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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"
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/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.
52 460 : inline bool ModuleHasARC(const Module &M) {
53 : return
54 882 : M.getNamedValue("objc_retain") ||
55 830 : M.getNamedValue("objc_release") ||
56 816 : M.getNamedValue("objc_autorelease") ||
57 815 : M.getNamedValue("objc_retainAutoreleasedReturnValue") ||
58 814 : M.getNamedValue("objc_unsafeClaimAutoreleasedReturnValue") ||
59 814 : M.getNamedValue("objc_retainBlock") ||
60 813 : M.getNamedValue("objc_autoreleaseReturnValue") ||
61 810 : M.getNamedValue("objc_autoreleasePoolPush") ||
62 805 : M.getNamedValue("objc_loadWeakRetained") ||
63 802 : M.getNamedValue("objc_loadWeak") ||
64 802 : M.getNamedValue("objc_destroyWeak") ||
65 802 : M.getNamedValue("objc_storeWeak") ||
66 801 : M.getNamedValue("objc_initWeak") ||
67 800 : M.getNamedValue("objc_moveWeak") ||
68 800 : M.getNamedValue("objc_copyWeak") ||
69 800 : M.getNamedValue("objc_retainedObject") ||
70 800 : M.getNamedValue("objc_unretainedObject") ||
71 1260 : M.getNamedValue("objc_unretainedPointer") ||
72 400 : 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 4821 : inline const Value *GetUnderlyingObjCPtr(const Value *V,
79 : const DataLayout &DL) {
80 : for (;;) {
81 : V = GetUnderlyingObject(V, DL);
82 4880 : if (!IsForwarding(GetBasicARCInstKind(V)))
83 : break;
84 59 : V = cast<CallInst>(V)->getArgOperand(0);
85 : }
86 :
87 4821 : return V;
88 : }
89 :
90 : /// A wrapper for GetUnderlyingObjCPtr used for results memoization.
91 : inline const Value *
92 2800 : GetUnderlyingObjCPtrCached(const Value *V, const DataLayout &DL,
93 : DenseMap<const Value *, WeakTrackingVH> &Cache) {
94 2800 : if (auto InCache = Cache.lookup(V))
95 : return InCache;
96 :
97 538 : const Value *Computed = GetUnderlyingObjCPtr(V, DL);
98 : Cache[V] = const_cast<Value *>(Computed);
99 538 : 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 7227 : inline const Value *GetRCIdentityRoot(const Value *V) {
118 : for (;;) {
119 7701 : V = V->stripPointerCasts();
120 7701 : if (!IsForwarding(GetBasicARCInstKind(V)))
121 : break;
122 474 : V = cast<CallInst>(V)->getArgOperand(0);
123 : }
124 7227 : 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.
131 : inline Value *GetRCIdentityRoot(Value *V) {
132 2420 : 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.
138 : inline Value *GetArgRCIdentityRoot(Value *Inst) {
139 2306 : return GetRCIdentityRoot(cast<CallInst>(Inst)->getArgOperand(0));
140 : }
141 :
142 : inline bool IsNullOrUndef(const Value *V) {
143 884 : return isa<ConstantPointerNull>(V) || isa<UndefValue>(V);
144 : }
145 :
146 : inline bool IsNoopInstruction(const Instruction *I) {
147 0 : return isa<BitCastInst>(I) ||
148 0 : (isa<GetElementPtrInst>(I) &&
149 0 : cast<GetElementPtrInst>(I)->hasAllZeroIndices());
150 : }
151 :
152 : /// Test whether the given value is possible a retainable object pointer.
153 4331 : inline bool IsPotentialRetainableObjPtr(const Value *Op) {
154 : // Pointers to static or stack storage are not valid retainable object
155 : // pointers.
