1 //===- ObjCARCExpand.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 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 deals with early optimizations which perform certain
14 /// cleanup operations.
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 #include "llvm/Analysis/ObjCARCAnalysisUtils.h"
26 #include "llvm/IR/Function.h"
27 #include "llvm/IR/InstIterator.h"
28 #include "llvm/IR/Instruction.h"
29 #include "llvm/IR/Instructions.h"
30 #include "llvm/IR/PassManager.h"
31 #include "llvm/IR/Value.h"
32 #include "llvm/InitializePasses.h"
33 #include "llvm/Pass.h"
34 #include "llvm/PassRegistry.h"
35 #include "llvm/Support/Casting.h"
36 #include "llvm/Support/Debug.h"
37 #include "llvm/Support/raw_ostream.h"
38 #include "llvm/Transforms/ObjCARC.h"
39
40 #define DEBUG_TYPE "objc-arc-expand"
41
42 using namespace llvm;
43 using namespace llvm::objcarc;
44
45 namespace {
runImpl(Function & F)46 static bool runImpl(Function &F) {
47 if (!EnableARCOpts)
48 return false;
49
50 // If nothing in the Module uses ARC, don't do anything.
51 if (!ModuleHasARC(*F.getParent()))
52 return false;
53
54 bool Changed = false;
55
56 LLVM_DEBUG(dbgs() << "ObjCARCExpand: Visiting Function: " << F.getName()
57 << "\n");
58
59 for (Instruction &Inst : instructions(&F)) {
60 LLVM_DEBUG(dbgs() << "ObjCARCExpand: Visiting: " << Inst << "\n");
61
62 switch (GetBasicARCInstKind(&Inst)) {
63 case ARCInstKind::Retain:
64 case ARCInstKind::RetainRV:
65 case ARCInstKind::Autorelease:
66 case ARCInstKind::AutoreleaseRV:
67 case ARCInstKind::FusedRetainAutorelease:
68 case ARCInstKind::FusedRetainAutoreleaseRV: {
69 // These calls return their argument verbatim, as a low-level
70 // optimization. However, this makes high-level optimizations
71 // harder. Undo any uses of this optimization that the front-end
72 // emitted here. We'll redo them in the contract pass.
73 Changed = true;
74 Value *Value = cast<CallInst>(&Inst)->getArgOperand(0);
75 LLVM_DEBUG(dbgs() << "ObjCARCExpand: Old = " << Inst
76 << "\n"
77 " New = "
78 << *Value << "\n");
79 Inst.replaceAllUsesWith(Value);
80 break;
81 }
82 default:
83 break;
84 }
85 }
86
87 LLVM_DEBUG(dbgs() << "ObjCARCExpand: Finished List.\n\n");
88
89 return Changed;
90 }
91
92 /// Early ARC transformations.
93 class ObjCARCExpand : public FunctionPass {
94 void getAnalysisUsage(AnalysisUsage &AU) const override;
95 bool runOnFunction(Function &F) override;
96
97 public:
98 static char ID;
ObjCARCExpand()99 ObjCARCExpand() : FunctionPass(ID) {
100 initializeObjCARCExpandPass(*PassRegistry::getPassRegistry());
101 }
102 };
103 } // namespace
104
105 char ObjCARCExpand::ID = 0;
106 INITIALIZE_PASS(ObjCARCExpand, "objc-arc-expand", "ObjC ARC expansion", false,
107 false)
108
createObjCARCExpandPass()109 Pass *llvm::createObjCARCExpandPass() { return new ObjCARCExpand(); }
110
getAnalysisUsage(AnalysisUsage & AU) const111 void ObjCARCExpand::getAnalysisUsage(AnalysisUsage &AU) const {
112 AU.setPreservesCFG();
113 }
114
runOnFunction(Function & F)115 bool ObjCARCExpand::runOnFunction(Function &F) { return runImpl(F); }
116
run(Function & F,FunctionAnalysisManager & AM)117 PreservedAnalyses ObjCARCExpandPass::run(Function &F,
118 FunctionAnalysisManager &AM) {
119 if (!runImpl(F))
120 return PreservedAnalyses::all();
121 PreservedAnalyses PA;
122 PA.preserveSet<CFGAnalyses>();
123 return PA;
124 }
125