[JS IR] A bunch of fixes to make PIR mode work

- provide required mappings
 - fix fake overrides
 - fix local declaration lowering
 - fix DCE

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

@@ -15,6 +15,9 @@ interface Mapping {
     val suspendFunctionToCoroutineConstructor: Delegate<IrFunction, IrConstructor>
     val lateInitFieldToNullableField: Delegate<IrField, IrField>
     val inlineClassMemberToStatic: Delegate<IrFunction, IrSimpleFunction>
+    val capturedFields: Delegate<IrClass, Collection<IrField>>
+    val capturedConstructors: Delegate<IrConstructor, IrConstructor>
+    val reflectedNameAccessor: Delegate<IrClass, IrSimpleFunction>
 
     abstract class Delegate<K : IrDeclaration, V> {
         abstract operator fun get(key: K): V?
@@ -36,6 +39,9 @@ open class DefaultMapping : Mapping {
     override val suspendFunctionToCoroutineConstructor: Mapping.Delegate<IrFunction, IrConstructor> = newMapping()
     override val lateInitFieldToNullableField: Mapping.Delegate<IrField, IrField> = newMapping()
     override val inlineClassMemberToStatic: Mapping.Delegate<IrFunction, IrSimpleFunction> = newMapping()
+    override val capturedFields: Mapping.Delegate<IrClass, Collection<IrField>> = newMapping()
+    override val capturedConstructors: Mapping.Delegate<IrConstructor, IrConstructor> = newMapping()
+    override val reflectedNameAccessor: Mapping.Delegate<IrClass, IrSimpleFunction> = newMapping()
 
     protected open fun <K : IrDeclaration, V> newMapping() = object : Mapping.Delegate<K, V>() {
         private val map: MutableMap<K, V> = mutableMapOf()

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

@@ -33,9 +33,7 @@ import org.jetbrains.kotlin.ir.symbols.impl.IrSimpleFunctionSymbolImpl
 import org.jetbrains.kotlin.ir.symbols.impl.IrTypeParameterSymbolImpl
 import org.jetbrains.kotlin.ir.symbols.impl.IrValueParameterSymbolImpl
 import org.jetbrains.kotlin.ir.types.*
-import org.jetbrains.kotlin.ir.types.impl.IrSimpleTypeBuilder
 import org.jetbrains.kotlin.ir.types.impl.IrSimpleTypeImpl
-import org.jetbrains.kotlin.ir.types.impl.buildSimpleType
 import org.jetbrains.kotlin.ir.types.impl.makeTypeProjection
 import org.jetbrains.kotlin.ir.util.*
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
@@ -479,14 +477,14 @@ val IrFunction.allParameters: List<IrValueParameter>
         explicitParameters
     }
 
-fun IrClass.addFakeOverrides() {
+fun IrClass.addFakeOverrides(implementedMembers: List<IrSimpleFunction> = emptyList()) {
     fun IrDeclaration.toList() = when (this) {
         is IrSimpleFunction -> listOf(this)
         is IrProperty -> listOfNotNull(getter, setter)
         else -> emptyList()
     }
 
-    val overriddenFunctions = declarations
+    val overriddenFunctions = (declarations + implementedMembers)
         .flatMap { it.toList() }
         .flatMap { it.overriddenSymbols.map { it.owner } }
         .toSet()

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

@@ -37,9 +37,6 @@ class ClosureAnnotator(body: IrBody, declaration: IrDeclaration) {
 
     init {
         // Collect all closures for classes and functions. Collect call graph
-        if (declaration is IrSimpleFunction && declaration.name.asString() == "arrayIterator") {
-            1
-        }
         body.accept(ClosureCollectorVisitor(), declaration.closureBuilderOrNull ?: declaration.parentClosureBuilder)
     }
 

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

@@ -7,10 +7,14 @@ package org.jetbrains.kotlin.backend.common.lower
 
 import org.jetbrains.kotlin.backend.common.*
 import org.jetbrains.kotlin.backend.common.ir.addChild
+import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.IrStatement
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.expressions.IrBody
 import org.jetbrains.kotlin.ir.expressions.impl.IrCompositeImpl
+import org.jetbrains.kotlin.ir.visitors.IrElementVisitorVoid
+import org.jetbrains.kotlin.ir.visitors.acceptChildrenVoid
+import org.jetbrains.kotlin.ir.visitors.acceptVoid
 
 //This lower takes part of old LocalDeclarationLowering job to pop up local classes from functions
 open class LocalClassPopupLowering(val context: BackendContext) : BodyLoweringPass {
@@ -44,7 +48,20 @@ open class LocalClassPopupLowering(val context: BackendContext) : BodyLoweringPa
 
         for ((local, newContainer) in extractedLocalClasses) {
             newContainer.addChild(local)
-            context.extractedLocalClasses += local
+
+            local.acceptVoid(object : IrElementVisitorVoid {
+                override fun visitElement(element: IrElement) {
+                    element.acceptChildrenVoid(this)
+                }
+
+                override fun visitBody(body: IrBody) {
+                }
+
+                override fun visitClass(declaration: IrClass) {
+                    super.visitClass(declaration)
+                    context.extractedLocalClasses += declaration
+                }
+            })
         }
     }
 

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

@@ -90,7 +90,7 @@ object BOUND_RECEIVER_PARAMETER : IrDeclarationOriginImpl("BOUND_RECEIVER_PARAME
   to proceed nevertheless.
 */
 class LocalDeclarationsLowering(
-    val context: BackendContext,
+    val context: CommonBackendContext,
     val localNameProvider: LocalNameProvider = LocalNameProvider.DEFAULT,
     val visibilityPolicy: VisibilityPolicy = VisibilityPolicy.DEFAULT
 ) :
@@ -463,6 +463,9 @@ class LocalDeclarationsLowering(
 
             irClass.declarations += localClassContext.capturedValueToField.values
 
+            context.mapping.capturedFields[irClass] =
+                (context.mapping.capturedFields[irClass] ?: emptyList()) + localClassContext.capturedValueToField.values
+
             for (constructorContext in constructorsCallingSuper) {
                 val blockBody = constructorContext.declaration.body as? IrBlockBody
                     ?: throw AssertionError("Unexpected constructor body: ${constructorContext.declaration.body}")
@@ -733,6 +736,7 @@ class LocalDeclarationsLowering(
             newDeclaration.metadata = oldDeclaration.metadata
 
             transformedDeclarations[oldDeclaration] = newDeclaration
+            context.mapping.capturedConstructors[oldDeclaration] = newDeclaration
         }
 
         private fun createFieldForCapturedValue(