[IR] Unify MFVC bridge redirection, fix related bugs, support MFVC overriding functions with default parameters

#KT-1179

compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirLightTreeBlackBoxCodegenTestGenerated.java

@@ -52095,6 +52095,12 @@ public class FirLightTreeBlackBoxCodegenTestGenerated extends AbstractFirLightTr
             runTest("compiler/testData/codegen/box/valueClasses/mutableSharedMfvcVar.kt");
         }
 
+        @Test
+        @TestMetadata("nothingAsParameterType.kt")
+        public void testNothingAsParameterType() throws Exception {
+            runTest("compiler/testData/codegen/box/valueClasses/nothingAsParameterType.kt", TransformersFunctions.getReplaceOptionalJvmInlineAnnotationWithReal());
+        }
+
         @Test
         @TestMetadata("overrideFunctionWithDefaultParameter.kt")
         public void testOverrideFunctionWithDefaultParameter() throws Exception {

compiler/fir/fir2ir/tests-gen/org/jetbrains/kotlin/test/runners/codegen/FirPsiBlackBoxCodegenTestGenerated.java

@@ -52095,6 +52095,12 @@ public class FirPsiBlackBoxCodegenTestGenerated extends AbstractFirPsiBlackBoxCo
             runTest("compiler/testData/codegen/box/valueClasses/mutableSharedMfvcVar.kt");
         }
 
+        @Test
+        @TestMetadata("nothingAsParameterType.kt")
+        public void testNothingAsParameterType() throws Exception {
+            runTest("compiler/testData/codegen/box/valueClasses/nothingAsParameterType.kt", TransformersFunctions.getReplaceOptionalJvmInlineAnnotationWithReal());
+        }
+
         @Test
         @TestMetadata("overrideFunctionWithDefaultParameter.kt")
         public void testOverrideFunctionWithDefaultParameter() throws Exception {

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

@@ -5,11 +5,10 @@
 
 package org.jetbrains.kotlin.backend.common.lower
 
-import org.jetbrains.kotlin.backend.common.BodyLoweringPass
-import org.jetbrains.kotlin.backend.common.CommonBackendContext
-import org.jetbrains.kotlin.backend.common.DeclarationTransformer
+import org.jetbrains.kotlin.backend.common.*
 import org.jetbrains.kotlin.backend.common.descriptors.synthesizedString
 import org.jetbrains.kotlin.backend.common.ir.ValueRemapper
+import org.jetbrains.kotlin.backend.common.lower.isMovedReceiver
 import org.jetbrains.kotlin.descriptors.DescriptorVisibilities
 import org.jetbrains.kotlin.ir.UNDEFINED_OFFSET
 import org.jetbrains.kotlin.ir.builders.*
@@ -30,6 +29,7 @@ import org.jetbrains.kotlin.ir.visitors.IrElementTransformerVoid
 import org.jetbrains.kotlin.ir.visitors.transformChildrenVoid
 import org.jetbrains.kotlin.util.OperatorNameConventions
 import org.jetbrains.kotlin.utils.memoryOptimizedPlus
+import org.jetbrains.kotlin.backend.common.lower.isMovedReceiver as isMovedReceiverImpl
 
 // TODO: fix expect/actual default parameters
 
@@ -263,8 +263,11 @@ open class DefaultParameterInjector<TContext : CommonBackendContext>(
     protected val forceSetOverrideSymbols: Boolean = true,
 ) : IrElementTransformerVoid(), BodyLoweringPass {
 
+    private val declarationStack = mutableListOf<IrDeclaration>()
     override fun lower(irBody: IrBody, container: IrDeclaration) {
+        declarationStack.push(container)
         irBody.transformChildrenVoid(this)
+        declarationStack.pop()
     }
 
     protected open fun shouldReplaceWithSyntheticFunction(functionAccess: IrFunctionAccessExpression): Boolean {
@@ -275,50 +278,44 @@ open class DefaultParameterInjector<TContext : CommonBackendContext>(
         if (!shouldReplaceWithSyntheticFunction(expression))
             return expression
 
-        val (symbol, params) = parametersForCall(expression) ?: return expression
+        val symbol = createStubFunction(expression) ?: return expression
         for (i in 0 until expression.typeArgumentsCount) {
             log { "$symbol[$i]: ${expression.getTypeArgument(i)}" }
         }
-        symbol.owner.typeParameters.forEach { log { "${symbol.owner}[${it.index}] : $it" } }
+        val stubFunction = symbol.owner
+        stubFunction.typeParameters.forEach { log { "$stubFunction[${it.index}] : $it" } }
 
-        val isStatic = isStatic(expression.symbol.owner)
-
-        val newCall = builder(symbol).apply {
-            copyTypeArgumentsFrom(expression)
-
-            var receivers = 0
-
-            if (isStatic) {
-                if (symbol.owner.dispatchReceiverParameter != null) {
-                    dispatchReceiver = params[receivers++]
+        val declaration = expression.symbol.owner
+        val currentDeclaration = declarationStack.last()
+        return context.createIrBuilder(
+            currentDeclaration.symbol, startOffset = expression.startOffset, endOffset = expression.endOffset
+        ).irBlock {
+            val newCall = builder(symbol).apply {
+                val offset = if (needsTypeArgumentOffset(declaration)) declaration.parentAsClass.typeParameters.size else 0
+                for (i in 0 until typeArgumentsCount) {
+                    putTypeArgument(i, expression.getTypeArgument(i + offset))
                 }
-                if (symbol.owner.extensionReceiverParameter != null) {
-                    extensionReceiver = params[receivers++]
+                val parameter2arguments = argumentsForCall(expression, stubFunction)
+
+                for ((parameter, argument) in parameter2arguments) {
+                    when (parameter) {
+                        stubFunction.dispatchReceiverParameter -> log { "call::dispatch@: ${ir2string(argument)}" }
+                        stubFunction.extensionReceiverParameter -> log { "call::extension@: ${ir2string(argument)}" }
+                        else -> log { "call::params@$${parameter.index}/${parameter.name}: ${ir2string(argument)}" }
+                    }
+                    if (argument != null) {
+                        putArgument(parameter, argument)
+                    }
                 }
-            } else {
-                dispatchReceiver = expression.dispatchReceiver
-                extensionReceiver = expression.extensionReceiver
             }
 
-            params.drop(receivers).forEachIndexed { i, value ->
-                log { "call::params@$i/${symbol.owner.valueParameters[i].name}: ${ir2string(value)}" }
-                putValueArgument(i, value)
-            }
-
-            log { "call::extension@: ${ir2string(expression.extensionReceiver)}" }
-            log { "call::dispatch@: ${ir2string(expression.dispatchReceiver)}" }
-        }
-
-        return newCall.takeIf { it.type == expression.type } ?: IrTypeOperatorCallImpl(
-            startOffset = newCall.startOffset,
-            endOffset = newCall.endOffset,
-            type = expression.type,
-            operator = IrTypeOperator.IMPLICIT_CAST,
-            typeOperand = expression.type,
-            argument = newCall
-        )
+            +irCastIfNeeded(newCall, expression.type)
+        }.unwrapBlock()
     }
 
+    private fun needsTypeArgumentOffset(declaration: IrFunction) =
+        isStatic(declaration) && declaration.parentAsClass.isMultiFieldValueClass && declaration is IrSimpleFunction
+
     override fun visitDelegatingConstructorCall(expression: IrDelegatingConstructorCall): IrExpression {
         expression.transformChildrenVoid()
         return visitFunctionAccessExpression(expression) {
@@ -362,11 +359,13 @@ open class DefaultParameterInjector<TContext : CommonBackendContext>(
 
     override fun visitCall(expression: IrCall): IrExpression {
         expression.transformChildrenVoid()
+        val declaration = expression.symbol.owner
+        val typeParametersToRemove = if (needsTypeArgumentOffset(declaration)) declaration.parentAsClass.typeParameters.size else 0
         with(expression) {
             return visitFunctionAccessExpression(expression) {
                 IrCallImpl(
                     startOffset, endOffset, (it as IrSimpleFunctionSymbol).owner.returnType, it,
-                    typeArgumentsCount = typeArgumentsCount,
+                    typeArgumentsCount = typeArgumentsCount - typeParametersToRemove,
                     valueArgumentsCount = it.owner.valueParameters.size,
                     origin = LoweredStatementOrigins.DEFAULT_DISPATCH_CALL,
                     superQualifierSymbol = superQualifierSymbol
@@ -375,9 +374,7 @@ open class DefaultParameterInjector<TContext : CommonBackendContext>(
         }
     }
 
-    open protected fun parametersForCall(expression: IrFunctionAccessExpression): Pair<IrFunctionSymbol, List<IrExpression?>>? {
-        val startOffset = expression.startOffset
-        val endOffset = expression.endOffset
+    private fun createStubFunction(expression: IrFunctionAccessExpression): IrFunctionSymbol? {
         val declaration = expression.symbol.owner
 
         // We *have* to find the actual function here since on the JVM, a default stub for a function implemented
@@ -396,8 +393,14 @@ open class DefaultParameterInjector<TContext : CommonBackendContext>(
                 baseFunction.copyAnnotations(),
             )
         } ?: return null
-
         log { "$declaration -> $stubFunction" }
+        return stubFunction.symbol
+    }
+
+    protected open fun IrBlockBuilder.argumentsForCall(expression: IrFunctionAccessExpression, stubFunction: IrFunction): Map<IrValueParameter, IrExpression?> {
+        val startOffset = expression.startOffset
+        val endOffset = expression.endOffset
+        val declaration = expression.symbol.owner
 
         val realArgumentsNumber = declaration.valueParameters.filterNot { it.isMovedReceiver() }.size
         val maskValues = IntArray((realArgumentsNumber + 31) / 32)
@@ -408,32 +411,48 @@ open class DefaultParameterInjector<TContext : CommonBackendContext>(
         }
 
