package scala.tools.nsc
package backend.jvm
package opt

import org.junit.runner.RunWith
import org.junit.runners.JUnit4
import org.junit.Test
import scala.tools.asm.Opcodes._
import org.junit.Assert._

import scala.tools.asm.tree.ClassNode
import scala.tools.nsc.backend.jvm.AsmUtils._
import scala.tools.testing.AssertUtil._

import CodeGenTools._
import scala.tools.partest.ASMConverters
import ASMConverters._
import scala.tools.testing.ClearAfterClass
import scala.collection.convert.decorateAsScala._

object MethodLevelOptsTest extends ClearAfterClass.Clearable {
  var methodOptCompiler = newCompiler(extraArgs = "-Yopt:l:method")
  def clear(): Unit = { methodOptCompiler = null }
}

@RunWith(classOf[JUnit4])
class MethodLevelOptsTest extends ClearAfterClass {
  ClearAfterClass.stateToClear = MethodLevelOptsTest

  val methodOptCompiler = MethodLevelOptsTest.methodOptCompiler

  def wrapInDefault(code: Instruction*) = List(Label(0), LineNumber(1, Label(0))) ::: code.toList ::: List(Label(1))

  def locals(c: ClassNode, m: String) = findAsmMethod(c, m).localVariables.asScala.toList.map(l => (l.name, l.index)).sortBy(_._2)

  @Test
  def eliminateEmptyTry(): Unit = {
    val code = "def f = { try {} catch { case _: Throwable => 0; () }; 1 }"
    val warn = "a pure expression does nothing in statement position"
    assertSameCode(singleMethodInstructions(methodOptCompiler)(code, allowMessage = _.msg contains warn), wrapInDefault(Op(ICONST_1), Op(IRETURN)))
  }

  @Test
  def eliminateLoadBoxedUnit(): Unit = {
    // the compiler inserts a boxed into the try block. it's therefore non-empty (and live) and not eliminated.
    val code = "def f = { try {} catch { case _: Throwable => 0 }; 1 }"
    val m = singleMethod(methodOptCompiler)(code)
    assertTrue(m.handlers.length == 0)
    assertSameCode(m, List(Op(ICONST_1), Op(IRETURN)))
  }

  @Test
  def inlineThrowInCatchNotTry(): Unit = {
    // the try block does not contain the `ATHROW` instruction, but in the catch block, `ATHROW` is inlined
    val code = "def f(e: Exception) = throw { try e catch { case _: Throwable => e } }"
    val m = singleMethod(methodOptCompiler)(code)
    assertHandlerLabelPostions(m.handlers.head, m.instructions, 0, 3, 5)
    assertSameCode(m.instructions,
      wrapInDefault(VarOp(ALOAD, 1), Label(3), Op(ATHROW), Label(5), FrameEntry(4, List(), List("java/lang/Throwable")), Op(POP), VarOp(ALOAD, 1), Op(ATHROW))
    )
  }

  @Test
  def inlineReturnInCatchNotTry(): Unit = {
    val code = "def f: Int = return { try 1 catch { case _: Throwable => 2 } }"
    // cannot inline the IRETURN into the try block (because RETURN may throw IllegalMonitorState)
    val m = singleMethod(methodOptCompiler)(code)
    assertHandlerLabelPostions(m.handlers.head, m.instructions, 0, 3, 5)
    assertSameCode(m.instructions,
      wrapInDefault(Op(ICONST_1), Label(3), Op(IRETURN), Label(5), FrameEntry(4, List(), List("java/lang/Throwable")), Op(POP), Op(ICONST_2), Op(IRETURN)))
  }

  @Test
  def simplifyJumpsInTryCatchFinally(): Unit = {
    val code =
      """def f: Int =
        |  try {
        |    return 1
        |  } catch {
        |    case _: Throwable =>
        |    return 2
        |  } finally {
        |    return 3
        |    // dead
        |    val x = try 10 catch { case _: Throwable => 11 }
        |    println(x)
        |  }
      """.stripMargin
    val m = singleMethod(methodOptCompiler)(code)
    assertTrue(m.handlers.isEmpty)
    assertSameCode(m, List(Op(ICONST_3), Op(IRETURN)))
  }

