IR: use String instead of FqName in IdSignature.PublicSignature

FqName/FqNameUnsafe tend to eagerly compute things like
safe/parent/shortName which take a lot of space.

This change helps to lower strongly reachable memory just before codegen
in JVM IR by about 5% on a relatively big project.

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/signaturer/FirBasedSignatureComposer.kt

@@ -10,12 +10,11 @@ import org.jetbrains.kotlin.fir.FirEffectiveVisibilityImpl
 import org.jetbrains.kotlin.fir.FirElement
 import org.jetbrains.kotlin.fir.backend.Fir2IrSignatureComposer
 import org.jetbrains.kotlin.fir.declarations.*
-import org.jetbrains.kotlin.fir.symbols.CallableId
 import org.jetbrains.kotlin.fir.render
+import org.jetbrains.kotlin.fir.symbols.CallableId
 import org.jetbrains.kotlin.fir.visitors.FirVisitorVoid
 import org.jetbrains.kotlin.ir.util.IdSignature
 import org.jetbrains.kotlin.name.FqName
-import org.jetbrains.kotlin.name.Name
 
 class FirBasedSignatureComposer(private val mangler: FirMangler) : Fir2IrSignatureComposer {
     inner class SignatureBuilder : FirVisitorVoid() {
@@ -70,15 +69,21 @@ class FirBasedSignatureComposer(private val mangler: FirMangler) : Fir2IrSignatu
         return when {
             declaration is FirRegularClass && declaration.visibility != Visibilities.LOCAL -> {
                 val classId = declaration.classId
-                IdSignature.PublicSignature(classId.packageFqName, classId.relativeClassName, builder.hashId, builder.mask)
+                IdSignature.PublicSignature(
+                    classId.packageFqName.asString(), classId.relativeClassName.asString(), builder.hashId, builder.mask
+                )
             }
             declaration is FirTypeAlias -> {
                 val classId = declaration.symbol.classId
-                IdSignature.PublicSignature(classId.packageFqName, classId.relativeClassName, builder.hashId, builder.mask)
+                IdSignature.PublicSignature(
+                    classId.packageFqName.asString(), classId.relativeClassName.asString(), builder.hashId, builder.mask
+                )
             }
             declaration is FirCallableMemberDeclaration<*> -> {
                 val callableId = declaration.symbol.callableId
-                IdSignature.PublicSignature(callableId.packageName, callableId.relativeCallableName, builder.hashId, builder.mask)
+                IdSignature.PublicSignature(
+                    callableId.packageName.asString(), callableId.relativeCallableName.asString(), builder.hashId, builder.mask
+                )
             }
             else -> throw AssertionError("Unsupported FIR declaration in signature composer: ${declaration.render()}")
         }
@@ -87,10 +92,10 @@ class FirBasedSignatureComposer(private val mangler: FirMangler) : Fir2IrSignatu
     override fun composeAccessorSignature(property: FirProperty, isSetter: Boolean): IdSignature? {
         val propertySignature = composeSignature(property) as? IdSignature.PublicSignature ?: return null
         val accessorFqName = if (isSetter) {
-            propertySignature.declarationFqn.child(Name.special("<set-${property.name}>"))
+            propertySignature.declarationFqName + ".<set-${property.name.asString()}>"
         } else {
-            propertySignature.declarationFqn.child(Name.special("<get-${property.name}>"))
+            propertySignature.declarationFqName + ".<get-${property.name.asString()}>"
         }
-        return IdSignature.PublicSignature(propertySignature.packageFqn, accessorFqName, propertySignature.id, propertySignature.mask)
+        return IdSignature.PublicSignature(propertySignature.packageFqName, accessorFqName, propertySignature.id, propertySignature.mask)
     }
-}
+}

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/DeclarationStubGenerator.kt

