[Commonizer] Reduce memory consumption during approximation phase

^KT-39320

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/builder/DeclarationsBuilderVisitor1.kt

@@ -13,6 +13,8 @@ import org.jetbrains.kotlin.descriptors.commonizer.Target
 import org.jetbrains.kotlin.descriptors.commonizer.builder.CommonizedMemberScope.Companion.plusAssign
 import org.jetbrains.kotlin.descriptors.commonizer.builder.CommonizedPackageFragmentProvider.Companion.plusAssign
 import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.*
+import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirNode.Companion.dimension
+import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirNode.Companion.indexOfCommon
 import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroup
 import org.jetbrains.kotlin.descriptors.impl.ModuleDescriptorImpl
 import org.jetbrains.kotlin.utils.addIfNotNull
@@ -29,12 +31,12 @@ internal class DeclarationsBuilderVisitor1(
         check(data.isEmpty()) // root node may not have containing declarations
         check(components.targetComponents.size == node.dimension)
 
-        val allTargets = (node.target + node.common()!!).map { it!!.target }
+        val allTargets = (node.targetDeclarations.toList() + node.commonDeclaration()!!).map { it!!.target }
 
         val modulesByTargets = HashMap<Target, MutableList<ModuleDescriptorImpl>>()
 
         // collect module descriptors:
-        for (moduleNode in node.modules) {
+        for (moduleNode in node.modules.values) {
             val modules = moduleNode.accept(this, noContainingDeclarations()).asListContaining<ModuleDescriptorImpl>()
             modules.forEachIndexed { index, module ->
                 val target = allTargets[index]
@@ -58,7 +60,7 @@ internal class DeclarationsBuilderVisitor1(
 
         // build package fragments:
         val packageFragmentProviders = CommonizedPackageFragmentProvider.createArray(node.dimension)
-        for (packageNode in node.packages) {
+        for (packageNode in node.packages.values) {
             val packageFragments = packageNode.accept(this, moduleDescriptors).asListContaining<PackageFragmentDescriptor>()
             packageFragmentProviders += packageFragments
         }
@@ -81,10 +83,10 @@ internal class DeclarationsBuilderVisitor1(
 
         // build package members:
         val packageMemberScopes = CommonizedMemberScope.createArray(node.dimension)
-        for (classNode in node.classes) {
+        for (classNode in node.classes.values) {
             packageMemberScopes += classNode.accept(this, packageFragments)
         }
-        for (typeAliasNode in node.typeAliases) {
+        for (typeAliasNode in node.typeAliases.values) {
             packageMemberScopes += typeAliasNode.accept(this, packageFragments)
         }
 
@@ -109,7 +111,7 @@ internal class DeclarationsBuilderVisitor1(
 
         // build class members:
         val classMemberScopes = CommonizedMemberScope.createArray(node.dimension)
-        for (classNode in node.classes) {
+        for (classNode in node.classes.values) {
             classMemberScopes += classNode.accept(this, classes)
         }
 

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/builder/DeclarationsBuilderVisitor2.kt

@@ -11,6 +11,7 @@ import org.jetbrains.kotlin.descriptors.commonizer.builder.DeclarationsBuilderVi
 import org.jetbrains.kotlin.descriptors.commonizer.builder.DeclarationsBuilderVisitor1.Companion.noContainingDeclarations
 import org.jetbrains.kotlin.descriptors.commonizer.builder.DeclarationsBuilderVisitor1.Companion.noReturningDeclarations
 import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.*
+import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirNode.Companion.dimension
 import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroup
 import org.jetbrains.kotlin.descriptors.impl.ModuleDescriptorImpl
 
@@ -29,7 +30,7 @@ internal class DeclarationsBuilderVisitor2(
         check(components.targetComponents.size == node.dimension)
 
         // visit module descriptors:
-        for (moduleNode in node.modules) {
+        for (moduleNode in node.modules.values) {
             moduleNode.accept(this, noContainingDeclarations())
         }
 
@@ -38,7 +39,7 @@ internal class DeclarationsBuilderVisitor2(
 
     override fun visitModuleNode(node: CirModuleNode, data: List<DeclarationDescriptor?>): List<ModuleDescriptorImpl?> {
         // visit package fragment descriptors:
-        for (packageNode in node.packages) {
+        for (packageNode in node.packages.values) {
             packageNode.accept(this, noContainingDeclarations())
         }
 
@@ -50,14 +51,14 @@ internal class DeclarationsBuilderVisitor2(
 
         // build non-classifier package members:
         val packageMemberScopes = packageFragments.map { it?.getMemberScope() }
-        for (propertyNode in node.properties) {
+        for (propertyNode in node.properties.values) {
             packageMemberScopes += propertyNode.accept(this, packageFragments)
         }
-        for (functionNode in node.functions) {
+        for (functionNode in node.functions.values) {
             packageMemberScopes += functionNode.accept(this, packageFragments)
         }
 
-        for (classNode in node.classes) {
+        for (classNode in node.classes.values) {
             classNode.accept(this, noContainingDeclarations())
         }
 
@@ -83,7 +84,7 @@ internal class DeclarationsBuilderVisitor2(
 
         // build class constructors:
         val allConstructorsByTargets = Array<MutableList<CommonizedClassConstructorDescriptor>>(node.dimension) { ArrayList() }
-        for (constructorNode in node.constructors) {
+        for (constructorNode in node.constructors.values) {
             val constructorsByTargets = constructorNode.accept(this, classes).asListContaining<CommonizedClassConstructorDescriptor>()
             constructorsByTargets.forEachIndexed { index, constructor ->
                 if (constructor != null) allConstructorsByTargets[index].add(constructor)
@@ -97,14 +98,14 @@ internal class DeclarationsBuilderVisitor2(
 
         // build class members:
         val classMemberScopes = classes.map { it?.unsubstitutedMemberScope }
-        for (propertyNode in node.properties) {
+        for (propertyNode in node.properties.values) {
             classMemberScopes += propertyNode.accept(this, classes)
         }
-        for (functionNode in node.functions) {
+        for (functionNode in node.functions.values) {
             classMemberScopes += functionNode.accept(this, classes)
         }
 
-        for (classNode in node.classes) {
+        for (classNode in node.classes.values) {
             classNode.accept(this, noContainingDeclarations())
         }
 

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/builder/classDescriptors.kt

@@ -13,7 +13,7 @@ import org.jetbrains.kotlin.descriptors.commonizer.cir.CirClass
 import org.jetbrains.kotlin.descriptors.commonizer.cir.CirClassConstructor
 import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirClassConstructorNode
 import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirClassNode
-import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.indexOfCommon
+import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirNode.Companion.indexOfCommon
 import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroup
 import org.jetbrains.kotlin.name.FqName
 
@@ -22,10 +22,10 @@ internal fun CirClassNode.buildDescriptors(
     output: CommonizedGroup<ClassifierDescriptorWithTypeParameters>,
     containingDeclarations: List<DeclarationDescriptor?>
 ) {
-    val commonClass = common()
+    val commonClass = commonDeclaration()
     val markAsActual = commonClass != null && commonClass.kind != ClassKind.ENUM_ENTRY
 
-    target.forEachIndexed { index, clazz ->
+    targetDeclarations.toList().forEachIndexed { index, clazz ->
         clazz?.buildDescriptor(components, output, index, containingDeclarations, fqName, isActual = markAsActual)
     }
 
@@ -78,10 +78,10 @@ internal fun CirClassConstructorNode.buildDescriptors(
     output: CommonizedGroup<ClassConstructorDescriptor>,
     containingDeclarations: List<CommonizedClassDescriptor?>
 ) {
-    val commonConstructor = common()
+    val commonConstructor = commonDeclaration()
     val markAsActual = commonConstructor != null
 
-    target.forEachIndexed { index, constructor ->
+    targetDeclarations.toList().forEachIndexed { index, constructor ->
         constructor?.buildDescriptor(components, output, index, containingDeclarations, isActual = markAsActual)
     }
 

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/builder/context.kt

@@ -8,9 +8,9 @@ package org.jetbrains.kotlin.descriptors.commonizer.builder
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
 import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.descriptors.commonizer.Target
+import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirNode.Companion.dimension
+import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirNode.Companion.indexOfCommon
 import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirRootNode
-import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.dimension
-import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.indexOfCommon
 import org.jetbrains.kotlin.descriptors.commonizer.stats.StatsCollector
 import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroup
 import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroupMap
@@ -172,7 +172,7 @@ fun CirRootNode.createGlobalBuilderComponents(
 
     val targetContexts = (0 until dimension).map { index ->
         val isCommon = index == indexOfCommon
-        val root = if (isCommon) common()!! else target[index]!!
+        val root = if (isCommon) commonDeclaration()!! else targetDeclarations[index]!!
 
         val builtIns = root.builtInsProvider.loadBuiltIns()
         check(builtIns::class.java.name == root.builtInsClass) {

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/builder/functionDescriptors.kt

@@ -11,7 +11,7 @@ import org.jetbrains.kotlin.descriptors.SimpleFunctionDescriptor
 import org.jetbrains.kotlin.descriptors.SourceElement
 import org.jetbrains.kotlin.descriptors.commonizer.cir.CirFunction
 import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirFunctionNode
-import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.indexOfCommon
+import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirNode.Companion.indexOfCommon
 import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroup
 import org.jetbrains.kotlin.descriptors.impl.SimpleFunctionDescriptorImpl
 
@@ -20,10 +20,10 @@ internal fun CirFunctionNode.buildDescriptors(
     output: CommonizedGroup<SimpleFunctionDescriptor>,
     containingDeclarations: List<DeclarationDescriptor?>
 ) {
-    val commonFunction = common()
+    val commonFunction = commonDeclaration()
     val markAsExpectAndActual = commonFunction != null && commonFunction.kind != CallableMemberDescriptor.Kind.SYNTHESIZED
 
-    target.forEachIndexed { index, function ->
+    targetDeclarations.toList().forEachIndexed { index, function ->
         function?.buildDescriptor(components, output, index, containingDeclarations, isActual = markAsExpectAndActual)
     }
 

