lib/Transforms/ObjCARC/ObjCARCExpand.cpp

   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 "ObjCARC.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/Value.h"
  31 #include "llvm/Pass.h"
  32 #include "llvm/PassAnalysisSupport.h"
  33 #include "llvm/PassRegistry.h"
  34 #include "llvm/PassSupport.h"
  35 #include "llvm/Support/Casting.h"
  36 #include "llvm/Support/Debug.h"
  37 #include "llvm/Support/raw_ostream.h"
  38
  39 #define DEBUG_TYPE "objc-arc-expand"
  40
  41 namespace llvm {
  42   class Module;
  43 }
  44
  45 using namespace llvm;
  46 using namespace llvm::objcarc;
  47
  48 namespace {
  49   /// Early ARC transformations.
  50   class ObjCARCExpand : public FunctionPass {
  51     void getAnalysisUsage(AnalysisUsage &AU) const override;
  52     bool doInitialization(Module &M) override;
  53     bool runOnFunction(Function &F) override;
  54
  55     /// A flag indicating whether this optimization pass should run.
  56     bool Run;
  57
  58   public:
  59     static char ID;
  60     ObjCARCExpand() : FunctionPass(ID) {
  61       initializeObjCARCExpandPass(*PassRegistry::getPassRegistry());
  62     }
  63   };
  64 }
  65
  66 char ObjCARCExpand::ID = 0;
  67 INITIALIZE_PASS(ObjCARCExpand,
  68                 "objc-arc-expand", "ObjC ARC expansion", false, false)
  69
  70 Pass *llvm::createObjCARCExpandPass() {
  71   return new ObjCARCExpand();
  72 }
  73
  74 void ObjCARCExpand::getAnalysisUsage(AnalysisUsage &AU) const {
  75   AU.setPreservesCFG();
  76 }
  77
  78 bool ObjCARCExpand::doInitialization(Module &M) {
  79   Run = ModuleHasARC(M);
  80   return false;
  81 }
  82
  83 bool ObjCARCExpand::runOnFunction(Function &F) {
  84   if (!EnableARCOpts)
  85     return false;
  86
  87   // If nothing in the Module uses ARC, don't do anything.
  88   if (!Run)
  89     return false;
  90
  91   bool Changed = false;
  92
  93   LLVM_DEBUG(dbgs() << "ObjCARCExpand: Visiting Function: " << F.getName()
  94                     << "\n");
  95
  96   for (inst_iterator I = inst_begin(&F), E = inst_end(&F); I != E; ++I) {
  97     Instruction *Inst = &*I;
  98
  99     LLVM_DEBUG(dbgs() << "ObjCARCExpand: Visiting: " << *Inst << "\n");
 100
 101     switch (GetBasicARCInstKind(Inst)) {
 102     case ARCInstKind::Retain:
 103     case ARCInstKind::RetainRV:
 104     case ARCInstKind::Autorelease:
 105     case ARCInstKind::AutoreleaseRV:
 106     case ARCInstKind::FusedRetainAutorelease:
 107     case ARCInstKind::FusedRetainAutoreleaseRV: {
 108       // These calls return their argument verbatim, as a low-level
 109       // optimization. However, this makes high-level optimizations
 110       // harder. Undo any uses of this optimization that the front-end
 111       // emitted here. We'll redo them in the contract pass.
 112       Changed = true;
 113       Value *Value = cast<CallInst>(Inst)->getArgOperand(0);
 114       LLVM_DEBUG(dbgs() << "ObjCARCExpand: Old = " << *Inst
 115                         << "\n"
 116                            "               New = "
 117                         << *Value << "\n");
 118       Inst->replaceAllUsesWith(Value);
 119       break;
 120     }
 121     default:
 122       break;
 123     }
 124   }
 125
 126   LLVM_DEBUG(dbgs() << "ObjCARCExpand: Finished List.\n\n");
 127
 128   return Changed;
 129 }