path: root/src/compiler/scala/tools/nsc/backend/icode/Linearizers.scala

/* NSC -- new scala compiler
 * Copyright 2005-2013 LAMP/EPFL
 * @author  Martin Odersky
 */


package scala
package tools.nsc
package backend
package icode

import scala.collection.{ mutable, immutable }
import mutable.ListBuffer

trait Linearizers {
  self: ICodes =>

  import global.debuglog
  import opcodes._

  abstract class Linearizer {
    def linearize(c: IMethod): List[BasicBlock]
    def linearizeAt(c: IMethod, start: BasicBlock): List[BasicBlock]
  }

  /**
   * A simple linearizer which predicts all branches to
   * take the 'success' branch and tries to schedule those
   * blocks immediately after the test. This is in sync with
   * how 'while' statements are translated (if the test is
   * 'true', the loop continues).
   */
  class NormalLinearizer extends Linearizer with WorklistAlgorithm {
    type Elem = BasicBlock
    val worklist: WList = new mutable.Stack()
    var blocks: List[BasicBlock] = Nil

    def linearize(m: IMethod): List[BasicBlock] = {
      val b = m.startBlock
      blocks = Nil

      run {
        worklist pushAll (m.exh map (_.startBlock))
        worklist.push(b)
      }

      blocks.reverse
    }

    def linearizeAt(m: IMethod, start: BasicBlock): List[BasicBlock] = {
      blocks = Nil
      worklist.clear()
      linearize(start)
    }

    /** Linearize another subtree and append it to the existing blocks. */
    def linearize(startBlock: BasicBlock): List[BasicBlock] = {
      //blocks = startBlock :: Nil;
      run( { worklist.push(startBlock); } )
      blocks.reverse
    }

    def processElement(b: BasicBlock) =
      if (b.nonEmpty) {
        add(b)
        b.lastInstruction match {
          case JUMP(whereto) =>
            add(whereto)
          case CJUMP(success, failure, _, _) =>
            add(success)
            add(failure)
          case CZJUMP(success, failure, _, _) =>
            add(success)
            add(failure)
          case SWITCH(_, labels) =>
            add(labels)
          case RETURN(_) => ()
          case THROW(clasz) =>   ()
        }
      }

    def dequeue: Elem = worklist.pop()

    /**
     * Prepend b to the list, if not already scheduled.
     * TODO: use better test than linear search
     */
    def add(b: BasicBlock) {
      if (blocks.contains(b))
        ()
      else {
        blocks = b :: blocks
        worklist push b
      }
    }

    def add(bs: List[BasicBlock]): Unit = bs foreach add
  }

  /**
   * Linearize code using a depth first traversal.
   */
  class DepthFirstLinerizer extends Linearizer {
    var blocks: List[BasicBlock] = Nil

    def linearize(m: IMethod): List[BasicBlock] = {
      blocks = Nil

      dfs(m.startBlock)
      m.exh foreach (b => dfs(b.startBlock))

      blocks.reverse
    }

    def linearizeAt(m: IMethod, start: BasicBlock): List[BasicBlock] = {
      blocks = Nil
      dfs(start)
      blocks.reverse
    }

    def dfs(b: BasicBlock): Unit =
      if (b.nonEmpty && add(b))
        b.successors foreach dfs

    /**
     * Prepend b to the list, if not already scheduled.
     * TODO: use better test than linear search
     * @return Returns true if the block was added.
     */
    def add(b: BasicBlock): Boolean =
      !(blocks contains b) && {
        blocks = b :: blocks
        true
      }
  }

  /**
   * Linearize code in reverse post order. In fact, it does
   * a post order traversal, prepending visited nodes to the list.
   * This way, it is constructed already in reverse post order.
   */
  class ReversePostOrderLinearizer extends Linearizer {
    var blocks: List[BasicBlock] = Nil
    val visited = new mutable.HashSet[BasicBlock]
    val added = new mutable.BitSet

    def linearize(m: IMethod): List[BasicBlock] = {
      blocks = Nil
      visited.clear()
      added.clear()

      m.exh foreach (b => rpo(b.startBlock))
      rpo(m.startBlock)

      // if the start block has predecessors, it won't be the first one
      // in the linearization, so we need to enforce it here
      if (m.startBlock.predecessors eq Nil)
        blocks
      else
        m.startBlock :: (blocks.filterNot(_ == m.startBlock))
    }

    def linearizeAt(m: IMethod, start: BasicBlock): List[BasicBlock] = {
      blocks = Nil
      visited.clear()
      added.clear()

      rpo(start)
      blocks
    }

    def rpo(b: BasicBlock): Unit =
      if (b.nonEmpty && !visited(b)) {
        visited += b
        b.successors foreach rpo
        add(b)
      }

    /**
     * Prepend b to the list, if not already scheduled.
     * @return Returns true if the block was added.
     */
    def add(b: BasicBlock) = {
      debuglog("Linearizer adding block " + b.label)

      if (!added(b.label)) {
        added += b.label
        blocks = b :: blocks
      }
    }
  }

  /** A 'dump' of the blocks in this method, which does not
   *  require any well-formedness of the basic blocks (like
   *  the last instruction being a jump).
   */
  class DumpLinearizer extends Linearizer {
    def linearize(m: IMethod): List[BasicBlock] = m.blocks
    def linearizeAt(m: IMethod, start: BasicBlock): List[BasicBlock] = sys.error("not implemented")
  }
}