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Use Labeled blocks in TailRec, instead of label-defs. #5115

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Merged
merged 2 commits into from
Nov 6, 2018
Merged

Use Labeled blocks in TailRec, instead of label-defs. #5115

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b3b59d5
Use `Labeled` blocks in `TailRec`, instead of label-defs.
sjrd Sep 17, 2018
3084b1a
Use `EmptyTree` for the `cond` of infinite `WhileDo` loops.
sjrd Sep 27, 2018
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13 changes: 5 additions & 8 deletions compiler/src/dotty/tools/dotc/transform/TailRec.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -32,7 +32,7 @@ import reporting.diagnostic.messages.TailrecNotApplicable
* {{{
* var localForParam1: T1 = param1
* ...
* while (true) {
* while (<empty>) {
* tailResult[ResultType]: {
* return {
* // original rhs with tail recursive calls transformed (see below)
Expand Down Expand Up @@ -60,7 +60,7 @@ import reporting.diagnostic.messages.TailrecNotApplicable
* def fact(n: Int, acc: Int): Int = {
* var acc$tailLocal1: Int = acc
* var n$tailLocal1: Int = n
* while (true) {
* while (<empty>) {
* tailLabel1[Unit]: {
* return {
* if (n$tailLocal1 == 0)
Expand All @@ -75,7 +75,6 @@ import reporting.diagnostic.messages.TailrecNotApplicable
* }
* }
* }
* throw null // unreachable
* }
* }}}
*
Expand Down Expand Up @@ -163,14 +162,12 @@ class TailRec extends MiniPhase {
}

Block(
initialVarDefs :::
WhileDo(Literal(Constant(true)), {
initialVarDefs,
WhileDo(EmptyTree, {
Labeled(transformer.continueLabel.asTerm, {
Return(rhsFullyTransformed, origMeth)
})
}) ::
Nil,
Throw(Literal(Constant(null))) // unreachable code
})
)
} else {
if (mandatory) ctx.error(
Expand Down
5 changes: 5 additions & 0 deletions compiler/src/dotty/tools/dotc/transform/TreeChecker.scala
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Expand Up @@ -452,6 +452,11 @@ class TreeChecker extends Phase with SymTransformer {
tree1
}

override def typedWhileDo(tree: untpd.WhileDo)(implicit ctx: Context): Tree = {
assert((tree.cond ne EmptyTree) || ctx.phase.refChecked, i"invalid empty condition in while at $tree")
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Why ctx.phase.refChecked? Why not an equivalent method for TailRec?

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Because it existed, and the only requirement is that an infinite loop must not be pickled. It doesn't have anything to do with tailrec per se.

super.typedWhileDo(tree)
}
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And here is the addition of an explicit Ycheck test that WhileDo(EmptyTree, _) is not used too early, as requested by @smarter.


override def ensureNoLocalRefs(tree: Tree, pt: Type, localSyms: => List[Symbol])(implicit ctx: Context): Tree =
tree

Expand Down
2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/typer/TypeAssigner.scala
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Expand Up @@ -486,7 +486,7 @@ trait TypeAssigner {
tree.withType(defn.NothingType)

def assignType(tree: untpd.WhileDo)(implicit ctx: Context): WhileDo =
tree.withType(defn.UnitType)
tree.withType(if (tree.cond eq EmptyTree) defn.NothingType else defn.UnitType)
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Why does this occur ?

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Because we want a way to represent an infinite while loop, whose type is therefore Nothing. It's the whole point of the second commit in this PR.


def assignType(tree: untpd.Try, expr: Tree, cases: List[CaseDef])(implicit ctx: Context): Try =
if (cases.isEmpty) tree.withType(expr.tpe)
Expand Down
4 changes: 3 additions & 1 deletion compiler/src/dotty/tools/dotc/typer/Typer.scala
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Expand Up @@ -1127,7 +1127,9 @@ class Typer extends Namer
}

def typedWhileDo(tree: untpd.WhileDo)(implicit ctx: Context): Tree = track("typedWhileDo") {
val cond1 = typed(tree.cond, defn.BooleanType)
val cond1 =
if (tree.cond eq EmptyTree) EmptyTree
else typed(tree.cond, defn.BooleanType)
val body1 = typed(tree.body, defn.UnitType)
assignType(cpy.WhileDo(tree)(cond1, body1))
}
Expand Down
2 changes: 1 addition & 1 deletion scala-backend
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Submodule scala-backend updated 1 files
+4 −6 src/compiler/scala/tools/nsc/backend/jvm/BCodeBodyBuilder.scala