Example #1
0
  /**
   * This routine is called to split blocks during register allocation. At this point we know that
   * the block was legal before the spill stores and loads were inserted. For every hyperblock with
   * spills that is no longer legal, we pick its largest predicate block and split that in half. One
   * half is then placed into a new hyperblock.
   *
   * <p>The case that was causing trouble results from the classic diamond-shaped predicate flow
   * graph:
   *
   * <pre>
   *     a
   *    / \
   *   b   c
   *    \ /
   *     d
   * </pre>
   *
   * where predicate block <code>a</code> contains most of the instructions, blocks <code>b</code>
   * and <code>c</code> each contain a predicated branch, and block <code>d</code> is empty. Because
   * of spilling, the hyperblock was too big but all of the predicate blocks were legal. As a result
   * we attempted to split block <code>d</code> which did no good.
   *
   * @param blocks is a list of hyperblocks that have had spills inserted
   * @return true if a block was split
   */
  public final boolean splitBlocksWithSpills(Hyperblock hbStart, Vector<Hyperblock> blocks) {
    // If all the blocks with spills are legal we are done.

    boolean illegal = false;
    int bs = blocks.size();
    for (int i = 0; i < bs; i++) {
      Hyperblock hb = blocks.get(i);
      if (!hb.isLegalBlock(true)) {
        illegal = true;
      }
    }

    if (!illegal) {
      return false;
    }

    // Remove any spill code because the register allocator will run again.
    // And remove any blocks which are legal from the set to split.

    for (int i = bs - 1; i > -1; i--) {
      Hyperblock hb = blocks.get(i);
      if (hb.isLegalBlock(true)) {
        blocks.remove(i);
      }
      hb.removeSpillCode();
      workingSet.add(hb);
    }

    // Split hyperblocks that have violations.

    int bl = blocks.size();
    for (int i = bl - 1; i > -1; i--) {
      Hyperblock hb = blocks.remove(i);
      splitHyperblock(hb);
    }

    // The register allocator and block splitter are going to run again.
    // Analyze all the hyperblocks that were created or changed.

    DataflowAnalysis df = new DataflowAnalysis(hbStart, regs);
    df.computeLiveness3();

    int sl = workingSet.size();
    for (int i = sl - 1; i > -1; i--) {
      Hyperblock hb = workingSet.remove(i);
      hb.enterSSA();
      hb.analyzeLeaveSSA();
    }

    return true;
  }
Example #2
0
  /**
   * Find a split point for a block with spills. <br>
   * We know the hyperblock was legal before the insertion of spill code. Return the "deepest" split
   * point in the predicate flow graph, or if there are no split points, the block with the most
   * instructions.
   */
  private PredicateBlock findSplitPointSpills(Hyperblock hb) {
    Vector<PredicateBlock> wl = new Vector<PredicateBlock>();

    PredicateBlock start = hb.getFirstBlock();
    PredicateBlock last = hb.getLastBlock();
    PredicateBlock biggest = null;
    PredicateBlock splitPoint = null;
    int biggestSize = 0;

    if (start.numOutEdges() == 0) {
      return start;
    }

    start.nextVisit();
    start.setVisited();
    wl.add(start);

    // Find the block with the most "real" instructions.
    // We do not include fanout, nulls, or spill code.

    while (!wl.isEmpty()) {
      int sl = wl.size();
      for (int i = 0; i < sl; i++) {
        PredicateBlock block = wl.get(i);
        int size = 0;

        for (Instruction inst = block.getFirstInstruction(); inst != null; inst = inst.getNext()) {
          size++; // TODO?  Should we use the real size of the instruction?
        }

        if (size >= biggestSize) {
          if (block != last) {
            biggestSize = size;
            biggest = block;
          }
        }

        if (block.isSplitPoint() && (block != start)) {
          splitPoint = block;
        }
      }

      wl = hb.getNextPFGLevel(wl);
    }

    return (splitPoint != null) ? splitPoint : biggest;
  }
Example #3
0
  /** The main routine for block splitting. */
  public final void split(Hyperblock hbStart) {
    Stack<Node> wl = WorkArea.<Node>getStack("split");
    DataflowAnalysis df = new DataflowAnalysis(hbStart, regs);
    int trips = 0;

    // Add all the hyperblocks to the working set.

    hbStart.nextVisit();
    hbStart.setVisited();
    wl.push(hbStart);

    while (!wl.isEmpty()) {
      Hyperblock hb = (Hyperblock) wl.pop();
      hb.pushOutEdges(wl);
      workingSet.add(hb);
    }

    // Split the hyperblocks.

    while (!workingSet.isEmpty()) {
      df.computeLiveness3();
      wl.addAll(workingSet);

      while (!wl.isEmpty()) {
        Hyperblock hb = (Hyperblock) wl.pop();
        hb.enterSSA();
        hb.analyzeLeaveSSA();

        if (!hb.isLegalBlock(true)) {
          splitHyperblock(hb);
        } else {
          workingSet.remove(hb);
        }
      }

      if ((++trips % WARN_SPLIT_ATTEMPTS) == 0) {
        System.err.println(
            "** Warning: the block splitter has run "
                + trips
                + " times for "
                + gen.getCurrentRoutine().getName()
                + "().");
      }
    }