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/builder/moduleDescriptors.kt

@@ -7,7 +7,7 @@ package org.jetbrains.kotlin.descriptors.commonizer.builder
 
 import org.jetbrains.kotlin.descriptors.commonizer.cir.CirModule
 import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirModuleNode
-import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.indexOfCommon
+import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirNode.Companion.indexOfCommon
 import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroup
 import org.jetbrains.kotlin.descriptors.impl.ModuleDescriptorImpl
 
@@ -15,11 +15,11 @@ internal fun CirModuleNode.buildDescriptors(
     components: GlobalDeclarationsBuilderComponents,
     output: CommonizedGroup<ModuleDescriptorImpl>
 ) {
-    target.forEachIndexed { index, module ->
+    targetDeclarations.toList().forEachIndexed { index, module ->
         module?.buildDescriptor(components, output, index)
     }
 
-    common()?.buildDescriptor(components, output, indexOfCommon)
+    commonDeclaration()?.buildDescriptor(components, output, indexOfCommon)
 
     // log stats
     components.statsCollector?.logStats(output.toList())

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/builder/packageFragments.kt

@@ -8,7 +8,7 @@ package org.jetbrains.kotlin.descriptors.commonizer.builder
 import org.jetbrains.kotlin.descriptors.ModuleDescriptor
 import org.jetbrains.kotlin.descriptors.commonizer.cir.CirPackage
 import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirPackageNode
-import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.indexOfCommon
+import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirNode.Companion.indexOfCommon
 import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroup
 import org.jetbrains.kotlin.descriptors.impl.ModuleDescriptorImpl
 import org.jetbrains.kotlin.descriptors.impl.PackageFragmentDescriptorImpl
@@ -19,11 +19,11 @@ internal fun CirPackageNode.buildDescriptors(
     output: CommonizedGroup<CommonizedPackageFragmentDescriptor>,
     modules: List<ModuleDescriptorImpl?>
 ) {
-    target.forEachIndexed { index, pkg ->
+    targetDeclarations.toList().forEachIndexed { index, pkg ->
         pkg?.buildDescriptor(components, output, index, modules)
     }
 
-    common()?.buildDescriptor(components, output, indexOfCommon, modules)
+    commonDeclaration()?.buildDescriptor(components, output, indexOfCommon, modules)
 }
 
 private fun CirPackage.buildDescriptor(

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/builder/propertyDescriptors.kt

@@ -11,7 +11,7 @@ import org.jetbrains.kotlin.descriptors.PropertyDescriptor
 import org.jetbrains.kotlin.descriptors.SourceElement
 import org.jetbrains.kotlin.descriptors.commonizer.cir.CirProperty
 import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirPropertyNode
-import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.indexOfCommon
+import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirNode.Companion.indexOfCommon
 import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroup
 import org.jetbrains.kotlin.descriptors.impl.FieldDescriptorImpl
 import org.jetbrains.kotlin.descriptors.impl.PropertyDescriptorImpl
@@ -23,7 +23,7 @@ internal fun CirPropertyNode.buildDescriptors(
     output: CommonizedGroup<PropertyDescriptor>,
     containingDeclarations: List<DeclarationDescriptor?>
 ) {
-    val commonProperty = common()
+    val commonProperty = commonDeclaration()
 
     val isLiftedUp = commonProperty?.isLiftedUp == true
     val markAsExpectAndActual = commonProperty != null
@@ -31,7 +31,7 @@ internal fun CirPropertyNode.buildDescriptors(
             && !isLiftedUp
 
     if (!isLiftedUp) {
-        target.forEachIndexed { index, property ->
+        targetDeclarations.toList().forEachIndexed { index, property ->
             property?.buildDescriptor(components, output, index, containingDeclarations, isActual = markAsExpectAndActual)
         }
     }

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/builder/typeAliasDescriptors.kt

@@ -11,7 +11,7 @@ import org.jetbrains.kotlin.descriptors.commonizer.cir.CirClass
 import org.jetbrains.kotlin.descriptors.commonizer.cir.CirClassifier
 import org.jetbrains.kotlin.descriptors.commonizer.cir.CirTypeAlias
 import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirTypeAliasNode
-import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.indexOfCommon
+import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirNode.Companion.indexOfCommon
 import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroup
 import org.jetbrains.kotlin.name.FqName
 
@@ -20,7 +20,7 @@ internal fun CirTypeAliasNode.buildDescriptors(
     output: CommonizedGroup<ClassifierDescriptorWithTypeParameters>,
     containingDeclarations: List<DeclarationDescriptor?>
 ) {
-    val commonClassifier: CirClassifier? = common()
+    val commonClassifier: CirClassifier? = commonDeclaration()
     // Note: 'expect class' and lifted up 'typealias' both can't be non-null
     val commonTypeAlias: CirTypeAlias? = commonClassifier as? CirTypeAlias?
 
@@ -28,7 +28,7 @@ internal fun CirTypeAliasNode.buildDescriptors(
     val markAsActual = commonClassifier != null
 
     if (!isLiftedUp) {
-        target.forEachIndexed { index, typeAlias ->
+        targetDeclarations.toList().forEachIndexed { index, typeAlias ->
             typeAlias?.buildDescriptor(components, output, index, containingDeclarations, fqName, isActual = markAsActual)
         }
     }

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/core/CommonizationVisitor.kt

@@ -14,91 +14,91 @@ internal class CommonizationVisitor(
 ) : CirNodeVisitor<Unit, Unit> {
     override fun visitRootNode(node: CirRootNode, data: Unit) {
         check(node === root)
-        check(node.common() != null) // root should already be commonized
+        check(node.commonDeclaration() != null) // root should already be commonized
 
-        node.modules.forEach { module ->
+        node.modules.values.forEach { module ->
             module.accept(this, Unit)
         }
     }
 
     override fun visitModuleNode(node: CirModuleNode, data: Unit) {
-        node.common() // commonize module
+        node.commonDeclaration() // commonize module
 
-        node.packages.forEach { pkg ->
+        node.packages.values.forEach { pkg ->
             pkg.accept(this, Unit)
         }
     }
 
     override fun visitPackageNode(node: CirPackageNode, data: Unit) {
-        node.common() // commonize package
+        node.commonDeclaration() // commonize package
 
-        node.properties.forEach { property ->
+        node.properties.values.forEach { property ->
             property.accept(this, Unit)
         }
 
-        node.functions.forEach { function ->
+        node.functions.values.forEach { function ->
             function.accept(this, Unit)
         }
 
-        node.classes.forEach { clazz ->
+        node.classes.values.forEach { clazz ->
             clazz.accept(this, Unit)
         }
 
-        node.typeAliases.forEach { typeAlias ->
+        node.typeAliases.values.forEach { typeAlias ->
             typeAlias.accept(this, Unit)
         }
     }
 
     override fun visitPropertyNode(node: CirPropertyNode, data: Unit) {
-        node.common() // commonize property
+        node.commonDeclaration() // commonize property
     }
 
     override fun visitFunctionNode(node: CirFunctionNode, data: Unit) {
-        node.common() // commonize function
+        node.commonDeclaration() // commonize function
     }
 
     override fun visitClassNode(node: CirClassNode, data: Unit) {
-        val commonClass = node.common() // commonized class
+        val commonClass = node.commonDeclaration() // commonized class
 
-        node.constructors.forEach { constructor ->
+        node.constructors.values.forEach { constructor ->
             constructor.accept(this, Unit)
         }
 
-        node.properties.forEach { property ->
+        node.properties.values.forEach { property ->
             property.accept(this, Unit)
         }
 
-        node.functions.forEach { function ->
+        node.functions.values.forEach { function ->
             function.accept(this, Unit)
         }
 
-        node.classes.forEach { clazz ->
+        node.classes.values.forEach { clazz ->
             clazz.accept(this, Unit)
         }
 
         if (commonClass != null) {
             // companion object should have the same FQ name for each target class, then it could be set to common class
-            val companionObjectFqName = node.target.mapTo(HashSet()) { it!!.companion }.singleOrNull()
+            val companionObjectFqName = node.targetDeclarations.toList().mapTo(HashSet()) { it!!.companion }.singleOrNull()
             if (companionObjectFqName != null) {
                 val companionObjectNode = root.cache.classes[companionObjectFqName]
                     ?: error("Can't find companion object with FQ name $companionObjectFqName")
 
-                if (companionObjectNode.common() != null) {
+                if (companionObjectNode.commonDeclaration() != null) {
                     // companion object has been successfully commonized
                     commonClass.companion = companionObjectFqName
                 }
             }
 
             // find out common (and commonized) supertypes
-            val supertypesMap = CommonizedGroupMap<String, CirType>(node.target.size)
-            node.target.forEachIndexed { index, clazz ->
+            val supertypesMap = CommonizedGroupMap<String, CirType>(node.targetDeclarations.size)
+            node.targetDeclarations.toList().forEachIndexed { index, clazz ->
                 for (supertype in clazz!!.supertypes) {
                     supertypesMap[supertype.fqNameWithTypeParameters][index] = supertype
                 }
             }
 
             for ((_, supertypesGroup) in supertypesMap) {
-                val commonSupertype = commonize(supertypesGroup.toList(), TypeCommonizer(root.cache))
+                val commonSupertype = commonize(supertypesGroup, TypeCommonizer(root.cache))
                 if (commonSupertype != null)
                     commonClass.supertypes.add(commonSupertype)
             }
@@ -106,10 +106,10 @@ internal class CommonizationVisitor(
     }
 
     override fun visitClassConstructorNode(node: CirClassConstructorNode, data: Unit) {
-        node.common() // commonize constructor
+        node.commonDeclaration() // commonize constructor
     }
 
     override fun visitTypeAliasNode(node: CirTypeAliasNode, data: Unit) {
-        node.common() // commonize type alias
+        node.commonDeclaration() // commonize type alias
     }
 }

