LLVM  15.0.0git
ObjCARCAPElim.cpp
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1 //===- ObjCARCAPElim.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 ///
10 /// This file defines ObjC ARC optimizations. ARC stands for Automatic
11 /// Reference Counting and is a system for managing reference counts for objects
12 /// in Objective C.
13 ///
14 /// This specific file implements optimizations which remove extraneous
15 /// autorelease pools.
16 ///
17 /// WARNING: This file knows about certain library functions. It recognizes them
18 /// by name, and hardwires knowledge of their semantics.
19 ///
20 /// WARNING: This file knows about how certain Objective-C library functions are
21 /// used. Naive LLVM IR transformations which would otherwise be
22 /// behavior-preserving may break these assumptions.
23 ///
24 //===----------------------------------------------------------------------===//
25 
26 #include "llvm/ADT/STLExtras.h"
29 #include "llvm/IR/Constants.h"
30 #include "llvm/IR/InstrTypes.h"
31 #include "llvm/IR/PassManager.h"
32 #include "llvm/InitializePasses.h"
33 #include "llvm/Pass.h"
34 #include "llvm/Support/Debug.h"
37 
38 using namespace llvm;
39 using namespace llvm::objcarc;
40 
41 #define DEBUG_TYPE "objc-arc-ap-elim"
42 
43 namespace {
44 
45 /// Interprocedurally determine if calls made by the given call site can
46 /// possibly produce autoreleases.
47 bool MayAutorelease(const CallBase &CB, unsigned Depth = 0) {
48  if (const Function *Callee = CB.getCalledFunction()) {
49  if (!Callee->hasExactDefinition())
50  return true;
51  for (const BasicBlock &BB : *Callee) {
52  for (const Instruction &I : BB)
53  if (const CallBase *JCB = dyn_cast<CallBase>(&I))
54  // This recursion depth limit is arbitrary. It's just great
55  // enough to cover known interesting testcases.
56  if (Depth < 3 && !JCB->onlyReadsMemory() &&
57  MayAutorelease(*JCB, Depth + 1))
58  return true;
59  }
60  return false;
61  }
62 
63  return true;
64 }
65 
66 bool OptimizeBB(BasicBlock *BB) {
67  bool Changed = false;
68 
69  Instruction *Push = nullptr;
70  for (Instruction &Inst : llvm::make_early_inc_range(*BB)) {
71  switch (GetBasicARCInstKind(&Inst)) {
73  Push = &Inst;
74  break;
76  // If this pop matches a push and nothing in between can autorelease,
77  // zap the pair.
78  if (Push && cast<CallInst>(&Inst)->getArgOperand(0) == Push) {
79  Changed = true;
80  LLVM_DEBUG(dbgs() << "ObjCARCAPElim::OptimizeBB: Zapping push pop "
81  "autorelease pair:\n"
82  " Pop: "
83  << Inst << "\n"
84  << " Push: " << *Push
85  << "\n");
86  Inst.eraseFromParent();
87  Push->eraseFromParent();
88  }
89  Push = nullptr;
90  break;
92  if (MayAutorelease(cast<CallBase>(Inst)))
93  Push = nullptr;
94  break;
95  default:
96  break;
97  }
98  }
99 
100  return Changed;
101 }
102 
103 bool runImpl(Module &M) {
104  if (!EnableARCOpts)
105  return false;
106 
107  // If nothing in the Module uses ARC, don't do anything.
108  if (!ModuleHasARC(M))
109  return false;
110  // Find the llvm.global_ctors variable, as the first step in
111  // identifying the global constructors. In theory, unnecessary autorelease
112  // pools could occur anywhere, but in practice it's pretty rare. Global
113  // ctors are a place where autorelease pools get inserted automatically,
114  // so it's pretty common for them to be unnecessary, and it's pretty
115  // profitable to eliminate them.
116  GlobalVariable *GV = M.getGlobalVariable("llvm.global_ctors");
117  if (!GV)
118  return false;
119 
121  "llvm.global_ctors is uncooperative!");
122 
123  bool Changed = false;
124 
125  // Dig the constructor functions out of GV's initializer.
126  ConstantArray *Init = cast<ConstantArray>(GV->getInitializer());
127  for (User::op_iterator OI = Init->op_begin(), OE = Init->op_end();
128  OI != OE; ++OI) {
129  Value *Op = *OI;
130  // llvm.global_ctors is an array of three-field structs where the second
131  // members are constructor functions.
