text: /*
   * Copyright (C) 2014 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   *
   * Modified by Intel Corporation
   *
   */
  #include <iostream>
  
  #include "parallel_move_resolver.h"
  #include "nodes.h"
  
  namespace art {
  
  void ParallelMoveResolver::BuildInitialMoveList(HParallelMove* parallel_move) {
    // Perform a linear sweep of the moves to add them to the initial list of
    // moves to perform, ignoring any move that is redundant (the source is
    // the same as the destination, the destination is ignored and
    // unallocated, or the move was already eliminated).
    for (size_t i = 0; i < parallel_move->NumMoves(); ++i) {
      MoveOperands* move = parallel_move->MoveOperandsAt(i);
      if (!move->IsRedundant()) {
        moves_.Add(move);
      }
    }
  }
  
  void ParallelMoveResolverWithSwap::EmitNativeCode(HParallelMove* parallel_move) {
    DCHECK(moves_.IsEmpty());
    // Build up a worklist of moves.
    BuildInitialMoveList(parallel_move);
  
    // Move stack/stack slot to take advantage of a free register on constrained machines.
    for (size_t i = 0; i < moves_.Size(); ++i) {
      const MoveOperands& move = *moves_.Get(i);
      // Ignore constants and moves already eliminated.
      if (move.IsEliminated() || move.GetSource().IsConstant()) {
        continue;
      }
  
      if ((move.GetSource().IsStackSlot() || move.GetSource().IsDoubleStackSlot()) &&
          (move.GetDestination().IsStackSlot() || move.GetDestination().IsDoubleStackSlot())) {
        PerformMove(i);
      }
    }
  
    for (size_t i = 0; i < moves_.Size(); ++i) {
      const MoveOperands& move = *moves_.Get(i);
      // Skip constants to perform them last.  They don't block other moves
      // and skipping such moves with register destinations keeps those
      // registers free for the whole algorithm.
      if (!move.IsEliminated() && !move.GetSource().IsConstant()) {
        PerformMove(i);
      }
    }
  
    // Perform the moves with constant sources.
    for (size_t i = 0; i < moves_.Size(); ++i) {
      MoveOperands* move = moves_.Get(i);
      if (!move->IsEliminated()) {
        DCHECK(move->GetSource().IsConstant());
        EmitMove(i);
        // Eliminate the move, in case following moves need a scratch register.
        move->Eliminate();
      }
    }
  
    moves_.Reset();
  }
  
  Location LowOf(Location location) {
    if (location.IsRegisterPair()) {
      return Location::RegisterLocation(location.low());
    } else if (location.IsFpuRegisterPair()) {
      return Location::FpuRegisterLocation(location.low());
    } else if (location.IsDoubleStackSlot()) {
      return Location::StackSlot(location.GetStackIndex());
    } else {
      return Location::NoLocation();
    }
  }
  
  Location HighOf(Location location) {
    if (location.IsRegisterPair()) {
      return Location::RegisterLocation(location.high());
    } else if (location.IsFpuRegisterPair()) {
      return Location::FpuRegisterLocation(location.high());
    } else if (location.IsDoubleStackSlot()) {
      return Location::StackSlot(location.GetHighStackIndex(4));
    } else {
      return Location::NoLocation();
    }
  }
  
  // Update the source of `move`, knowing that `updated_location` has been swapped
  // with `new_source`. Note that `updated_location` can be a pair, therefore if
  // `move` is non-pair, we need to extract which register to use.
  static void UpdateSourceOf(MoveOperands* move, Location updated_location, Location new_source) {
    Location source = move->GetSource();
    if (LowOf(updated_location).Equals(source)) {
      move->SetSource(LowOf(new_source));
    } else if (HighOf(updated_location).Equals(source)) {
      move->SetSource(HighOf(new_source));
    } else {
      DCHECK(updated_location.Equals(source)) << updated_location << " " << source;
      move->SetSource(new_source);
    }
  }
  
  MoveOperands* ParallelMoveResolverWithSwap::PerformMove(size_t index) {
    // Each call to this function performs a move and deletes it from the move
    // graph.  We first recursively perform any move blocking this one.  We
    // mark a move as "pending" on entry to PerformMove in order to detect
    // cycles in the move graph.  We use operand swaps to resolve cycles,
    // which means that a call to PerformMove could change any source operand
    // in the move graph.
  