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/core/PackageCommonizer.kt

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.descriptors.commonizer.core
+
+import org.jetbrains.kotlin.descriptors.commonizer.cir.CirPackage
+import org.jetbrains.kotlin.descriptors.commonizer.cir.factory.CirPackageFactory
+import org.jetbrains.kotlin.name.FqName
+
+class PackageCommonizer : AbstractStandardCommonizer<CirPackage, CirPackage>() {
+    private lateinit var fqName: FqName
+
+    override fun commonizationResult() = CirPackageFactory.create(fqName = fqName)
+
+    override fun initialize(first: CirPackage) {
+        fqName = first.fqName
+    }
+
+    override fun doCommonizeWith(next: CirPackage) = true
+}

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/core/TypeCommonizer.kt

@@ -98,5 +98,5 @@ private inline fun CirNode<*, *>?.canBeCommonized() =
         true
     } else {
         // If entry is present, then contents (common declaration) should not be null.
-        common() != null
+        commonDeclaration() != null
     }

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/facade.kt

@@ -10,7 +10,7 @@ import org.jetbrains.kotlin.descriptors.commonizer.builder.DeclarationsBuilderVi
 import org.jetbrains.kotlin.descriptors.commonizer.builder.DeclarationsBuilderVisitor2
 import org.jetbrains.kotlin.descriptors.commonizer.builder.createGlobalBuilderComponents
 import org.jetbrains.kotlin.descriptors.commonizer.core.CommonizationVisitor
-import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.mergeRoots
+import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirTreeMerger
 import org.jetbrains.kotlin.storage.LockBasedStorageManager
 
 fun runCommonization(parameters: Parameters): Result {
@@ -20,7 +20,7 @@ fun runCommonization(parameters: Parameters): Result {
     val storageManager = LockBasedStorageManager("Declaration descriptors commonization")
 
     // build merged tree:
-    val mergedTree = mergeRoots(storageManager, parameters.targetProviders)
+    val mergedTree = CirTreeMerger(storageManager, parameters.targetProviders).merge()
 
     // commonize:
     mergedTree.accept(CommonizationVisitor(mergedTree), Unit)

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/mergedtree/CirClassConstructorNode.kt

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.descriptors.commonizer.mergedtree
+
+import org.jetbrains.kotlin.descriptors.commonizer.cir.CirClassConstructor
+import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroup
+import org.jetbrains.kotlin.storage.NullableLazyValue
+
+class CirClassConstructorNode(
+    override val targetDeclarations: CommonizedGroup<CirClassConstructor>,
+    override val commonDeclaration: NullableLazyValue<CirClassConstructor>
+) : CirNode<CirClassConstructor, CirClassConstructor> {
+    override fun <R, T> accept(visitor: CirNodeVisitor<R, T>, data: T): R =
+        visitor.visitClassConstructorNode(this, data)
+
+    override fun toString() = CirNode.toString(this)
+}

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/mergedtree/CirClassNode.kt

@@ -0,0 +1,29 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.descriptors.commonizer.mergedtree
+
+import org.jetbrains.kotlin.descriptors.commonizer.cir.CirClass
+import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroup
+import org.jetbrains.kotlin.name.FqName
+import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.storage.NullableLazyValue
+
+class CirClassNode(
+    override val targetDeclarations: CommonizedGroup<CirClass>,
+    override val commonDeclaration: NullableLazyValue<CirClass>,
+    override val fqName: FqName
+) : CirNodeWithFqName<CirClass, CirClass> {
+
+    val constructors: MutableMap<ConstructorApproximationKey, CirClassConstructorNode> = HashMap()
+    val properties: MutableMap<PropertyApproximationKey, CirPropertyNode> = HashMap()
+    val functions: MutableMap<FunctionApproximationKey, CirFunctionNode> = HashMap()
+    val classes: MutableMap<Name, CirClassNode> = HashMap()
+
+    override fun <R, T> accept(visitor: CirNodeVisitor<R, T>, data: T): R =
+        visitor.visitClassNode(this, data)
+
+    override fun toString() = CirNode.toString(this)
+}

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/mergedtree/CirClassifiersCache.kt

@@ -0,0 +1,13 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.descriptors.commonizer.mergedtree
+
+import org.jetbrains.kotlin.name.FqName
+
+interface CirClassifiersCache {
+    val classes: Map<FqName, CirClassNode>
+    val typeAliases: Map<FqName, CirTypeAliasNode>
+}

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/mergedtree/CirFunctionNode.kt

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.descriptors.commonizer.mergedtree
+
+import org.jetbrains.kotlin.descriptors.commonizer.cir.CirFunction
+import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroup
+import org.jetbrains.kotlin.storage.NullableLazyValue
+
+class CirFunctionNode(
+    override val targetDeclarations: CommonizedGroup<CirFunction>,
+    override val commonDeclaration: NullableLazyValue<CirFunction>
+) : CirNode<CirFunction, CirFunction> {
+    override fun <R, T> accept(visitor: CirNodeVisitor<R, T>, data: T) =
+        visitor.visitFunctionNode(this, data)
+
+    override fun toString() = CirNode.toString(this)
+}

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/mergedtree/CirModuleNode.kt

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.descriptors.commonizer.mergedtree
+
+import org.jetbrains.kotlin.descriptors.commonizer.cir.CirModule
+import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroup
+import org.jetbrains.kotlin.name.FqName
+import org.jetbrains.kotlin.storage.NullableLazyValue
+
+class CirModuleNode(
+    override val targetDeclarations: CommonizedGroup<CirModule>,
+    override val commonDeclaration: NullableLazyValue<CirModule>
+) : CirNode<CirModule, CirModule> {
+    val packages: MutableMap<FqName, CirPackageNode> = HashMap()
+
+    override fun <R, T> accept(visitor: CirNodeVisitor<R, T>, data: T) =
+        visitor.visitModuleNode(this, data)
+
+    override fun toString() = CirNode.toString(this)
+}

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/mergedtree/CirNode.kt

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.descriptors.commonizer.mergedtree
+
+import org.jetbrains.kotlin.descriptors.commonizer.cir.CirDeclaration
+import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroup
+import org.jetbrains.kotlin.storage.NullableLazyValue
+
+interface CirNode<T : CirDeclaration, R : CirDeclaration> {
+    val targetDeclarations: CommonizedGroup<T>
+    val commonDeclaration: NullableLazyValue<R>
+
+    fun <R, T> accept(visitor: CirNodeVisitor<R, T>, data: T): R
+
+    companion object {
+        inline val CirNode<*, *>.indexOfCommon: Int
+            get() = targetDeclarations.size
+
+        internal inline val CirNode<*, *>.dimension: Int
+            get() = targetDeclarations.size + 1
+
+        fun toString(node: CirNode<*, *>) = buildString {
+            if (node is CirNodeWithFqName) {
+                append("fqName=").append(node.fqName).append(", ")
+            }
+            append("target=")
+            node.targetDeclarations.toList().joinTo(this)
+            append(", common=")
+            append(if (node.commonDeclaration.isComputed()) node.commonDeclaration() else "<NOT COMPUTED>")
+        }
+    }
+}
+

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/mergedtree/CirNodeWithFqName.kt

@@ -0,0 +1,13 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.descriptors.commonizer.mergedtree
+
+import org.jetbrains.kotlin.descriptors.commonizer.cir.CirDeclaration
+import org.jetbrains.kotlin.name.FqName
+
+interface CirNodeWithFqName<T : CirDeclaration, R : CirDeclaration> : CirNode<T, R> {
+    val fqName: FqName
+}

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/mergedtree/CirPackageNode.kt

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.descriptors.commonizer.mergedtree
+
+import org.jetbrains.kotlin.descriptors.commonizer.cir.CirPackage
+import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroup
+import org.jetbrains.kotlin.name.FqName
+import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.storage.NullableLazyValue
+
+class CirPackageNode(
+    override val targetDeclarations: CommonizedGroup<CirPackage>,
+    override val commonDeclaration: NullableLazyValue<CirPackage>,
+    override val fqName: FqName,
+    val moduleName: Name
+) : CirNodeWithFqName<CirPackage, CirPackage> {
+
+    val properties: MutableMap<PropertyApproximationKey, CirPropertyNode> = HashMap()
+    val functions: MutableMap<FunctionApproximationKey, CirFunctionNode> = HashMap()
+    val classes: MutableMap<Name, CirClassNode> = HashMap()
+    val typeAliases: MutableMap<Name, CirTypeAliasNode> = HashMap()
+
+    override fun <R, T> accept(visitor: CirNodeVisitor<R, T>, data: T) =
+        visitor.visitPackageNode(this, data)
+
+    override fun toString() = CirNode.toString(this)
+}

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/mergedtree/CirPropertyNode.kt

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.descriptors.commonizer.mergedtree
+
+import org.jetbrains.kotlin.descriptors.commonizer.cir.CirProperty
+import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroup
+import org.jetbrains.kotlin.storage.NullableLazyValue
+
+class CirPropertyNode(
+    override val targetDeclarations: CommonizedGroup<CirProperty>,
+    override val commonDeclaration: NullableLazyValue<CirProperty>
+) : CirNode<CirProperty, CirProperty> {
+    override fun <R, T> accept(visitor: CirNodeVisitor<R, T>, data: T) =
+        visitor.visitPropertyNode(this, data)
+
+    override fun toString() = CirNode.toString(this)
+}

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/mergedtree/CirRootNode.kt

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.descriptors.commonizer.mergedtree
+
+import org.jetbrains.kotlin.descriptors.commonizer.cir.CirRoot
+import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroup
+import org.jetbrains.kotlin.name.FqName
+import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.storage.NullableLazyValue
+
+class CirRootNode(
+    override val targetDeclarations: CommonizedGroup<CirRoot>,
+    override val commonDeclaration: NullableLazyValue<CirRoot>
+) : CirNode<CirRoot, CirRoot> {
+    class CirClassifiersCacheImpl : CirClassifiersCache {
+        override val classes = HashMap<FqName, CirClassNode>()
+        override val typeAliases = HashMap<FqName, CirTypeAliasNode>()
+    }
+
+    val modules: MutableMap<Name, CirModuleNode> = HashMap()
+    val cache = CirClassifiersCacheImpl()
+
+    override fun <R, T> accept(visitor: CirNodeVisitor<R, T>, data: T): R =
+        visitor.visitRootNode(this, data)
+
+    override fun toString() = CirNode.toString(this)
+}

