/* NSC -- new Scala compiler
 * Copyright 2005-2011 LAMP/EPFL
 * @author  Martin Odersky
 */


package scala.tools.nsc
package backend
package icode

import scala.collection.{ mutable, immutable }
import mutable.{ ArrayBuffer }
import util.{ Position, NoPosition }
import backend.icode.analysis.ProgramPoint

trait BasicBlocks {
  self: ICodes =>
  
  import opcodes._
  import global.{ settings, log, nme }
  import nme.isExceptionResultName

  /** This class represents a basic block. Each
   *  basic block contains a list of instructions that are
   *  either executed all, or none. No jumps
   *  to/from the "middle" of the basic block are allowed (modulo exceptions).
   */
  class BasicBlock(val label: Int, val method: IMethod)
        extends AnyRef
        with ProgramPoint[BasicBlock]
        with Seq[Instruction] {

    import BBFlags._
    
    def code = method.code
    
    /** Flags of this basic block. */
    private var flags: Int = 0

    /** Does this block have the given flag? */
    def hasFlag(flag: Int): Boolean = (flags & flag) != 0
    
    /** Set the given flag. */
    private def setFlag(flag: Int): Unit = flags |= flag
    private def resetFlag(flag: Int) {
      flags &= ~flag
    }
    
    /** Is this block closed? */
    def closed: Boolean = hasFlag(CLOSED)
    def closed_=(b: Boolean) = if (b) setFlag(CLOSED) else resetFlag(CLOSED)
    
    /** When set, the <code>emit</code> methods will be ignored. */
    def ignore: Boolean = hasFlag(IGNORING)
    def ignore_=(b: Boolean) = if (b) setFlag(IGNORING) else resetFlag(IGNORING)

    /** Is this block the head of a while? */
    def loopHeader = hasFlag(LOOP_HEADER)
    def loopHeader_=(b: Boolean) = 
      if (b) setFlag(LOOP_HEADER) else resetFlag(LOOP_HEADER)
    
    /** Is this block the start block of an exception handler? */
    def exceptionHandlerStart = hasFlag(EX_HEADER)
    def exceptionHandlerStart_=(b: Boolean) = 
      if (b) setFlag(EX_HEADER) else resetFlag(EX_HEADER)

    /** Has this basic block been modified since the last call to 'successors'? */
    def touched = hasFlag(DIRTYSUCCS)
    def touched_=(b: Boolean) = if (b) {
      setFlag(DIRTYSUCCS | DIRTYPREDS)
    } else {
      resetFlag(DIRTYSUCCS | DIRTYPREDS)
    }

    // basic blocks start in a dirty state
    setFlag(DIRTYSUCCS | DIRTYPREDS)

    /** Cached predecessors. */
    var preds: List[BasicBlock] = null
    
    /** Local variables that are in scope at entry of this basic block. Used
     *  for debugging information.
     */
    var varsInScope: mutable.Set[Local] = new mutable.LinkedHashSet()
    
    /** ICode instructions, used as temporary storage while emitting code.
     * Once closed is called, only the `instrs' array should be used.
     */
    private var instructionList: List[Instruction] = Nil

    private var instrs: Array[Instruction] = _

    override def toList: List[Instruction] =
      if (closed) instrs.toList else instructionList.reverse
    
    /** Return an iterator over the instructions in this basic block. */
    def iterator: Iterator[Instruction] =
      if (closed) instrs.iterator else instructionList.reverse.iterator
    
    /** return the underlying array of instructions */
    def getArray: Array[Instruction] = {
      assert(closed)
      instrs
    }

    def fromList(is: List[Instruction]) {
      code.touched = true
      instrs = is.toArray
      closed = true
    }

    /** Return the index of inst. Uses reference equality.
     *  Returns -1 if not found.
     */
    def indexOf(inst: Instruction): Int = {
      assert(closed)
      instrs indexWhere (_ eq inst)
    }

    /** Apply a function to all the instructions of the block. */
    override def foreach[U](f: Instruction => U) = {
      if (!closed) {
        method.dump
        global.abort("Traversing an open block!: " + label + " in " + method)
      }
      instrs foreach f
    }

    /** The number of instructions in this basic block so far. */
    def length = if (closed) instrs.length else instructionList.length

    /** Return the n-th instruction. */
    def apply(n: Int): Instruction =
      if (closed) instrs(n) else instructionList.reverse(n)

    ///////////////////// Substitutions ///////////////////////

    /**
     * Replace the instruction at the given position. Used by labels when
     * they are anchored. It retains the position of the previous instruction.
     */
    def replaceInstruction(pos: Int, instr: Instruction): Boolean = {
      assert(closed, "Instructions can be replaced only after the basic block is closed")
      instr.setPos(instrs(pos).pos)
      instrs(pos) = instr
      code.touched = true
      true
    }

    /**
     * Replace the given instruction with the new one. 
     * Returns `true' if it actually changed something. 
     * It retains the position of the previous instruction.
     */
    def replaceInstruction(oldInstr: Instruction, newInstr: Instruction): Boolean = {
      assert(closed, "Instructions can be replaced only after the basic block is closed")
      
      indexOf(oldInstr) match {
        case -1   => false
        case idx  =>
          newInstr setPos oldInstr.pos
          instrs(idx) = newInstr
          code.touched = true
          true
      }
    }

