LazyVals: fix underflows in binary shifts.

src/dotty/runtime/LazyVals.scala

@@ -8,8 +8,8 @@ import scala.annotation.tailrec
 object LazyVals {
   private val unsafe = scala.concurrent.util.Unsafe.instance
 
-  final val BITS_PER_LAZY_VAL = 2
-  final val LAZY_VAL_MASK = 3
+  final val BITS_PER_LAZY_VAL = 2L
+  final val LAZY_VAL_MASK = 3L
 
   @inline def STATE(cur: Long, ord: Int) = (cur >> (ord * BITS_PER_LAZY_VAL)) & LAZY_VAL_MASK
   @inline def CAS(t: Object, offset: Long, e: Long, v: Int, ord: Int) = {

src/dotty/tools/dotc/transform/LazyVals.scala

@@ -341,7 +341,7 @@ class LazyVals extends MiniPhaseTransform with IdentityDenotTransformer {
         // compute or create appropriate offsetSymol, bitmap and bits used by current ValDef
         appendOffsetDefs.get(companion.moduleClass) match {
           case Some(info) =>
-            val flagsPerLong = 64 / dotty.runtime.LazyVals.BITS_PER_LAZY_VAL
+            val flagsPerLong = (64 / dotty.runtime.LazyVals.BITS_PER_LAZY_VAL).toInt
             info.ord += 1
             ord = info.ord % flagsPerLong
             val id = info.ord / flagsPerLong

tests/run/LazyValsLongs.scala

@@ -0,0 +1,65 @@
+class I {
+  object A1
+  object A2
+  object A3
+  object A4
+  object A5
+  object A6
+  object A7
+  object A8
+  object A9
+  object A10
+  object A11
+  object A12
+  object A13
+  object A14
+  object A15
+  object A16
+  object A17
+  object A18
+}
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    val c = new I
+    import c._
+    val l1 = List(A1, 
+		  A2, 
+		  A3, 
+                  A4, 
+                  A5, 
+                  A6, 
+                  A7, 
+                  A8, 
+                  A9, 
+                  A10, 
+                  A11, 
+                  A12, 
+                  A13, 
+                  A14, 
+                  A15, 
+                  A16, 
+                  A17, 
+                  A18)
+    val l2 = List(A1, 
+		  A2, 
+		  A3, 
+                  A4, 
+                  A5, 
+                  A6, 
+                  A7, 
+                  A8, 
+                  A9, 
+                  A10, 
+                  A11, 
+                  A12, 
+                  A13, 
+                  A14, 
+                  A15, 
+                  A16, 
+                  A17, 
+                  A18)
+    assert(l1.mkString == l2.mkString)
+    assert(!l1.contains(null))
+  }
+}