llvm/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 "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 }