  @Test
  def nullStoreLoadElim(): Unit = {
    // point of this test: we have two cleanups
    //   - remove `ACONST_NULL; ASTORE x` if x is otherwise not live
    //   - remove `ASTORE x; ALOAD x` if x is otherwise not live
    // in the example below, we have `ACONST_NULL; ASTORE x; ALOAD x`. in this case the store-load
    // should be removed (even though it looks like a null-store at first).
    val code =
      """class C {
        |  def t = {
        |    val x = null
        |    x.toString
        |  }
        |}
      """.stripMargin
    val List(c) = compileClasses(methodOptCompiler)(code)
    assertSameCode(getSingleMethod(c, "t"), List(
      Op(ACONST_NULL), Invoke(INVOKEVIRTUAL, "java/lang/Object", "toString", "()Ljava/lang/String;", false), Op(ARETURN)))
  }

  @Test
  def deadStoreReferenceElim(): Unit = {
    val code =
      """class C {
        |  def t = {
        |    var a = "a"   // assign to non-initialized, directly removed by dead store
        |    a = "b"       // assign to initialized, replaced by null-store, which is then removed: the var is not live, the uses are null-store or store-load
        |    a = "c"
        |    a             // store-load pair will be eliminated
        |  }
        |}
      """.stripMargin
    val List(c) = compileClasses(methodOptCompiler)(code)
    assertSameCode(
      getSingleMethod(c, "t"), List(Ldc(LDC, "c"), Op(ARETURN)))
  }

  @Test
  def deadStoreReferenceKeepNull(): Unit = {
    val code =
      """class C {
        |  def t = {
        |    var a = "el"  // this store is live, used in the println.
        |    println(a)
        |    a = "met"     // since it's an ASTORE to a live variable, cannot elim the store (SI-5313), but store null instead.
        |                  // so we get `LDC met; POP; ACONST_NULL; ASTORE 1`. the `LDC met; POP` is eliminated by push-pop.
        |    a = "zit"     // this store is live, so we get `LDC zit; ASOTRE 1; ALOAD 1; ARETURN`.
        |                  // we cannot eliminated the store-load sequence, because the local is live (again SI-5313).
        |    a
        |  }
        |}
      """.stripMargin
    val List(c) = compileClasses(methodOptCompiler)(code)

    assertSameCode(getSingleMethod(c, "t"), List(
      Ldc(LDC, "el"), VarOp(ASTORE, 1),
      Field(GETSTATIC, "scala/Predef$", "MODULE$", "Lscala/Predef$;"), VarOp(ALOAD, 1), Invoke(INVOKEVIRTUAL, "scala/Predef$", "println", "(Ljava/lang/Object;)V", false),
      Op(ACONST_NULL), VarOp(ASTORE, 1),
      Ldc(LDC, "zit"), VarOp(ASTORE, 1), VarOp(ALOAD, 1), Op(ARETURN)))
  }

  @Test
  def elimUnusedTupleObjectStringBox(): Unit = {
    val code =
      """class C {
        |  def t(x: Int, y: Int): Int = {
        |    val a = (x, y)                            // Tuple2$mcII$sp
        |    val b = (a, y)                            // Tuple2
        |    val c = (new Object, "krik", new String)  // unused java/lang/Object, java/lang/String allocation and string constant is also eliminated
        |    val d = new java.lang.Integer(x)
        |    val e = new String(new Array[Char](23))   // array allocation not eliminated, as it may throw (negative size, SI-8601)
        |    val f = new scala.runtime.IntRef(11)
        |    x + y
        |  }
        |}
      """.stripMargin
    val List(c) = compileClasses(methodOptCompiler)(code)
    assertSameCode(getSingleMethod(c, "t"), List(
      IntOp(BIPUSH, 23), IntOp(NEWARRAY, 5), Op(POP), VarOp(ILOAD, 1), VarOp(ILOAD, 2), Op(IADD), Op(IRETURN)))
  }

