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/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 { 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 (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ++I) { 60 Instruction *Inst = &*I; 61 62 LLVM_DEBUG(dbgs() << "ObjCARCExpand: Visiting: " << *Inst << "\n"); 63 64 switch (GetBasicARCInstKind(Inst)) { 65 case ARCInstKind::Retain: 66 case ARCInstKind::RetainRV: 67 case ARCInstKind::Autorelease: 68 case ARCInstKind::AutoreleaseRV: 69 case ARCInstKind::FusedRetainAutorelease: 70 case ARCInstKind::FusedRetainAutoreleaseRV: { 71 // These calls return their argument verbatim, as a low-level 72 // optimization. However, this makes high-level optimizations 73 // harder. Undo any uses of this optimization that the front-end 74 // emitted here. We'll redo them in the contract pass. 75 Changed = true; 76 Value *Value = cast<CallInst>(Inst)->getArgOperand(0); 77 LLVM_DEBUG(dbgs() << "ObjCARCExpand: Old = " << *Inst 78 << "\n" 79 " New = " 80 << *Value << "\n"); 81 Inst->replaceAllUsesWith(Value); 82 break; 83 } 84 default: 85 break; 86 } 87 } 88 89 LLVM_DEBUG(dbgs() << "ObjCARCExpand: Finished List.\n\n"); 90 91 return Changed; 92 } 93 94 /// Early ARC transformations. 95 class ObjCARCExpand : public FunctionPass { 96 void getAnalysisUsage(AnalysisUsage &AU) const override; 97 bool runOnFunction(Function &F) override; 98 99 public: 100 static char ID; 101 ObjCARCExpand() : FunctionPass(ID) { 102 initializeObjCARCExpandPass(*PassRegistry::getPassRegistry()); 103 } 104 }; 105 } // namespace 106 107 char ObjCARCExpand::ID = 0; 108 INITIALIZE_PASS(ObjCARCExpand, "objc-arc-expand", "ObjC ARC expansion", false, 109 false) 110 111 Pass *llvm::createObjCARCExpandPass() { return new ObjCARCExpand(); } 112 113 void ObjCARCExpand::getAnalysisUsage(AnalysisUsage &AU) const { 114 AU.setPreservesCFG(); 115 } 116 117 bool ObjCARCExpand::runOnFunction(Function &F) { return runImpl(F); } 118 119 PreservedAnalyses ObjCARCExpandPass::run(Function &F, 120 FunctionAnalysisManager &AM) { 121 if (!runImpl(F)) 122 return PreservedAnalyses::all(); 123 PreservedAnalyses PA; 124 PA.preserveSet<CFGAnalyses>(); 125 return PA; 126 } 127