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/mergedtree/CirTreeMerger.kt

@@ -0,0 +1,175 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.descriptors.commonizer.mergedtree
+
+import org.jetbrains.kotlin.descriptors.*
+import org.jetbrains.kotlin.descriptors.commonizer.TargetProvider
+import org.jetbrains.kotlin.descriptors.commonizer.cir.CirClass
+import org.jetbrains.kotlin.descriptors.commonizer.cir.factory.*
+import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirRootNode.CirClassifiersCacheImpl
+import org.jetbrains.kotlin.descriptors.commonizer.utils.intern
+import org.jetbrains.kotlin.name.FqName
+import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.resolve.descriptorUtil.fqNameSafe
+import org.jetbrains.kotlin.resolve.scopes.MemberScope
+import org.jetbrains.kotlin.storage.NullableLazyValue
+import org.jetbrains.kotlin.storage.StorageManager
+
+class CirTreeMerger(
+    private val storageManager: StorageManager,
+    private val targetProviders: List<TargetProvider>
+) {
+    private val size = targetProviders.size
+    private lateinit var cacheRW: CirClassifiersCacheImpl
+
+    fun merge(): CirRootNode {
+        val rootNode: CirRootNode = buildRootNode(storageManager, size)
+        cacheRW = rootNode.cache
+
+        targetProviders.forEachIndexed { targetIndex, targetProvider ->
+            processTarget(rootNode, targetIndex, targetProvider)
+            System.gc()
+        }
+
+        return rootNode
+    }
+
+    private fun processTarget(
+        rootNode: CirRootNode,
+        targetIndex: Int,
+        targetProvider: TargetProvider
+    ) {
+        rootNode.targetDeclarations[targetIndex] = CirRootFactory.create(
+            targetProvider.target,
+            targetProvider.builtInsClass.name,
+            targetProvider.builtInsProvider
+        )
+
+        val moduleDescriptors: Collection<ModuleDescriptor> = targetProvider.modulesProvider.loadModules()
+        val modules: MutableMap<Name, CirModuleNode> = rootNode.modules
+
+        moduleDescriptors.forEach { moduleDescriptor ->
+            processModule(modules, targetIndex, moduleDescriptor)
+        }
+    }
+
+    private fun processModule(
+        modules: MutableMap<Name, CirModuleNode>,
+        targetIndex: Int,
+        moduleDescriptor: ModuleDescriptor
+    ) {
+        val moduleName: Name = moduleDescriptor.name.intern()
+        val moduleNode: CirModuleNode = modules.computeIfAbsent(moduleName) {
+            buildModuleNode(storageManager, size)
+        }
+        moduleNode.targetDeclarations[targetIndex] = CirModuleFactory.create(moduleDescriptor)
+
+        val packages: MutableMap<FqName, CirPackageNode> = moduleNode.packages
+
+        moduleDescriptor.collectNonEmptyPackageMemberScopes { packageFqName, packageMemberScope ->
+            processPackage(packages, targetIndex, packageFqName.intern(), packageMemberScope, moduleName)
+        }
+    }
+
+    private fun processPackage(
+        packages: MutableMap<FqName, CirPackageNode>,
+        targetIndex: Int,
+        packageFqName: FqName,
+        packageMemberScope: MemberScope,
+        moduleName: Name
+    ) {
+        val packageNode: CirPackageNode = packages.computeIfAbsent(packageFqName) {
+            buildPackageNode(storageManager, size, packageFqName, moduleName)
+        }
+        packageNode.targetDeclarations[targetIndex] = CirPackageFactory.create(packageFqName)
+
+        val properties: MutableMap<PropertyApproximationKey, CirPropertyNode> = packageNode.properties
+        val functions: MutableMap<FunctionApproximationKey, CirFunctionNode> = packageNode.functions
+        val classes: MutableMap<Name, CirClassNode> = packageNode.classes
+        val typeAliases: MutableMap<Name, CirTypeAliasNode> = packageNode.typeAliases
+
+        packageMemberScope.collectMembers(
+            PropertyCollector { processProperty(properties, targetIndex, it, null) },
+            FunctionCollector { processFunction(functions, targetIndex, it, null) },
+            ClassCollector { processClass(classes, targetIndex, it, null) },
+            TypeAliasCollector { processTypeAlias(typeAliases, targetIndex, it) }
+        )
+    }
+
+    private fun processProperty(
+        properties: MutableMap<PropertyApproximationKey, CirPropertyNode>,
+        targetIndex: Int,
+        propertyDescriptor: PropertyDescriptor,
+        parentCommonDeclaration: NullableLazyValue<*>?
+    ) {
+        val propertyNode: CirPropertyNode = properties.computeIfAbsent(PropertyApproximationKey(propertyDescriptor)) {
+            buildPropertyNode(storageManager, size, cacheRW, parentCommonDeclaration)
+        }
+        propertyNode.targetDeclarations[targetIndex] = CirPropertyFactory.create(propertyDescriptor)
+    }
+
+    private fun processFunction(
+        functions: MutableMap<FunctionApproximationKey, CirFunctionNode>,
+        targetIndex: Int,
+        functionDescriptor: SimpleFunctionDescriptor,
+        parentCommonDeclaration: NullableLazyValue<*>?
+    ) {
+        val functionNode: CirFunctionNode = functions.computeIfAbsent(FunctionApproximationKey(functionDescriptor)) {
+            buildFunctionNode(storageManager, size, cacheRW, parentCommonDeclaration)
+        }
+        functionNode.targetDeclarations[targetIndex] = CirFunctionFactory.create(functionDescriptor)
+    }
+
+    private fun processClass(
+        classes: MutableMap<Name, CirClassNode>,
+        targetIndex: Int,
+        classDescriptor: ClassDescriptor,
+        parentCommonDeclaration: NullableLazyValue<*>?
+    ) {
+        val classNode: CirClassNode = classes.computeIfAbsent(classDescriptor.name.intern()) {
+            buildClassNode(storageManager, size, cacheRW, parentCommonDeclaration, classDescriptor.fqNameSafe.intern())
+        }
+        classNode.targetDeclarations[targetIndex] = CirClassFactory.create(classDescriptor)
+
+        val parentCommonDeclarationForMembers: NullableLazyValue<CirClass> = classNode.commonDeclaration
+
+        val constructors: MutableMap<ConstructorApproximationKey, CirClassConstructorNode> = classNode.constructors
+        val properties: MutableMap<PropertyApproximationKey, CirPropertyNode> = classNode.properties
+        val functions: MutableMap<FunctionApproximationKey, CirFunctionNode> = classNode.functions
+        val nestedClasses: MutableMap<Name, CirClassNode> = classNode.classes
+
+        classDescriptor.constructors.forEach { processClassConstructor(constructors, targetIndex, it, parentCommonDeclarationForMembers) }
+
+        classDescriptor.unsubstitutedMemberScope.collectMembers(
+            PropertyCollector { processProperty(properties, targetIndex, it, parentCommonDeclarationForMembers) },
+            FunctionCollector { processFunction(functions, targetIndex, it, parentCommonDeclarationForMembers) },
+            ClassCollector { processClass(nestedClasses, targetIndex, it, parentCommonDeclarationForMembers) }
+        )
+    }
+
+    private fun processClassConstructor(
+        constructors: MutableMap<ConstructorApproximationKey, CirClassConstructorNode>,
+        targetIndex: Int,
+        constructorDescriptor: ClassConstructorDescriptor,
+        parentCommonDeclaration: NullableLazyValue<*>?
+    ) {
+        val constructorNode: CirClassConstructorNode = constructors.computeIfAbsent(ConstructorApproximationKey(constructorDescriptor)) {
+            buildClassConstructorNode(storageManager, size, cacheRW, parentCommonDeclaration)
+        }
+        constructorNode.targetDeclarations[targetIndex] = CirClassConstructorFactory.create(constructorDescriptor)
+    }
+
+    private fun processTypeAlias(
+        typeAliases: MutableMap<Name, CirTypeAliasNode>,
+        targetIndex: Int,
+        typeAliasDescriptor: TypeAliasDescriptor
+    ) {
+        val typeAliasNode: CirTypeAliasNode = typeAliases.computeIfAbsent(typeAliasDescriptor.name.intern()) {
+            buildTypeAliasNode(storageManager, size, cacheRW, typeAliasDescriptor.fqNameSafe.intern())
+        }
+        typeAliasNode.targetDeclarations[targetIndex] = CirTypeAliasFactory.create(typeAliasDescriptor)
+    }
+}

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/mergedtree/CirTypeAliasNode.kt

@@ -0,0 +1,24 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.descriptors.commonizer.mergedtree
+
+import org.jetbrains.kotlin.descriptors.commonizer.cir.CirClassifier
+import org.jetbrains.kotlin.descriptors.commonizer.cir.CirTypeAlias
+import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroup
+import org.jetbrains.kotlin.name.FqName
+import org.jetbrains.kotlin.storage.NullableLazyValue
+
+class CirTypeAliasNode(
+    override val targetDeclarations: CommonizedGroup<CirTypeAlias>,
+    override val commonDeclaration: NullableLazyValue<CirClassifier>,
+    override val fqName: FqName
+) : CirNodeWithFqName<CirTypeAlias, CirClassifier> {
+
+    override fun <R, T> accept(visitor: CirNodeVisitor<R, T>, data: T): R =
+        visitor.visitTypeAliasNode(this, data)
+
+    override fun toString() = CirNode.toString(this)
+}

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/mergedtree/approximationKeys.kt