  @Test
  def noElimImpureConstructor(): Unit = {
    val code =
      """class C {
        |  def t(x: Int, y: Int): Int = {
        |    val a = new java.lang.Integer("nono")
        |    x + y
        |  }
        |}
      """.stripMargin
    val List(c) = compileClasses(methodOptCompiler)(code)
    assertSameCode(getSingleMethod(c, "t"), List(
      TypeOp(NEW, "java/lang/Integer"), Ldc(LDC, "nono"), Invoke(INVOKESPECIAL, "java/lang/Integer", "<init>", "(Ljava/lang/String;)V", false),
      VarOp(ILOAD, 1), VarOp(ILOAD, 2), Op(IADD), Op(IRETURN)))
  }

  @Test
  def elimUnusedBoxUnbox(): Unit = {
    val code =
      """class C {
        |  def t(a: Long): Int = {
        |    val t = 3 + a
        |    val u = a + t
        |    val v: Any = u // scala/runtime/BoxesRunTime.boxToLong
        |
        |    val w = (v, a) // a Tuple2 (not specialized because first value is Any)
        |                   // so calls scala/runtime/BoxesRunTime.boxToLong on the second value
        |
        |    val x = v.asInstanceOf[Long] // scala/runtime/BoxesRunTime.unboxToLong
        |
        |    val z = (java.lang.Long.valueOf(a), t)  // java box call on the left, scala/runtime/BoxesRunTime.boxToLong on the right
        |
        |    0
        |  }
        |}
      """.stripMargin
    val List(c) = compileClasses(methodOptCompiler)(code)
    assertSameCode(getSingleMethod(c, "t"), List(Op(ICONST_0), Op(IRETURN)))
  }

  @Test
  def elimUnusedClosure(): Unit = {
    val code =
      """class C {
        |  def t(x: Int, y: Int): Int = {
        |    val f = (a: Int) => a + x + y
        |    val g = (b: Int) => b - x
        |    val h = (s: String) => println(s)
        |    f(30)
        |  }
        |}
      """.stripMargin
    val List(c) = compileClasses(methodOptCompiler)(code)
    assertSameCode(getSingleMethod(c, "t"), List(
      IntOp(BIPUSH, 30), VarOp(ISTORE, 3),  // no constant propagation, so we keep the store (and load below) of a const
      VarOp(ILOAD, 1),
      VarOp(ILOAD, 2),
      VarOp(ILOAD, 3),
      Invoke(INVOKESTATIC, "C", "C$$$anonfun$1", "(III)I", false), Op(IRETURN)))
  }

  @Test
  def rewriteSpecializedClosureCall(): Unit = {
    val code =
      """class C {
        |  def t = {
        |    val f1 = (x: Int) => println(x)       // int-unit specialization
        |    val f2 = (x: Int, y: Long) => x == y  // int-long-boolean
        |    f1(1)
        |    f2(3, 4)
        |  }
        |}
      """.stripMargin
    val List(c) = compileClasses(methodOptCompiler)(code)
    val t = getSingleMethod(c, "t")
    assert(!t.instructions.exists(_.opcode == INVOKEDYNAMIC), t)
  }