    MoveOperands* move = moves_.Get(index);
    DCHECK(!move->IsPending());
    if (move->IsRedundant()) {
      // Because we swap register pairs first, following, un-pending
      // moves may become redundant.
      move->Eliminate();
      return nullptr;
    }
  
    // Clear this move's destination to indicate a pending move.  The actual
    // destination is saved in a stack-allocated local.  Recursion may allow
    // multiple moves to be pending.
    DCHECK(!move->GetSource().IsInvalid());
    Location destination = move->MarkPending();
  
    // Perform a depth-first traversal of the move graph to resolve
    // dependencies.  Any unperformed, unpending move with a source the same
    // as this one's destination blocks this one so recursively perform all
    // such moves.
    MoveOperands* required_swap = nullptr;
    for (size_t i = 0; i < moves_.Size(); ++i) {
      const MoveOperands& other_move = *moves_.Get(i);
      if (other_move.Blocks(destination) && !other_move.IsPending()) {
        // Though PerformMove can change any source operand in the move graph,
        // calling `PerformMove` cannot create a blocking move via a swap
        // (this loop does not miss any).
        // For example, assume there is a non-blocking move with source A
        // and this move is blocked on source B and there is a swap of A and
        // B.  Then A and B must be involved in the same cycle (or they would
        // not be swapped).  Since this move's destination is B and there is
        // only a single incoming edge to an operand, this move must also be
        // involved in the same cycle.  In that case, the blocking move will
        // be created but will be "pending" when we return from PerformMove.
        required_swap = PerformMove(i);
  
        if (required_swap == move) {
          // If this move is required to swap, we do so without looking
          // at the next moves. Swapping is not blocked by anything, it just
          // updates other moves's source.
          break;
        } else if (required_swap == moves_.Get(i)) {
          // If `other_move` was swapped, we iterate again to find a new
          // potential cycle.
          required_swap = nullptr;
          i = 0;
        } else if (required_swap != nullptr) {
          // A move is required to swap. We walk back the cycle to find the
          // move by just returning from this `PerforrmMove`.
          moves_.Get(index)->ClearPending(destination);
          return required_swap;
        }
      }
    }
  
    // We are about to resolve this move and don't need it marked as
    // pending, so restore its destination.
    move->ClearPending(destination);
  
    // This move's source may have changed due to swaps to resolve cycles and
    // so it may now be the last move in the cycle.  If so remove it.
    if (move->GetSource().Equals(destination)) {
      move->Eliminate();
      DCHECK(required_swap == nullptr);
      return nullptr;
    }
  
    // The move may be blocked on a (at most one) pending move, in which case
    // we have a cycle.  Search for such a blocking move and perform a swap to
    // resolve it.
    bool do_swap = false;
    if (required_swap != nullptr) {
      DCHECK_EQ(required_swap, move);
      do_swap = true;
    } else {
      for (size_t i = 0; i < moves_.Size(); ++i) {
        const MoveOperands& other_move = *moves_.Get(i);
        if (other_move.Blocks(destination)) {
          DCHECK(other_move.IsPending());
          if (!move->Is64BitMove() && other_move.Is64BitMove()) {
            // We swap 64bits moves before swapping 32bits moves. Go back from the
            // cycle by returning the move that must be swapped.
            return moves_.Get(i);
          }
          do_swap = true;
          break;
        }
      }
    }
  
    if (do_swap) {
      EmitSwap(index);
      // Any unperformed (including pending) move with a source of either
      // this move's source or destination needs to have their source
      // changed to reflect the state of affairs after the swap.
      Location source = move->GetSource();
      Location swap_destination = move->GetDestination();
      move->Eliminate();
      for (size_t i = 0; i < moves_.Size(); ++i) {
        const MoveOperands& other_move = *moves_.Get(i);
        if (other_move.Blocks(source)) {
          UpdateSourceOf(moves_.Get(i), source, swap_destination);
        } else if (other_move.Blocks(swap_destination)) {
          UpdateSourceOf(moves_.Get(i), swap_destination, source);
        }
      }
      // If the swap was required because of a 64bits move in the middle of a cycle,
      // we return the swapped move, so that the caller knows it needs to re-iterate
      // its dependency loop.
      return required_swap;
    } else {
      // This move is not blocked.
      EmitMove(index);
      move->Eliminate();
      DCHECK(required_swap == nullptr);
      return nullptr;
    }
  }
  
