BFEarlyBypasser.cc

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/**
 * @file BFEarlyBypasser.cc
 *
 * Definition of BFEarlyBypassed class.
 *
 * Before scheduling an operand move, searches for a move which might be a
 * bypass source and then tries class BFEarlyBypass or BFLoopBypass class
 * to perform the actual bypass.
 *
 * @author Heikki Kultala 2014-2020(heikki.kultala-no.spam-tuni.fi)
 * @note rating: red
 */
 
#include "BFEarlyBypasser.hh"
#include "BFDREEarly.hh"
#include "MachineConnectivityCheck.hh"
#include "DataDependenceGraph.hh"
#include "BF2Scheduler.hh"
#include "BF2ScheduleFront.hh"
#include "BFEarlyBypass.hh"
#include "SchedulerCmdLineOptions.hh"
 
bool
BFEarlyBypasser::operator()() {
 
    if (bypassDistance_ == 0) return false;
 
    DataDependenceEdge* bypassEdge = sched_.findBypassEdge(dst_);
    if (bypassEdge == NULL) {
        return false;
    }
    MoveNode& src = ddg().tailNode(*bypassEdge);
 
    if (sched_.currentFront()->illegalBypassSources_.count(&src)) {
#ifdef DEBUG_BUBBLEFISH_SCHEDULER
        std::cerr << "Bypass source illegal: " << src.toString() << std::endl;
#endif
        return 0;
    }
 
    if (!ddg().guardsAllowBypass(src, dst_, bypassEdge->isBackEdge())) {
        return false;
    }
 
    if (!MachineConnectivityCheck::canBypass(
            src, dst_, sched_.targetMachine())) {
        return false;
    }
 
    int bypassSourceLC = bypassSourceLatestCycle(src, dst_);
    if (bypassSourceLC == -1) {
        return false;
    }
 
    if (bypassEdge->isBackEdge()) {
        if (!src.isScheduled() || src.cycle() < (int)ii()) {
            return false;
        }
    } else {
        return runPreChild(new BFEarlyBypass(sched_, src, dst_));
    }
    return false;
}
 
/**
 * Checks that bypass source does not WHAT??? */
int BFEarlyBypasser::bypassSourceLatestCycle(
    MoveNode& bypassSrc, MoveNode& bypassDst) {
    DataDependenceGraph::NodeSet nodes;
 
    int lc = INT_MAX;
 
    if (bypassSrc.isSourceOperation()) {
        ProgramOperation& po = bypassSrc.sourceOperation();
        for (int j = 0; j < po.inputMoveCount(); j++) {
            MoveNode& inputMove = po.inputMove(j);
            // may also be a shared operand
            if (!sched_.isPreLoopSharedOperand(inputMove)) {
                nodes.insert(&inputMove);
            }
        }
 
        for (int j = 0; j < po.outputMoveCount(); j++) {
            MoveNode& outputMove = po.outputMove(j);
            if (!sched_.isDeadResult(outputMove)) {
                nodes.insert(&outputMove);
            }
        }
    } else {
        nodes.insert(&bypassSrc);
    }
 
    for (auto mn : nodes) {
        DataDependenceGraph::EdgeSet edges = ddg().outEdges(*mn);
        for (auto e : edges) {
            MoveNode& head = ddg().headNode(*e);
            if (head.isScheduled()) {
                lc = std::min(lc, head.cycle());
                continue;
            }
            if (&head == &bypassDst || head.isInFrontier() ||
                e->isBackEdge() || nodes.count(&head)) {
                continue;
            }
#ifdef DEBUG_BUBBLEFISH_SCHEDULER
            std::cerr << "\t\t\t\tEdge almost preventing bypass from: "
                      << bypassSrc.toString() << "to: " <<bypassDst.toString()
                      << ": " << e->toString() << " dst: "
                      << head.toString() << std::endl;
#endif
            return -1;
        }
    }
    return lc;
}
 
BFEarlyBypasser::BFEarlyBypasser(BF2Scheduler& sched, MoveNode& mn) :
    BFOptimization(sched),  dst_(mn) {
    SchedulerCmdLineOptions* opts =
        dynamic_cast<SchedulerCmdLineOptions*>(Application::cmdLineOptions());
    if (opts != NULL && opts->bypassDistance() > -1) {
        bypassDistance_ = opts->bypassDistance();
    }
}