  @Test
  def boxUnboxPrimitive(): Unit = {
    val code =
      """class C {
        |  def t1 = {
        |    val a: Any = runtime.BoxesRunTime.boxToInteger(1)
        |    runtime.BoxesRunTime.unboxToInt(a) + 1
        |  }
        |
        |  // two box and two unbox operations
        |  def t2(b: Boolean) = {
        |    val a = if (b) (3l: Any) else 2l
        |    a.asInstanceOf[Long] + 1 + a.asInstanceOf[Long]
        |  }
        |
        |  def t3(i: Integer): Int = i.asInstanceOf[Int]
        |
        |  def t4(l: Long): Any = l
        |
        |  def t5(i: Int): Int = {
        |    val b = Integer.valueOf(i)
        |    val c: Integer = i
        |    b.asInstanceOf[Int] + c.intValue
        |  }
        |
        |  def t6: Long = {
        |    val y = new java.lang.Boolean(true)
        |    val i: Integer = if (y) new Integer(10) else 13
        |    val j: java.lang.Long = 3l
        |    j + i
        |  }
        |
        |  def t7: Int = {
        |    val a: Any = 3
        |    a.asInstanceOf[Int] + a.asInstanceOf[Int]
        |  }
        |
        |  def t8 = null.asInstanceOf[Int]
        |
        |  def t9: Int = {
        |    val a = Integer.valueOf(10)
        |    val b = runtime.BoxesRunTime.unboxToInt(a)
        |    a + b
        |  }
        |
        |  @noinline def escape(a: Any) = ()
        |
        |  // example E4 in BoxUnbox doc comment
        |  def t10: Int = {
        |    val a = Integer.valueOf(10) // int 10 is stored into local
        |    escape(a)
        |    a                           // no unbox, 10 is read from local
        |  }
        |
        |  // the boxes here cannot be eliminated. see doc comment in BoxUnbox, example E1.
        |  def t11(b: Boolean): Int = {
        |    val i = Integer.valueOf(10)
        |    val j = Integer.valueOf(41)
        |    escape(i)                          // force rewrite method M1 (see doc in BoxUnbox)
        |    val res: Integer = if (b) i else j
        |    res.toInt                          // cannot be re-written to a local variable read - we don't know which local to read
        |  }
        |
        |  // both boxes have a single unboxing consumer, and the escape. note that the escape does
        |  // NOT put the two boxes into the same set of rewrite operations: we can rewrite both
        |  // boxes with their unbox individually. in both cases the box also escapes, so method
        |  // M1 will keep the box around.
        |  def t12(b: Boolean): Int = {
        |    val i = Integer.valueOf(10)
        |    val j = Integer.valueOf(32)
        |    escape(if (b) i else j)      // force method M1. the escape here is a consumer for both boxes
        |    if (b) i.toInt else j.toInt  // both boxes (i, j) have their own unboxing consumer
        |  }
        |}
      """.stripMargin

    val List(c) = compileClasses(methodOptCompiler)(code)

    assertNoInvoke(getSingleMethod(c, "t1"))
    assertNoInvoke(getSingleMethod(c, "t2"))
    assertInvoke(getSingleMethod(c, "t3"), "scala/runtime/BoxesRunTime", "unboxToInt")
    assertInvoke(getSingleMethod(c, "t4"), "scala/runtime/BoxesRunTime", "boxToLong")
    assertNoInvoke(getSingleMethod(c, "t5"))
    assertNoInvoke(getSingleMethod(c, "t6"))
    assertNoInvoke(getSingleMethod(c, "t7"))
    assertSameSummary(getSingleMethod(c, "t8"), List(ICONST_0, IRETURN))
    assertNoInvoke(getSingleMethod(c, "t9"))
    // t10: no invocation of unbox
    assertEquals(getSingleMethod(c, "t10").instructions collect { case Invoke(_, owner, name, _, _) => (owner, name) }, List(
      ("java/lang/Integer", "valueOf"),
      ("C", "escape")))

    assertSameSummary(getSingleMethod(c, "t11"), List(
      BIPUSH, "valueOf", ASTORE /*2*/,
      BIPUSH, "valueOf", ASTORE /*3*/,
      ALOAD /*0*/, ALOAD /*2*/, "escape",
      ILOAD /*1*/, IFEQ /*L1*/, ALOAD /*2*/, GOTO /*L2*/,  /*Label L1*/ -1, ALOAD /*3*/,  /*Label L2*/ -1,
      ASTORE /*4*/, GETSTATIC /*Predef*/, ALOAD /*4*/, "Integer2int", IRETURN))

