corda/src/powerpc.cpp

/* Copyright (c) 2009, Avian Contributors

   Permission to use, copy, modify, and/or distribute this software
   for any purpose with or without fee is hereby granted, provided
   that the above copyright notice and this permission notice appear
   in all copies.

   There is NO WARRANTY for this software.  See license.txt for
   details. */

#include "assembler.h"
#include "vector.h"

#define CAST1(x) reinterpret_cast<UnaryOperationType>(x)
#define CAST2(x) reinterpret_cast<BinaryOperationType>(x)
#define CAST3(x) reinterpret_cast<TernaryOperationType>(x)

using namespace vm;

namespace {

namespace field {
// BITFIELD MASKS
const int64_t MASK_LO32 = 0x0ffffffff;
const int     MASK_LO16 = 0x0ffff;
const int     MASK_LO8  = 0x0ff;
// BITFIELD EXTRACTORS
inline int lo32(int64_t i) { return (int)(i & MASK_LO32); }
inline int hi32(int64_t i) { return lo32(i >> 32); }
inline int lo16(int64_t i) { return (int)(i & MASK_LO16); }
inline int hi16(int64_t i) { return lo16(i >> 16); }
inline int lo8(int64_t i) { return (int)(i & MASK_LO8); }
inline int hi8(int64_t i) { return lo8(i >> 8); }
}

namespace isa {
// INSTRUCTION FORMATS
inline int D(int op, int rt, int ra, int d) { return op<<26|rt<<21|ra<<16|(d & 0xFFFF); }
inline int DS(int op, int rt, int ra, int ds, int xo) { return op<<26|rt<<21|ra<<16|ds<<2|xo; }
inline int I(int op, int li, int aa, int lk) { return op<<26|li<<2|aa<<1|lk; }
inline int B(int op, int bo, int bi, int bd, int aa, int lk) { return op<<26|bo<<21|bi<<16|bd<<2|aa<<1|lk; }
inline int SC(int op, int lev) { return op<<26|lev<<5|2; }
inline int X(int op, int rt, int ra, int rb, int xo, int rc) { return op<<26|rt<<21|ra<<16|rb<<11|xo<<1|rc; }
inline int XL(int op, int bt, int ba, int bb, int xo, int lk) { return op<<26|bt<<21|ba<<16|bb<<11|xo<<1|lk; }
inline int XFX(int op, int rt, int spr, int xo) { return op<<26|rt<<21|((spr >> 5) | ((spr << 5) & 0x3E0))<<11|xo<<1; }
inline int XFL(int op, int flm, int frb, int xo, int rc) { return op<<26|flm<<17|frb<<11|xo<<1|rc; }
inline int XS(int op, int rs, int ra, int sh, int xo, int sh2, int rc) { return op<<26|rs<<21|ra<<16|sh<<11|xo<<2|sh2<<1|rc; }
inline int XO(int op, int rt, int ra, int rb, int oe, int xo, int rc) { return op<<26|rt<<21|ra<<16|rb<<11|oe<<10|xo<<1|rc; }
inline int A(int op, int frt, int fra, int frb, int frc, int xo, int rc) { return op<<26|frt<<21|fra<<16|frb<<11|frc<<6|xo<<1|rc; }
inline int M(int op, int rs, int ra, int rb, int mb, int me, int rc) { return op<<26|rs<<21|ra<<16|rb<<11|mb<<6|me<<1|rc; }
inline int MD(int op, int rs, int ra, int sh, int mb, int xo, int sh2, int rc) { return op<<26|rs<<21|ra<<16|sh<<11|mb<<5|xo<<2|sh2<<1|rc; }
inline int MDS(int op, int rs, int ra, int rb, int mb, int xo, int rc) { return op<<26|rs<<21|ra<<16|rb<<11|mb<<5|xo<<1|rc; }
// INSTRUCTIONS
inline int lbz(int rt, int ra, int i) { return D(34, rt, ra, i); }
inline int lbzx(int rt, int ra, int rb) { return X(34, rt, ra, rb, 87, 0); }
inline int lhz(int rt, int ra, int i) { return D(40, rt, ra, i); }
inline int lha(int rt, int ra, int i) { return D(42, rt, ra, i); }
inline int lhax(int rt, int ra, int rb) { return X(31, rt, ra, rb, 343, 0); }
inline int lwz(int rt, int ra, int i) { return D(32, rt, ra, i); }
inline int lwzx(int rt, int ra, int rb) { return X(31, rt, ra, rb, 23, 0); }
inline int stb(int rs, int ra, int i) { return D(38, rs, ra, i); }
inline int stbx(int rs, int ra, int rb) { return X(31, rs, ra, rb, 215, 0); }
inline int sth(int rs, int ra, int i) { return D(44, rs, ra, i); }
inline int sthx(int rs, int ra, int rb) { return X(31, rs, ra, rb, 407, 0); }
inline int stw(int rs, int ra, int i) { return D(36, rs, ra, i); }
inline int stwu(int rs, int ra, int i) { return D(37, rs, ra, i); }
inline int stwx(int rs, int ra, int rb) { return X(31, rs, ra, rb, 151, 0); }
inline int add(int rt, int ra, int rb) { return XO(31, rt, ra, rb, 0, 266, 0); }
inline int addc(int rt, int ra, int rb) { return XO(31, rt, ra, rb, 0, 10, 0); }
inline int adde(int rt, int ra, int rb) { return XO(31, rt, ra, rb, 0, 138, 0); }
inline int addi(int rt, int ra, int i) { return D(14, rt, ra, i); }
inline int addis(int rt, int ra, int i) { return D(15, rt, ra, i); }
inline int subf(int rt, int ra, int rb) { return XO(31, rt, ra, rb, 0, 40, 0); }
inline int subfc(int rt, int ra, int rb) { return XO(31, rt, ra, rb, 0, 8, 0); }
inline int subfe(int rt, int ra, int rb) { return XO(31, rt, ra, rb, 0, 136, 0); }
inline int subfic(int rt, int ra, int i) { return D(8, rt, ra, i); }
inline int mullw(int rt, int ra, int rb) { return XO(31, rt, ra, rb, 0, 235, 0); }
inline int mulhw(int rt, int ra, int rb) { return XO(31, rt, ra, rb, 0, 75, 0); }
inline int mulhwu(int rt, int ra, int rb) { return XO(31, rt, ra, rb, 0, 11, 0); }
inline int mulli(int rt, int ra, int i) { return D(7, rt, ra, i); }
inline int divw(int rt, int ra, int rb) { return XO(31, rt, ra, rb, 0, 491, 0); }
inline int divwu(int rt, int ra, int rb) { return XO(31, rt, ra, rb, 0, 459, 0); }
inline int divd(int rt, int ra, int rb) { return XO(31, rt, ra, rb, 0, 489, 0); }
inline int divdu(int rt, int ra, int rb) { return XO(31, rt, ra, rb, 0, 457, 0); }
inline int and_(int rt, int ra, int rb) { return X(31, ra, rt, rb, 28, 0); }
inline int andi(int rt, int ra, int i) { return D(28, ra, rt, i); }
inline int andis(int rt, int ra, int i) { return D(29, ra, rt, i); }
inline int or_(int rt, int ra, int rb) { return X(31, ra, rt, rb, 444, 0); }
inline int ori(int rt, int ra, int i) { return D(24, rt, ra, i); }
inline int oris(int rt, int ra, int i) { return D(25, rt, ra, i); }
inline int rlwinm(int rt, int ra, int i, int mb, int me) { return M(21, ra, rt, i, mb, me, 0); }
inline int rlwimi(int rt, int ra, int i, int mb, int me) { return M(20, ra, rt, i, mb, me, 0); }
inline int slw(int rt, int ra, int sh) { return X(31, ra, rt, sh, 21, 0); }
inline int sld(int rt, int ra, int rb) { return X(31, ra, rt, rb, 27, 0); }
inline int srw(int rt, int ra, int sh) { return X(31, ra, rt, sh, 536, 0); }
inline int sraw(int rt, int ra, int sh) { return X(31, ra, rt, sh, 792, 0); }
inline int srawi(int rt, int ra, int sh) { return X(31, ra, rt, sh, 824, 0); }
inline int extsb(int rt, int rs) { return X(31, rs, rt, 0, 954, 0); }
inline int extsh(int rt, int rs) { return X(31, rs, rt, 0, 922, 0); }
inline int mfspr(int rt, int spr) { return XFX(31, rt, spr, 339); }
inline int mtspr(int spr, int rs) { return XFX(31, rs, spr, 467); }
inline int b(int i) { return I(18, i, 0, 0); }
inline int bl(int i) { return I(18, i, 0, 1); }
inline int bcctr(int bo, int bi, int lk) { return XL(19, bo, bi, 0, 528, lk); }
inline int bclr(int bo, int bi, int lk) { return XL(19, bo, bi, 0, 16, lk); }
inline int bc(int bo, int bi, int bd, int lk) { return B(16, bo, bi, bd, 0, lk); }
inline int cmp(int bf, int ra, int rb) { return X(31, bf << 2, ra, rb, 0, 0); }
inline int cmpl(int bf, int ra, int rb) { return X(31, bf << 2, ra, rb, 32, 0); }
// PSEUDO-INSTRUCTIONS
inline int li(int rt, int i) { return addi(rt, 0, i); }
inline int lis(int rt, int i) { return addis(rt, 0, i); }
inline int slwi(int rt, int ra, int i) { return rlwinm(rt, ra, i, 0, 31-i); }
inline int srwi(int rt, int ra, int i) { return rlwinm(rt, ra, 32-i, i, 31); }
inline int sub(int rt, int ra, int rb) { return subf(rt, rb, ra); }
inline int subc(int rt, int ra, int rb) { return subfc(rt, rb, ra); }
inline int subi(int rt, int ra, int i) { return addi(rt, ra, -i); }
inline int subis(int rt, int ra, int i) { return addis(rt, ra, -i); }
inline int mr(int rt, int ra) { return or_(rt, ra, ra); }
inline int mflr(int rx) { return mfspr(rx, 8); }
inline int mtlr(int rx) { return mtspr(8, rx); }
inline int mtctr(int rd) { return mtspr(9, rd); }
inline int bctr() { return bcctr(20, 0, 0); }
inline int bctrl() { return bcctr(20, 0, 1); }
inline int blr() { return bclr(20, 0, 0); }
inline int blt(int i) { return bc(12, 0, i, 0); }
inline int bgt(int i) { return bc(12, 1, i, 0); }
inline int bge(int i) { return bc(4, 0, i, 0); }
inline int ble(int i) { return bc(4, 1, i, 0); }
inline int be(int i) { return bc(12, 2, i, 0); }
inline int cmpw(int ra, int rb) { return cmp(0, ra, rb); }
inline int cmplw(int ra, int rb) { return cmpl(0, ra, rb); }
}

