From 001b95473ab90cadd4fac73d4ee9cf7d07cef2a8 Mon Sep 17 00:00:00 2001
From: Dmitry Petrov <Dmitry.Petrov@jetbrains.com>
Date: Wed, 14 Sep 2016 18:54:38 +0300
Subject: [PATCH] Drop 'parent' and 'slot'.

---
 .../FoldStringConcatenation.kt                |  80 ----------
 .../transformations/InlineDesugaredBlocks.kt  |  53 -------
 .../transformations/InsertImplicitCasts.kt    | 146 +++++++++++-------
 .../ReplaceTemporaryVariable.kt               |  37 -----
 .../src/org/jetbrains/kotlin/ir/IrElement.kt  |  53 ++-----
 .../org/jetbrains/kotlin/ir/IrElementBase.kt  |  19 +++
 .../src/org/jetbrains/kotlin/ir/IrSlots.kt    |  50 ------
 .../ir/declarations/IrAnonymousInitializer.kt |   4 +-
 .../kotlin/ir/declarations/IrDeclaration.kt   |   4 +
 .../kotlin/ir/declarations/IrFile.kt          |   4 +
 .../ir/declarations/IrGeneralFunction.kt      |   4 +-
 .../ir/declarations/IrModuleFragment.kt       |  19 +--
 .../kotlin/ir/declarations/IrProperty.kt      |   3 +-
 .../impl/IrAnonymousInitializerImpl.kt        |  28 +---
 .../ir/declarations/impl/IrClassImpl.kt       |  21 +--
 .../ir/declarations/impl/IrConstructorImpl.kt |  14 +-
 .../ir/declarations/impl/IrEnumEntryImpl.kt   |  38 +----
 .../impl/IrErrorDeclarationImpl.kt            |   9 +-
 .../ir/declarations/impl/IrFieldImpl.kt       |  27 +---
 .../kotlin/ir/declarations/impl/IrFileImpl.kt |  21 +--
 .../ir/declarations/impl/IrFunctionBase.kt    |  19 ++-
 .../impl/IrGeneralFunctionBase.kt             |  18 ---
 .../impl/IrLocalDelegatedPropertyImpl.kt      |  56 ++-----
 .../declarations/impl/IrModuleFragmentImpl.kt |  19 +--
 .../ir/declarations/impl/IrPropertyImpl.kt    |  41 +----
 .../ir/declarations/impl/IrTypeAliasImpl.kt   |  10 +-
 .../ir/declarations/impl/IrVariableImpl.kt    |  25 +--
 .../jetbrains/kotlin/ir/expressions/IrBody.kt |  10 +-
 .../kotlin/ir/expressions/IrBreakContinue.kt  |  21 ---
 .../kotlin/ir/expressions/IrExpression.kt     |   4 +
 .../kotlin/ir/expressions/IrTryCatch.kt       |   3 +
 .../kotlin/ir/expressions/IrVararg.kt         |   7 +
 .../jetbrains/kotlin/ir/expressions/IrWhen.kt |   6 +
 .../ir/expressions/impl/IrBlockBodyImpl.kt    |  23 +--
 .../kotlin/ir/expressions/impl/IrBlockImpl.kt |   9 +-
 .../ir/expressions/impl/IrCompositeImpl.kt    |   3 -
 .../impl/IrContainerExpressionBase.kt         |  36 ++---
 .../ir/expressions/impl/IrDoWhileLoopImpl.kt  |   7 +-
 .../ir/expressions/impl/IrEmptyBlockImpl.kt   |  44 ------
 .../impl/IrErrorCallExpressionImpl.kt         |  23 +--
 .../expressions/impl/IrErrorExpressionImpl.kt |   4 -
 .../expressions/impl/IrExpressionBodyImpl.kt  |  27 +---
 .../expressions/impl/IrFieldExpressionBase.kt |  18 ---
 .../ir/expressions/impl/IrGeneralCallBase.kt  |  29 ++--
 .../ir/expressions/impl/IrGetClassImpl.kt     |  28 +---
 .../ir/expressions/impl/IrGetFieldImpl.kt     |  12 +-
 .../ir/expressions/impl/IrIfThenElseImpl.kt   |  60 +++----
 .../kotlin/ir/expressions/impl/IrLoopBase.kt  |  29 +---
 .../impl/IrMemberAccessExpressionBase.kt      |  34 +---
 .../ir/expressions/impl/IrPrimitiveCall.kt    | 113 +++++++-------
 .../impl/IrPropertyAccessorCall.kt            |  28 +---
 .../ir/expressions/impl/IrReturnImpl.kt       |  25 +--
 .../ir/expressions/impl/IrSetFieldImpl.kt     |  28 +---
 .../ir/expressions/impl/IrSetVariableImpl.kt  |  27 +---
 .../expressions/impl/IrSpreadElementImpl.kt   |  28 +---
 .../impl/IrStringConcatenationImpl.kt         |  19 +--
 .../expressions/impl/IrSyntheticBodyImpl.kt   |   9 +-
 .../IrTerminalDeclarationReferenceBase.kt     |  14 +-
 .../impl/IrTerminalExpressionBase.kt          |  14 +-
 .../expressions/impl/IrThisReferenceImpl.kt   |   1 -
 .../kotlin/ir/expressions/impl/IrThrowImpl.kt |  29 +---
 .../ir/expressions/impl/IrTryCatchImpl.kt     |  76 +++------
 .../impl/IrTypeOperatorCallImpl.kt            |  27 +---
 .../ir/expressions/impl/IrVarargImpl.kt       |  21 ++-
 .../kotlin/ir/expressions/impl/IrWhenImpl.kt  |  45 ++----
 .../ir/expressions/impl/IrWhileLoopImpl.kt    |   6 +
 .../kotlin/ir/util/RenderIrElement.kt         |   4 +-
 .../kotlin/ir/util/ValidateIrTree.kt          |  40 -----
 .../ir/visitors/IrElementTransformer.kt       | 119 ++++++++++++++
 .../ir/irText/expressions/breakContinue.txt   |  28 ++--
 .../expressions/breakContinueInLoopHeader.txt |   8 +-
 .../expressions/forWithBreakContinue.txt      |  20 +--
 72 files changed, 674 insertions(+), 1314 deletions(-)
 delete mode 100644 compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/transformations/FoldStringConcatenation.kt
 delete mode 100644 compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/transformations/InlineDesugaredBlocks.kt
 delete mode 100644 compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/transformations/ReplaceTemporaryVariable.kt
 create mode 100644 compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/IrElementBase.kt
 delete mode 100644 compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/IrSlots.kt
 delete mode 100644 compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrEmptyBlockImpl.kt
 delete mode 100644 compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/ValidateIrTree.kt
 create mode 100644 compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/visitors/IrElementTransformer.kt