  bool ParallelMoveResolverWithSwap::IsScratchLocation(Location loc) {
    for (size_t i = 0; i < moves_.Size(); ++i) {
      if (moves_.Get(i)->Blocks(loc)) {
        return false;
      }
    }
  
    for (size_t i = 0; i < moves_.Size(); ++i) {
      if (moves_.Get(i)->GetDestination().Equals(loc)) {
        return true;
      }
    }
  
    return false;
  }
  
  int ParallelMoveResolverWithSwap::AllocateScratchRegister(int blocked,
                                                            int register_count,
                                                            int if_scratch,
                                                            bool* spilled) {
    DCHECK_NE(blocked, if_scratch);
    int scratch = -1;
    for (int reg = 0; reg < register_count; ++reg) {
      if ((blocked != reg) && IsScratchLocation(Location::RegisterLocation(reg))) {
        scratch = reg;
        break;
      }
    }
  
    if (scratch == -1) {
      *spilled = true;
      scratch = if_scratch;
    } else {
      *spilled = false;
    }
  
    return scratch;
  }
  
  
  ParallelMoveResolverWithSwap::ScratchRegisterScope::ScratchRegisterScope(
      ParallelMoveResolverWithSwap* resolver, int blocked, int if_scratch, int number_of_registers)
      : resolver_(resolver),
        reg_(kNoRegister),
        spilled_(false) {
    reg_ = resolver_->AllocateScratchRegister(blocked, number_of_registers, if_scratch, &spilled_);
  
    if (spilled_) {
      resolver->SpillScratch(reg_);
    }
  }
  
  
  ParallelMoveResolverWithSwap::ScratchRegisterScope::~ScratchRegisterScope() {
    if (spilled_) {
      resolver_->RestoreScratch(reg_);
    }
  }
  
  void ParallelMoveResolverNoSwap::EmitNativeCode(HParallelMove* parallel_move) {
    DCHECK_EQ(GetNumberOfPendingMoves(), 0u);
    DCHECK(moves_.IsEmpty());
    DCHECK(scratches_.IsEmpty());
  
    // Backend dependent initialization.
    PrepareForEmitNativeCode();
  
    // Build up a worklist of moves.
    BuildInitialMoveList(parallel_move);
  
    for (size_t i = 0; i < moves_.Size(); ++i) {
      const MoveOperands& move = *moves_.Get(i);
      // Skip constants to perform them last. They don't block other moves and
      // skipping such moves with register destinations keeps those registers
      // free for the whole algorithm.
      if (!move.IsEliminated() && !move.GetSource().IsConstant()) {
        PerformMove(i);
      }
    }
  
    // Perform the moves with constant sources and register destinations with UpdateMoveSource()
    // to reduce the number of literal loads. Stack destinations are skipped since we won't be benefit
    // from changing the constant sources to stack locations.
    for (size_t i = 0; i < moves_.Size(); ++i) {
      MoveOperands* move = moves_.Get(i);
      Location destination = move->GetDestination();
      if (!move->IsEliminated() && !destination.IsStackSlot() && !destination.IsDoubleStackSlot()) {
        Location source = move->GetSource();
        EmitMove(i);
        move->Eliminate();
        // This may introduce additional instruction dependency, but reduce number
        // of moves and possible literal loads. For example,
        // Original moves:
        //   1234.5678 -> D0
        //   1234.5678 -> D1
        // Updated moves:
        //   1234.5678 -> D0
        //   D0 -> D1
        UpdateMoveSource(source, destination);
      }
    }
  
    // Perform the rest of the moves.
    for (size_t i = 0; i < moves_.Size(); ++i) {
      MoveOperands* move = moves_.Get(i);
      if (!move->IsEliminated()) {
        EmitMove(i);
        move->Eliminate();
      }
    }
  
    // All pending moves that we have added for resolve cycles should be performed.
    DCHECK_EQ(GetNumberOfPendingMoves(), 0u);
  
