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Scala example source code file (CopyPropagation.scala)

This example Scala source code file (CopyPropagation.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Scala tags/keywords

boolean, boxed, deref, deref, location, nil, record, record, state, symbol, unknown, unknown, value, value

The Scala CopyPropagation.scala source code

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


package scala.tools.nsc
package backend.icode.analysis

import scala.collection.mutable.{ Map, HashMap }

/** A modified copy-propagation like analysis. It 
 *  is augmented with a record-like value which is used
 *  to represent closures.
 *
 *  @author Iulian Dragos
 */
abstract class CopyPropagation {
  val global: Global
  import global._
  import icodes._

  /** Locations can be local variables, this, and fields. */
  abstract sealed class Location
  case class LocalVar(l: Local) extends Location
  case class Field(r: Record, sym: Symbol) extends Location
  case object This extends Location

  /** Values that can be on the stack. */
  abstract class Value {
    def isRecord = false
  }
  case class Record(cls: Symbol, bindings: Map[Symbol, Value]) extends Value {
    override def isRecord = true
  }
  /** The value of some location in memory. */
  case class Deref(l: Location) extends Value
  
  /** The boxed value of some location. */
  case class Boxed(l: Location) extends Value
  
  /** The constant value c. */
  case class Const(c: Constant) extends Value
  
  /** Unknown. */
  case object Unknown extends Value
  
  /** The bottom record. */
  object AllRecords extends Record(NoSymbol, new HashMap[Symbol, Value])

  /** The lattice for this analysis.   */
  object copyLattice extends SemiLattice {
    type Bindings = Map[Location, Value]

    def emptyBinding = new HashMap[Location, Value]()

    class State(val bindings: Bindings, var stack: List[Value]) {
      
      override def hashCode = bindings.hashCode + stack.hashCode
      /* comparison with bottom is reference equality! */
      override def equals(that: Any): Boolean = that match {
        case x: State =>
          if ((this eq bottom) || (this eq top) || (x eq bottom) || (x eq top)) this eq x
          else bindings == x.bindings && stack == x.stack
        case _ =>
          false
      }

      /* Return an alias for the given local. It returns the last
       * local in the chain of aliased locals. Cycles are not allowed
       * to exist (by construction).
       */
      def getAlias(l: Local): Local = {
        var target = l
        var stop = false
        
        while (bindings.isDefinedAt(LocalVar(target)) && !stop) {
          bindings(LocalVar(target)) match {
            case Deref(LocalVar(t)) => target = t
            case _ => stop = true
          }
        }
        target
      }

      /* Return the value bound to the given local. */
      def getBinding(l: Local): Value = {
        def loop(lv: Local): Option[Value] = (bindings get LocalVar(lv)) match {
          case Some(Deref(LocalVar(t))) => loop(t)
          case x                        => x
        }
        loop(l) getOrElse Deref(LocalVar(l))
      }

      /* Return the binding for the given field of the given record */
      def getBinding(r: Record, f: Symbol): Value = {
        assert(r.bindings contains f, "Record " + r + " does not contain a field " + f)
        
        r.bindings(f) match {
          case Deref(LocalVar(l)) => getBinding(l)
          case target             => target
        }
      }
      
      /** Return a local which contains the same value as this field, if any.
       * If the field holds a reference to a local, the returned value is the
       * binding of that local.
       */
      def getFieldValue(r: Record, f: Symbol): Option[Value] = r.bindings get f map {
        case Deref(LocalVar(l))             => getBinding(l)
        case target @ Deref(Field(r1, f1))  => getFieldValue(r1, f1) getOrElse target
        case target                         => target
      }
      
      /** The same as getFieldValue, but never returns Record/Field values. Use
       *  this when you want to find a replacement for a field value (either a local,
       *  or a constant/this value). 
       */
      def getFieldNonRecordValue(r: Record, f: Symbol): Option[Value] = {
        assert(r.bindings contains f, "Record " + r + " does not contain a field " + f)

        r.bindings(f) match {
          case Deref(LocalVar(l)) => 
            val alias = getAlias(l)
            val derefAlias = Deref(LocalVar(alias))
            
