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/ADT/StringRef.h" 28 #include "llvm/IR/Function.h" 29 #include "llvm/IR/InstIterator.h" 30 #include "llvm/IR/Instruction.h" 31 #include "llvm/IR/Instructions.h" 32 #include "llvm/IR/Value.h" 33 #include "llvm/Pass.h" 34 #include "llvm/PassAnalysisSupport.h" 35 #include "llvm/PassRegistry.h" 36 #include "llvm/PassSupport.h" 37 #include "llvm/Support/Casting.h" 38 #include "llvm/Support/Debug.h" 39 #include "llvm/Support/raw_ostream.h" 40 41 #define DEBUG_TYPE "objc-arc-expand" 42 43 namespace llvm { 44 class Module; 45 } 46 47 using namespace llvm; 48 using namespace llvm::objcarc; 49 50 namespace { 51 /// \brief Early ARC transformations. 52 class ObjCARCExpand : public FunctionPass { 53 void getAnalysisUsage(AnalysisUsage &AU) const override; 54 bool doInitialization(Module &M) override; 55 bool runOnFunction(Function &F) override; 56 57 /// A flag indicating whether this optimization pass should run. 58 bool Run; 59 60 public: 61 static char ID; ObjCARCExpand()62 ObjCARCExpand() : FunctionPass(ID) { 63 initializeObjCARCExpandPass(*PassRegistry::getPassRegistry()); 64 } 65 }; 66 } 67 68 char ObjCARCExpand::ID = 0; 69 INITIALIZE_PASS(ObjCARCExpand, 70 "objc-arc-expand", "ObjC ARC expansion", false, false) 71 createObjCARCExpandPass()72Pass *llvm::createObjCARCExpandPass() { 73 return new ObjCARCExpand(); 74 } 75 getAnalysisUsage(AnalysisUsage & AU) const76void ObjCARCExpand::getAnalysisUsage(AnalysisUsage &AU) const { 77 AU.setPreservesCFG(); 78 } 79 doInitialization(Module & M)80bool ObjCARCExpand::doInitialization(Module &M) { 81 Run = ModuleHasARC(M); 82 return false; 83 } 84 runOnFunction(Function & F)85bool ObjCARCExpand::runOnFunction(Function &F) { 86 if (!EnableARCOpts) 87 return false; 88 89 // If nothing in the Module uses ARC, don't do anything. 90 if (!Run) 91 return false; 92 93 bool Changed = false; 94 95 DEBUG(dbgs() << "ObjCARCExpand: Visiting Function: " << F.getName() << "\n"); 96 97 for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ++I) { 98 Instruction *Inst = &*I; 99 100 DEBUG(dbgs() << "ObjCARCExpand: Visiting: " << *Inst << "\n"); 101 102 switch (GetBasicARCInstKind(Inst)) { 103 case ARCInstKind::Retain: 104 case ARCInstKind::RetainRV: 105 case ARCInstKind::Autorelease: 106 case ARCInstKind::AutoreleaseRV: 107 case ARCInstKind::FusedRetainAutorelease: 108 case ARCInstKind::FusedRetainAutoreleaseRV: { 109 // These calls return their argument verbatim, as a low-level 110 // optimization. However, this makes high-level optimizations 111 // harder. Undo any uses of this optimization that the front-end 112 // emitted here. We'll redo them in the contract pass. 113 Changed = true; 114 Value *Value = cast<CallInst>(Inst)->getArgOperand(0); 115 DEBUG(dbgs() << "ObjCARCExpand: Old = " << *Inst << "\n" 116 " New = " << *Value << "\n"); 117 Inst->replaceAllUsesWith(Value); 118 break; 119 } 120 default: 121 break; 122 } 123 } 124 125 DEBUG(dbgs() << "ObjCARCExpand: Finished List.\n\n"); 126 127 return Changed; 128 } 129