path: root/js/src/jit/arm/MoveEmitter-arm.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * vim: set ts=8 sts=2 et sw=2 tw=80:
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "jit/arm/MoveEmitter-arm.h"

#include "jit/MacroAssembler-inl.h"

using namespace js;
using namespace js::jit;

MoveEmitterARM::MoveEmitterARM(MacroAssembler& masm)
    : inCycle_(0),
      masm(masm),
      pushedAtCycle_(-1),
      pushedAtSpill_(-1),
      spilledReg_(InvalidReg),
      spilledFloatReg_(InvalidFloatReg) {
  pushedAtStart_ = masm.framePushed();
}

void MoveEmitterARM::emit(const MoveResolver& moves) {
  if (moves.numCycles()) {
    // Reserve stack for cycle resolution
    static_assert(SpillSlotSize == 8);
    masm.reserveStack(moves.numCycles() * SpillSlotSize);
    pushedAtCycle_ = masm.framePushed();
  }

  for (size_t i = 0; i < moves.numMoves(); i++) {
    emit(moves.getMove(i));
  }
}

MoveEmitterARM::~MoveEmitterARM() { assertDone(); }

Address MoveEmitterARM::cycleSlot(uint32_t slot, uint32_t subslot) const {
  int32_t offset = masm.framePushed() - pushedAtCycle_;
  MOZ_ASSERT(offset < 4096 && offset > -4096);
  return Address(StackPointer, offset + slot * sizeof(double) + subslot);
}

Address MoveEmitterARM::spillSlot() const {
  int32_t offset = masm.framePushed() - pushedAtSpill_;
  MOZ_ASSERT(offset < 4096 && offset > -4096);
  return Address(StackPointer, offset);
}

Address MoveEmitterARM::toAddress(const MoveOperand& operand) const {
  MOZ_ASSERT(operand.isMemoryOrEffectiveAddress());

  if (operand.base() != StackPointer) {
    return Address(operand.base(), operand.disp());
  }

  MOZ_ASSERT(operand.disp() >= 0);

  // Otherwise, the stack offset may need to be adjusted.
  return Address(StackPointer,
                 operand.disp() + (masm.framePushed() - pushedAtStart_));
}

Register MoveEmitterARM::tempReg() {
  if (spilledReg_ != InvalidReg) {
    return spilledReg_;
  }

  // For now, just pick r12/ip as the eviction point. This is totally random,
  // and if it ends up being bad, we can use actual heuristics later. r12 is
  // actually a bad choice. It is the scratch register, which is frequently
  // used for address computations, such as those found when we attempt to
  // access values more than 4096 off of the stack pointer. Instead, use lr,
  // the LinkRegister.
  spilledReg_ = r14;
  if (pushedAtSpill_ == -1) {
    masm.Push(spilledReg_);
    pushedAtSpill_ = masm.framePushed();
  } else {
    ScratchRegisterScope scratch(masm);
    masm.ma_str(spilledReg_, spillSlot(), scratch);
  }
  return spilledReg_;
}

void MoveEmitterARM::breakCycle(const MoveOperand& from, const MoveOperand& to,
                                MoveOp::Type type, uint32_t slotId) {
  // There is some pattern:
  //   (A -> B)
  //   (B -> A)
  //
  // This case handles (A -> B), which we reach first. We save B, then allow
  // the original move to continue.

  ScratchRegisterScope scratch(masm);

