Minor fixes in the optimizer

Fixes the variable indices in the local variable table (debug info)
for inlined locals.

After re-writing a closure invocation to the body method, mark the
callsite method as potentially having dead code. The body method may
return Nothing$, creating new unreachable code in the callsite method.

4 files changed, 10 insertions, 7 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
index df8dcc690a..ede572dfb4 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/opt/BytecodeUtils.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/opt/BytecodeUtils.scala
@@ -308,14 +308,14 @@ object BytecodeUtils {
    * Clone the local variable descriptors of `methodNode` and map their `start` and `end` labels
    * according to the `labelMap`.
    */
-  def cloneLocalVariableNodes(methodNode: MethodNode, labelMap: Map[LabelNode, LabelNode], prefix: String): List[LocalVariableNode] = {
+  def cloneLocalVariableNodes(methodNode: MethodNode, labelMap: Map[LabelNode, LabelNode], prefix: String, shift: Int): List[LocalVariableNode] = {
     methodNode.localVariables.iterator().asScala.map(localVariable => new LocalVariableNode(
       prefix + localVariable.name,
       localVariable.desc,
       localVariable.signature,
       labelMap(localVariable.start),
       labelMap(localVariable.end),
-      localVariable.index
+      localVariable.index + shift
     )).toList
   }
 
diff --git a/src/compiler/scala/tools/nsc/backend/jvm/opt/ClosureOptimizer.scala b/src/compiler/scala/tools/nsc/backend/jvm/opt/ClosureOptimizer.scala
index 30b7f2edad..1a1a6942dc 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/opt/ClosureOptimizer.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/opt/ClosureOptimizer.scala
@@ -78,10 +78,10 @@ class ClosureOptimizer[BT <: BTypes](val btypes: BT) {
       closureInstantiations.iterator.flatMap({
         case (methodNode, closureInits) =>
           // A lazy val to ensure the analysis only runs if necessary (the value is passed by name to `closureCallsites`)
-          lazy val prodCons = new ProdConsAnalyzer(methodNode, closureInits.valuesIterator.next.ownerClass.internalName)
+          lazy val prodCons = new ProdConsAnalyzer(methodNode, closureInits.valuesIterator.next().ownerClass.internalName)
           val sortedInits = immutable.TreeSet.empty ++ closureInits.values
-          sortedInits.iterator.map(init => (init, closureCallsites(init, prodCons)))
-      }).toList // mapping to a list (not a map) to keep the sorting of closureInstantiationsByMethod
+          sortedInits.iterator.map(init => (init, closureCallsites(init, prodCons))).filter(_._2.nonEmpty)
+      }).toList // mapping to a list (not a map) to keep the sorting
     }
 
     // Rewrite all closure callsites (or issue inliner warnings for those that cannot be rewritten)
@@ -268,6 +268,10 @@ class ClosureOptimizer[BT <: BTypes](val btypes: BT) {
     // Explanation: If the lambda body method is non-static, the receiver is a captured
     // value. It can only be captured within some instance method, so we know it's non-null.
     callGraph.addCallsite(bodyMethodCallsite)
+
+    // Rewriting a closure invocation may render code unreachable. For example, the body method of
+    // (x: T) => ??? has return type Nothing$, and an ATHROW is added (see fixLoadedNothingOrNullValue).
+    unreachableCodeEliminated -= ownerMethod
   }
 
   /**
diff --git a/src/compiler/scala/tools/nsc/backend/jvm/opt/Inliner.scala b/src/compiler/scala/tools/nsc/backend/jvm/opt/Inliner.scala
index 1550f942c7..8dff7ef446 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/opt/Inliner.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/opt/Inliner.scala
@@ -406,7 +406,7 @@ class Inliner[BT <: BTypes](val btypes: BT) {
     callsiteMethod.instructions.insert(callsiteInstruction, clonedInstructions)
     callsiteMethod.instructions.remove(callsiteInstruction)
 
-    callsiteMethod.localVariables.addAll(cloneLocalVariableNodes(callee, labelsMap, callee.name + "_").asJava)
+    callsiteMethod.localVariables.addAll(cloneLocalVariableNodes(callee, labelsMap, callee.name + "_", localVarShift).asJava)
     callsiteMethod.tryCatchBlocks.addAll(cloneTryCatchBlockNodes(callee, labelsMap).asJava)
 
     callsiteMethod.maxLocals += returnType.getSize + callee.maxLocals
diff --git a/src/compiler/scala/tools/nsc/backend/jvm/opt/LocalOpt.scala b/src/compiler/scala/tools/nsc/backend/jvm/opt/LocalOpt.scala
index 4132710a96..f5e6653344 100644
--- a/src/compiler/scala/tools/nsc/backend/jvm/opt/LocalOpt.scala
+++ b/src/compiler/scala/tools/nsc/backend/jvm/opt/LocalOpt.scala
@@ -196,7 +196,6 @@ object LocalOptImpls {
     a.analyze(ownerClassName, method)
     val frames = a.getFrames
 
-    val initialSize = method.instructions.size
     var i = 0
     var liveLabels = Set.empty[LabelNode]
     var removedInstructions = Set.empty[AbstractInsnNode]