    WorkArea.<Node>returnStack(wl);
  }
Example #4
0
  /** Split an unpredicated predicate block. */
  private void splitBlock(Hyperblock hb, PredicateBlock block) {
    int chunkSize = (block.getBlockSize() + block.getFanout()) / 2;
    int maxChunk = (int) (Trips2Machine.maxBlockSize * MAXFILL);

    if (chunkSize > maxChunk) {
      chunkSize = maxChunk;
    }

    Instruction splitLocation = findSplitLocation(hb, block, chunkSize);
    PredicateBlock start = block.cut(splitLocation, gen);
    Hyperblock nhb = new Hyperblock(start, regs);

    // Insert the new hyperblock into the HFG.

    for (int i = hb.numOutEdges() - 1; i > -1; i--) {
      Hyperblock out = (Hyperblock) hb.getOutEdge(i);
      out.replaceInEdge(hb, nhb);
      hb.deleteOutEdge(out);
      nhb.addOutEdge(out);
    }

    hb.addOutEdge(nhb);
    nhb.addInEdge(hb);
    workingSet.add(nhb);

    hb.invalidateDomination();
    hb.findLastBlock();
    hb.determinePredicatesBranches();
    nhb.findLastBlock();
    nhb.determinePredicatesBranches();

    // Update the return block if it has changed.

    if (gen.getReturnBlock() == hb) {
      gen.setReturnBlock(nhb);
    }
  }
Example #5
0
  /** Reverse if-convert the given predicate block from the hyperblock. */
  private void reverseIfConvert(Hyperblock hb, PredicateBlock start) {
    Stack<Node> wl = WorkArea.<Node>getStack("reverseIfConvert");
    Stack<PredicateBlock> reverse = WorkArea.<PredicateBlock>getStack("reverseIfConvert");
    Vector<PredicateBlock> blocks = new Vector<PredicateBlock>();
    Vector<Hyperblock> hbs = new Vector<Hyperblock>();

    // Find the blocks which need to be reverse if-converted.

    start.nextVisit();
    start.setVisited();
    wl.add(start);

    while (!wl.isEmpty()) {
      PredicateBlock block = (PredicateBlock) wl.pop();
      block.pushOutEdges(wl);

      for (int i = 0; i < block.numInEdges(); i++) {
        PredicateBlock pred = (PredicateBlock) block.getInEdge(i);
        if (!pred.visited()) {
          blocks.add(block);
          break;
        } else if (blocks.contains(pred) && block.numInEdges() > 1) {
          blocks.add(block);
          break;
        }
      }
    }

    // Order the blocks to reverse if-convert based on their depth from the root.

    PredicateBlock head = hb.getFirstBlock();
    Vector<PredicateBlock> wl2 = new Vector<PredicateBlock>();

    head.nextVisit();
    head.setVisited();
    wl2.add(head);

    while (!wl2.isEmpty()) {
      int l = wl2.size();

      for (int i = 0; i < l; i++) {
        PredicateBlock block = wl2.get(i);
        if (blocks.contains(block)) {
          blocks.remove(block);
          reverse.push(block);
        }
      }

      wl2 = hb.getNextPFGLevel(wl2);
    }

    // Remove the special "dummy" last block from the PFG.

    PredicateBlock last = hb.getLastBlock();
    assert (last.numOutEdges() == 0 && !last.isPredicated());

    if (last.getFirstInstruction() == null) {
      for (int i = last.numInEdges() - 1; i > -1; i--) {
        PredicateBlock pred = (PredicateBlock) last.getInEdge(i);
        pred.deleteOutEdge(last);
        last.deleteInEdge(pred);
      }
      reverse.remove(last);
    }

    // Reverse if-convert.

    while (!reverse.isEmpty()) {
      PredicateBlock block = reverse.pop();
      Hyperblock hbn = reverseIfConvertBlock(block);

      hbs.add(hbn);
      workingSet.add(hbn);
    }

    // Update the PFG.

    hb.updateLastBlock();
    hb.invalidateDomination(); // The dominators are now invalid.

    // Insert the new hyperblocks in the HFG.