@@ -32,6 +32,7 @@ import org.jetbrains.kotlin.ir.symbols.IrTypeParameterSymbol
 import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlin.resolve.DescriptorUtils
 import org.jetbrains.kotlin.resolve.descriptorUtil.isEffectivelyExternal
+import org.jetbrains.kotlin.resolve.scopes.getDescriptorsFiltered
 import org.jetbrains.kotlin.serialization.deserialization.descriptors.DescriptorWithContainerSource
 import org.jetbrains.kotlin.serialization.deserialization.descriptors.DeserializedContainerSource
 import org.jetbrains.kotlin.types.KotlinType
@@ -361,22 +362,19 @@ class DeclarationStubGenerator(
 
     private fun findDescriptorForAccessorSignature(signature: IdSignature.AccessorSignature): DeclarationDescriptor? {
         val propertyDescriptor = findDescriptorBySignature(signature.propertySignature) as? PropertyDescriptor ?: return null
-        return propertyDescriptor.accessors.singleOrNull {
+        val shortName = signature.accessorSignature.shortName
-            it.name == signature.accessorSignature.declarationFqn.shortName()
+        return propertyDescriptor.accessors.singleOrNull { it.name.asString() == shortName }
-        }
     }
 
     private fun findDescriptorForPublicSignature(signature: IdSignature.PublicSignature): DeclarationDescriptor? {
         val packageDescriptor = moduleDescriptor.getPackage(signature.packageFqName())
-        val pathSegments = signature.declarationFqn.pathSegments()
+        val nameSegments = signature.nameSegments
-        val toplevelDescriptors = packageDescriptor.memberScope.getContributedDescriptors { name -> name == pathSegments.first() }
+        val toplevelDescriptors = packageDescriptor.memberScope.getDescriptorsFiltered { name -> name.asString() == nameSegments.first() }
-            .filter { it.name == pathSegments.first() }
+        val candidates = nameSegments.drop(1).fold(toplevelDescriptors) { acc, current ->
-        val candidates = pathSegments.drop(1).fold(toplevelDescriptors) { acc, current ->
             acc.flatMap { container ->
                 val classDescriptor = container as? ClassDescriptor ?: return@flatMap emptyList()
-                val nextStepCandidates = classDescriptor.constructors +
+                classDescriptor.constructors.filter { it.name.asString() == current } +
-                        classDescriptor.unsubstitutedMemberScope.getContributedDescriptors { name -> name == current }
+                        classDescriptor.unsubstitutedMemberScope.getDescriptorsFiltered { name -> name.asString() == current }
-                nextStepCandidates.filter { it.name == current }
             }
         }
         return candidates.firstOrNull { symbolTable.signaturer.composeSignature(it) == signature }

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/IdSignature.kt

@@ -46,10 +46,16 @@ sealed class IdSignature {
         return "${if (isPublic) "public" else "private"} ${render()}"
     }
 
-    class PublicSignature(val packageFqn: FqName, val declarationFqn: FqName, val id: Long?, val mask: Long) : IdSignature() {
+    class PublicSignature(val packageFqName: String, val declarationFqName: String, val id: Long?, val mask: Long) : IdSignature() {
         override val isPublic = true
 
-        override fun packageFqName() = packageFqn
+        override fun packageFqName(): FqName = FqName(packageFqName)
+
+        val shortName: String get() = declarationFqName.substringAfterLast('.')
+
+        val firstNameSegment: String get() = declarationFqName.substringBefore('.')
+
+        val nameSegments: List<String> get() = declarationFqName.split('.')
 
         private fun adaptMask(old: Long): Long {
             return old xor Flags.values().fold(0L) { a, f ->
@@ -59,35 +65,34 @@ sealed class IdSignature {
         }
 
         override fun topLevelSignature(): IdSignature {
-            if (declarationFqn.isRoot) {
+            if (declarationFqName.isEmpty()) {
                 assert(id == null)
                 // package signature
                 return this
             }
 
-            val pathSegments = declarationFqn.pathSegments()
+            val nameSegments = nameSegments
+            if (nameSegments.size == 1) return this
 
