no null check for type-tested unapply arg

pattern matching on case classes where pattern
is not known to be a subclass of the unapply's argument type
used to result in code like:

```
if (x1.isInstanceOf[Foo]) {
  val x2 = x1.asInstanceOf[Foo]
  if (x2 != null) { // redundant
    ...
  }
}
```

this wastes byte code on the redundant null check
with this patch, when previous type tests imply
the variable cannot be null, there's no null check

2 files changed, 33 insertions, 0 deletions

diff --git a/test/files/jvm/patmat_opt_no_nullcheck/Analyzed_1.scala b/test/files/jvm/patmat_opt_no_nullcheck/Analyzed_1.scala
new file mode 100644
index 0000000000..1594eb523c
--- /dev/null
+++ b/test/files/jvm/patmat_opt_no_nullcheck/Analyzed_1.scala
@@ -0,0 +1,25 @@
+// this class's bytecode, compiled under -optimize is analyzed by the test
+// method a's bytecode should be identical to method b's bytecode
+case class Foo(x: Any)
+
+class SameBytecode {
+  def a = 
+    (Foo(1): Any) match {
+      case Foo(_: String) =>
+    }
+
+  // there's no null check
+  def b: Unit = {
+    val x1: Any = Foo(1)
+    if (x1.isInstanceOf[Foo]) {
+      val x3 = x1.asInstanceOf[Foo]
+      if (x3.x.isInstanceOf[String]) {
+        val x4 = x3.x.asInstanceOf[String]
+        val x = ()
+        return
+      }
+    }
+
+    throw new MatchError(x1)
+  }
+}
\ No newline at end of file
diff --git a/test/files/jvm/patmat_opt_no_nullcheck/test.scala b/test/files/jvm/patmat_opt_no_nullcheck/test.scala
new file mode 100644
index 0000000000..2927e763d5
--- /dev/null
+++ b/test/files/jvm/patmat_opt_no_nullcheck/test.scala
@@ -0,0 +1,8 @@
+import scala.tools.partest.BytecodeTest
+
+object Test extends BytecodeTest {
+  def show: Unit = {
+    val classNode = loadClassNode("SameBytecode")
+    sameBytecode(getMethod(classNode, "a"), getMethod(classNode, "b"))
+  }
+}