SI-7006 Eliminate unreachable blocks

GenASM was doing a bunch of stuff to eliminate unreachable exception
handlers, but it was still leaving behind other unreachable blocks, for
instance a finally block associated with an exception handler that got
removed would still be left lying around. ASM would in turn turn those
into a big pile of NOPs, which just take up space uselessly.

This commit replaces all the logic for eliding exception handlers with
a single unreachable block remover that catches unused exception
handlers and a whole lot more.

3 files changed, 28 insertions, 0 deletions

diff --git a/test/files/jvm/t7006/Foo_1.flags b/test/files/jvm/t7006/Foo_1.flags
new file mode 100644
index 0000000000..72fe7b1aa0
--- /dev/null
+++ b/test/files/jvm/t7006/Foo_1.flags
@@ -0,0 +1 @@
+ -Ydead-code -Ydebug -Xfatal-warnings
diff --git a/test/files/jvm/t7006/Foo_1.scala b/test/files/jvm/t7006/Foo_1.scala
new file mode 100644
index 0000000000..f84269daf2
--- /dev/null
+++ b/test/files/jvm/t7006/Foo_1.scala
@@ -0,0 +1,9 @@
+class Foo_1 {
+  def foo {
+    try {
+      val x = 3
+    } finally {
+      print("hello")
+    }
+  }
+}
diff --git a/test/files/jvm/t7006/Test.scala b/test/files/jvm/t7006/Test.scala
new file mode 100644
index 0000000000..5cc38e42a2
--- /dev/null
+++ b/test/files/jvm/t7006/Test.scala
@@ -0,0 +1,18 @@
+import scala.tools.partest.BytecodeTest
+import scala.tools.asm
+import asm.tree.InsnList
+import scala.collection.JavaConverters._
+
+object Test extends BytecodeTest {
+  def show: Unit = {
+    val classNode = loadClassNode("Foo_1")
+    val methodNode = getMethod(classNode, "foo")
+    assert(countNops(methodNode.instructions) == 0)
+  }
+
+  def countNops(insnList: InsnList): Int = {
+    def isNop(node: asm.tree.AbstractInsnNode): Boolean =
+      (node.getOpcode == asm.Opcodes.NOP)
+    insnList.iterator.asScala.count(isNop)
+  }
+}