Improve tuple specialization code

Author: nicolasstucki

compiler/src/dotty/tools/dotc/core/Definitions.scala

@@ -814,6 +814,7 @@ class Definitions {
     def TupleXXL_fromIterator(implicit ctx: Context): Symbol = TupleXXLModule.requiredMethod("fromIterator")
 
   lazy val DynamicTupleModule: Symbol = ctx.requiredModule("scala.runtime.DynamicTuple")
+  lazy val DynamicTupleModuleClass: Symbol = DynamicTupleModule.moduleClass
     lazy val DynamicTuple_consIterator: Symbol = DynamicTupleModule.requiredMethod("consIterator")
     lazy val DynamicTuple_concatIterator: Symbol = DynamicTupleModule.requiredMethod("concatIterator")
     lazy val DynamicTuple_dynamicApply: Symbol = DynamicTupleModule.requiredMethod("dynamicApply")

compiler/src/dotty/tools/dotc/transform/TupleOptimizations.scala

@@ -24,7 +24,8 @@ class TupleOptimizations extends MiniPhase with IdentityDenotTransformer {
   def phaseName: String = "genericTuples"
 
   override def transformApply(tree: tpd.Apply)(implicit ctx: Context): tpd.Tree = {
-    if (tree.symbol == defn.DynamicTuple_dynamicCons) transformTupleCons(tree)
+    if (!tree.symbol.exists || tree.symbol.owner != defn.DynamicTupleModuleClass) super.transformApply(tree)
+    else if (tree.symbol == defn.DynamicTuple_dynamicCons) transformTupleCons(tree)
     else if (tree.symbol == defn.DynamicTuple_dynamicTail) transformTupleTail(tree)
     else if (tree.symbol == defn.DynamicTuple_dynamicSize) transformTupleSize(tree)
     else if (tree.symbol == defn.DynamicTuple_dynamicConcat) transformTupleConcat(tree)
@@ -34,8 +35,7 @@ class TupleOptimizations extends MiniPhase with IdentityDenotTransformer {
   }
 
   private def transformTupleCons(tree: tpd.Apply)(implicit ctx: Context): Tree = {
-    val TypeApply(_, headType :: tailType :: Nil) = tree.fun
-    val tail :: head :: Nil = tree.args
+    val head :: tail :: Nil = tree.args
     tupleTypes(tree.tpe) match {
       case Some(tpes) =>
         // Generate a the tuple directly with TupleN+1.apply
@@ -44,7 +44,7 @@ class TupleOptimizations extends MiniPhase with IdentityDenotTransformer {
           // val t = tail
           // TupleN+1(head, t._1, ..., t._n)
           evalOnce(Typed(tail, TypeTree(defn.tupleType(tpes.tail)))) { tup =>
-            val elements = head :: (0 until size - 1).map(i => tup.select(nme.selectorName(i))).toList
+            val elements = head :: tupleSelectors(tup, size - 1)
             knownTupleFromElements(tpes, elements)
           }
         } else {
@@ -77,7 +77,7 @@ class TupleOptimizations extends MiniPhase with IdentityDenotTransformer {
           // val t = tup.asInstanceOf[TupleN[...]]
           // TupleN-1(t._2, ..., t._n)
           evalOnce(Typed(tup, TypeTree(defn.tupleType(tpes)))) { tup =>
-            val elements = (1 until size).map(i => tup.select(nme.selectorName(i))).toList
+            val elements = tupleSelectors(tup, size).tail
             knownTupleFromElements(tpes.tail, elements)
           }
         } else if (size <= MaxTupleArity + 1) {
@@ -125,10 +125,7 @@ class TupleOptimizations extends MiniPhase with IdentityDenotTransformer {
           evalOnce(Typed(self, TypeTree(defn.tupleType(tpes1)))) { self =>
             evalOnce(Typed(that, TypeTree(defn.tupleType(tpes2)))) { that =>
               val types = tpes1 ::: tpes2
-              val elements = {
-                (0 until n).map(i => self.select(nme.selectorName(i))) ++
-                (0 until m).map(i => that.select(nme.selectorName(i)))
-              }.toList
+              val elements = tupleSelectors(self, n) ::: tupleSelectors(that, m)
               knownTupleFromElements(types, elements)
             }
           }
@@ -235,4 +232,8 @@ class TupleOptimizations extends MiniPhase with IdentityDenotTransformer {
     }
     rec(tp.stripTypeVar, Nil, bound)
   }
+
+  private def tupleSelectors(tup: Tree, size: Int)(implicit ctx: Context): List[Tree] =
+    (0 until size).map(i => tup.select(nme.selectorName(i))).toList
+
 }

library/src-3.x/scala/Tuple.scala

@@ -17,7 +17,7 @@ sealed trait Tuple extends Any {
    *  This opteration is O(this.size)
    */
   inline def *: [H, This >: this.type <: Tuple] (x: H): H *: This =
-    DynamicTuple.dynamicCons[This, H](this, x)
+    DynamicTuple.dynamicCons[H, This](x, this)
 
   /** Return a new tuple by concatenating `this` tuple with `that` tuple.
    *  This opteration is O(this.size + that.size)

library/src-3.x/scala/runtime/DynamicTuple.scala

@@ -186,7 +186,7 @@ object DynamicTuple {
     arr
   }
 
-  def dynamicCons[This <: Tuple, H] (self: Tuple, x: H): H *: This = {
+  def dynamicCons[H, This <: Tuple](x: H, self: Tuple): H *: This = {
     type Result = H *: This
     (self: Any) match {
       case () =>

tests/run-with-compiler/staged-tuples/StagedTuple.scala

@@ -184,7 +184,7 @@ object StagedTuple {
   }
 
   def consStaged[T <: Tuple & Singleton : Type, H : Type](self: Expr[T], x: Expr[H], tailSize: Option[Int]): Expr[H *: T] =
-  if (!specialize) '{dynamicCons[T, H]($self, $x)}
+  if (!specialize) '{dynamicCons[H, T]($x, $self)}
   else {
     val res = tailSize match {
       case Some(0) =>
@@ -200,7 +200,7 @@ object StagedTuple {
       case Some(n) =>
         fromArrayStaged[H *: T]('{cons$Array($x, ${ toArrayStaged(self, tailSize) })}, Some(n + 1))
       case _ =>
-        '{dynamicCons[T, H]($self, $x)}
+        '{dynamicCons[H, T]($x, $self)}
     }
     res.as[H *: T]
   }