swift-mirror/lib/SILOptimizer/Transforms/OwnershipModelEliminator.cpp

//===- OwnershipModelEliminator.cpp - Eliminate SILOwnership Instructions -===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
///
///  \file
///
///  This file contains a small pass that lowers SIL ownership instructions to
///  their constituant operations. This will enable us to separate
///  implementation
///  of Semantic ARC in SIL and SILGen from ensuring that all of the optimizer
///  passes respect Semantic ARC. This is done by running this pass right after
///  SILGen and as the pass pipeline is updated, moving this pass further and
///  further back in the pipeline.
///
//===----------------------------------------------------------------------===//

#define DEBUG_TYPE "sil-ownership-model-eliminator"
#include "swift/SILOptimizer/PassManager/Transforms.h"
#include "swift/SIL/SILBuilder.h"
#include "swift/SIL/SILFunction.h"

using namespace swift;

//===----------------------------------------------------------------------===//
//                               Implementation
//===----------------------------------------------------------------------===//

namespace {

struct OwnershipModelEliminator : SILFunctionTransform {

  bool processLoad(SILBuilder &B, LoadInst *LI) {
    auto Qualifier = LI->getOwnershipQualifier();

    // If the qualifier is unqualified, there is nothing further to do
    // here. Just return.
    if (Qualifier == LoadOwnershipQualifier::Unqualified)
      return false;

    // Otherwise, we need to break down the load inst into its unqualified
    // components.
    B.setInsertionPoint(LI);
    B.setCurrentDebugScope(LI->getDebugScope());
    auto *UnqualifiedLoad = B.createLoad(LI->getLoc(), LI->getOperand());

    // If we have a copy, insert a retain_value. All other copies do not require
    // more work.
    if (Qualifier == LoadOwnershipQualifier::Copy) {
      B.createRetainValue(UnqualifiedLoad->getLoc(), UnqualifiedLoad,
                          Atomicity::Atomic);
    }

    // Then remove the qualified load and use the unqualified load as the def of
    // all of LI's uses.
    LI->replaceAllUsesWith(UnqualifiedLoad);
    LI->removeFromParent();
    return true;
  }

  bool processStore(SILBuilder &B, StoreInst *SI) {
    auto Qualifier = SI->getOwnershipQualifier();

    // If the qualifier is unqualified, there is nothing further to do
    // here. Just return.
    if (Qualifier == StoreOwnershipQualifier::Unqualified)
      return false;

    // Otherwise, we need to break down the load.
    B.setInsertionPoint(SI);
    B.setCurrentDebugScope(SI->getDebugScope());

    if (Qualifier != StoreOwnershipQualifier::Assign) {
      // If the ownership qualifier is not an assign, we can just emit an
      // unqualified store.
      B.createStore(SI->getLoc(), SI->getSrc(), SI->getDest());
    } else {
      // If the ownership qualifier is [assign], then we need to eliminate the
      // old value.
      //
      // 1. Load old value.
      // 2. Store new value.
      // 3. Release old value.
      auto *Old = B.createLoad(SI->getLoc(), SI->getDest());
      B.createStore(SI->getLoc(), SI->getSrc(), SI->getDest());
      B.createReleaseValue(SI->getLoc(), Old, Atomicity::Atomic);
    }

    // Then remove the qualified store.
    SI->removeFromParent();
    return true;
  }

  void run() override {
    bool MadeChange = false;
    SILFunction *F = getFunction();
    SILBuilder B(*F);
    for (auto &BB : *F) {
      for (auto II = BB.begin(), IE = BB.end(); II != IE;) {
        // Since we are going to be potentially removing instructions, we need
        // to make sure to grab out instruction and increment first.
        SILInstruction *I = &*II;
        ++II;

        if (auto *LI = dyn_cast<LoadInst>(I)) {
          MadeChange |= processLoad(B, LI);
          continue;
        }

        auto *SI = dyn_cast<StoreInst>(I);
        if (!SI)
          continue;

        MadeChange |= processStore(B, SI);
      }
    }

    if (MadeChange) {
      // If we made any changes, we just changed instructions, so invalidate
      // that analysis.
      invalidateAnalysis(SILAnalysis::InvalidationKind::Instructions);
    }
  }

  StringRef getName() override { return "Ownership Model Eliminator"; }
};

} // end anonymous namespace

//===----------------------------------------------------------------------===//
//                           Top Level Entry Point
//===----------------------------------------------------------------------===//

SILTransform *swift::createOwnershipModelEliminator() {
  return new OwnershipModelEliminator();
}