package scala.tools.nsc
package transform;
import scala.tools.nsc._
import scala.collection.mutable.HashMap
abstract class LazyVals extends Transform with ast.TreeDSL {
// 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 CODE._
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 {
/** 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
* - blocks in template bodies behave almost like methods. A single bitmaps section is
* added in the first block, for all lazy values defined in such blocks.
* - remove ACCESSOR flags: accessors in traits are not statically implemented,
* but moved to the host class. local lazy values should be statically implemented.
*/
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 enclosingDummyOrMethod =
if (sym.enclMethod == NoSymbol) sym.owner else sym.enclMethod
val idx = lazyVals(enclosingDummyOrMethod)
val rhs1 = mkLazyDef(enclosingDummyOrMethod, super.transform(rhs), idx)
lazyVals(sym.owner) = idx + 1
sym.resetFlag(LAZY | ACCESSOR)
rhs1
} else
super.transform(rhs)
treeCopy.DefDef(tree, mods, name, tparams, vparams, tpt,
typed(addBitmapDefs(sym, res)))
case Template(parents, self, body) =>
val body1 = super.transformTrees(body)
var added = false
val stats =
for (stat <- body1) yield stat match {
case Block(_, _) if !added =>
added = true
typed(addBitmapDefs(sym, stat))
case ValDef(mods, name, tpt, rhs) =>
typed(treeCopy.ValDef(stat, mods, name, tpt, addBitmapDefs(stat.symbol, rhs)))
case _ =>
stat
}
treeCopy.Template(tree, parents, self, stats)
case _ => super.transform(tree)
}
}
/** Add the bitmap definitions to the rhs of a method definition.
* If the rhs has been tail-call transformed, insert the bitmap
* definitions inside the top-level label definition, so that each
* iteration has the lazy values un-initialized. Otherwise add them
* at the very beginning of the method.
*/
private def addBitmapDefs(methSym: Symbol, rhs: Tree): Tree = {
def prependStats(stats: List[Tree], tree: Tree): Block = tree match {
case Block(stats1, res) => Block(stats ::: stats1, res)
case _ => Block(stats, tree)
}
val bmps = bitmaps(methSym) map (ValDef(_, ZERO))
def isMatch(params: List[Ident]) = (params.tail, methSym.tpe.paramTypes).zipped forall (_.tpe == _)
if (bmps.isEmpty) rhs else rhs match {
case Block(assign, l @ LabelDef(name, params, rhs1))
if name.toString == ("_" + methSym.name) && isMatch(params) =>
val sym = l.symbol
Block(assign, treeCopy.LabelDef(l, name, params, typed(prependStats(bmps, rhs1))))
case _ => prependStats(bmps, rhs)
}
}
/** return a 'lazified' version of rhs. Rhs should conform to the
* following schema:
* {
* l$ = <rhs>
* l$
* } or
* <rhs> when the lazy value has type Unit (for which there is no field
* to cache it's value.
*
* The result will be a tree of the form
* {
* if ((bitmap$n & MASK) == 0) {
* l$ = <rhs>
* bitmap$n = bimap$n | MASK
* }
* l$
* }
* where bitmap$n is an int value acting as a bitmap of initialized values. It is
* the 'n' is (offset / 32), the MASK is (1 << (offset % 32)). If the value has type
* unit, no field is used to chache the value, so the resulting code is:
* {
* if ((bitmap$n & MASK) == 0) {
* <rhs>;
* bitmap$n = bimap$n | MASK
* }
* ()
* }
*/
private def mkLazyDef(meth: Symbol, tree: Tree, offset: Int): Tree = {
val bitmapSym = getBitmapFor(meth, offset)
val mask = LIT(1 << (offset % FLAGS_PER_WORD))
def mkBlock(stmt: Tree) = BLOCK(stmt, mkSetFlag(bitmapSym, mask), UNIT)
val (block, res) = tree match {
case Block(List(assignment), res) => (mkBlock(assignment), res)
case rhs => (mkBlock(rhs), UNIT)
}
assert(res != UNIT || meth.tpe.finalResultType.typeSymbol == UnitClass)
atPos(tree.pos)(typed {
def body = { IF ((Ident(bitmapSym) INT_& mask) INT_== ZERO) THEN block ENDIF }
BLOCK(body, res)
})
}
private def mkSetFlag(bmp: Symbol, mask: Tree): Tree =
Ident(bmp) === (Ident(bmp) INT_| 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
}
}
}
}