inline bool
isInt16(intptr_t v)
{
  return v == static_cast<int16_t>(v);
}

const unsigned FrameFooterSize = 6;

const int StackRegister = 1;
const int ThreadRegister = 13;

class MyBlock: public Assembler::Block {
 public:
  MyBlock(unsigned offset):
    next(0), offset(offset), start(~0), size(0)
  { }

  virtual unsigned resolve(unsigned start, Assembler::Block* next) {
    this->start = start;
    this->next = static_cast<MyBlock*>(next);

    return start + size;
  }

  MyBlock* next;
  unsigned offset;
  unsigned start;
  unsigned size;
};

class Task;

class Context {
 public:
  Context(System* s, Allocator* a, Zone* zone):
    s(s), zone(zone), client(0), code(s, a, 1024), tasks(0), result(0),
    firstBlock(new (zone->allocate(sizeof(MyBlock))) MyBlock(0)),
    lastBlock(firstBlock)
  { }

  System* s;
  Zone* zone;
  Assembler::Client* client;
  Vector code;
  Task* tasks;
  uint8_t* result;
  MyBlock* firstBlock;
  MyBlock* lastBlock;
};

class Task {
 public:
  Task(Task* next): next(next) { }

  virtual void run(Context* c) = 0;

  Task* next;
};

typedef void (*OperationType)(Context*);

typedef void (*UnaryOperationType)(Context*, unsigned, Assembler::Operand*);

typedef void (*BinaryOperationType)
(Context*, unsigned, Assembler::Operand*, unsigned, Assembler::Operand*);

typedef void (*TernaryOperationType)
(Context*, unsigned, Assembler::Operand*, Assembler::Operand*,
 Assembler::Operand*);

class ArchitectureContext {
 public:
  ArchitectureContext(System* s): s(s) { }

  System* s;
  OperationType operations[OperationCount];
  UnaryOperationType unaryOperations[UnaryOperationCount
                                     * OperandTypeCount];
  BinaryOperationType binaryOperations
  [BinaryOperationCount * OperandTypeCount * OperandTypeCount];
  TernaryOperationType ternaryOperations
  [TernaryOperationCount * OperandTypeCount];
};

inline void NO_RETURN
abort(Context* c)
{
  abort(c->s);
}

inline void NO_RETURN
abort(ArchitectureContext* c)
{
  abort(c->s);
}

#ifndef NDEBUG
inline void
assert(Context* c, bool v)
{
  assert(c->s, v);
}

inline void
assert(ArchitectureContext* c, bool v)
{
  assert(c->s, v);
}
#endif // not NDEBUG

inline void
expect(Context* c, bool v)
{
  expect(c->s, v);
}

class Offset: public Promise {
 public:
  Offset(Context* c, MyBlock* block, unsigned offset):
    c(c), block(block), offset(offset)
  { }

  virtual bool resolved() {
    return block->start != static_cast<unsigned>(~0);
  }
  
  virtual int64_t value() {
    assert(c, resolved());

    return block->start + (offset - block->offset);
  }

  Context* c;
  MyBlock* block;
  unsigned offset;
};