         var sourceParameterIndex = -1
-        val valueParametersPrefix =
-            if (isStatic(declaration))
+        return buildMap {
+            val valueParametersPrefix: List<IrValueParameter> = if (isStatic(declaration)) {
                 listOfNotNull(stubFunction.dispatchReceiverParameter, stubFunction.extensionReceiverParameter)
-            else emptyList()
-        return stubFunction.symbol to (valueParametersPrefix + stubFunction.valueParameters).mapIndexed { i, parameter ->
-            if (!parameter.isMovedReceiver() && parameter != stubFunction.dispatchReceiverParameter && parameter != stubFunction.extensionReceiverParameter) {
-                ++sourceParameterIndex
+            } else {
+                stubFunction.dispatchReceiverParameter?.let { put(it, expression.dispatchReceiver) }
+                stubFunction.extensionReceiverParameter?.let { put(it, expression.extensionReceiver) }
+                listOf()
             }
-            when {
-                sourceParameterIndex >= realArgumentsNumber + maskValues.size -> IrConstImpl.constNull(startOffset, endOffset, parameter.type)
-                sourceParameterIndex >= realArgumentsNumber -> IrConstImpl.int(startOffset, endOffset, parameter.type, maskValues[sourceParameterIndex - realArgumentsNumber])
-                else -> {
-                    val valueArgument = expression.getValueArgument(i)
-                    if (valueArgument == null) {
-                        maskValues[sourceParameterIndex / 32] = maskValues[sourceParameterIndex / 32] or (1 shl (sourceParameterIndex % 32))
-                    }
-                    valueArgument ?: nullConst(startOffset, endOffset, parameter)?.let {
-                        IrCompositeImpl(
-                            expression.startOffset,
-                            expression.endOffset,
-                            parameter.type,
-                            IrStatementOrigin.DEFAULT_VALUE,
-                            listOf(it)
-                        )
+            for ((i, parameter) in (valueParametersPrefix + stubFunction.valueParameters).withIndex()) {
+                if (!parameter.isMovedReceiver() && parameter != stubFunction.dispatchReceiverParameter && parameter != stubFunction.extensionReceiverParameter) {
+                    ++sourceParameterIndex
+                }
+                val newArgument = when {
+                    sourceParameterIndex >= realArgumentsNumber + maskValues.size -> IrConstImpl.constNull(
+                        startOffset,
+                        endOffset,
+                        parameter.type
+                    )
+                    sourceParameterIndex >= realArgumentsNumber -> IrConstImpl.int(
+                        startOffset,
+                        endOffset,
+                        parameter.type,
+                        maskValues[sourceParameterIndex - realArgumentsNumber]
+                    )
+                    else -> {
+                        val valueArgument = expression.getValueArgument(i)
+                        if (valueArgument == null) {
+                            maskValues[sourceParameterIndex / 32] =
+                                maskValues[sourceParameterIndex / 32] or (1 shl (sourceParameterIndex % 32))
+                        }
+                        valueArgument ?: nullConst(startOffset, endOffset, parameter)?.let {
+                            IrCompositeImpl(
+                                expression.startOffset,
+                                expression.endOffset,
+                                parameter.type,
+                                IrStatementOrigin.DEFAULT_VALUE,
+                                listOf(it)
+                            )
+                        }
                     }
                 }
+                put(parameter, newArgument)
             }
         }
     }
@@ -455,6 +474,8 @@ open class DefaultParameterInjector<TContext : CommonBackendContext>(
     protected open fun isStatic(function: IrFunction): Boolean = false
 
     private fun log(msg: () -> String) = context.log { "DEFAULT-INJECTOR: ${msg()}" }
+
+    protected fun IrValueParameter.isMovedReceiver() = isMovedReceiverImpl()
 }
 
 // Remove default argument initializers.

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

@@ -374,6 +374,7 @@ class InlineClassLowering(val context: CommonBackendContext) {
             function.parent,
             function.toInlineClassImplementationName(),
             function,
-            typeParametersFromContext = extractTypeParameters(function.parentAsClass)
+            typeParametersFromContext = extractTypeParameters(function.parentAsClass),
+            remapMultiFieldValueClassStructure = context::remapMultiFieldValueClassStructure
         )
 }

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/JsDefaultParameterInjector.kt

@@ -5,14 +5,15 @@
 
 package org.jetbrains.kotlin.ir.backend.js.lower
 
-import org.jetbrains.kotlin.ir.backend.js.JsIrBackendContext
 import org.jetbrains.kotlin.backend.common.lower.DefaultParameterInjector
 import org.jetbrains.kotlin.ir.UNDEFINED_OFFSET
+import org.jetbrains.kotlin.ir.backend.js.JsIrBackendContext
 import org.jetbrains.kotlin.ir.backend.js.JsLoweredDeclarationOrigin
 import org.jetbrains.kotlin.ir.backend.js.JsStatementOrigins
 import org.jetbrains.kotlin.ir.backend.js.export.isExported
 import org.jetbrains.kotlin.ir.backend.js.utils.getVoid
 import org.jetbrains.kotlin.ir.backend.js.utils.jsConstructorReference
+import org.jetbrains.kotlin.ir.builders.IrBlockBuilder
 import org.jetbrains.kotlin.ir.declarations.IrFunction
 import org.jetbrains.kotlin.ir.declarations.IrValueParameter
 import org.jetbrains.kotlin.ir.expressions.IrCall
@@ -20,8 +21,6 @@ import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrFunctionAccessExpression
 import org.jetbrains.kotlin.ir.expressions.impl.IrCallImpl
 import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
-import org.jetbrains.kotlin.ir.symbols.IrFunctionSymbol
-import org.jetbrains.kotlin.ir.util.copyAnnotations
 import org.jetbrains.kotlin.ir.util.isTopLevel
 import org.jetbrains.kotlin.ir.util.isVararg
 
@@ -48,32 +47,24 @@ class JsDefaultParameterInjector(context: JsIrBackendContext) :
         }
     }
 
-    override fun parametersForCall(expression: IrFunctionAccessExpression): Pair<IrFunctionSymbol, List<IrExpression?>>? {
+    override fun IrBlockBuilder.argumentsForCall(expression: IrFunctionAccessExpression, stubFunction: IrFunction): Map<IrValueParameter, IrExpression?> {
         val startOffset = expression.startOffset
         val endOffset = expression.endOffset
-        val declaration = expression.symbol.owner
 
-        val stubFunction = factory.findBaseFunctionWithDefaultArgumentsFor(declaration, skipInline, skipExternalMethods)?.let {
-            factory.generateDefaultsFunction(
-                it,
-                skipInline,
-                skipExternalMethods,
-                forceSetOverrideSymbols,
-                defaultArgumentStubVisibility(declaration),
-                useConstructorMarker(declaration),
-                it.copyAnnotations(),
-            )
-        } ?: return null
-
-        return stubFunction.symbol to buildList {
+        return buildMap {
+            stubFunction.dispatchReceiverParameter?.let { put(it, expression.dispatchReceiver) }
+            stubFunction.extensionReceiverParameter?.let { put(it, expression.extensionReceiver) }
             for (i in 0 until expression.valueArgumentsCount) {
                 val declaredParameter = stubFunction.valueParameters[i]
-                val actualParameter = expression.getValueArgument(i)
-                add(actualParameter ?: nullConst(startOffset, endOffset, declaredParameter))
+                val actualArgument = expression.getValueArgument(i)
+                put(declaredParameter, actualArgument ?: nullConst(startOffset, endOffset, declaredParameter))
             }
 
             if (expression is IrCall && stubFunction.hasSuperContextParameter()) {
-                add(expression.superQualifierSymbol?.prototypeOf() ?: context.getVoid())
+                put(
+                    stubFunction.valueParameters[expression.valueArgumentsCount],
+                    expression.superQualifierSymbol?.prototypeOf() ?: this@JsDefaultParameterInjector.context.getVoid()
+                )
             }
         }
     }

compiler/ir/backend.jvm/lower/src/org/jetbrains/kotlin/backend/jvm/lower/AddContinuationLowering.kt

@@ -226,7 +226,8 @@ private class AddContinuationLowering(context: JvmBackendContext) : SuspendLower
                 JavaDescriptorVisibilities.PACKAGE_VISIBILITY,
             isFakeOverride = false,
             copyMetadata = false,
-            typeParametersFromContext = extractTypeParameters(irFunction.parentAsClass)
+            typeParametersFromContext = extractTypeParameters(irFunction.parentAsClass),
+            remapMultiFieldValueClassStructure = context::remapMultiFieldValueClassStructure
         )
         static.body = irFunction.moveBodyTo(static)
         // Fixup dispatch parameter to outer class

compiler/ir/backend.jvm/lower/src/org/jetbrains/kotlin/backend/jvm/lower/BridgeLowering.kt

@@ -10,9 +10,10 @@ import org.jetbrains.kotlin.backend.common.lower.SpecialMethodWithDefaultInfo
 import org.jetbrains.kotlin.backend.common.lower.createIrBuilder
 import org.jetbrains.kotlin.backend.common.lower.irNot
 import org.jetbrains.kotlin.backend.common.phaser.makeIrFilePhase
-import org.jetbrains.kotlin.backend.jvm.*
-import org.jetbrains.kotlin.backend.jvm.MemoizedMultiFieldValueClassReplacements.RemappedParameter.MultiFieldValueClassMapping
-import org.jetbrains.kotlin.backend.jvm.MemoizedMultiFieldValueClassReplacements.RemappedParameter.RegularMapping
+import org.jetbrains.kotlin.backend.jvm.JvmBackendContext
+import org.jetbrains.kotlin.backend.jvm.JvmLoweredDeclarationOrigin
+import org.jetbrains.kotlin.backend.jvm.MemoizedMultiFieldValueClassReplacements
+import org.jetbrains.kotlin.backend.jvm.SpecialBridge
 import org.jetbrains.kotlin.backend.jvm.ir.*
 import org.jetbrains.kotlin.codegen.AsmUtil
 import org.jetbrains.kotlin.descriptors.DescriptorVisibilities
@@ -24,7 +25,10 @@ import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.expressions.*
 import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
 import org.jetbrains.kotlin.ir.symbols.IrSimpleFunctionSymbol
-import org.jetbrains.kotlin.ir.types.*
+import org.jetbrains.kotlin.ir.types.IrType
+import org.jetbrains.kotlin.ir.types.isNullable
+import org.jetbrains.kotlin.ir.types.isPrimitiveType
+import org.jetbrains.kotlin.ir.types.makeNullable
 import org.jetbrains.kotlin.ir.util.*
 import org.jetbrains.kotlin.ir.visitors.IrElementTransformerVoid
 import org.jetbrains.kotlin.name.Name
@@ -598,22 +602,20 @@ internal class BridgeLowering(val context: JvmBackendContext) : FileLoweringPass
         bridge: IrSimpleFunction,
         target: IrSimpleFunction,
         superQualifierSymbol: IrClassSymbol? = null
-    ) =
-        irCastIfNeeded(irBlock {
-            +irReturn(irCall(target, origin = IrStatementOrigin.BRIDGE_DELEGATION, superQualifierSymbol = superQualifierSymbol).apply {
-
-                val targetStructure = getStructure(target)
-                val bridgeStructure = getStructure(bridge)
-
-                if (targetStructure == null && bridgeStructure == null) {
-                    for ((param, targetParam) in bridge.explicitParameters.zip(target.explicitParameters)) {
-                        putArgument(targetParam, irGetOrCast(bridge, param, targetParam))
+    ) = irCastIfNeeded(irBlock {
+        +irReturn(irCall(target, origin = IrStatementOrigin.BRIDGE_DELEGATION, superQualifierSymbol = superQualifierSymbol).apply {
+            if (getStructure(target) == null && getStructure(bridge) == null) {
+                for ((param, targetParam) in bridge.explicitParameters.zip(target.explicitParameters)) {
+                    val argument = irGet(param).let { argument ->
+                        if (param == bridge.dispatchReceiverParameter) argument else irCastIfNeeded(argument, targetParam.type.upperBound)
                     }
-                } else {
-                    this@irBlock.addBoxedAndUnboxedMfvcArguments(targetStructure, bridgeStructure, target, bridge, this)
+                    putArgument(targetParam, argument)
                 }
-            })
-        }.unwrapBlock(), bridge.returnType.upperBound)
+            } else {
+                this@irBlock.addBoxedAndUnboxedMfvcArguments(target, bridge, this)
+            }
+        })
+    }.unwrapBlock(), bridge.returnType.upperBound)
 
     private fun getStructure(function: IrSimpleFunction): List<MemoizedMultiFieldValueClassReplacements.RemappedParameter>? {
         val structure = context.multiFieldValueClassReplacements.bindingNewFunctionToParameterTemplateStructure[function] ?: return null
@@ -625,106 +627,22 @@ internal class BridgeLowering(val context: JvmBackendContext) : FileLoweringPass
     }
 