    /** Replaces <code>oldInstr</code> with <code>is</code>. It does not update
     *  the position field in the newly inserted instructions, so it behaves
     *  differently than the one-instruction versions of this function.
     *
     *  @param iold ..
     *  @param is   ..
     *  @return     ..
     */
    def replaceInstruction(oldInstr: Instruction, is: List[Instruction]): Boolean = {
      assert(closed, "Instructions can be replaced only after the basic block is closed")
      
      indexOf(oldInstr) match {
        case -1   => false
        case idx  =>
          instrs = instrs.patch(idx, is, 1)
          code.touched = true
          true
      }
    }
    
    /** Insert instructions in 'is' immediately after index 'idx'. */
    def insertAfter(idx: Int, is: List[Instruction]) {
      assert(closed, "Instructions can be replaced only after the basic block is closed")
      
      instrs = instrs.patch(idx + 1, is, 0)
      code.touched = true
    }

    /** Removes instructions found at the given positions.
     *
     *  @param positions ...
     */
    def removeInstructionsAt(positions: Int*) {
      assert(closed)
      instrs = instrs.indices.toArray filterNot positions.toSet map instrs
      code.touched = true
    }
    
    /** Remove the last instruction of this basic block. It is
     *  fast for an open block, but slower when the block is closed.
     */
    def removeLastInstruction() {
      if (closed) 
        removeInstructionsAt(size)
      else {
        instructionList = instructionList.tail
        code.touched = true
      }
    }

    /** Replaces all instructions found in the map.
     *
     *  @param map ...
     */
    def subst(map: Map[Instruction, Instruction]): Unit =
      if (!closed)
        instructionList = instructionList map (x => map.getOrElse(x, x))
      else
        instrs.zipWithIndex collect {
          case (oldInstr, i) if map contains oldInstr =>
            code.touched |= replaceInstruction(i, map(oldInstr))
        }

    ////////////////////// Emit //////////////////////


    /** Add a new instruction at the end of the block,
     *  using the same source position as the last emitted instruction
     */
    def emit(instr: Instruction) {
      val pos = if (instructionList.isEmpty) NoPosition else instructionList.head.pos
      emit(instr, pos)
    }

    /** Emitting does not set touched to true. During code generation this is a hotspot and
     *  setting the flag for each emit is a waste. Caching should happen only after a block
     *  is closed, which sets the DIRTYSUCCS flag.
     */
    def emit(instr: Instruction, pos: Position) {
/*      if (closed) {
        print()
        Console.println("trying to emit: " + instr)
      } */
      assert(!closed || ignore, "BasicBlock closed")

      if (ignore) {
        if (settings.debug.value) {
          /** Trying to pin down what it's likely to see after a block has been
           *  put into ignore mode so we hear about it if there's a problem.
           */
          instr match {
            case JUMP(_) | RETURN(_) | THROW(_) | SCOPE_EXIT(_)               => // ok
            case STORE_LOCAL(local) if isExceptionResultName(local.sym.name)  => // ok
            case x => log("Ignoring instruction, possibly at our peril, at " + pos + ": " + x)
          }
        }
      }
      else {
        instr.setPos(pos)
        instructionList ::= instr
      }
    }
    
    def emit(instrs: Seq[Instruction]) {
      instrs foreach (i => emit(i, i.pos))
    }
    
    /** The semantics of this are a little odd but it's designed to work
     *  seamlessly with the existing code.  It emits each supplied instruction,
     *  then closes the block.  The odd part is that if the instruction has
     *  pos == NoPosition, it calls the 1-arg emit, but otherwise it calls
     *  the 2-arg emit.  This way I could retain existing behavior exactly by
     *  calling setPos on any instruction using the two arg version which
     *  I wanted to include in a call to emitOnly.
     */
    def emitOnly(instrs: Instruction*) {
      instrs foreach (i => if (i.pos == NoPosition) emit(i) else emit(i, i.pos))
      this.close
    }

    /** do nothing if block is already closed */
    def closeWith(instr: Instruction) {
      if (closed) () else {
        emit(instr)
        close
      }
    }

    def closeWith(instr: Instruction, pos: Position) {
      if (closed) () else {
        emit(instr, pos)
        close
      }
    }

    /** Close the block */
    def close() {
      assert(!closed || ignore)
      assert(instructionList.nonEmpty, "Empty block.")
      closed = true
      setFlag(DIRTYSUCCS)
      instructionList = instructionList.reverse
      instrs = instructionList.toArray
    }

    def open() {
      assert(closed)
      closed = false
      ignore = false
      touched = true
      instructionList = instructionList.reverse  // prepare for appending to the head
    }

    def clear() {
      instructionList = Nil
      instrs = null
      preds  = null
    }

    override def isEmpty: Boolean = instructionList.isEmpty

    /** Enter ignore mode: new 'emit'ted instructions will not be
     *  added to this basic block. It makes the generation of THROW
     *  and RETURNs easier.
     */
    def enterIgnoreMode() = {
      ignore = true
    }

    def exitIgnoreMode() {
      assert(ignore, "Exit ignore mode when not in ignore mode.")
      ignore = false
    }

