on \p U.
      92             : ///
      93             : /// We use this in the ARC optimizer to make it easier to match up ARC
      94             : /// operations by always mapping ARC operations to RCIdentityRoots instead of
      95             : /// pointers themselves.
      96             : ///
      97             : /// The two ways that we see RCIdentical values in ObjC are via:
      98             : ///
      99             : ///   1. PointerCasts
     100             : ///   2. Forwarding Calls that return their argument verbatim.
     101             : ///
     102             : /// Thus this function strips off pointer casts and forwarding calls. *NOTE*
     103             : /// This implies that two RCIdentical values must alias.
     104        6919 : inline const Value *GetRCIdentityRoot(const Value *V) {
     105             :   for (;;) {
     106        7394 :     V = V->stripPointerCasts();
     107        7394 :     if (!IsForwarding(GetBasicARCInstKind(V)))
     108             :       break;
     109         475 :     V = cast<CallInst>(V)->getArgOperand(0);
     110             :   }
     111        6919 :   return V;
     112             : }
     113             : 
     114             : /// Helper which calls const Value *GetRCIdentityRoot(const Value *V) and just
     115             : /// casts away the const of the result. For documentation about what an
     116             : /// RCIdentityRoot (and by extension GetRCIdentityRoot is) look at that
     117             : /// function.
     118             : inline Value *GetRCIdentityRoot(Value *V) {
     119        2424 :   return const_cast<Value *>(GetRCIdentityRoot((const Value *)V));
     120             : }
     121             : 
     122             : /// \brief Assuming the given instruction is one of the special calls such as
     123             : /// objc_retain or objc_release, return the RCIdentity root of the argument of
     124             : /// the call.
     125             : inline Value *GetArgRCIdentityRoot(Value *Inst) {
     126        6978 :   return GetRCIdentityRoot(cast<CallInst>(Inst)->getArgOperand(0));
     127             : }
     128             : 
     129             : inline bool IsNullOrUndef(const Value *V) {
     130        2426 :   return isa<ConstantPointerNull>(V) || isa<UndefValue>(V);
     131             : }
     132             : 
     133             : inline bool IsNoopInstruction(const Instruction *I) {
     134         178 :   return isa<BitCastInst>(I) ||
     135          50 :     (isa<GetElementPtrInst>(I) &&
     136           0 :      cast<GetElementPtrInst>(I)->hasAllZeroIndices());
     137             : }
     138             : 
     139             : /// \brief Test whether the given value is possible a retainable object pointer.
     140        4079 : inline bool IsPotentialRetainableObjPtr(const Value *Op) {
     141             :   // Pointers to static or stack storage are not valid retainable object
     142             :   // pointers.
     143        6443 :   if (isa<Constant>(Op) || isa<AllocaInst>(Op))
     144             :     return false;
     145             :   // Special arguments can not be a valid retainable object pointer.
     146        2826 :   if (const Argument *Arg = dyn_cast<Argument>(Op))
     147        1122 :     if (Arg->hasByValAttr() ||
     148        1122 :         Arg->hasInAllocaAttr() ||
     149        1683 :         Arg->hasNestAttr() ||
     150         561 :         Arg->hasStructRetAttr())
     151             :       return false;
     152             :   // Only consider values with pointer types.
     153             :   //
     154             :   // It seemes intuitive to exclude function pointer types as well, since
     155             :   // functions are never retainable object pointers, however clang occasionally
     156             :   // bitcasts retainable object pointers to function-pointer type temporarily.
     157        4422 :   PointerType *Ty = dyn_cast<PointerType>(Op->getType());
     158             :   if (!Ty)
     159             :     return false;
     160             :   // Conservatively assume anything else is a potential retainable object
     161             :   // pointer.
     162        2157 :   return true;
     163             : }
     164             : 
     165        1039 : inline bool IsPotentialRetainableObjPtr(const Value *Op,
     166             :                                                AliasAnalysis &AA) {
     167             :   // First make the rudimentary check.
     168        1039 :   if (!IsPotentialRetainableObjPtr(Op))
     169             :     return false;
     170             : 
     171             :   // Objects in constant memory are not reference-counted.
     172         912 :   if (AA.pointsToConstantMemory(Op))
     173             :     return false;
     174             : 
     175             :   // Pointers in constant memory are not pointing to reference-counted objects.
     176         206 :   if (const LoadInst *LI = dyn_cast<LoadInst>(Op))
     177         412 :     if (AA.pointsToConstantMemory(LI->getPointerOperand()))
     178             :       return false;
     179             : 
     180             :   // Otherwise assume the worst.
     181             :   return true;
     182             : }
     183             : 
     184             : /// \brief Helper for GetARCInstKind. Determines what kind of construct CS
     185             : /// is.