     private fun IrBlockBuilder.addBoxedAndUnboxedMfvcArguments(
-        targetStructure: List<MemoizedMultiFieldValueClassReplacements.RemappedParameter>?,
-        bridgeStructure: List<MemoizedMultiFieldValueClassReplacements.RemappedParameter>?,
         target: IrSimpleFunction,
         bridge: IrSimpleFunction,
         irCall: IrCall
     ) {
-        require(
-            targetStructure == null || bridgeStructure == null ||
-                    bridgeStructure.size == targetStructure.size &&
-                    (targetStructure zip bridgeStructure).none { (targetParameter, bridgeParameter) ->
-                        targetParameter is MultiFieldValueClassMapping && bridgeParameter is MultiFieldValueClassMapping &&
-                                targetParameter.rootMfvcNode != bridgeParameter.rootMfvcNode
-                    }
-        ) { "Incompatible structures: $bridgeStructure and $targetStructure" }
-
-        val targetExplicitParameters = target.explicitParameters
-        val bridgeExplicitParameters = bridge.explicitParameters
-        var targetIndex = 0
-        var bridgeIndex = 0
-        var structureIndex = 0
-        while (targetIndex < targetExplicitParameters.size && bridgeIndex < bridgeExplicitParameters.size) {
-            val targetRemappedParameter = targetStructure?.get(structureIndex)
-            val bridgeRemappedParameter = bridgeStructure?.get(structureIndex)
-            when (targetRemappedParameter) {
-                is MultiFieldValueClassMapping -> when (bridgeRemappedParameter) {
-                    is MultiFieldValueClassMapping -> {
-                        require(bridgeRemappedParameter.rootMfvcNode == targetRemappedParameter.rootMfvcNode) {
-                            "Incompatible parameters: $bridgeRemappedParameter, $targetRemappedParameter"
-                        }
-                        repeat(bridgeRemappedParameter.valueParameters.size) {
-                            val bridgeParameter = bridgeExplicitParameters[bridgeIndex++]
-                            val targetParameter = targetExplicitParameters[targetIndex++]
-                            irCall.putArgument(targetParameter, irGetOrCast(bridge, bridgeParameter, targetParameter))
-                        }
-                    }
-
-                    is RegularMapping, null -> {
-                        val bridgeParameter = bridgeExplicitParameters[bridgeIndex++]
-                        val targetParameterType = targetRemappedParameter.rootMfvcNode.mfvc.defaultType
-                        val instance = targetRemappedParameter.rootMfvcNode.createInstanceFromBox(
-                            this,
-                            irCastIfNeeded(irGet(bridgeParameter), targetParameterType),
-                            AccessType.ChooseEffective
-                        ) { error("Not applicable") }
-                        val newArguments = instance.makeFlattenedGetterExpressions(this, bridge.parentAsClass, registerPossibleExtraBoxCreation = {})
-                        for (newArgument in newArguments) {
-                            irCall.putArgument(targetExplicitParameters[targetIndex++], newArgument)
-                        }
-                    }
-                }
-
-                is RegularMapping, null -> {
-                    val targetParameter = targetExplicitParameters[targetIndex]
-                    when (bridgeRemappedParameter) {
-                        is MultiFieldValueClassMapping -> {
-                            val valueArguments = List(bridgeRemappedParameter.rootMfvcNode.leavesCount) {
-                                irGet(bridgeExplicitParameters[bridgeIndex++])
-                            }
-                            val boxCall = bridgeRemappedParameter.rootMfvcNode.makeBoxedExpression(
-                                this, bridgeRemappedParameter.typeArguments, valueArguments, registerPossibleExtraBoxCreation = {}
-                            )
-                            irCall.putArgument(targetParameter, irCastIfNeeded(boxCall, targetParameter.type.upperBound))
-                        }
-
-                        is RegularMapping, null -> {
-                            val bridgeParameter = bridgeExplicitParameters[bridgeIndex++]
-                            irCall.putArgument(targetParameter, irGetOrCast(bridge, bridgeParameter, targetParameter))
-                        }
-                    }
-                    targetIndex++
-                }
+        val parameters2arguments = this@BridgeLowering.context.multiFieldValueClassReplacements
+            .mapFunctionMfvcStructures(this, target, bridge) { sourceParameter, targetParameterType ->
+                if (sourceParameter == bridge.dispatchReceiverParameter) irGet(sourceParameter)
+                else irCastIfNeeded(irGet(sourceParameter), targetParameterType)
+            }
+        for ((parameter, argument) in parameters2arguments) {
+            if (argument != null) {
+                irCall.putArgument(parameter, argument)
             }
-            structureIndex++
-        }
-        require(targetIndex == targetExplicitParameters.size && bridgeIndex == bridgeExplicitParameters.size) {
-            "Incorrect bridge:\n${bridge.dump()}\n\nfor target\n${target.dump()}"
-        }
-        require((targetStructure == null || structureIndex == targetStructure.size)) {
-            "Invalid structure index $structureIndex for $targetStructure"
-        }
-        require((bridgeStructure == null || structureIndex == bridgeStructure.size)) {
-            "Invalid structure index $structureIndex for $bridgeStructure"
         }
     }
 
-    private fun IrBuilderWithScope.irGetOrCast(
-        bridge: IrSimpleFunction,
-        bridgeParameter: IrValueParameter,
-        targetParameter: IrValueParameter
-    ) =
-        irGet(bridgeParameter).let { argument ->
-            if (bridgeParameter == bridge.dispatchReceiverParameter)
-                argument
-            else
-                irCastIfNeeded(argument, targetParameter.type.upperBound)
-        }
-
-    private fun IrBuilderWithScope.irCastIfNeeded(expression: IrExpression, to: IrType): IrExpression =
-        if (expression.type == to || to.isAny() || to.isNullableAny()) expression else irImplicitCast(expression, to)
-
     private val IrFunction.jvmMethod: Method
         get() = context.bridgeLoweringCache.computeJvmMethod(this)
 }

compiler/ir/backend.jvm/lower/src/org/jetbrains/kotlin/backend/jvm/lower/InheritedDefaultMethodsOnClassesLowering.kt

@@ -12,26 +12,20 @@ import org.jetbrains.kotlin.backend.common.lower.createIrBuilder
 import org.jetbrains.kotlin.backend.common.phaser.makeIrFilePhase
 import org.jetbrains.kotlin.backend.jvm.JvmBackendContext
 import org.jetbrains.kotlin.backend.jvm.JvmLoweredDeclarationOrigin
-import org.jetbrains.kotlin.backend.jvm.MemoizedMultiFieldValueClassReplacements.RemappedParameter.MultiFieldValueClassMapping
-import org.jetbrains.kotlin.backend.jvm.MemoizedMultiFieldValueClassReplacements.RemappedParameter.RegularMapping
-import org.jetbrains.kotlin.backend.jvm.fullValueParameterList
 import org.jetbrains.kotlin.backend.jvm.ir.*
-import org.jetbrains.kotlin.backend.jvm.makeBoxedExpression
 import org.jetbrains.kotlin.builtins.StandardNames
 import org.jetbrains.kotlin.config.JvmDefaultMode
 import org.jetbrains.kotlin.descriptors.DescriptorVisibilities
 import org.jetbrains.kotlin.descriptors.Modality
 import org.jetbrains.kotlin.descriptors.deserialization.PLATFORM_DEPENDENT_ANNOTATION_FQ_NAME
 import org.jetbrains.kotlin.ir.IrElement
-import org.jetbrains.kotlin.ir.builders.irBlockBody
-import org.jetbrains.kotlin.ir.builders.irCall
-import org.jetbrains.kotlin.ir.builders.irGet
-import org.jetbrains.kotlin.ir.builders.irReturn
+import org.jetbrains.kotlin.ir.builders.*
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.expressions.IrCall
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrTypeOperator
 import org.jetbrains.kotlin.ir.expressions.impl.IrTypeOperatorCallImpl
+import org.jetbrains.kotlin.ir.expressions.putArgument
 import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.util.*
 import org.jetbrains.kotlin.ir.visitors.*
@@ -96,59 +90,27 @@ private class InheritedDefaultMethodsOnClassesLowering(val context: JvmBackendCo
         val classStartOffset = classOverride.parentAsClass.startOffset
         val backendContext = context
         context.createIrBuilder(irFunction.symbol, classStartOffset, classStartOffset).apply {
-            irFunction.body = irBlockBody {
-                +irReturn(
-                    irCall(defaultImplFun.symbol, irFunction.returnType).apply {
-                        superMethod.parentAsClass.typeParameters.forEachIndexed { index, _ ->
-                            putTypeArgument(index, createPlaceholderAnyNType(context.irBuiltIns))
-                        }
-                        passTypeArgumentsFrom(irFunction, offset = superMethod.parentAsClass.typeParameters.size)
-
-                        irFunction.dispatchReceiverParameter?.let {
-                            putValueArgument(0, irGet(it).reinterpretAsDispatchReceiverOfType(superClassType))
-                        }
-                        val bindingNewFunctionToParameterTemplateStructure = backendContext.multiFieldValueClassReplacements
-                            .bindingNewFunctionToParameterTemplateStructure
-                        val structure = bindingNewFunctionToParameterTemplateStructure[classOverride]?.let { structure ->
-                            require(structure.sumOf { it.valueParameters.size } == classOverride.explicitParametersCount) {
-                                "Bad parameters structure: $structure"
-                            }
-                            if (defaultImplFun.explicitParametersCount == irFunction.explicitParametersCount) {
-                                null
-                            } else {
-                                require(structure.size == defaultImplFun.explicitParametersCount) { "Bad parameters structure: $structure" }
-                                structure
-                            }
-                        }
-                        require(structure == null || structure.first() is RegularMapping) {
-                            "Dispatch receiver for method replacement cannot be flattened"
-                        }
-                        val sourceFullValueParameterList = irFunction.fullValueParameterList
-                        if (structure == null) {
-                            for ((index, parameter) in sourceFullValueParameterList.withIndex()) {
-                                putValueArgument(1 + index, irGet(parameter))
-                            }
-                        } else {
-                            var flattenedIndex = 0
-                            for (i in 1 until structure.size) {
-                                when (val remappedParameter = structure[i]) {
-                                    is MultiFieldValueClassMapping -> {
-                                        val valueArguments = remappedParameter.valueParameters.indices.map {
-                                            irGet(sourceFullValueParameterList[flattenedIndex++])
-                                        }
-                                        val boxedExpression = remappedParameter.rootMfvcNode.makeBoxedExpression(
-                                            this@irBlockBody, remappedParameter.typeArguments, valueArguments, registerPossibleExtraBoxCreation = {}
-                                        )
-                                        putValueArgument(i, boxedExpression)
-                                    }
-
-                                    is RegularMapping -> putValueArgument(i, irGet(sourceFullValueParameterList[flattenedIndex++]))
-                                }
-                            }
+            irFunction.body = irExprBody(irBlock {
+                val parameter2arguments = backendContext.multiFieldValueClassReplacements
+                    .mapFunctionMfvcStructures(this, defaultImplFun, irFunction) { sourceParameter, _ ->
+                        irGet(sourceParameter).let {
+                            if (sourceParameter != irFunction.dispatchReceiverParameter) it
+                            else it.reinterpretAsDispatchReceiverOfType(superClassType)
                         }
                     }
-                )
-            }
+                +irCall(defaultImplFun.symbol, irFunction.returnType).apply {
+                    for (index in superMethod.parentAsClass.typeParameters.indices) {
+                        putTypeArgument(index, createPlaceholderAnyNType(context.irBuiltIns))
+                    }
+                    passTypeArgumentsFrom(irFunction, offset = superMethod.parentAsClass.typeParameters.size)
+
+                    for ((parameter, argument) in parameter2arguments) {
+                        if (argument != null) {
+                            putArgument(parameter, argument)
+                        }
+                    }
+                }
+            })
         }
 
         return irFunction

compiler/ir/backend.jvm/lower/src/org/jetbrains/kotlin/backend/jvm/lower/JvmDefaultParameterInjector.kt