Promise*
offset(Context* c)
{
  return new (c->zone->allocate(sizeof(Offset)))
    Offset(c, c->lastBlock, c->code.length());
}

bool
bounded(int right, int left, int32_t v)
{
  return ((v << left) >> left) == v and ((v >> right) << right) == v;
}

void*
updateOffset(System* s, uint8_t* instruction, bool conditional, int64_t value)
{
  int32_t v = reinterpret_cast<uint8_t*>(value) - instruction;
   
  int32_t mask;
  if (conditional) {
    expect(s, bounded(2, 16, v));
    mask = 0xFFFC;
  } else {
    expect(s, bounded(2, 6, v));
    mask = 0x3FFFFFC;
  }

  int32_t* p = reinterpret_cast<int32_t*>(instruction);
  *p = (v & mask) | ((~mask) & *p);

  return instruction + 4;
}

class OffsetListener: public Promise::Listener {
 public:
  OffsetListener(System* s, uint8_t* instruction, bool conditional):
    s(s),
    instruction(instruction),
    conditional(conditional)
  { }

  virtual void* resolve(int64_t value) {
    return updateOffset(s, instruction, conditional, value);
  }

  System* s;
  uint8_t* instruction;
  bool conditional;
};

class OffsetTask: public Task {
 public:
  OffsetTask(Task* next, Promise* promise, Promise* instructionOffset,
             bool conditional):
    Task(next),
    promise(promise),
    instructionOffset(instructionOffset),
    conditional(conditional)
  { }

  virtual void run(Context* c) {
    if (promise->resolved()) {
      updateOffset
        (c->s, c->result + instructionOffset->value(), conditional,
         promise->value());
    } else {
      new (promise->listen(sizeof(OffsetListener)))
        OffsetListener(c->s, c->result + instructionOffset->value(),
                       conditional);
    }
  }

  Promise* promise;
  Promise* instructionOffset;
  bool conditional;
};

void
appendOffsetTask(Context* c, Promise* promise, Promise* instructionOffset,
                 bool conditional)
{
  c->tasks = new (c->zone->allocate(sizeof(OffsetTask))) OffsetTask
    (c->tasks, promise, instructionOffset, conditional);
}

inline unsigned
index(UnaryOperation operation, OperandType operand)
{
  return operation + (UnaryOperationCount * operand);
}

inline unsigned
index(BinaryOperation operation,
      OperandType operand1,
      OperandType operand2)
{
  return operation
    + (BinaryOperationCount * operand1)
    + (BinaryOperationCount * OperandTypeCount * operand2);
}

inline unsigned
index(TernaryOperation operation,
      OperandType operand1)
{
  return operation + (TernaryOperationCount * operand1);
}


// BEGIN OPERATION COMPILERS

using namespace field;
using namespace isa;

typedef Assembler::Register Reg;
typedef Assembler::Constant Const;

inline void issue(Context* con, int code) { con->code.append4(code); }
inline int getTemp(Context* con) { return con->client->acquireTemporary(); }
inline int64_t getVal(Const* c) { return c->value->value(); }
inline int R(Reg* r) { return r->low; }
inline int H(Reg* r) { return r->high; }


void shiftLeftR(Context* con, unsigned size, Reg* a, Reg* b, Reg* t)
{
  if(size == 8) {
    issue(con, subfic(31, R(a), 32));
    issue(con, slw(R(b), R(b), R(a)));
    issue(con, srw(0, H(b), 31));
    issue(con, or_(R(b), R(b), 0));
    issue(con, addi(31, R(a), -32));
    issue(con, slw(0, H(b), 31));
    issue(con, or_(R(b), R(b), 0));
    issue(con, slw(H(b), H(b), R(a)));
  } else
    issue(con, slw(R(t), R(b), R(a)));
}

void shiftLeftC(Context* con, unsigned size, Const* a, Reg* b, Reg* t)
{
  int sh = getVal(a);
  if (size == 8) {
    abort(con); // todo
  } else
    issue(con, slwi(R(t), R(b), sh));
}

void shiftRightR(Context* con, unsigned size, Reg* a, Reg* b, Reg* t)
{
  if(size == 8) {
    abort(con); // todo
  } else
    issue(con, sraw(R(t), R(b), R(a)));
}

void shiftRightC(Context* con, unsigned size, Const* a, Reg* b, Reg* t)
{
  int sh = getVal(a);
  if(size == 8) {
    abort(con); // todo
  } else
    issue(con, srawi(R(t), R(b), sh));
}

void unsignedShiftRightR(Context* con, unsigned size, Reg* a, Reg* b, Reg* t)
{
  if(size == 8) {
    abort(con); // todo
  } else
    issue(con, srw(R(t), R(b), R(a)));
}

void unsignedShiftRightC(Context* con, unsigned size, Const* a, Reg* b, Reg* t)
{
  int sh = getVal(a);
  if (size == 8) {
    abort(con); // todo
  } else
    issue(con, srwi(R(t), R(b), sh));
}

void
updateImmediate(System* s, void* dst, int64_t src, unsigned size)
{
  switch (size) {
  case 4: {
    int32_t* p = static_cast<int32_t*>(dst);
    p[0] = (src >> 16) | ((~0xFFFF) & p[0]);
    p[1] = (src & 0xFFFF) | ((~0xFFFF) & p[1]);
  } break;

  default: abort(s);
  }
}

class ImmediateListener: public Promise::Listener {
 public:
  ImmediateListener(System* s, void* dst, unsigned size, unsigned offset):
    s(s), dst(dst), size(size), offset(offset)
  { }

  virtual void* resolve(int64_t value) {
    updateImmediate(s, dst, value, size);
    return static_cast<uint8_t*>(dst) + offset;
  }

  System* s;
  void* dst;
  unsigned size;
  unsigned offset;
};

class ImmediateTask: public Task {
 public:
  ImmediateTask(Task* next, Promise* promise, Promise* offset, unsigned size,
                unsigned promiseOffset):
    Task(next),
    promise(promise),
    offset(offset),
    size(size),
    promiseOffset(promiseOffset)
  { }

  virtual void run(Context* c) {
    if (promise->resolved()) {
      updateImmediate
        (c->s, c->result + offset->value(), promise->value(), size);
    } else {
      new (promise->listen(sizeof(ImmediateListener))) ImmediateListener
        (c->s, c->result + offset->value(), size, promiseOffset);
    }
  }

