Bug Summary

File:build/llvm-toolchain-snapshot-16~++20221003111214+1fa2019828ca/llvm/lib/Transforms/ObjCARC/ObjCARCContract.cpp
Warning:line 713, column 3
Address of stack memory associated with local variable 'BRV' is still referred to by the stack variable 'OCAC' upon returning to the caller. This will be a dangling reference

Annotated Source Code

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clang -cc1 -cc1 -triple x86_64-pc-linux-gnu -analyze -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name ObjCARCContract.cpp -analyzer-checker=core -analyzer-checker=apiModeling -analyzer-checker=unix -analyzer-checker=deadcode -analyzer-checker=cplusplus -analyzer-checker=security.insecureAPI.UncheckedReturn -analyzer-checker=security.insecureAPI.getpw -analyzer-checker=security.insecureAPI.gets -analyzer-checker=security.insecureAPI.mktemp -analyzer-checker=security.insecureAPI.mkstemp -analyzer-checker=security.insecureAPI.vfork -analyzer-checker=nullability.NullPassedToNonnull -analyzer-checker=nullability.NullReturnedFromNonnull -analyzer-output plist -w -setup-static-analyzer -analyzer-config-compatibility-mode=true -mrelocation-model pic -pic-level 2 -mframe-pointer=none -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -funwind-tables=2 -target-cpu x86-64 -tune-cpu generic -debugger-tuning=gdb -ffunction-sections -fdata-sections -fcoverage-compilation-dir=/build/llvm-toolchain-snapshot-16~++20221003111214+1fa2019828ca/build-llvm -resource-dir /usr/lib/llvm-16/lib/clang/16.0.0 -D _DEBUG -D _GNU_SOURCE -D __STDC_CONSTANT_MACROS -D __STDC_FORMAT_MACROS -D __STDC_LIMIT_MACROS -I lib/Transforms/ObjCARC -I /build/llvm-toolchain-snapshot-16~++20221003111214+1fa2019828ca/llvm/lib/Transforms/ObjCARC -I include -I /build/llvm-toolchain-snapshot-16~++20221003111214+1fa2019828ca/llvm/include -D _FORTIFY_SOURCE=2 -D NDEBUG -U NDEBUG -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/x86_64-linux-gnu/c++/10 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../include/c++/10/backward -internal-isystem /usr/lib/llvm-16/lib/clang/16.0.0/include -internal-isystem /usr/local/include -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/10/../../../../x86_64-linux-gnu/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -fmacro-prefix-map=/build/llvm-toolchain-snapshot-16~++20221003111214+1fa2019828ca/build-llvm=build-llvm -fmacro-prefix-map=/build/llvm-toolchain-snapshot-16~++20221003111214+1fa2019828ca/= -fcoverage-prefix-map=/build/llvm-toolchain-snapshot-16~++20221003111214+1fa2019828ca/build-llvm=build-llvm -fcoverage-prefix-map=/build/llvm-toolchain-snapshot-16~++20221003111214+1fa2019828ca/= -O3 -Wno-unused-command-line-argument -Wno-unused-parameter -Wwrite-strings -Wno-missing-field-initializers -Wno-long-long -Wno-maybe-uninitialized -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wno-comment -Wno-misleading-indentation -std=c++17 -fdeprecated-macro -fdebug-compilation-dir=/build/llvm-toolchain-snapshot-16~++20221003111214+1fa2019828ca/build-llvm -fdebug-prefix-map=/build/llvm-toolchain-snapshot-16~++20221003111214+1fa2019828ca/build-llvm=build-llvm -fdebug-prefix-map=/build/llvm-toolchain-snapshot-16~++20221003111214+1fa2019828ca/= -ferror-limit 19 -fvisibility-inlines-hidden -stack-protector 2 -fgnuc-version=4.2.1 -fcolor-diagnostics -vectorize-loops -vectorize-slp -analyzer-output=html -analyzer-config stable-report-filename=true -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /tmp/scan-build-2022-10-03-140002-15933-1 -x c++ /build/llvm-toolchain-snapshot-16~++20221003111214+1fa2019828ca/llvm/lib/Transforms/ObjCARC/ObjCARCContract.cpp
1//===- ObjCARCContract.cpp - ObjC ARC Optimization ------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8/// \file
9/// This file defines late ObjC ARC optimizations. ARC stands for Automatic
10/// Reference Counting and is a system for managing reference counts for objects
11/// in Objective C.
12///
13/// This specific file mainly deals with ``contracting'' multiple lower level
14/// operations into singular higher level operations through pattern matching.
15///
16/// WARNING: This file knows about certain library functions. It recognizes them
17/// by name, and hardwires knowledge of their semantics.
18///
19/// WARNING: This file knows about how certain Objective-C library functions are
20/// used. Naive LLVM IR transformations which would otherwise be
21/// behavior-preserving may break these assumptions.
22///
23//===----------------------------------------------------------------------===//
24
25// TODO: ObjCARCContract could insert PHI nodes when uses aren't
26// dominated by single calls.