-            if (pathSegments.size == 1) return this
+            return PublicSignature(packageFqName, nameSegments.first(), null, adaptMask(mask))
-
-            return PublicSignature(packageFqn, FqName(pathSegments.first().asString()), null, adaptMask(mask))
         }
 
-        override fun isPackageSignature(): Boolean = id == null && declarationFqn.isRoot
+        override fun isPackageSignature(): Boolean = id == null && declarationFqName.isEmpty()
 
         override fun nearestPublicSig(): PublicSignature = this
 
         override fun flags(): Long = mask
 
-        override fun render(): String = "${packageFqn.asString()}/${declarationFqn.asString()}|$id[${mask.toString(2)}]"
+        override fun render(): String = "$packageFqName/$declarationFqName|$id[${mask.toString(2)}]"
 
         override fun asPublic(): PublicSignature? = this
 
         override fun equals(other: Any?): Boolean =
-            other is PublicSignature &&
+            other is PublicSignature && packageFqName == other.packageFqName && declarationFqName == other.declarationFqName &&
-                    packageFqn == other.packageFqn && declarationFqn == other.declarationFqn && id == other.id && mask == other.mask
+                    id == other.id && mask == other.mask
 
         override fun hashCode(): Int =
-            ((packageFqn.hashCode() * 31 + declarationFqn.hashCode()) * 31 + id.hashCode()) * 31 + mask.hashCode()
+            ((packageFqName.hashCode() * 31 + declarationFqName.hashCode()) * 31 + id.hashCode()) * 31 + mask.hashCode()
     }
 
     class AccessorSignature(val propertySignature: IdSignature, val accessorSignature: PublicSignature) : IdSignature() {
@@ -121,7 +126,7 @@ sealed class IdSignature {
         override fun topLevelSignature(): IdSignature {
             val topLevelContainer = container.topLevelSignature()
             if (topLevelContainer === container) {
-                if (topLevelContainer is PublicSignature && topLevelContainer.declarationFqn.isRoot) {
+                if (topLevelContainer is PublicSignature && topLevelContainer.declarationFqName.isEmpty()) {
                     // private top level
                     return this
                 }

compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/DescriptorByIdSignatureFinder.kt

@@ -9,6 +9,7 @@ import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.descriptors.impl.ModuleDescriptorImpl
 import org.jetbrains.kotlin.ir.util.IdSignature
 import org.jetbrains.kotlin.ir.util.KotlinMangler
+import org.jetbrains.kotlin.resolve.scopes.getDescriptorsFiltered
 
 class DescriptorByIdSignatureFinder(
     private val moduleDescriptor: ModuleDescriptor,
@@ -43,26 +44,25 @@ class DescriptorByIdSignatureFinder(
     private fun findDescriptorForAccessorSignature(signature: IdSignature.AccessorSignature): DeclarationDescriptor? {
         val propertyDescriptor = findDescriptorBySignature(signature.propertySignature) as? PropertyDescriptor
             ?: return null
-        return propertyDescriptor.accessors.singleOrNull {
+        val shortName = signature.accessorSignature.shortName
-            it.name == signature.accessorSignature.declarationFqn.shortName()
+        return propertyDescriptor.accessors.singleOrNull { it.name.asString() == shortName }
-        }
     }
 