  Promise* promise;
  Promise* offset;
  unsigned size;
  unsigned promiseOffset;
};

void
appendImmediateTask(Context* c, Promise* promise, Promise* offset,
                    unsigned size, unsigned promiseOffset = 0)
{
  c->tasks = new (c->zone->allocate(sizeof(ImmediateTask))) ImmediateTask
    (c->tasks, promise, offset, size, promiseOffset);
}

void
jumpR(Context* c, unsigned size UNUSED, Assembler::Register* target)
{
  assert(c, size == BytesPerWord);

  issue(c, mtctr(target->low));
  issue(c, bctr());
}

void
moveRR(Context* c, unsigned srcSize, Assembler::Register* src,
       unsigned dstSize, Assembler::Register* dst);

void
swapRR(Context* c, unsigned aSize, Assembler::Register* a,
       unsigned bSize, Assembler::Register* b)
{
  assert(c, aSize == BytesPerWord);
  assert(c, bSize == BytesPerWord);

  Assembler::Register tmp(c->client->acquireTemporary());
  moveRR(c, aSize, a, bSize, &tmp);
  moveRR(c, bSize, b, aSize, a);
  moveRR(c, bSize, &tmp, bSize, b);
}

void
moveRR(Context* c, unsigned srcSize, Assembler::Register* src,
       unsigned dstSize, Assembler::Register* dst)
{
  switch (srcSize) {
  case 1:
    issue(c, extsb(src->low, dst->low));
    break;
    
  case 2:
    issue(c, extsh(src->low, dst->low));
    break;
    
  case 4:
  case 8:
    if (srcSize == 4 and dstSize == 8) {
      Assembler::Register dstHigh(dst->high);
      moveRR(c, 4, src, 4, dst);
      moveRR(c, 4, src, 4, &dstHigh);
      issue(c, srawi(dst->high, dst->high, 31));
    } else if (srcSize == 8 and dstSize == 8) {
      Assembler::Register srcHigh(src->high);
      Assembler::Register dstHigh(dst->high);

      if (src->high == dst->low) {
        if (src->low == dst->high) {
          swapRR(c, 4, src, 4, dst);
        } else {
          moveRR(c, 4, &srcHigh, 4, &dstHigh);
          moveRR(c, 4, src, 4, dst);
        }
      } else {
        moveRR(c, 4, src, 4, dst);
        moveRR(c, 4, &srcHigh, 4, &dstHigh);
      }
    } else if (src->low != dst->low) {
      issue(c, mr(dst->low, src->low));
    }
    break;
  }
}

void addR(Context* con, unsigned size, Reg* a, Reg* b, Reg* t) {
  if(size == 8) {
    issue(con, addc(R(t), R(a), R(b)));
    issue(con, adde(H(t), H(a), H(b)));
  } else {
    issue(con, add(R(t), R(a), R(b)));
  }
}

void addC(Context* con, unsigned size, Const* a, Reg* b, Reg* t) {
  assert(con, size == 4);

  int32_t i = getVal(a);
  if(i) {
    issue(con, addi(R(t), R(b), lo16(i)));
    if(not isInt16(i))
      issue(con, addis(R(t), R(t), hi16(i)));
  }
}

void subR(Context* con, unsigned size, Reg* a, Reg* b, Reg* t) {
  if(size == 8) {
    issue(con, subfc(R(t), R(a), R(b)));
    issue(con, subfe(H(t), H(a), H(b)));
  } else {
    issue(con, subf(R(t), R(a), R(b)));
  }
}

void subC(Context* con, unsigned size, Const* a, Reg* b, Reg* t) {
  assert(con, size == 4);

  int64_t i = getVal(a);
  if(i) {
    issue(con, subi(R(t), R(b), lo16(i)));
    if(not isInt16(i))
      issue(con, subis(R(t), R(t), hi16(i)));
  }
}

void multiplyR(Context* con, unsigned size, Reg* a, Reg* b, Reg* t) {
  if(size == 8) {
    Reg tmp(getTemp(con));
    issue(con, mullw(H(t), H(a), R(b)));
    issue(con, mullw(R(&tmp), R(a), H(b)));
    issue(con, add(H(t), H(t), R(&tmp)));
    issue(con, mulhw(R(&tmp), R(a), R(b)));
    issue(con, add(H(t), H(t), R(&tmp)));
  } else {
    issue(con, mullw(R(t), R(a), R(b)));
  }
}

void multiplyC(Context* con, unsigned size, Const* a, Reg* b, Reg* t) {
  assert(con, size == 4);
  int64_t i = getVal(a);
  issue(con, mulli(R(t), R(b), i));
}

void divideR(Context* con, unsigned size, Reg* a, Reg* b, Reg* t) {
  if(size == 8) {
    issue(con, 0);
    issue(con, 0);
  } else {
    issue(con, divw(R(t), R(b), R(a)));
  }
}

void remainderR(Context* con, unsigned size, Reg* a, Reg* b, Reg* t) {
  divideR(con, size, a, b, t);
  multiplyR(con, size, b, t, t);
  subR(con, size, t, a, t);
}

void andC(Context* c, unsigned size, Assembler::Constant* a,
          Assembler::Register* b, Assembler::Register* dst)
{
  abort(c); // todo

  int64_t v = a->value->value();

  if(size == 8) {
    ResolvedPromise high((v >> 32) & 0xFFFFFFFF);
    Assembler::Constant ah(&high);

    ResolvedPromise low(v & 0xFFFFFFFF);
    Assembler::Constant al(&low);

    Assembler::Register bh(b->high);
    Assembler::Register dh(dst->high);

    andC(c, 4, &al, b, dst);
    andC(c, 4, &ah, &bh, &dh);
  } else {
    issue(c, andi(dst->low, b->low, v));
    if (v >> 16) {
      issue(c, andis(dst->low, b->low, v >> 16));
    }
  }
}

int
normalize(Context* c, int offset, int index, unsigned scale, 
          bool* preserveIndex)
{
  if (offset != 0 or scale != 1) {
    Assembler::Register normalizedIndex
      (*preserveIndex ? c->client->acquireTemporary() : index);
    
    *preserveIndex = false;

    int scaled;

    if (scale != 1) {
      Assembler::Register unscaledIndex(index);

      ResolvedPromise scalePromise(log(scale));
      Assembler::Constant scaleConstant(&scalePromise);
      
      shiftLeftC(c, BytesPerWord, &scaleConstant,
                 &unscaledIndex, &normalizedIndex);

      scaled = normalizedIndex.low;
    } else {
      scaled = index;
    }

    if (offset != 0) {
      Assembler::Register untranslatedIndex(scaled);