27
28#include "ARCRuntimeEntryPoints.h"
29#include "DependencyAnalysis.h"
30#include "ObjCARC.h"
31#include "ProvenanceAnalysis.h"
32#include "llvm/ADT/Statistic.h"
33#include "llvm/Analysis/AliasAnalysis.h"
34#include "llvm/Analysis/EHPersonalities.h"
35#include "llvm/Analysis/ObjCARCUtil.h"
36#include "llvm/IR/Dominators.h"
37#include "llvm/IR/InlineAsm.h"
38#include "llvm/IR/InstIterator.h"
39#include "llvm/IR/Operator.h"
40#include "llvm/IR/PassManager.h"
41#include "llvm/InitializePasses.h"
42#include "llvm/Support/CommandLine.h"
43#include "llvm/Support/Debug.h"
44#include "llvm/Support/raw_ostream.h"
45#include "llvm/Transforms/ObjCARC.h"
46
47using namespace llvm;
48using namespace llvm::objcarc;
49
50#define DEBUG_TYPE"objc-arc-contract" "objc-arc-contract"
51
52STATISTIC(NumPeeps, "Number of calls peephole-optimized")static llvm::Statistic NumPeeps = {"objc-arc-contract", "NumPeeps"
, "Number of calls peephole-optimized"}
;
53STATISTIC(NumStoreStrongs, "Number objc_storeStrong calls formed")static llvm::Statistic NumStoreStrongs = {"objc-arc-contract"
, "NumStoreStrongs", "Number objc_storeStrong calls formed"}
;
54
55//===----------------------------------------------------------------------===//
56// Declarations
57//===----------------------------------------------------------------------===//
58
59namespace {
60/// Late ARC optimizations
61///
62/// These change the IR in a way that makes it difficult to be analyzed by
63/// ObjCARCOpt, so it's run late.
64
65class ObjCARCContract {
66 bool Changed;
67 bool CFGChanged;
68 AAResults *AA;
69 DominatorTree *DT;
70 ProvenanceAnalysis PA;
71 ARCRuntimeEntryPoints EP;
72 BundledRetainClaimRVs *BundledInsts = nullptr;
73
74 /// The inline asm string to insert between calls and RetainRV calls to make
75 /// the optimization work on targets which need it.
76 const MDString *RVInstMarker;
77
78 /// The set of inserted objc_storeStrong calls. If at the end of walking the
79 /// function we have found no alloca instructions, these calls can be marked
80 /// "tail".
81 SmallPtrSet<CallInst *, 8> StoreStrongCalls;
82
83 /// Returns true if we eliminated Inst.
84 bool tryToPeepholeInstruction(
85 Function &F, Instruction *Inst, inst_iterator &Iter,
86 bool &TailOkForStoreStrong,
87 const DenseMap<BasicBlock *, ColorVector> &BlockColors);
88
89 bool optimizeRetainCall(Function &F, Instruction *Retain);
90
91 bool contractAutorelease(Function &F, Instruction *Autorelease,
92 ARCInstKind Class);
93
94 void tryToContractReleaseIntoStoreStrong(
95 Instruction *Release, inst_iterator &Iter,
96 const DenseMap<BasicBlock *, ColorVector> &BlockColors);
97
98public:
99 bool init(Module &M);
100 bool run(Function &F, AAResults *AA, DominatorTree *DT);
101 bool hasCFGChanged() const { return CFGChanged; }
102};
103
104class ObjCARCContractLegacyPass : public FunctionPass {
105public:
106 void getAnalysisUsage(AnalysisUsage &AU) const override;
107 bool runOnFunction(Function &F) override;
108
109 static char ID;
110 ObjCARCContractLegacyPass() : FunctionPass(ID) {
111 initializeObjCARCContractLegacyPassPass(*PassRegistry::getPassRegistry());
112 }
113};
114}
115
116//===----------------------------------------------------------------------===//
117// Implementation
118//===----------------------------------------------------------------------===//
119
120/// Turn objc_retain into objc_retainAutoreleasedReturnValue if the operand is a
121/// return value. We do this late so we do not disrupt the dataflow analysis in
122/// ObjCARCOpt.
123bool ObjCARCContract::optimizeRetainCall(Function &F, Instruction *Retain) {
124 const auto *Call = dyn_cast<CallBase>(GetArgRCIdentityRoot(Retain));
125 if (!Call)
126 return false;
127 if (Call->getParent() != Retain->getParent())
128 return false;
129
130 // Check that the call is next to the retain.
131 BasicBlock::const_iterator I = ++Call->getIterator();
132 while (IsNoopInstruction(&*I))
133 ++I;
134 if (&*I != Retain)
135 return false;
136
137 // Turn it to an objc_retainAutoreleasedReturnValue.
138 Changed = true;
139 ++NumPeeps;
140
141 LLVM_DEBUG(do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { dbgs() << "Transforming objc_retain => "
"objc_retainAutoreleasedReturnValue since the operand is a "
"return value.\nOld: " << *Retain << "\n"; } } while
(false)
142 dbgs() << "Transforming objc_retain => "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { dbgs() << "Transforming objc_retain => "
"objc_retainAutoreleasedReturnValue since the operand is a "
"return value.\nOld: " << *Retain << "\n"; } } while
(false)
143 "objc_retainAutoreleasedReturnValue since the operand is a "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { dbgs() << "Transforming objc_retain => "
"objc_retainAutoreleasedReturnValue since the operand is a "
"return value.\nOld: " << *Retain << "\n"; } } while
(false)
144 "return value.\nOld: "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { dbgs() << "Transforming objc_retain => "
"objc_retainAutoreleasedReturnValue since the operand is a "
"return value.\nOld: " << *Retain << "\n"; } } while
(false)
145 << *Retain << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { dbgs() << "Transforming objc_retain => "
"objc_retainAutoreleasedReturnValue since the operand is a "
"return value.\nOld: " << *Retain << "\n"; } } while
(false)
;
146
147 // We do not have to worry about tail calls/does not throw since
148 // retain/retainRV have the same properties.
