path: root/core/vm/jit_optimiser.go

// Copyright 2015 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library 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 Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.

package vm

import (
    "math/big"
    "time"

    "github.com/ethereum/go-ethereum/logger"
    "github.com/ethereum/go-ethereum/logger/glog"
)

// optimeProgram optimises a JIT program creating segments out of program
// instructions. Currently covered are multi-pushes and static jumps
func optimiseProgram(program *Program) {
    var load []instruction

    var (
        statsJump = 0
        statsPush = 0
    )

    if glog.V(logger.Debug) {
        glog.Infof("optimising %x\n", program.Id[:4])
        tstart := time.Now()
        defer func() {
            glog.Infof("optimised %x done in %v with JMP: %d PSH: %d\n", program.Id[:4], time.Since(tstart), statsJump, statsPush)
        }()
    }

    /*
        code := Parse(program.code)
        for _, test := range [][]OpCode{
            []OpCode{PUSH, PUSH, ADD},
            []OpCode{PUSH, PUSH, SUB},
            []OpCode{PUSH, PUSH, MUL},
            []OpCode{PUSH, PUSH, DIV},
        } {
            matchCount := 0
            MatchFn(code, test, func(i int) bool {
                matchCount++
                return true
            })
            fmt.Printf("found %d match count on: %v\n", matchCount, test)
        }
    */

    for i := 0; i < len(program.instructions); i++ {
        instr := program.instructions[i].(instruction)

        switch {
        case instr.op.IsPush():
            load = append(load, instr)
        case instr.op.IsStaticJump():
            if len(load) == 0 {
                continue
            }
            // if the push load is greater than 1, finalise that
            // segment first
            if len(load) > 2 {
                seg, size := makePushSeg(load[:len(load)-1])
                program.instructions[i-size-1] = seg
                statsPush++
            }
            // create a segment consisting of a pre determined
            // jump, destination and validity.
            seg := makeStaticJumpSeg(load[len(load)-1].data, program)
            program.instructions[i-1] = seg
            statsJump++

            load = nil
        default:
            // create a new N pushes segment
            if len(load) > 1 {
                seg, size := makePushSeg(load)
                program.instructions[i-size] = seg
                statsPush++
            }
            load = nil
        }
    }
}

// makePushSeg creates a new push segment from N amount of push instructions
func makePushSeg(instrs []instruction) (pushSeg, int) {
    var (
        data []*big.Int
        gas  = new(big.Int)
    )

    for _, instr := range instrs {
        data = append(data, instr.data)
        gas.Add(gas, instr.gas)
    }

    return pushSeg{data, gas}, len(instrs)
}

// makeStaticJumpSeg creates a new static jump segment from a predefined
// destination (PUSH, JUMP).
func makeStaticJumpSeg(to *big.Int, program *Program) jumpSeg {
    gas := new(big.Int)
    gas.Add(gas, _baseCheck[PUSH1].gas)
    gas.Add(gas, _baseCheck[JUMP].gas)

    contract := &Contract{Code: program.code}
    pos, err := jump(program.mapping, program.destinations, contract, to)
    return jumpSeg{pos, err, gas}
}