      ResolvedPromise offsetPromise(offset);
      Assembler::Constant offsetConstant(&offsetPromise);

      addC(c, BytesPerWord, &offsetConstant,
           &untranslatedIndex, &normalizedIndex);
    }

    return normalizedIndex.low;
  } else {
    return index;
  }
}

void
store(Context* c, unsigned size, Assembler::Register* src,
      int base, int offset, int index, unsigned scale, bool preserveIndex)
{
  if (index != NoRegister) {
    int normalized = normalize(c, offset, index, scale, &preserveIndex);

    switch (size) {
    case 1:
      issue(c, stbx(src->low, base, normalized));
      break;

    case 2:
      issue(c, sthx(src->low, base, normalized));
      break;

    case 4:
      issue(c, stwx(src->low, base, normalized));
      break;

    case 8: {
      Assembler::Register srcHigh(src->high);
      store(c, 4, &srcHigh, base, 0, normalized, 1, preserveIndex);
      store(c, 4, src, base, 4, normalized, 1, preserveIndex);
    } break;

    default: abort(c);
    }
  } else {
    switch (size) {
    case 1:
      issue(c, stb(src->low, base, offset));
      break;

    case 2:
      issue(c, sth(src->low, base, offset));
      break;

    case 4:
      issue(c, stw(src->low, base, offset));
      break;

    case 8: {
      Assembler::Register srcHigh(src->high);
      store(c, 4, &srcHigh, base, offset, NoRegister, 1, false);
      store(c, 4, src, base, offset + 4, NoRegister, 1, false);
    } break;

    default: abort(c);
    }
  }
}

void
moveRM(Context* c, unsigned srcSize, Assembler::Register* src,
       unsigned dstSize UNUSED, Assembler::Memory* dst)
{
  assert(c, srcSize == dstSize);

  store(c, srcSize, src, dst->base, dst->offset, dst->index, dst->scale, true);
}

void
moveAndUpdateRM(Context* c, unsigned srcSize, Assembler::Register* src,
                unsigned dstSize UNUSED, Assembler::Memory* dst)
{
  assert(c, srcSize == BytesPerWord);
  assert(c, dstSize == BytesPerWord);
  assert(c, dst->index == NoRegister);

  issue(c, stwu(src->low, dst->base, dst->offset));
}

void
load(Context* c, unsigned srcSize, int base, int offset, int index,
     unsigned scale, unsigned dstSize, Assembler::Register* dst,
     bool preserveIndex)
{
  if (index != NoRegister) {
    int normalized = normalize(c, offset, index, scale, &preserveIndex);

    switch (srcSize) {
    case 1:
      issue(c, lbzx(dst->low, base, normalized));
      moveRR(c, 1, dst, BytesPerWord, dst);
      break;

    case 2:
      issue(c, lhax(dst->low, base, normalized));
      break;

    case 4:
    case 8: {
      if (srcSize == 4 and dstSize == 8) {
        load(c, 4, base, 0, normalized, 1, 4, dst, preserveIndex);
        moveRR(c, 4, dst, 8, dst);
      } else if (srcSize == 8 and dstSize == 8) {
        Assembler::Register dstHigh(dst->high);
        load(c, 4, base, 0, normalized, 1, 4, &dstHigh, preserveIndex);
        load(c, 4, base, 4, normalized, 1, 4, dst, preserveIndex);
      } else {
        issue(c, lwzx(dst->low, base, offset));
      }
    } break;

    default: abort(c);
    }
  } else {
    switch (srcSize) {
    case 1:
      issue(c, lbz(dst->low, base, offset));
      issue(c, extsb(dst->low, dst->low));
      break;

    case 2:
      issue(c, lha(dst->low, base, offset));
      break;

    case 4:
      issue(c, lwz(dst->low, base, offset));
      break;

    case 8: {
      if (srcSize == 4 and dstSize == 8) {
        load(c, 4, base, offset, NoRegister, 1, 4, dst, false);
        moveRR(c, 4, dst, 8, dst);
      } else if (srcSize == 8 and dstSize == 8) {
        Assembler::Register dstHigh(dst->high);
        load(c, 4, base, offset, NoRegister, 1, 4, &dstHigh, false);
        load(c, 4, base, offset + 4, NoRegister, 1, 4, dst, false);
      } else {
        issue(c, lwzx(dst->low, base, offset));
      }
    } break;

    default: abort(c);
    }
  }
}

void
moveMR(Context* c, unsigned srcSize, Assembler::Memory* src,
       unsigned dstSize, Assembler::Register* dst)
{
  load(c, srcSize, src->base, src->offset, src->index, src->scale,
       dstSize, dst, true);
}

void
moveCR2(Context* c, unsigned, Assembler::Constant* src,
       unsigned dstSize, Assembler::Register* dst, unsigned promiseOffset)
{
  if (dstSize == 4) {
    if (src->value->resolved()) {
      int32_t v = src->value->value();
      if (isInt16(v)) {
        issue(c, li(dst->low, v));
      } else {
        issue(c, lis(dst->low, v >> 16));
        issue(c, ori(dst->low, dst->low, v));
      }
    } else {
      appendImmediateTask
        (c, src->value, offset(c), BytesPerWord, promiseOffset);
      issue(c, lis(dst->low, 0));
      issue(c, ori(dst->low, dst->low, 0));
    }
  } else {
    abort(c); // todo
  }
}

void
moveCR(Context* c, unsigned srcSize, Assembler::Constant* src,
       unsigned dstSize, Assembler::Register* dst)
{
  moveCR2(c, srcSize, src, dstSize, dst, 0);
}

// void moveCR3(Context* con, unsigned aSize, Const* a, unsigned tSize, Reg* t) {
//   int64_t i = getVal(a);
//   if(tSize == 8) {
//     int64_t j;
//     if(aSize == 8) j = i; // 64-bit const -> load high bits into high register
//     else           j = 0; // 32-bit const -> clear high register
//     issue(con, lis(H(t), hi16(hi32(j))));
//     issue(con, ori(H(t), H(t), lo16(hi32(j))));
//   }
//   issue(con, lis(R(t), hi16(i)));
//   issue(con, ori(R(t), R(t), lo16(i)));
// }

void
moveAR(Context* c, unsigned srcSize, Assembler::Address* src,
       unsigned dstSize, Assembler::Register* dst)
{
  assert(c, srcSize == 4 and dstSize == 4);

  Assembler::Constant constant(src->address);
  Assembler::Memory memory(dst->low, 0, -1, 0);

  moveCR(c, srcSize, &constant, dstSize, dst);
  moveMR(c, dstSize, &memory, dstSize, dst);
}

void
compareRR(Context* c, unsigned aSize, Assembler::Register* a,
          unsigned bSize, Assembler::Register* b)
{
  assert(c, aSize == 4 and bSize == 4);
  
  issue(c, cmpw(b->low, a->low));
}

void
compareCR(Context* c, unsigned aSize, Assembler::Constant* a,
          unsigned bSize, Assembler::Register* b)
{
  assert(c, aSize == 4 and bSize == 4);

