Merge pull request #3994 from dotty-staging/fix-3857

Fix #3857: partial fix to generate more shallow tree in LabelDef

Author: nicolasstucki

compiler/src/dotty/tools/backend/jvm/LabelDefs.scala

@@ -29,7 +29,7 @@ import scala.collection.mutable
  * <label> def foo(i: Int) = dough(i)
  * <label> def dough(i: Int) = if (i == 0) bar else foo(i-1)
  * <label> def bar = 2
- *   foo(100)
+ * foo(100)
  * ```
  *
  * Proposed way to generate this pattern in backend is:
@@ -49,7 +49,7 @@ import scala.collection.mutable
  * Unreachable jumps will be eliminated by local dead code analysis.
  * After JVM is smart enough to remove next-line jumps
  *
- * Note that his phase Ychecking this phase required softening scoping rules
+ * Note that Ychecking this phase requires softening scoping rules
  * as it intentionally allowed to break scoping rules inside methods for labels.
  * This is modified by setting `labelsReordered` flag in Phases.
  *
@@ -76,7 +76,25 @@ class LabelDefs extends MiniPhase {
             case t: DefDef =>
               assert(t.symbol is Label)
               EmptyTree
-            case _ => if (!labelDefs.isEmpty) super.transform(tree) else tree
+            case t: If =>
+              // Trees generated by pattern matcher usually looks like the
+              // following:
+              //
+              //      ...
+              //               }
+              //              else case58(x704)
+              //           }
+              //          else case58(x704)
+              //       }
+              //      else case58(x704)
+              //
+              // First transform on the else branch will make labeldef
+              // inserted on a shallow node.
+              val elsep2 = transform(t.elsep)
+              val thenp2 = transform(t.thenp)
+              cpy.If(tree)(transform(t.cond), thenp2, elsep2)
+            case _ =>
+              if (!labelDefs.isEmpty) super.transform(tree) else tree
           }
         }
       }

tests/pos/i3857.scala

@@ -0,0 +1,59 @@
+object foo {
+  abstract sealed class num
+  final case class One() extends num
+  final case class Bit0(a: num) extends num
+  final case class Bit1(a: num) extends num
+
+  abstract sealed class abschar
+  final case class zero_char() extends abschar
+  final case class Char(a: num) extends abschar
+
+  def integer_of_char(x0: abschar): BigInt = {
+    def f(x: Int): Int = x
+    x0 match {
+    case Char(Bit0(Bit1(Bit0(Bit1(Bit0(One())))))) => BigInt(42)
+    case Char(Bit1(Bit0(Bit0(Bit1(Bit0(One())))))) => BigInt(41)
+    case Char(Bit0(Bit0(Bit0(Bit1(Bit0(One())))))) => BigInt(40)
+    case Char(Bit1(Bit1(Bit1(Bit0(Bit0(One())))))) => BigInt(39)
+    case Char(Bit0(Bit1(Bit1(Bit0(Bit0(One())))))) => BigInt(38)
+    case Char(Bit1(Bit0(Bit1(Bit0(Bit0(One())))))) => BigInt(37)
+    case Char(Bit0(Bit0(Bit1(Bit0(Bit0(One())))))) => BigInt(36)
+    case Char(Bit1(Bit1(Bit0(Bit0(Bit0(One())))))) => BigInt(35)
+    case Char(Bit0(Bit1(Bit0(Bit0(Bit0(One())))))) => BigInt(34)
+    case Char(Bit1(Bit0(Bit0(Bit0(Bit0(One())))))) => BigInt(33)
+    case Char(Bit0(Bit0(Bit0(Bit0(Bit0(One())))))) => BigInt(32)
+    case Char(Bit1(Bit1(Bit1(Bit1(One()))))) => BigInt(31)
+    case Char(Bit0(Bit1(Bit1(Bit1(One()))))) => BigInt(30)
+    case Char(Bit1(Bit0(Bit1(Bit1(One()))))) => BigInt(29)
+    case Char(Bit0(Bit0(Bit1(Bit1(One()))))) => BigInt(28)
+    case Char(Bit1(Bit1(Bit0(Bit1(One()))))) => BigInt(27)
+    case Char(Bit0(Bit1(Bit0(Bit1(One()))))) => BigInt(26)
+    case Char(Bit1(Bit0(Bit0(Bit1(One()))))) => BigInt(25)
+    case Char(Bit0(Bit0(Bit0(Bit1(One()))))) => BigInt(24)
+    case Char(Bit1(Bit1(Bit1(Bit0(One()))))) => BigInt(23)
+    case Char(Bit0(Bit1(Bit1(Bit0(One()))))) => BigInt(22)
+    case Char(Bit1(Bit0(Bit1(Bit0(One()))))) => BigInt(21)
+    case Char(Bit0(Bit0(Bit1(Bit0(One()))))) => BigInt(20)
+    case Char(Bit1(Bit1(Bit0(Bit0(One()))))) => BigInt(19)
+    case Char(Bit0(Bit1(Bit0(Bit0(One()))))) => BigInt(18)
+    case Char(Bit1(Bit0(Bit0(Bit0(One()))))) => BigInt(17)
+    case Char(Bit0(Bit0(Bit0(Bit0(One()))))) => BigInt(16)
+    case Char(Bit1(Bit1(Bit1(One())))) => BigInt(15)
+    case Char(Bit0(Bit1(Bit1(One())))) => BigInt(14)
+    case Char(Bit1(Bit0(Bit1(One())))) => BigInt(13)
+    case Char(Bit0(Bit0(Bit1(One())))) => BigInt(12)
+    case Char(Bit1(Bit1(Bit0(One())))) => BigInt(11)
+    case Char(Bit0(Bit1(Bit0(One())))) => BigInt(10)
+    case Char(Bit1(Bit0(Bit0(One())))) => BigInt(9)
+    case Char(Bit0(Bit0(Bit0(One())))) => BigInt(8)
+    case Char(Bit1(Bit1(One()))) => BigInt(7)
+    case Char(Bit0(Bit1(One()))) => BigInt(6)
+    case Char(Bit1(Bit0(One()))) => BigInt(5)
+    case Char(Bit0(Bit0(One()))) => BigInt(4)
+    case Char(Bit1(One())) => BigInt(3)
+    case Char(Bit0(One())) => BigInt(2)
+    case Char(One()) => BigInt(1)
+    case zero_char() => BigInt(0)
+  }
+  }
+}