    // Backend dependent cleanup.
    FinishEmitNativeCode();
  
    moves_.Reset();
    scratches_.Reset();
  }
  
  Location ParallelMoveResolverNoSwap::GetScratchLocation(Location::Kind kind) {
    for (size_t i = 0; i < scratches_.Size(); ++i) {
      Location loc = scratches_.Get(i);
      if (loc.GetKind() == kind && !IsBlockedByMoves(loc)) {
        return loc;
      }
    }
    for (size_t i = 0; i < moves_.Size(); ++i) {
      Location loc = moves_.Get(i)->GetDestination();
      if (loc.GetKind() == kind && !IsBlockedByMoves(loc)) {
        return loc;
      }
    }
    return Location::NoLocation();
  }
  
  void ParallelMoveResolverNoSwap::AddScratchLocation(Location loc) {
    if (kIsDebugBuild) {
      for (size_t i = 0; i < scratches_.Size(); ++i) {
        DCHECK(!loc.Equals(scratches_.Get(i)));
      }
    }
    scratches_.Add(loc);
  }
  
  void ParallelMoveResolverNoSwap::RemoveScratchLocation(Location loc) {
    DCHECK(!IsBlockedByMoves(loc));
    for (size_t i = 0; i < scratches_.Size(); ++i) {
      if (loc.Equals(scratches_.Get(i))) {
        scratches_.DeleteAt(i);
        break;
      }
    }
  }
  
  void ParallelMoveResolverNoSwap::PerformMove(size_t index) {
    // Each call to this function performs a move and deletes it from the move
    // graph. We first recursively perform any move blocking this one. We mark
    // a move as "pending" on entry to PerformMove in order to detect cycles
    // in the move graph. We use scratch location to resolve cycles, also
    // additional pending moves might be added. After move has been performed,
    // we will update source operand in the move graph to reduce dependencies in
    // the graph.
  
    MoveOperands* move = moves_.Get(index);
    DCHECK(!move->IsPending());
    DCHECK(!move->IsEliminated());
    if (move->IsRedundant()) {
      // Previous operations on the list of moves have caused this particular move
      // to become a no-op, so we can safely eliminate it. Consider for example
      // (0 -> 1) (1 -> 0) (1 -> 2). There is a cycle (0 -> 1) (1 -> 0), that we will
      // resolve as (1 -> scratch) (0 -> 1) (scratch -> 0). If, by chance, '2' is
      // used as the scratch location, the move (1 -> 2) will occur while resolving
      // the cycle. When that move is emitted, the code will update moves with a '1'
      // as their source to use '2' instead (see `UpdateMoveSource()`. In our example
      // the initial move (1 -> 2) would then become the no-op (2 -> 2) that can be
      // eliminated here.
      move->Eliminate();
      return;
    }
  
    // Clear this move's destination to indicate a pending move. The actual
    // destination is saved in a stack-allocated local. Recursion may allow
    // multiple moves to be pending.
    DCHECK(!move->GetSource().IsInvalid());
    Location destination = move->MarkPending();
  
    // Perform a depth-first traversal of the move graph to resolve
    // dependencies. Any unperformed, unpending move with a source the same
    // as this one's destination blocks this one so recursively perform all
    // such moves.
    for (size_t i = 0; i < moves_.Size(); ++i) {
      const MoveOperands& other_move = *moves_.Get(i);
      if (other_move.Blocks(destination) && !other_move.IsPending()) {
        PerformMove(i);
      }
    }
  
    // We are about to resolve this move and don't need it marked as
    // pending, so restore its destination.
    move->ClearPending(destination);
  
    // No one else should write to the move destination when the it is pending.
    DCHECK(!move->IsRedundant());
  
    Location source = move->GetSource();
    // The move may be blocked on several pending moves, in case we have a cycle.
    if (IsBlockedByMoves(destination)) {
      // For a cycle like: (A -> B) (B -> C) (C -> A), we change it to following
      // sequence:
      // (C -> scratch)     # Emit right now.
      // (A -> B) (B -> C)  # Unblocked.
      // (scratch -> A)     # Add to pending_moves_, blocked by (A -> B).
      Location::Kind kind = source.GetKind();
      DCHECK_NE(kind, Location::kConstant);
      Location scratch = AllocateScratchLocationFor(kind);
      // We only care about the move size.
      Primitive::Type type = move->Is64BitMove() ? Primitive::kPrimLong : Primitive::kPrimInt;
      // Perform (C -> scratch)
      move->SetDestination(scratch);
      EmitMove(index);
      move->Eliminate();
      UpdateMoveSource(source, scratch);
      // Add (scratch -> A).
      AddPendingMove(scratch, destination, type);
    } else {
      // This move is not blocked.
      EmitMove(index);
      move->Eliminate();
      UpdateMoveSource(source, destination);
    }
  