diff --git a/compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/transformations/FoldStringConcatenation.kt b/compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/transformations/FoldStringConcatenation.kt
deleted file mode 100644
index f2e59035452..00000000000
--- a/compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/transformations/FoldStringConcatenation.kt
+++ /dev/null
@@ -1,80 +0,0 @@
-/*
- * Copyright 2010-2016 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.jetbrains.kotlin.psi2ir.transformations
-
-import org.jetbrains.kotlin.builtins.KotlinBuiltIns
-import org.jetbrains.kotlin.descriptors.CallableDescriptor
-import org.jetbrains.kotlin.ir.IrElement
-import org.jetbrains.kotlin.ir.detach
-import org.jetbrains.kotlin.ir.expressions.IrExpression
-import org.jetbrains.kotlin.ir.expressions.IrGeneralCall
-import org.jetbrains.kotlin.ir.expressions.IrStringConcatenation
-import org.jetbrains.kotlin.ir.expressions.impl.IrStringConcatenationImpl
-import org.jetbrains.kotlin.ir.replaceWith
-import org.jetbrains.kotlin.ir.visitors.IrElementVisitorVoid
-import org.jetbrains.kotlin.ir.visitors.acceptChildrenVoid
-import org.jetbrains.kotlin.ir.visitors.acceptVoid
-import org.jetbrains.kotlin.util.OperatorNameConventions
-import java.util.*
-
-fun foldStringConcatenation(element: IrElement) {
-    element.acceptVoid(FoldStringConcatenation())
-}
-
-class FoldStringConcatenation : IrElementVisitorVoid {
-    override fun visitElement(element: IrElement) {
-        element.acceptChildrenVoid(this)
-    }
-
-    override fun visitGeneralCall(expression: IrGeneralCall) {
-        if (!isStringPlus(expression.descriptor)) {
-            visitElement(expression)
-            return
-        }
-
-        val arguments = ArrayList<IrExpression>()
-        collectStringConcatenationArguments(expression, arguments)
-        val irStringConcatenation = IrStringConcatenationImpl(expression.startOffset, expression.endOffset, expression.type)
-        arguments.forEach { irStringConcatenation.addArgument(it) }
-
-        expression.replaceWith(irStringConcatenation)
-    }
-
-    private fun collectStringConcatenationArguments(expression: IrExpression, arguments: ArrayList<IrExpression>) {
-        when {
-            expression is IrGeneralCall && isStringPlus(expression.descriptor)-> {
-                collectStringConcatenationArguments(expression.dispatchReceiver!!, arguments)
-                collectStringConcatenationArguments(expression.getArgument(0)!!, arguments)
-            }
-            expression is IrStringConcatenation -> {
-                arguments.addAll(expression.arguments)
-                expression.arguments.forEach { it.detach() }
-            }
-            else -> {
-                arguments.add(expression)
-                expression.detach()
-            }
-        }
-    }
-
-    private fun isStringPlus(descriptor: CallableDescriptor): Boolean {
-        if (descriptor.name != OperatorNameConventions.PLUS) return false
-        val dispatchReceiverType = descriptor.dispatchReceiverParameter?.type ?: return false
-        if (!KotlinBuiltIns.isString(dispatchReceiverType)) return false
-        return true
-    }
-}
diff --git a/compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/transformations/InlineDesugaredBlocks.kt b/compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/transformations/InlineDesugaredBlocks.kt
deleted file mode 100644
index 1ebb5618ef5..00000000000
--- a/compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/transformations/InlineDesugaredBlocks.kt
+++ /dev/null
@@ -1,53 +0,0 @@
-/*
- * Copyright 2010-2016 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.jetbrains.kotlin.psi2ir.transformations
-
-import org.jetbrains.kotlin.ir.IrElement
-import org.jetbrains.kotlin.ir.detach
-import org.jetbrains.kotlin.ir.expressions.IrBlock
-import org.jetbrains.kotlin.ir.expressions.impl.IrBlockImpl
-import org.jetbrains.kotlin.ir.replaceWith
-import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
-import org.jetbrains.kotlin.ir.visitors.IrElementVisitorVoid
-import org.jetbrains.kotlin.ir.visitors.acceptChildrenVoid
-import org.jetbrains.kotlin.ir.visitors.acceptVoid
-
-fun inlineDesugaredBlocks(element: IrElement) {
-    element.acceptVoid(InlineDesugaredBlocks())
-}
-
-class InlineDesugaredBlocks : IrElementVisitorVoid {
-    override fun visitElement(element: IrElement) {
-        element.acceptChildrenVoid(this)
-    }
-
-    override fun visitBlock(expression: IrBlock) {
-        val transformedBlock = IrBlockImpl(expression.startOffset, expression.endOffset, expression.type, expression.origin)
-        for (statement in expression.statements) {
-            statement.acceptVoid(this)
-            if (statement is IrBlock && statement.origin != null) {
-                statement.statements.forEach {
-                    transformedBlock.addStatement(it.detach())
-                }
-            }
-            else {
-                transformedBlock.addStatement(statement.detach())
-            }
-        }
-        expression.replaceWith(transformedBlock)
-    }
-}
diff --git a/compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/transformations/InsertImplicitCasts.kt b/compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/transformations/InsertImplicitCasts.kt
index 74296ebeb48..dd0032f8f80 100644
--- a/compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/transformations/InsertImplicitCasts.kt
+++ b/compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/transformations/InsertImplicitCasts.kt
@@ -19,13 +19,9 @@ package org.jetbrains.kotlin.psi2ir.transformations
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
 import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.declarations.IrVariable
-import org.jetbrains.kotlin.ir.detach
 import org.jetbrains.kotlin.ir.expressions.*
 import org.jetbrains.kotlin.ir.expressions.impl.IrTypeOperatorCallImpl
-import org.jetbrains.kotlin.ir.replaceWith
-import org.jetbrains.kotlin.ir.visitors.IrElementVisitorVoid
-import org.jetbrains.kotlin.ir.visitors.acceptChildrenVoid
-import org.jetbrains.kotlin.ir.visitors.acceptVoid
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.psi2ir.containsNull
 import org.jetbrains.kotlin.types.KotlinType
 import org.jetbrains.kotlin.types.checker.KotlinTypeChecker
@@ -34,109 +30,141 @@ import org.jetbrains.kotlin.types.typeUtil.makeNotNullable
 import org.jetbrains.kotlin.types.upperIfFlexible
 
 fun insertImplicitCasts(builtIns: KotlinBuiltIns, element: IrElement) {
-    element.acceptVoid(InsertImplicitCasts(builtIns))
+    element.transformChildren(InsertImplicitCasts(builtIns), null)
 }
 
-class InsertImplicitCasts(val builtIns: KotlinBuiltIns): IrElementVisitorVoid {
-    override fun visitElement(element: IrElement) {
-        element.acceptChildrenVoid(this)
+class InsertImplicitCasts(val builtIns: KotlinBuiltIns): IrElementTransformer<Nothing?> {
+    override fun visitElement(element: IrElement, data: Nothing?): IrElement {
+        element.transformChildren(this, data)
+        return element
     }
 
-    override fun visitGeneralCall(expression: IrGeneralCall) {
-        expression.acceptChildrenVoid(this)
+    override fun visitGeneralCall(expression: IrGeneralCall, data: Nothing?): IrExpression {
+        expression.transformChildren(this, data)
 
         with(expression) {
-            dispatchReceiver?.replaceWithCast(descriptor.dispatchReceiverParameter?.type)
-            extensionReceiver?.replaceWithCast(descriptor.extensionReceiverParameter?.type)
+            dispatchReceiver = dispatchReceiver?.wrapWithImplicitCast(descriptor.dispatchReceiverParameter?.type)
+            extensionReceiver = extensionReceiver?.wrapWithImplicitCast(descriptor.extensionReceiverParameter?.type)
             for (index in descriptor.valueParameters.indices) {
+                val argument = getArgument(index) ?: continue
                 val parameterType = descriptor.valueParameters[index].type
-                getArgument(index)?.replaceWithCast(parameterType)
+                putArgument(index, argument.wrapWithImplicitCast(parameterType))
             }
         }
+
+        return expression
     }
 
-    override fun visitBlock(expression: IrBlock) {
-        expression.acceptChildrenVoid(this)
+    override fun visitBlock(expression: IrBlock, data: Nothing?): IrExpression {
+        expression.transformChildren(this, data)
+
         val type = expression.type
-        if (KotlinBuiltIns.isUnit(type)) return
-        if (expression.statements.isEmpty()) return
+        if (expression.statements.isEmpty() || KotlinBuiltIns.isUnit(type) || KotlinBuiltIns.isNothing(type)) {
+            return expression
+        }
 
         val lastStatement = expression.statements.last()
         if (lastStatement is IrExpression) {
-            lastStatement.replaceWithCast(type)
+            expression.putStatement(expression.statements.lastIndex, lastStatement.wrapWithImplicitCast(type))
         }
+
+        return expression
     }
 
-    override fun visitReturn(expression: IrReturn) {
-        expression.acceptChildrenVoid(this)
+    override fun visitReturn(expression: IrReturn, data: Nothing?): IrExpression {
+        expression.transformChildren(this, data)
 
-        expression.value?.replaceWithCast(expression.returnTarget.returnType)
+        expression.value = expression.value?.wrapWithImplicitCast(expression.returnTarget.returnType)
+
+        return expression
     }
 
-    override fun visitSetVariable(expression: IrSetVariable) {
-        expression.acceptChildrenVoid(this)
+    override fun visitSetVariable(expression: IrSetVariable, data: Nothing?): IrExpression {
+        expression.transformChildren(this, data)
 
-        expression.value.replaceWithCast(expression.descriptor.type)
+        expression.value = expression.value.wrapWithImplicitCast(expression.descriptor.type)
+
+        return expression
     }
 
