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(M: *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: &F)) {
57 LLVM_DEBUG(dbgs() << "ObjCARCExpand: Visiting: " << Inst << "\n");
58
59 switch (GetBasicARCInstKind(V: &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>(Val: &Inst)->getArgOperand(i: 0);
72 LLVM_DEBUG(dbgs() << "ObjCARCExpand: Old = " << Inst
73 << "\n"
74 " New = "
75 << *Value << "\n");
76 Inst.replaceAllUsesWith(V: 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