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//===- ObjCARCExpand.cpp - ObjC ARC Optimization --------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
/// \file
/// This file defines ObjC ARC optimizations. ARC stands for Automatic
/// Reference Counting and is a system for managing reference counts for objects
/// in Objective C.
///
/// This specific file deals with early optimizations which perform certain
/// cleanup operations.
///
/// WARNING: This file knows about certain library functions. It recognizes them
/// by name, and hardwires knowledge of their semantics.
///
/// WARNING: This file knows about how certain Objective-C library functions are
/// used. Naive LLVM IR transformations which would otherwise be
/// behavior-preserving may break these assumptions.
///
//===----------------------------------------------------------------------===//
#include "ObjCARC.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/Value.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/PassRegistry.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/ObjCARC.h"
#define DEBUG_TYPE "objc-arc-expand"
using namespace llvm;
using namespace llvm::objcarc;
namespace {
static bool runImpl(Function &F) {
if (!EnableARCOpts)
return false;
// If nothing in the Module uses ARC, don't do anything.
if (!ModuleHasARC(*F.getParent()))
return false;
bool Changed = false;
LLVM_DEBUG(dbgs() << "ObjCARCExpand: Visiting Function: " << F.getName()
<< "\n");
for (Instruction &Inst : instructions(&F)) {
LLVM_DEBUG(dbgs() << "ObjCARCExpand: Visiting: " << Inst << "\n");
switch (GetBasicARCInstKind(&Inst)) {
case ARCInstKind::Retain:
case ARCInstKind::RetainRV:
case ARCInstKind::Autorelease:
case ARCInstKind::AutoreleaseRV:
case ARCInstKind::FusedRetainAutorelease:
case ARCInstKind::FusedRetainAutoreleaseRV: {
// These calls return their argument verbatim, as a low-level
// optimization. However, this makes high-level optimizations
// harder. Undo any uses of this optimization that the front-end
// emitted here. We'll redo them in the contract pass.
Changed = true;
Value *Value = cast<CallInst>(&Inst)->getArgOperand(0);
LLVM_DEBUG(dbgs() << "ObjCARCExpand: Old = " << Inst
<< "\n"
" New = "
<< *Value << "\n");
Inst.replaceAllUsesWith(Value);
break;
}
default:
break;
}
}
LLVM_DEBUG(dbgs() << "ObjCARCExpand: Finished List.\n\n");
return Changed;
}
/// Early ARC transformations.
class ObjCARCExpand : public FunctionPass {
void getAnalysisUsage(AnalysisUsage &AU) const override;
bool runOnFunction(Function &F) override;
public:
static char ID;
ObjCARCExpand() : FunctionPass(ID) {
initializeObjCARCExpandPass(*PassRegistry::getPassRegistry());
}
};
} // namespace
char ObjCARCExpand::ID = 0;
INITIALIZE_PASS(ObjCARCExpand, "objc-arc-expand", "ObjC ARC expansion", false,
false)
Pass *llvm::createObjCARCExpandPass() { return new ObjCARCExpand(); }
void ObjCARCExpand::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
}
bool ObjCARCExpand::runOnFunction(Function &F) { return runImpl(F); }
PreservedAnalyses ObjCARCExpandPass::run(Function &F,
FunctionAnalysisManager &AM) {
if (!runImpl(F))
return PreservedAnalyses::all();
PreservedAnalyses PA;
PA.preserveSet<CFGAnalyses>();
return PA;
}
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