LLVM  8.0.0svn
ObjCARCAnalysisUtils.h
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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"
30 #include "llvm/Analysis/Passes.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/IR/ValueHandle.h"
38 #include "llvm/Pass.h"
39 
40 namespace llvm {
41 class raw_ostream;
42 }
43 
44 namespace llvm {
45 namespace objcarc {
46 
47 /// A handy option to enable/disable all ARC Optimizations.
48 extern bool EnableARCOpts;
49 
50 /// Test if the given module looks interesting to run ARC optimization
51 /// on.
52 inline bool ModuleHasARC(const Module &M) {
53  return
54  M.getNamedValue("objc_retain") ||
55  M.getNamedValue("objc_release") ||
56  M.getNamedValue("objc_autorelease") ||
57  M.getNamedValue("objc_retainAutoreleasedReturnValue") ||
58  M.getNamedValue("objc_unsafeClaimAutoreleasedReturnValue") ||
59  M.getNamedValue("objc_retainBlock") ||
60  M.getNamedValue("objc_autoreleaseReturnValue") ||
61  M.getNamedValue("objc_autoreleasePoolPush") ||
62  M.getNamedValue("objc_loadWeakRetained") ||
63  M.getNamedValue("objc_loadWeak") ||
64  M.getNamedValue("objc_destroyWeak") ||
65  M.getNamedValue("objc_storeWeak") ||
66  M.getNamedValue("objc_initWeak") ||
67  M.getNamedValue("objc_moveWeak") ||
68  M.getNamedValue("objc_copyWeak") ||
69  M.getNamedValue("objc_retainedObject") ||
70  M.getNamedValue("objc_unretainedObject") ||
71  M.getNamedValue("objc_unretainedPointer") ||
72  M.getNamedValue("clang.arc.use");
73 }
74 
75 /// This is a wrapper around getUnderlyingObject which also knows how to
76 /// look through objc_retain and objc_autorelease calls, which we know to return
77 /// their argument verbatim.
78 inline const Value *GetUnderlyingObjCPtr(const Value *V,
79  const DataLayout &DL) {
80  for (;;) {
81  V = GetUnderlyingObject(V, DL);
83  break;
84  V = cast<CallInst>(V)->getArgOperand(0);
85  }
86 
87  return V;
88 }
89 
90 /// A wrapper for GetUnderlyingObjCPtr used for results memoization.
91 inline const Value *
94  if (auto InCache = Cache.lookup(V))
95  return InCache;
96 
97  const Value *Computed = GetUnderlyingObjCPtr(V, DL);
98  Cache[V] = const_cast<Value *>(Computed);
99  return Computed;
100 }
101 
102 /// The RCIdentity root of a value \p V is a dominating value U for which
103 /// retaining or releasing U is equivalent to retaining or releasing V. In other
104 /// words, ARC operations on \p V are equivalent to ARC operations on \p U.
105 ///
106 /// We use this in the ARC optimizer to make it easier to match up ARC
107 /// operations by always mapping ARC operations to RCIdentityRoots instead of
108 /// pointers themselves.
109 ///
110 /// The two ways that we see RCIdentical values in ObjC are via:
111 ///
112 /// 1. PointerCasts
113 /// 2. Forwarding Calls that return their argument verbatim.
114 ///
115 /// Thus this function strips off pointer casts and forwarding calls. *NOTE*
116 /// This implies that two RCIdentical values must alias.
117 inline const Value *GetRCIdentityRoot(const Value *V) {
118  for (;;) {
119  V = V->stripPointerCasts();
121  break;
122  V = cast<CallInst>(V)->getArgOperand(0);
123  }
124  return V;
125 }
126 
127 /// Helper which calls const Value *GetRCIdentityRoot(const Value *V) and just
128 /// casts away the const of the result. For documentation about what an
129 /// RCIdentityRoot (and by extension GetRCIdentityRoot is) look at that
130 /// function.
132  return const_cast<Value *>(GetRCIdentityRoot((const Value *)V));
133 }
134 
135 /// Assuming the given instruction is one of the special calls such as
136 /// objc_retain or objc_release, return the RCIdentity root of the argument of
137 /// the call.
139  return GetRCIdentityRoot(cast<CallInst>(Inst)->getArgOperand(0));
140 }
141 
142 inline bool IsNullOrUndef(const Value *V) {
143  return isa<ConstantPointerNull>(V) || isa<UndefValue>(V);
144 }
145 
146 inline bool IsNoopInstruction(const Instruction *I) {
147  return isa<BitCastInst>(I) ||
148  (isa<GetElementPtrInst>(I) &&
149  cast<GetElementPtrInst>(I)->hasAllZeroIndices());
150 }
151 
152 /// Test whether the given value is possible a retainable object pointer.
153 inline bool IsPotentialRetainableObjPtr(const Value *Op) {
154  // Pointers to static or stack storage are not valid retainable object
155  // pointers.
156  if (isa<Constant>(Op) || isa<AllocaInst>(Op))
157  return false;
158  // Special arguments can not be a valid retainable object pointer.