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.descriptors.commonizer.mergedtree
+
+import org.jetbrains.kotlin.descriptors.ConstructorDescriptor
+import org.jetbrains.kotlin.descriptors.PropertyDescriptor
+import org.jetbrains.kotlin.descriptors.SimpleFunctionDescriptor
+import org.jetbrains.kotlin.descriptors.commonizer.core.Commonizer
+import org.jetbrains.kotlin.descriptors.commonizer.utils.fqNameWithTypeParameters
+import org.jetbrains.kotlin.descriptors.commonizer.utils.intern
+import org.jetbrains.kotlin.name.Name
+
+/** Used for approximation of [PropertyDescriptor]s before running concrete [Commonizer]s */
+data class PropertyApproximationKey(
+    val name: Name,
+    val extensionReceiverParameter: String?
+) {
+    constructor(property: PropertyDescriptor) : this(
+        property.name.intern(),
+        property.extensionReceiverParameter?.type?.fqNameWithTypeParameters
+    )
+}
+
+/** Used for approximation of [SimpleFunctionDescriptor]s before running concrete [Commonizer]s */
+data class FunctionApproximationKey(
+    val name: Name,
+    val valueParameters: List<Pair<Name, String>>,
+    val extensionReceiverParameter: String?
+) {
+    constructor(function: SimpleFunctionDescriptor) : this(
+        function.name.intern(),
+        function.valueParameters.map { it.name.intern() to it.type.fqNameWithTypeParameters },
+        function.extensionReceiverParameter?.type?.fqNameWithTypeParameters
+    )
+}
+
+/** Used for approximation of [ConstructorDescriptor]s before running concrete [Commonizer]s */
+data class ConstructorApproximationKey(
+    val valueParameters: List<Pair<Name, String>>
+) {
+    constructor(constructor: ConstructorDescriptor) : this(
+        constructor.valueParameters.map { it.name.intern() to it.type.fqNameWithTypeParameters }
+    )
+}

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/mergedtree/callableMembers.kt

@@ -1,33 +0,0 @@
-/*
- * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
- * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
- */
-
-package org.jetbrains.kotlin.descriptors.commonizer.mergedtree
-
-import org.jetbrains.kotlin.descriptors.ClassConstructorDescriptor
-import org.jetbrains.kotlin.descriptors.PropertyDescriptor
-import org.jetbrains.kotlin.descriptors.SimpleFunctionDescriptor
-import org.jetbrains.kotlin.storage.NullableLazyValue
-import org.jetbrains.kotlin.storage.StorageManager
-
-internal fun mergeProperties(
-    storageManager: StorageManager,
-    cache: CirClassifiersCache,
-    containingDeclarationCommon: NullableLazyValue<*>?,
-    properties: List<PropertyDescriptor?>
-) = buildPropertyNode(storageManager, cache, containingDeclarationCommon, properties)
-
-internal fun mergeFunctions(
-    storageManager: StorageManager,
-    cache: CirClassifiersCache,
-    containingDeclarationCommon: NullableLazyValue<*>?,
-    properties: List<SimpleFunctionDescriptor?>
-) = buildFunctionNode(storageManager, cache, containingDeclarationCommon, properties)
-
-internal fun mergeClassConstructors(
-    storageManager: StorageManager,
-    cache: CirClassifiersCache,
-    containingDeclarationCommon: NullableLazyValue<*>?,
-    constructors: List<ClassConstructorDescriptor?>
-) = buildClassConstructorNode(storageManager, cache, containingDeclarationCommon, constructors)

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/mergedtree/classifiers.kt

@@ -1,62 +0,0 @@
-/*
- * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
- * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
- */
-
-package org.jetbrains.kotlin.descriptors.commonizer.mergedtree
-
-import org.jetbrains.kotlin.descriptors.*
-import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirRootNode.ClassifiersCacheImpl
-import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroupMap
-import org.jetbrains.kotlin.descriptors.commonizer.utils.intern
-import org.jetbrains.kotlin.name.Name
-import org.jetbrains.kotlin.storage.NullableLazyValue
-import org.jetbrains.kotlin.storage.StorageManager
-
-internal fun mergeClasses(
-    storageManager: StorageManager,
-    cacheRW: ClassifiersCacheImpl,
-    containingDeclarationCommon: NullableLazyValue<*>?,
-    classes: List<ClassDescriptor?>
-): CirClassNode {
-    val node = buildClassNode(storageManager, cacheRW, containingDeclarationCommon, classes)
-
-    val constructorsMap = CommonizedGroupMap<ConstructorApproximationKey, ClassConstructorDescriptor>(classes.size)
-    val propertiesMap = CommonizedGroupMap<PropertyApproximationKey, PropertyDescriptor>(classes.size)
-    val functionsMap = CommonizedGroupMap<FunctionApproximationKey, SimpleFunctionDescriptor>(classes.size)
-    val classesMap = CommonizedGroupMap<Name, ClassDescriptor>(classes.size)
-
-    classes.forEachIndexed { index, clazz ->
-        clazz?.constructors?.forEach { constructorsMap[ConstructorApproximationKey(it)][index] = it }
-        clazz?.unsubstitutedMemberScope?.collectMembers(
-            PropertyCollector { propertiesMap[PropertyApproximationKey(it)][index] = it },
-            FunctionCollector { functionsMap[FunctionApproximationKey(it)][index] = it },
-            ClassCollector { classesMap[it.name.intern()][index] = it }
-        )
-    }
-
-    for ((_, constructorsGroup) in constructorsMap) {
-        node.constructors += mergeClassConstructors(storageManager, cacheRW, node.common, constructorsGroup.toList())
-    }
-
-    for ((_, propertiesGroup) in propertiesMap) {
-        node.properties += mergeProperties(storageManager, cacheRW, node.common, propertiesGroup.toList())
-    }
-
-    for ((_, functionsGroup) in functionsMap) {
-        node.functions += mergeFunctions(storageManager, cacheRW, node.common, functionsGroup.toList())
-    }
-
-    for ((_, classesGroup) in classesMap) {
-        node.classes += mergeClasses(storageManager, cacheRW, node.common, classesGroup.toList())
-    }
-
-    return node
-}
-
-internal fun mergeTypeAliases(
-    storageManager: StorageManager,
-    cacheRW: ClassifiersCacheImpl,
-    typeAliases: List<TypeAliasDescriptor?>
-) = buildTypeAliasNode(storageManager, cacheRW, typeAliases)
-

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/mergedtree/collectors.kt

@@ -5,11 +5,13 @@
 
 package org.jetbrains.kotlin.descriptors.commonizer.mergedtree
 
+import org.jetbrains.kotlin.backend.common.serialization.metadata.impl.ExportedForwardDeclarationsPackageFragmentDescriptor
 import org.jetbrains.kotlin.descriptors.*
-import org.jetbrains.kotlin.descriptors.commonizer.core.Commonizer
 import org.jetbrains.kotlin.descriptors.commonizer.utils.*
-import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.name.FqName
+import org.jetbrains.kotlin.resolve.scopes.ChainedMemberScope
 import org.jetbrains.kotlin.resolve.scopes.MemberScope
+import org.jetbrains.kotlin.utils.alwaysTrue
 
 internal fun MemberScope.collectMembers(vararg collectors: (DeclarationDescriptor) -> Boolean) =
     getContributedDescriptors().forEach { member ->
@@ -60,35 +62,34 @@ internal inline fun FunctionCollector(
     }
 }
 
-/** Used for approximation of [PropertyDescriptor]s before running concrete [Commonizer]s */
-internal data class PropertyApproximationKey(
-    val name: Name,
-    val extensionReceiverParameter: String?
-) {
-    constructor(property: PropertyDescriptor) : this(
-        property.name.intern(),
-        property.extensionReceiverParameter?.type?.fqNameWithTypeParameters
-    )
-}
+// collects member scopes for every non-empty package provided by this module
+internal fun ModuleDescriptor.collectNonEmptyPackageMemberScopes(collector: (FqName, MemberScope) -> Unit) {
+    // we don's need to process fragments from other modules which are the dependencies of this module, so
+    // let's use the appropriate package fragment provider
+    val packageFragmentProvider = this.packageFragmentProvider
 
-/** Used for approximation of [SimpleFunctionDescriptor]s before running concrete [Commonizer]s */
-internal data class FunctionApproximationKey(
-    val name: Name,
-    val valueParameters: List<Pair<Name, String>>,
-    val extensionReceiverParameter: String?
-) {
-    constructor(function: SimpleFunctionDescriptor) : this(
-        function.name.intern(),
-        function.valueParameters.map { it.name.intern() to it.type.fqNameWithTypeParameters },
-        function.extensionReceiverParameter?.type?.fqNameWithTypeParameters
-    )
-}
+    fun recurse(packageFqName: FqName) {
+        if (packageFqName.isUnderStandardKotlinPackages || packageFqName.isUnderKotlinNativeSyntheticPackages)
+            return
 
-/** Used for approximation of [ConstructorDescriptor]s before running concrete [Commonizer]s */
-internal data class ConstructorApproximationKey(
-    val valueParameters: List<Pair<Name, String>>
-) {
-    constructor(constructor: ConstructorDescriptor) : this(
-        constructor.valueParameters.map { it.name.intern() to it.type.fqNameWithTypeParameters }
-    )
-}
+        val ownPackageFragments = packageFragmentProvider.getPackageFragments(packageFqName)
+        val ownPackageMemberScopes = ownPackageFragments.asSequence()
+            .filter { it !is ExportedForwardDeclarationsPackageFragmentDescriptor }
+            .map { it.getMemberScope() }
+            .filter { it != MemberScope.Empty }
+            .toList(ownPackageFragments.size)
+
+        if (ownPackageMemberScopes.isNotEmpty()) {
+            // don't include subpackages into chained member scope
+            val memberScope = ChainedMemberScope.create(
+                "package member scope for $packageFqName in $name",
+                ownPackageMemberScopes
+            )
+            collector(packageFqName, memberScope)
+        }
+
+        packageFragmentProvider.getSubPackagesOf(packageFqName, alwaysTrue()).toSet().map { recurse(it) }
+    }
+
+    recurse(FqName.ROOT)
+}