     186        1074 : inline ARCInstKind GetCallSiteClass(ImmutableCallSite CS) {
     187        2087 :   for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
     188        2087 :        I != E; ++I)
     189        1528 :     if (IsPotentialRetainableObjPtr(*I))
     190         515 :       return CS.onlyReadsMemory() ? ARCInstKind::User : ARCInstKind::CallOrUser;
     191             : 
     192         559 :   return CS.onlyReadsMemory() ? ARCInstKind::None : ARCInstKind::Call;
     193             : }
     194             : 
     195             : /// \brief Return true if this value refers to a distinct and identifiable
     196             : /// object.
     197             : ///
     198             : /// This is similar to AliasAnalysis's isIdentifiedObject, except that it uses
     199             : /// special knowledge of ObjC conventions.
     200        1383 : inline bool IsObjCIdentifiedObject(const Value *V) {
     201             :   // Assume that call results and arguments have their own "provenance".
     202             :   // Constants (including GlobalVariables) and Allocas are never
     203             :   // reference-counted.
     204        3378 :   if (isa<CallInst>(V) || isa<InvokeInst>(V) ||
     205        1761 :       isa<Argument>(V) || isa<Constant>(V) ||
     206         638 :       isa<AllocaInst>(V))
     207             :     return true;
     208             : 
     209        1027 :   if (const LoadInst *LI = dyn_cast<LoadInst>(V)) {
     210             :     const Value *Pointer =
     211         425 :       GetRCIdentityRoot(LI->getPointerOperand());
     212         265 :     if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Pointer)) {
     213             :       // A constant pointer can't be pointing to an object on the heap. It may
     214             :       // be reference-counted, but it won't be deleted.
     215         265 :       if (GV->isConstant())
     216         159 :         return true;
     217         261 :       StringRef Name = GV->getName();
     218             :       // These special variables are known to hold values which are not
     219             :       // reference-counted pointers.
     220         261 :       if (Name.startswith("\01l_objc_msgSend_fixup_"))
     221             :         return true;
     222             : 
     223         486 :       StringRef Section = GV->getSection();
     224         711 :       if (Section.find("__message_refs") != StringRef::npos ||
     225         628 :           Section.find("__objc_classrefs") != StringRef::npos ||
     226         545 :           Section.find("__objc_superrefs") != StringRef::npos ||
     227         752 :           Section.find("__objc_methname") != StringRef::npos ||
     228         367 :           Section.find("__cstring") != StringRef::npos)
     229             :         return true;
     230             :     }
     231             :   }
     232             : 
     233             :   return false;
     234             : }
     235             : 
     236             : enum class ARCMDKindID {
     237             :   ImpreciseRelease,
     238             :   CopyOnEscape,
     239             :   NoObjCARCExceptions,
     240             : };
     241             : 
     242             : /// A cache of MDKinds used by various ARC optimizations.
     243         216 : class ARCMDKindCache {
     244             :   Module *M;
     245             : 
     246             :   /// The Metadata Kind for clang.imprecise_release metadata.
     247             :   llvm::Optional<unsigned> ImpreciseReleaseMDKind;
     248             : 
     249             :   /// The Metadata Kind for clang.arc.copy_on_escape metadata.
     250             :   llvm::Optional<unsigned> CopyOnEscapeMDKind;
     251             : 
     252             :   /// The Metadata Kind for clang.arc.no_objc_arc_exceptions metadata.
     253             :   llvm::Optional<unsigned> NoObjCARCExceptionsMDKind;
     254             : 
     255             : public:
     256             :   void init(Module *Mod) {
     257          27 :     M = Mod;
     258          81 :     ImpreciseReleaseMDKind = NoneType::None;
     259          81 :     CopyOnEscapeMDKind = NoneType::None;
     260          81 :     NoObjCARCExceptionsMDKind = NoneType::None;
     261             :   }
     262             : 
     263         840 :   unsigned get(ARCMDKindID ID) {
     264         840 :     switch (ID) {
     265         649 :     case ARCMDKindID::ImpreciseRelease:
     266         649 :       if (!ImpreciseReleaseMDKind)
     267          42 :         ImpreciseReleaseMDKind =
     268          63 :             M->getContext().getMDKindID("clang.imprecise_release");
     269        1298 :       return *ImpreciseReleaseMDKind;
     270           0 :     case ARCMDKindID::CopyOnEscape:
     271           0 :       if (!CopyOnEscapeMDKind)
     272           0 :         CopyOnEscapeMDKind =
     273           0 :             M->getContext().getMDKindID("clang.arc.copy_on_escape");
     274           0 :       return *CopyOnEscapeMDKind;
     275         191 :     case ARCMDKindID::NoObjCARCExceptions:
     276         191 :       if (!NoObjCARCExceptionsMDKind)
     277          42 :         NoObjCARCExceptionsMDKind =
     278          63 :             M->getContext().getMDKindID("clang.arc.no_objc_arc_exceptions");
     279         382 :       return *NoObjCARCExceptionsMDKind;
     280             :     }
     281           0 :     llvm_unreachable("Covered switch isn't covered?!");
     282             :   }
     283             : };
     284             : 
     285             : } // end namespace objcarc
     286             : } // end namespace llvm
     287             : 
     288             : #endif

Generated by: LCOV version 1.13