-    override fun visitSetField(expression: IrSetField) {
-        expression.acceptChildrenVoid(this)
+    override fun visitSetField(expression: IrSetField, data: Nothing?): IrExpression {
+        expression.transformChildren(this, data)
 
-        expression.value.replaceWithCast(expression.descriptor.type)
+        expression.value = expression.value.wrapWithImplicitCast(expression.descriptor.type)
+
+        return expression
     }
 
-    override fun visitVariable(declaration: IrVariable) {
-        declaration.acceptChildrenVoid(this)
+    override fun visitVariable(declaration: IrVariable, data: Nothing?): IrVariable {
+        declaration.transformChildren(this, data)
 
-        declaration.initializer?.replaceWithCast(declaration.descriptor.type)
+        declaration.initializer = declaration.initializer?.wrapWithImplicitCast(declaration.descriptor.type)
+
+        return declaration
     }
 
-    override fun visitWhen(expression: IrWhen) {
-        expression.acceptChildrenVoid(this)
+    override fun visitWhen(expression: IrWhen, data: Nothing?): IrExpression {
+        expression.transformChildren(this, data)
 
-        for (branchIndex in expression.branchIndices) {
-            expression.getNthCondition(branchIndex)!!.replaceWithCast(builtIns.booleanType)
-            expression.getNthResult(branchIndex)!!.replaceWithCast(expression.type)
+        val resultType = expression.type
+
+        for (i in expression.branchIndices) {
+            val nthCondition = expression.getNthCondition(i)!!
+            val nthResult = expression.getNthResult(i)!!
+
+            expression.putNthCondition(i, nthCondition.wrapWithImplicitCast(builtIns.booleanType))
+            expression.putNthResult(i, nthResult.wrapWithImplicitCast(resultType))
         }
-        expression.elseBranch?.replaceWithCast(expression.type)
+
+        expression.elseBranch = expression.elseBranch?.wrapWithImplicitCast(resultType)
+
+        return expression
     }
 
-    override fun visitLoop(loop: IrLoop) {
-        loop.acceptChildrenVoid(this)
+    override fun visitLoop(loop: IrLoop, data: Nothing?): IrExpression {
+        loop.transformChildren(this, data)
 
-        loop.condition.replaceWithCast(builtIns.booleanType)
+        loop.condition = loop.condition.wrapWithImplicitCast(builtIns.booleanType)
+
+        return loop
     }
 
-    override fun visitThrow(expression: IrThrow) {
-        expression.acceptChildrenVoid(this)
+    override fun visitThrow(expression: IrThrow, data: Nothing?): IrExpression {
+        expression.transformChildren(this, data)
 
-        expression.value.replaceWithCast(builtIns.throwable.defaultType)
+        expression.value = expression.value.wrapWithImplicitCast(builtIns.throwable.defaultType)
+
+        return expression
     }
 
-    override fun visitTryCatch(tryCatch: IrTryCatch) {
-        tryCatch.acceptChildrenVoid(this)
+    override fun visitTryCatch(tryCatch: IrTryCatch, data: Nothing?): IrExpression {
+        tryCatch.transformChildren(this, data)
 
         val resultType = tryCatch.type
 
-        tryCatch.tryResult.replaceWithCast(resultType)
-        for (catchClauseIndex in tryCatch.catchClauseIndices) {
-            tryCatch.getNthCatchResult(catchClauseIndex)!!.replaceWithCast(resultType)
+        tryCatch.tryResult = tryCatch.tryResult.wrapWithImplicitCast(resultType)
+
+        for (i in tryCatch.catchClauseIndices) {
+            val nthCatchResult = tryCatch.getNthCatchResult(i)!!
+            tryCatch.putNthCatchResult(i, nthCatchResult.wrapWithImplicitCast(resultType))
         }
+
+        return tryCatch
     }
 
-    override fun visitVararg(expression: IrVararg) {
-        expression.acceptChildrenVoid(this)
+    override fun visitVararg(expression: IrVararg, data: Nothing?): IrExpression {
+        expression.transformChildren(this, data)
 
-        for (element in expression.elements) {
+        expression.elements.forEachIndexed { i, element ->
             when (element) {
-                is IrSpreadElement -> element.expression.replaceWithCast(expression.type)
-                is IrExpression -> element.replaceWithCast(expression.varargElementType)
+                is IrSpreadElement ->
+                    element.expression = element.expression.wrapWithImplicitCast(expression.type)
+                is IrExpression ->
+                    expression.putElement(i, element.wrapWithImplicitCast(expression.varargElementType))
             }
         }
-    }
 
-    private fun IrExpression.replaceWithCast(expectedType: KotlinType?) {
-        replaceWith { it.wrapWithImplicitCast(expectedType) }
+        return expression
     }
 
     private fun IrExpression.wrapWithImplicitCast(expectedType: KotlinType?): IrExpression {
@@ -147,16 +175,16 @@ class InsertImplicitCasts(val builtIns: KotlinBuiltIns): IrElementVisitorVoid {
         val valueType = this.type
 
         if (valueType.isNullabilityFlexible() && valueType.containsNull() && !expectedType.containsNull()) {
-            val nonNullValueType = valueType.upperIfFlexible().makeNotNullable();
+            val nonNullValueType = valueType.upperIfFlexible().makeNotNullable()
             return IrTypeOperatorCallImpl(
                     this.startOffset, this.endOffset, nonNullValueType,
-                    IrTypeOperator.IMPLICIT_NOTNULL, nonNullValueType, this.detach()
+                    IrTypeOperator.IMPLICIT_NOTNULL, nonNullValueType, this
             ).wrapWithImplicitCast(expectedType)
         }
 
         if (!KotlinTypeChecker.DEFAULT.isSubtypeOf(valueType.makeNotNullable(), expectedType)) {
             return IrTypeOperatorCallImpl(this.startOffset, this.endOffset, expectedType,
-                                                                              IrTypeOperator.IMPLICIT_CAST, expectedType, this.detach())
+                                          IrTypeOperator.IMPLICIT_CAST, expectedType, this)
         }
 
         return this
diff --git a/compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/transformations/ReplaceTemporaryVariable.kt b/compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/transformations/ReplaceTemporaryVariable.kt
deleted file mode 100644
index 5bf6074c35d..00000000000
--- a/compiler/ir/ir.psi2ir/src/org/jetbrains/kotlin/psi2ir/transformations/ReplaceTemporaryVariable.kt
+++ /dev/null
@@ -1,37 +0,0 @@
-/*
- * Copyright 2010-2016 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.jetbrains.kotlin.psi2ir.transformations
-
-import org.jetbrains.kotlin.ir.IrElement
-import org.jetbrains.kotlin.ir.declarations.IrVariable
-import org.jetbrains.kotlin.ir.expressions.IrGetVariable
-import org.jetbrains.kotlin.ir.replaceWith
-import org.jetbrains.kotlin.ir.visitors.IrElementVisitorVoid
-import org.jetbrains.kotlin.ir.visitors.acceptChildrenVoid
-import org.jetbrains.kotlin.psi2ir.intermediate.IntermediateValue
-
-class ReplaceTemporaryVariable(val from: IrVariable, val to: IntermediateValue) : IrElementVisitorVoid {
-    override fun visitElement(element: IrElement) {
-        element.acceptChildrenVoid(this)
-    }
-
-    override fun visitGetVariable(expression: IrGetVariable) {
-        if (expression.descriptor == from.descriptor) {
-            expression.replaceWith { to.load() }
-        }
-    }
-}
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/IrElement.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/IrElement.kt
index 7a2c3183fb6..8dac42ce18f 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/IrElement.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/IrElement.kt
@@ -16,57 +16,28 @@
 
 package org.jetbrains.kotlin.ir
 
-import org.jetbrains.kotlin.ir.util.render
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
+import java.lang.AssertionError
 
 interface IrElement {
     val startOffset: Int
     val endOffset: Int
 
-    val parent: IrElement?
-    val slot: Int
-    fun setTreeLocation(newParent: IrElement?, newSlot: Int)
-    fun getChild(slot: Int): IrElement?
-    fun replaceChild(slot: Int, newChild: IrElement)
-
     fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R
+
     fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D): Unit
+
+    fun <D> transform(transformer: IrElementTransformer<D>, data: D): IrElement =
+            accept(transformer, data)
+
+    fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D): Unit
 }
 
