SI-8601 Don't treat newarray as dead code

Otherwise we lose the side effect of a `NegativeArraySizeException`.

Author: retronym

src/compiler/scala/tools/nsc/backend/opt/DeadCodeElimination.scala

@@ -169,7 +169,7 @@ abstract class DeadCodeElimination extends SubComponent {
 
             case RETURN(_) | JUMP(_) | CJUMP(_, _, _, _) | CZJUMP(_, _, _, _) | STORE_FIELD(_, _) | LOAD_FIELD(_, _) | // Why LOAD_FIELD? It can NPE!
                  THROW(_)   | LOAD_ARRAY_ITEM(_) | STORE_ARRAY_ITEM(_) | SCOPE_ENTER(_) | SCOPE_EXIT(_) | STORE_THIS(_) |
-                 LOAD_EXCEPTION(_) | SWITCH(_, _) | MONITOR_ENTER() | MONITOR_EXIT() | CHECK_CAST(_) =>
+                 LOAD_EXCEPTION(_) | SWITCH(_, _) | MONITOR_ENTER() | MONITOR_EXIT() | CHECK_CAST(_) | CREATE_ARRAY(_, _) =>
               moveToWorkList()
 
             case CALL_METHOD(m1, _) if isSideEffecting(m1) =>

test/files/run/t8601b.scala

@@ -1,11 +1,14 @@
 object Test {
   def len(x: Array[String]): Unit = x.length
   def load(x: Array[String]): Unit = x(0)
+  def newarray(i: Int): Unit = new Array[Int](i)
 
   def check(x: => Any) = try { x; sys.error("failed to throw NPE!") } catch { case _: NullPointerException => }
+  def checkNegSize(x: => Any) = try { x; sys.error("failed to throw NegativeArraySizeException!") } catch { case _: NegativeArraySizeException => }
 
   def main(args: Array[String]) {
     check(len(null)) // bug: did not NPE
     check(load(null))
+    checkNegSize(newarray(-1))
   }
 }