    /** Return the last instruction of this basic block. */
    def lastInstruction =
      if (closed) instrs.last
      else instructionList.head

    def firstInstruction =
      if (closed) instrs(0)
      else instructionList.last
    
    def exceptionSuccessorsForBlock(block: BasicBlock): List[BasicBlock] =
      method.exh collect { case x if x covers block => x.startBlock }

    /** Cached value of successors. Must be recomputed whenever a block in the current method is changed. */
    private var succs: List[BasicBlock] = Nil
    private def updateSuccs() {
      resetFlag(DIRTYSUCCS)      
      succs =
        if (isEmpty) Nil
        else exceptionSuccessors ++ directSuccessors ++ indirectExceptionSuccessors
    }

    def successors : List[BasicBlock] = {    
      if (touched) updateSuccs()
      succs
    }

    def directSuccessors: List[BasicBlock] =
      if (isEmpty) Nil else lastInstruction match {
        case JUMP(whereto)              => List(whereto)
        case CJUMP(succ, fail, _, _)    => fail :: succ :: Nil
        case CZJUMP(succ, fail, _, _)   => fail :: succ :: Nil
        case SWITCH(_, labels)          => labels
        case RETURN(_)                  => Nil
        case THROW(_)                   => Nil
        case _ =>
          if (closed) {
            dump
            global.abort("The last instruction is not a control flow instruction: " + lastInstruction)
          }
          else Nil
      }
    
    def exceptionSuccessors: List[BasicBlock] =
      exceptionSuccessorsForBlock(this)

    /** Return a list of successors for 'b' that come from exception handlers
     *  covering b's (non-exceptional) successors. These exception handlers 
     *  might not cover 'b' itself. This situation corresponds to an 
     *  exception being thrown as the first thing of one of b's successors.
     */
    def indirectExceptionSuccessors: List[BasicBlock] =
      directSuccessors flatMap exceptionSuccessorsForBlock distinct

    /** Returns the predecessors of this block.     */
    def predecessors: List[BasicBlock] = {
      if (hasFlag(DIRTYPREDS)) {
        resetFlag(DIRTYPREDS)
        preds = code.blocks.iterator filter (_.successors contains this) toList
      }
      preds
    }

    override def equals(other: Any): Boolean = other match {
      case that: BasicBlock => (that.label == label) && (that.code == code)
      case _ => false
    }

    override def hashCode = label * 41 + code.hashCode
    
    // Instead of it, rather use a printer
    def print() { print(java.lang.System.out) }

    def print(out: java.io.PrintStream) {
      out.println("block #"+label+" :")
      foreach(i => out.println("  " + i))
      out.print("Successors: ")
      successors.foreach((x: BasicBlock) => out.print(" "+x.label.toString()))
      out.println()
    }

    private def succString = if (successors.isEmpty) "[S: N/A]" else successors.distinct.mkString("[S: ", ", ", "]")
    private def predString = if (predecessors.isEmpty) "[P: N/A]" else predecessors.distinct.mkString("[P: ", ", ", "]")

    override def toString(): String = "" + label

    def blockContents = {
      def posStr(p: Position) = if (p.isDefined) p.line.toString else "<??>"
      val xs = this.toList map (instr => posStr(instr.pos) + "\t" + instr)
      xs.mkString(fullString + " {\n  ", "\n  ", "\n}")
    }
    def predContents = predecessors.map(_.blockContents).mkString(predecessors.size + " preds:\n", "\n", "\n")
    def succContents = successors.map(_.blockContents).mkString(successors.size + " succs:\n", "\n", "\n")

    def fullString: String = List("Block", label, succString, predString, flagsString) mkString " "    
    def flagsString: String = BBFlags.flagsToString(flags)
  }
}

object BBFlags {
  val flagMap = Map[Int, String](
    LOOP_HEADER -> "loopheader",
    IGNORING -> "ignore",
    EX_HEADER -> "exheader",
    CLOSED -> "closed",
    DIRTYSUCCS -> "dirtysuccs",
    DIRTYPREDS -> "dirtypreds"
  )
  def flagsToString(flags: Int) = {
    flagMap collect { case (bit, name) if (bit & flags) != 0 => "<" + name + ">" } mkString " "
  }

  /** This block is a loop header (was translated from a while). */
  final val LOOP_HEADER = (1 << 0)
  
  /** Ignoring mode: emit instructions are dropped. */
  final val IGNORING    = (1 << 1)
  
  /** This block is the header of an exception handler. */
  final val EX_HEADER   = (1 << 2)
  
  /** This block is closed. No new instructions can be added. */
  final val CLOSED      = (1 << 3)

  /** Code has been changed, recompute successors. */
  final val DIRTYSUCCS  = (1 << 4)

  /** Code has been changed, recompute predecessors. */
  final val DIRTYPREDS  = (1 << 5)
}