    // no unbox invocations
    assertEquals(getSingleMethod(c, "t12").instructions collect { case Invoke(_, owner, name, _, _) => (owner, name) }, List(
      ("java/lang/Integer", "valueOf"),
      ("java/lang/Integer", "valueOf"),
      ("C", "escape")))
  }

  @Test
  def refEliminiation(): Unit = {
    val code =
      """class C {
        |  import runtime._
        |  @noinline def escape(a: Any) = ()
        |
        |  def t1 = { // box eliminated
        |    val r = new IntRef(0)
        |    r.elem
        |  }
        |
        |  def t2(b: Boolean) = {
        |    val r1 = IntRef.zero()    // both eliminated
        |    val r2 = IntRef.create(1)
        |    val res: IntRef = if (b) r1 else r2
        |    res.elem
        |  }
        |
        |  def t3 = {
        |    val r = LongRef.create(10l) // eliminated
        |    r.elem += 3
        |    r.elem
        |  }
        |
        |  def t4(b: Boolean) = {
        |    val x = BooleanRef.create(false) // eliminated
        |    if (b) x.elem = true
        |    if (x.elem) "a" else "b"
        |  }
        |
        |  def t5 = {
        |    val r = IntRef.create(10) // not eliminated: the box might be modified in the escape
        |    escape(r)
        |    r.elem
        |  }
        |
        |  def t6(b: Boolean) = {
        |    val r1 = IntRef.zero()
        |    val r2 = IntRef.create(1)
        |    r1.elem = 39
        |    val res: IntRef = if (b) r1 else r2
        |    res.elem // boxes remain: can't rewrite this read, don't know which local
        |  }
        |}
      """.stripMargin
    val List(c) = compileClasses(methodOptCompiler)(code)
    assertSameSummary(getSingleMethod(c, "t1"), List(ICONST_0, IRETURN))
    assertNoInvoke(getSingleMethod(c, "t2"))
    assertSameSummary(getSingleMethod(c, "t3"), List(LDC, LDC, LADD, LRETURN))
    assertNoInvoke(getSingleMethod(c, "t4"))
    assertEquals(getSingleMethod(c, "t5").instructions collect { case Field(_, owner, name, _) => s"$owner.$name" },
      List("scala/runtime/IntRef.elem"))
    assertEquals(getSingleMethod(c, "t6").instructions collect { case Field(op, owner, name, _) => s"$op $owner.$name" },
      List(s"$PUTFIELD scala/runtime/IntRef.elem", s"$GETFIELD scala/runtime/IntRef.elem"))
  }