149 Function *Decl = EP.get(ARCRuntimeEntryPointKind::RetainRV);
150 cast<CallInst>(Retain)->setCalledFunction(Decl);
151
152 LLVM_DEBUG(dbgs() << "New: " << *Retain << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { dbgs() << "New: " << *Retain
<< "\n"; } } while (false)
;
153 return true;
154}
155
156/// Merge an autorelease with a retain into a fused call.
157bool ObjCARCContract::contractAutorelease(Function &F, Instruction *Autorelease,
158 ARCInstKind Class) {
159 const Value *Arg = GetArgRCIdentityRoot(Autorelease);
160
161 // Check that there are no instructions between the retain and the autorelease
162 // (such as an autorelease_pop) which may change the count.
163 DependenceKind DK = Class == ARCInstKind::AutoreleaseRV
164 ? RetainAutoreleaseRVDep
165 : RetainAutoreleaseDep;
166 auto *Retain = dyn_cast_or_null<CallInst>(
167 findSingleDependency(DK, Arg, Autorelease->getParent(), Autorelease, PA));
168
169 if (!Retain || GetBasicARCInstKind(Retain) != ARCInstKind::Retain ||
170 GetArgRCIdentityRoot(Retain) != Arg)
171 return false;
172
173 Changed = true;
174 ++NumPeeps;
175
176 LLVM_DEBUG(dbgs() << " Fusing retain/autorelease!\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { dbgs() << " Fusing retain/autorelease!\n"
" Autorelease:" << *Autorelease << "\n" " Retain: "
<< *Retain << "\n"; } } while (false)
177 " Autorelease:"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { dbgs() << " Fusing retain/autorelease!\n"
" Autorelease:" << *Autorelease << "\n" " Retain: "
<< *Retain << "\n"; } } while (false)
178 << *Autoreleasedo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { dbgs() << " Fusing retain/autorelease!\n"
" Autorelease:" << *Autorelease << "\n" " Retain: "
<< *Retain << "\n"; } } while (false)
179 << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { dbgs() << " Fusing retain/autorelease!\n"
" Autorelease:" << *Autorelease << "\n" " Retain: "
<< *Retain << "\n"; } } while (false)
180 " Retain: "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { dbgs() << " Fusing retain/autorelease!\n"
" Autorelease:" << *Autorelease << "\n" " Retain: "
<< *Retain << "\n"; } } while (false)
181 << *Retain << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { dbgs() << " Fusing retain/autorelease!\n"
" Autorelease:" << *Autorelease << "\n" " Retain: "
<< *Retain << "\n"; } } while (false)
;
182
183 Function *Decl = EP.get(Class == ARCInstKind::AutoreleaseRV
184 ? ARCRuntimeEntryPointKind::RetainAutoreleaseRV
185 : ARCRuntimeEntryPointKind::RetainAutorelease);
186 Retain->setCalledFunction(Decl);
187
188 LLVM_DEBUG(dbgs() << " New RetainAutorelease: " << *Retain << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { dbgs() << " New RetainAutorelease: "
<< *Retain << "\n"; } } while (false)
;
189
190 EraseInstruction(Autorelease);
191 return true;
192}
193
194static StoreInst *findSafeStoreForStoreStrongContraction(LoadInst *Load,
195 Instruction *Release,
196 ProvenanceAnalysis &PA,
197 AAResults *AA) {
198 StoreInst *Store = nullptr;
199 bool SawRelease = false;
200
201 // Get the location associated with Load.
202 MemoryLocation Loc = MemoryLocation::get(Load);
203 auto *LocPtr = Loc.Ptr->stripPointerCasts();
204
205 // Walk down to find the store and the release, which may be in either order.
206 for (auto I = std::next(BasicBlock::iterator(Load)),
207 E = Load->getParent()->end();
208 I != E; ++I) {
209 // If we found the store we were looking for and saw the release,
210 // break. There is no more work to be done.
211 if (Store && SawRelease)
212 break;
213
214 // Now we know that we have not seen either the store or the release. If I
215 // is the release, mark that we saw the release and continue.
216 Instruction *Inst = &*I;
217 if (Inst == Release) {
218 SawRelease = true;
219 continue;
220 }
221
222 // Otherwise, we check if Inst is a "good" store. Grab the instruction class
223 // of Inst.
224 ARCInstKind Class = GetBasicARCInstKind(Inst);
225
226 // If we have seen the store, but not the release...
227 if (Store) {
228 // We need to make sure that it is safe to move the release from its
229 // current position to the store. This implies proving that any
230 // instruction in between Store and the Release conservatively can not use
231 // the RCIdentityRoot of Release. If we can prove we can ignore Inst, so
232 // continue...
233 if (!CanUse(Inst, Load, PA, Class)) {
234 continue;
235 }
236
237 // Otherwise, be conservative and return nullptr.
238 return nullptr;
239 }
240
241 // Ok, now we know we have not seen a store yet.
242
243 // If Inst is a retain, we don't care about it as it doesn't prevent moving
244 // the load to the store.
245 //
246 // TODO: This is one area where the optimization could be made more
247 // aggressive.
248 if (IsRetain(Class))
249 continue;
250
251 // See if Inst can write to our load location, if it can not, just ignore
252 // the instruction.
