DCE-driven mode

:js:js.tests:jsIrTest works same as before
:js:js.tests:jsPirTest runs tests in DCE-driven mode

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/BackendContext.kt

@@ -20,6 +20,7 @@ import org.jetbrains.kotlin.backend.common.ir.DeclarationFactory
 import org.jetbrains.kotlin.backend.common.ir.Ir
 import org.jetbrains.kotlin.backend.common.ir.SharedVariablesManager
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
+import org.jetbrains.kotlin.ir.declarations.IrClass
 import org.jetbrains.kotlin.ir.declarations.IrField
 import org.jetbrains.kotlin.ir.descriptors.IrBuiltIns
 import org.jetbrains.kotlin.ir.symbols.IrFunctionSymbol
@@ -35,4 +36,5 @@ interface BackendContext {
     val internalPackageFqn: FqName
     val transformedFunction: MutableMap<IrFunctionSymbol, IrSimpleFunctionSymbol>
     val lateinitNullableFields: MutableMap<IrField, IrField>
+    val extractedLocalClasses: MutableSet<IrClass>
 }

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/Mappings.kt

@@ -37,7 +37,7 @@ open class DefaultMapping : Mapping {
     override val lateInitFieldToNullableField: Mapping.Delegate<IrField, IrField> = newMapping()
     override val inlineClassMemberToStatic: Mapping.Delegate<IrFunction, IrSimpleFunction> = newMapping()
 
-    protected fun <K : IrDeclaration, V> newMapping() = object : Mapping.Delegate<K, V>() {
+    protected open fun <K : IrDeclaration, V> newMapping() = object : Mapping.Delegate<K, V>() {
         private val map: MutableMap<K, V> = mutableMapOf()
 
         override operator fun get(key: K): V? {

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/LocalClassPopupLowering.kt

@@ -44,6 +44,7 @@ open class LocalClassPopupLowering(val context: BackendContext) : BodyLoweringPa
 
         for ((local, newContainer) in extractedLocalClasses) {
             newContainer.addChild(local)
+            context.extractedLocalClasses += local
         }
     }