156 4331 : 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 1150 : if (Arg->hasByValAttr() ||
161 1150 : Arg->hasInAllocaAttr() ||
162 1725 : Arg->hasNestAttr() ||
163 575 : Arg->hasStructRetAttr())
164 0 : 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 2433 : PointerType *Ty = dyn_cast<PointerType>(Op->getType());
171 : if (!Ty)
172 146 : return false;
173 : // Conservatively assume anything else is a potential retainable object
174 : // pointer.
175 : return true;
176 : }
177 :
178 1076 : inline bool IsPotentialRetainableObjPtr(const Value *Op,
179 : AliasAnalysis &AA) {
180 : // First make the rudimentary check.
181 1076 : if (!IsPotentialRetainableObjPtr(Op))
182 : return false;
183 :
184 : // Objects in constant memory are not reference-counted.
185 949 : 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))
190 207 : if (AA.pointsToConstantMemory(LI->getPointerOperand()))
191 17 : 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.
199 1167 : inline ARCInstKind GetCallSiteClass(ImmutableCallSite CS) {
200 2200 : for (ImmutableCallSite::arg_iterator I = CS.arg_begin(), E = CS.arg_end();
201 2200 : I != E; ++I)
202 1589 : if (IsPotentialRetainableObjPtr(*I))
203 556 : return CS.onlyReadsMemory() ? ARCInstKind::User : ARCInstKind::CallOrUser;
204 :
205 611 : return CS.onlyReadsMemory() ? ARCInstKind::None : ARCInstKind::Call;
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 1309 : 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.
217 990 : if (isa<CallInst>(V) || isa<InvokeInst>(V) ||
218 757 : 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 =
224 429 : 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.
228 264 : if (GV->isConstant())
229 159 : return true;
230 260 : 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 :
236 477 : StringRef Section = GV->getSection();
237 466 : if (Section.find("__message_refs") != StringRef::npos ||
238 383 : Section.find("__objc_classrefs") != StringRef::npos ||
239 300 : Section.find("__objc_superrefs") != StringRef::npos ||
240 506 : Section.find("__objc_methname") != StringRef::npos ||
241 228 : Section.find("__cstring") != StringRef::npos)
242 137 : return true;
243 : }
244 : }
245 :
246 : return false;
247 : }
248 :
249 : enum class ARCMDKindID {
250 : ImpreciseRelease,
251 : CopyOnEscape,
252 : NoObjCARCExceptions,
253 : };
254 :
255 : /// A cache of MDKinds used by various ARC optimizations.
256 : class ARCMDKindCache {
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 31 : M = Mod;
271 : ImpreciseReleaseMDKind = NoneType::None;
272 : CopyOnEscapeMDKind = NoneType::None;
273 : NoObjCARCExceptionsMDKind = NoneType::None;
274 : }
275 :
276 1197 : unsigned get(ARCMDKindID ID) {
277 1197 : switch (ID) {
278 1000 : case ARCMDKindID::ImpreciseRelease:
279 1000 : if (!ImpreciseReleaseMDKind)
280 : ImpreciseReleaseMDKind =
281 84 : M->getContext().getMDKindID("clang.imprecise_release");
282 1000 : return *ImpreciseReleaseMDKind;
283 0 : case ARCMDKindID::CopyOnEscape:
284 0 : if (!CopyOnEscapeMDKind)
285 : CopyOnEscapeMDKind =
286 0 : M->getContext().getMDKindID("clang.arc.copy_on_escape");
287 0 : return *CopyOnEscapeMDKind;
288 197 : case ARCMDKindID::NoObjCARCExceptions:
289 197 : if (!NoObjCARCExceptionsMDKind)
290 : NoObjCARCExceptionsMDKind =
291 75 : M->getContext().getMDKindID("clang.arc.no_objc_arc_exceptions");
292 197 : return *NoObjCARCExceptionsMDKind;
293 : }
294 0 : llvm_unreachable("Covered switch isn't covered?!");
295 : }
296 : };
297 :
298 : } // end namespace objcarc
299 : } // end namespace llvm
300 :
301 : #endif
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