253 if (!isModSet(AA->getModRefInfo(Inst, Loc)))
254 continue;
255
256 Store = dyn_cast<StoreInst>(Inst);
257
258 // If Inst can, then check if Inst is a simple store. If Inst is not a
259 // store or a store that is not simple, then we have some we do not
260 // understand writing to this memory implying we can not move the load
261 // over the write to any subsequent store that we may find.
262 if (!Store || !Store->isSimple())
263 return nullptr;
264
265 // Then make sure that the pointer we are storing to is Ptr. If so, we
266 // found our Store!
267 if (Store->getPointerOperand()->stripPointerCasts() == LocPtr)
268 continue;
269
270 // Otherwise, we have an unknown store to some other ptr that clobbers
271 // Loc.Ptr. Bail!
272 return nullptr;
273 }
274
275 // If we did not find the store or did not see the release, fail.
276 if (!Store || !SawRelease)
277 return nullptr;
278
279 // We succeeded!
280 return Store;
281}
282
283static Instruction *
284findRetainForStoreStrongContraction(Value *New, StoreInst *Store,
285 Instruction *Release,
286 ProvenanceAnalysis &PA) {
287 // Walk up from the Store to find the retain.
288 BasicBlock::iterator I = Store->getIterator();
289 BasicBlock::iterator Begin = Store->getParent()->begin();
290 while (I != Begin && GetBasicARCInstKind(&*I) != ARCInstKind::Retain) {
291 Instruction *Inst = &*I;
292
293 // It is only safe to move the retain to the store if we can prove
294 // conservatively that nothing besides the release can decrement reference
295 // counts in between the retain and the store.
296 if (CanDecrementRefCount(Inst, New, PA) && Inst != Release)
297 return nullptr;
298 --I;
299 }
300 Instruction *Retain = &*I;
301 if (GetBasicARCInstKind(Retain) != ARCInstKind::Retain)
302 return nullptr;
303 if (GetArgRCIdentityRoot(Retain) != New)
304 return nullptr;
305 return Retain;
306}
307
308/// Attempt to merge an objc_release with a store, load, and objc_retain to form
309/// an objc_storeStrong. An objc_storeStrong:
310///
311/// objc_storeStrong(i8** %old_ptr, i8* new_value)
312///
313/// is equivalent to the following IR sequence:
314///
315/// ; Load old value.
316/// %old_value = load i8** %old_ptr (1)
317///
318/// ; Increment the new value and then release the old value. This must occur
319/// ; in order in case old_value releases new_value in its destructor causing
320/// ; us to potentially have a dangling ptr.
321/// tail call i8* @objc_retain(i8* %new_value) (2)
322/// tail call void @objc_release(i8* %old_value) (3)
323///
324/// ; Store the new_value into old_ptr
325/// store i8* %new_value, i8** %old_ptr (4)
326///
327/// The safety of this optimization is based around the following
328/// considerations:
329///
330/// 1. We are forming the store strong at the store. Thus to perform this
331/// optimization it must be safe to move the retain, load, and release to
332/// (4).
333/// 2. We need to make sure that any re-orderings of (1), (2), (3), (4) are
334/// safe.
335void ObjCARCContract::tryToContractReleaseIntoStoreStrong(
336 Instruction *Release, inst_iterator &Iter,
337 const DenseMap<BasicBlock *, ColorVector> &BlockColors) {
338 // See if we are releasing something that we just loaded.
339 auto *Load = dyn_cast<LoadInst>(GetArgRCIdentityRoot(Release));
340 if (!Load || !Load->isSimple())
341 return;
342
343 // For now, require everything to be in one basic block.
344 BasicBlock *BB = Release->getParent();
345 if (Load->getParent() != BB)
346 return;
347
348 // First scan down the BB from Load, looking for a store of the RCIdentityRoot
349 // of Load's
350 StoreInst *Store =
351 findSafeStoreForStoreStrongContraction(Load, Release, PA, AA);
352 // If we fail, bail.
353 if (!Store)
354 return;
355
356 // Then find what new_value's RCIdentity Root is.
357 Value *New = GetRCIdentityRoot(Store->getValueOperand());
358
359 // Then walk up the BB and look for a retain on New without any intervening
360 // instructions which conservatively might decrement ref counts.
361 Instruction *Retain =
362 findRetainForStoreStrongContraction(New, Store, Release, PA);
363
364 // If we fail, bail.
