Beispiel #1
0
  public Cost computeRefCost(LoopHeaderChord loop, SubscriptExpr se) {
    Cost tripL = loop.getTripCount();
    InductionVar ivar = loop.getPrimaryInductionVar();
    if (ivar == null) return tripL;

    // Compute
    // tripL = (ubL - lbL + stepL) / stepL

    int nsubs = se.numSubscripts(); // number of subscripts in the subscript
    LoopHeaderChord tloop = loop.getTopLoop();
    VariableDecl iv = ivar.getVar();

    for (int i = 0; i < nsubs - 1; i++) { // for c code
      // If the loop index variable of this loop appears in any of the
      // subscripts other then the last, then return tripL.
      Expr sI = se.getSubscript(i);
      AffineExpr ae = tloop.isAffine(sI);

      if (ae == null) return null;

      if (ae.hasTerm(iv)) return tripL;
    }

    int fs = nsubs - 1;
    Expr s0 = se.getSubscript(fs);
    AffineExpr ae = tloop.isAffine(s0);
    if (ae == null) return null;

    int at = ae.getTermIndexOrig(iv);
    long coeff = 0;
    if (at >= 0) coeff = ae.getCoefficient(at);

    if (coeff == 0) // Invariant Reuse.
    return new Cost(1.0, 0);

    long stepL = loop.getStepValue();
    long stride = stepL * coeff;
    if (stride < 0) stride = -stride;

    // Unit Reuse.

    Type et = se.getCoreType().getPointedTo();
    int bs = et.memorySizeAsInt(Machine.currentMachine);
    int cs = Machine.currentMachine.getCacheSize(bs);
    if (stride <= cs) { // cache line or block size
      tripL.multiply(stride);
      tripL.divide(cs);
      return tripL;
    }

    // No Reuse.

    return tripL;
  }
Beispiel #2
0
  /**
   * Compute the reference groups for this loop. Two array references are in the same group with
   * respect to this loop if - there is a loop-independent dependence between them, or - the
   * dependence distance(dependence vector entry dl) for this loop is less than some constant
   * *dist*, and all other dependence vector entries are 0. - the two array refer to the same array
   * and differ by at most *dist2* in the first subscript dimension, where d is less than or equal
   * to the cache line size in terms of array elements. All other subscripts must be identical.
   * Notes: Here we assume dist1 = dist2 = 2
   */
  private void computeRefGroups(
      int level,
      int dist1,
      int dist2,
      Table<Declaration, SubscriptExpr> arrayRefs,
      Vector<RefGroup> refGroups) {
    if (arrayRefs == null) return;

    Enumeration<Declaration> ek = arrayRefs.keys();
    while (ek.hasMoreElements()) {
      VariableDecl vd = (VariableDecl) ek.nextElement();
      String s = vd.getName(); // array name
      Object[] v = arrayRefs.getRowArray(vd); // vector of SubscriptExpr's
      int vi = v.length;

      for (int j = vi - 1; j >= 0; j--) {
        SubscriptExpr sr = (SubscriptExpr) v[j];
        Vector<LoopHeaderChord> allRelatedLoops =
            sr.allRelatedLoops(); // ** Incorrect when something like a[(j+i][j]
        int arls = allRelatedLoops.size();
        int firstsub = arls - 1; // ** Making an invalid assumption here

        // Process the list of references r' with which r has a data
        // dependence, and  r is the source(data flows from r to r').

        RefGroup rg = new RefGroup(s, sr);
        Object[] edges = graph.getEdges(sr);
        int len = edges.length;

        for (int i = 0; i < len; i++) {
          DDEdge edge = (DDEdge) edges[i];

          if (edge.isSpatial()) continue;

          // Condition(1)-(a) in McKinley's paper

          if (edge.isLoopIndependentDependency()) { // add rP to the RefGroup of r:
            rg.add(edge);
            continue;
          }

          // Condition(1)-(b) in McKinley's paper

          computeEdgeRefs(edge, rg, level, dist1);

          if (arls <= 0) continue;

          // Condition(2) in McKinley's paper
          // rlevel is the level of the loop related to the first subscript.

          int rlevel = allRelatedLoops.elementAt(firstsub).getNestedLevel();

          computeEdgeRefs(edge, rg, rlevel, dist2);
        }

        boolean isInExistingRefGroups = false;
        int rgl = refGroups.size();
        for (int i = 0; i < rgl; i++) {
          RefGroup rg2 = refGroups.elementAt(i);
          if (!rg2.getName().equals(s)) continue;

          isInExistingRefGroups = rg2.contains(rg);

          if (isInExistingRefGroups) {
            rg2.add(rg);
            break;
          }
        }

        if (!isInExistingRefGroups) refGroups.addElement(rg);
      }
    }
  }