@@ -10,11 +10,18 @@ import org.jetbrains.kotlin.backend.jvm.JvmBackendContext
 import org.jetbrains.kotlin.backend.jvm.JvmLoweredDeclarationOrigin
 import org.jetbrains.kotlin.backend.jvm.ir.defaultValue
 import org.jetbrains.kotlin.backend.jvm.ir.getJvmVisibilityOfDefaultArgumentStub
+import org.jetbrains.kotlin.ir.builders.IrBlockBuilder
 import org.jetbrains.kotlin.ir.declarations.IrConstructor
 import org.jetbrains.kotlin.ir.declarations.IrFunction
 import org.jetbrains.kotlin.ir.declarations.IrValueParameter
 import org.jetbrains.kotlin.ir.expressions.IrExpression
+import org.jetbrains.kotlin.ir.expressions.IrFunctionAccessExpression
+import org.jetbrains.kotlin.ir.expressions.IrStatementOrigin
+import org.jetbrains.kotlin.ir.expressions.impl.IrCompositeImpl
+import org.jetbrains.kotlin.ir.expressions.impl.IrConstImpl
 import org.jetbrains.kotlin.ir.types.IrType
+import org.jetbrains.kotlin.ir.util.explicitParametersCount
+import org.jetbrains.kotlin.ir.util.render
 
 class JvmDefaultParameterInjector(context: JvmBackendContext) : DefaultParameterInjector<JvmBackendContext>(
     context = context,
@@ -40,4 +47,57 @@ class JvmDefaultParameterInjector(context: JvmBackendContext) : DefaultParameter
     override fun isStatic(function: IrFunction): Boolean =
         function.origin == JvmLoweredDeclarationOrigin.STATIC_INLINE_CLASS_REPLACEMENT ||
                 function.origin == JvmLoweredDeclarationOrigin.STATIC_MULTI_FIELD_VALUE_CLASS_REPLACEMENT
+
+
+    override fun IrBlockBuilder.argumentsForCall(
+        expression: IrFunctionAccessExpression, stubFunction: IrFunction
+    ): Map<IrValueParameter, IrExpression?> {
+        val startOffset = expression.startOffset
+        val endOffset = expression.endOffset
+        val declaration = expression.symbol.owner
+
+        val realArgumentsNumber = declaration.valueParameters.filterNot { it.isMovedReceiver() }.size
+        val maskValues = IntArray((realArgumentsNumber + 31) / 32)
+
+        val oldArguments: Map<IrValueParameter, IrExpression?> = buildMap {
+            declaration.dispatchReceiverParameter?.let { put(it, expression.dispatchReceiver) }
+            declaration.extensionReceiverParameter?.let { put(it, expression.extensionReceiver) }
+            putAll(declaration.valueParameters.mapIndexed { index, parameter -> parameter to expression.getValueArgument(index) })
+        }
+
+        val indexes = declaration.valueParameters.filterNot { it.isMovedReceiver() }.withIndex().associate { it.value to it.index }
+        val mainArguments = this@JvmDefaultParameterInjector.context.multiFieldValueClassReplacements
+            .mapFunctionMfvcStructures(this, stubFunction, declaration) { sourceParameter: IrValueParameter, targetParameterType: IrType ->
+                val valueArgument = oldArguments[sourceParameter]
+                if (valueArgument == null) {
+                    val index = indexes[sourceParameter]!!
+                    maskValues[index / 32] = maskValues[index / 32] or (1 shl (index % 32))
+                }
+                valueArgument ?: IrCompositeImpl(
+                    expression.startOffset,
+                    expression.endOffset,
+                    targetParameterType,
+                    IrStatementOrigin.DEFAULT_VALUE,
+                    listOf(nullConst(startOffset, endOffset, targetParameterType))
+                )
+            }
+
+
+        assert(stubFunction.explicitParametersCount - mainArguments.size - maskValues.size in listOf(0, 1)) {
+            "argument count mismatch: expected $realArgumentsNumber arguments + ${maskValues.size} masks + optional handler/marker, " +
+                    "got ${stubFunction.explicitParametersCount} total in ${stubFunction.render()}"
+        }
+
+        return buildMap {
+            putAll(mainArguments)
+            val restParameters = stubFunction.valueParameters.filterNot { it in mainArguments }
+            for ((maskParameter, maskValue) in restParameters zip maskValues.asList()) {
+                put(maskParameter, IrConstImpl.int(startOffset, endOffset, maskParameter.type, maskValue))
+            }
+            if (restParameters.size > maskValues.size) {
+                val lastParameter = restParameters.last()
+                put(lastParameter, IrConstImpl.constNull(startOffset, endOffset, lastParameter.type))
+            }
+        }
+    }
 }

compiler/ir/backend.jvm/lower/src/org/jetbrains/kotlin/backend/jvm/lower/JvmMultiFieldValueClassLowering.kt

@@ -518,15 +518,21 @@ internal class JvmMultiFieldValueClassLowering(
             name = mangledName
             returnType = source.returnType
         }.apply {
-            val isAnyOverriddenReplaced = replacement.overriddenSymbols.any {
-                it.owner in replacements.bindingNewFunctionToParameterTemplateStructure
+            val implementationStructure = if (isFakeOverride) {
+                val superDeclaration = replacement.allOverridden().singleOrNull { it.body != null }
+                    ?: error("${this.render()} is fake override and has no implementation")
+                replacements.bindingNewFunctionToParameterTemplateStructure[superDeclaration]
+                    ?: superDeclaration.explicitParameters.map { RegularMapping(it) }
+            } else {
+                replacements.bindingNewFunctionToParameterTemplateStructure[replacement]
+                    ?: error("${replacement.render()} must have MFVC structure")
             }
-            if (source.parentAsClass.isMultiFieldValueClass && isAnyOverriddenReplaced) {
-                copyTypeParametersFrom(source) // without static type parameters
-                val substitutionMap = makeTypeParameterSubstitutionMap(source, this)
-                dispatchReceiverParameter = source.dispatchReceiverParameter!!.let { // source!!!
-                    it.copyTo(this, type = it.type.substitute(substitutionMap))
-                }
+            copyTypeParametersFrom(source) // without static type parameters
+            val substitutionMap = makeTypeParameterSubstitutionMap(source, this)
+            dispatchReceiverParameter = source.dispatchReceiverParameter!!.let { // source!!!
+                it.copyTo(this, type = it.type.substitute(substitutionMap))
+            }
+            if ((source.parent as? IrClass)?.isMultiFieldValueClass == true) {
                 require(replacement.dispatchReceiverParameter == null) {
                     """
                         Ambiguous receivers:
@@ -534,19 +540,32 @@ internal class JvmMultiFieldValueClassLowering(
                         ${replacement.dispatchReceiverParameter!!.render()}
                         """.trimIndent()
                 }
-                require(replacement.extensionReceiverParameter == null) {
-                    "Static replacement must have no extension receiver but ${replacement.extensionReceiverParameter!!.render()} found"
-                }
-                val replacementStructure = replacements.bindingNewFunctionToParameterTemplateStructure[replacement]!!
-                val offset = replacementStructure[0].valueParameters.size
-                valueParameters = replacement.valueParameters.drop(offset).map {
-                    it.copyTo(this, type = it.type.substitute(substitutionMap), index = it.index - offset)
-                }
-                val parametersMapping = (replacement.valueParameters.drop(offset) zip valueParameters).toMap()
-                context.remapMultiFieldValueClassStructure(replacement, this, parametersMapping)
-            } else {
-                copyParameterDeclarationsFrom(source)
             }
+            require(replacement.extensionReceiverParameter == null) {
+                "Static replacement must have no extension receiver but ${replacement.extensionReceiverParameter!!.render()} found"
+            }
+            val structure = buildList(implementationStructure.size) {
+                var valueParameterIndex = 0
+                add(RegularMapping(dispatchReceiverParameter!!))
+                val valueParametersAsMutableList = mutableListOf<IrValueParameter>()
+                for (expectedParameterStructure in implementationStructure.asSequence().drop(this.size)) {
+                    fun IrValueParameter.copy() =
+                        copyTo(this@apply, type = type.substitute(substitutionMap), index = valueParameterIndex++)
+
+                    val parameterStructure = when (expectedParameterStructure) {
+                        is RegularMapping -> RegularMapping(expectedParameterStructure.valueParameter.copy())
+                        is MultiFieldValueClassMapping -> MultiFieldValueClassMapping(
+                            expectedParameterStructure.rootMfvcNode,
+                            substitutionMap,
+                            expectedParameterStructure.valueParameters.map { it.copy() }
+                        )
+                    }
+                    add(parameterStructure)
+                    valueParametersAsMutableList.addAll(parameterStructure.valueParameters)
+                }
+                valueParameters = valueParametersAsMutableList
+            }
+            replacements.bindingNewFunctionToParameterTemplateStructure[this] = structure
             annotations = source.annotations
             parent = source.parent
             // We need to ensure that this bridge has the same attribute owner as its static inline class replacement, since this
@@ -557,110 +576,17 @@ internal class JvmMultiFieldValueClassLowering(
 