  switch (type) {
    case MoveOp::FLOAT32:
      if (to.isMemory()) {
        ScratchFloat32Scope scratchFloat32(masm);
        masm.ma_vldr(toAddress(to), scratchFloat32, scratch);
        // Since it is uncertain if the load will be aligned or not
        // just fill both of them with the same value.
        masm.ma_vstr(scratchFloat32, cycleSlot(slotId, 0), scratch);
        masm.ma_vstr(scratchFloat32, cycleSlot(slotId, 4), scratch);
      } else if (to.isGeneralReg()) {
        // Since it is uncertain if the load will be aligned or not
        // just fill both of them with the same value.
        masm.ma_str(to.reg(), cycleSlot(slotId, 0), scratch);
        masm.ma_str(to.reg(), cycleSlot(slotId, 4), scratch);
      } else {
        FloatRegister src = to.floatReg();
        // Just always store the largest possible size. Currently, this is
        // a double. When SIMD is added, two doubles will need to be stored.
        masm.ma_vstr(src.doubleOverlay(), cycleSlot(slotId, 0), scratch);
      }
      break;
    case MoveOp::DOUBLE:
      if (to.isMemory()) {
        ScratchDoubleScope scratchDouble(masm);
        masm.ma_vldr(toAddress(to), scratchDouble, scratch);
        masm.ma_vstr(scratchDouble, cycleSlot(slotId, 0), scratch);
      } else if (to.isGeneralRegPair()) {
        ScratchDoubleScope scratchDouble(masm);
        masm.ma_vxfer(to.evenReg(), to.oddReg(), scratchDouble);
        masm.ma_vstr(scratchDouble, cycleSlot(slotId, 0), scratch);
      } else {
        masm.ma_vstr(to.floatReg().doubleOverlay(), cycleSlot(slotId, 0),
                     scratch);
      }
      break;
    case MoveOp::INT32:
    case MoveOp::GENERAL:
      // an non-vfp value
      if (to.isMemory()) {
        Register temp = tempReg();
        masm.ma_ldr(toAddress(to), temp, scratch);
        masm.ma_str(temp, cycleSlot(0, 0), scratch);
      } else {
        if (to.reg() == spilledReg_) {
          // If the destination was spilled, restore it first.
          masm.ma_ldr(spillSlot(), spilledReg_, scratch);
          spilledReg_ = InvalidReg;
        }
        masm.ma_str(to.reg(), cycleSlot(0, 0), scratch);
      }
      break;
    default:
      MOZ_CRASH("Unexpected move type");
  }
}

void MoveEmitterARM::completeCycle(const MoveOperand& from,
                                   const MoveOperand& to, MoveOp::Type type,
                                   uint32_t slotId) {
  // There is some pattern:
  //   (A -> B)
  //   (B -> A)
  //
  // This case handles (B -> A), which we reach last. We emit a move from the
  // saved value of B, to A.

  ScratchRegisterScope scratch(masm);

  switch (type) {
    case MoveOp::FLOAT32:
      MOZ_ASSERT(!to.isGeneralRegPair());
      if (to.isMemory()) {
        ScratchFloat32Scope scratchFloat32(masm);
        masm.ma_vldr(cycleSlot(slotId, 0), scratchFloat32, scratch);
        masm.ma_vstr(scratchFloat32, toAddress(to), scratch);
      } else if (to.isGeneralReg()) {
        MOZ_ASSERT(type == MoveOp::FLOAT32);
        masm.ma_ldr(toAddress(from), to.reg(), scratch);
      } else {
        uint32_t offset = 0;
        if ((!from.isMemory()) && from.floatReg().numAlignedAliased() == 1) {
          offset = sizeof(float);
        }
        masm.ma_vldr(cycleSlot(slotId, offset), to.floatReg(), scratch);
      }
      break;
    case MoveOp::DOUBLE:
      MOZ_ASSERT(!to.isGeneralReg());
      if (to.isMemory()) {
        ScratchDoubleScope scratchDouble(masm);
        masm.ma_vldr(cycleSlot(slotId, 0), scratchDouble, scratch);
        masm.ma_vstr(scratchDouble, toAddress(to), scratch);
      } else if (to.isGeneralRegPair()) {
        MOZ_ASSERT(type == MoveOp::DOUBLE);
        ScratchDoubleScope scratchDouble(masm);
        masm.ma_vldr(toAddress(from), scratchDouble, scratch);
        masm.ma_vxfer(scratchDouble, to.evenReg(), to.oddReg());
      } else {
        uint32_t offset = 0;
        if ((!from.isMemory()) && from.floatReg().numAlignedAliased() == 1) {
          offset = sizeof(float);
        }
        masm.ma_vldr(cycleSlot(slotId, offset), to.floatReg(), scratch);
      }
      break;
    case MoveOp::INT32:
    case MoveOp::GENERAL:
      MOZ_ASSERT(slotId == 0);
      if (to.isMemory()) {
        Register temp = tempReg();
        masm.ma_ldr(cycleSlot(slotId, 0), temp, scratch);
        masm.ma_str(temp, toAddress(to), scratch);
      } else {
        if (to.reg() == spilledReg_) {
          // Make sure we don't re-clobber the spilled register later.
          spilledReg_ = InvalidReg;
        }
        masm.ma_ldr(cycleSlot(slotId, 0), to.reg(), scratch);
      }
      break;
    default:
      MOZ_CRASH("Unexpected move type");
  }
}