-interface IrStatement : IrElement
-
-abstract class IrElementBase(override val startOffset: Int, override val endOffset: Int) : IrElement {
-    override var parent: IrElement? = null
-    override var slot: Int = DETACHED_SLOT
-
-    override fun setTreeLocation(newParent: IrElement?, newSlot: Int) {
-        parent = newParent
-        slot = newSlot
-    }
+interface IrStatement : IrElement {
+    override fun <D> transform(transformer: IrElementTransformer<D>, data: D): IrStatement =
+            super.transform(transformer, data) as IrStatement
 }
 
-fun <T : IrElement?> T.detach(): T {
-    this?.setTreeLocation(null, DETACHED_SLOT)
-    return this
-}
-
-fun IrElement.replaceWith(otherElement: IrElement) {
-    if (otherElement == this) return
-    val parent = this.parent ?: throw AssertionError("Can't replace a non-root element $this")
-    parent.replaceChild(slot, otherElement.detach())
-}
-
-inline fun <T : IrElement> T.replaceWith(transformation: (T) -> IrElement) {
-    val originalParent = this.parent ?: throw AssertionError("Can't replace a non-root element $this")
-    val originalSlot = this.slot
-    val transformed = transformation(this)
-    if (transformed != this) {
-        originalParent.replaceChild(originalSlot, transformed)
-    }
-}
-
-fun IrElement.throwNoSuchSlot(slot: Int): Nothing =
-        throw AssertionError("${this.render()}: no such slot $slot")
-
 inline fun <reified T : IrElement> IrElement.assertCast(): T =
-        if (this is T) this else throw AssertionError("Expected ${T::class.simpleName}: $this")
\ No newline at end of file
+        if (this is T) this else throw AssertionError("Expected ${T::class.simpleName}: $this")
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/IrElementBase.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/IrElementBase.kt
new file mode 100644
index 00000000000..bee88304def
--- /dev/null
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/IrElementBase.kt
@@ -0,0 +1,19 @@
+/*
+ * Copyright 2010-2016 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jetbrains.kotlin.ir
+
+abstract class IrElementBase(override val startOffset: Int, override val endOffset: Int) : IrElement
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/IrSlots.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/IrSlots.kt
deleted file mode 100644
index 76927795866..00000000000
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/IrSlots.kt
+++ /dev/null
@@ -1,50 +0,0 @@
-/*
- * Copyright 2010-2016 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.jetbrains.kotlin.ir
-
-// Slots should be unique within children of particular node type.
-// Non-negative numbers are used for slots in indexed container elements, for example, value arguments in a call.
-// NB a node can potentially contain several "containers"; it's up to a node how to organize numbering in such case.
-// Negative numbers are used for "named" slots, for example, dispatch and extension receivers in a call.
-
-const val DETACHED_SLOT = Int.MIN_VALUE
-
-const val CHILD_EXPRESSION_SLOT = 0
-const val ARGUMENT0_SLOT = 0
-const val ARGUMENT1_SLOT = 1
-const val SETTER_ARGUMENT_INDEX = 0
-
-const val DISPATCH_RECEIVER_SLOT = -1
-const val EXTENSION_RECEIVER_SLOT = -2
-const val BACKING_FIELD_RECEIVER_SLOT = -3
-const val FUNCTION_BODY_SLOT = -4
-const val ANONYMOUS_INITIALIZER_BODY_SLOT = -5
-const val MODULE_SLOT = -6
-const val INITIALIZER_SLOT = -7
-const val IF_CONDITION_SLOT = -8
-const val IF_THEN_SLOT = -9
-const val IF_ELSE_SLOT = -10
-const val LOOP_BODY_SLOT = -11
-const val LOOP_CONDITION_SLOT = -12
-const val TRY_RESULT_SLOT = -13
-const val FINALLY_EXPRESSION_SLOT = -14
-const val PROPERTY_GETTER_SLOT = -15
-const val PROPERTY_SETTER_SLOT = -16
-const val BACKING_FIELD_SLOT = -17
-const val ENUM_ENTRY_CLASS_SLOT = -18
-const val ENUM_ENTRY_INITIALIZER_SLOT = -19
-const val LOCAL_DELEGATE_SLOT = -20
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrAnonymousInitializer.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrAnonymousInitializer.kt
index 693c87ba1da..f61e81bf593 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrAnonymousInitializer.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrAnonymousInitializer.kt
@@ -17,7 +17,7 @@
 package org.jetbrains.kotlin.ir.declarations
 
 import org.jetbrains.kotlin.descriptors.ClassDescriptor
-import org.jetbrains.kotlin.ir.expressions.IrBlockBody
+import org.jetbrains.kotlin.ir.expressions.IrBody
 
 interface IrAnonymousInitializer : IrDeclaration {
     override val descriptor: ClassDescriptor // TODO special descriptor for anonymous initializer blocks
@@ -25,6 +25,6 @@ interface IrAnonymousInitializer : IrDeclaration {
     override val declarationKind: IrDeclarationKind
         get() = IrDeclarationKind.ANONYMOUS_INITIALIZER
 
-    var body: IrBlockBody
+    var body: IrBody
 }
 
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrDeclaration.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrDeclaration.kt
index a899558464b..25612100949 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrDeclaration.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrDeclaration.kt
@@ -18,11 +18,15 @@ package org.jetbrains.kotlin.ir.declarations
 
 import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
 import org.jetbrains.kotlin.ir.IrStatement
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 
 interface IrDeclaration : IrStatement {
     val descriptor: DeclarationDescriptor
     val declarationKind: IrDeclarationKind
     val origin: IrDeclarationOrigin
+
+    override fun <D> transform(transformer: IrElementTransformer<D>, data: D): IrDeclaration =
+            accept(transformer, data) as IrDeclaration
 }
 
 enum class IrDeclarationKind {
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrFile.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrFile.kt
index 75d8a780e7c..61fe5bcd0b5 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrFile.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrFile.kt
@@ -21,6 +21,7 @@ import org.jetbrains.kotlin.descriptors.annotations.AnnotationDescriptor
 import org.jetbrains.kotlin.descriptors.annotations.checkAnnotationName
 import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.SourceManager
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.name.FqName
 
 interface IrFile : IrElement, IrDeclarationContainer {
@@ -37,6 +38,9 @@ interface IrFile : IrElement, IrDeclarationContainer {
 
         override fun build(): IrFile
     }
+
+    override fun <D> transform(transformer: IrElementTransformer<D>, data: D): IrFile =
+            accept(transformer, data) as IrFile
 }
 
 val IrFile.name: String get() = fileEntry.name
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrGeneralFunction.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrGeneralFunction.kt
index bb8236ab1b7..ebabc80287c 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrGeneralFunction.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrGeneralFunction.kt
@@ -28,7 +28,7 @@ interface IrFunction : IrDeclaration {
     override val declarationKind: IrDeclarationKind
         get() = IrDeclarationKind.FUNCTION
 
-    fun putDefault(parameter: ValueParameterDescriptor, expressionBody: IrExpressionBody)
-    fun getDefault(parameter: ValueParameterDescriptor): IrExpressionBody?
+    fun putDefault(parameter: ValueParameterDescriptor, expressionBody: IrBody)
+    fun getDefault(parameter: ValueParameterDescriptor): IrBody?
 }
 
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrModuleFragment.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrModuleFragment.kt
index f6ed998f5e7..b77967ab435 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrModuleFragment.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrModuleFragment.kt
@@ -18,23 +18,20 @@ package org.jetbrains.kotlin.ir.declarations
 
 import org.jetbrains.kotlin.descriptors.ModuleDescriptor
 import org.jetbrains.kotlin.ir.IrElement
-import org.jetbrains.kotlin.ir.MODULE_SLOT
 import org.jetbrains.kotlin.ir.UNDEFINED_OFFSET
 import org.jetbrains.kotlin.ir.descriptors.IrBuiltIns
-import java.lang.AssertionError
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
+import java.lang.UnsupportedOperationException
 
 interface IrModuleFragment : IrElement {
-    override val startOffset: Int get() = UNDEFINED_OFFSET
-    override val endOffset: Int get() = UNDEFINED_OFFSET
-
-    override val parent: IrElement? get() = null
-    override val slot: Int get() = MODULE_SLOT
-    override fun setTreeLocation(newParent: IrElement?, newSlot: Int) {
-        throw AssertionError("IrModule can't have a parent element")
-    }
-
     val descriptor: ModuleDescriptor
     val irBuiltins: IrBuiltIns
     val files: List<IrFile>
+
+    override val startOffset: Int get() = UNDEFINED_OFFSET
+    override val endOffset: Int get() = UNDEFINED_OFFSET
+
+    override fun <D> transform(transformer: IrElementTransformer<D>, data: D): IrElement =
+            accept(transformer, data) as IrModuleFragment
 }
 