365 if (!Retain)
366 return;
367
368 Changed = true;
369 ++NumStoreStrongs;
370
371 LLVM_DEBUG(do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { llvm::dbgs() << " Contracting retain, release into objc_storeStrong.\n"
<< " Old:\n" << " Store: " <<
*Store << "\n" << " Release: " <<
*Release << "\n" << " Retain: " <<
*Retain << "\n" << " Load: " <<
*Load << "\n"; } } while (false)
372 llvm::dbgs() << " Contracting retain, release into objc_storeStrong.\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { llvm::dbgs() << " Contracting retain, release into objc_storeStrong.\n"
<< " Old:\n" << " Store: " <<
*Store << "\n" << " Release: " <<
*Release << "\n" << " Retain: " <<
*Retain << "\n" << " Load: " <<
*Load << "\n"; } } while (false)
373 << " Old:\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { llvm::dbgs() << " Contracting retain, release into objc_storeStrong.\n"
<< " Old:\n" << " Store: " <<
*Store << "\n" << " Release: " <<
*Release << "\n" << " Retain: " <<
*Retain << "\n" << " Load: " <<
*Load << "\n"; } } while (false)
374 << " Store: " << *Store << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { llvm::dbgs() << " Contracting retain, release into objc_storeStrong.\n"
<< " Old:\n" << " Store: " <<
*Store << "\n" << " Release: " <<
*Release << "\n" << " Retain: " <<
*Retain << "\n" << " Load: " <<
*Load << "\n"; } } while (false)
375 << " Release: " << *Release << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { llvm::dbgs() << " Contracting retain, release into objc_storeStrong.\n"
<< " Old:\n" << " Store: " <<
*Store << "\n" << " Release: " <<
*Release << "\n" << " Retain: " <<
*Retain << "\n" << " Load: " <<
*Load << "\n"; } } while (false)
376 << " Retain: " << *Retain << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { llvm::dbgs() << " Contracting retain, release into objc_storeStrong.\n"
<< " Old:\n" << " Store: " <<
*Store << "\n" << " Release: " <<
*Release << "\n" << " Retain: " <<
*Retain << "\n" << " Load: " <<
*Load << "\n"; } } while (false)
377 << " Load: " << *Load << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { llvm::dbgs() << " Contracting retain, release into objc_storeStrong.\n"
<< " Old:\n" << " Store: " <<
*Store << "\n" << " Release: " <<
*Release << "\n" << " Retain: " <<
*Retain << "\n" << " Load: " <<
*Load << "\n"; } } while (false)
;
378
379 LLVMContext &C = Release->getContext();
380 Type *I8X = PointerType::getUnqual(Type::getInt8Ty(C));
381 Type *I8XX = PointerType::getUnqual(I8X);
382
383 Value *Args[] = { Load->getPointerOperand(), New };
384 if (Args[0]->getType() != I8XX)
385 Args[0] = new BitCastInst(Args[0], I8XX, "", Store);
386 if (Args[1]->getType() != I8X)
387 Args[1] = new BitCastInst(Args[1], I8X, "", Store);
388 Function *Decl = EP.get(ARCRuntimeEntryPointKind::StoreStrong);
389 CallInst *StoreStrong =
390 objcarc::createCallInstWithColors(Decl, Args, "", Store, BlockColors);
391 StoreStrong->setDoesNotThrow();
392 StoreStrong->setDebugLoc(Store->getDebugLoc());
393
394 // We can't set the tail flag yet, because we haven't yet determined
395 // whether there are any escaping allocas. Remember this call, so that
396 // we can set the tail flag once we know it's safe.
397 StoreStrongCalls.insert(StoreStrong);
398
399 LLVM_DEBUG(llvm::dbgs() << " New Store Strong: " << *StoreStrongdo { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { llvm::dbgs() << " New Store Strong: "
<< *StoreStrong << "\n"; } } while (false)
400 << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { llvm::dbgs() << " New Store Strong: "
<< *StoreStrong << "\n"; } } while (false)
;
401
402 if (&*Iter == Retain) ++Iter;
403 if (&*Iter == Store) ++Iter;
404 Store->eraseFromParent();
405 Release->eraseFromParent();
406 EraseInstruction(Retain);
407 if (Load->use_empty())
408 Load->eraseFromParent();
409}
410
411bool ObjCARCContract::tryToPeepholeInstruction(
412 Function &F, Instruction *Inst, inst_iterator &Iter,
413 bool &TailOkForStoreStrongs,
414 const DenseMap<BasicBlock *, ColorVector> &BlockColors) {
415 // Only these library routines return their argument. In particular,
416 // objc_retainBlock does not necessarily return its argument.
417 ARCInstKind Class = GetBasicARCInstKind(Inst);
418 switch (Class) {
419 case ARCInstKind::FusedRetainAutorelease:
420 case ARCInstKind::FusedRetainAutoreleaseRV:
421 return false;
422 case ARCInstKind::Autorelease:
423 case ARCInstKind::AutoreleaseRV:
424 return contractAutorelease(F, Inst, Class);
425 case ARCInstKind::Retain:
426 // Attempt to convert retains to retainrvs if they are next to function
427 // calls.
428 if (!optimizeRetainCall(F, Inst))
429 return false;
430 // If we succeed in our optimization, fall through.
431 [[fallthrough]];
432 case ARCInstKind::RetainRV:
433 case ARCInstKind::UnsafeClaimRV: {
434 // Return true if this is a bundled retainRV/claimRV call, which is always
435 // redundant with the attachedcall in the bundle, and is going to be erased
436 // at the end of this pass. This avoids undoing objc-arc-expand and
437 // replacing uses of the retainRV/claimRV call's argument with its result.
438 if (BundledInsts->contains(Inst))
439 return true;
440
441 // If this isn't a bundled call, and the target doesn't need a special
442 // inline-asm marker, we're done: return now, and undo objc-arc-expand.
443 if (!RVInstMarker)
444 return false;
445
446 // The target needs a special inline-asm marker. Insert it.
447
448 BasicBlock::iterator BBI = Inst->getIterator();
449 BasicBlock *InstParent = Inst->getParent();
450
451 // Step up to see if the call immediately precedes the RV call.
452 // If it's an invoke, we have to cross a block boundary. And we have
453 // to carefully dodge no-op instructions.
