Esempio n. 1
0
bool
MoveResolver::resolve()
{
    resetState();
    orderedMoves_.clear();

    InlineList<PendingMove> stack;

    // This is a depth-first-search without recursion, which tries to find
    // cycles in a list of moves.
    //
    // Algorithm.
    //
    // S = Traversal stack.
    // P = Pending move list.
    // O = Ordered list of moves.
    //
    // As long as there are pending moves in P:
    //      Let |root| be any pending move removed from P
    //      Add |root| to the traversal stack.
    //      As long as S is not empty:
    //          Let |L| be the most recent move added to S.
    //
    //          Find any pending move M whose source is L's destination, thus
    //          preventing L's move until M has completed.
    //
    //          If a move M was found,
    //              Remove M from the pending list.
    //              If M's destination is |root|,
    //                  Annotate M and |root| as cycles.
    //                  Add M to S.
    //                  do not Add M to O, since M may have other conflictors in P that have not yet been processed.
    //              Otherwise,
    //                  Add M to S.
    //         Otherwise,
    //              Remove L from S.
    //              Add L to O.
    //
    while (!pending_.empty()) {
        PendingMove* pm = pending_.popBack();

        // Add this pending move to the cycle detection stack.
        stack.pushBack(pm);

        while (!stack.empty()) {
            PendingMove* blocking = findBlockingMove(stack.peekBack());

            if (blocking) {
                PendingMoveIterator stackiter = stack.begin();
                PendingMove* cycled = findCycledMove(&stackiter, stack.end(), blocking);
                if (cycled) {
                    // Find the cycle's start.
                    // We annotate cycles at each move in the cycle, and
                    // assert that we do not find two cycles in one move chain
                    // traversal (which would indicate two moves to the same
                    // destination).
                    // Since there can be more than one cycle, find them all.
                    do {
                        cycled->setCycleEnd(curCycles_);
                        cycled = findCycledMove(&stackiter, stack.end(), blocking);
                    } while (cycled);

                    blocking->setCycleBegin(pm->type(), curCycles_);
                    curCycles_++;
                    pending_.remove(blocking);
                    stack.pushBack(blocking);
                } else {
                    // This is a new link in the move chain, so keep
                    // searching for a cycle.
                    pending_.remove(blocking);
                    stack.pushBack(blocking);
                }
            } else {
                // Otherwise, pop the last move on the search stack because it's
                // complete and not participating in a cycle. The resulting
                // move can safely be added to the ordered move list.
                PendingMove* done = stack.popBack();
                if (!addOrderedMove(*done))
                    return false;
                movePool_.free(done);
            }
        }
        // If the current queue is empty, it is certain that there are
        // all previous cycles cannot conflict with future cycles,
        // so re-set the counter of pending cycles, while keeping a high-water mark.
        if (numCycles_ < curCycles_)
            numCycles_ = curCycles_;
        curCycles_ = 0;
    }

    return true;
}
Esempio n. 2
0
bool
MoveResolver::resolve()
{
    resetState();
    orderedMoves_.clear();

    InlineList<PendingMove> stack;

    // This is a depth-first-search without recursion, which tries to find
    // cycles in a list of moves. The output is not entirely optimal for cases
    // where a source has multiple destinations, i.e.:
    //      [stack0] -> A
    //      [stack0] -> B
    //
    // These moves may not occur next to each other in the list, making it
    // harder for the emitter to optimize memory to memory traffic. However, we
    // expect duplicate sources to be rare in greedy allocation, and indicative
    // of an error in LSRA.
    //
    // Algorithm.
    //
    // S = Traversal stack.
    // P = Pending move list.
    // O = Ordered list of moves.
    //
    // As long as there are pending moves in P:
    //      Let |root| be any pending move removed from P
    //      Add |root| to the traversal stack.
    //      As long as S is not empty:
    //          Let |L| be the most recent move added to S.
    //
    //          Find any pending move M whose source is L's destination, thus
    //          preventing L's move until M has completed.
    //
    //          If a move M was found,
    //              Remove M from the pending list.
    //              If M's destination is |root|,
    //                  Annotate M and |root| as cycles.
    //                  Add M to S.
    //                  do not Add M to O, since M may have other conflictors in P that have not yet been processed.
    //              Otherwise,
    //                  Add M to S.
    //         Otherwise,
    //              Remove L from S.
    //              Add L to O.
    //
    while (!pending_.empty()) {
        PendingMove *pm = pending_.popBack();

        // Add this pending move to the cycle detection stack.
        stack.pushBack(pm);

        while (!stack.empty()) {
            PendingMove *blocking = findBlockingMove(stack.peekBack());

            if (blocking) {
                if (blocking->to() == pm->from()) {
                    // We annotate cycles at each move in the cycle, and
                    // assert that we do not find two cycles in one move chain
                    // traversal (which would indicate two moves to the same
                    // destination).
                    pm->setInCycle();
                    blocking->setInCycle();
                    hasCycles_ = true;
                    pending_.remove(blocking);
                    stack.pushBack(blocking);
                } else {
                    // This is a new link in the move chain, so keep
                    // searching for a cycle.
                    pending_.remove(blocking);
                    stack.pushBack(blocking);
                }
            } else {
                // Otherwise, pop the last move on the search stack because it's
                // complete and not participating in a cycle. The resulting
                // move can safely be added to the ordered move list.
                PendingMove *done = stack.popBack();
                if (!orderedMoves_.append(*done))
                    return false;
                movePool_.free(done);
            }
        }
    }

    return true;
}