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrProperty.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrProperty.kt
index d613e30b38d..6b08f08b8c2 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrProperty.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/IrProperty.kt
@@ -17,6 +17,7 @@
 package org.jetbrains.kotlin.ir.declarations
 
 import org.jetbrains.kotlin.descriptors.PropertyDescriptor
+import org.jetbrains.kotlin.ir.expressions.IrBody
 import org.jetbrains.kotlin.ir.expressions.IrExpressionBody
 
 interface IrProperty : IrDeclaration {
@@ -36,5 +37,5 @@ interface IrField : IrDeclaration {
     override val declarationKind: IrDeclarationKind
         get() = IrDeclarationKind.FIELD
 
-    var initializer: IrExpressionBody?
+    var initializer: IrBody?
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrAnonymousInitializerImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrAnonymousInitializerImpl.kt
index f83aa03da2b..f296d8364c1 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrAnonymousInitializerImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrAnonymousInitializerImpl.kt
@@ -22,6 +22,8 @@ import org.jetbrains.kotlin.ir.declarations.IrAnonymousInitializer
 import org.jetbrains.kotlin.ir.declarations.impl.IrDeclarationBase
 import org.jetbrains.kotlin.ir.declarations.IrDeclarationOrigin
 import org.jetbrains.kotlin.ir.expressions.IrBlockBody
+import org.jetbrains.kotlin.ir.expressions.IrBody
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
 class IrAnonymousInitializerImpl(
@@ -30,27 +32,7 @@ class IrAnonymousInitializerImpl(
         origin: IrDeclarationOrigin,
         override val descriptor: ClassDescriptor
 ) : IrDeclarationBase(startOffset, endOffset, origin), IrAnonymousInitializer {
-    private var bodyImpl: IrBlockBody? = null
-    override var body: IrBlockBody
-        get() = bodyImpl!!
-        set(value) {
-            bodyImpl?.detach()
-            bodyImpl = value
-            value.setTreeLocation(this, ANONYMOUS_INITIALIZER_BODY_SLOT)
-        }
-
-    override fun getChild(slot: Int): IrElement? =
-            when (slot) {
-                ANONYMOUS_INITIALIZER_BODY_SLOT -> body
-                else -> null
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            ANONYMOUS_INITIALIZER_BODY_SLOT -> body = newChild.assertCast()
-            else -> throwNoSuchSlot(slot)
-        }
-    }
+    override lateinit var body: IrBody
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R {
         return visitor.visitAnonymousInitializer(this, data)
@@ -59,4 +41,8 @@ class IrAnonymousInitializerImpl(
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         body.accept(visitor, data)
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        body = body.transform(transformer, data)
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrClassImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrClassImpl.kt
index 3935e89b0d6..835ab00d610 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrClassImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrClassImpl.kt
@@ -17,11 +17,11 @@
 package org.jetbrains.kotlin.ir.declarations.impl
 
 import org.jetbrains.kotlin.descriptors.ClassDescriptor
-import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.declarations.IrClass
 import org.jetbrains.kotlin.ir.declarations.IrDeclaration
 import org.jetbrains.kotlin.ir.declarations.IrDeclarationContainer
 import org.jetbrains.kotlin.ir.declarations.IrDeclarationOrigin
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import java.util.*
 
@@ -41,35 +41,28 @@ class IrClassImpl(
     override val declarations: MutableList<IrDeclaration> = ArrayList()
 
     fun addMember(member: IrDeclaration) {
-        member.setTreeLocation(this, declarations.size)
         declarations.add(member)
     }
 
     fun addAll(members: List<IrDeclaration>) {
-        val originalSize = declarations.size
         declarations.addAll(members)
-        members.forEachIndexed { i, irDeclaration -> irDeclaration.setTreeLocation(this, originalSize + i) }
     }
 
     override fun toBuilder(): IrDeclarationContainer.Builder =
             IrClassBuilderImpl(this)
 
-    override fun getChild(slot: Int): IrElement? =
-            declarations.getOrNull(slot)
-
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        declarations.getOrNull(slot)?.detach() ?: throwNoSuchSlot(slot)
-        declarations[slot] = newChild.assertCast()
-        newChild.setTreeLocation(this, slot)
-    }
-
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
             visitor.visitClass(this, data)
 
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         declarations.forEach { it.accept(visitor, data) }
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        declarations.forEachIndexed { i, irDeclaration ->
+            declarations[i] = irDeclaration.transform(transformer, data)
+        }
+    }
 }
 
 class IrClassBuilderImpl(
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrConstructorImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrConstructorImpl.kt
index d1ef2c842a9..6fc510ba2e6 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrConstructorImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrConstructorImpl.kt
@@ -19,21 +19,13 @@ package org.jetbrains.kotlin.ir.declarations.impl
 import org.jetbrains.kotlin.descriptors.ConstructorDescriptor
 import org.jetbrains.kotlin.ir.declarations.IrConstructor
 import org.jetbrains.kotlin.ir.declarations.IrDeclarationOrigin
-import org.jetbrains.kotlin.ir.declarations.impl.IrFunctionBase
 import org.jetbrains.kotlin.ir.expressions.IrBody
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
-class IrConstructorImpl(
-        startOffset: Int,
-        endOffset: Int,
-        origin: IrDeclarationOrigin,
-        override val descriptor: ConstructorDescriptor
-) : IrFunctionBase(startOffset, endOffset, origin), IrConstructor {
+class IrConstructorImpl(startOffset: Int, endOffset: Int, origin: IrDeclarationOrigin, override val descriptor: ConstructorDescriptor) :
+        IrFunctionBase(startOffset, endOffset, origin), IrConstructor {
     constructor(
-            startOffset: Int,
-            endOffset: Int,
-            origin: IrDeclarationOrigin,
-            descriptor: ConstructorDescriptor,
+            startOffset: Int, endOffset: Int, origin: IrDeclarationOrigin, descriptor: ConstructorDescriptor,
             body: IrBody
     ) : this(startOffset, endOffset, origin, descriptor) {
         this.body = body
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrEnumEntryImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrEnumEntryImpl.kt
index 2179524abf6..e08f36681ff 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrEnumEntryImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrEnumEntryImpl.kt
@@ -17,11 +17,11 @@
 package org.jetbrains.kotlin.ir.declarations.impl
 
 import org.jetbrains.kotlin.descriptors.ClassDescriptor
-import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.declarations.IrClass
 import org.jetbrains.kotlin.ir.declarations.IrDeclarationOrigin
 import org.jetbrains.kotlin.ir.declarations.IrEnumEntry
 import org.jetbrains.kotlin.ir.expressions.IrExpression
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
 class IrEnumEntryImpl(
@@ -31,36 +31,7 @@ class IrEnumEntryImpl(
         override val descriptor: ClassDescriptor
 ) : IrDeclarationBase(startOffset, endOffset, origin), IrEnumEntry {
     override var correspondingClass: IrClass? = null
-        set(value) {
-            field?.detach()
-            field = value
-            value?.setTreeLocation(this, ENUM_ENTRY_CLASS_SLOT)
-        }
-
-    private var initializerExpressionImpl: IrExpression? = null
-    override var initializerExpression: IrExpression
-        get() = initializerExpressionImpl!!
-        set(value) {
-            initializerExpressionImpl?.detach()
-            initializerExpressionImpl = value
-            value.setTreeLocation(this, ENUM_ENTRY_INITIALIZER_SLOT)
-        }
-
-    override fun getChild(slot: Int): IrElement? {
-        return when (slot) {
-            ENUM_ENTRY_CLASS_SLOT -> correspondingClass
-            ENUM_ENTRY_INITIALIZER_SLOT -> initializerExpression
-            else -> null
-        }
-    }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            ENUM_ENTRY_CLASS_SLOT -> correspondingClass = newChild.assertCast()
-            ENUM_ENTRY_INITIALIZER_SLOT -> initializerExpression = newChild.assertCast()
-            else -> throwNoSuchSlot(slot)
-        }
-    }
+    override lateinit var initializerExpression: IrExpression
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R {
         return visitor.visitEnumEntry(this, data)
@@ -70,4 +41,9 @@ class IrEnumEntryImpl(
         initializerExpression.accept(visitor, data)
         correspondingClass?.accept(visitor, data)
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        initializerExpression = initializerExpression.transform(transformer, data)
+        correspondingClass = correspondingClass?.transform(transformer, data) as? IrClass
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrErrorDeclarationImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrErrorDeclarationImpl.kt
index 50c927b7f13..be493f70cdb 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrErrorDeclarationImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrErrorDeclarationImpl.kt
@@ -17,11 +17,10 @@
 package org.jetbrains.kotlin.ir.declarations.impl
 
 import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
-import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.declarations.IrDeclarationKind
 import org.jetbrains.kotlin.ir.declarations.IrDeclarationOrigin
 import org.jetbrains.kotlin.ir.declarations.IrErrorDeclaration
-import org.jetbrains.kotlin.ir.throwNoSuchSlot
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
 class IrErrorDeclarationImpl(
@@ -39,7 +38,7 @@ class IrErrorDeclarationImpl(
         // no children
     }
 
