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Generate less code for lazy vals #706

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Jul 20, 2015
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Generate less code for lazy vals #706

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8f47f16
#676 generate less code for lazy vals
DarkDimius Jul 1, 2015
688feee
Address review comments.
DarkDimius Jul 13, 2015
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56 changes: 43 additions & 13 deletions src/dotty/tools/dotc/transform/LazyVals.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -46,18 +46,35 @@ class LazyVals extends MiniPhaseTransform with IdentityDenotTransformer {
* before this phase starts processing same tree */
override def runsAfter = Set(classOf[Mixin])

override def transformDefDef(tree: DefDef)(implicit ctx: Context, info: TransformerInfo): Tree = {
if (!(tree.symbol is Flags.Lazy) || tree.symbol.owner.is(Flags.Trait)) tree
else {
val isField = tree.symbol.owner.isClass

if (isField) {
if (tree.symbol.isVolatile || tree.symbol.is(Flags.Module)) transformMemberDefVolatile(tree)
else transformMemberDefNonVolatile(tree)
}
else transformLocalDef(tree)
override def transformDefDef(tree: tpd.DefDef)(implicit ctx: Context, info: TransformerInfo): tpd.Tree =
transformLazyVal(tree)


override def transformValDef(tree: tpd.ValDef)(implicit ctx: Context, info: TransformerInfo): tpd.Tree = {
transformLazyVal(tree)
}

def transformLazyVal(tree: ValOrDefDef)(implicit ctx: Context, info: TransformerInfo): Tree = {
val sym = tree.symbol
if (!(sym is Flags.Lazy) || sym.owner.is(Flags.Trait) || (sym.isStatic && sym.is(Flags.Module))) tree
else {

val isField = sym.owner.isClass

if (isField) {
if (sym.isVolatile ||
(sym.is(Flags.Module) && !sym.is(Flags.Synthetic)))
// module class is user-defined.
// Should be threadsafe, to mimic safety guaranteed by global object
transformMemberDefVolatile(tree)
else if (sym.is(Flags.Module)) { // synthetic module
transformSyntheticModule(tree)
}
else transformMemberDefNonVolatile(tree)
}
else transformLocalDef(tree)
}
}


/** Append offset fields to companion objects
Expand All @@ -78,11 +95,24 @@ class LazyVals extends MiniPhaseTransform with IdentityDenotTransformer {
case _ => prefix ::: stats
}

/** Make an eager val that would implement synthetic module.
* Eager val ensures thread safety and has less code generated.
*
*/
def transformSyntheticModule(tree: ValOrDefDef)(implicit ctx: Context) = {
val sym = tree.symbol
val holderSymbol = ctx.newSymbol(sym.owner, sym.asTerm.name ++ nme.LAZY_LOCAL,
Flags.Synthetic, sym.info.widen.resultType).enteredAfter(this)
val field = ValDef(holderSymbol, tree.rhs.changeOwnerAfter(sym, holderSymbol, this))
val getter = DefDef(sym.asTerm, ref(holderSymbol))
Thicket(field, getter)
}

/** Replace a local lazy val inside a method,
* with a LazyHolder from
* dotty.runtime(eg dotty.runtime.LazyInt)
*/
def transformLocalDef(x: DefDef)(implicit ctx: Context) = {
def transformLocalDef(x: ValOrDefDef)(implicit ctx: Context) = {
val valueInitter = x.rhs
val holderName = ctx.freshName(x.name ++ StdNames.nme.LAZY_LOCAL).toTermName
val initName = ctx.freshName(x.name ++ StdNames.nme.LAZY_LOCAL_INIT).toTermName
Expand Down Expand Up @@ -172,7 +202,7 @@ class LazyVals extends MiniPhaseTransform with IdentityDenotTransformer {
If(cond, init, exp)
}

def transformMemberDefNonVolatile(x: DefDef)(implicit ctx: Context) = {
def transformMemberDefNonVolatile(x: ValOrDefDef)(implicit ctx: Context) = {
val claz = x.symbol.owner.asClass
val tpe = x.tpe.widen.resultType.widen
assert(!(x.mods is Flags.Mutable))
Expand Down Expand Up @@ -293,7 +323,7 @@ class LazyVals extends MiniPhaseTransform with IdentityDenotTransformer {
DefDef(methodSymbol, Block(resultDef :: retryDef :: flagDef :: cycle :: Nil, ref(resultSymbol)))
}

def transformMemberDefVolatile(x: DefDef)(implicit ctx: Context) = {
def transformMemberDefVolatile(x: ValOrDefDef)(implicit ctx: Context) = {
assert(!(x.mods is Flags.Mutable))

val tpe = x.tpe.widen.resultType.widen
Expand Down