1 //===- ObjCARCExpand.cpp - ObjC ARC Optimization --------------------------===// 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 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 deals with early optimizations which perform certain 15 /// cleanup operations. 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 "ObjCARC.h" 27 #include "llvm/IR/Function.h" 28 #include "llvm/IR/InstIterator.h" 29 #include "llvm/IR/Instruction.h" 30 #include "llvm/IR/Instructions.h" 31 #include "llvm/IR/Value.h" 32 #include "llvm/Pass.h" 33 #include "llvm/PassAnalysisSupport.h" 34 #include "llvm/PassRegistry.h" 35 #include "llvm/PassSupport.h" 36 #include "llvm/Support/Casting.h" 37 #include "llvm/Support/Debug.h" 38 #include "llvm/Support/raw_ostream.h" 39 40 #define DEBUG_TYPE "objc-arc-expand" 41 42 namespace llvm { 43 class Module; 44 } 45 46 using namespace llvm; 47 using namespace llvm::objcarc; 48 49 namespace { 50 /// \brief Early ARC transformations. 51 class ObjCARCExpand : public FunctionPass { 52 void getAnalysisUsage(AnalysisUsage &AU) const override; 53 bool doInitialization(Module &M) override; 54 bool runOnFunction(Function &F) override; 55 56 /// A flag indicating whether this optimization pass should run. 57 bool Run; 58 59 public: 60 static char ID; ObjCARCExpand()61 ObjCARCExpand() : FunctionPass(ID) { 62 initializeObjCARCExpandPass(*PassRegistry::getPassRegistry()); 63 } 64 }; 65 } 66 67 char ObjCARCExpand::ID = 0; 68 INITIALIZE_PASS(ObjCARCExpand, 69 "objc-arc-expand", "ObjC ARC expansion", false, false) 70 createObjCARCExpandPass()71Pass *llvm::createObjCARCExpandPass() { 72 return new ObjCARCExpand(); 73 } 74 getAnalysisUsage(AnalysisUsage & AU) const75void ObjCARCExpand::getAnalysisUsage(AnalysisUsage &AU) const { 76 AU.setPreservesCFG(); 77 } 78 doInitialization(Module & M)79bool ObjCARCExpand::doInitialization(Module &M) { 80 Run = ModuleHasARC(M); 81 return false; 82 } 83 runOnFunction(Function & F)84bool ObjCARCExpand::runOnFunction(Function &F) { 85 if (!EnableARCOpts) 86 return false; 87 88 // If nothing in the Module uses ARC, don't do anything. 89 if (!Run) 90 return false; 91 92 bool Changed = false; 93 94 DEBUG(dbgs() << "ObjCARCExpand: Visiting Function: " << F.getName() << "\n"); 95 96 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ++I) { 97 Instruction *Inst = &*I; 98 99 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 DEBUG(dbgs() << "ObjCARCExpand: Old = " << *Inst << "\n" 115 " New = " << *Value << "\n"); 116 Inst->replaceAllUsesWith(Value); 117 break; 118 } 119 default: 120 break; 121 } 122 } 123 124 DEBUG(dbgs() << "ObjCARCExpand: Finished List.\n\n"); 125 126 return Changed; 127 } 128