[backport] SI-9376 don't crash when inlining a closure body that throws.

If the closure body method has return type Nothing$, add an `ATHROW`
instruction after the callsite. This is required for computing stack
map frames, as explained in a comment in BCodeBodyBuilder.adapt.

Similar for closure bodies with return type Null$.

Author: lrytz

src/compiler/scala/tools/nsc/backend/jvm/opt/BytecodeUtils.scala

@@ -12,7 +12,7 @@ import scala.collection.mutable
 import scala.reflect.internal.util.Collections._
 import scala.tools.asm.commons.CodeSizeEvaluator
 import scala.tools.asm.tree.analysis._
-import scala.tools.asm.{MethodWriter, ClassWriter, Label, Opcodes}
+import scala.tools.asm.{MethodWriter, ClassWriter, Label, Opcodes, Type}
 import scala.tools.asm.tree._
 import GenBCode._
 import scala.collection.convert.decorateAsScala._
@@ -330,6 +330,26 @@ object BytecodeUtils {
     )).toList
   }
 
+  /**
+   * This method is used by optimizer components to eliminate phantom values of instruction
+   * that load a value of type `Nothing$` or `Null$`. Such values on the stack don't interact well
+   * with stack map frames.
+   *
+   * For example, `opt.getOrElse(throw e)` is re-written to an invocation of the lambda body, a
+   * method with return type `Nothing$`. Similarly for `opt.getOrElse(null)` and `Null$`.
+   *
+   * During bytecode generation this is handled by BCodeBodyBuilder.adapt. See the comment in that
+   * method which explains the issue with such phantom values.
+   */
+  def fixLoadedNothingOrNullValue(loadedType: Type, loadInstr: AbstractInsnNode, methodNode: MethodNode, bTypes: BTypes): Unit = {
+    if (loadedType == bTypes.coreBTypes.RT_NOTHING.toASMType) {
+      methodNode.instructions.insert(loadInstr, new InsnNode(Opcodes.ATHROW))
+    } else if (loadedType == bTypes.coreBTypes.RT_NULL.toASMType) {
+      methodNode.instructions.insert(loadInstr, new InsnNode(Opcodes.ACONST_NULL))
+      methodNode.instructions.insert(loadInstr, new InsnNode(Opcodes.POP))
+    }
+  }
+
   /**
    * A wrapper to make ASM's Analyzer a bit easier to use.
    */

src/compiler/scala/tools/nsc/backend/jvm/opt/ClosureOptimizer.scala

@@ -283,6 +283,10 @@ class ClosureOptimizer[BT <: BTypes](val btypes: BT) {
           val isInterface = bodyOpcode == INVOKEINTERFACE
           val bodyInvocation = new MethodInsnNode(bodyOpcode, lambdaBodyHandle.getOwner, lambdaBodyHandle.getName, lambdaBodyHandle.getDesc, isInterface)
           methodNode.instructions.insertBefore(invocation, bodyInvocation)
+
+          val returnType = Type.getReturnType(lambdaBodyHandle.getDesc)
+          fixLoadedNothingOrNullValue(returnType, bodyInvocation, methodNode, btypes) // see comment of that method
+
           methodNode.instructions.remove(invocation)
 
           // update the call graph