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 "llvm/Analysis/ObjCARCAnalysisUtils.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/Support/Casting.h"
33#include "llvm/Support/Debug.h"
34#include "llvm/Support/raw_ostream.h"
35#include "llvm/Transforms/ObjCARC.h"
36
37#define DEBUG_TYPE "objc-arc-expand"
38
39using namespace llvm;
40using namespace llvm::objcarc;
41
42namespace {
43static bool runImpl(Function &F) {
44  if (!EnableARCOpts)
45    return false;
46
47  // If nothing in the Module uses ARC, don't do anything.
48  if (!ModuleHasARC(*F.getParent()))
49    return false;
50
51  bool Changed = false;
52
53  LLVM_DEBUG(dbgs() << "ObjCARCExpand: Visiting Function: " << F.getName()
54                    << "\n");
55
56  for (Instruction &Inst : instructions(&F)) {
57    LLVM_DEBUG(dbgs() << "ObjCARCExpand: Visiting: " << Inst << "\n");
58
59    switch (GetBasicARCInstKind(&Inst)) {
60    case ARCInstKind::Retain:
61    case ARCInstKind::RetainRV:
62    case ARCInstKind::Autorelease:
63    case ARCInstKind::AutoreleaseRV:
64    case ARCInstKind::FusedRetainAutorelease:
65    case ARCInstKind::FusedRetainAutoreleaseRV: {
66      // These calls return their argument verbatim, as a low-level
67      // optimization. However, this makes high-level optimizations
68      // harder. Undo any uses of this optimization that the front-end
69      // emitted here. We'll redo them in the contract pass.
70      Changed = true;
71      Value *Value = cast<CallInst>(&Inst)->getArgOperand(0);
72      LLVM_DEBUG(dbgs() << "ObjCARCExpand: Old = " << Inst
73                        << "\n"
74                           "               New = "
75                        << *Value << "\n");
76      Inst.replaceAllUsesWith(Value);
77      break;
78    }
79    default:
80      break;
81    }
82  }
83
84  LLVM_DEBUG(dbgs() << "ObjCARCExpand: Finished List.\n\n");
85
86  return Changed;
87}
88
89} // namespace
90
91PreservedAnalyses ObjCARCExpandPass::run(Function &F,
92                                         FunctionAnalysisManager &AM) {
93  if (!runImpl(F))
94    return PreservedAnalyses::all();
95  PreservedAnalyses PA;
96  PA.preserveSet<CFGAnalyses>();
97  return PA;
98}
99