/*

 * Copyright (C) 2012 David Anderson

 *

 * This file is part of JITCraft.

 *

 * JITCraft is free software: you can redistribute it and/or modify it under

 * the terms of the GNU General Public License as published by the Free

 * Software Foundation, either version 3 of the License, or (at your option)

 * any later version.

 * 

 * Foobar is distributed in the hope that it will be useful, but WITHOUT ANY

 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS

 * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License along with

 * JITCraft. If not, see http://www.gnu.org/licenses/.

 */

#ifndef _include_bytecode_emitter_h_

#define _include_bytecode_emitter_h_

#include <assert.h>

#include <limits.h>

#include "Opcodes.h"

namespace jc {

class Type;

class BytecodeEmitter

{

    bytecode *buffer_;

    bytecode *buffer_pos_;

    bytecode *buffer_end_;

    bytecode inline_buffer_[512];

    bool oom_;

    unsigned maxStackDepth_;

    unsigned stackDepth_;

  private:

    static const size_t MAX_LENGTH = INT_MAX / 2;

  private:

    bool growBuffer(size_t bytes);

    // Checking the return value is not necessary, since the inline buffer is

    // used as a ballast.

    bool ensure(size_t bytes) {

        if (buffer_pos_ + bytes > buffer_end_)

            return growBuffer(bytes);

        return true;

    }

    void writeUint8(unsigned value) {

        assert(value >= 0 && value <= UCHAR_MAX);

        *buffer_pos_++ = value;

    }

    void writeFloat(float value) {

        *(float *)buffer_pos_ = value;

        buffer_pos_ += sizeof(float);

    }

    void writeInt32(int value) {

        *(int *)buffer_pos_ = value;

        buffer_pos_ += sizeof(int);

    }

    void writeUint32(unsigned value) {

        *(unsigned *)buffer_pos_ = value;

        buffer_pos_ += sizeof(unsigned);

    }

    void writeOp(Opcode op) {

        writeUint8(op);

        stackDepth_ += OpcodeInfo[op].ndefs;

        if (OpcodeInfo[op].nuses != -1)

            stackDepth_ -= OpcodeInfo[op].nuses;

        if (stackDepth_ > maxStackDepth_)

            maxStackDepth_ = stackDepth_;

    }

    int position() const {

        assert(buffer_pos_ - buffer_ < INT_MAX / 2);

        return int(buffer_pos_ - buffer_);

    }

  public:

    BytecodeEmitter();

    bytecode *buffer() const {

        return buffer_;

    }

    unsigned length() const {

        return unsigned(buffer_pos_ - buffer_);

    }

    bool oom() const {

        return oom_;

    }

    unsigned stackDepth() const {

        return stackDepth_;

    }

    unsigned maxStackDepth() const {

        return maxStackDepth_;

    }

  public:

    // A label represents a local control-flow target in the bytecode. A label

    // may be in three states:

    //

    // (1) Empty - the label is not used yet.

    // (2) Pending - the label has incoming jumps, but the actual location of

    //               is not yet known. The list of jumps is threaded through

    //               the four bytes reserved for each emitted jump target. In

    //               this case, the offset field is the location of the most

    //               recently emitted incoming jump.

    // (3) Bound   - the label's position has been pinned.

    //

    // A jump can be emitted to a label in any state. Binding a label

    // immediately backpatches all pending incoming jumps. A label must be

    // bound if it is used.

    class Label

    {

        int offset_ : 31;

        bool bound_ : 1;

        void setOffset(int offset) {

            offset_ = offset;

            assert(offset_ == offset);

        }

      public:

        static const int INVALID_OFFSET = -1;

      public:

        Label()

          : offset_(INVALID_OFFSET),

            bound_(false)

        {

        }

        ~Label()

        {

            assert(bound_ || offset_ == INVALID_OFFSET);

        }

        bool bound() const {

            return bound_;

        }

        int offset() const {

            return offset_;

        }

        void bind(int offset) {

            assert(!bound_);

            setOffset(offset);

            bound_ = true;

        }

        int link(int offset) {

            assert(!bound_);

            int old = offset_;

            setOffset(offset);

            return old;

        }

    };

  private:

    int patchJumpAt(int at, int to) {

        assert(at >= 0 && at < position());

        int old = *(int *)(buffer_ + at + 1);

        *(int *)(buffer_ + at + 1) = (to - at);

        return old;

    }

    void singleByteOp(Opcode op) {

        assert(OpcodeInfo[op].length == 1);

        ensure(OpcodeInfo[op].length);

        writeOp(op);

    }

  public:

    void int_(int value) {

        ensure(OP_INT);

        writeOp(OP_INT);

        writeInt32(value);

    }

    void return_() {

        ensure(OP_RETURN);

        writeOp(OP_RETURN);

    }

    void getlocal(unsigned local) {

        ensure(OP_GETLOCAL_LENGTH);

        writeOp(OP_GETLOCAL);

        writeUint32(local);

    }

    void setlocal(unsigned local) {

        ensure(OP_SETLOCAL_LENGTH);

        writeOp(OP_SETLOCAL);

        writeUint32(local);

    }

    void getarg(unsigned slot) {

        ensure(OP_GETARG_LENGTH);

        writeOp(OP_GETARG);

        writeUint32(slot);

    }

    void setarg(unsigned slot) {

        ensure(OP_SETARG_LENGTH);

        writeOp(OP_SETARG);

        writeUint32(slot);

    }

    void j(Opcode op, Label *label) {

        // Since jumps can skip around the stream, do not try to do anything

        // in a potentially truncated state.

        if (oom())

            return;

        assert(op >= OP_JL && op <= OP_JUMP);

        ensure(OP_JUMP_LENGTH);

        if (label->bound()) {

            // We can immediately emit this jump.

            int distance = label->offset() - position();

            writeOp(op);

            writeInt32(distance);

        } else {

            // We can't emit this jump yet. Add a placeholder.

            int old = label->link(position());

            writeOp(op);

            writeInt32(old);

        }

    }

    void bind(Label *label) {

        if (oom())

            return;

        assert(!label->bound());

        int offset = label->offset();

        while (offset != Label::INVALID_OFFSET)

            offset = patchJumpAt(offset, position());

        label->bind(position());

    }

    void jump(Label *label) {

        j(OP_JUMP, label);

    }

    void binary(Opcode op) {

        singleByteOp(op);

    }

    void pop() {

        singleByteOp(OP_POP);

    }

    void stop() {

        singleByteOp(OP_STOP);

    }

    void callglobal(unsigned nargs, unsigned index) {

        ensure(OP_CALLGLOBAL_LENGTH);

        writeOp(OP_CALLGLOBAL);

        writeUint32(nargs);

        writeUint32(index);

        stackDepth_ -= nargs;

    }

    void ld_sta_i() {

        singleByteOp(OP_LD_STA_I);

    }

    void st_sta_i() {

        singleByteOp(OP_ST_STA_I);

    }

    void ld_sta_p() {

        singleByteOp(OP_LD_STA_P);

    }

    void stackarray(Type *type);

    void unwind(unsigned slot) {

        ensure(OP_UNWIND_LENGTH);

        writeOp(OP_UNWIND);

        writeUint32(slot);

    }

    void bounds_sta() {

        singleByteOp(OP_BOUNDS_STA);

    }

    void float_(float value) {

        ensure(OP_FLOAT_LENGTH);

        writeOp(OP_FLOAT);

        writeFloat(value);

    }

    void cvt_i2f() {

        singleByteOp(OP_CVT_I2F);

    }

};

}

#endif // _include_bytecode_emitter_h_