     private fun performLookup(signature: IdSignature.PublicSignature): Collection<DeclarationDescriptor> {
-        val declarationName = signature.declarationFqn.pathSegments().first()
+        val declarationName = signature.firstNameSegment
         return when (lookupMode) {
             LookupMode.MODULE_WITH_DEPENDENCIES -> {
                 moduleDescriptor
                     .getPackage(signature.packageFqName())
                     .memberScope
-                    .getContributedDescriptors { name -> name == declarationName }
+                    .getContributedDescriptors { name -> name.asString() == declarationName }
             }
             LookupMode.MODULE_ONLY -> {
                 (moduleDescriptor as ModuleDescriptorImpl)
                     .packageFragmentProviderForModuleContentWithoutDependencies
                     .getPackageFragments(signature.packageFqName())
                     .map { it.getMemberScope() }
-                    .flatMap { it.getContributedDescriptors { name -> name == declarationName } }
+                    .flatMap { it.getContributedDescriptors { name -> name.asString() == declarationName } }
             }
         }
     }
@@ -70,16 +70,13 @@ class DescriptorByIdSignatureFinder(
     private fun findDescriptorForPublicSignature(signature: IdSignature.PublicSignature): DeclarationDescriptor? {
         val toplevelDescriptors = performLookup(signature)
             .ifEmpty { return null }
-        val pathSegments = signature.declarationFqn.pathSegments()
+        val candidates = signature.nameSegments.drop(1).fold(toplevelDescriptors) { acc, current ->
-        val candidates = pathSegments.drop(1).fold(toplevelDescriptors) { acc, current ->
             acc.flatMap { container ->
-                val classDescriptor = container as? ClassDescriptor
+                val classDescriptor = container as? ClassDescriptor ?: return@flatMap emptyList<DeclarationDescriptor>()
-                    ?: return@flatMap emptyList<DeclarationDescriptor>()
+                classDescriptor.constructors.filter { it.name.asString() == current } +
-                val nextStepCandidates = classDescriptor.constructors +
+                        classDescriptor.unsubstitutedMemberScope.getDescriptorsFiltered { name -> name.asString() == current } +
-                        classDescriptor.unsubstitutedMemberScope.getContributedDescriptors { name -> name == current } +
                         // Static scope is required only for Enum.values() and Enum.valueOf().
-                        classDescriptor.staticScope.getContributedDescriptors { name -> name == current }
+                        classDescriptor.staticScope.getDescriptorsFiltered { name -> name.asString() == current }
-                nextStepCandidates.filter { it.name == current }
             }
         }
 
@@ -102,4 +99,4 @@ class DescriptorByIdSignatureFinder(
                 candidateHash == id
             }
         }
-}
+}

compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/FunctionalInterfacesUtils.kt

@@ -5,14 +5,8 @@
 
 package org.jetbrains.kotlin.backend.common.serialization
 
-import org.jetbrains.kotlin.name.FqName
-import org.jetbrains.kotlin.name.Name
 import java.util.regex.Pattern
 
 internal val functionPattern = Pattern.compile("^K?(Suspend)?Function\\d+$")
 
-internal val kotlinFqn = FqName("kotlin")
+internal val functionalPackages = listOf("kotlin", "kotlin.coroutines", "kotlin.reflect")
-internal val kotlinCoroutinesFqn = kotlinFqn.child(Name.identifier("coroutines"))
-internal val kotlinReflectFqn = kotlinFqn.child(Name.identifier("reflect"))
-
-internal val functionalPackages = listOf(kotlinFqn, kotlinCoroutinesFqn, kotlinReflectFqn)

compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IrFileDeserializer.kt

@@ -12,12 +12,12 @@ import org.jetbrains.kotlin.backend.common.peek
 import org.jetbrains.kotlin.backend.common.pop
 import org.jetbrains.kotlin.backend.common.push
 import org.jetbrains.kotlin.backend.common.serialization.encodings.*
+import org.jetbrains.kotlin.backend.common.serialization.proto.IdSignature.IdsigCase.*
 import org.jetbrains.kotlin.backend.common.serialization.proto.IrConst.ValueCase.*
 import org.jetbrains.kotlin.backend.common.serialization.proto.IrDeclaration.DeclaratorCase.*
 import org.jetbrains.kotlin.backend.common.serialization.proto.IrOperation.OperationCase.*
 import org.jetbrains.kotlin.backend.common.serialization.proto.IrStatement.StatementCase
 import org.jetbrains.kotlin.backend.common.serialization.proto.IrType.KindCase.*
-import org.jetbrains.kotlin.backend.common.serialization.proto.IdSignature.IdsigCase.*
 import org.jetbrains.kotlin.backend.common.serialization.proto.IrVarargElement.VarargElementCase
 import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.IrStatement
@@ -30,9 +30,11 @@ import org.jetbrains.kotlin.ir.symbols.*
 import org.jetbrains.kotlin.ir.types.*
 import org.jetbrains.kotlin.ir.types.impl.*
 import org.jetbrains.kotlin.ir.util.*
-import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.types.Variance
+import org.jetbrains.kotlin.backend.common.serialization.proto.AccessorIdSignature as ProtoAccessorIdSignature
+import org.jetbrains.kotlin.backend.common.serialization.proto.FileLocalIdSignature as ProtoFileLocalIdSignature
+import org.jetbrains.kotlin.backend.common.serialization.proto.IdSignature as ProtoIdSignature
 import org.jetbrains.kotlin.backend.common.serialization.proto.IrAnonymousInit as ProtoAnonymousInit
 import org.jetbrains.kotlin.backend.common.serialization.proto.IrBlock as ProtoBlock
 import org.jetbrains.kotlin.backend.common.serialization.proto.IrBlockBody as ProtoBlockBody
@@ -99,10 +101,7 @@ import org.jetbrains.kotlin.backend.common.serialization.proto.IrWhen as ProtoWh
 import org.jetbrains.kotlin.backend.common.serialization.proto.IrWhile as ProtoWhile
 import org.jetbrains.kotlin.backend.common.serialization.proto.Loop as ProtoLoop
 import org.jetbrains.kotlin.backend.common.serialization.proto.MemberAccessCommon as ProtoMemberAccessCommon
-import org.jetbrains.kotlin.backend.common.serialization.proto.IdSignature as ProtoIdSignature
 import org.jetbrains.kotlin.backend.common.serialization.proto.PublicIdSignature as ProtoPublicIdSignature
-import org.jetbrains.kotlin.backend.common.serialization.proto.AccessorIdSignature as ProtoAccessorIdSignature
-import org.jetbrains.kotlin.backend.common.serialization.proto.FileLocalIdSignature as ProtoFileLocalIdSignature
 
 abstract class IrFileDeserializer(val logger: LoggingContext, val builtIns: IrBuiltIns, val symbolTable: SymbolTable, var constructFakeOverrides: Boolean, protected var deserializeBodies: Boolean) {
 
@@ -122,11 +121,8 @@ abstract class IrFileDeserializer(val logger: LoggingContext, val builtIns: IrBu
 
     abstract val deserializeInlineFunctions: Boolean
 
-    fun deserializeFqName(fqn: List<Int>): FqName {
+    fun deserializeFqName(fqn: List<Int>): String =
-        return fqn.run {
+        fqn.joinToString(".", transform = ::deserializeString)
-            if (isEmpty()) FqName.ROOT else FqName.fromSegments(map { deserializeString(it) })
-        }
-    }
 
     private fun deserializeIrSymbolAndRemap(code: Long): IrSymbol {
         // TODO: could be simplified
@@ -224,9 +220,8 @@ abstract class IrFileDeserializer(val logger: LoggingContext, val builtIns: IrBu
         val hash = proto.accessorHashId
         val mask = proto.flags
 
-        val accessorSignature = with(propertySignature) {
+        val accessorSignature =
-            IdSignature.PublicSignature(packageFqn, declarationFqn.child(Name.special(name)), hash, mask)
+            IdSignature.PublicSignature(propertySignature.packageFqName, "${propertySignature.declarationFqName}.$name", hash, mask)
-        }
 
         return IdSignature.AccessorSignature(propertySignature, accessorSignature)
     }

compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IrFileSerializer.kt

@@ -184,8 +184,8 @@ open class IrFileSerializer(
 
     private fun serializePublicSignature(signature: IdSignature.PublicSignature): ProtoPublicIdSignature {
         val proto = ProtoPublicIdSignature.newBuilder()
-        proto.addAllPackageFqName(serializeFqName(signature.packageFqn))
+        proto.addAllPackageFqName(serializeFqName(signature.packageFqName))
-        proto.addAllDeclarationFqName(serializeFqName(signature.declarationFqn))
+        proto.addAllDeclarationFqName(serializeFqName(signature.declarationFqName))
 
         signature.id?.let { proto.memberUniqId = it }
         if (signature.mask != 0L) {
@@ -200,7 +200,7 @@ open class IrFileSerializer(
 
         proto.propertySignature = protoIdSignature(signature.propertySignature)
         with(signature.accessorSignature) {
-            proto.name = serializeString(declarationFqn.shortName().asString())
+            proto.name = serializeString(shortName)
             proto.accessorHashId = id ?: error("Expected hash Id")
             if (mask != 0L) {
                 proto.flags = mask
@@ -297,7 +297,7 @@ open class IrFileSerializer(
     private fun serializeAnnotations(annotations: List<IrConstructorCall>) =
         annotations.map { serializeConstructorCall(it) }
 
-    private fun serializeFqName(fqName: FqName) = fqName.pathSegments().map { serializeString(it.asString()) }
+    private fun serializeFqName(fqName: String): List<Int> = fqName.split(".").map(::serializeString)
 
     private fun serializeIrStarProjection() = BinaryTypeProjection.STAR_CODE
 
@@ -1228,7 +1228,7 @@ open class IrFileSerializer(
 
         val proto = ProtoFile.newBuilder()
             .setFileEntry(serializeFileEntry(file.fileEntry))
-            .addAllFqName(serializeFqName(file.fqName))
+            .addAllFqName(serializeFqName(file.fqName.asString()))
             .addAllAnnotation(serializeAnnotations(file.annotations))
 
         file.declarations.forEach {

compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/IrModuleDeserializer.kt

@@ -7,16 +7,17 @@ package org.jetbrains.kotlin.backend.common.serialization
 
 import org.jetbrains.kotlin.backend.common.serialization.encodings.BinarySymbolData
 import org.jetbrains.kotlin.builtins.functions.FunctionClassDescriptor
-import org.jetbrains.kotlin.descriptors.*
+import org.jetbrains.kotlin.descriptors.ModuleDescriptor
-import org.jetbrains.kotlin.ir.declarations.*
+import org.jetbrains.kotlin.ir.declarations.IrDeclarationWithName
+import org.jetbrains.kotlin.ir.declarations.IrModuleFragment
+import org.jetbrains.kotlin.ir.declarations.IrProperty
+import org.jetbrains.kotlin.ir.declarations.IrSymbolOwner
 import org.jetbrains.kotlin.ir.descriptors.IrAbstractFunctionFactory
 import org.jetbrains.kotlin.ir.descriptors.IrBuiltIns
 import org.jetbrains.kotlin.ir.descriptors.WrappedDeclarationDescriptor
 import org.jetbrains.kotlin.ir.symbols.*
 import org.jetbrains.kotlin.ir.util.IdSignature
 import org.jetbrains.kotlin.library.IrLibrary
-import org.jetbrains.kotlin.name.FqName
-import org.jetbrains.kotlin.name.Name
 
 internal fun IrSymbol.kind(): BinarySymbolData.SymbolKind {
     return when (this) {
@@ -81,19 +82,11 @@ class IrModuleDeserializerWithBuiltIns(
     }.toMap()
 