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/mergedtree/modules.kt

@@ -1,70 +0,0 @@
-/*
- * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
- * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
- */
-
-package org.jetbrains.kotlin.descriptors.commonizer.mergedtree
-
-import org.jetbrains.kotlin.backend.common.serialization.metadata.impl.ExportedForwardDeclarationsPackageFragmentDescriptor
-import org.jetbrains.kotlin.descriptors.ModuleDescriptor
-import org.jetbrains.kotlin.descriptors.commonizer.utils.*
-import org.jetbrains.kotlin.name.FqName
-import org.jetbrains.kotlin.resolve.scopes.ChainedMemberScope
-import org.jetbrains.kotlin.resolve.scopes.MemberScope
-import org.jetbrains.kotlin.storage.StorageManager
-import org.jetbrains.kotlin.utils.alwaysTrue
-
-internal fun mergeModules(
-    storageManager: StorageManager,
-    cacheRW: CirRootNode.ClassifiersCacheImpl,
-    modules: List<ModuleDescriptor?>
-): CirModuleNode {
-    val node = buildModuleNode(storageManager, modules)
-
-    val packageMemberScopesMap = CommonizedGroupMap<FqName, MemberScope>(modules.size)
-
-    modules.forEachIndexed { index, module ->
-        module?.collectNonEmptyPackageMemberScopes { packageFqName, memberScope ->
-            packageMemberScopesMap[packageFqName.intern()][index] = memberScope
-        }
-    }
-
-    val moduleName = modules.firstNonNull().name.intern()
-    for ((packageFqName, packageMemberScopesGroup) in packageMemberScopesMap) {
-        node.packages += mergePackages(storageManager, cacheRW, moduleName, packageFqName, packageMemberScopesGroup.toList())
-    }
-
-    return node
-}
-
-// collects member scopes for every non-empty package provided by this module
-internal fun ModuleDescriptor.collectNonEmptyPackageMemberScopes(collector: (FqName, MemberScope) -> Unit) {
-    // we don's need to process fragments from other modules which are the dependencies of this module, so
-    // let's use the appropriate package fragment provider
-    val packageFragmentProvider = this.packageFragmentProvider
-
-    fun recurse(packageFqName: FqName) {
-        if (packageFqName.isUnderStandardKotlinPackages || packageFqName.isUnderKotlinNativeSyntheticPackages)
-            return
-
-        val ownPackageFragments = packageFragmentProvider.getPackageFragments(packageFqName)
-        val ownPackageMemberScopes = ownPackageFragments.asSequence()
-            .filter { it !is ExportedForwardDeclarationsPackageFragmentDescriptor }
-            .map { it.getMemberScope() }
-            .filter { it != MemberScope.Empty }
-            .toList(ownPackageFragments.size)
-
-        if (ownPackageMemberScopes.isNotEmpty()) {
-            // don't include subpackages into chained member scope
-            val memberScope = ChainedMemberScope.create(
-                "package member scope for $packageFqName in $name",
-                ownPackageMemberScopes
-            )
-            collector(packageFqName, memberScope)
-        }
-
-        packageFragmentProvider.getSubPackagesOf(packageFqName, alwaysTrue()).toSet().map { recurse(it) }
-    }
-
-    recurse(FqName.ROOT)
-}

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/mergedtree/nodeBuilders.kt

@@ -5,186 +5,152 @@
 
 package org.jetbrains.kotlin.descriptors.commonizer.mergedtree
 
-import org.jetbrains.kotlin.descriptors.*
-import org.jetbrains.kotlin.descriptors.commonizer.TargetProvider
-import org.jetbrains.kotlin.descriptors.commonizer.cir.CirDeclaration
-import org.jetbrains.kotlin.descriptors.commonizer.cir.factory.*
+import org.jetbrains.kotlin.descriptors.commonizer.cir.*
 import org.jetbrains.kotlin.descriptors.commonizer.cir.impl.CirClassRecursionMarker
 import org.jetbrains.kotlin.descriptors.commonizer.cir.impl.CirClassifierRecursionMarker
 import org.jetbrains.kotlin.descriptors.commonizer.core.*
-import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirRootNode.ClassifiersCacheImpl
+import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirRootNode.CirClassifiersCacheImpl
 import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroup
-import org.jetbrains.kotlin.descriptors.commonizer.utils.firstNonNull
-import org.jetbrains.kotlin.descriptors.commonizer.utils.intern
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
-import org.jetbrains.kotlin.resolve.descriptorUtil.fqNameSafe
-import org.jetbrains.kotlin.resolve.scopes.MemberScope
 import org.jetbrains.kotlin.storage.NullableLazyValue
 import org.jetbrains.kotlin.storage.StorageManager
 
 internal fun buildRootNode(
     storageManager: StorageManager,
-    targetProviders: List<TargetProvider>
+    size: Int
 ): CirRootNode = buildNode(
     storageManager = storageManager,
-    descriptors = targetProviders,
-    targetDeclarationProducer = { CirRootFactory.create(it.target, it.builtInsClass.name, it.builtInsProvider) },
-    commonValueProducer = { commonize(it, RootCommonizer()) },
-    recursionMarker = null,
+    size = size,
+    commonizerProducer = ::RootCommonizer,
     nodeProducer = ::CirRootNode
 )
 
 internal fun buildModuleNode(
     storageManager: StorageManager,
-    modules: List<ModuleDescriptor?>
+    size: Int
 ): CirModuleNode = buildNode(
     storageManager = storageManager,
-    descriptors = modules,
-    targetDeclarationProducer = CirModuleFactory::create,
-    commonValueProducer = { commonize(it, ModuleCommonizer()) },
-    recursionMarker = null,
+    size = size,
+    commonizerProducer = ::ModuleCommonizer,
     nodeProducer = ::CirModuleNode
 )
 
 internal fun buildPackageNode(
     storageManager: StorageManager,
-    moduleName: Name,
-    packageFqName: FqName,
-    packageMemberScopes: List<MemberScope?>
+    size: Int,
+    fqName: FqName,
+    moduleName: Name
 ): CirPackageNode = buildNode(
     storageManager = storageManager,
-    descriptors = packageMemberScopes,
-    targetDeclarationProducer = { CirPackageFactory.create(packageFqName) },
-    commonValueProducer = { CirPackageFactory.create(packageFqName) },
-    recursionMarker = null,
-    nodeProducer = ::CirPackageNode
-).also { node ->
-    node.moduleName = moduleName
-    node.fqName = packageFqName
-}
+    size = size,
+    commonizerProducer = ::PackageCommonizer,
+    nodeProducer = { targetDeclarations, commonDeclaration ->
+        CirPackageNode(targetDeclarations, commonDeclaration, fqName, moduleName)
+    }
+)
 
 internal fun buildPropertyNode(
     storageManager: StorageManager,
+    size: Int,
     cache: CirClassifiersCache,
-    containingDeclarationCommon: NullableLazyValue<*>?,
-    properties: List<PropertyDescriptor?>
+    parentCommonDeclaration: NullableLazyValue<*>?
 ): CirPropertyNode = buildNode(
     storageManager = storageManager,
-    descriptors = properties,
-    targetDeclarationProducer = CirPropertyFactory::create,
-    commonValueProducer = { commonize(containingDeclarationCommon, it, PropertyCommonizer(cache)) },
-    recursionMarker = null,
+    size = size,
+    parentCommonDeclaration = parentCommonDeclaration,
+    commonizerProducer = { PropertyCommonizer(cache) },
     nodeProducer = ::CirPropertyNode
 )
 
 internal fun buildFunctionNode(
     storageManager: StorageManager,
+    size: Int,
     cache: CirClassifiersCache,
-    containingDeclarationCommon: NullableLazyValue<*>?,
-    functions: List<SimpleFunctionDescriptor?>
+    parentCommonDeclaration: NullableLazyValue<*>?
 ): CirFunctionNode = buildNode(
     storageManager = storageManager,
-    descriptors = functions,
-    targetDeclarationProducer = CirFunctionFactory::create,
-    commonValueProducer = { commonize(containingDeclarationCommon, it, FunctionCommonizer(cache)) },
-    recursionMarker = null,
+    size = size,
+    parentCommonDeclaration = parentCommonDeclaration,
+    commonizerProducer = { FunctionCommonizer(cache) },
     nodeProducer = ::CirFunctionNode
 )
 
 internal fun buildClassNode(
     storageManager: StorageManager,
-    cacheRW: ClassifiersCacheImpl,
-    containingDeclarationCommon: NullableLazyValue<*>?,
-    classes: List<ClassDescriptor?>
+    size: Int,
+    cacheRW: CirClassifiersCacheImpl,
+    parentCommonDeclaration: NullableLazyValue<*>?,
+    fqName: FqName
 ): CirClassNode = buildNode(
     storageManager = storageManager,
-    descriptors = classes,
-    targetDeclarationProducer = CirClassFactory::create,
-    commonValueProducer = { commonize(containingDeclarationCommon, it, ClassCommonizer(cacheRW)) },
+    size = size,
+    parentCommonDeclaration = parentCommonDeclaration,
+    commonizerProducer = { ClassCommonizer(cacheRW) },
     recursionMarker = CirClassRecursionMarker,
-    nodeProducer = ::CirClassNode
-).also { node ->
-    classes.firstNonNull().fqNameSafe.intern().let { fqName ->
-        node.fqName = fqName
-        cacheRW.classes.putSafe(fqName, node)
+    nodeProducer = { targetDeclarations, commonDeclaration ->
+        CirClassNode(targetDeclarations, commonDeclaration, fqName).also {
+            cacheRW.classes[fqName] = it
+        }
     }
-}
+)
 
