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 #include "ObjCARC.h"
27 #include "llvm/ADT/StringRef.h"
28 #include "llvm/IR/Function.h"
29 #include "llvm/IR/InstIterator.h"
30 #include "llvm/IR/Instruction.h"
31 #include "llvm/IR/Instructions.h"
32 #include "llvm/IR/Value.h"
33 #include "llvm/Pass.h"
34 #include "llvm/PassAnalysisSupport.h"
35 #include "llvm/PassRegistry.h"
36 #include "llvm/PassSupport.h"
37 #include "llvm/Support/Casting.h"
38 #include "llvm/Support/Debug.h"
39 #include "llvm/Support/raw_ostream.h"
40 
41 #define DEBUG_TYPE "objc-arc-expand"
42 
43 namespace llvm {
44   class Module;
45 }
46 
47 using namespace llvm;
48 using namespace llvm::objcarc;
49 
50 namespace {
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;
ObjCARCExpand()62     ObjCARCExpand() : FunctionPass(ID) {
63       initializeObjCARCExpandPass(*PassRegistry::getPassRegistry());
64     }
65   };
66 }
67 
68 char ObjCARCExpand::ID = 0;
69 INITIALIZE_PASS(ObjCARCExpand,
70                 "objc-arc-expand", "ObjC ARC expansion", false, false)
71 
createObjCARCExpandPass()72 Pass *llvm::createObjCARCExpandPass() {
73   return new ObjCARCExpand();
74 }
75 
getAnalysisUsage(AnalysisUsage & AU) const76 void ObjCARCExpand::getAnalysisUsage(AnalysisUsage &AU) const {
77   AU.setPreservesCFG();
78 }
79 
doInitialization(Module & M)80 bool ObjCARCExpand::doInitialization(Module &M) {
81   Run = ModuleHasARC(M);
82   return false;
83 }
84 
runOnFunction(Function & F)85 bool 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 (GetBasicARCInstKind(Inst)) {
103     case ARCInstKind::Retain:
104     case ARCInstKind::RetainRV:
105     case ARCInstKind::Autorelease:
106     case ARCInstKind::AutoreleaseRV:
107     case ARCInstKind::FusedRetainAutorelease:
108     case ARCInstKind::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