     override fun createBridgeBody(source: IrSimpleFunction, target: IrSimpleFunction, original: IrFunction, inverted: Boolean) {
         allScopes.push(createScope(source))
-        source.body = context.createJvmIrBuilder(source.symbol).run {
-            val sourceExplicitParameters = source.explicitParameters
-            val targetExplicitParameters = target.explicitParameters
+        source.body = with(context.createJvmIrBuilder(source.symbol)) {
             irExprBody(irBlock {
+                val parameters2arguments = replacements.mapFunctionMfvcStructures(this, target, source) { sourceParameter, _ ->
+                    irGet(sourceParameter)
+                }
                 +irReturn(irCall(target).apply {
                     passTypeArgumentsWithOffsets(target, source) { source.typeParameters[it].defaultType }
-                    val sourceStructure: List<RemappedParameter>? = replacements.bindingNewFunctionToParameterTemplateStructure[source]
-                    val targetStructure: List<RemappedParameter>? = replacements.bindingNewFunctionToParameterTemplateStructure[target]
-                    val errorMessage = {
-                        """
-                        Incompatible structures for
-                        Source: $sourceStructure
-                        ${source.render()}
-                        Target: $targetStructure
-                        ${target.render()}
-                        """.trimIndent()
-                    }
-                    when (targetStructure) {
-                        null -> when (sourceStructure) {
-                            null -> require(targetExplicitParameters.size == sourceExplicitParameters.size, errorMessage)
-                            else -> {
-                                require(targetExplicitParameters.size == sourceStructure.size, errorMessage)
-                                require(sourceExplicitParameters.size == sourceStructure.sumOf { it.valueParameters.size }, errorMessage)
-                            }
+                    for ((parameter, argument) in parameters2arguments) {
+                        if (argument != null) {
+                            putArgument(parameter, argument)
                         }
-
-                        else -> when (sourceStructure) {
-                            null -> {
-                                require(targetStructure.size == sourceExplicitParameters.size, errorMessage)
-                                require(targetStructure.sumOf { it.valueParameters.size } == targetExplicitParameters.size, errorMessage)
-                            }
-
-                            else -> {
-                                require(targetStructure.size == sourceStructure.size, errorMessage)
-                                require(sourceStructure.sumOf { it.valueParameters.size } == sourceExplicitParameters.size, errorMessage)
-                                require(targetStructure.sumOf { it.valueParameters.size } == targetExplicitParameters.size, errorMessage)
-                                require((targetStructure zip sourceStructure).none { (t, s) ->
-                                    t is MultiFieldValueClassMapping && s is MultiFieldValueClassMapping && t.rootMfvcNode != s.rootMfvcNode
-                                }, errorMessage)
-                            }
-                        }
-                    }
-                    val structuresSizes = sourceStructure?.size ?: targetStructure?.size ?: targetExplicitParameters.size
-                    var flattenedSourceIndex = 0
-                    var flattenedTargetIndex = 0
-                    for (i in 0 until structuresSizes) {
-                        val remappedSourceParameter = sourceStructure?.get(i)
-                        val remappedTargetParameter = targetStructure?.get(i)
-                        when (remappedSourceParameter) {
-                            is MultiFieldValueClassMapping -> {
-                                when (remappedTargetParameter) {
-                                    is MultiFieldValueClassMapping -> {
-                                        require(remappedTargetParameter.valueParameters.size == remappedSourceParameter.valueParameters.size) {
-                                            "Incompatible structures: $remappedTargetParameter, $remappedSourceParameter"
-                                        }
-                                        repeat(remappedTargetParameter.valueParameters.size) {
-                                            putArgument(
-                                                targetExplicitParameters[flattenedTargetIndex++],
-                                                irGet(sourceExplicitParameters[flattenedSourceIndex++])
-                                            )
-                                        }
-                                    }
-
-                                    is RegularMapping, null -> {
-                                        val valueArguments = sourceExplicitParameters
-                                            .slice(flattenedSourceIndex until flattenedSourceIndex + remappedSourceParameter.valueParameters.size)
-                                            .map { irGet(it) }
-                                        val targetParameter = targetExplicitParameters[flattenedTargetIndex++]
-                                        val boxedExpression = remappedSourceParameter.rootMfvcNode.makeBoxedExpression(
-                                            this@irBlock,
-                                            remappedSourceParameter.typeArguments,
-                                            valueArguments,
-                                            ::registerPossibleExtraBoxUsage
-                                        )
-                                        putArgument(targetParameter, boxedExpression)
-                                            .also { flattenedSourceIndex += remappedSourceParameter.valueParameters.size }
-                                    }
-                                }
-                            }
-
-                            is RegularMapping, null -> when (remappedTargetParameter) {
-                                is MultiFieldValueClassMapping -> {
-                                    val receiver = sourceExplicitParameters[flattenedSourceIndex++]
-                                    val rootNode = remappedTargetParameter.rootMfvcNode
-                                    val instance = rootNode.createInstanceFromBox(
-                                        this@irBlock, irGet(receiver), AccessType.ChooseEffective, ::variablesSaver,
-                                    )
-                                    val flattenedExpressions = instance.makeFlattenedGetterExpressions(
-                                        this@irBlock, irCurrentClass, ::registerPossibleExtraBoxUsage
-                                    )
-                                    for (expression in flattenedExpressions) {
-                                        putArgument(targetExplicitParameters[flattenedTargetIndex++], expression)
-                                    }
-                                }
-
-                                else -> putArgument(
-                                    targetExplicitParameters[flattenedTargetIndex++],
-                                    irGet(sourceExplicitParameters[flattenedSourceIndex++])
-                                )
-                            }
-                        }
-                    }
-                    require(flattenedTargetIndex == targetExplicitParameters.size && flattenedSourceIndex == sourceExplicitParameters.size) {
-                        "Incorrect source:\n${source.dump()}\n\nfor target\n${target.dump()}"
                     }
                 })
             })
@@ -1076,7 +1002,9 @@ internal class JvmMultiFieldValueClassLowering(
         originalFunction: IrFunction,
         original: IrMemberAccessExpression<*>,
         replacement: IrFunction,
-        makeMemberAccessExpression: (IrFunctionSymbol) -> IrMemberAccessExpression<*> = ::irCall,
+        makeMemberAccessExpression: (IrFunctionSymbol) -> IrMemberAccessExpression<*> = { callee: IrFunctionSymbol ->
+            irCall(callee.owner, superQualifierSymbol = (original as? IrCall)?.superQualifierSymbol)
+        },
     ): IrMemberAccessExpression<*> {
         val parameter2expression = typedArgumentList(originalFunction, original)
         val structure = replacements.bindingOldFunctionToParameterTemplateStructure[originalFunction]!!
@@ -1302,6 +1230,9 @@ internal class JvmMultiFieldValueClassLowering(
             if (expression is IrConstructorCall) expression.symbol.owner.constructedClass else expression.type.erasedUpperBound
         )
         val type = if (expression is IrConstructorCall) expression.symbol.owner.constructedClass.defaultType else expression.type
+        if (type == context.irBuiltIns.nothingType) {
+            return flattenExpressionTo(irImplicitCast(expression, instance.type), instance)
+        }
         val lowering = this@JvmMultiFieldValueClassLowering
         if (rootNode == null || !type.needsMfvcFlattening() || instance.size == 1) {
             require(instance.size == 1) { "Required 1 variable/field to store regular value but got ${instance.size}" }

compiler/ir/backend.jvm/lower/src/org/jetbrains/kotlin/backend/jvm/lower/JvmValueClassAbstractLowering.kt

@@ -211,7 +211,7 @@ internal abstract class JvmValueClassAbstractLowering(
             }
         )
 
-        // Update the overridden symbols to point to their inline class replacements
+        // Update the overridden symbols to point to their value class replacements
         bridgeFunction.overriddenSymbols = replacement.overriddenSymbols
 
         // Replace the function body with a wrapper

compiler/ir/backend.jvm/lower/src/org/jetbrains/kotlin/backend/jvm/lower/StaticDefaultFunctionLowering.kt

@@ -80,6 +80,11 @@ private class StaticDefaultFunctionLowering(val context: JvmBackendContext) : Ir
 
     private fun getStaticFunctionWithReceivers(function: IrSimpleFunction): IrSimpleFunction =
         context.staticDefaultStubs.getOrPut(function.symbol) {
-            context.irFactory.createStaticFunctionWithReceivers(function.parent, function.name, function)
+            context.irFactory.createStaticFunctionWithReceivers(
+                function.parent,
+                function.name,
+                function,
+                remapMultiFieldValueClassStructure = context::remapMultiFieldValueClassStructure
+            )
         }
 }

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmCachedDeclarations.kt

@@ -220,7 +220,8 @@ class JvmCachedDeclarations(
                 modality = Modality.OPEN,
                 visibility = defaultImplsVisibility,
                 isFakeOverride = false,
-                typeParametersFromContext = parent.typeParameters
+                typeParametersFromContext = parent.typeParameters,
+                remapMultiFieldValueClassStructure = context::remapMultiFieldValueClassStructure
             ).also {
                 it.copyCorrespondingPropertyFrom(interfaceFun)
 
@@ -257,7 +258,6 @@ class JvmCachedDeclarations(
         defaultImplsRedirections.getOrPut(fakeOverride) {
             assert(fakeOverride.isFakeOverride)
             val irClass = fakeOverride.parentAsClass
-            val mfvcReplacementStructure = context.multiFieldValueClassReplacements.bindingNewFunctionToParameterTemplateStructure
             val redirectFunction = context.irFactory.buildFun {
                 origin = JvmLoweredDeclarationOrigin.SUPER_INTERFACE_METHOD_BRIDGE
                 name = fakeOverride.name
@@ -282,7 +282,7 @@ class JvmCachedDeclarations(
                 annotations = fakeOverride.annotations
                 copyCorrespondingPropertyFrom(fakeOverride)
             }
-            mfvcReplacementStructure[fakeOverride]?.let { mfvcReplacementStructure[redirectFunction] = it }
+            context.remapMultiFieldValueClassStructure(fakeOverride, redirectFunction, parametersMappingOrNull = null)
             redirectFunction
         }
 

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/MemoizedMultiFieldValueClassReplacements.kt

@@ -5,23 +5,32 @@
 
 package org.jetbrains.kotlin.backend.jvm
 
+import org.jetbrains.kotlin.backend.common.lower.parents
 import org.jetbrains.kotlin.backend.jvm.MemoizedMultiFieldValueClassReplacements.RemappedParameter.MultiFieldValueClassMapping
+import org.jetbrains.kotlin.backend.jvm.MemoizedMultiFieldValueClassReplacements.RemappedParameter.RegularMapping
 import org.jetbrains.kotlin.backend.jvm.ir.*
 import org.jetbrains.kotlin.descriptors.DescriptorVisibilities
+import org.jetbrains.kotlin.ir.UNDEFINED_OFFSET
+import org.jetbrains.kotlin.ir.builders.IrBlockBuilder
 import org.jetbrains.kotlin.ir.builders.declarations.addValueParameter
 import org.jetbrains.kotlin.ir.builders.declarations.buildConstructor
+import org.jetbrains.kotlin.ir.builders.irComposite
 import org.jetbrains.kotlin.ir.builders.irExprBody
 import org.jetbrains.kotlin.ir.builders.irGet
 import org.jetbrains.kotlin.ir.declarations.*
+import org.jetbrains.kotlin.ir.expressions.IrComposite
 import org.jetbrains.kotlin.ir.expressions.IrExpression
+import org.jetbrains.kotlin.ir.expressions.IrStatementOriginImpl
 import org.jetbrains.kotlin.ir.symbols.IrTypeParameterSymbol
 import org.jetbrains.kotlin.ir.types.IrSimpleType
 import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.types.defaultType
+import org.jetbrains.kotlin.ir.types.isNothing
 import org.jetbrains.kotlin.ir.util.*
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.resolve.InlineClassDescriptorResolver
 import org.jetbrains.kotlin.storage.LockBasedStorageManager
+import org.jetbrains.kotlin.utils.addToStdlib.firstIsInstance
 import java.util.concurrent.ConcurrentHashMap
 
 /**
@@ -43,7 +52,7 @@ class MemoizedMultiFieldValueClassReplacements(
         originWhenFlattened: IrDeclarationOrigin,
     ): RemappedParameter {
         val oldParam = this
-        if (!type.needsMfvcFlattening()) return RemappedParameter.RegularMapping(
+        if (!type.needsMfvcFlattening()) return RegularMapping(
             targetFunction.addValueParameter {
                 updateFrom(oldParam)
                 this.name = oldParam.name
@@ -238,7 +247,7 @@ class MemoizedMultiFieldValueClassReplacements(
         dispatchReceiverParameter = function.dispatchReceiverParameter?.copyTo(this, index = -1)
         val newFlattenedParameters = makeAndAddGroupedValueParametersFrom(function, includeDispatcherReceiver = false, mapOf(), this)
         val receiver = dispatchReceiverParameter
-        return if (receiver != null) listOf(RemappedParameter.RegularMapping(receiver)) + newFlattenedParameters else newFlattenedParameters
+        return if (receiver != null) listOf(RegularMapping(receiver)) + newFlattenedParameters else newFlattenedParameters
     }
 