    HashMap<Instruction, Hyperblock> entries = computeEntries(hb, hbs);
    hbs.add(hb);
    Hyperblock.computeHyperblockFlowGraph(hbs, entries);

    // Update the return block.  Since 'hbs' is an ordered list, the
    // first element in the list is the hyperblock with the return
    // because this was the original tail of the PFG which was reverse
    // if-converted.

    if (hb == gen.getReturnBlock()) {
      gen.setReturnBlock(hbs.firstElement());
    }

    WorkArea.<Node>returnStack(wl);
    WorkArea.<PredicateBlock>returnStack(reverse);
  }
Example #6
0
  /** Find the predicate block in a hyperblock to split. */
  private PredicateBlock findSplitPoint(Hyperblock hb) {
    Vector<PredicateBlock> wl = new Vector<PredicateBlock>();

    int totalSize = hb.getFanout() + hb.getBlockSize();
    int splits = (totalSize / Trips2Machine.maxBlockSize) + 1;
    int splitSize = totalSize / splits;
    int hbSize = 0;
    PredicateBlock start = hb.getFirstBlock();
    PredicateBlock lastUnpredicated = null;
    int lastUnpredicatedHBSize = 0;

    assert (hb.numSpills() == 0) : "This method should not be called for blocks with spills.";

    start.nextVisit();
    start.setVisited();
    wl.add(start);

    while (!wl.isEmpty()) {
      int l = wl.size();
      int levelSize = 0;
      int levelLSID = 0;

      // Compute the statistics for this level of the PFG.

      for (int i = 0; i < l; i++) {
        PredicateBlock block = wl.get(i);
        int blockSize = block.getBlockSize() + block.getFanout();
        int id = block.maxLSID();

        levelSize += blockSize;
        if (id > levelLSID) {
          levelLSID = id;
        }

        // Remember the block and the hyperblock size if this block is unpredicated
        // and not the special exit block.
        // TODO - Can we remove the restriction on being the last block now?

        if (!block.isPredicated()) {
          if (block.numOutEdges() > 0) {
            if (lastUnpredicatedHBSize < (blockSize + hbSize)) {
              lastUnpredicatedHBSize = blockSize + hbSize;
              lastUnpredicated = block;
            }
          }
        }
      }

      // Determine if all the blocks can be added to the hyperblock.

      int size = hbSize + levelSize;
      if ((size > Trips2Machine.maxBlockSize) || (levelLSID >= Trips2Machine.maxLSQEntries)) {
        break;
      }

      hbSize = size;
      wl = hb.getNextPFGLevel(wl);
    }

    assert (!wl.isEmpty()) : "This block does not need to be split?";

    // If there is only one unpredicated block in the level and it is
    // not the special exit block use it.  Or if this is the only
    // block in the PFG.

    int l = wl.size();
    if (l == 1) {
      PredicateBlock block = wl.get(0);
      if (!block.isPredicated()) {
        if ((start == block) || (block.numOutEdges() > 0)) {
          // System.out.println("block");
          return block;
        }
      }
    }

    // Is there a last known unpredicated block of adequate size use it.

    if (lastUnpredicated != null) {
      if (lastUnpredicatedHBSize >= splitSize) {
        // System.out.println("*** last unpred is greater than split sz " + splitSize);
        return lastUnpredicated;
      }
    }

    // Try to find a parent that's unpredicated unless the parent is
    // the first block.

    for (int i = 0; i < l; i++) {
      PredicateBlock block = wl.get(i);
      int pl = block.numInEdges();
      for (int j = 0; j < pl; j++) {
        PredicateBlock pred = (PredicateBlock) block.getInEdge(j);
        if (!pred.isPredicated() && pred.numInEdges() > 1) {
          // System.out.println("unpred parent not start");
          return pred;
        }
      }
    }

    // Reverse if-convert the largest block in this level which is not
    // an exit.  Although this seems like a good idea, there is not
    // always enough room in the hyperblock to fanout the live-outs to
    // the write instructions.  Don't do this for now. -- Aaron

    PredicateBlock candidate = null;
    int largest = 0;
    //     for (int i = 0; i < l; i++) {
    //       PredicateBlock block = (PredicateBlock) wl.get(i);
    //       int            bsize = block.getBlockSize() + block.getFanout() + block.getSpillSize();
    //       if ((bsize > largest) && (block.numBranches() == 0)) {
    //         largest   = bsize;
    //         candidate = block;
    //       }
    //     }

    //     if (candidate != null) {
    //       //System.out.println("level no exit");
    //       return candidate;
    //     }

    // Reverse if-convert a parent which is not start.
    // Prefer parents that are split points.

    for (int i = 0; i < l; i++) {
      PredicateBlock block = wl.get(i);
      int pl = block.numInEdges();
      for (int j = 0; j < pl; j++) {
        PredicateBlock pred = (PredicateBlock) block.getInEdge(j);
        if (pred != start) {
          if (pred.isSplitPoint()) {
            // System.out.println("pred out isSplit not start");
            return pred;
          }
          candidate = pred;
        }
      }
    }

    if (candidate != null) {
      // System.out.println("pred out not start");
      return candidate;
    }

    // Reverse if-convert the largest successor of start without an exit.

    largest = 0;
    for (int i = 0; i < start.numOutEdges(); i++) {
      PredicateBlock block = (PredicateBlock) start.getOutEdge(i);
      int bsize = block.getBlockSize() + block.getFanout() + block.getSpillSize();
      if ((bsize > largest) && !block.hasBranch()) {
        largest = bsize;
        candidate = block;
      }
    }

    if (candidate != null) {
      // System.out.println("start successor no exit");
      return candidate;
    }

    // System.out.println("1st start successor ?");
    return (PredicateBlock) start.getOutEdge(0);
  }