void MoveEmitterARM::emitMove(const MoveOperand& from, const MoveOperand& to) {
  // Register pairs are used to store Double values during calls.
  MOZ_ASSERT(!from.isGeneralRegPair());
  MOZ_ASSERT(!to.isGeneralRegPair());

  ScratchRegisterScope scratch(masm);

  if (to.isGeneralReg() && to.reg() == spilledReg_) {
    // If the destination is the spilled register, make sure we
    // don't re-clobber its value.
    spilledReg_ = InvalidReg;
  }

  if (from.isGeneralReg()) {
    if (from.reg() == spilledReg_) {
      // If the source is a register that has been spilled, make sure
      // to load the source back into that register.
      masm.ma_ldr(spillSlot(), spilledReg_, scratch);
      spilledReg_ = InvalidReg;
    }
    if (to.isMemoryOrEffectiveAddress()) {
      masm.ma_str(from.reg(), toAddress(to), scratch);
    } else {
      masm.ma_mov(from.reg(), to.reg());
    }
  } else if (to.isGeneralReg()) {
    MOZ_ASSERT(from.isMemoryOrEffectiveAddress());
    if (from.isMemory()) {
      masm.ma_ldr(toAddress(from), to.reg(), scratch);
    } else {
      masm.ma_add(from.base(), Imm32(from.disp()), to.reg(), scratch);
    }
  } else {
    // Memory to memory gpr move.
    Register reg = tempReg();

    MOZ_ASSERT(from.isMemoryOrEffectiveAddress());
    if (from.isMemory()) {
      masm.ma_ldr(toAddress(from), reg, scratch);
    } else {
      masm.ma_add(from.base(), Imm32(from.disp()), reg, scratch);
    }
    MOZ_ASSERT(to.base() != reg);
    masm.ma_str(reg, toAddress(to), scratch);
  }
}

void MoveEmitterARM::emitFloat32Move(const MoveOperand& from,
                                     const MoveOperand& to) {
  // Register pairs are used to store Double values during calls.
  MOZ_ASSERT(!from.isGeneralRegPair());
  MOZ_ASSERT(!to.isGeneralRegPair());

  ScratchRegisterScope scratch(masm);

  if (from.isFloatReg()) {
    if (to.isFloatReg()) {
      masm.ma_vmov_f32(from.floatReg(), to.floatReg());
    } else if (to.isGeneralReg()) {
      masm.ma_vxfer(from.floatReg(), to.reg());
    } else {
      masm.ma_vstr(VFPRegister(from.floatReg()).singleOverlay(), toAddress(to),
                   scratch);
    }
  } else if (from.isGeneralReg()) {
    if (to.isFloatReg()) {
      masm.ma_vxfer(from.reg(), to.floatReg());
    } else if (to.isGeneralReg()) {
      masm.ma_mov(from.reg(), to.reg());
    } else {
      masm.ma_str(from.reg(), toAddress(to), scratch);
    }
  } else if (to.isFloatReg()) {
    masm.ma_vldr(toAddress(from), VFPRegister(to.floatReg()).singleOverlay(),
                 scratch);
  } else if (to.isGeneralReg()) {
    masm.ma_ldr(toAddress(from), to.reg(), scratch);
  } else {
    // Memory to memory move.
    MOZ_ASSERT(from.isMemory());
    ScratchFloat32Scope scratchFloat32(masm);
    masm.ma_vldr(toAddress(from), scratchFloat32, scratch);
    masm.ma_vstr(scratchFloat32, toAddress(to), scratch);
  }
}

void MoveEmitterARM::emitDoubleMove(const MoveOperand& from,
                                    const MoveOperand& to) {
  // Registers are used to store pointers / int32 / float32 values.
  MOZ_ASSERT(!from.isGeneralReg());
  MOZ_ASSERT(!to.isGeneralReg());

