1 //===- ObjCARC.h - ObjC ARC Optimization --------------*- C++ -*-----------===//
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 common definitions/declarations used by the ObjC ARC
11 /// Optimizer. ARC stands for Automatic Reference Counting and is a system for
12 /// managing reference counts for objects in Objective C.
13 ///
14 /// WARNING: This file knows about certain library functions. It recognizes them
15 /// by name, and hardwires knowledge of their semantics.
16 ///
17 /// WARNING: This file knows about how certain Objective-C library functions are
18 /// used. Naive LLVM IR transformations which would otherwise be
19 /// behavior-preserving may break these assumptions.
20 ///
21 //===----------------------------------------------------------------------===//
22 
23 #ifndef LLVM_LIB_TRANSFORMS_OBJCARC_OBJCARC_H
24 #define LLVM_LIB_TRANSFORMS_OBJCARC_OBJCARC_H
25 
26 #include "llvm/ADT/StringSwitch.h"
27 #include "llvm/ADT/Optional.h"
28 #include "llvm/Analysis/AliasAnalysis.h"
29 #include "llvm/Analysis/ObjCARCAnalysisUtils.h"
30 #include "llvm/Analysis/ObjCARCInstKind.h"
31 #include "llvm/Analysis/Passes.h"
32 #include "llvm/Analysis/ValueTracking.h"
33 #include "llvm/IR/CallSite.h"
34 #include "llvm/IR/InstIterator.h"
35 #include "llvm/IR/Module.h"
36 #include "llvm/Pass.h"
37 #include "llvm/Transforms/ObjCARC.h"
38 #include "llvm/Transforms/Utils/Local.h"
39 
40 namespace llvm {
41 class raw_ostream;
42 }
43 
44 namespace llvm {
45 namespace objcarc {
46 
47 /// \brief Erase the given instruction.
48 ///
49 /// Many ObjC calls return their argument verbatim,
50 /// so if it's such a call and the return value has users, replace them with the
51 /// argument value.
52 ///
EraseInstruction(Instruction * CI)53 static inline void EraseInstruction(Instruction *CI) {
54   Value *OldArg = cast<CallInst>(CI)->getArgOperand(0);
55 
56   bool Unused = CI->use_empty();
57 
58   if (!Unused) {
59     // Replace the return value with the argument.
60     assert((IsForwarding(GetBasicARCInstKind(CI)) ||
61             (IsNoopOnNull(GetBasicARCInstKind(CI)) &&
62              isa<ConstantPointerNull>(OldArg))) &&
63            "Can't delete non-forwarding instruction with users!");
64     CI->replaceAllUsesWith(OldArg);
65   }
66 
67   CI->eraseFromParent();
68 
69   if (Unused)
70     RecursivelyDeleteTriviallyDeadInstructions(OldArg);
71 }
72 
73 } // end namespace objcarc
74 } // end namespace llvm
75 
76 #endif
77