132  Function *F = dyn_cast<Function>(cast<ConstantStruct>(Op)->getOperand(1));
133  // If the user used a constructor function with the wrong signature and
134  // it got bitcasted or whatever, look the other way.
135  if (!F)
136  continue;
137  // Only look at function definitions.
138  if (F->isDeclaration())
139  continue;
140  // Only look at functions with one basic block.
141  if (std::next(F->begin()) != F->end())
142  continue;
143  // Ok, a single-block constructor function definition. Try to optimize it.
144  Changed |= OptimizeBB(&F->front());
145  }
146 
147  return Changed;
148 }
149 
150 /// Autorelease pool elimination.
151 class ObjCARCAPElim : public ModulePass {
152  void getAnalysisUsage(AnalysisUsage &AU) const override;
153  bool runOnModule(Module &M) override;
154 
155 public:
156  static char ID;
157  ObjCARCAPElim() : ModulePass(ID) {
159  }
160 };
161 } // namespace
162 
163 char ObjCARCAPElim::ID = 0;
164 INITIALIZE_PASS(ObjCARCAPElim, "objc-arc-apelim",
165  "ObjC ARC autorelease pool elimination", false, false)
166 
167 Pass *llvm::createObjCARCAPElimPass() { return new ObjCARCAPElim(); }
168 
169 void ObjCARCAPElim::getAnalysisUsage(AnalysisUsage &AU) const {
170  AU.setPreservesCFG();
171 }
172 
173 bool ObjCARCAPElim::runOnModule(Module &M) {
174  if (skipModule(M))
175  return false;
176  return runImpl(M);
177 }
178 
180  if (!runImpl(M))
181  return PreservedAnalyses::all();
183  PA.preserveSet<CFGAnalyses>();
184  return PA;
185 }
llvm::objcarc::GetBasicARCInstKind
ARCInstKind GetBasicARCInstKind(const Value *V)
Determine which objc runtime call instruction class V belongs to.
Definition: ObjCARCInstKind.h:104
llvm::PreservedAnalyses
A set of analyses that are preserved following a run of a transformation pass.
Definition: PassManager.h:152
llvm
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:17
M
We currently emits eax Perhaps this is what we really should generate is Is imull three or four cycles eax eax The current instruction priority is based on pattern complexity The former is more complex because it folds a load so the latter will not be emitted Perhaps we should use AddedComplexity to give LEA32r a higher priority We should always try to match LEA first since the LEA matching code does some estimate to determine whether the match is profitable if we care more about code then imull is better It s two bytes shorter than movl leal On a Pentium M
Definition: README.txt:252
llvm::ModulePass
ModulePass class - This class is used to implement unstructured interprocedural optimizations and ana...
Definition: Pass.h:248
llvm::Function
Definition: Function.h:60
Pass.h
llvm::ObjCARCAPElimPass::run
PreservedAnalyses run(Module &M, ModuleAnalysisManager &AM)
Definition: ObjCARCAPElim.cpp:179
llvm::GlobalVariable
Definition: GlobalVariable.h:39
llvm::Depth
@ Depth
Definition: SIMachineScheduler.h:36
INITIALIZE_PASS
INITIALIZE_PASS(ObjCARCAPElim, "objc-arc-apelim", "ObjC ARC autorelease pool elimination", false, false) Pass *llvm
Definition: ObjCARCAPElim.cpp:164
STLExtras.h
LLVM_DEBUG
#define LLVM_DEBUG(X)
Definition: Debug.h:101
F
#define F(x, y, z)
Definition: MD5.cpp:55
llvm::BasicBlock
LLVM Basic Block Representation.
Definition: BasicBlock.h:55
llvm::dbgs
raw_ostream & dbgs()
dbgs() - This returns a reference to a raw_ostream for debugging messages.
Definition: Debug.cpp:163
llvm::PassRegistry::getPassRegistry
static PassRegistry * getPassRegistry()
getPassRegistry - Access the global registry object, which is automatically initialized at applicatio...
Definition: PassRegistry.cpp:31
Constants.h
llvm::objcarc::ARCInstKind::CallOrUser
@ CallOrUser
could call objc_release and/or "use" pointers
InstrTypes.h
llvm::CallBase::getCalledFunction
Function * getCalledFunction() const
Returns the function called, or null if this is an indirect function invocation or the function signa...
Definition: InstrTypes.h:1396
llvm::AnalysisUsage
Represent the analysis usage information of a pass.