  Assembler::Register tmp(c->client->acquireTemporary());
  moveCR(c, aSize, a, bSize, &tmp);
  compareRR(c, bSize, &tmp, bSize, b);
}

void
compareRM(Context* c, unsigned aSize, Assembler::Register* a,
          unsigned bSize, Assembler::Memory* b)
{
  assert(c, aSize == 4 and bSize == 4);

  Assembler::Register tmp(c->client->acquireTemporary());
  moveMR(c, bSize, b, bSize, &tmp);
  compareRR(c, aSize, a, bSize, &tmp);
}

void
compareUnsignedRR(Context* c, unsigned aSize, Assembler::Register* a,
                  unsigned bSize, Assembler::Register* b)
{
  assert(c, aSize == 4 and bSize == 4);
  
  issue(c, cmplw(b->low, a->low));
}

void
longCompare(Context* c, Assembler::Operand* al, Assembler::Operand* ah,
            Assembler::Operand* bl, Assembler::Operand* bh,
            Assembler::Register* dst, BinaryOperationType compareSigned,
            BinaryOperationType compareUnsigned)
{
  ResolvedPromise negativePromise(-1);
  Assembler::Constant negative(&negativePromise);

  ResolvedPromise zeroPromise(0);
  Assembler::Constant zero(&zeroPromise);

  ResolvedPromise positivePromise(1);
  Assembler::Constant positive(&positivePromise);

  compareSigned(c, 4, ah, 4, bh);

  unsigned less = c->code.length();
  issue(c, blt(0));

  unsigned greater = c->code.length();
  issue(c, bgt(0));

  compareUnsigned(c, 4, al, 4, bl);

  unsigned above = c->code.length();
  issue(c, bgt(0));

  unsigned below = c->code.length();
  issue(c, blt(0));

  moveCR(c, 4, &zero, 4, dst);

  unsigned nextFirst = c->code.length();
  issue(c, b(0));

  updateOffset
    (c->s, c->code.data + less, true, reinterpret_cast<intptr_t>
     (c->code.data + c->code.length()));

  updateOffset
    (c->s, c->code.data + above, true, reinterpret_cast<intptr_t>
     (c->code.data + c->code.length()));

  moveCR(c, 4, &negative, 4, dst);

  unsigned nextSecond = c->code.length();
  issue(c, b(0));

  updateOffset
    (c->s, c->code.data + greater, true, reinterpret_cast<intptr_t>
     (c->code.data + c->code.length()));

  updateOffset
    (c->s, c->code.data + below, true, reinterpret_cast<intptr_t>
     (c->code.data + c->code.length()));

  moveCR(c, 4, &positive, 4, dst);

  updateOffset
    (c->s, c->code.data + nextFirst, false, reinterpret_cast<intptr_t>
     (c->code.data + c->code.length()));

  updateOffset
    (c->s, c->code.data + nextSecond, false, reinterpret_cast<intptr_t>
     (c->code.data + c->code.length()));
}

void
longCompareR(Context* c, unsigned size UNUSED, Assembler::Register* a,
             Assembler::Register* b, Assembler::Register* dst)
{
  assert(c, size == 8);
  
  Assembler::Register ah(a->high);
  Assembler::Register bh(b->high);
  
  longCompare(c, a, &ah, b, &bh, dst, CAST2(compareRR),
              CAST2(compareUnsignedRR));
}

ShiftMaskPromise*
shiftMaskPromise(Context* c, Promise* base, unsigned shift, int64_t mask)
{
  return new (c->zone->allocate(sizeof(ShiftMaskPromise)))
    ShiftMaskPromise(base, shift, mask);
}

void
moveCM(Context* c, unsigned srcSize, Assembler::Constant* src,
       unsigned dstSize, Assembler::Memory* dst)
{
  switch (dstSize) {
  case 8: {
    Assembler::Constant srcHigh
      (shiftMaskPromise(c, src->value, 32, 0xFFFFFFFF));
    Assembler::Constant srcLow
      (shiftMaskPromise(c, src->value, 0, 0xFFFFFFFF));
    
    Assembler::Memory dstLow
      (dst->base, dst->offset + 4, dst->index, dst->scale);
    
    moveCM(c, 4, &srcLow, 4, &dstLow);
    moveCM(c, 4, &srcHigh, 4, dst);
  } break;

  default:
    Assembler::Register tmp(c->client->acquireTemporary());
    moveCR(c, srcSize, src, dstSize, &tmp);
    moveRM(c, dstSize, &tmp, dstSize, dst);
  }
}

void
callR(Context* c, unsigned size, Assembler::Register* target)
{
  assert(c, size == BytesPerWord);

  issue(c, mtctr(target->low));
  issue(c, bctrl());
}

void
callC(Context* c, unsigned size, Assembler::Constant* target)
{
  assert(c, size == BytesPerWord);

  appendOffsetTask(c, target->value, offset(c), false);
  issue(c, bl(0));
}

void
longCallC(Context* c, unsigned size, Assembler::Constant* target)
{
  assert(c, size == BytesPerWord);

  Assembler::Register tmp(0);
  moveCR2(c, BytesPerWord, target, BytesPerWord, &tmp, 12);
  callR(c, BytesPerWord, &tmp);
}

void
longJumpC(Context* c, unsigned size, Assembler::Constant* target)
{
  assert(c, size == BytesPerWord);

  Assembler::Register tmp(0);
  moveCR2(c, BytesPerWord, target, BytesPerWord, &tmp, 12);
  jumpR(c, BytesPerWord, &tmp);
}

void
jumpC(Context* c, unsigned size UNUSED, Assembler::Constant* target)
{
  assert(c, size == BytesPerWord);

  appendOffsetTask(c, target->value, offset(c), false);
  issue(c, b(0));
}

void
jumpIfEqualC(Context* c, unsigned size UNUSED, Assembler::Constant* target)
{
  assert(c, size == BytesPerWord);

  appendOffsetTask(c, target->value, offset(c), true);
  issue(c, be(0));
}

void
jumpIfGreaterC(Context* c, unsigned size UNUSED, Assembler::Constant* target)
{
  assert(c, size == BytesPerWord);

  appendOffsetTask(c, target->value, offset(c), true);
  issue(c, bgt(0));
}

void
jumpIfGreaterOrEqualC(Context* c, unsigned size UNUSED,
                      Assembler::Constant* target)
{
  assert(c, size == BytesPerWord);

  appendOffsetTask(c, target->value, offset(c), true);
  issue(c, bge(0));
}

void
jumpIfLessC(Context* c, unsigned size UNUSED, Assembler::Constant* target)
{
  assert(c, size == BytesPerWord);

  appendOffsetTask(c, target->value, offset(c), true);
  issue(c, blt(0));
}

void
jumpIfLessOrEqualC(Context* c, unsigned size UNUSED,
                   Assembler::Constant* target)
{
  assert(c, size == BytesPerWord);

  appendOffsetTask(c, target->value, offset(c), true);
  issue(c, ble(0));
}

void
return_(Context* c)
{
  issue(c, blr());
}

// END OPERATION COMPILERS


void
populateTables(ArchitectureContext* c)
{
  const OperandType C = ConstantOperand;
  const OperandType A = AddressOperand;
  const OperandType R = RegisterOperand;
  const OperandType M = MemoryOperand;