     /**
@@ -369,4 +378,107 @@ class MemoizedMultiFieldValueClassReplacements(
     }
 
     private val IrProperty.backingFieldIfNotToRemove get() = backingField?.takeUnless { it in getFieldsToRemove(this.parentAsClass) }
+
+    @Suppress("ClassName")
+    private object FLATTENED_NOTHING_DEFAULT_VALUE : IrStatementOriginImpl("FLATTENED_NOTHING_DEFAULT_VALUE")
+
+    fun mapFunctionMfvcStructures(
+        irBuilder: IrBlockBuilder,
+        targetFunction: IrFunction,
+        sourceFunction: IrFunction,
+        getArgument: (sourceParameter: IrValueParameter, targetParameterType: IrType) -> IrExpression?
+    ): Map<IrValueParameter, IrExpression?> {
+        val targetStructure = bindingNewFunctionToParameterTemplateStructure[targetFunction]
+            ?: targetFunction.explicitParameters.map { RegularMapping(it) }
+        val sourceStructure = bindingNewFunctionToParameterTemplateStructure[sourceFunction]
+            ?: sourceFunction.explicitParameters.map { RegularMapping(it) }
+        verifyStructureCompatibility(targetStructure, sourceStructure)
+        return buildMap {
+            for ((targetParameterStructure, sourceParameterStructure) in targetStructure zip sourceStructure) {
+                when (targetParameterStructure) {
+                    is RegularMapping -> when (sourceParameterStructure) {
+                        is RegularMapping -> put(
+                            targetParameterStructure.valueParameter,
+                            getArgument(sourceParameterStructure.valueParameter, targetParameterStructure.valueParameter.type)
+                        )
+                        is MultiFieldValueClassMapping -> {
+                            val valueArguments = sourceParameterStructure.valueParameters.map {
+                                getArgument(it, it.type) ?: error("Expected an argument for $sourceParameterStructure")
+                            }
+                            val newArgument =
+                                if (valueArguments.all { it is IrComposite && it.origin == FLATTENED_NOTHING_DEFAULT_VALUE }) {
+                                    (valueArguments[0] as IrComposite).statements[0] as IrExpression
+                                } else {
+                                    sourceParameterStructure.rootMfvcNode.makeBoxedExpression(
+                                        irBuilder,
+                                        sourceParameterStructure.typeArguments,
+                                        valueArguments,
+                                        registerPossibleExtraBoxCreation = {}
+                                    )
+                                }
+                            put(targetParameterStructure.valueParameter, newArgument)
+                        }
+                    }
+                    is MultiFieldValueClassMapping -> when (sourceParameterStructure) {
+                        is RegularMapping -> with(irBuilder) {
+                            val argument = getArgument(sourceParameterStructure.valueParameter, targetParameterStructure.boxedType)
+                                ?: error("Expected an argument for $sourceParameterStructure")
+                            if (sourceParameterStructure.valueParameter.type.isNothing()) {
+                                for ((index, parameter) in targetParameterStructure.valueParameters.withIndex()) {
+                                    put(parameter, irComposite(origin = FLATTENED_NOTHING_DEFAULT_VALUE) {
+                                        if (index == 0) +argument
+                                        +parameter.type.defaultValue(
+                                            UNDEFINED_OFFSET, UNDEFINED_OFFSET, this@MemoizedMultiFieldValueClassReplacements.context
+                                        )
+                                    })
+                                }
+                            } else {
+                                val instance = targetParameterStructure.rootMfvcNode.createInstanceFromBox(
+                                    scope = this,
+                                    receiver = argument,
+                                    accessType = AccessType.ChooseEffective,
+                                    saveVariable = { +it }
+                                )
+                                val arguments = instance.makeFlattenedGetterExpressions(
+                                    this, sourceFunction.parents.firstIsInstance<IrClass>(), registerPossibleExtraBoxCreation = {}
+                                )
+                                for ((targetParameter, expression) in targetParameterStructure.valueParameters zip arguments) {
+                                    put(targetParameter, expression)
+                                }
+                            }
+                        }
+                        is MultiFieldValueClassMapping -> {
+                            for ((sourceParameter, targetParameter) in sourceParameterStructure.valueParameters zip targetParameterStructure.valueParameters) {
+                                put(targetParameter, getArgument(sourceParameter, targetParameter.type))
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    @OptIn(ExperimentalStdlibApi::class)
+    private fun verifyStructureCompatibility(
+        targetStructure: List<RemappedParameter>,
+        sourceStructure: List<RemappedParameter>
+    ) {
+        for ((targetParameterStructure, sourceParameterStructure) in targetStructure zip sourceStructure) {
+            if (targetParameterStructure is MultiFieldValueClassMapping && sourceParameterStructure is MultiFieldValueClassMapping) {
+                require(targetParameterStructure.rootMfvcNode.mfvc.classId == sourceParameterStructure.rootMfvcNode.mfvc.classId) {
+                    "Incompatible parameter structures:\n$targetParameterStructure inside $targetStructure\n$sourceParameterStructure inside $sourceStructure"
+                }
+            }
+        }
+        for (extraParameterStructure in targetStructure.slice(sourceStructure.size..<targetStructure.size)) {
+            require(extraParameterStructure is RegularMapping && extraParameterStructure.valueParameter.origin != IrDeclarationOrigin.DEFINED) {
+                "Unexpected target MFVC parameter structure:\n$extraParameterStructure inside $targetStructure"
+            }
+        }
+        for (extraParameterStructure in sourceStructure.slice(targetStructure.size..<sourceStructure.size)) {
+            require(extraParameterStructure is RegularMapping && extraParameterStructure.valueParameter.origin != IrDeclarationOrigin.DEFINED) {
+                "Unexpected source MFVC parameter structure:\n$extraParameterStructure inside $sourceStructure"
+            }
+        }
+    }
 }

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/MfvcNode.kt

@@ -27,10 +27,16 @@ import org.jetbrains.kotlin.name.Name
 
 typealias TypeArguments = Map<IrTypeParameterSymbol, IrType>
 
+/**
+ * Instance-agnostic tree node describing structure of multi-field value class
+ */
 sealed interface MfvcNode {
     val type: IrType
     val leavesCount: Int
 
+    /**
+     * Create instance-specific [ReceiverBasedMfvcNodeInstance] from instance-agnostic [MfvcNode] using a boxed [receiver] as data source.
+     */
     fun createInstanceFromBox(
         scope: IrBlockBuilder,
         typeArguments: TypeArguments,
@@ -40,6 +46,9 @@ sealed interface MfvcNode {
     ): ReceiverBasedMfvcNodeInstance
 }
 
+/**
+ * Create instance-specific [ReceiverBasedMfvcNodeInstance] from instance-agnostic [MfvcNode] using a boxed [receiver] as data source.
+ */
 fun MfvcNode.createInstanceFromBox(
     scope: IrBlockBuilder,
     receiver: IrExpression,
@@ -48,10 +57,16 @@ fun MfvcNode.createInstanceFromBox(
 ) =
     createInstanceFromBox(scope, makeTypeArgumentsFromType(receiver.type as IrSimpleType), receiver, accessType, saveVariable)
 
+/**
+ * Create instance-specific [ValueDeclarationMfvcNodeInstance] from instance-agnostic [MfvcNode] using new flattened variables as data source.
+ */
 fun MfvcNode.createInstanceFromValueDeclarationsAndBoxType(
     scope: IrBuilderWithScope, type: IrSimpleType, name: Name, saveVariable: (IrVariable) -> Unit, isVar: Boolean
 ): ValueDeclarationMfvcNodeInstance = createInstanceFromValueDeclarations(scope, makeTypeArgumentsFromType(type), name, saveVariable, isVar)
 
+/**
+ * Create instance-specific [ValueDeclarationMfvcNodeInstance] from instance-agnostic [MfvcNode] using new flattened variables as data source.
+ */
 fun MfvcNode.createInstanceFromValueDeclarations(
     scope: IrBuilderWithScope, typeArguments: TypeArguments, name: Name, saveVariable: (IrVariable) -> Unit, isVar: Boolean
 ): ValueDeclarationMfvcNodeInstance {
@@ -67,6 +82,9 @@ fun MfvcNode.createInstanceFromValueDeclarations(
     return ValueDeclarationMfvcNodeInstance(this, typeArguments, valueDeclarations)
 }
 
+/**
+ * Create instance-specific [ValueDeclarationMfvcNodeInstance] from instance-agnostic [MfvcNode] using flattened [fieldValues] as data source.
+ */
 fun MfvcNode.createInstanceFromValueDeclarationsAndBoxType(
     type: IrSimpleType, fieldValues: List<IrValueDeclaration>
 ): ValueDeclarationMfvcNodeInstance =
@@ -83,19 +101,41 @@ fun makeTypeArgumentsFromType(type: IrSimpleType): TypeArguments {
 
 }
 
+/**
+ * Non-root [MfvcNode]. It contains an unbox method and a name.
+ */
 sealed interface NameableMfvcNode : MfvcNode {
     val namedNodeImpl: NameableMfvcNodeImpl
     val hasPureUnboxMethod: Boolean
 }
 
+/**
+ * List of names of the root node of the [NameableMfvcNode] up to the node.
+ */
 val NameableMfvcNode.nameParts: List<Name>
     get() = namedNodeImpl.nameParts
+
+/**
+ * The last [nameParts] which distinguishes the [NameableMfvcNode] from its parent.
+ */
 val NameableMfvcNode.name: Name
     get() = nameParts.last()
+
+/**
+ * Unbox method of the [NameableMfvcNode].
+ */
 val NameableMfvcNode.unboxMethod: IrSimpleFunction
     get() = namedNodeImpl.unboxMethod
+
+/**
+ * An unbox function or getter function method name of the [NameableMfvcNode].
+ */
 val NameableMfvcNode.fullMethodName: Name
     get() = namedNodeImpl.fullMethodName
+
+/**
+ * A field name corresponding to the [NameableMfvcNode].
+ */
 val NameableMfvcNode.fullFieldName: Name
     get() = namedNodeImpl.fullFieldName
 
@@ -138,7 +178,9 @@ fun MfvcNode.getSubnodeAndIndices(name: Name): Pair<NameableMfvcNode, IntRange>?
     val indices = subnodeIndices[node] ?: error("existing node without indices")
     return node to indices
 }
-
+/**
+ * Non-leaf [MfvcNode]. It contains a box method and children.
+ */
 sealed class MfvcNodeWithSubnodes(val subnodes: List<NameableMfvcNode>) : MfvcNode {
     abstract override val type: IrSimpleType
     abstract val boxMethod: IrSimpleFunction
@@ -159,6 +201,9 @@ sealed class MfvcNodeWithSubnodes(val subnodes: List<NameableMfvcNode>) : MfvcNo
         }
     }
 
+    /**
+     * Get child by [name].
+     */
     operator fun get(name: Name): NameableMfvcNode? = mapping[name]
 
     val leaves: List<LeafMfvcNode> = subnodes.leaves
@@ -178,6 +223,9 @@ sealed class MfvcNodeWithSubnodes(val subnodes: List<NameableMfvcNode>) : MfvcNo
 
