diff --git a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/lazy/Fir2IrLazySimpleFunction.kt b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/lazy/Fir2IrLazySimpleFunction.kt
index 90e7a44b2c9..6bfdd4fc1e2 100644
--- a/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/lazy/Fir2IrLazySimpleFunction.kt
+++ b/compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/lazy/Fir2IrLazySimpleFunction.kt
@@ -72,8 +72,11 @@ class Fir2IrLazySimpleFunction(
     override val name: Name
         get() = fir.name
 
-    override val visibility: Visibility
+    override var visibility: Visibility
         get() = fir.visibility
+        set(_) {
+            error("Mutating Fir2Ir lazy elements is not possible")
+        }
 
     override val modality: Modality
         get() = fir.modality!!
diff --git a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/ToArrayLowering.kt b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/ToArrayLowering.kt
index 348ad0f5424..0c1f34e5b3c 100644
--- a/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/ToArrayLowering.kt
+++ b/compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/ToArrayLowering.kt
@@ -24,7 +24,6 @@ import org.jetbrains.kotlin.ir.builders.irReturn
 import org.jetbrains.kotlin.ir.declarations.IrClass
 import org.jetbrains.kotlin.ir.declarations.IrDeclarationOrigin
 import org.jetbrains.kotlin.ir.declarations.IrSimpleFunction
-import org.jetbrains.kotlin.ir.declarations.impl.IrFunctionImpl
 import org.jetbrains.kotlin.ir.symbols.IrClassifierSymbol
 import org.jetbrains.kotlin.ir.types.*
 import org.jetbrains.kotlin.ir.util.defaultType
@@ -97,7 +96,7 @@ private class ToArrayLowering(private val context: JvmBackendContext) : ClassLow
     }
 
     private fun IrClass.findOrCreate(indirectSubclass: Boolean, matcher: (IrSimpleFunction) -> Boolean, fallback: () -> IrSimpleFunction) {
-        val existing = functions.find(matcher) as? IrFunctionImpl
+        val existing = functions.find(matcher)
         if (existing != null) {
             // This is an explicit override of a method defined in `kotlin.collections.AbstractCollection`
             // or `java.util.Collection`. From here on, the frontend will check the existence of implementations;
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrClass.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrClass.kt
index e77404781ef..11f0b8bff56 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrClass.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrClass.kt
@@ -16,7 +16,10 @@
 
 package org.jetbrains.kotlin.ir.declarations
 
-import org.jetbrains.kotlin.descriptors.*
+import org.jetbrains.kotlin.descriptors.ClassDescriptor
+import org.jetbrains.kotlin.descriptors.ClassKind
+import org.jetbrains.kotlin.descriptors.Modality
+import org.jetbrains.kotlin.descriptors.SourceElement
 import org.jetbrains.kotlin.ir.ObsoleteDescriptorBasedAPI
 import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
 import org.jetbrains.kotlin.ir.types.IrType
@@ -28,8 +31,6 @@ interface IrClass :
     @ObsoleteDescriptorBasedAPI
     override val descriptor: ClassDescriptor
 
-    override var visibility: Visibility
-
     val kind: ClassKind
     var modality: Modality
     val isCompanion: Boolean
@@ -54,16 +55,3 @@ fun IrClass.addMember(member: IrDeclaration) {
 fun IrClass.addAll(members: List<IrDeclaration>) {
     declarations.addAll(members)
 }
-
-fun IrClass.getInstanceInitializerMembers() =
-    declarations.filter {
-        when (it) {
-            is IrAnonymousInitializer ->
-                true
-            is IrProperty ->
-                it.backingField?.initializer != null
-            is IrField ->
-                it.initializer != null
-            else -> false
-        }
-    }
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrConstructor.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrConstructor.kt
index 16df356e0f9..a5c93c63f69 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrConstructor.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrConstructor.kt
@@ -17,17 +17,12 @@
 package org.jetbrains.kotlin.ir.declarations
 
 import org.jetbrains.kotlin.descriptors.ClassConstructorDescriptor
-import org.jetbrains.kotlin.descriptors.Visibility
 import org.jetbrains.kotlin.ir.ObsoleteDescriptorBasedAPI
 import org.jetbrains.kotlin.ir.symbols.IrConstructorSymbol
 