  OperationType* zo = c->operations;
  UnaryOperationType* uo = c->unaryOperations;
  BinaryOperationType* bo = c->binaryOperations;
  TernaryOperationType* to = c->ternaryOperations;

  zo[Return] = return_;

  uo[index(LongCall, C)] = CAST1(longCallC);

  uo[index(LongJump, C)] = CAST1(longJumpC);

  uo[index(Jump, R)] = CAST1(jumpR);
  uo[index(Jump, C)] = CAST1(jumpC);

  uo[index(JumpIfEqual, C)] = CAST1(jumpIfEqualC);
  uo[index(JumpIfGreater, C)] = CAST1(jumpIfGreaterC);
  uo[index(JumpIfGreaterOrEqual, C)] = CAST1(jumpIfGreaterOrEqualC);
  uo[index(JumpIfLess, C)] = CAST1(jumpIfLessC);
  uo[index(JumpIfLessOrEqual, C)] = CAST1(jumpIfLessOrEqualC);

  uo[index(Call, C)] = CAST1(callC);
  uo[index(Call, R)] = CAST1(callR);

  uo[index(AlignedCall, C)] = CAST1(callC);
  uo[index(AlignedCall, R)] = CAST1(callR);

  bo[index(Move, R, R)] = CAST2(moveRR);
  bo[index(Move, C, R)] = CAST2(moveCR);
  bo[index(Move, C, M)] = CAST2(moveCM);
  bo[index(Move, M, R)] = CAST2(moveMR);
  bo[index(Move, R, M)] = CAST2(moveRM);
  bo[index(Move, A, R)] = CAST2(moveAR);

  bo[index(Compare, R, R)] = CAST2(compareRR);
  bo[index(Compare, C, R)] = CAST2(compareCR);
  bo[index(Compare, R, M)] = CAST2(compareRM);

  to[index(Add, R)] = CAST3(addR);
  to[index(Add, C)] = CAST3(addC);

  to[index(Subtract, R)] = CAST3(subR);
  to[index(Subtract, C)] = CAST3(subC);

  to[index(And, C)] = CAST3(andC);

  to[index(LongCompare, R)] = CAST3(longCompareR);
}

class MyArchitecture: public Assembler::Architecture {
 public:
  MyArchitecture(System* system): c(system), referenceCount(0) {
    populateTables(&c);
  }

  virtual unsigned registerCount() {
    return 32;
  }

  virtual int stack() {
    return StackRegister;
  }

  virtual int thread() {
    return ThreadRegister;
  }

  virtual int returnLow(unsigned size) {
    return (size > BytesPerWord ? 4 : 3);
  }

  virtual int returnHigh() {
    return (BytesPerWord == 4 ? 3 : NoRegister);
  }

  virtual bool condensedAddressing() {
    return false;
  }

  virtual bool reserved(int register_) {
    switch (register_) {
    case StackRegister:
    case ThreadRegister:
      return true;

    default:
      return false;
    }
  }

  virtual unsigned argumentFootprint(unsigned footprint) {
    return footprint;
  }

  virtual unsigned argumentRegisterCount() {
    return 8;
  }

  virtual int argumentRegister(unsigned index) {
    assert(&c, index < argumentRegisterCount());

    return index + 3;
  }

  virtual void updateCall(UnaryOperation op UNUSED,
                          bool assertAlignment UNUSED, void* returnAddress,
                          void* newTarget)
  {
    switch (op) {
    case Call:
    case Jump: {
      updateOffset(c.s, static_cast<uint8_t*>(returnAddress) - 4, false,
                   reinterpret_cast<intptr_t>(newTarget));
    } break;

    default: abort(&c);
    }
  }

  virtual unsigned alignFrameSize(unsigned sizeInWords) {
    const unsigned alignment = 16 / BytesPerWord;
    return (ceiling(sizeInWords + FrameFooterSize, alignment) * alignment);
  }

  virtual void* frameIp(void* stack) {
    return stack ? static_cast<void**>(stack)[2] : 0;
  }

  virtual unsigned frameHeaderSize() {
    return 0;
  }

  virtual unsigned frameReturnAddressSize() {
    return 1;
  }

  virtual unsigned frameFooterSize() {
    return FrameFooterSize;
  }

  virtual void nextFrame(void** stack, void**) {
    assert(&c, *static_cast<void**>(*stack) != *stack);

    *stack = *static_cast<void**>(*stack);
  }

  virtual void plan
  (UnaryOperation,
   unsigned, uint8_t* aTypeMask, uint64_t* aRegisterMask,
   bool* thunk)
  {
    *aTypeMask = (1 << RegisterOperand) | (1 << ConstantOperand);
    *aRegisterMask = ~static_cast<uint64_t>(0);
    *thunk = false;
  }

  virtual void plan
  (BinaryOperation op,
   unsigned, uint8_t* aTypeMask, uint64_t* aRegisterMask,
   unsigned, uint8_t* bTypeMask, uint64_t* bRegisterMask,
   bool* thunk)
  {
    *aTypeMask = ~0;
    *aRegisterMask = ~static_cast<uint64_t>(0);

    *bTypeMask = (1 << RegisterOperand) | (1 << MemoryOperand);
    *bRegisterMask = ~static_cast<uint64_t>(0);

    *thunk = false;

    switch (op) {
    case Compare:
      *aTypeMask = (1 << RegisterOperand);
      *bTypeMask = (1 << RegisterOperand);
      break;

    case Negate:
      *aTypeMask = (1 << RegisterOperand);
      *bTypeMask = (1 << RegisterOperand);
      break;

    default:
      break;
    }
  }

  virtual void plan
  (TernaryOperation op,
   unsigned aSize, uint8_t* aTypeMask, uint64_t* aRegisterMask,
   unsigned, uint8_t* bTypeMask, uint64_t* bRegisterMask,
   unsigned, uint8_t* cTypeMask, uint64_t* cRegisterMask,
   bool* thunk)
  {
    *aTypeMask = (1 << RegisterOperand) | (1 << ConstantOperand);
    *aRegisterMask = ~static_cast<uint64_t>(0);

    *bTypeMask = (1 << RegisterOperand);
    *bRegisterMask = ~static_cast<uint64_t>(0);

