PostpassOperandSharer.cc

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/*
    Copyright (c) 2002-2009 Tampere University.
 
    This file is part of TTA-Based Codesign Environment (TCE).
 
    Permission is hereby granted, free of charge, to any person obtaining a
    copy of this software and associated documentation files (the "Software"),
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    the rights to use, copy, modify, merge, publish, distribute, sublicense,
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    Software is furnished to do so, subject to the following conditions:
 
    The above copyright notice and this permission notice shall be included in
    all copies or substantial portions of the Software.
 
    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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 */
/**
 * @file PostpassOperandSharer.cc
 *
 * Implementation of PostpassOperandSharer class.
 *
 * This optimizer removes operand writes which are redundant due
 * other operations using same value. 
 * This is executed after the main scheduler, so this mainly helps
 * to reduce power consumption, not to improve performance.
 *
 * @author Heikki Kultala 2009 (hkultala-no.spam-cs.tut.fi)
 * @note rating: red
 */
 
#include "PostpassOperandSharer.hh"
 
#include "Move.hh"
#include "Instruction.hh"
#include "Terminal.hh"
#include "BasicBlock.hh"
#include "Guard.hh"
#include "MoveGuard.hh"
#include "RegisterFile.hh"
#include "InstructionReferenceManager.hh"
#include "Bus.hh"
 
using TTAProgram::Move;
using TTAProgram::Instruction;
using TTAProgram::Terminal;
using TTAMachine::Guard;
using TTAMachine::RegisterGuard;
using TTAMachine::RegisterFile;
 
// this makes the code run slower but gives the trigger operand
// statistics
#define GET_BETTER_STATISTICS
 
void
PostpassOperandSharer::handleBasicBlock(
    TTAProgram::BasicBlock& basicBlock, const TTAMachine::Machine&,
    TTAProgram::InstructionReferenceManager&, BasicBlockNode*) {
    for (int i = basicBlock.instructionCount()-1; i >= 0; i--) {
        Instruction& ins = basicBlock.instructionAtIndex(i);
        for (int j = 0; j < ins.moveCount(); j++) {
            Move& move = ins.move(j);
            moveCount_++;
            if (tryRemoveOperandWrite(basicBlock, i, move)) {
                ins.removeMove(move);
                // TODO: make sure there is no movenode to this.
//                delete &move;
                j--;
            }
        }
    }
}
 
/**
 * 
 */
bool PostpassOperandSharer::tryRemoveOperandWrite(
    TTAProgram::BasicBlock& basicBlock, int insIndex, TTAProgram::Move& move) {
 
    bool guardOK = false;
    Terminal& dest = move.destination();
    Terminal& src = move.source();
 
    if (src.isGPR()) {
        registerReads_++;
    }
 
#ifdef GET_BETTER_STATISTICS
    if (!dest.isFUPort())
    {
        return false;
    }
#else
 
    if (!dest.isFUPort() ||
        dest.isTriggering() ||
        dest.isOpcodeSetting()) {
        return false;
    }
#endif
 
    operandCount_++;
    if (src.isFUPort()) {
        return false;
    }
 
    if (src.isImmediateRegister()) {
        return false;
    }
 
    const TTAMachine::RegisterFile* guardRF = NULL;
    int guardIndex = -1;
    if (!move.isUnconditional()) {
        const TTAMachine::Guard& guard = move.guard().guard();
        const RegisterGuard* rg = dynamic_cast<const TTAMachine::RegisterGuard*>(&guard);
        if (rg) {
            guardRF = rg->registerFile();
            guardIndex = rg->registerIndex();
        }
    }
 
    int srcIndex = -1;
    const TTAMachine::RegisterFile* srcRF = NULL;
    if (src.isGPR()) {
        srcIndex = src.index();
        srcRF = &src.registerFile();
    }
 
    int glat = move.guardLatency();
    bool lastDueJump = false;
 
    for (int i = insIndex -1; i >= basicBlock.skippedFirstInstructions() && !lastDueJump; i--) {
 
        // first check guard writes..
        // if guard has longer latency than 1 , this has to go to previous
        // cycles.
        int k = i+1 - glat;
        if (k>= 0) {
            Instruction& gIns = basicBlock.instructionAtIndex(k);
            
            // check that does not overwrite the source
            for (int j = 0; j < gIns.moveCount(); j++) {
                Move& gMove = gIns.move(j);
                Terminal& gDst = gMove.destination();
                if (gDst.isGPR()) {
                    int pdIndex = gDst.index();
                    const RegisterFile* pdRF = &gDst.registerFile();
                    if (guardIndex == pdIndex && guardRF == pdRF) {
                        guardOK = false;
                    }
                }
            }
        }
 
        Instruction& prevIns = basicBlock.instructionAtIndex(i);
        if (irm_->hasReference(prevIns)) {
            lastDueJump = true;
        }
        // check that does not overwrite the source
        for (int j = 0; j < prevIns.moveCount(); j++) {
            Move& prevMove = prevIns.move(j);
            Terminal& prevDst = prevMove.destination();
 
            if (prevDst.isGPR()) {
                int pdIndex = prevDst.index();
                const RegisterFile* pdRF = &prevDst.registerFile();
                if ((srcIndex == pdIndex && srcRF == pdRF) &&
                    (!guardOK || prevMove.isUnconditional() ||
                     move.isUnconditional() || 
                     !prevMove.guard().guard().isOpposite(
                         move.guard().guard()))) {
                    return false;
                }
            }
        }
 
        // check if writes the same operand
        for (int j = 0; j < prevIns.moveCount(); j++) {
            Move& prevMove = prevIns.move(j);
            Terminal& prevDest = prevMove.destination();
 
            // write to same port..
            if (&prevDest.port() == &dest.port()) {
                // Check if previous move used narrower bus and
                // potentially cut  upper bits of the transported value.
                // This is possible is the value was previously used in
                // operation which used only the lower bits of the value
                // (see BusResource::canAssign()).
                if (move.source().equals(prevMove.source())
                    && move.bus().width() <= prevMove.bus().width()) {
 
                    // TODO: what if guard is conditional, ok or not?
                    if (!prevMove.isUnconditional() &&
                        (move.isUnconditional() || 
                         (!guardOK || !prevMove.guard().guard().isEqual(
                              move.guard().guard())))) {
                        continue;
                    }
                    
                    if (prevDest.isTriggering() ||
                        prevDest.isOpcodeSetting()) {
                        triggerCannotRemove_++;
                        return false;
                    }
                    
                    removedOperands_++;
                    return true;
                } else {
                    return false;
                }
            }
        }
    }
    return false;
}
 
PostpassOperandSharer::~PostpassOperandSharer() {}
 
void PostpassOperandSharer::printStats() {
    std::cerr << "PostpassOperandSharer statistics: " << std::endl 
              << "\tTotal moves: " << moveCount_ << std::endl
              << "\tTotal reg reads: " << registerReads_ << std::endl
              << "\tTotal operands: "<<operandCount_ 
              << std::endl
              << "\tRemoved operands: " << removedOperands_ << std::endl
              << "\tCannot share trigger count: " << triggerCannotRemove_ 
              << std::endl;
    
}
 
unsigned int PostpassOperandSharer::moveCount_ = 0;
unsigned int PostpassOperandSharer::operandCount_ = 0;
unsigned int PostpassOperandSharer::removedOperands_ = 0;
unsigned int PostpassOperandSharer::registerReads_ = 0;
unsigned int PostpassOperandSharer::triggerCannotRemove_ = 0;