-
 interface IrConstructor : IrFunction, IrSymbolDeclaration<IrConstructorSymbol> {
     @ObsoleteDescriptorBasedAPI
     override val descriptor: ClassConstructorDescriptor
 
-    override var visibility: Visibility
-
     val isPrimary: Boolean
 }
-
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrDeclaration.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrDeclaration.kt
index 25b13304e93..9c13df2d4a4 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrDeclaration.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrDeclaration.kt
@@ -55,7 +55,7 @@ interface IrOverridableDeclaration<S : IrSymbol> : IrDeclaration {
 }
 
 interface IrDeclarationWithVisibility : IrDeclaration {
-    val visibility: Visibility
+    var visibility: Visibility
 }
 
 interface IrDeclarationWithName : IrDeclaration {
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrFieldImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrFieldImpl.kt
index 49edc85ef76..dc9c1f4b20a 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrFieldImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrFieldImpl.kt
@@ -38,7 +38,7 @@ class IrFieldImpl(
     override val symbol: IrFieldSymbol,
     override val name: Name,
     override val type: IrType,
-    override val visibility: Visibility,
+    override var visibility: Visibility,
     override val isFinal: Boolean,
     override val isExternal: Boolean,
     override val isStatic: Boolean
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrPropertyImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrPropertyImpl.kt
index 3b8e6808b58..f5a83c2139e 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrPropertyImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrPropertyImpl.kt
@@ -33,7 +33,7 @@ abstract class IrPropertyCommonImpl(
     endOffset: Int,
     origin: IrDeclarationOrigin,
     override val name: Name,
-    override val visibility: Visibility,
+    override var visibility: Visibility,
     override val modality: Modality,
     override val isVar: Boolean,
     override val isConst: Boolean,
@@ -113,7 +113,7 @@ class IrPropertyImpl(
     origin: IrDeclarationOrigin,
     override val symbol: IrPropertySymbol,
     override val name: Name,
-    override val visibility: Visibility,
+    override var visibility: Visibility,
     override val modality: Modality,
     override val isVar: Boolean,
     override val isConst: Boolean,
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrTypeAliasImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrTypeAliasImpl.kt
index 36e0ae22d07..87ddd368656 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrTypeAliasImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrTypeAliasImpl.kt
@@ -24,7 +24,7 @@ class IrTypeAliasImpl(
     endOffset: Int,
     override val symbol: IrTypeAliasSymbol,
     override val name: Name,
-    override val visibility: Visibility,
+    override var visibility: Visibility,
     override val expandedType: IrType,
     override val isActual: Boolean,
     origin: IrDeclarationOrigin
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyField.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyField.kt
index 4d49e1744b6..bb0403d5c31 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyField.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyField.kt
@@ -32,7 +32,7 @@ class IrLazyField(
     override val symbol: IrFieldSymbol,
     override val descriptor: PropertyDescriptor,
     override val name: Name,
-    override val visibility: Visibility,
+    override var visibility: Visibility,
     override val isFinal: Boolean,
     override val isExternal: Boolean,
     override val isStatic: Boolean,
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyProperty.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyProperty.kt
index a95d303427d..286534c46c2 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyProperty.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyProperty.kt
@@ -27,7 +27,7 @@ class IrLazyProperty(
     override val symbol: IrPropertySymbol,
     override val descriptor: PropertyDescriptor,
     override val name: Name,
-    override val visibility: Visibility,
+    override var visibility: Visibility,
     override val modality: Modality,
     override val isVar: Boolean,
     override val isConst: Boolean,
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyTypeAlias.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyTypeAlias.kt
index b9b10f4935d..89d5aee9d7c 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyTypeAlias.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/lazy/IrLazyTypeAlias.kt
@@ -29,7 +29,7 @@ class IrLazyTypeAlias(
     override val symbol: IrTypeAliasSymbol,
     override val descriptor: TypeAliasDescriptor,
     override val name: Name,
-    override val visibility: Visibility,
+    override var visibility: Visibility,
     override val isActual: Boolean,
     stubGenerator: DeclarationStubGenerator,
     typeTranslator: TypeTranslator