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 
39 using namespace llvm;
40 using namespace llvm::objcarc;
41 
42 namespace {
43 static 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 
91 PreservedAnalyses 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