  ScratchRegisterScope scratch(masm);

  if (from.isFloatReg()) {
    if (to.isFloatReg()) {
      masm.ma_vmov(from.floatReg(), to.floatReg());
    } else if (to.isGeneralRegPair()) {
      masm.ma_vxfer(from.floatReg(), to.evenReg(), to.oddReg());
    } else {
      masm.ma_vstr(from.floatReg(), toAddress(to), scratch);
    }
  } else if (from.isGeneralRegPair()) {
    if (to.isFloatReg()) {
      masm.ma_vxfer(from.evenReg(), from.oddReg(), to.floatReg());
    } else if (to.isGeneralRegPair()) {
      MOZ_ASSERT(!from.aliases(to));
      masm.ma_mov(from.evenReg(), to.evenReg());
      masm.ma_mov(from.oddReg(), to.oddReg());
    } else {
      ScratchDoubleScope scratchDouble(masm);
      masm.ma_vxfer(from.evenReg(), from.oddReg(), scratchDouble);
      masm.ma_vstr(scratchDouble, toAddress(to), scratch);
    }
  } else if (to.isFloatReg()) {
    masm.ma_vldr(toAddress(from), to.floatReg(), scratch);
  } else if (to.isGeneralRegPair()) {
    MOZ_ASSERT(from.isMemory());
    Address src = toAddress(from);
    // Note: We can safely use the MoveOperand's displacement here,
    // even if the base is SP: MoveEmitter::toOperand adjusts
    // SP-relative operands by the difference between the current
    // stack usage and stackAdjust, which emitter.finish() resets to
    // 0.
    //
    // Warning: if the offset isn't within [-255,+255] then this
    // will assert-fail (or, if non-debug, load the wrong words).
    // Nothing uses such an offset at the time of this writing.
    masm.ma_ldrd(EDtrAddr(src.base, EDtrOffImm(src.offset)), to.evenReg(),
                 to.oddReg());
  } else {
    // Memory to memory move.
    MOZ_ASSERT(from.isMemory());
    ScratchDoubleScope scratchDouble(masm);
    masm.ma_vldr(toAddress(from), scratchDouble, scratch);
    masm.ma_vstr(scratchDouble, toAddress(to), scratch);
  }
}

void MoveEmitterARM::emit(const MoveOp& move) {
  const MoveOperand& from = move.from();
  const MoveOperand& to = move.to();

  if (move.isCycleEnd() && move.isCycleBegin()) {
    // A fun consequence of aliased registers is you can have multiple
    // cycles at once, and one can end exactly where another begins.
    breakCycle(from, to, move.endCycleType(), move.cycleBeginSlot());
    completeCycle(from, to, move.type(), move.cycleEndSlot());
    return;
  }

  if (move.isCycleEnd()) {
    MOZ_ASSERT(inCycle_);
    completeCycle(from, to, move.type(), move.cycleEndSlot());
    MOZ_ASSERT(inCycle_ > 0);
    inCycle_--;
    return;
  }

  if (move.isCycleBegin()) {
    breakCycle(from, to, move.endCycleType(), move.cycleBeginSlot());
    inCycle_++;
  }

  switch (move.type()) {
    case MoveOp::FLOAT32:
      emitFloat32Move(from, to);
      break;
    case MoveOp::DOUBLE:
      emitDoubleMove(from, to);
      break;
    case MoveOp::INT32:
    case MoveOp::GENERAL:
      emitMove(from, to);
      break;
    default:
      MOZ_CRASH("Unexpected move type");
  }
}

void MoveEmitterARM::assertDone() { MOZ_ASSERT(inCycle_ == 0); }

void MoveEmitterARM::finish() {
  assertDone();

  if (pushedAtSpill_ != -1 && spilledReg_ != InvalidReg) {
    ScratchRegisterScope scratch(masm);
    masm.ma_ldr(spillSlot(), spilledReg_, scratch);
  }
  masm.freeStack(masm.framePushed() - pushedAtStart_);
}