159  if (const Argument *Arg = dyn_cast<Argument>(Op))
160  if (Arg->hasByValAttr() ||
161  Arg->hasInAllocaAttr() ||
162  Arg->hasNestAttr() ||
163  Arg->hasStructRetAttr())
164  return false;
165  // Only consider values with pointer types.
166  //
167  // It seemes intuitive to exclude function pointer types as well, since
168  // functions are never retainable object pointers, however clang occasionally
169  // bitcasts retainable object pointers to function-pointer type temporarily.
170  PointerType *Ty = dyn_cast<PointerType>(Op->getType());
171  if (!Ty)
172  return false;
173  // Conservatively assume anything else is a potential retainable object
174  // pointer.
175  return true;
176 }
177 
179  AliasAnalysis &AA) {
180  // First make the rudimentary check.
182  return false;
183 
184  // Objects in constant memory are not reference-counted.
185  if (AA.pointsToConstantMemory(Op))
186  return false;
187 
188  // Pointers in constant memory are not pointing to reference-counted objects.
189  if (const LoadInst *LI = dyn_cast<LoadInst>(Op))
190  if (AA.pointsToConstantMemory(LI->getPointerOperand()))
191  return false;
192 
193  // Otherwise assume the worst.
194  return true;
195 }
196 
197 /// Helper for GetARCInstKind. Determines what kind of construct CS
198 /// is.
201  I != E; ++I)
204 
206 }
207 
208 /// Return true if this value refers to a distinct and identifiable
209 /// object.
210 ///
211 /// This is similar to AliasAnalysis's isIdentifiedObject, except that it uses
212 /// special knowledge of ObjC conventions.
213 inline bool IsObjCIdentifiedObject(const Value *V) {
214  // Assume that call results and arguments have their own "provenance".
215  // Constants (including GlobalVariables) and Allocas are never
216  // reference-counted.
217  if (isa<CallInst>(V) || isa<InvokeInst>(V) ||
218  isa<Argument>(V) || isa<Constant>(V) ||
219  isa<AllocaInst>(V))
220  return true;
221 
222  if (const LoadInst *LI = dyn_cast<LoadInst>(V)) {
223  const Value *Pointer =
224  GetRCIdentityRoot(LI->getPointerOperand());
225  if (const GlobalVariable *GV = dyn_cast<GlobalVariable>(Pointer)) {
226  // A constant pointer can't be pointing to an object on the heap. It may
227  // be reference-counted, but it won't be deleted.
228  if (GV->isConstant())
229  return true;
230  StringRef Name = GV->getName();
231  // These special variables are known to hold values which are not
232  // reference-counted pointers.
233  if (Name.startswith("\01l_objc_msgSend_fixup_"))
234  return true;
235 
236  StringRef Section = GV->getSection();
237  if (Section.find("__message_refs") != StringRef::npos ||
238  Section.find("__objc_classrefs") != StringRef::npos ||
239  Section.find("__objc_superrefs") != StringRef::npos ||
240  Section.find("__objc_methname") != StringRef::npos ||
241  Section.find("__cstring") != StringRef::npos)
242  return true;
243  }
244  }
245 
246  return false;
247 }
248 
249 enum class ARCMDKindID {
251  CopyOnEscape,
253 };
254 
255 /// A cache of MDKinds used by various ARC optimizations.
257  Module *M;
258 
259  /// The Metadata Kind for clang.imprecise_release metadata.
260  llvm::Optional<unsigned> ImpreciseReleaseMDKind;
261 
262  /// The Metadata Kind for clang.arc.copy_on_escape metadata.
263  llvm::Optional<unsigned> CopyOnEscapeMDKind;
264 
265  /// The Metadata Kind for clang.arc.no_objc_arc_exceptions metadata.
266  llvm::Optional<unsigned> NoObjCARCExceptionsMDKind;
267 
268 public:
269  void init(Module *Mod) {
270  M = Mod;
271  ImpreciseReleaseMDKind = NoneType::None;
272  CopyOnEscapeMDKind = NoneType::None;
273  NoObjCARCExceptionsMDKind = NoneType::None;
274  }
275 
276  unsigned get(ARCMDKindID ID) {
277  switch (ID) {
279  if (!ImpreciseReleaseMDKind)
280  ImpreciseReleaseMDKind =
281  M->getContext().getMDKindID("clang.imprecise_release");
282  return *ImpreciseReleaseMDKind;
284  if (!CopyOnEscapeMDKind)
285  CopyOnEscapeMDKind =
286  M->getContext().getMDKindID("clang.arc.copy_on_escape");
287  return *CopyOnEscapeMDKind;
289  if (!NoObjCARCExceptionsMDKind)
290  NoObjCARCExceptionsMDKind =
291  M->getContext().getMDKindID("clang.arc.no_objc_arc_exceptions");
292  return *NoObjCARCExceptionsMDKind;
293  }
294  llvm_unreachable("Covered switch isn't covered?!");
295  }
296 };
297 
298 } // end namespace objcarc
299 } // end namespace llvm
300 
301 #endif
A parsed version of the target data layout string in and methods for querying it. ...