  @Test
  def tupleElimination(): Unit = {
    val code =
      """class C {
        |  def t1(b: Boolean) = {
        |    val t = ("hi", "fish")
        |    if (b) t._1 else t._2
        |  }
        |
        |  def t2 = {
        |    val t = (1, 3) // specialized tuple
        |    t._1 + t._2    // specialized accessors (_1$mcII$sp)
        |  }
        |
        |  def t3 = {
        |    // boxed before tuple creation, a non-specialized tuple is created
        |    val t = (new Integer(3), Integer.valueOf(4))
        |    t._1 + t._2 // invokes the generic `_1` / `_2` getters, both values unboxed by Integer2int
        |  }
        |
        |  def t4: Any = {
        |    val t = (3, 3) // specialized tuple is created, ints are not boxed
        |    (t: Tuple2[Any, Any])._1 // when eliminating the _1 call, need to insert a boxing operation
        |  }
        |
        |  // the inverse of t4 also happens: an Tuple[Integer] where _1$mcI$sp is invoked. In this
        |  // case, an unbox operation needs to be added when eliminating the extraction. The only
        |  // way I found to test this is with an inlined generic method, see InlinerTest.tupleElimination.
        |  def tpl[A, B](a: A, b: B) = (a, b)
        |  def t5: Int = tpl(1, 2)._1 // invokes _1$mcI$sp
        |
        |  def t6 = {
        |    val (a, b) = (1, 2)
        |    a - b
        |  }
        |
        |  def t7 = {
        |    // this example is more tricky to handle than it looks, see doc comment in BoxUnbox.
        |    val ((a, b), c) = ((1, 2), 3)
        |    a + b + c
        |  }
        |
        |  def t8 = {
        |    val ((a, b), (c, d)) = ((1, 2), (3, Integer.valueOf(10)))
        |    a + b + c + d
        |  }
        |
        |  def t9(a: Int, b: Int) = (a, b) match { // tuple is optimized away
        |    case (x, y) if x == y => 0
        |    case (x, y) => x + y
        |  }
        |}
      """.stripMargin
    val List(c) = compileClasses(methodOptCompiler)(code)
    assertNoInvoke(getSingleMethod(c, "t1"))
    assertSameSummary(getSingleMethod(c, "t2"), List(ICONST_1, ICONST_3, IADD, IRETURN))
    assertSameSummary(getSingleMethod(c, "t3"), List(ICONST_3, ICONST_4, IADD, IRETURN))
    assertSameSummary(getSingleMethod(c, "t4"), List(ICONST_3, "boxToInteger", ARETURN))
    assertEquals(getSingleMethod(c, "t5").instructions collect { case Invoke(_, owner, name, _, _) => (owner, name) }, List(
      ("scala/runtime/BoxesRunTime", "boxToInteger"),
      ("scala/runtime/BoxesRunTime", "boxToInteger"),
      ("C", "tpl"),
      ("scala/Tuple2", "_1$mcI$sp")))
    assertSameSummary(getSingleMethod(c, "t6"), List(ICONST_1, ICONST_2, ISUB, IRETURN))
    assertSameSummary(getSingleMethod(c, "t7"), List(
      ICONST_1, ICONST_2, ISTORE, ISTORE,
      ICONST_3, ISTORE,
      ILOAD, ILOAD, IADD, ILOAD, IADD, IRETURN))
    assertNoInvoke(getSingleMethod(c, "t8"))
    assertNoInvoke(getSingleMethod(c, "t9"))
  }

  @Test
  def nullnessOpts(): Unit = {
    val code =
      """class C {
        |  def t1 = {
        |    val a = new C
        |    if (a == null)
        |      println() // eliminated
        |    a
        |  }
        |
        |  def t2 = null.asInstanceOf[Long] // replaced by zero value
        |
        |  def t3 = {
        |    val t = (1, 3)
        |    val a = null
        |    if (t ne a) t._1
        |    else throw new Error()
        |  }
        |
        |  def t4 = {
        |    val i = Integer.valueOf(1)
        |    val a = null
        |    if (i eq a) throw new Error()
        |    else i.toInt
        |  }
        |
        |  def t5 = {
        |    val i = runtime.DoubleRef.zero()
        |    if (i == null) throw new Error()
        |    else i.elem
        |  }
        |
        |  def t6 = {
        |    var a = null
        |    var i = null
        |    a = i // eliminated (store of null to variable that is already null)
        |    a // replaced by ACONST_NULL (load of variable that is known null)
        |  }
        |
        |  def t7 = {
        |    val a = null
        |    a.isInstanceOf[String] // eliminated, replaced by 0 (null.isInstanceOf is always false)
        |  }
        |}
      """.stripMargin
    val List(c) = compileClasses(methodOptCompiler)(code)
    assertSameSummary(getSingleMethod(c, "t1"), List(NEW, DUP, "<init>", ARETURN))
    assertSameCode(getSingleMethod(c, "t2"), List(Op(LCONST_0), Op(LRETURN)))
    assertSameCode(getSingleMethod(c, "t3"), List(Op(ICONST_1), Op(IRETURN)))
    assertSameCode(getSingleMethod(c, "t4"), List(Op(ICONST_1), Op(IRETURN)))
    assertSameCode(getSingleMethod(c, "t5"), List(Op(DCONST_0), Op(DRETURN)))
    assertSameCode(getSingleMethod(c, "t6"), List(Op(ACONST_NULL), Op(ARETURN)))
    assertSameCode(getSingleMethod(c, "t7"), List(Op(ICONST_0), Op(IRETURN)))
  }

