CSE2410 Fall 2014 Bounce

// Copyright 2012 the V8 project authors. All rights reserved.

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#include "v8.h"

#include "arm/lithium-gap-resolver-arm.h"

#include "arm/lithium-codegen-arm.h"

namespace v8 {

namespace internal {

static const Register kSavedValueRegister = { 9 };

LGapResolver::LGapResolver(LCodeGen* owner)

    : cgen_(owner), moves_(32, owner->zone()), root_index_(0), in_cycle_(false),

      saved_destination_(NULL) { }

void LGapResolver::Resolve(LParallelMove* parallel_move) {

  ASSERT(moves_.is_empty());

  // Build up a worklist of moves.

  BuildInitialMoveList(parallel_move);

  for (int i = 0; i < moves_.length(); ++i) {

    LMoveOperands move = moves_[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.source()->IsConstantOperand()) {

      root_index_ = i;  // Any cycle is found when by reaching this move again.

      PerformMove(i);

      if (in_cycle_) {

        RestoreValue();

      }

    }

  }

  // Perform the moves with constant sources.

  for (int i = 0; i < moves_.length(); ++i) {

    if (!moves_[i].IsEliminated()) {

      ASSERT(moves_[i].source()->IsConstantOperand());

      EmitMove(i);

    }

  }

  moves_.Rewind(0);

}

void LGapResolver::BuildInitialMoveList(LParallelMove* 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).

  const ZoneList<LMoveOperands>* moves = parallel_move->move_operands();

  for (int i = 0; i < moves->length(); ++i) {

    LMoveOperands move = moves->at(i);

    if (!move.IsRedundant()) moves_.Add(move, cgen_->zone());

  }

  Verify();

}

void LGapResolver::PerformMove(int 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 can only find a cycle, when doing a depth-first traversal of moves,

  // be encountering the starting move again. So by spilling the source of

  // the starting move, we break the cycle.  All moves are then unblocked,

  // and the starting move is completed by writing the spilled value to

  // its destination.  All other moves from the spilled source have been

  // completed prior to breaking the cycle.

  // An additional complication is that moves to MemOperands with large

  // offsets (more than 1K or 4K) require us to spill this spilled value to

  // the stack, to free up the register.

  ASSERT(!moves_[index].IsPending());

  ASSERT(!moves_[index].IsRedundant());

  // Clear this move's destination to indicate a pending move.  The actual

  // destination is saved in a stack allocated local.  Multiple moves can

  // be pending because this function is recursive.

  ASSERT(moves_[index].source() != NULL);  // Or else it will look eliminated.

  LOperand* destination = moves_[index].destination();

  moves_[index].set_destination(NULL);

  // 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 (int i = 0; i < moves_.length(); ++i) {

    LMoveOperands other_move = moves_[i];

    if (other_move.Blocks(destination) && !other_move.IsPending()) {

      PerformMove(i);

      // If there is a blocking, pending move it must be moves_[root_index_]

      // and all other moves with the same source as moves_[root_index_] are

      // sucessfully executed (because they are cycle-free) by this loop.

    }

  }

  // We are about to resolve this move and don't need it marked as

  // pending, so restore its destination.

  moves_[index].set_destination(destination);

  // The move may be blocked on a pending move, which must be the starting move.

  // In this case, we have a cycle, and we save the source of this move to

  // a scratch register to break it.

  LMoveOperands other_move = moves_[root_index_];

  if (other_move.Blocks(destination)) {

    ASSERT(other_move.IsPending());

    BreakCycle(index);

    return;

  }

  // This move is no longer blocked.

  EmitMove(index);

}

void LGapResolver::Verify() {

#ifdef ENABLE_SLOW_ASSERTS

  // No operand should be the destination for more than one move.

  for (int i = 0; i < moves_.length(); ++i) {

    LOperand* destination = moves_[i].destination();

    for (int j = i + 1; j < moves_.length(); ++j) {

      SLOW_ASSERT(!destination->Equals(moves_[j].destination()));

    }

  }

#endif

}

#define __ ACCESS_MASM(cgen_->masm())

void LGapResolver::BreakCycle(int index) {

  // We save in a register the value that should end up in the source of

  // moves_[root_index].  After performing all moves in the tree rooted

  // in that move, we save the value to that source.

  ASSERT(moves_[index].destination()->Equals(moves_[root_index_].source()));

  ASSERT(!in_cycle_);

  in_cycle_ = true;

  LOperand* source = moves_[index].source();

  saved_destination_ = moves_[index].destination();

  if (source->IsRegister()) {

    __ mov(kSavedValueRegister, cgen_->ToRegister(source));

  } else if (source->IsStackSlot()) {

    __ ldr(kSavedValueRegister, cgen_->ToMemOperand(source));

  } else if (source->IsDoubleRegister()) {

    __ vmov(kScratchDoubleReg, cgen_->ToDoubleRegister(source));

  } else if (source->IsDoubleStackSlot()) {

    __ vldr(kScratchDoubleReg, cgen_->ToMemOperand(source));

  } else {

    UNREACHABLE();

  }

  // This move will be done by restoring the saved value to the destination.

  moves_[index].Eliminate();

}

void LGapResolver::RestoreValue() {

  ASSERT(in_cycle_);

  ASSERT(saved_destination_ != NULL);