Definition: DataLayout.h:111
This class represents an incoming formal argument to a Function.
Definition: Argument.h:30
This class represents lattice values for constants.
Definition: AllocatorList.h:24
could call objc_release and/or "use" pointers
A Module instance is used to store all the information related to an LLVM module. ...
Definition: Module.h:65
Value * GetArgRCIdentityRoot(Value *Inst)
Assuming the given instruction is one of the special calls such as objc_retain or objc_release...
could call objc_release
An instruction for reading from memory.
Definition: Instructions.h:168
bool IsForwarding(ARCInstKind Class)
Test if the given class represents instructions which return their argument verbatim.
bool IsObjCIdentifiedObject(const Value *V)
Return true if this value refers to a distinct and identifiable object.
bool onlyReadsMemory() const
Determine if the call does not access or only reads memory.
Definition: CallSite.h:454
unsigned getMDKindID(StringRef Name) const
getMDKindID - Return a unique non-zero ID for the specified metadata kind.
amdgpu Simplify well known AMD library false Value Value const Twine & Name
LLVMContext & getContext() const
Get the global data context.
Definition: Module.h:244
A Use represents the edge between a Value definition and its users.
Definition: Use.h:56
IterTy arg_end() const
Definition: CallSite.h:575
bool IsNullOrUndef(const Value *V)
LLVM_NODISCARD LLVM_ATTRIBUTE_ALWAYS_INLINE bool startswith(StringRef Prefix) const
Check if this string starts with the given Prefix.
Definition: StringRef.h:267
Type * getType() const
All values are typed, get the type of this value.
Definition: Value.h:245
bool IsPotentialRetainableObjPtr(const Value *Op)
Test whether the given value is possible a retainable object pointer.
bool EnableARCOpts
A handy option to enable/disable all ARC Optimizations.
GlobalValue * getNamedValue(StringRef Name) const
Return the global value in the module with the specified name, of arbitrary type. ...
Definition: Module.cpp:114
bool ModuleHasARC(const Module &M)
Test if the given module looks interesting to run ARC optimization on.
Class to represent pointers.
Definition: DerivedTypes.h:467
bool pointsToConstantMemory(const MemoryLocation &Loc, bool OrLocal=false)
Checks whether the given location points to constant memory, or if OrLocal is true whether it points ...
static GCRegistry::Add< CoreCLRGC > E("coreclr", "CoreCLR-compatible GC")
This file contains the declarations for the subclasses of Constant, which represent the different fla...
A cache of MDKinds used by various ARC optimizations.
const Value * stripPointerCasts() const
Strip off pointer casts, all-zero GEPs, and aliases.
Definition: Value.cpp:530
anything that is inert from an ARC perspective.
Value * GetUnderlyingObject(Value *V, const DataLayout &DL, unsigned MaxLookup=6)
This method strips off any GEP address adjustments and pointer casts from the specified value...
#define llvm_unreachable(msg)
Marks that the current location is not supposed to be reachable.
ARCInstKind GetBasicARCInstKind(const Value *V)
Determine which objc runtime call instruction class V belongs to.
IterTy arg_begin() const
Definition: CallSite.h:571
ARCInstKind
Equivalence classes of instructions in the ARC Model.
Module.h This file contains the declarations for the Module class.
const Value * GetUnderlyingObjCPtrCached(const Value *V, const DataLayout &DL, DenseMap< const Value *, WeakTrackingVH > &Cache)
A wrapper for GetUnderlyingObjCPtr used for results memoization.
amdgpu Simplify well known AMD library false Value Value * Arg
could "use" a pointer
static const size_t npos
Definition: StringRef.h:51
Establish a view to a call site for examination.
Definition: CallSite.h:711
#define I(x, y, z)
Definition: MD5.cpp:58
LLVM_NODISCARD std::enable_if<!is_simple_type< Y >::value, typename cast_retty< X, const Y >::ret_type >::type dyn_cast(const Y &Val)
Definition: Casting.h:323
ARCInstKind GetCallSiteClass(ImmutableCallSite CS)
Helper for GetARCInstKind.
const Value * GetUnderlyingObjCPtr(const Value *V, const DataLayout &DL)
This is a wrapper around getUnderlyingObject which also knows how to look through objc_retain and obj...
ValueT lookup(const_arg_type_t< KeyT > Val) const
lookup - Return the entry for the specified key, or a default constructed value if no such entry exis...
Definition: DenseMap.h:211
LLVM Value Representation.
Definition: Value.h:73
const Value * GetRCIdentityRoot(const Value *V)
The RCIdentity root of a value V is a dominating value U for which retaining or releasing U is equiva...
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:49
LLVM_NODISCARD LLVM_ATTRIBUTE_ALWAYS_INLINE size_t find(char C, size_t From=0) const
Search for the first character C in the string.
Definition: StringRef.h:298
bool IsNoopInstruction(const Instruction *I)