     private fun checkIsFunctionInterface(idSig: IdSignature): Boolean {
-        val publicSig = idSig.asPublic() ?: return false
+        val publicSig = idSig.asPublic()
-
+        return publicSig != null &&
-        if (publicSig.packageFqn !in functionalPackages) return false
+                publicSig.packageFqName in functionalPackages &&
-
+                publicSig.declarationFqName.isNotEmpty() &&
-        val declarationFqn = publicSig.declarationFqn
+                functionPattern.matcher(publicSig.firstNameSegment).find()
-
-        if (declarationFqn.isRoot) return false
-
-        val fqnParts = declarationFqn.pathSegments()
-
-        val className = fqnParts.first()
-
-        return functionPattern.matcher(className.asString()).find()
     }
 
     override operator fun contains(idSig: IdSignature): Boolean {
@@ -106,11 +99,10 @@ class IrModuleDeserializerWithBuiltIns(
         delegate.deserializeReachableDeclarations()
     }
 
-    private fun computeFunctionDescriptor(className: Name): FunctionClassDescriptor {
+    private fun computeFunctionDescriptor(className: String): FunctionClassDescriptor {
-        val nameString = className.asString()
+        val isK = className[0] == 'K'
-        val isK = nameString[0] == 'K'
+        val isSuspend = (if (isK) className[1] else className[0]) == 'S'
-        val isSuspend = (if (isK) nameString[1] else nameString[0]) == 'S'
+        val arity = className.run { substring(indexOfFirst { it.isDigit() }).toInt(10) }
-        val arity = nameString.run { substring(indexOfFirst { it.isDigit() }).toInt(10) }
         return functionFactory.run {
             when {
                 isK && isSuspend -> kSuspendFunctionClassDescriptor(arity)
@@ -124,11 +116,11 @@ class IrModuleDeserializerWithBuiltIns(
     private fun resolveFunctionalInterface(idSig: IdSignature, symbolKind: BinarySymbolData.SymbolKind): IrSymbol {
         val publicSig = idSig.asPublic() ?: error("$idSig has to be public")
 
-        val fqnParts = publicSig.declarationFqn.pathSegments()
+        val fqnParts = publicSig.nameSegments
         val className = fqnParts.firstOrNull() ?: error("Expected class name for $idSig")
 
         val functionDescriptor = computeFunctionDescriptor(className)
-        val topLevelSignature = IdSignature.PublicSignature(publicSig.packageFqn, FqName(className.asString()), null, publicSig.mask)
+        val topLevelSignature = IdSignature.PublicSignature(publicSig.packageFqName, className, null, publicSig.mask)
 
         val functionClass = when (functionDescriptor.functionKind) {
             FunctionClassDescriptor.Kind.KSuspendFunction -> functionFactory.kSuspendFunctionN(functionDescriptor.arity) { callback ->
@@ -148,19 +140,19 @@ class IrModuleDeserializerWithBuiltIns(
         return when (fqnParts.size) {
             1 -> functionClass.symbol.also { assert(symbolKind == BinarySymbolData.SymbolKind.CLASS_SYMBOL) }
             2 -> {
-                val memberName = fqnParts[1]!!
+                val memberName = fqnParts[1]
-                functionClass.declarations.single { it is IrDeclarationWithName && it.name == memberName }.let {
+                functionClass.declarations.single { it is IrDeclarationWithName && it.name.asString() == memberName }.let {
                     (it as IrSymbolOwner).symbol
                 }
             }
             3 -> {
                 assert(idSig is IdSignature.AccessorSignature)
                 assert(symbolKind == BinarySymbolData.SymbolKind.FUNCTION_SYMBOL)
-                val propertyName = fqnParts[1]!!
+                val propertyName = fqnParts[1]
-                val accessorName = fqnParts[2]!!
+                val accessorName = fqnParts[2]
-                functionClass.declarations.filterIsInstance<IrProperty>().single { it.name == propertyName }.let { p ->
+                functionClass.declarations.filterIsInstance<IrProperty>().single { it.name.asString() == propertyName }.let { p ->
-                    p.getter?.let { g -> if (g.name == accessorName) return g.symbol }
+                    p.getter?.let { g -> if (g.name.asString() == accessorName) return g.symbol }
-                    p.setter?.let { s -> if (s.name == accessorName) return s.symbol }
+                    p.setter?.let { s -> if (s.name.asString() == accessorName) return s.symbol }
                     error("No accessor found for signature $idSig")
                 }
             }

compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/KotlinIrLinker.kt

@@ -32,6 +32,7 @@ import org.jetbrains.kotlin.ir.util.NaiveSourceBasedFileEntryImpl
 import org.jetbrains.kotlin.ir.util.SymbolTable
 import org.jetbrains.kotlin.library.IrLibrary
 import org.jetbrains.kotlin.library.KotlinLibrary
+import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.protobuf.CodedInputStream
 import org.jetbrains.kotlin.protobuf.ExtensionRegistryLite.newInstance
 import org.jetbrains.kotlin.resolve.descriptorUtil.module
@@ -173,7 +174,7 @@ abstract class KotlinIrLinker(
                     }
                 }
 
-            val fqName = fileDeserializer.deserializeFqName(fileProto.fqNameList)
+            val fqName = FqName(fileDeserializer.deserializeFqName(fileProto.fqNameList))
 
             val packageFragmentDescriptor = EmptyPackageFragmentDescriptor(moduleDescriptor, fqName)
 

compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/signature/IdSignatureBuilder.kt

@@ -26,10 +26,12 @@ abstract class IdSignatureBuilder<D> {
     }
 
     protected fun build(): IdSignature {
+        val packageFqName = packageFqn.asString()
+        val classFqName = classFqnSegments.joinToString(".")
         return if (hashIdAcc == null) {
-            IdSignature.PublicSignature(packageFqn, FqName.fromSegments(classFqnSegments), hashId, mask)
+            IdSignature.PublicSignature(packageFqName, classFqName, hashId, mask)
         } else {
-            val accessorSignature = IdSignature.PublicSignature(packageFqn, FqName.fromSegments(classFqnSegments), hashIdAcc, mask)
+            val accessorSignature = IdSignature.PublicSignature(packageFqName, classFqName, hashIdAcc, mask)
             hashIdAcc = null
             classFqnSegments.run { removeAt(lastIndex) }
             val propertySignature = build()

compiler/ir/serialization.common/src/org/jetbrains/kotlin/backend/common/serialization/signature/IdSignatureSerializer.kt

@@ -13,7 +13,6 @@ import org.jetbrains.kotlin.ir.util.KotlinMangler
 import org.jetbrains.kotlin.ir.util.render
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitorVoid
 import org.jetbrains.kotlin.ir.visitors.acceptVoid
-import org.jetbrains.kotlin.name.FqName
 
 open class IdSignatureSerializer(val mangler: KotlinMangler.IrMangler) : IdSignatureComputer {
 
@@ -96,11 +95,12 @@ open class IdSignatureSerializer(val mangler: KotlinMangler.IrMangler) : IdSigna
 
     private val publicSignatureBuilder = PublicIdSigBuilder()
 
-    private fun composeContainerIdSignature(container: IrDeclarationParent): IdSignature {
+    private fun composeContainerIdSignature(container: IrDeclarationParent): IdSignature =
-        if (container is IrPackageFragment) return IdSignature.PublicSignature(container.fqName, FqName.ROOT, null, 0)
+        when (container) {
-        if (container is IrDeclaration) return table.signatureByDeclaration(container)
+            is IrPackageFragment -> IdSignature.PublicSignature(container.fqName.asString(), "", null, 0)
-        error("Unexpected container ${container.render()}")
+            is IrDeclaration -> table.signatureByDeclaration(container)
-    }
+            else -> error("Unexpected container ${container.render()}")
+        }
 
     fun composePublicIdSignature(declaration: IrDeclaration): IdSignature {
         assert(mangler.run { declaration.isExported() }) {
@@ -130,4 +130,4 @@ open class IdSignatureSerializer(val mangler: KotlinMangler.IrMangler) : IdSigna
             }
         }
     }
-}
+}