Avoiding redundant tuple formations.

In a case like

     val (x, y) = if (...) (a, b) else (c, d)

we can pass the tuples directly. Previously, this would have been translated to

    val (x, y) = (if (...) (a, b) else (c, d): @unchecked) match {
      case (s, t) => (s, t)
    }

1 files changed, 10 insertions, 0 deletions

diff --git a/src/dotty/tools/dotc/ast/TreeInfo.scala b/src/dotty/tools/dotc/ast/TreeInfo.scala
index 29ff492d4..e1715ae26 100644
--- a/src/dotty/tools/dotc/ast/TreeInfo.scala
+++ b/src/dotty/tools/dotc/ast/TreeInfo.scala
@@ -260,6 +260,16 @@ trait TreeInfo[T >: Untyped] { self: Trees.Instance[T] =>
     case Bind(_, y) => unbind(y)
     case y          => y
   }
+
+  /** Checks whether predicate `p` is true for all result parts of this epression,
+   *  where we zoom into Ifs, Matches, and Blocks.
+   */
+  def forallResults(tree: Tree, p: Tree => Boolean): Boolean = tree match {
+    case If(_, thenp, elsep) => forallResults(thenp, p) && forallResults(elsep, p)
+    case Match(_, cases) => cases forall (c => forallResults(c.body, p))
+    case Block(_, expr) => forallResults(expr, p)
+    case _ => p(tree)
+  }
 }
 
 trait TypedTreeInfo extends TreeInfo[Type] {self: Trees.Instance[Type] =>