  @Test
  def elimRedundantNullCheck(): Unit = {
    val code =
      """class C {
        |  def t(x: Object) = {
        |    val bool = x == null
        |    if (x != null) 1 else 0
        |  }
        |}
      """.stripMargin
    val List(c) = compileClasses(methodOptCompiler)(code)
    assertSameCode(
      getSingleMethod(c, "t"), List(
        VarOp(ALOAD, 1), Jump(IFNULL, Label(6)), Op(ICONST_1), Op(IRETURN), Label(6), Op(ICONST_0), Op(IRETURN)))
  }

  @Test
  def t5313(): Unit = {
    val code =
      """class C {
        |  def randomBoolean = scala.util.Random.nextInt % 2 == 0
        |
        |  // 3 stores to kept1 (slot 1), 1 store to result (slot 2)
        |  def t1 = {
        |    var kept1 = new Object
        |    val result = new java.lang.ref.WeakReference(kept1)
        |    kept1 = null // we can't eliminate this assignment because result can observe
        |                 // when the object has no more references. See SI-5313
        |    kept1 = new Object // could eliminate this one with a more elaborate analysis (we know it contains null)
        |                       // however, such is not implemented: if a var is live, then stores are kept.
        |    result
        |  }
        |
        |  // only two variables are live: kept2 and kept3. they end up on slots 1 and 2.
        |  // kept2 has 2 stores, kept3 has 1 store.
        |  def t2 = {
        |    var erased2 = null    // we can eliminate this store because it's never used
        |    val erased3 = erased2 // and this
        |    var erased4 = erased2 // and this
        |    val erased5 = erased4 // and this
        |    var kept2: Object = new Object // ultimately can't be eliminated
        |    while(randomBoolean) {
        |      val kept3 = kept2
        |      kept2 = null // this can't, because it clobbers kept2, which is used
        |      erased4 = null // safe to eliminate
        |      println(kept3)
        |    }
        |    0
        |  }
        |
        |  def t3 = {
        |    var kept4 = new Object // have to keep, it's used
        |    try
        |      println(kept4)
        |    catch {
        |      case _ : Throwable => kept4 = null // have to keep, it clobbers kept4 which is used
        |    }
        |    0
        |  }
        |
        |  def t4 = {
        |    var kept5 = new Object
        |    print(kept5)
        |    kept5 = null // can't eliminate it's a clobber and it's used
        |    print(kept5)
        |    kept5 = null // eliminated by nullness analysis (store null to a local that is known to be null)
        |    0
        |  }
        |
        |  def t5 = {
        |    while(randomBoolean) {
        |      var kept6: AnyRef = null // not used, but have to keep because it clobbers the next used store
        |                               // on the back edge of the loop
        |      kept6 = new Object // used
        |      println(kept6)
        |    }
        |    0
        |  }
        |}
      """.stripMargin

    val List(c) = compileClasses(methodOptCompiler)(code)
    def stores(m: String) = getSingleMethod(c, m).instructions.filter(_.opcode == ASTORE)

    assertEquals(locals(c, "t1"), List(("this",0), ("kept1",1), ("result",2)))
    assert(stores("t1") == List(VarOp(ASTORE, 1), VarOp(ASTORE, 2), VarOp(ASTORE, 1), VarOp(ASTORE, 1)),
      textify(findAsmMethod(c, "t1")))

    assertEquals(locals(c, "t2"), List(("this",0), ("kept2",1), ("kept3",2)))
    assert(stores("t2") == List(VarOp(ASTORE, 1), VarOp(ASTORE, 2), VarOp(ASTORE, 1)),
      textify(findAsmMethod(c, "t2")))