 }
 
+/**
+ * Creates a box expression for the given [MfvcNodeWithSubnodes] by calling box methods with the given [typeArguments] and [valueArguments].
+ */
 fun MfvcNodeWithSubnodes.makeBoxedExpression(
     scope: IrBuilderWithScope,
     typeArguments: TypeArguments,
@@ -195,6 +243,9 @@ fun MfvcNodeWithSubnodes.makeBoxedExpression(
     registerPossibleExtraBoxCreation()
 }
 
+/**
+ * A shortcut to get children by name several times.
+ */
 operator fun MfvcNodeWithSubnodes.get(names: List<Name>): MfvcNode? {
     var cur: MfvcNode = this
     for (name in names) {
@@ -267,6 +318,9 @@ private fun validateGettingAccessorParameters(function: IrSimpleFunction) {
     require(function.typeParameters.isEmpty()) { "Type parameters are not expected for ${function.render()}" }
 }
 
+/**
+ * [MfvcNode] which corresponds to non-MFVC field which is a field of some MFVC.
+ */
 class LeafMfvcNode(
     override val type: IrType,
     methodFullNameMode: MethodFullNameMode,
@@ -310,6 +364,9 @@ val MfvcNode.fields
         is LeafMfvcNode -> field?.let(::listOf)
     }
 
+/**
+ * [MfvcNode] which corresponds to MFVC field which is a field of some class.
+ */
 class IntermediateMfvcNode(
     override val type: IrSimpleType,
     methodFullNameMode: MethodFullNameMode,
@@ -373,7 +430,9 @@ fun IrSimpleFunction.getGetterField(): IrField? {
     val statement = (body?.statements?.singleOrNull() as? IrReturn)?.value as? IrGetField ?: return null
     return statement.symbol.owner
 }
-
+/**
+ * [MfvcNode] which corresponds to MFVC itself.
+ */
 class RootMfvcNode internal constructor(
     val mfvc: IrClass,
     subnodes: List<NameableMfvcNode>,

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/MfvcNodeInstance.kt

@@ -18,29 +18,52 @@ import org.jetbrains.kotlin.ir.types.IrType
 import org.jetbrains.kotlin.ir.util.*
 import org.jetbrains.kotlin.name.Name
 
+/**
+ * Instance-specific tree node describing structure of multi-field value class corresponding to the [MfvcNode]
+ */
 interface MfvcNodeInstance {
     val node: MfvcNode
     val typeArguments: TypeArguments
     val type: IrSimpleType
 
+    /**
+     * Make expressions corresponding to the flattened representation of the [MfvcNodeInstance].
+     */
     fun makeFlattenedGetterExpressions(
         scope: IrBlockBuilder, currentClass: IrClass, registerPossibleExtraBoxCreation: () -> Unit
     ): List<IrExpression>
 
+    /**
+     * Make expression that corresponds to read access of the instance
+     */
     fun makeGetterExpression(scope: IrBuilderWithScope, currentClass: IrClass, registerPossibleExtraBoxCreation: () -> Unit): IrExpression
+
+    /**
+     * Get child [MfvcNodeInstance] by [name]
+     */
     operator fun get(name: Name): MfvcNodeInstance?
-    fun makeStatements(scope: IrBuilderWithScope, values: List<IrExpression>): List<IrStatement>
+
+    /**
+     * Make setter statements corresponding assignments to the [values] of the given flattened representation.
+     */
+    fun makeSetterStatements(scope: IrBuilderWithScope, values: List<IrExpression>): List<IrStatement>
 }
 
 private fun makeTypeFromMfvcNodeAndTypeArguments(node: MfvcNode, typeArguments: TypeArguments) =
     node.type.substitute(typeArguments) as IrSimpleType
 
+/**
+ * Make and add setter statements corresponding assignments to the [values] of the given flattened representation.
+ */
 fun MfvcNodeInstance.addSetterStatements(scope: IrBlockBuilder, values: List<IrExpression>) = with(scope) {
-    for (statement in makeStatements(this, values)) {
+    for (statement in makeSetterStatements(this, values)) {
         +statement
     }
 }
 
+/**
+ * Make a block of setter statements corresponding assignments to the [values] of the given flattened representation.
+ */
 fun MfvcNodeInstance.makeSetterExpressions(scope: IrBuilderWithScope, values: List<IrExpression>): IrExpression = scope.irBlock {
     addSetterStatements(this, values)
 }
@@ -49,6 +72,9 @@ private fun MfvcNodeInstance.checkValuesCount(values: List<IrExpression>) {
     require(values.size == node.leavesCount) { "Node $node requires ${node.leavesCount} values but got ${values.map { it.render() }}" }
 }
 
+/**
+ * [MfvcNodeInstance] that stores flattened instance in variables and parameters.
+ */
 class ValueDeclarationMfvcNodeInstance(
     override val node: MfvcNode,
     override val typeArguments: TypeArguments,
@@ -77,7 +103,7 @@ class ValueDeclarationMfvcNodeInstance(
         return ValueDeclarationMfvcNodeInstance(newNode, typeArguments, valueDeclarations.slice(indices))
     }
 
-    override fun makeStatements(scope: IrBuilderWithScope, values: List<IrExpression>): List<IrStatement> {
+    override fun makeSetterStatements(scope: IrBuilderWithScope, values: List<IrExpression>): List<IrStatement> {
         checkValuesCount(values)
         return valueDeclarations.zip(values) { declaration, value -> scope.irSet(declaration, value) }
     }
@@ -143,6 +169,9 @@ fun IrExpression?.isRepeatableAccessor(): Boolean = isRepeatableGetter() || isRe
 
 enum class AccessType { UseFields, ChooseEffective }
 
+/**
+ * [MfvcNodeInstance] that stores boxed instance in variables and parameters.
+ */
 class ReceiverBasedMfvcNodeInstance(
     private val scope: IrBlockBuilder,
     override val node: MfvcNode,
@@ -235,7 +264,7 @@ class ReceiverBasedMfvcNodeInstance(
         return newNode.createInstanceFromBox(scope, typeArguments, makeReceiverCopy(), accessType, saveVariable)
     }
 
-    override fun makeStatements(scope: IrBuilderWithScope, values: List<IrExpression>): List<IrStatement> {
+    override fun makeSetterStatements(scope: IrBuilderWithScope, values: List<IrExpression>): List<IrStatement> {
         checkValuesCount(values)
         require(fields != null) { "$node is immutable as it has custom getter and so no backing fields" }
         return fields.zip(values) { field, expr -> scope.irSetField(makeReceiverCopy(), field, expr) }
@@ -245,8 +274,6 @@ class ReceiverBasedMfvcNodeInstance(
 val MfvcNodeInstance.size: Int
     get() = node.leavesCount
 
-fun IrContainerExpression.unwrapBlock(): IrExpression = statements.singleOrNull() as? IrExpression ?: this
-
 /**
  * Creates a variable and doesn't add it to a container. It saves the variable with given saveVariable.
  *

compiler/ir/backend.wasm/src/org/jetbrains/kotlin/backend/wasm/lower/JsInteropFunctionsLowering.kt

@@ -110,7 +110,8 @@ class JsInteropFunctionsLowering(val context: WasmBackendContext) : DeclarationT
         val newFun = context.irFactory.createStaticFunctionWithReceivers(
             function.parent,
             name = Name.identifier(function.name.asStringStripSpecialMarkers() + "__externalAdapter"),
-            function
+            function,
+            remapMultiFieldValueClassStructure = context::remapMultiFieldValueClassStructure
         )
 
         function.valueParameters.forEachIndexed { index, newParameter ->
@@ -157,7 +158,8 @@ class JsInteropFunctionsLowering(val context: WasmBackendContext) : DeclarationT
         val newFun = context.irFactory.createStaticFunctionWithReceivers(
             function.parent,
             name = Name.identifier(function.name.asStringStripSpecialMarkers() + "__JsExportAdapter"),
-            function
+            function,
+            remapMultiFieldValueClassStructure = context::remapMultiFieldValueClassStructure
         )
 
         newFun.valueParameters.forEachIndexed { index, newParameter ->

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

@@ -7,10 +7,12 @@ package org.jetbrains.kotlin.ir.util
 
 import org.jetbrains.kotlin.descriptors.*
 import org.jetbrains.kotlin.ir.*
+import org.jetbrains.kotlin.ir.builders.IrBuilderWithScope
 import org.jetbrains.kotlin.ir.builders.declarations.addConstructor
 import org.jetbrains.kotlin.ir.builders.declarations.buildClass
 import org.jetbrains.kotlin.ir.builders.declarations.buildReceiverParameter
 import org.jetbrains.kotlin.ir.builders.declarations.buildTypeParameter
+import org.jetbrains.kotlin.ir.builders.irImplicitCast
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.expressions.*
 import org.jetbrains.kotlin.ir.expressions.impl.*
@@ -1183,7 +1185,8 @@ fun IrFactory.createStaticFunctionWithReceivers(
     visibility: DescriptorVisibility = oldFunction.visibility,
     isFakeOverride: Boolean = oldFunction.isFakeOverride,
     copyMetadata: Boolean = true,
-    typeParametersFromContext: List<IrTypeParameter> = listOf()
+    typeParametersFromContext: List<IrTypeParameter> = listOf(),
+    remapMultiFieldValueClassStructure: (IrFunction, IrFunction, Map<IrValueParameter, IrValueParameter>?) -> Unit
 ): IrSimpleFunction {
     return createFunction(
         oldFunction.startOffset, oldFunction.endOffset,
@@ -1271,12 +1274,19 @@ fun IrFactory.createStaticFunctionWithReceivers(
             )
         }
 
+        remapMultiFieldValueClassStructure(oldFunction, this, null)
+
         if (copyMetadata) metadata = oldFunction.metadata
 
         copyAttributes(oldFunction as? IrAttributeContainer)
     }
 }
 
+fun IrBuilderWithScope.irCastIfNeeded(expression: IrExpression, to: IrType): IrExpression =
+    if (expression.type == to || to.isAny() || to.isNullableAny()) expression else irImplicitCast(expression, to)
+
+fun IrContainerExpression.unwrapBlock(): IrExpression = statements.singleOrNull() as? IrExpression ?: this
+
 /**
  * Appends the parameters in [contextParameters] to the type parameters of
  * [this] function, renaming those that may clash with a provided collection of