-    override fun getChild(slot: Int): IrElement? = null
-
-    override fun replaceChild(slot: Int, newChild: IrElement) = throwNoSuchSlot(slot)
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        // no children
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrFieldImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrFieldImpl.kt
index 7ef8f50c9de..9793912d235 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrFieldImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrFieldImpl.kt
@@ -17,10 +17,11 @@
 package org.jetbrains.kotlin.ir.declarations.impl
 
 import org.jetbrains.kotlin.descriptors.PropertyDescriptor
-import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.declarations.IrDeclarationOrigin
 import org.jetbrains.kotlin.ir.declarations.IrField
+import org.jetbrains.kotlin.ir.expressions.IrBody
 import org.jetbrains.kotlin.ir.expressions.IrExpressionBody
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
 
@@ -36,25 +37,7 @@ class IrFieldImpl(
         this.initializer = initializer
     }
 
-    override var initializer: IrExpressionBody? = null
-        set(value) {
-            field?.detach()
-            field = value
-            value?.setTreeLocation(this, INITIALIZER_SLOT)
-        }
-
-    override fun getChild(slot: Int): IrElement? =
-            when (slot) {
-                INITIALIZER_SLOT -> initializer
-                else -> null
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            INITIALIZER_SLOT -> initializer = newChild.assertCast()
-            else -> throwNoSuchSlot(slot)
-        }
-    }
+    override var initializer: IrBody? = null
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R {
         return visitor.visitField(this, data)
@@ -63,4 +46,8 @@ class IrFieldImpl(
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         initializer?.accept(visitor, data)
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        initializer = initializer?.transform(transformer, data)
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrFileImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrFileImpl.kt
index 327ed101f49..c1a91169251 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrFileImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrFileImpl.kt
@@ -21,6 +21,7 @@ import org.jetbrains.kotlin.descriptors.annotations.AnnotationDescriptor
 import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.declarations.IrDeclaration
 import org.jetbrains.kotlin.ir.declarations.IrFile
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.utils.SmartList
 import java.util.*
@@ -50,25 +51,11 @@ class IrFileImpl(
     override val declarations: MutableList<IrDeclaration> = ArrayList()
 
     fun addDeclaration(declaration: IrDeclaration) {
-        declaration.setTreeLocation(this, declarations.size)
         declarations.add(declaration)
     }
 
     fun addAll(newDeclarations: List<IrDeclaration>) {
-        val originalSize = declarations.size
         declarations.addAll(newDeclarations)
-        newDeclarations.forEachIndexed { i, irDeclaration ->
-            irDeclaration.setTreeLocation(this, originalSize + i)
-        }
-    }
-
-    override fun getChild(slot: Int): IrElement? =
-            declarations.getOrNull(slot)
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        declarations.getOrNull(slot)?.detach() ?: throwNoSuchSlot(slot)
-        declarations[slot] = newChild.assertCast()
-        newChild.setTreeLocation(this, slot)
     }
 
     override fun toBuilder(): IrFile.Builder =
@@ -81,7 +68,11 @@ class IrFileImpl(
         declarations.forEach { it.accept(visitor, data) }
     }
 
-
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        declarations.forEachIndexed { i, irDeclaration ->
+            declarations[i] = irDeclaration.transform(transformer, data)
+        }
+    }
 }
 
 class IrFileBuilderImpl(
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrFunctionBase.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrFunctionBase.kt
index a2244f9d314..17b7a402276 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrFunctionBase.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrFunctionBase.kt
@@ -19,8 +19,8 @@ package org.jetbrains.kotlin.ir.declarations.impl
 import org.jetbrains.kotlin.descriptors.ValueParameterDescriptor
 import org.jetbrains.kotlin.ir.declarations.IrDeclarationOrigin
 import org.jetbrains.kotlin.ir.declarations.IrFunction
-import org.jetbrains.kotlin.ir.detach
-import org.jetbrains.kotlin.ir.expressions.IrExpressionBody
+import org.jetbrains.kotlin.ir.expressions.IrBody
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import java.util.*
 
@@ -29,19 +29,24 @@ abstract class IrFunctionBase(
         endOffset: Int,
         origin: IrDeclarationOrigin
 ) : IrGeneralFunctionBase(startOffset, endOffset, origin), IrFunction {
-    private val defaults = LinkedHashMap<ValueParameterDescriptor, IrExpressionBody>()
+    private val defaults = LinkedHashMap<ValueParameterDescriptor, IrBody>()
 
-    override fun getDefault(parameter: ValueParameterDescriptor): IrExpressionBody? =
+    override fun getDefault(parameter: ValueParameterDescriptor): IrBody? =
             defaults[parameter]
 
-    override fun putDefault(parameter: ValueParameterDescriptor, expressionBody: IrExpressionBody) {
-        defaults[parameter]?.detach()
+    override fun putDefault(parameter: ValueParameterDescriptor, expressionBody: IrBody) {
         defaults[parameter] = expressionBody
-        expressionBody.setTreeLocation(this, parameter.index)
     }
 
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         defaults.values.forEach { it.accept(visitor, data) }
         body?.accept(visitor, data)
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        for ((valueParameter, defaultValue) in defaults) {
+            putDefault(valueParameter, defaultValue.transform(transformer, data))
+        }
+        body = body?.transform(transformer, data)
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrGeneralFunctionBase.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrGeneralFunctionBase.kt
index 601c8d0abc8..92488527e01 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrGeneralFunctionBase.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrGeneralFunctionBase.kt
@@ -28,24 +28,6 @@ abstract class IrGeneralFunctionBase(
         origin: IrDeclarationOrigin
 ) : IrDeclarationBase(startOffset, endOffset, origin), IrFunction {
     final override var body: IrBody? = null
-        set(newValue) {
-            field?.detach()
-            field = newValue
-            newValue?.setTreeLocation(this, FUNCTION_BODY_SLOT)
-        }
-
-    override fun getChild(slot: Int): IrElement? =
-            when (slot) {
-                FUNCTION_BODY_SLOT -> body
-                else -> null
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            FUNCTION_BODY_SLOT -> body = newChild.assertCast()
-            else -> throwNoSuchSlot(slot)
-        }
-    }
 
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         body?.accept(visitor, data)
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrLocalDelegatedPropertyImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrLocalDelegatedPropertyImpl.kt
index 3d97ac38765..8f7eea08130 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrLocalDelegatedPropertyImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrLocalDelegatedPropertyImpl.kt
@@ -17,9 +17,11 @@
 package org.jetbrains.kotlin.ir.declarations.impl
 
 import org.jetbrains.kotlin.descriptors.VariableDescriptorWithAccessors
-import org.jetbrains.kotlin.ir.*
-import org.jetbrains.kotlin.ir.declarations.*
-import org.jetbrains.kotlin.ir.declarations.impl.IrDeclarationBase
+import org.jetbrains.kotlin.ir.declarations.IrDeclarationOrigin
+import org.jetbrains.kotlin.ir.declarations.IrFunction
+import org.jetbrains.kotlin.ir.declarations.IrLocalDelegatedProperty
+import org.jetbrains.kotlin.ir.declarations.IrVariable
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
 class IrLocalDelegatedPropertyImpl(
@@ -38,47 +40,9 @@ class IrLocalDelegatedPropertyImpl(
         this.delegate = delegate
     }
 
