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 "ObjCARC.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/Value.h" 31 #include "llvm/Pass.h" 32 #include "llvm/PassAnalysisSupport.h" 33 #include "llvm/PassRegistry.h" 34 #include "llvm/PassSupport.h" 35 #include "llvm/Support/Casting.h" 36 #include "llvm/Support/Debug.h" 37 #include "llvm/Support/raw_ostream.h" 38 39 #define DEBUG_TYPE "objc-arc-expand" 40 41 namespace llvm { 42 class Module; 43 } 44 45 using namespace llvm; 46 using namespace llvm::objcarc; 47 48 namespace { 49 /// Early ARC transformations. 50 class ObjCARCExpand : public FunctionPass { 51 void getAnalysisUsage(AnalysisUsage &AU) const override; 52 bool doInitialization(Module &M) override; 53 bool runOnFunction(Function &F) override; 54 55 /// A flag indicating whether this optimization pass should run. 56 bool Run; 57 58 public: 59 static char ID; 60 ObjCARCExpand() : FunctionPass(ID) { 61 initializeObjCARCExpandPass(*PassRegistry::getPassRegistry()); 62 } 63 }; 64 } 65 66 char ObjCARCExpand::ID = 0; 67 INITIALIZE_PASS(ObjCARCExpand, 68 "objc-arc-expand", "ObjC ARC expansion", false, false) 69 70 Pass *llvm::createObjCARCExpandPass() { 71 return new ObjCARCExpand(); 72 } 73 74 void ObjCARCExpand::getAnalysisUsage(AnalysisUsage &AU) const { 75 AU.setPreservesCFG(); 76 } 77 78 bool ObjCARCExpand::doInitialization(Module &M) { 79 Run = ModuleHasARC(M); 80 return false; 81 } 82 83 bool ObjCARCExpand::runOnFunction(Function &F) { 84 if (!EnableARCOpts) 85 return false; 86 87 // If nothing in the Module uses ARC, don't do anything. 88 if (!Run) 89 return false; 90 91 bool Changed = false; 92 93 LLVM_DEBUG(dbgs() << "ObjCARCExpand: Visiting Function: " << F.getName() 94 << "\n"); 95 96 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ++I) { 97 Instruction *Inst = &*I; 98 99 LLVM_DEBUG(dbgs() << "ObjCARCExpand: Visiting: " << *Inst << "\n"); 100 101 switch (GetBasicARCInstKind(Inst)) { 102 case ARCInstKind::Retain: 103 case ARCInstKind::RetainRV: 104 case ARCInstKind::Autorelease: 105 case ARCInstKind::AutoreleaseRV: 106 case ARCInstKind::FusedRetainAutorelease: 107 case ARCInstKind::FusedRetainAutoreleaseRV: { 108 // These calls return their argument verbatim, as a low-level 109 // optimization. However, this makes high-level optimizations 110 // harder. Undo any uses of this optimization that the front-end 111 // emitted here. We'll redo them in the contract pass. 112 Changed = true; 113 Value *Value = cast<CallInst>(Inst)->getArgOperand(0); 114 LLVM_DEBUG(dbgs() << "ObjCARCExpand: Old = " << *Inst 115 << "\n" 116 " New = " 117 << *Value << "\n"); 118 Inst->replaceAllUsesWith(Value); 119 break; 120 } 121 default: 122 break; 123 } 124 } 125 126 LLVM_DEBUG(dbgs() << "ObjCARCExpand: Finished List.\n\n"); 127 128 return Changed; 129 } 130