    assertEquals(locals(c, "t3"), List(("this",0), ("kept4",1)))
    assert(stores("t3") == List(VarOp(ASTORE, 1), VarOp(ASTORE, 1)),
      textify(findAsmMethod(c, "t3")))

    assertEquals(locals(c, "t4"), List(("this",0), ("kept5",1)))
    assert(stores("t4") == List(VarOp(ASTORE, 1), VarOp(ASTORE, 1)),
      textify(findAsmMethod(c, "t4")))

    assertEquals(locals(c, "t5"), List(("this",0), ("kept6",1)))
    assert(stores("t5") == List(VarOp(ASTORE, 1), VarOp(ASTORE, 1)),
      textify(findAsmMethod(c, "t5")))
  }

  @Test
  def testCpp(): Unit = {
    // copied from an old test (run/test-cpp.scala)
    val code =
      """class C {
        |  import scala.util.Random._
        |
        |  def t1(x: Int) = {
        |    val y = x
        |    println(y)
        |  }
        |
        |  def t2 = {
        |    val x = 2
        |    val y = x
        |    println(y)
        |  }
        |
        |  def t3 = {
        |    val x = this
        |    val y = x
        |    println(y)
        |  }
        |
        |  def f = nextInt
        |
        |  def t4 = {
        |    val x = f
        |    val y = x
        |    println(y)
        |  }
        |
        |  def t5 = {
        |    var x = nextInt
        |    var y = x
        |    println(y)
        |
        |    y = nextInt
        |    x = y
        |    println(x)
        |  }
        |}
      """.stripMargin

    val List(c) = compileClasses(methodOptCompiler)(code)
    assertEquals(locals(c, "t1"), List(("this", 0), ("x", 1)))

    assertEquals(locals(c, "t2"), List(("this", 0), ("x", 1)))
    // we don't have constant propagation (yet).
    // the local var can't be optimized as a store;laod sequence, there's a GETSTATIC between the two
    assertSameSummary(getSingleMethod(c, "t2"), List(
      ICONST_2, ISTORE, GETSTATIC, ILOAD, "boxToInteger", "println", RETURN))

    assertEquals(locals(c, "t3"), List(("this", 0)))
    assertEquals(locals(c, "t4"), List(("this", 0), ("x", 1)))
    assertEquals(locals(c, "t5"), List(("this", 0), ("x", 1)))
  }

  @Test
  def t7006(): Unit = {
    val code =
      """class C {
        |  def t: Unit = {
        |    try {
        |      val x = 3
        |    } finally {
        |      print("hello")
        |    }
        |    while(true) { }
        |  }
        |}
      """.stripMargin
    val List(c) = compileClasses(methodOptCompiler)(code)
    val t = getSingleMethod(c, "t")
    assertEquals(t.handlers, Nil)
    assertEquals(locals(c, "t"), List(("this", 0)))
    assertSameSummary(t, List(GETSTATIC, LDC, "print", -1, GOTO))
  }

  @Test
  def booleanOrderingCompare(): Unit = {
    val code =
      """class C {
        |  def compare(x: Boolean, y: Boolean) = (x, y) match {
        |    case (false, true) => -1
        |    case (true, false) => 1
        |    case _ => 0
        |  }
        |}
      """.stripMargin
    val List(c) = compileClasses(methodOptCompiler)(code)
    assertNoInvoke(getSingleMethod(c, "compare"))
  }

  @Test
  def t8790(): Unit = {
    val code =
      """class C {
        |  def t(x: Int, y: Int): String = (x, y) match {
        |    case (7, 8) => "a"
        |    case _ => "b"
        |  }
        |}
      """.stripMargin
    val List(c) = compileClasses(methodOptCompiler)(code)

    assertSameSummary(getSingleMethod(c, "t"), List(
      BIPUSH, ILOAD, IF_ICMPNE,
      BIPUSH, ILOAD, IF_ICMPNE,
      LDC, ASTORE, GOTO,
      -1, LDC, ASTORE,
      -1, ALOAD, ARETURN))
  }
}