454 do {
455 if (BBI == InstParent->begin()) {
456 BasicBlock *Pred = InstParent->getSinglePredecessor();
457 if (!Pred)
458 goto decline_rv_optimization;
459 BBI = Pred->getTerminator()->getIterator();
460 break;
461 }
462 --BBI;
463 } while (IsNoopInstruction(&*BBI));
464
465 if (GetRCIdentityRoot(&*BBI) == GetArgRCIdentityRoot(Inst)) {
466 LLVM_DEBUG(dbgs() << "Adding inline asm marker for the return value "do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { dbgs() << "Adding inline asm marker for the return value "
"optimization.\n"; } } while (false)
467 "optimization.\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { dbgs() << "Adding inline asm marker for the return value "
"optimization.\n"; } } while (false)
;
468 Changed = true;
469 InlineAsm *IA =
470 InlineAsm::get(FunctionType::get(Type::getVoidTy(Inst->getContext()),
471 /*isVarArg=*/false),
472 RVInstMarker->getString(),
473 /*Constraints=*/"", /*hasSideEffects=*/true);
474
475 objcarc::createCallInstWithColors(IA, None, "", Inst, BlockColors);
476 }
477 decline_rv_optimization:
478 return false;
479 }
480 case ARCInstKind::InitWeak: {
481 // objc_initWeak(p, null) => *p = null
482 CallInst *CI = cast<CallInst>(Inst);
483 if (IsNullOrUndef(CI->getArgOperand(1))) {
484 Value *Null = ConstantPointerNull::get(cast<PointerType>(CI->getType()));
485 Changed = true;
486 new StoreInst(Null, CI->getArgOperand(0), CI);
487
488 LLVM_DEBUG(dbgs() << "OBJCARCContract: Old = " << *CI << "\n"do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { dbgs() << "OBJCARCContract: Old = "
<< *CI << "\n" << " New = "
<< *Null << "\n"; } } while (false)
489 << " New = " << *Null << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { dbgs() << "OBJCARCContract: Old = "
<< *CI << "\n" << " New = "
<< *Null << "\n"; } } while (false)
;
490
491 CI->replaceAllUsesWith(Null);
492 CI->eraseFromParent();
493 }
494 return true;
495 }
496 case ARCInstKind::Release:
497 // Try to form an objc store strong from our release. If we fail, there is
498 // nothing further to do below, so continue.
499 tryToContractReleaseIntoStoreStrong(Inst, Iter, BlockColors);
500 return true;
501 case ARCInstKind::User:
502 // Be conservative if the function has any alloca instructions.
503 // Technically we only care about escaping alloca instructions,
504 // but this is sufficient to handle some interesting cases.
505 if (isa<AllocaInst>(Inst))
506 TailOkForStoreStrongs = false;
507 return true;
508 case ARCInstKind::IntrinsicUser:
509 // Remove calls to @llvm.objc.clang.arc.use(...).
510 Changed = true;
511 Inst->eraseFromParent();
512 return true;
513 default:
514 if (auto *CI = dyn_cast<CallInst>(Inst))
515 if (CI->getIntrinsicID() == Intrinsic::objc_clang_arc_noop_use) {
516 // Remove calls to @llvm.objc.clang.arc.noop.use(...).
517 Changed = true;
518 CI->eraseFromParent();
519 }
520 return true;
521 }
522}
523
524//===----------------------------------------------------------------------===//
525// Top Level Driver
526//===----------------------------------------------------------------------===//
527
528bool ObjCARCContract::init(Module &M) {
529 EP.init(&M);
530
531 // Initialize RVInstMarker.
532 RVInstMarker = getRVInstMarker(M);
533
534 return false;
535}
536
537bool ObjCARCContract::run(Function &F, AAResults *A, DominatorTree *D) {
538 if (!EnableARCOpts)
2
Assuming 'EnableARCOpts' is true
3
Taking false branch
539 return false;
540
541 Changed = CFGChanged = false;
542 AA = A;
543 DT = D;
544 PA.setAA(A);
545 BundledRetainClaimRVs BRV(/*ContractPass=*/true);
546 BundledInsts = &BRV;
547
548 std::pair<bool, bool> R = BundledInsts->insertAfterInvokes(F, DT);
549 Changed |= R.first;
550 CFGChanged |= R.second;
551
552 DenseMap<BasicBlock *, ColorVector> BlockColors;
553 if (F.hasPersonalityFn() &&
4
Assuming the condition is false
554 isScopedEHPersonality(classifyEHPersonality(F.getPersonalityFn())))
555 BlockColors = colorEHFunclets(F);
556
557 LLVM_DEBUG(llvm::dbgs() << "**** ObjCARC Contract ****\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { llvm::dbgs() << "**** ObjCARC Contract ****\n"
; } } while (false)
;
5
Assuming 'DebugFlag' is false
558
559 // Track whether it's ok to mark objc_storeStrong calls with the "tail"
560 // keyword. Be conservative if the function has variadic arguments.
561 // It seems that functions which "return twice" are also unsafe for the
562 // "tail" argument, because they are setjmp, which could need to
563 // return to an earlier stack state.
564 bool TailOkForStoreStrongs =
565 !F.isVarArg() && !F.callsFunctionThatReturnsTwice();
6
Assuming the condition is false
566
567 // For ObjC library calls which return their argument, replace uses of the
568 // argument with uses of the call return value, if it dominates the use. This
569 // reduces register pressure.
