ObjCARCExpand.cpp revision 36b56886974eae4f9c5ebc96befd3e7bfe5de338 
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#define DEBUG_TYPE "objc-arc-expand"
27
28#include "ObjCARC.h"
29#include "llvm/ADT/StringRef.h"
30#include "llvm/IR/Function.h"
31#include "llvm/IR/InstIterator.h"
32#include "llvm/IR/Instruction.h"
33#include "llvm/IR/Instructions.h"
34#include "llvm/IR/Value.h"
35#include "llvm/Pass.h"
36#include "llvm/PassAnalysisSupport.h"
37#include "llvm/PassRegistry.h"
38#include "llvm/PassSupport.h"
39#include "llvm/Support/Casting.h"
40#include "llvm/Support/Debug.h"
41#include "llvm/Support/raw_ostream.h"
42
43namespace llvm {
44  class Module;
45}
46
47using namespace llvm;
48using namespace llvm::objcarc;
49
50namespace {
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;
62    ObjCARCExpand() : FunctionPass(ID) {
63      initializeObjCARCExpandPass(*PassRegistry::getPassRegistry());
64    }
65  };
66}
67
68char ObjCARCExpand::ID = 0;
69INITIALIZE_PASS(ObjCARCExpand,
70                "objc-arc-expand", "ObjC ARC expansion", false, false)
71
72Pass *llvm::createObjCARCExpandPass() {
73  return new ObjCARCExpand();
74}
75
76void ObjCARCExpand::getAnalysisUsage(AnalysisUsage &AU) const {
77  AU.setPreservesCFG();
78}
79
80bool ObjCARCExpand::doInitialization(Module &M) {
81  Run = ModuleHasARC(M);
82  return false;
83}
84
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 (GetBasicInstructionClass(Inst)) {
103    case IC_Retain:
104    case IC_RetainRV:
105    case IC_Autorelease:
106    case IC_AutoreleaseRV:
107    case IC_FusedRetainAutorelease:
108    case IC_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