package scala.tools.nsc.transform;
import scala.tools.nsc._
import scala.collection.mutable.HashMap
abstract class LazyVals extends Transform {
// inherits abstract value `global' and class `Phase' from Transform
import global._ // the global environment
import definitions._ // standard classes and methods
import typer.{typed, atOwner} // methods to type trees
import posAssigner.atPos // for filling in tree positions
val phaseName: String = "lazyvals"
def newTransformer(unit: CompilationUnit): Transformer =
new LazyValues(unit)
/** Create a new phase which applies transformer */
override def newPhase(prev: scala.tools.nsc.Phase): StdPhase = new Phase(prev)
/** The phase defined by this transform */
class Phase(prev: scala.tools.nsc.Phase) extends StdPhase(prev) {
def apply(unit: global.CompilationUnit): Unit =
newTransformer(unit).transformUnit(unit);
}
/**
* Transform local lazy accessors to check for the initialized bit.
*/
class LazyValues(unit: CompilationUnit) extends Transformer {
import definitions.{Int_And, Int_Or, Int_==}
/** map from method symbols to the number of lazy values it defines. */
private val lazyVals = new HashMap[Symbol, Int] {
override def default(meth: Symbol) = 0
}
import symtab.Flags._
import lazyVals._
/** Perform the following transformations:
* - for a lazy accessor inside a method, make it check the initialization bitmap
* - for all methods, add enough int vars to allow one flag per lazy local value
*/
override def transform(tree: Tree): Tree = {
val sym = tree.symbol
tree match {
case DefDef(mods, name, tparams, vparams, tpt, rhs) =>
val res = if (!sym.owner.isClass && sym.hasFlag(LAZY)) {
val idx = lazyVals(sym.enclMethod)
val rhs1 = mkLazyDef(sym.enclMethod, super.transform(rhs), idx)
lazyVals(sym.owner) = idx + 1
sym.resetFlag(LAZY)
rhs1
} else
super.transform(rhs)
val bmps = bitmaps(sym) map { b => ValDef(b, Literal(Constant(0))) }
copy.DefDef(tree, mods, name, tparams, vparams, tpt, typed(if (bmps.isEmpty) res else Block(bmps, res)))
case _ => super.transform(tree)
}
}
/** return a 'lazified' version of rhs. Rhs should conform to the
* following schema:
* {
* l$ = <rhs>
* l$
* }
* The result will be a tree of the form
* {
* if ((bitmap$n & MASK) == 0) {
* l$ = <rhs>
* bitmap$n = bimap$n | MASK
* }
* l$
* }
* where bitmap$n is an int value acting as a bitmap of initialized values. It is
* the 'n' is (offset / 32), the MASK is (1 << (offset % 32)).
*/
private def mkLazyDef(meth: Symbol, tree: Tree, offset: Int): Tree = {
val bitmapSym = getBitmapFor(meth, offset)
val Block(List(assignment), res) = tree
val mask = Literal(Constant(1 << (offset % FLAGS_PER_WORD)))
val result =
If(Apply(
Select(
Apply(Select(Ident(bitmapSym), Int_And),
List(mask)),
Int_==),
List(Literal(Constant(0)))), Block(List(assignment, mkSetFlag(bitmapSym, mask)), Literal(Constant(()))), EmptyTree)
typed(Block(List(result), res))
}
private def mkSetFlag(bmp: Symbol, mask: Tree): Tree =
Assign(Ident(bmp),
Apply(Select(Ident(bmp), Int_Or), List(mask)))
final val FLAGS_PER_WORD = 32
val bitmaps = new HashMap[Symbol, List[Symbol]] {
override def default(meth: Symbol) = Nil
}
/** Return the symbol corresponding of the right bitmap int inside meth,
* given offset.
*/
private def getBitmapFor(meth: Symbol, offset: Int): Symbol = {
val n = offset / FLAGS_PER_WORD
val bmps = bitmaps(meth)
if (bmps.length > n)
bmps(n)
else {
val sym = meth.newVariable(meth.pos, nme.bitmapName(n)).setInfo(IntClass.tpe)
bitmaps(meth) = (sym :: bmps).reverse
sym
}
}
}
}