 internal fun buildClassConstructorNode(
     storageManager: StorageManager,
+    size: Int,
     cache: CirClassifiersCache,
-    containingDeclarationCommon: NullableLazyValue<*>?,
-    constructors: List<ClassConstructorDescriptor?>
+    parentCommonDeclaration: NullableLazyValue<*>?
 ): CirClassConstructorNode = buildNode(
     storageManager = storageManager,
-    descriptors = constructors,
-    targetDeclarationProducer = CirClassConstructorFactory::create,
-    commonValueProducer = { commonize(containingDeclarationCommon, it, ClassConstructorCommonizer(cache)) },
-    recursionMarker = null,
+    size = size,
+    parentCommonDeclaration = parentCommonDeclaration,
+    commonizerProducer = { ClassConstructorCommonizer(cache) },
     nodeProducer = ::CirClassConstructorNode
 )
 
 internal fun buildTypeAliasNode(
     storageManager: StorageManager,
-    cacheRW: ClassifiersCacheImpl,
-    typeAliases: List<TypeAliasDescriptor?>
+    size: Int,
+    cacheRW: CirClassifiersCacheImpl,
+    fqName: FqName
 ): CirTypeAliasNode = buildNode(
     storageManager = storageManager,
-    descriptors = typeAliases,
-    targetDeclarationProducer = CirTypeAliasFactory::create,
-    commonValueProducer = { commonize(it, TypeAliasCommonizer(cacheRW)) },
+    size = size,
+    commonizerProducer = { TypeAliasCommonizer(cacheRW) },
     recursionMarker = CirClassifierRecursionMarker,
-    nodeProducer = ::CirTypeAliasNode
-).also { node ->
-    typeAliases.firstNonNull().fqNameSafe.intern().let { fqName ->
-        node.fqName = fqName
-        cacheRW.typeAliases.putSafe(fqName, node)
+    nodeProducer = { targetDeclarations, commonDeclaration ->
+        CirTypeAliasNode(targetDeclarations, commonDeclaration, fqName).also {
+            cacheRW.typeAliases[fqName] = it
+        }
     }
-}
+)
 
-private fun <D : Any, T : CirDeclaration, R : CirDeclaration, N : CirNode<T, R>> buildNode(
+private fun <T : CirDeclaration, R : CirDeclaration, N : CirNode<T, R>> buildNode(
     storageManager: StorageManager,
-    descriptors: List<D?>,
-    targetDeclarationProducer: (D) -> T,
-    commonValueProducer: (List<T?>) -> R?,
-    recursionMarker: R?,
-    nodeProducer: (List<T?>, NullableLazyValue<R>) -> N
+    size: Int,
+    parentCommonDeclaration: NullableLazyValue<*>? = null,
+    commonizerProducer: () -> Commonizer<T, R>,
+    recursionMarker: R? = null,
+    nodeProducer: (CommonizedGroup<T>, NullableLazyValue<R>) -> N
 ): N {
-    val declarationsGroup = CommonizedGroup<T>(descriptors.size)
-    var canHaveCommon = descriptors.size > 1
+    val targetDeclarations = CommonizedGroup<T>(size)
 
-    descriptors.forEachIndexed { index, descriptor ->
-        if (descriptor != null)
-            declarationsGroup[index] = targetDeclarationProducer(descriptor)
-        else
-            canHaveCommon = false
-    }
-
-    val declarations = declarationsGroup.toList()
-
-    val commonComputable: () -> R? = if (canHaveCommon) {
-        { commonValueProducer(declarations) }
-    } else {
-        { null }
-    }
+    val commonComputable = { commonize(parentCommonDeclaration, targetDeclarations, commonizerProducer()) }
 
     val commonLazyValue = if (recursionMarker != null)
         storageManager.createRecursionTolerantNullableLazyValue(commonComputable, recursionMarker)
     else
         storageManager.createNullableLazyValue(commonComputable)
 
-    return nodeProducer(declarations, commonLazyValue)
+    return nodeProducer(targetDeclarations, commonLazyValue)
 }
 
-@Suppress("NOTHING_TO_INLINE")
-private inline fun <K, V : Any> MutableMap<K, V>.putSafe(key: K, value: V) = put(key, value)?.let { oldValue ->
-    error("${oldValue::class.java} with key=$key has been overwritten: $oldValue")
-}
-
-internal fun <T, R> commonize(declarations: List<T?>, commonizer: Commonizer<T, R>): R? {
-    for (declaration in declarations) {
-        if (declaration == null || !commonizer.commonizeWith(declaration))
+internal fun <T : Any, R> commonize(
+    targetDeclarations: CommonizedGroup<T>,
+    commonizer: Commonizer<T, R>
+): R? {
+    for (targetDeclaration in targetDeclarations.toList()) {
+        if (targetDeclaration == null || !commonizer.commonizeWith(targetDeclaration))
             return null
     }
 
@@ -192,15 +158,15 @@ internal fun <T, R> commonize(declarations: List<T?>, commonizer: Commonizer<T,
 }
 
 @Suppress("NOTHING_TO_INLINE")
-private inline fun <T, R> commonize(
-    containingDeclarationCommon: NullableLazyValue<*>?,
-    declarations: List<T?>,
+private inline fun <T : Any, R> commonize(
+    parentCommonDeclaration: NullableLazyValue<*>?,
+    targetDeclarations: CommonizedGroup<T>,
     commonizer: Commonizer<T, R>
 ): R? {
-    if (containingDeclarationCommon != null && containingDeclarationCommon.invoke() == null) {
-        // don't commonize declaration if it has commonizable containing declaration that has not been successfully commonized
+    if (parentCommonDeclaration != null && parentCommonDeclaration.invoke() == null) {
+        // don't commonize declaration if it's parent failed to commonize
         return null
     }
 
-    return commonize(declarations, commonizer)
+    return commonize(targetDeclarations, commonizer)
 }

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/mergedtree/nodes.kt

@@ -1,150 +0,0 @@
-/*
- * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
- * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
- */
-
-package org.jetbrains.kotlin.descriptors.commonizer.mergedtree
-
-import org.jetbrains.kotlin.descriptors.commonizer.cir.*
-import org.jetbrains.kotlin.name.FqName
-import org.jetbrains.kotlin.name.Name
-import org.jetbrains.kotlin.storage.NullableLazyValue
-
-interface CirNode<T : CirDeclaration, R : CirDeclaration> {
-    val target: List<T?>
-    val common: NullableLazyValue<R>
-
-    fun <R, T> accept(visitor: CirNodeVisitor<R, T>, data: T): R
-}
-
-interface CirNodeWithFqName<T : CirDeclaration, R : CirDeclaration> : CirNode<T, R> {
-    val fqName: FqName
-}
-
-class CirRootNode(
-    override val target: List<CirRoot?>,
-    override val common: NullableLazyValue<CirRoot>
-) : CirNode<CirRoot, CirRoot> {
-    class ClassifiersCacheImpl : CirClassifiersCache {
-        override val classes = HashMap<FqName, CirClassNode>()
-        override val typeAliases = HashMap<FqName, CirTypeAliasNode>()
-    }
-
-    val modules: MutableList<CirModuleNode> = ArrayList()
-    val cache = ClassifiersCacheImpl()
-
-    override fun <R, T> accept(visitor: CirNodeVisitor<R, T>, data: T): R =
-        visitor.visitRootNode(this, data)
-
-    override fun toString() = toString(this)
-}
-
-class CirModuleNode(
-    override val target: List<CirModule?>,
-    override val common: NullableLazyValue<CirModule>
-) : CirNode<CirModule, CirModule> {
-    val packages: MutableList<CirPackageNode> = ArrayList()
-
-    override fun <R, T> accept(visitor: CirNodeVisitor<R, T>, data: T) =
-        visitor.visitModuleNode(this, data)
-
-    override fun toString() = toString(this)
-}
-
-class CirPackageNode(
-    override val target: List<CirPackage?>,
-    override val common: NullableLazyValue<CirPackage>
-) : CirNodeWithFqName<CirPackage, CirPackage> {
-    lateinit var moduleName: Name
-    override lateinit var fqName: FqName
-
-    val properties: MutableList<CirPropertyNode> = ArrayList()
-    val functions: MutableList<CirFunctionNode> = ArrayList()
-    val classes: MutableList<CirClassNode> = ArrayList()
-    val typeAliases: MutableList<CirTypeAliasNode> = ArrayList()
-
-    override fun <R, T> accept(visitor: CirNodeVisitor<R, T>, data: T) =
-        visitor.visitPackageNode(this, data)
-
-    override fun toString() = toString(this)
-}
-
-class CirPropertyNode(
-    override val target: List<CirProperty?>,
-    override val common: NullableLazyValue<CirProperty>
-) : CirNode<CirProperty, CirProperty> {
-    override fun <R, T> accept(visitor: CirNodeVisitor<R, T>, data: T) =
-        visitor.visitPropertyNode(this, data)
-
-    override fun toString() = toString(this)
-}
-
-class CirFunctionNode(
-    override val target: List<CirFunction?>,
-    override val common: NullableLazyValue<CirFunction>
-) : CirNode<CirFunction, CirFunction> {
-    override fun <R, T> accept(visitor: CirNodeVisitor<R, T>, data: T) =
-        visitor.visitFunctionNode(this, data)
-
-    override fun toString() = toString(this)
-}
-
-class CirClassNode(
-    override val target: List<CirClass?>,
-    override val common: NullableLazyValue<CirClass>
-) : CirNodeWithFqName<CirClass, CirClass> {
-    override lateinit var fqName: FqName
-
-    val constructors: MutableList<CirClassConstructorNode> = ArrayList()
-    val properties: MutableList<CirPropertyNode> = ArrayList()
-    val functions: MutableList<CirFunctionNode> = ArrayList()
-    val classes: MutableList<CirClassNode> = ArrayList()
-
-    override fun <R, T> accept(visitor: CirNodeVisitor<R, T>, data: T): R =
-        visitor.visitClassNode(this, data)
-
-    override fun toString() = toString(this)
-}
-
-class CirClassConstructorNode(
-    override val target: List<CirClassConstructor?>,
-    override val common: NullableLazyValue<CirClassConstructor>
-) : CirNode<CirClassConstructor, CirClassConstructor> {
-    override fun <R, T> accept(visitor: CirNodeVisitor<R, T>, data: T): R =
-        visitor.visitClassConstructorNode(this, data)
-
-    override fun toString() = toString(this)
-}
-
-class CirTypeAliasNode(
-    override val target: List<CirTypeAlias?>,
-    override val common: NullableLazyValue<CirClassifier>
-) : CirNodeWithFqName<CirTypeAlias, CirClassifier> {
-    override lateinit var fqName: FqName
-
-    override fun <R, T> accept(visitor: CirNodeVisitor<R, T>, data: T): R =
-        visitor.visitTypeAliasNode(this, data)
-
-    override fun toString() = toString(this)
-}
-
-interface CirClassifiersCache {
-    val classes: Map<FqName, CirClassNode>
-    val typeAliases: Map<FqName, CirTypeAliasNode>
-}
-
-internal inline val CirNode<*, *>.indexOfCommon: Int
-    get() = target.size
-
-internal inline val CirNode<*, *>.dimension: Int
-    get() = target.size + 1
-
-private fun toString(node: CirNode<*, *>) = buildString {
-    if (node is CirNodeWithFqName) {
-        append("fqName=").append(node.fqName).append(", ")
-    }
-    append("target=")
-    node.target.joinTo(this)
-    append(", common=")
-    append(if (node.common.isComputed()) node.common() else "<NOT COMPUTED>")
-}