compiler/testData/codegen/box/valueClasses/nothingAsParameterType.kt

@@ -0,0 +1,50 @@
+// WITH_STDLIB
+// WORKS_WHEN_VALUE_CLASS
+// LANGUAGE: +ValueClasses
+// TARGET_BACKEND: JVM_IR
+
+interface I<T: A> {
+    fun f(x: T) = println(x)
+    fun g(x: T = error("OK")) = println(x)
+    fun T.f(x: T) = println(x)
+    fun T.g(x: T = error("OK")) = println(x)
+}
+
+@JvmInline
+value class A(val x: Int, val y: Int): I<Nothing>
+
+@JvmInline
+value class B(val x: Int, val y: Int): I<Nothing> {
+    override fun f(x: Nothing) = println(this)
+    override fun g(x: Nothing) = println(this)
+    fun h(x: Nothing) = println(this)
+    fun t(x: Nothing = error("OK")) = println(this)
+    override fun Nothing.f(x: Nothing) = println(this@B)
+    override fun Nothing.g(x: Nothing) = println(this@B)
+    fun Nothing.h(x: Nothing) = println(this@B)
+    fun Nothing.t(x: Nothing = error("OK")) = println(this@B)
+}
+
+fun box(): String {
+    require(runCatching { A(1, 2).f(error("OK1")) }.exceptionOrNull()!!.message!! == "OK1")
+    require(runCatching { B(1, 2).f(error("OK2")) }.exceptionOrNull()!!.message!! == "OK2")
+    require(runCatching { A(1, 2).g(error("OK3")) }.exceptionOrNull()!!.message!! == "OK3")
+    require(runCatching { B(1, 2).g(error("OK4")) }.exceptionOrNull()!!.message!! == "OK4")
+    require(runCatching { A(1, 2).g() }.exceptionOrNull()!!.message!! == "OK")
+    require(runCatching { B(1, 2).g() }.exceptionOrNull()!!.message!! == "OK")
+    require(runCatching { B(1, 2).h(error("OK5")) }.exceptionOrNull()!!.message!! == "OK5")
+    require(runCatching { B(1, 2).t(error("OK6")) }.exceptionOrNull()!!.message!! == "OK6")
+    require(runCatching { B(1, 2).t() }.exceptionOrNull()!!.message!! == "OK")
+
+    require(runCatching { A(1, 2).run { error("OK1").f(error("OK")) } }.exceptionOrNull()!!.message!! == "OK1")
+    require(runCatching { B(1, 2).run { error("OK2").f(error("OK")) } }.exceptionOrNull()!!.message!! == "OK2")
+    require(runCatching { A(1, 2).run { error("OK3").g(error("OK")) } }.exceptionOrNull()!!.message!! == "OK3")
+    require(runCatching { B(1, 2).run { error("OK4").g(error("OK")) } }.exceptionOrNull()!!.message!! == "OK4") 
+    require(runCatching { A(1, 2).run { error("OK5").g() } }.exceptionOrNull()!!.message!! == "OK5")
+    require(runCatching { B(1, 2).run { error("OK6").g() } }.exceptionOrNull()!!.message!! == "OK6")
+    require(runCatching { B(1, 2).run { error("OK7").h(error("OK")) } }.exceptionOrNull()!!.message!! == "OK7")
+    require(runCatching { B(1, 2).run { error("OK8").t(error("OK")) } }.exceptionOrNull()!!.message!! == "OK8")
+    require(runCatching { B(1, 2).run { error("OK9").t() } }.exceptionOrNull()!!.message!! == "OK9")
+    
+    return "OK"
+}

compiler/testData/codegen/box/valueClasses/overrideFunctionWithDefaultParameter.kt

@@ -2,9 +2,7 @@
 // WORKS_WHEN_VALUE_CLASS
 // LANGUAGE: +ValueClasses
 
-// TARGET_BACKEND: JVM
-// IGNORE_BACKEND: JVM_IR
-// Depends on KT-57973
+// TARGET_BACKEND: JVM_IR
 // JVM_TARGET: 1.8
 
 interface Path {

compiler/testData/codegen/box/valueClasses/overrideFunctionWithDefaultParameterGeneric.kt

@@ -2,9 +2,7 @@
 // WORKS_WHEN_VALUE_CLASS
 // LANGUAGE: +ValueClasses, +GenericInlineClassParameter
 
-// TARGET_BACKEND: JVM
-// IGNORE_BACKEND: JVM_IR
-// Depends on KT-57973
+// TARGET_BACKEND: JVM_IR
 // JVM_TARGET: 1.8
 
 interface Path {

compiler/testData/codegen/box/valueClasses/overrides.txt

@@ -154,11 +154,11 @@ public final class GenericFakeOverrideMFVC {
     public method hashCode(): int
     public static method hashCode-impl(p0: double, p1: double): int
     public synthetic bridge method setP(p0: java.lang.Object): void
-    public method setP-nuuzChU(@org.jetbrains.annotations.NotNull p0: DPoint): void
     public static method setP-nuuzChU(p0: double, p1: double, p2: double, p3: double): void
+    public method setP-nuuzChU(p0: java.lang.Object): void
     public synthetic bridge method setP1(p0: java.lang.Object): void
-    public method setP1-nuuzChU(@org.jetbrains.annotations.NotNull p0: DPoint): void
     public static method setP1-nuuzChU(p0: double, p1: double, p2: double, p3: double): void
+    public method setP1-nuuzChU(p0: java.lang.Object): void
     public @org.jetbrains.annotations.NotNull method toString(): java.lang.String
     public static method toString-impl(p0: double, p1: double): java.lang.String
     public synthetic final method unbox-impl-field1(): double

compiler/testData/codegen/box/valueClasses/overrides_inlineClass.txt

@@ -154,11 +154,11 @@ public final class GenericFakeOverrideMFVC {
     public method hashCode(): int
     public static method hashCode-impl(p0: double, p1: double): int
     public synthetic bridge method setP(p0: java.lang.Object): void
-    public method setP-nuuzChU(@org.jetbrains.annotations.NotNull p0: DPoint): void
     public static method setP-nuuzChU(p0: double, p1: double, p2: double, p3: double): void
+    public method setP-nuuzChU(p0: java.lang.Object): void
     public synthetic bridge method setP1(p0: java.lang.Object): void
-    public method setP1-nuuzChU(@org.jetbrains.annotations.NotNull p0: DPoint): void
     public static method setP1-nuuzChU(p0: double, p1: double, p2: double, p3: double): void
+    public method setP1-nuuzChU(p0: java.lang.Object): void
     public @org.jetbrains.annotations.NotNull method toString(): java.lang.String
     public static method toString-impl(p0: double, p1: double): java.lang.String
     public synthetic final method unbox-impl-field1(): double

compiler/testData/codegen/box/valueClasses/overrides_typeParameters.txt

@@ -64,10 +64,10 @@ public final class GenericFakeOverrideMFVC {
     public method hashCode(): int
     public static method hashCode-impl(p0: java.lang.Object, p1: java.lang.Object): int
     public synthetic bridge method setP(p0: java.lang.Object): void
-    public method setP-E-wHi0Q(@org.jetbrains.annotations.NotNull p0: XPoint): void
+    public method setP-E-wHi0Q(p0: java.lang.Object): void
     public static method setP-E-wHi0Q(p0: java.lang.Object, p1: java.lang.Object, p2: java.lang.Object, p3: java.lang.Object): void
     public synthetic bridge method setP1(p0: java.lang.Object): void
-    public method setP1-E-wHi0Q(@org.jetbrains.annotations.NotNull p0: XPoint): void
+    public method setP1-E-wHi0Q(p0: java.lang.Object): void
     public static method setP1-E-wHi0Q(p0: java.lang.Object, p1: java.lang.Object, p2: java.lang.Object, p3: java.lang.Object): void
     public @org.jetbrains.annotations.NotNull method toString(): java.lang.String
     public static method toString-impl(p0: java.lang.Object, p1: java.lang.Object): java.lang.String

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/BlackBoxCodegenTestGenerated.java

@@ -49328,18 +49328,6 @@ public class BlackBoxCodegenTestGenerated extends AbstractBlackBoxCodegenTest {
         public void testAllFilesPresentInValueClasses() throws Exception {
             KtTestUtil.assertAllTestsPresentByMetadataWithExcluded(this.getClass(), new File("compiler/testData/codegen/box/valueClasses"), Pattern.compile("^(.+)\\.kt$"), null, TargetBackend.JVM, true);
         }
-
-        @Test
-        @TestMetadata("overrideFunctionWithDefaultParameter.kt")
-        public void testOverrideFunctionWithDefaultParameter() throws Exception {
-            runTest("compiler/testData/codegen/box/valueClasses/overrideFunctionWithDefaultParameter.kt", TransformersFunctions.getReplaceOptionalJvmInlineAnnotationWithReal());
-        }
-
-        @Test
-        @TestMetadata("overrideFunctionWithDefaultParameterGeneric.kt")
-        public void testOverrideFunctionWithDefaultParameterGeneric() throws Exception {
-            runTest("compiler/testData/codegen/box/valueClasses/overrideFunctionWithDefaultParameterGeneric.kt", TransformersFunctions.getReplaceOptionalJvmInlineAnnotationWithReal());
-        }
     }
 
     @Nested

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/IrBlackBoxCodegenTestGenerated.java

@@ -52095,6 +52095,12 @@ public class IrBlackBoxCodegenTestGenerated extends AbstractIrBlackBoxCodegenTes
             runTest("compiler/testData/codegen/box/valueClasses/mutableSharedMfvcVar.kt");
         }
 
+        @Test
+        @TestMetadata("nothingAsParameterType.kt")
+        public void testNothingAsParameterType() throws Exception {
+            runTest("compiler/testData/codegen/box/valueClasses/nothingAsParameterType.kt", TransformersFunctions.getReplaceOptionalJvmInlineAnnotationWithReal());
+        }
+
         @Test
         @TestMetadata("overrideFunctionWithDefaultParameter.kt")
         public void testOverrideFunctionWithDefaultParameter() throws Exception {

compiler/tests-common-new/tests-gen/org/jetbrains/kotlin/test/runners/codegen/IrBlackBoxCodegenWithIrInlinerTestGenerated.java

@@ -52095,6 +52095,12 @@ public class IrBlackBoxCodegenWithIrInlinerTestGenerated extends AbstractIrBlack
             runTest("compiler/testData/codegen/box/valueClasses/mutableSharedMfvcVar.kt");
         }
 
+        @Test
+        @TestMetadata("nothingAsParameterType.kt")
+        public void testNothingAsParameterType() throws Exception {
+            runTest("compiler/testData/codegen/box/valueClasses/nothingAsParameterType.kt", TransformersFunctions.getReplaceOptionalJvmInlineAnnotationWithReal());
+        }
+
         @Test
         @TestMetadata("overrideFunctionWithDefaultParameter.kt")
         public void testOverrideFunctionWithDefaultParameter() throws Exception {

compiler/tests-gen/org/jetbrains/kotlin/codegen/LightAnalysisModeTestGenerated.java

@@ -40165,23 +40165,9 @@ public class LightAnalysisModeTestGenerated extends AbstractLightAnalysisModeTes
             KotlinTestUtils.runTest(this::doTest, TargetBackend.JVM, testDataFilePath);
         }
 
-        private void runTest(String testDataFilePath, java.util.function.Function<String, String> transformer) throws Exception {
-            KotlinTestUtils.runTest(path -> doTestWithTransformer(path, transformer), TargetBackend.JVM, testDataFilePath);
-        }
-
         public void testAllFilesPresentInValueClasses() throws Exception {
             KtTestUtil.assertAllTestsPresentByMetadataWithExcluded(this.getClass(), new File("compiler/testData/codegen/box/valueClasses"), Pattern.compile("^(.+)\\.kt$"), null, TargetBackend.JVM, true);
         }
-
-        @TestMetadata("overrideFunctionWithDefaultParameter.kt")
-        public void testOverrideFunctionWithDefaultParameter() throws Exception {
-            runTest("compiler/testData/codegen/box/valueClasses/overrideFunctionWithDefaultParameter.kt", TransformersFunctions.getReplaceOptionalJvmInlineAnnotationWithReal());
-        }
-
-        @TestMetadata("overrideFunctionWithDefaultParameterGeneric.kt")
-        public void testOverrideFunctionWithDefaultParameterGeneric() throws Exception {
-            runTest("compiler/testData/codegen/box/valueClasses/overrideFunctionWithDefaultParameterGeneric.kt", TransformersFunctions.getReplaceOptionalJvmInlineAnnotationWithReal());
-        }
     }
 
     @TestMetadata("compiler/testData/codegen/box/vararg")