-    private var delegateImpl: IrVariable? = null
-    override var delegate: IrVariable
-        get() = delegateImpl!!
-        set(value) {
-            delegateImpl?.detach()
-            delegateImpl = value
-            value.setTreeLocation(this, LOCAL_DELEGATE_SLOT)
-        }
-
-    private var getterImpl: IrFunction? = null
-    override var getter: IrFunction
-        get() = getterImpl!!
-        set(value) {
-            getterImpl?.detach()
-            getterImpl = value
-            value.setTreeLocation(this, PROPERTY_GETTER_SLOT)
-        }
-
+    override lateinit var delegate: IrVariable
+    override lateinit var getter: IrFunction
     override var setter: IrFunction? = null
-        set(value) {
-            field?.detach()
-            field = value
-            value?.setTreeLocation(this, PROPERTY_SETTER_SLOT)
-        }
-
-    override fun getChild(slot: Int): IrElement? =
-            when (slot) {
-                LOCAL_DELEGATE_SLOT -> delegate
-                PROPERTY_GETTER_SLOT -> getter
-                PROPERTY_SETTER_SLOT -> setter
-                else -> null
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            LOCAL_DELEGATE_SLOT -> delegate = newChild.assertCast()
-            PROPERTY_GETTER_SLOT -> getter = newChild.assertCast()
-            PROPERTY_SETTER_SLOT -> setter = newChild.assertCast()
-            else -> throwNoSuchSlot(slot)
-        }
-    }
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
             visitor.visitLocalDelegatedProperty(this, data)
@@ -88,4 +52,10 @@ class IrLocalDelegatedPropertyImpl(
         getter.accept(visitor, data)
         setter?.accept(visitor, data)
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        delegate = delegate.transform(transformer, data) as IrVariable
+        getter = getter.transform(transformer, data) as IrFunction
+        setter = setter?.transform(transformer, data) as? IrFunction
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrModuleFragmentImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrModuleFragmentImpl.kt
index f20b1f54abb..2136a8045b2 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrModuleFragmentImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrModuleFragmentImpl.kt
@@ -17,10 +17,10 @@
 package org.jetbrains.kotlin.ir.declarations.impl
 
 import org.jetbrains.kotlin.descriptors.ModuleDescriptor
-import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.declarations.IrFile
 import org.jetbrains.kotlin.ir.declarations.IrModuleFragment
 import org.jetbrains.kotlin.ir.descriptors.IrBuiltIns
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import java.util.*
 
@@ -35,22 +35,11 @@ class IrModuleFragmentImpl(
     override val files: MutableList<IrFile> = ArrayList()
 
     fun addFile(file: IrFile) {
-        file.setTreeLocation(this, files.size)
         files.add(file)
     }
 
     fun addAll(newFiles: List<IrFile>) {
-        val originalSize = files.size
         files.addAll(newFiles)
-        newFiles.forEachIndexed { i, irFile ->  irFile.setTreeLocation(this, originalSize + i) }
-    }
-
-    override fun getChild(slot: Int): IrElement? =
-            files.getOrNull(slot)
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        files.getOrNull(slot)?.detach() ?: throwNoSuchSlot(slot)
-        files[slot] = newChild.assertCast()
     }
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
@@ -59,4 +48,10 @@ class IrModuleFragmentImpl(
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         files.forEach { it.accept(visitor, data) }
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        files.forEachIndexed { i, irFile ->
+            files[i] = irFile.transform(transformer, data)
+        }
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrPropertyImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrPropertyImpl.kt
index f777b708c17..23851d6a459 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrPropertyImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrPropertyImpl.kt
@@ -22,6 +22,7 @@ import org.jetbrains.kotlin.ir.declarations.IrDeclarationOrigin
 import org.jetbrains.kotlin.ir.declarations.IrField
 import org.jetbrains.kotlin.ir.declarations.IrFunction
 import org.jetbrains.kotlin.ir.declarations.IrProperty
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
 class IrPropertyImpl(
@@ -47,42 +48,8 @@ class IrPropertyImpl(
     }
 
     override var backingField: IrField? = null
-        set(value) {
-            field?.detach()
-            field = value
-            value?.setTreeLocation(this, BACKING_FIELD_SLOT)
-        }
-
     override var getter: IrFunction? = null
-        set(value) {
-            field?.detach()
-            field = value
-            value?.setTreeLocation(this, PROPERTY_GETTER_SLOT)
-        }
-
     override var setter: IrFunction? = null
-        set(value) {
-            field?.detach()
-            field = value
-            value?.setTreeLocation(this, PROPERTY_SETTER_SLOT)
-        }
-
-    override fun getChild(slot: Int): IrElement? =
-            when (slot) {
-                BACKING_FIELD_SLOT -> backingField
-                PROPERTY_GETTER_SLOT -> getter
-                PROPERTY_SETTER_SLOT -> setter
-                else -> null
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            BACKING_FIELD_SLOT -> backingField = newChild.assertCast()
-            PROPERTY_GETTER_SLOT -> getter = newChild.assertCast()
-            PROPERTY_SETTER_SLOT -> setter = newChild.assertCast()
-            else -> throwNoSuchSlot(slot)
-        }
-    }
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R {
         return visitor.visitProperty(this, data)
@@ -93,4 +60,10 @@ class IrPropertyImpl(
         getter?.accept(visitor, data)
         setter?.accept(visitor, data)
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        backingField = backingField?.transform(transformer, data) as? IrField
+        getter = getter?.transform(transformer, data) as? IrFunction
+        setter = setter?.transform(transformer, data) as? IrFunction
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrTypeAliasImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrTypeAliasImpl.kt
index 91a8dbda816..9eff414834c 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrTypeAliasImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrTypeAliasImpl.kt
@@ -17,11 +17,9 @@
 package org.jetbrains.kotlin.ir.declarations.impl
 
 import org.jetbrains.kotlin.descriptors.TypeAliasDescriptor
-import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.declarations.IrDeclarationOrigin
 import org.jetbrains.kotlin.ir.declarations.IrTypeAlias
-import org.jetbrains.kotlin.ir.declarations.impl.IrDeclarationBase
-import org.jetbrains.kotlin.ir.throwNoSuchSlot
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
 class IrTypeAliasImpl(
@@ -38,9 +36,7 @@ class IrTypeAliasImpl(
         // no children
     }
 
-    override fun getChild(slot: Int): IrElement? = null
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        throwNoSuchSlot(slot)
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        // no children
     }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrVariableImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrVariableImpl.kt
index 35bd5eec784..ee4c838b2a4 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrVariableImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/declarations/impl/IrVariableImpl.kt
@@ -17,11 +17,10 @@
 package org.jetbrains.kotlin.ir.declarations.impl
 
 import org.jetbrains.kotlin.descriptors.VariableDescriptor
-import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.declarations.IrDeclarationOrigin
 import org.jetbrains.kotlin.ir.declarations.IrVariable
-import org.jetbrains.kotlin.ir.declarations.impl.IrDeclarationBase
 import org.jetbrains.kotlin.ir.expressions.IrExpression
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
 class IrVariableImpl(
@@ -41,24 +40,6 @@ class IrVariableImpl(
     }
 
     override var initializer: IrExpression? = null
-        set(value) {
-            field?.detach()
-            field = value
-            value?.setTreeLocation(this, INITIALIZER_SLOT)
-        }
-
-    override fun getChild(slot: Int): IrElement? =
-            when (slot) {
-                INITIALIZER_SLOT -> initializer
-                else -> null
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            INITIALIZER_SLOT -> initializer = newChild.assertCast<IrExpression>()
-            else -> throwNoSuchSlot(slot)
-        }
-    }
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R {
         return visitor.visitVariable(this, data)
@@ -67,4 +48,8 @@ class IrVariableImpl(
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         initializer?.accept(visitor, data)
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        initializer = initializer?.transform(transformer, data)
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrBody.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrBody.kt
index 42de05e1bb2..2f406f7d53c 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrBody.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrBody.kt
@@ -18,8 +18,12 @@ package org.jetbrains.kotlin.ir.expressions
 
 import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.IrStatement
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 
-interface IrBody : IrElement
+interface IrBody : IrElement {
+    override fun <D> transform(transformer: IrElementTransformer<D>, data: D): IrBody =
+            accept(transformer, data) as IrBody
+}
 