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/mergedtree/packages.kt

@@ -1,59 +0,0 @@
-/*
- * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
- * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
- */
-
-package org.jetbrains.kotlin.descriptors.commonizer.mergedtree
-
-import org.jetbrains.kotlin.descriptors.ClassDescriptor
-import org.jetbrains.kotlin.descriptors.PropertyDescriptor
-import org.jetbrains.kotlin.descriptors.SimpleFunctionDescriptor
-import org.jetbrains.kotlin.descriptors.TypeAliasDescriptor
-import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroupMap
-import org.jetbrains.kotlin.descriptors.commonizer.utils.intern
-import org.jetbrains.kotlin.name.FqName
-import org.jetbrains.kotlin.name.Name
-import org.jetbrains.kotlin.resolve.scopes.MemberScope
-import org.jetbrains.kotlin.storage.StorageManager
-
-internal fun mergePackages(
-    storageManager: StorageManager,
-    cacheRW: CirRootNode.ClassifiersCacheImpl,
-    moduleName: Name,
-    packageFqName: FqName,
-    packageMemberScopes: List<MemberScope?>
-): CirPackageNode {
-    val node = buildPackageNode(storageManager, moduleName, packageFqName, packageMemberScopes)
-
-    val propertiesMap = CommonizedGroupMap<PropertyApproximationKey, PropertyDescriptor>(packageMemberScopes.size)
-    val functionsMap = CommonizedGroupMap<FunctionApproximationKey, SimpleFunctionDescriptor>(packageMemberScopes.size)
-    val classesMap = CommonizedGroupMap<Name, ClassDescriptor>(packageMemberScopes.size)
-    val typeAliasesMap = CommonizedGroupMap<Name, TypeAliasDescriptor>(packageMemberScopes.size)
-
-    packageMemberScopes.forEachIndexed { index, memberScope ->
-        memberScope?.collectMembers(
-            PropertyCollector { propertiesMap[PropertyApproximationKey(it)][index] = it },
-            FunctionCollector { functionsMap[FunctionApproximationKey(it)][index] = it },
-            ClassCollector { classesMap[it.name.intern()][index] = it },
-            TypeAliasCollector { typeAliasesMap[it.name.intern()][index] = it }
-        )
-    }
-
-    for ((_, propertiesGroup) in propertiesMap) {
-        node.properties += mergeProperties(storageManager, cacheRW, null, propertiesGroup.toList())
-    }
-
-    for ((_, functionsGroup) in functionsMap) {
-        node.functions += mergeFunctions(storageManager, cacheRW, null, functionsGroup.toList())
-    }
-
-    for ((_, classesGroup) in classesMap) {
-        node.classes += mergeClasses(storageManager, cacheRW, null, classesGroup.toList())
-    }
-
-    for ((_, typeAliasesGroup) in typeAliasesMap) {
-        node.typeAliases += mergeTypeAliases(storageManager, cacheRW, typeAliasesGroup.toList())
-    }
-
-    return node
-}

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/mergedtree/root.kt

@@ -1,34 +0,0 @@
-/*
- * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
- * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
- */
-
-package org.jetbrains.kotlin.descriptors.commonizer.mergedtree
-
-import org.jetbrains.kotlin.descriptors.ModuleDescriptor
-import org.jetbrains.kotlin.descriptors.commonizer.TargetProvider
-import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroupMap
-import org.jetbrains.kotlin.descriptors.commonizer.utils.intern
-import org.jetbrains.kotlin.name.Name
-import org.jetbrains.kotlin.storage.StorageManager
-
-internal fun mergeRoots(
-    storageManager: StorageManager,
-    targetProviders: List<TargetProvider>
-): CirRootNode {
-    val node = buildRootNode(storageManager, targetProviders)
-
-    val modulesMap = CommonizedGroupMap<Name, ModuleDescriptor>(targetProviders.size)
-
-    targetProviders.forEachIndexed { index, targetProvider ->
-        for (module in targetProvider.modulesProvider.loadModules()) {
-            modulesMap[module.name.intern()][index] = module
-        }
-    }
-
-    for ((_, modulesGroup) in modulesMap) {
-        node.modules += mergeModules(storageManager, node.cache, modulesGroup.toList())
-    }
-
-    return node
-}

native/commonizer/src/org/jetbrains/kotlin/descriptors/commonizer/utils/commonizedGroup.kt

@@ -6,7 +6,7 @@
 package org.jetbrains.kotlin.descriptors.commonizer.utils
 
 /** Fixed-size ordered collection with no extra space that represents a commonized group of same-rank elements */
-internal class CommonizedGroup<T : Any>(
+class CommonizedGroup<T : Any>(
     val size: Int,
     initialize: (Int) -> T?
 ) {
@@ -30,6 +30,7 @@ internal class CommonizedGroup<T : Any>(
         elements[index] = value
     }
 
+    // TODO: consider removing this method
     fun toList(): List<T?> = object : AbstractList<T?>() {
         override val size
             get() = this@CommonizedGroup.size

native/commonizer/tests/org/jetbrains/kotlin/descriptors/commonizer/core/TypeCommonizerTest.kt

@@ -8,8 +8,10 @@ package org.jetbrains.kotlin.descriptors.commonizer.core
 import org.jetbrains.kotlin.descriptors.ClassDescriptor
 import org.jetbrains.kotlin.descriptors.TypeAliasDescriptor
 import org.jetbrains.kotlin.descriptors.commonizer.cir.CirType
+import org.jetbrains.kotlin.descriptors.commonizer.cir.factory.CirClassFactory
+import org.jetbrains.kotlin.descriptors.commonizer.cir.factory.CirTypeAliasFactory
 import org.jetbrains.kotlin.descriptors.commonizer.cir.factory.CirTypeFactory
-import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirRootNode.ClassifiersCacheImpl
+import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.CirRootNode.CirClassifiersCacheImpl
 import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.buildClassNode
 import org.jetbrains.kotlin.descriptors.commonizer.mergedtree.buildTypeAliasNode
 import org.jetbrains.kotlin.descriptors.commonizer.utils.CommonizedGroupMap
@@ -25,11 +27,11 @@ import org.junit.Test
 
 class TypeCommonizerTest : AbstractCommonizerTest<CirType, CirType>() {
 
-    private lateinit var cache: ClassifiersCacheImpl
+    private lateinit var cache: CirClassifiersCacheImpl
 
     @Before
     fun initialize() {
-        cache = ClassifiersCacheImpl() // reset cache
+        cache = CirClassifiersCacheImpl() // reset cache
     }
 
     @Test
@@ -454,10 +456,8 @@ class TypeCommonizerTest : AbstractCommonizerTest<CirType, CirType>() {
     private fun prepareCache(variants: Array<out KotlinType>) {
         check(variants.isNotEmpty())
 
-        val classesMap =
-            CommonizedGroupMap<FqName, ClassDescriptor>(variants.size)
-        val typeAliasesMap =
-            CommonizedGroupMap<FqName, TypeAliasDescriptor>(variants.size)
+        val classesMap = CommonizedGroupMap<FqName, ClassDescriptor>(variants.size)
+        val typeAliasesMap = CommonizedGroupMap<FqName, TypeAliasDescriptor>(variants.size)
 
         fun recurse(type: KotlinType, index: Int) {
             @Suppress("MoveVariableDeclarationIntoWhen")
@@ -476,12 +476,35 @@ class TypeCommonizerTest : AbstractCommonizerTest<CirType, CirType>() {
             recurse(type, index)
         }
 
-        for ((_, classesGroup) in classesMap) {
-            buildClassNode(LockBasedStorageManager.NO_LOCKS, cache, null, classesGroup.toList())
+        for ((fqName, classesGroup) in classesMap) {
+            buildClassNode(
+                LockBasedStorageManager.NO_LOCKS,
+                classesGroup.size,
+                cache,
+                null,
+                fqName
+            ).also {
+                classesGroup.toList().forEachIndexed { index, clazz ->
+                    if (clazz != null) {
+                        it.targetDeclarations[index] = CirClassFactory.create(clazz)
+                    }
+                }
+            }
         }
 
-        for ((_, typeAliasesGroup) in typeAliasesMap) {
-            buildTypeAliasNode(LockBasedStorageManager.NO_LOCKS, cache, typeAliasesGroup.toList())
+        for ((fqName, typeAliasesGroup) in typeAliasesMap) {
+            buildTypeAliasNode(
+                LockBasedStorageManager.NO_LOCKS,
+                typeAliasesGroup.size,
+                cache,
+                fqName
+            ).also {
+                typeAliasesGroup.toList().forEachIndexed { index, typeAlias ->
+                    if (typeAlias != null) {
+                        it.targetDeclarations[index] = CirTypeAliasFactory.create(typeAlias)
+                    }
+                }
+            }
         }
     }