570 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E;) {
7
Loop condition is false. Execution continues on line 708
571 Instruction *Inst = &*I++;
572
573 LLVM_DEBUG(dbgs() << "Visiting: " << *Inst << "\n")do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("objc-arc-contract")) { dbgs() << "Visiting: " <<
*Inst << "\n"; } } while (false)
;
574
575 if (auto *CI = dyn_cast<CallInst>(Inst))
576 if (objcarc::hasAttachedCallOpBundle(CI)) {
577 BundledInsts->insertRVCallWithColors(&*I, CI, BlockColors);
578 --I;
579 Changed = true;
580 }
581
582 // First try to peephole Inst. If there is nothing further we can do in
583 // terms of undoing objc-arc-expand, process the next inst.
584 if (tryToPeepholeInstruction(F, Inst, I, TailOkForStoreStrongs,
585 BlockColors))
586 continue;
587
588 // Otherwise, try to undo objc-arc-expand.
589
590 // Don't use GetArgRCIdentityRoot because we don't want to look through bitcasts
591 // and such; to do the replacement, the argument must have type i8*.
592
593 // Function for replacing uses of Arg dominated by Inst.
594 auto ReplaceArgUses = [Inst, this](Value *Arg) {
595 // If we're compiling bugpointed code, don't get in trouble.
596 if (!isa<Instruction>(Arg) && !isa<Argument>(Arg))
597 return;
598
599 // Look through the uses of the pointer.
600 for (Value::use_iterator UI = Arg->use_begin(), UE = Arg->use_end();
601 UI != UE; ) {
602 // Increment UI now, because we may unlink its element.
603 Use &U = *UI++;
604 unsigned OperandNo = U.getOperandNo();
605
606 // If the call's return value dominates a use of the call's argument
607 // value, rewrite the use to use the return value. We check for
608 // reachability here because an unreachable call is considered to
609 // trivially dominate itself, which would lead us to rewriting its
610 // argument in terms of its return value, which would lead to
611 // infinite loops in GetArgRCIdentityRoot.
612 if (!DT->isReachableFromEntry(U) || !DT->dominates(Inst, U))
613 continue;
614
615 Changed = true;
616 Instruction *Replacement = Inst;
617 Type *UseTy = U.get()->getType();
618 if (PHINode *PHI = dyn_cast<PHINode>(U.getUser())) {
619 // For PHI nodes, insert the bitcast in the predecessor block.
620 unsigned ValNo = PHINode::getIncomingValueNumForOperand(OperandNo);
621 BasicBlock *IncomingBB = PHI->getIncomingBlock(ValNo);
622 if (Replacement->getType() != UseTy) {
623 // A catchswitch is both a pad and a terminator, meaning a basic
624 // block with a catchswitch has no insertion point. Keep going up
625 // the dominator tree until we find a non-catchswitch.
626 BasicBlock *InsertBB = IncomingBB;
627 while (isa<CatchSwitchInst>(InsertBB->getFirstNonPHI())) {
628 InsertBB = DT->getNode(InsertBB)->getIDom()->getBlock();
629 }
630
631 assert(DT->dominates(Inst, &InsertBB->back()) &&(static_cast <bool> (DT->dominates(Inst, &InsertBB
->back()) && "Invalid insertion point for bitcast"
) ? void (0) : __assert_fail ("DT->dominates(Inst, &InsertBB->back()) && \"Invalid insertion point for bitcast\""
, "llvm/lib/Transforms/ObjCARC/ObjCARCContract.cpp", 632, __extension__
__PRETTY_FUNCTION__))
632 "Invalid insertion point for bitcast")(static_cast <bool> (DT->dominates(Inst, &InsertBB
->back()) && "Invalid insertion point for bitcast"
) ? void (0) : __assert_fail ("DT->dominates(Inst, &InsertBB->back()) && \"Invalid insertion point for bitcast\""
, "llvm/lib/Transforms/ObjCARC/ObjCARCContract.cpp", 632, __extension__
__PRETTY_FUNCTION__))
;
633 Replacement =
634 new BitCastInst(Replacement, UseTy, "", &InsertBB->back());
635 }
636
637 // While we're here, rewrite all edges for this PHI, rather
638 // than just one use at a time, to minimize the number of
639 // bitcasts we emit.
640 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
641 if (PHI->getIncomingBlock(i) == IncomingBB) {
642 // Keep the UI iterator valid.
643 if (UI != UE &&
644 &PHI->getOperandUse(
645 PHINode::getOperandNumForIncomingValue(i)) == &*UI)
646 ++UI;
647 PHI->setIncomingValue(i, Replacement);
648 }
649 } else {
650 if (Replacement->getType() != UseTy)
651 Replacement = new BitCastInst(Replacement, UseTy, "",
652 cast<Instruction>(U.getUser()));
653 U.set(Replacement);
654 }
655 }
656 };
657
658 Value *Arg = cast<CallInst>(Inst)->getArgOperand(0);
659 Value *OrigArg = Arg;
660
661 // TODO: Change this to a do-while.
662 for (;;) {
663 ReplaceArgUses(Arg);
664
665 // If Arg is a no-op casted pointer, strip one level of casts and iterate.
666 if (const BitCastInst *BI = dyn_cast<BitCastInst>(Arg))
667 Arg = BI->getOperand(0);
668 else if (isa<GEPOperator>(Arg) &&
669 cast<GEPOperator>(Arg)->hasAllZeroIndices())
670 Arg = cast<GEPOperator>(Arg)->getPointerOperand();
671 else if (isa<GlobalAlias>(Arg) &&
672 !cast<GlobalAlias>(Arg)->isInterposable())
673 Arg = cast<GlobalAlias>(Arg)->getAliasee();
674 else {
675 // If Arg is a PHI node, get PHIs that are equivalent to it and replace
676 // their uses.