            Some(getBinding(alias) match {
              case Record(_, _)         => derefAlias
              case Deref(Field(r1, f1)) => getFieldNonRecordValue(r1, f1) getOrElse derefAlias
              case Boxed(_)             => derefAlias
              case v                    => v
            })
          case Deref(Field(r1, f1)) => getFieldNonRecordValue(r1, f1)
          case target @ Deref(This) => Some(target)
          case target @ Const(k)    => Some(target)
          case _                    => None
        }
      }

      override def toString(): String =
        "\nBindings: " + bindings + "\nStack: " + stack;

      def dup: State = {
        val b: Bindings = new HashMap()
        b ++= bindings
        new State(b, stack)
      }
    }

    type Elem = State

    val top    = new State(emptyBinding, Nil)
    val bottom = new State(emptyBinding, Nil)

    val exceptionHandlerStack = Unknown :: Nil

    def lub2(exceptional: Boolean)(a: Elem, b: Elem): Elem = {
      if (a eq bottom) b
      else if (b eq bottom) a
      else if (a == b) a
      else {
        //assert(!(a.stack eq exceptionHandlerStack) && !(b.stack eq exceptionHandlerStack)) 
        val resStack = 
          if (exceptional) exceptionHandlerStack
          else {
//            if (a.stack.length != b.stack.length)
//              throw new LubException(a, b, "Invalid stacks in states: ");
            (a.stack, b.stack).zipped map { (v1, v2) => 
              if (v1 == v2) v1 else Unknown 
            }
          }
      
/*        if (a.stack.length != b.stack.length)
          throw new LubException(a, b, "Invalid stacks in states: ");
        val resStack = List.map2(a.stack, b.stack) { (v1, v2) => 
          if (v1 == v2) v1 else Unknown 
        }
        */
        val resBindings = new HashMap[Location, Value]
        
        for ((k, v) <- a.bindings if b.bindings.isDefinedAt(k) && v == b.bindings(k))
          resBindings += (k -> v);
        new State(resBindings, resStack)
      }
    }
  }

  final class CopyAnalysis extends DataFlowAnalysis[copyLattice.type] {
    type P = BasicBlock
    val lattice = copyLattice

    var method: IMethod = _

    def init(m: IMethod) {
      this.method = m

      init {
        worklist += m.code.startBlock
        worklist ++= (m.exh map (_.startBlock))
        m.code.blocks.foreach { b =>
          in(b)  = lattice.bottom
          out(b) = lattice.bottom
          assert(out.contains(b))
          log("Added point: " + b)
        } 
        m.exh foreach { e =>
          in(e.startBlock) = new copyLattice.State(copyLattice.emptyBinding, copyLattice.exceptionHandlerStack);
        }

        // first block is special: it's not bottom, but a precisely defined state with no bindings
        in(m.code.startBlock) = new lattice.State(lattice.emptyBinding, Nil);
      }
    }

    override def run() {
      forwardAnalysis(blockTransfer)
      if (settings.debug.value) {
        linearizer.linearize(method).foreach(b => if (b != method.code.startBlock)
          assert(in(b) != lattice.bottom, 
            "Block " + b + " in " + this.method + " has input equal to bottom -- not visited?"));
      }
    }

    def blockTransfer(b: BasicBlock, in: lattice.Elem): lattice.Elem =
      b.foldLeft(in)(interpret)
    
    import opcodes._
    
    private def retain[A, B](map: Map[A, B])(p: (A, B) => Boolean) = {
      for ((k, v) <- map ; if !p(k, v)) map -= k
      map
    }

    /** Abstract interpretation for one instruction. */
    def interpret(in: copyLattice.Elem, i: Instruction): copyLattice.Elem = {
      var out = in.dup

      if (settings.debug.value) {
        log("- " + i)
        log("in: " + in)
        log("\n")
      }

      i match {
        case THIS(_) =>
          out.stack = Deref(This) :: out.stack

        case CONSTANT(k) =>
          if (k.tag != UnitTag)
            out.stack = Const(k) :: out.stack;
          
        case LOAD_ARRAY_ITEM(_) =>
          out.stack = (Unknown :: out.stack.drop(2))

        case LOAD_LOCAL(local) =>
          out.stack = Deref(LocalVar(local)) :: out.stack

        case LOAD_FIELD(field, isStatic) =>
          if (isStatic)
            out.stack = Unknown :: out.stack; /* ignore static fields */
          else {
            val v1 = in.stack match {
              case (r @ Record(cls, bindings)) :: xs =>
                Deref(Field(r, field))
              
              case Deref(LocalVar(l)) :: _ =>
                in.getBinding(l) match {
                  case r @ Record(cls, bindings) => Deref(Field(r, field))
                  case _ => Unknown
                }
                
              case Deref(Field(r, f)) :: _ =>
                val fld = in.getFieldValue(r, f)
                fld match {
                  case Some(r @ Record(cls, bindings)) if bindings.isDefinedAt(f) =>
                  	in.getFieldValue(r, f).getOrElse(Unknown)
                  case _ => Unknown
                }
                
              case _ => Unknown
            }
            out.stack = v1 :: out.stack.drop(1)
          }
            
        case LOAD_MODULE(module) =>
          out.stack = Unknown :: out.stack
          
        case STORE_ARRAY_ITEM(kind) =>
          out.stack = out.stack.drop(3)