    *thunk = false;

    switch (op) {
    case Add:
    case Subtract:
    case Multiply:
      if (BytesPerWord == 4 and aSize == 8) {
        *aTypeMask = *bTypeMask = (1 << RegisterOperand);
      }
      break;

    case LongCompare:
      *aTypeMask = *bTypeMask = (1 << RegisterOperand);
      break;

    case Divide:
      *aTypeMask = (1 << RegisterOperand);
      if (BytesPerWord == 4 and aSize == 8) {
        *bTypeMask = ~0;
        *thunk = true;        
      }
      break;

    case Remainder:
      *aTypeMask = (1 << RegisterOperand);
      if (BytesPerWord == 4 and aSize == 8) {
        *bTypeMask = ~0;
        *thunk = true;
      }
      break;

    default:
      break;
    }

    *cTypeMask = *bTypeMask;
    *cRegisterMask = *bRegisterMask;
  }

  virtual void acquire() {
    ++ referenceCount;
  }

  virtual void release() {
    if (-- referenceCount == 0) {
      c.s->free(this);
    }
  }

  ArchitectureContext c;
  unsigned referenceCount;
};

class MyAssembler: public Assembler {
 public:
  MyAssembler(System* s, Allocator* a, Zone* zone, MyArchitecture* arch):
    c(s, a, zone), arch_(arch)
  { }

  virtual void setClient(Client* client) {
    assert(&c, c.client == 0);
    c.client = client;
  }

  virtual Architecture* arch() {
    return arch_;
  }

  virtual void saveFrame(unsigned stackOffset, unsigned) {
    Register stack(StackRegister);
    Memory stackDst(ThreadRegister, stackOffset);
    moveRM(&c, BytesPerWord, &stack, BytesPerWord, &stackDst);
  }

  virtual void pushFrame(unsigned argumentCount, ...) {
    struct {
      unsigned size;
      OperandType type;
      Operand* operand;
    } arguments[argumentCount];

    va_list a; va_start(a, argumentCount);
    unsigned footprint = 0;
    for (unsigned i = 0; i < argumentCount; ++i) {
      arguments[i].size = va_arg(a, unsigned);
      arguments[i].type = static_cast<OperandType>(va_arg(a, int));
      arguments[i].operand = va_arg(a, Operand*);
      footprint += ceiling(arguments[i].size, BytesPerWord);
    }
    va_end(a);

    allocateFrame(arch_->alignFrameSize(footprint));
    
    unsigned offset = 0;
    for (unsigned i = 0; i < argumentCount; ++i) {
      if (i < arch_->argumentRegisterCount()) {
        Register dst(arch_->argumentRegister(i));

        apply(Move,
              arguments[i].size, arguments[i].type, arguments[i].operand,
              pad(arguments[i].size), RegisterOperand, &dst);

        offset += ceiling(arguments[i].size, BytesPerWord);
      } else {
        Memory dst(ThreadRegister, (offset + FrameFooterSize) * BytesPerWord);

        apply(Move,
              arguments[i].size, arguments[i].type, arguments[i].operand,
              pad(arguments[i].size), MemoryOperand, &dst);

        offset += ceiling(arguments[i].size, BytesPerWord);
      }
    }
  }

  virtual void allocateFrame(unsigned footprint) {
    Register returnAddress(0);
    issue(&c, mflr(returnAddress.low));

    Memory returnAddressDst(StackRegister, 8);
    moveRM(&c, BytesPerWord, &returnAddress, BytesPerWord, &returnAddressDst);

    Register stack(StackRegister);
    Memory stackDst(StackRegister, -footprint * BytesPerWord);
    moveAndUpdateRM(&c, BytesPerWord, &stack, BytesPerWord, &stackDst);
  }

  virtual void popFrame() {
    Register stack(StackRegister);
    Memory stackSrc(StackRegister, 0);
    moveMR(&c, BytesPerWord, &stackSrc, BytesPerWord, &stack);

    Assembler::Register returnAddress(0);
    Assembler::Memory returnAddressSrc(StackRegister, 8);
    moveMR(&c, BytesPerWord, &returnAddressSrc, BytesPerWord, &returnAddress);
    
    issue(&c, mtlr(returnAddress.low));
  }

  virtual void apply(Operation op) {
    arch_->c.operations[op](&c);
  }

  virtual void apply(UnaryOperation op,
                     unsigned aSize, OperandType aType, Operand* aOperand)
  {
    arch_->c.unaryOperations[index(op, aType)](&c, aSize, aOperand);
  }

  virtual void apply(BinaryOperation op,
                     unsigned aSize, OperandType aType, Operand* aOperand,
                     unsigned bSize, OperandType bType, Operand* bOperand)
  {
    arch_->c.binaryOperations[index(op, aType, bType)]
      (&c, aSize, aOperand, bSize, bOperand);
  }

  virtual void apply(TernaryOperation op,
                     unsigned, OperandType aType, Operand* aOperand,
                     unsigned bSize, OperandType bType UNUSED,
                     Operand* bOperand,
                     unsigned cSize, OperandType cType UNUSED,
                     Operand* cOperand)
  {
    assert(&c, bSize == cSize);
    assert(&c, bType == RegisterOperand);
    assert(&c, cType == RegisterOperand);

    arch_->c.ternaryOperations[index(op, aType)]
      (&c, bSize, aOperand, bOperand, cOperand);
  }

  virtual void writeTo(uint8_t* dst) {
    c.result = dst;
    
    for (MyBlock* b = c.firstBlock; b; b = b->next) {
      memcpy(dst + b->start, c.code.data + b->offset, b->size);
    }
    
    for (Task* t = c.tasks; t; t = t->next) {
      t->run(&c);
    }
  }

  virtual Promise* offset() {
    return ::offset(&c);
  }

  virtual Block* endBlock(bool startNew) {
    MyBlock* b = c.lastBlock;
    b->size = c.code.length() - b->offset;
    if (startNew) {
      c.lastBlock = new (c.zone->allocate(sizeof(MyBlock)))
        MyBlock(c.code.length());
    } else {
      c.lastBlock = 0;
    }
    return b;
  }

  virtual unsigned length() {
    return c.code.length();
  }

  virtual void dispose() {
    c.code.dispose();
  }

  Context c;
  MyArchitecture* arch_;
};

} // namespace

namespace vm {

Assembler::Architecture*
makeArchitecture(System* system)
{
  return new (allocate(system, sizeof(MyArchitecture))) MyArchitecture(system);
}

Assembler*
makeAssembler(System* system, Allocator* allocator, Zone* zone,
              Assembler::Architecture* architecture)
{
  return new (zone->allocate(sizeof(MyAssembler)))
    MyAssembler(system, allocator, zone,
                static_cast<MyArchitecture*>(architecture));
}

} // namespace vm