Definition: PassAnalysisSupport.h:47
runImpl
static bool runImpl(const TargetLibraryInfo &TLI, Function &F)
Definition: ReplaceWithVeclib.cpp:176
llvm::ConstantArray
ConstantArray - Constant Array Declarations.
Definition: Constants.h:409
llvm::Instruction
Definition: Instruction.h:42
llvm::CallingConv::ID
unsigned ID
LLVM IR allows to use arbitrary numbers as calling convention identifiers.
Definition: CallingConv.h:24
llvm::objcarc::ARCInstKind::AutoreleasepoolPop
@ AutoreleasepoolPop
objc_autoreleasePoolPop
llvm::GlobalVariable::getInitializer
const Constant * getInitializer() const
getInitializer - Return the initializer for this global variable.
Definition: GlobalVariable.h:135
llvm::Instruction::eraseFromParent
SymbolTableList< Instruction >::iterator eraseFromParent()
This method unlinks 'this' from the containing basic block and deletes it.
Definition: Instruction.cpp:77
llvm::GlobalVariable::hasDefinitiveInitializer
bool hasDefinitiveInitializer() const
hasDefinitiveInitializer - Whether the global variable has an initializer, and any other instances of...
Definition: GlobalVariable.h:109
I
#define I(x, y, z)
Definition: MD5.cpp:58
llvm::make_early_inc_range
iterator_range< early_inc_iterator_impl< detail::IterOfRange< RangeT > > > make_early_inc_range(RangeT &&Range)
Make a range that does early increment to allow mutation of the underlying range without disrupting i...
Definition: STLExtras.h:608
ObjCARCInstKind.h
assert
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
llvm::objcarc::EnableARCOpts
bool EnableARCOpts
A handy option to enable/disable all ARC Optimizations.
Definition: ObjCARCAnalysisUtils.cpp:23
llvm::objcarc
Definition: ObjCARCAliasAnalysis.h:29
llvm::Module
A Module instance is used to store all the information related to an LLVM module.
Definition: Module.h:65
llvm::AnalysisUsage::setPreservesCFG
void setPreservesCFG()
This function should be called by the pass, iff they do not:
Definition: Pass.cpp:263
llvm::CFGAnalyses
Represents analyses that only rely on functions' control flow.
Definition: PassManager.h:113
llvm::Init
Definition: Record.h:281
ObjCARCAnalysisUtils.h
Callee
amdgpu Simplify well known AMD library false FunctionCallee Callee
Definition: AMDGPULibCalls.cpp:186
llvm::objcarc::ARCInstKind::AutoreleasepoolPush
@ AutoreleasepoolPush
objc_autoreleasePoolPush
llvm::AMDGPU::SendMsg::Op
Op
Definition: SIDefines.h:326
llvm::PreservedAnalyses::all
static PreservedAnalyses all()
Construct a special preserved set that preserves all passes.
Definition: PassManager.h:158
PassManager.h
llvm::objcarc::ModuleHasARC
bool ModuleHasARC(const Module &M)
Test if the given module looks interesting to run ARC optimization on.
Definition: ObjCARCAnalysisUtils.h:43
llvm::initializeObjCARCAPElimPass
void initializeObjCARCAPElimPass(PassRegistry &)
llvm::Pass
Pass interface - Implemented by all 'passes'.
Definition: Pass.h:91
llvm::PreservedAnalyses::preserveSet
void preserveSet()
Mark an analysis set as preserved.
Definition: PassManager.h:188
ObjCARC.h
llvm::CallBase
Base class for all callable instructions (InvokeInst and CallInst) Holds everything related to callin...
Definition: InstrTypes.h:1174
llvm::createObjCARCAPElimPass
Pass * createObjCARCAPElimPass()
llvm::AnalysisManager
A container for analyses that lazily runs them and caches their results.
Definition: InstructionSimplify.h:42
BB
Common register allocation spilling lr str ldr sxth r3 ldr mla r4 can lr mov lr str ldr sxth r3 mla r4 and then merge mul and lr str ldr sxth r3 mla r4 It also increase the likelihood the store may become dead bb27 Successors according to LLVM BB
Definition: README.txt:39
raw_ostream.h
InitializePasses.h
llvm::Value
LLVM Value Representation.
Definition: Value.h:74
Debug.h
llvm::Use
A Use represents the edge between a Value definition and its users.
Definition: Use.h:43
llvm::Intrinsic::ID
unsigned ID
Definition: TargetTransformInfo.h:37