        case STORE_LOCAL(local) =>
          cleanReferencesTo(out, LocalVar(local))
          in.stack match {
            case Unknown :: xs => ()
            case v :: vs => 
              v match {
                case Deref(LocalVar(other)) =>
                  if (other != local) 
                    out.bindings += (LocalVar(local) -> v);
                case _ =>
                  out.bindings += (LocalVar(local) -> v)
              }
            case Nil =>
              sys.error("Incorrect icode in " + method + ". Expecting something on the stack.")
          }
          out.stack = out.stack drop 1;
          
        case STORE_THIS(_) =>
          cleanReferencesTo(out, This)
          out.stack = out.stack drop 1
          
        case STORE_FIELD(field, isStatic) =>
          if (isStatic) 
            out.stack = out.stack.drop(1);
          else {
            out.stack = out.stack.drop(2);
            cleanReferencesTo(out, Field(AllRecords, field));
            in.stack match {
              case v :: Record(_, bindings) :: vs =>
                bindings += (field -> v)
              case _ => ();
            }
          }
          
        case CALL_PRIMITIVE(primitive) =>
          // TODO: model primitives
          out.stack = Unknown :: out.stack.drop(i.consumed)

        case CALL_METHOD(method, style) => style match {
          case Dynamic | InvokeDynamic =>
            out = simulateCall(in, method, false)

          case Static(onInstance) =>
            if (onInstance) {
              val obj = out.stack.drop(method.info.paramTypes.length).head
//              if (method.isPrimaryConstructor) {
              if (method.isPrimaryConstructor) {
                obj match {
                  case Record(_, bindings) =>
                    for (v <- out.stack.take(method.info.paramTypes.length + 1)
                         if v ne obj) {
                       bindings ++= getBindingsForPrimaryCtor(in, method);
                    }
                  case _ => ()
                }
                // put the Record back on the stack and remove the 'returned' value
                out.stack = out.stack.drop(1 + method.info.paramTypes.length)
              } else
                out = simulateCall(in, method, false)
            } else 
              out = simulateCall(in, method, true)

          case SuperCall(_) =>
            out = simulateCall(in, method, false)
        }
        
        case BOX(tpe) =>
          val top = out.stack.head match {
            case Deref(loc) => Boxed(loc)
            case _          => Unknown
          }
          out.stack = top :: out.stack.tail

        case UNBOX(tpe) =>
          val top = out.stack.head
          top match {
            case Boxed(loc) => Deref(loc) :: out.stack.tail
            case _          => out.stack = Unknown :: out.stack.drop(1)
          }
          
        case NEW(kind) =>
          val v1 = kind match {
            case REFERENCE(cls) => Record(cls, new HashMap[Symbol, Value])
            case _              => Unknown
          }
          out.stack = v1 :: out.stack

        case CREATE_ARRAY(elem, dims) =>
          out.stack = Unknown :: out.stack.drop(dims)
          
        case IS_INSTANCE(tpe) =>
          out.stack = Unknown :: out.stack.drop(1)
          
        case CHECK_CAST(tpe) =>
          out.stack = Unknown :: out.stack.drop(1)
          
        case SWITCH(tags, labels) =>
          out.stack = out.stack.drop(1)
          
        case JUMP(whereto) =>
          ()
          
        case CJUMP(success, failure, cond, kind) =>
          out.stack = out.stack.drop(2)
          
        case CZJUMP(success, failure, cond, kind) =>
          out.stack = out.stack.drop(1)
          
        case RETURN(kind) =>
          if (kind != UNIT)
            out.stack = out.stack.drop(1)
          
        case THROW(_) =>
          out.stack = out.stack.drop(1)
          
        case DROP(kind) =>
          out.stack = out.stack.drop(1)
          
        case DUP(kind) =>
          out.stack = out.stack.head :: out.stack
          
        case MONITOR_ENTER() =>
          out.stack = out.stack.drop(1);         

        case MONITOR_EXIT() =>
          out.stack = out.stack.drop(1)

        case SCOPE_ENTER(_) | SCOPE_EXIT(_) =>
          ()
        
        case LOAD_EXCEPTION(_) =>
          out.stack = Unknown :: Nil

        case _ =>
          dump
          abort("Unknown instruction: " + i)
      }
      out
    } /* def interpret */