    // Moves in the pending list should not block any other moves. But performing
    // unblocked moves in the pending list can free scratch registers, so we do this
    // as early as possible.
    MoveOperands* pending_move;
    while ((pending_move = GetUnblockedPendingMove(source)) != nullptr) {
      Location pending_source = pending_move->GetSource();
      Location pending_destination = pending_move->GetDestination();
      // We do not depend on the pending move index. So just delete the move instead
      // of eliminating it to make the pending list cleaner.
      DeletePendingMove(pending_move);
      move->SetSource(pending_source);
      move->SetDestination(pending_destination);
      EmitMove(index);
      move->Eliminate();
      UpdateMoveSource(pending_source, pending_destination);
      // Free any unblocked locations in the scratch location list.
      for (size_t i = 0; i < scratches_.Size(); ++i) {
        Location scratch = scratches_.Get(i);
        // Only scratch overlapping with performed move source can be unblocked.
        if (scratch.OverlapsWith(pending_source) && !IsBlockedByMoves(scratch)) {
          FreeScratchLocation(pending_source);
        }
      }
    }
  }
  
  void ParallelMoveResolverNoSwap::UpdateMoveSource(Location from, Location to) {
    // This function is used to reduce the dependencies in the graph after
    // (from -> to) has been performed. Since we ensure there is no move with the same
    // destination, (to -> X) can not be blocked while (from -> X) might still be
    // blocked. Consider for example the moves (0 -> 1) (1 -> 2) (1 -> 3). After
    // (1 -> 2) has been performed, the moves left are (0 -> 1) and (1 -> 3). There is
    // a dependency between the two. If we update the source location from 1 to 2, we
    // will get (0 -> 1) and (2 -> 3). There is no dependency between the two.
    //
    // This is not something we must do, but we can use fewer scratch locations with
    // this trick. For example, we can avoid using additional scratch locations for
    // moves (0 -> 1), (1 -> 2), (1 -> 0).
    for (size_t i = 0; i < moves_.Size(); ++i) {
      MoveOperands* move = moves_.Get(i);
      if (move->GetSource().Equals(from)) {
        move->SetSource(to);
      }
    }
  }
  
  void ParallelMoveResolverNoSwap::AddPendingMove(Location source,
      Location destination, Primitive::Type type) {
    pending_moves_.Add(new (allocator_) MoveOperands(source, destination, type, nullptr));
  }
  
  void ParallelMoveResolverNoSwap::DeletePendingMove(MoveOperands* move) {
    pending_moves_.Delete(move);
  }
  
  MoveOperands* ParallelMoveResolverNoSwap::GetUnblockedPendingMove(Location loc) {
    for (size_t i = 0; i < pending_moves_.Size(); ++i) {
      MoveOperands* move = pending_moves_.Get(i);
      Location destination = move->GetDestination();
      // Only moves with destination overlapping with input loc can be unblocked.
      if (destination.OverlapsWith(loc) && !IsBlockedByMoves(destination)) {
        return move;
      }
    }
    return nullptr;
  }
  
  bool ParallelMoveResolverNoSwap::IsBlockedByMoves(Location loc) {
    for (size_t i = 0; i < pending_moves_.Size(); ++i) {
      if (pending_moves_.Get(i)->Blocks(loc)) {
        return true;
      }
    }
    for (size_t i = 0; i < moves_.Size(); ++i) {
      if (moves_.Get(i)->Blocks(loc)) {
        return true;
      }
    }
    return false;
  }
  
  // So far it is only used for debugging purposes to make sure all pending moves
  // have been performed.
  size_t ParallelMoveResolverNoSwap::GetNumberOfPendingMoves() {
    return pending_moves_.Size();
  }
  
  }  // namespace art
  