  // Spilled value is in kSavedValueRegister or kSavedDoubleValueRegister.

  if (saved_destination_->IsRegister()) {

    __ mov(cgen_->ToRegister(saved_destination_), kSavedValueRegister);

  } else if (saved_destination_->IsStackSlot()) {

    __ str(kSavedValueRegister, cgen_->ToMemOperand(saved_destination_));

  } else if (saved_destination_->IsDoubleRegister()) {

    __ vmov(cgen_->ToDoubleRegister(saved_destination_), kScratchDoubleReg);

  } else if (saved_destination_->IsDoubleStackSlot()) {

    __ vstr(kScratchDoubleReg, cgen_->ToMemOperand(saved_destination_));

  } else {

    UNREACHABLE();

  }

  in_cycle_ = false;

  saved_destination_ = NULL;

}

void LGapResolver::EmitMove(int index) {

  LOperand* source = moves_[index].source();

  LOperand* destination = moves_[index].destination();

  // Dispatch on the source and destination operand kinds.  Not all

  // combinations are possible.

  if (source->IsRegister()) {

    Register source_register = cgen_->ToRegister(source);

    if (destination->IsRegister()) {

      __ mov(cgen_->ToRegister(destination), source_register);

    } else {

      ASSERT(destination->IsStackSlot());

      __ str(source_register, cgen_->ToMemOperand(destination));

    }

  } else if (source->IsStackSlot()) {

    MemOperand source_operand = cgen_->ToMemOperand(source);

    if (destination->IsRegister()) {

      __ ldr(cgen_->ToRegister(destination), source_operand);

    } else {

      ASSERT(destination->IsStackSlot());

      MemOperand destination_operand = cgen_->ToMemOperand(destination);

      if (in_cycle_) {

        if (!destination_operand.OffsetIsUint12Encodable()) {

          // ip is overwritten while saving the value to the destination.

          // Therefore we can't use ip.  It is OK if the read from the source

          // destroys ip, since that happens before the value is read.

          __ vldr(kScratchDoubleReg.low(), source_operand);

          __ vstr(kScratchDoubleReg.low(), destination_operand);

        } else {

          __ ldr(ip, source_operand);

          __ str(ip, destination_operand);

        }

      } else {

        __ ldr(kSavedValueRegister, source_operand);

        __ str(kSavedValueRegister, destination_operand);

      }

    }

  } else if (source->IsConstantOperand()) {

    LConstantOperand* constant_source = LConstantOperand::cast(source);

    if (destination->IsRegister()) {

      Register dst = cgen_->ToRegister(destination);

      Representation r = cgen_->IsSmi(constant_source)

          ? Representation::Smi() : Representation::Integer32();

      if (cgen_->IsInteger32(constant_source)) {

        __ mov(dst, Operand(cgen_->ToRepresentation(constant_source, r)));

      } else {

        __ Move(dst, cgen_->ToHandle(constant_source));

      }

    } else if (destination->IsDoubleRegister()) {

      DwVfpRegister result = cgen_->ToDoubleRegister(destination);

      double v = cgen_->ToDouble(constant_source);

      __ Vmov(result, v, ip);

    } else {

      ASSERT(destination->IsStackSlot());

      ASSERT(!in_cycle_);  // Constant moves happen after all cycles are gone.

      Representation r = cgen_->IsSmi(constant_source)

          ? Representation::Smi() : Representation::Integer32();

      if (cgen_->IsInteger32(constant_source)) {

        __ mov(kSavedValueRegister,

               Operand(cgen_->ToRepresentation(constant_source, r)));

      } else {

        __ Move(kSavedValueRegister,

                      cgen_->ToHandle(constant_source));

      }

      __ str(kSavedValueRegister, cgen_->ToMemOperand(destination));

    }

  } else if (source->IsDoubleRegister()) {

    DwVfpRegister source_register = cgen_->ToDoubleRegister(source);

    if (destination->IsDoubleRegister()) {

      __ vmov(cgen_->ToDoubleRegister(destination), source_register);

    } else {

      ASSERT(destination->IsDoubleStackSlot());

      __ vstr(source_register, cgen_->ToMemOperand(destination));

    }

  } else if (source->IsDoubleStackSlot()) {

    MemOperand source_operand = cgen_->ToMemOperand(source);

    if (destination->IsDoubleRegister()) {

      __ vldr(cgen_->ToDoubleRegister(destination), source_operand);

    } else {

      ASSERT(destination->IsDoubleStackSlot());

      MemOperand destination_operand = cgen_->ToMemOperand(destination);

      if (in_cycle_) {

        // kSavedDoubleValueRegister was used to break the cycle,

        // but kSavedValueRegister is free.

        MemOperand source_high_operand =

            cgen_->ToHighMemOperand(source);

        MemOperand destination_high_operand =

            cgen_->ToHighMemOperand(destination);

        __ ldr(kSavedValueRegister, source_operand);

        __ str(kSavedValueRegister, destination_operand);

        __ ldr(kSavedValueRegister, source_high_operand);

        __ str(kSavedValueRegister, destination_high_operand);

      } else {

        __ vldr(kScratchDoubleReg, source_operand);

        __ vstr(kScratchDoubleReg, destination_operand);

      }

    }

  } else {

    UNREACHABLE();

  }

  moves_[index].Eliminate();

}

#undef __

} }  // namespace v8::internal