    /** Remove all references to this local variable from both stack
     *  and bindings. It is called when a new assignment destroys 
     *  previous copy-relations.
     */
    final def cleanReferencesTo(s: copyLattice.State, target: Location) {
      def cleanRecord(r: Record): Record = {
        retain(r.bindings) { (loc, value) =>
          (value match {
            case Deref(loc1) if (loc1 == target) => false
            case Boxed(loc1) if (loc1 == target)  => false
            case _ => true
          }) && (target match {
            case Field(AllRecords, sym1) => !(loc == sym1)
            case _ => true
          })
        }
        r
      }

      s.stack = s.stack map { v => v match {
        case Record(_, bindings) =>
          cleanRecord(v.asInstanceOf[Record])
        case Boxed(loc1) if (loc1 == target) => Unknown
        case _ => v
      }}

      retain(s.bindings) { (loc, value) =>
        (value match {
          case Deref(loc1) if (loc1 == target) => false
          case Boxed(loc1) if (loc1 == target) => false
          case rec @ Record(_, _) =>
            cleanRecord(rec);
            true
          case _ => true
        }) && 
        (loc match {
          case l: Location if (l == target) => false
          case _ => true
        })
      }
    }

    /** Update the state <code>s after the call to method.
     *  The stack elements are dropped and replaced by the result of the call.
     *  If the method is impure, all bindings to record fields are cleared.
     *
     *  @param state  ...
     *  @param method ...
     *  @param static ...
     *  @return       ...
     */
    final def simulateCall(state: copyLattice.State, method: Symbol, static: Boolean): copyLattice.State = {
      val out = new copyLattice.State(state.bindings, state.stack);
      out.stack = out.stack.drop(method.info.paramTypes.length + (if (static) 0 else 1));
      if (method.info.resultType != definitions.UnitClass.tpe && !method.isConstructor)
        out.stack = Unknown :: out.stack;
      if (!isPureMethod(method))
        invalidateRecords(out);
      out
    }

    /** Drop everything known about mutable record fields.
     *  
     *  A simple escape analysis would help here. Some of the records we 
     *  track never leak to other methods, therefore they can not be changed.
     *  We should not drop their bindings in this case. A closure object 
     *  would be such an example. Some complications: 
     * 
     *   - outer pointers. An closure escapes as an outer pointer to another
     *     nested closure.
     */
    final def invalidateRecords(state: copyLattice.State) {
      def shouldRetain(sym: Symbol): Boolean = {
        if (sym.isMutable)
          log("dropping binding for " + sym.fullName)
        !sym.isMutable
      }
      state.stack = state.stack map { v => v match {
        case Record(cls, bindings) =>
          retain(bindings) { (sym, _) => shouldRetain(sym) }
          Record(cls, bindings)
        case _ => v
      }}

      retain(state.bindings) { (loc, value) =>
        value match {
          case Deref(Field(rec, sym)) => shouldRetain(sym)
          case Boxed(Field(rec, sym)) => shouldRetain(sym)
          case _ => true
        }
      }
    }

    /** Return bindings from an object fields to the values on the stack. This
     *  method has to find the correct mapping from fields to the order in which
     *  they are passed on the stack. It works for primary constructors.
     */
    private def getBindingsForPrimaryCtor(in: copyLattice.State, ctor: Symbol): Map[Symbol, Value] = {
      val paramAccessors = ctor.owner.constrParamAccessors;
      var values = in.stack.take(1 + ctor.info.paramTypes.length).reverse.drop(1);
      val bindings = new HashMap[Symbol, Value];

      if (settings.debug.value) log("getBindings for: " + ctor + " acc: " + paramAccessors)
      
      var paramTypes = ctor.tpe.paramTypes 
      val diff = paramTypes.length - paramAccessors.length
      diff match {
        case 0 => ()
        case 1 if ctor.tpe.paramTypes.head == ctor.owner.rawowner.tpe =>
          // it's an unused outer
          log("considering unused outer at position 0 in " + ctor.tpe.paramTypes)
          paramTypes = paramTypes.tail
          values = values.tail
        case _ =>
          log("giving up on " + ctor + "(diff: " + diff + ")")
          return bindings
      }
      
      // this relies on having the same order in paramAccessors and
      // the arguments on the stack. It should be the same!
      for ((p, i) <- paramAccessors.zipWithIndex) {
//        assert(p.tpe == paramTypes(i), "In: " + ctor.fullName
//               + " having acc: " + (paramAccessors map (_.tpe))+ " vs. params" + paramTypes
//               + "\n\t failed at pos " + i + " with " + p.tpe + " == " + paramTypes(i))
        if (p.tpe == paramTypes(i))
          bindings += (p -> values.head);
        values = values.tail;
      }

      if (settings.debug.value) log("\t" + bindings)
      bindings
    }

    /** Is symbol <code>m a pure method?
     *
     *  @param m ...
     *  @return  ...
     */
    final def isPureMethod(m: Symbol): Boolean = 
      m.isGetter // abstract getters are still pure, as we 'know'

    final override def toString(): String = {
      var res = ""
      for (b <- this.method.code.blocks.toList)
        res = (res + "\nIN(" + b.label + "):\t Bindings: " + in(b).bindings +
               "\nIN(" + b.label +"):\t Stack: " + in(b).stack) + "\n";
      res
    }

  } /* class CopyAnalysis */
}

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