677 if (PHINode *PN = dyn_cast<PHINode>(Arg)) {
678 SmallVector<Value *, 1> PHIList;
679 getEquivalentPHIs(*PN, PHIList);
680 for (Value *PHI : PHIList)
681 ReplaceArgUses(PHI);
682 }
683 break;
684 }
685 }
686
687 // Replace bitcast users of Arg that are dominated by Inst.
688 SmallVector<BitCastInst *, 2> BitCastUsers;
689
690 // Add all bitcast users of the function argument first.
691 for (User *U : OrigArg->users())
692 if (auto *BC = dyn_cast<BitCastInst>(U))
693 BitCastUsers.push_back(BC);
694
695 // Replace the bitcasts with the call return. Iterate until list is empty.
696 while (!BitCastUsers.empty()) {
697 auto *BC = BitCastUsers.pop_back_val();
698 for (User *U : BC->users())
699 if (auto *B = dyn_cast<BitCastInst>(U))
700 BitCastUsers.push_back(B);
701
702 ReplaceArgUses(BC);
703 }
704 }
705
706 // If this function has no escaping allocas or suspicious vararg usage,
707 // objc_storeStrong calls can be marked with the "tail" keyword.
708 if (TailOkForStoreStrongs
7.1
'TailOkForStoreStrongs' is false
)
8
Taking false branch
709 for (CallInst *CI : StoreStrongCalls)
710 CI->setTailCall();
711 StoreStrongCalls.clear();
712
713 return Changed;
9
Address of stack memory associated with local variable 'BRV' is still referred to by the stack variable 'OCAC' upon returning to the caller. This will be a dangling reference
714}
715
716//===----------------------------------------------------------------------===//
717// Misc Pass Manager
718//===----------------------------------------------------------------------===//
719
720char ObjCARCContractLegacyPass::ID = 0;
721INITIALIZE_PASS_BEGIN(ObjCARCContractLegacyPass, "objc-arc-contract",static void *initializeObjCARCContractLegacyPassPassOnce(PassRegistry
&Registry) {
722 "ObjC ARC contraction", false, false)static void *initializeObjCARCContractLegacyPassPassOnce(PassRegistry
&Registry) {
723INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)initializeAAResultsWrapperPassPass(Registry);
724INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)initializeDominatorTreeWrapperPassPass(Registry);
725INITIALIZE_PASS_END(ObjCARCContractLegacyPass, "objc-arc-contract",PassInfo *PI = new PassInfo( "ObjC ARC contraction", "objc-arc-contract"
, &ObjCARCContractLegacyPass::ID, PassInfo::NormalCtor_t(
callDefaultCtor<ObjCARCContractLegacyPass>), false, false
); Registry.registerPass(*PI, true); return PI; } static llvm
::once_flag InitializeObjCARCContractLegacyPassPassFlag; void
llvm::initializeObjCARCContractLegacyPassPass(PassRegistry &
Registry) { llvm::call_once(InitializeObjCARCContractLegacyPassPassFlag
, initializeObjCARCContractLegacyPassPassOnce, std::ref(Registry
)); }
726 "ObjC ARC contraction", false, false)PassInfo *PI = new PassInfo( "ObjC ARC contraction", "objc-arc-contract"
, &ObjCARCContractLegacyPass::ID, PassInfo::NormalCtor_t(
callDefaultCtor<ObjCARCContractLegacyPass>), false, false
); Registry.registerPass(*PI, true); return PI; } static llvm
::once_flag InitializeObjCARCContractLegacyPassPassFlag; void
llvm::initializeObjCARCContractLegacyPassPass(PassRegistry &
Registry) { llvm::call_once(InitializeObjCARCContractLegacyPassPassFlag
, initializeObjCARCContractLegacyPassPassOnce, std::ref(Registry
)); }
727
728void ObjCARCContractLegacyPass::getAnalysisUsage(AnalysisUsage &AU) const {
729 AU.addRequired<AAResultsWrapperPass>();
730 AU.addRequired<DominatorTreeWrapperPass>();
731}
732
733Pass *llvm::createObjCARCContractPass() {
734 return new ObjCARCContractLegacyPass();
735}
736
737bool ObjCARCContractLegacyPass::runOnFunction(Function &F) {
738 ObjCARCContract OCARCC;
739 OCARCC.init(*F.getParent());
740 auto *AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
741 auto *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
742 return OCARCC.run(F, AA, DT);
743}
744
745PreservedAnalyses ObjCARCContractPass::run(Function &F,
746 FunctionAnalysisManager &AM) {
747 ObjCARCContract OCAC;
748 OCAC.init(*F.getParent());
749
750 bool Changed = OCAC.run(F, &AM.getResult<AAManager>(F),
1
Calling 'ObjCARCContract::run'
751 &AM.getResult<DominatorTreeAnalysis>(F));
752 bool CFGChanged = OCAC.hasCFGChanged();
753 if (Changed) {
754 PreservedAnalyses PA;
755 if (!CFGChanged)
756 PA.preserveSet<CFGAnalyses>();
757 return PA;
758 }
759 return PreservedAnalyses::all();
760}