1 files changed, 123 insertions, 0 deletions
diff --git a/src/compiler/scala/tools/nsc/backend/jvm/opt/BytecodeUtils.scala b/src/compiler/scala/tools/nsc/backend/jvm/opt/BytecodeUtils.scala
new file mode 100644
index 0000000000..5718ad1c66
--- /dev/null
+++ b/src/compiler/scala/tools/nsc/backend/jvm/opt/BytecodeUtils.scala
@@ -0,0 +1,123 @@
+/* NSC -- new Scala compiler
+ * Copyright 2005-2014 LAMP/EPFL
+ * @author  Martin Odersky
+ */
+
+package scala.tools.nsc
+package backend.jvm
+package opt
+
+import scala.annotation.{tailrec, switch}
+import scala.collection.mutable
+import scala.tools.asm.Opcodes
+import scala.tools.asm.tree._
+import scala.collection.convert.decorateAsScala._
+
+object BytecodeUtils {
+
+  object Goto {
+    def unapply(instruction: AbstractInsnNode): Option[JumpInsnNode] = {
+      if (instruction.getOpcode == Opcodes.GOTO) Some(instruction.asInstanceOf[JumpInsnNode])
+      else None
+    }
+  }
+
+  object JumpNonJsr {
+    def unapply(instruction: AbstractInsnNode): Option[JumpInsnNode] = {
+      if (isJumpNonJsr(instruction)) Some(instruction.asInstanceOf[JumpInsnNode])
+      else None
+    }
+  }
+
+  object ConditionalJump {
+    def unapply(instruction: AbstractInsnNode): Option[JumpInsnNode] = {
+      if (isConditionalJump(instruction)) Some(instruction.asInstanceOf[JumpInsnNode])
+      else None
+    }
+  }
+
+  def isJumpNonJsr(instruction: AbstractInsnNode): Boolean = {
+    val op = instruction.getOpcode
+    // JSR is deprecated in classfile version 50, disallowed in 51. historically, it was used to implement finally.
+    op == Opcodes.GOTO || isConditionalJump(instruction)
+  }
+
+  def isConditionalJump(instruction: AbstractInsnNode): Boolean = {
+    val op = instruction.getOpcode
+    (op >= Opcodes.IFEQ && op <= Opcodes.IF_ACMPNE) || op == Opcodes.IFNULL || op == Opcodes.IFNONNULL
+  }
+
+  def isExecutable(instruction: AbstractInsnNode): Boolean = instruction.getOpcode >= 0
+
+  def nextExecutableInstruction(instruction: AbstractInsnNode, alsoKeep: AbstractInsnNode => Boolean = Set()): Option[AbstractInsnNode] = {
+    var result = instruction
+    do { result = result.getNext }
+    while (result != null && !isExecutable(result) && !alsoKeep(result))
+    Option(result)
+  }
+
+  def sameTargetExecutableInstruction(a: JumpInsnNode, b: JumpInsnNode): Boolean = {
+    // Compare next executable instead of the the labels. Identifies a, b as the same target:
+    //   LabelNode(a)
+    //   LabelNode(b)
+    //   Instr
+    nextExecutableInstruction(a.label) == nextExecutableInstruction(b.label)
+  }
+
+  def removeJumpAndAdjustStack(method: MethodNode, jump: JumpInsnNode) {
+    val instructions = method.instructions
+    val op = jump.getOpcode
+    if ((op >= Opcodes.IFEQ && op <= Opcodes.IFGE) || op == Opcodes.IFNULL || op == Opcodes.IFNONNULL) {
+      instructions.insert(jump, getPop(1))
+    } else if ((op >= Opcodes.IF_ICMPEQ && op <= Opcodes.IF_ICMPLE) || op == Opcodes.IF_ACMPEQ || op == Opcodes.IF_ACMPNE) {
+      instructions.insert(jump, getPop(1))
+      instructions.insert(jump, getPop(1))
+    } else {
+      // we can't remove JSR: its execution does not only jump, it also adds a return address to the stack
+      assert(jump.getOpcode == Opcodes.GOTO)
+    }
+    instructions.remove(jump)
+  }
+
+  def finalJumpTarget(source: JumpInsnNode): LabelNode = {
+    @tailrec def followGoto(label: LabelNode, seenLabels: Set[LabelNode]): LabelNode = nextExecutableInstruction(label) match {
+      case Some(Goto(dest)) =>
+        if (seenLabels(dest.label)) dest.label
+        else followGoto(dest.label, seenLabels + dest.label)
+
+      case _ => label
+    }
+    followGoto(source.label, Set(source.label))
+  }
+
+  def negateJumpOpcode(jumpOpcode: Int): Int = (jumpOpcode: @switch) match {
+    case Opcodes.IFEQ      => Opcodes.IFNE
+    case Opcodes.IFNE      => Opcodes.IFEQ
+
+    case Opcodes.IFLT      => Opcodes.IFGE
+    case Opcodes.IFGE      => Opcodes.IFLT
+
+    case Opcodes.IFGT      => Opcodes.IFLE
+    case Opcodes.IFLE      => Opcodes.IFGT
+
+    case Opcodes.IF_ICMPEQ => Opcodes.IF_ICMPNE
+    case Opcodes.IF_ICMPNE => Opcodes.IF_ICMPEQ
+
+    case Opcodes.IF_ICMPLT => Opcodes.IF_ICMPGE
+    case Opcodes.IF_ICMPGE => Opcodes.IF_ICMPLT
+
+    case Opcodes.IF_ICMPGT => Opcodes.IF_ICMPLE
+    case Opcodes.IF_ICMPLE => Opcodes.IF_ICMPGT
+
+    case Opcodes.IF_ACMPEQ => Opcodes.IF_ACMPNE
+    case Opcodes.IF_ACMPNE => Opcodes.IF_ACMPEQ
+
+    case Opcodes.IFNULL    => Opcodes.IFNONNULL
+    case Opcodes.IFNONNULL => Opcodes.IFNULL
+  }
+
+  def getPop(size: Int): InsnNode = {
+    val op = if (size == 1) Opcodes.POP else Opcodes.POP2
+    new InsnNode(op)
+  }
+}