 interface IrExpressionBody : IrBody {
     var expression: IrExpression
@@ -27,6 +31,10 @@ interface IrExpressionBody : IrBody {
 
 interface IrStatementContainer {
     val statements: List<IrStatement>
+
+    fun addStatement(statement: IrStatement)
+    fun addAll(statements: Collection<IrStatement>)
+    fun putStatement(index: Int, statement: IrStatement)
 }
 
 interface IrBlockBody : IrBody, IrStatementContainer
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrBreakContinue.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrBreakContinue.kt
index 3cdd5f1b80f..5f597b5323f 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrBreakContinue.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrBreakContinue.kt
@@ -16,11 +16,6 @@
 
 package org.jetbrains.kotlin.ir.expressions
 
-import org.jetbrains.kotlin.ir.IrElement
-import org.jetbrains.kotlin.ir.util.dump
-import org.jetbrains.kotlin.ir.util.render
-import java.lang.AssertionError
-
 interface IrBreakContinue : IrExpression {
     var loop: IrLoop
     val label: String?
@@ -29,19 +24,3 @@ interface IrBreakContinue : IrExpression {
 interface IrBreak: IrBreakContinue
 
 interface IrContinue: IrBreakContinue
-
-fun IrBreakContinue.getDepth(): Int {
-    var depth = 0
-    var finger: IrElement = this
-    while (true) {
-        val parent = finger.parent ?: throw AssertionError("No parent loop in tree for ${this.render()}:\n${finger.dump()}")
-        if (parent is IrLoop) {
-            if (parent == loop) {
-                return depth
-            }
-            depth++
-        }
-        finger = parent
-    }
-}
-
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrExpression.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrExpression.kt
index ee534f204fe..7e3c42ca272 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrExpression.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrExpression.kt
@@ -17,10 +17,14 @@
 package org.jetbrains.kotlin.ir.expressions
 
 import org.jetbrains.kotlin.ir.IrStatement
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.types.KotlinType
 
 interface IrExpression : IrStatement, IrVarargElement {
     val type: KotlinType
+
+    override fun <D> transform(transformer: IrElementTransformer<D>, data: D): IrExpression =
+            accept(transformer, data) as IrExpression
 }
 
 interface IrExpressionWithCopy : IrExpression {
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrTryCatch.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrTryCatch.kt
index 02cad96c228..589c16431e9 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrTryCatch.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrTryCatch.kt
@@ -22,8 +22,11 @@ interface IrTryCatch : IrExpression {
     var tryResult: IrExpression
 
     val catchClausesCount: Int
+
     fun getNthCatchParameter(n: Int): VariableDescriptor?
     fun getNthCatchResult(n: Int): IrExpression?
+    fun putNthCatchParameter(n: Int, variableDescriptor: VariableDescriptor)
+    fun putNthCatchResult(n: Int, expression: IrExpression)
 
     var finallyExpression : IrExpression?
 }
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrVararg.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrVararg.kt
index f149bbb6951..0d9115843b0 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrVararg.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrVararg.kt
@@ -17,16 +17,23 @@
 package org.jetbrains.kotlin.ir.expressions
 
 import org.jetbrains.kotlin.ir.IrElement
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.types.KotlinType
 
 interface IrVarargElement : IrElement
 
 interface IrVararg : IrExpression {
     val varargElementType : KotlinType
+
     val elements: List<IrVarargElement>
+
+    fun putElement(i: Int, element: IrVarargElement)
 }
 
 interface IrSpreadElement : IrVarargElement {
     var expression: IrExpression
+
+    override fun <D> transform(transformer: IrElementTransformer<D>, data: D): IrElement =
+            accept(transformer, data) as IrSpreadElement
 }
 
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrWhen.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrWhen.kt
index bbc5ff4bc85..57611b290c2 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrWhen.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/IrWhen.kt
@@ -18,9 +18,15 @@ package org.jetbrains.kotlin.ir.expressions
 
 interface IrWhen : IrExpression {
     val origin: IrStatementOrigin?
+
     val branchesCount: Int
+
     fun getNthCondition(n: Int): IrExpression?
     fun getNthResult(n: Int): IrExpression?
+
+    fun putNthCondition(n: Int, expression: IrExpression)
+    fun putNthResult(n: Int, expression: IrExpression)
+
     var elseBranch: IrExpression?
 }
 
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrBlockBodyImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrBlockBodyImpl.kt
index a13876a6e32..7f4f81542f4 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrBlockBodyImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrBlockBodyImpl.kt
@@ -18,26 +18,23 @@ package org.jetbrains.kotlin.ir.expressions.impl
 
 import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.expressions.IrBlockBody
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import java.util.*
 
 class IrBlockBodyImpl(startOffset: Int, endOffset: Int) : IrElementBase(startOffset, endOffset), IrBlockBody {
     override val statements: MutableList<IrStatement> = ArrayList()
 
-    fun addStatement(statement: IrStatement) {
-        statement.setTreeLocation(this, statements.size)
+    override fun addStatement(statement: IrStatement) {
         statements.add(statement)
     }
 
-    override fun getChild(slot: Int): IrElement? =
-            statements.getOrNull(slot)
+    override fun addAll(statements: Collection<IrStatement>) {
+        this.statements.addAll(statements)
+    }
 
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        if (slot < 0 || slot >= statements.size) throwNoSuchSlot(slot)
-
-        statements[slot].detach()
-        statements[slot] = newChild.assertCast()
-        newChild.setTreeLocation(this, slot)
+    override fun putStatement(index: Int, statement: IrStatement) {
+        statements[index] = statement
     }
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R {
@@ -47,4 +44,10 @@ class IrBlockBodyImpl(startOffset: Int, endOffset: Int) : IrElementBase(startOff
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         statements.forEach { it.accept(visitor, data) }
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        statements.forEachIndexed { i, irStatement ->
+            statements[i] = irStatement.transform(transformer, data)
+        }
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrBlockImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrBlockImpl.kt
index 3d49f33c76d..a29fc15c590 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrBlockImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrBlockImpl.kt
@@ -17,9 +17,9 @@
 package org.jetbrains.kotlin.ir.expressions.impl
 
 import org.jetbrains.kotlin.ir.IrStatement
-import org.jetbrains.kotlin.ir.detach
 import org.jetbrains.kotlin.ir.expressions.IrBlock
 import org.jetbrains.kotlin.ir.expressions.IrStatementOrigin
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.KotlinType
 
@@ -36,6 +36,12 @@ class IrBlockImpl(startOffset: Int, endOffset: Int, type: KotlinType, origin: Ir
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         statements.forEach { it.accept(visitor, data) }
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        statements.forEachIndexed { i, irStatement ->
+            statements[i] = irStatement.transform(transformer, data)
+        }
+    }
 }
 
 fun IrBlockImpl.addIfNotNull(statement: IrStatement?) {
@@ -44,7 +50,6 @@ fun IrBlockImpl.addIfNotNull(statement: IrStatement?) {
 
 fun IrBlockImpl.inlineStatement(statement: IrStatement) {
     if (statement is IrBlock) {
-        statement.statements.forEach { it.detach() }
         addAll(statement.statements)
     }
     else {
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrCompositeImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrCompositeImpl.kt
index 5f8ebd57275..019163d2ed4 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrCompositeImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrCompositeImpl.kt
@@ -33,7 +33,4 @@ class IrCompositeImpl(startOffset: Int, endOffset: Int, type: KotlinType, origin
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
             visitor.visitComposite(this, data)
 
-    override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
-        statements.forEach { it.accept(visitor, data) }
-    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrContainerExpressionBase.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrContainerExpressionBase.kt
index c7ac137f461..4d4dfbf655e 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrContainerExpressionBase.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrContainerExpressionBase.kt
@@ -19,6 +19,8 @@ package org.jetbrains.kotlin.ir.expressions.impl
 import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.expressions.IrStatementOrigin
 import org.jetbrains.kotlin.ir.expressions.IrContainerExpression
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
+import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.KotlinType
 import java.util.*
 
@@ -26,27 +28,25 @@ abstract class IrContainerExpressionBase(startOffset: Int, endOffset: Int, type:
         IrExpressionBase(startOffset, endOffset, type), IrContainerExpression {
     override val statements: MutableList<IrStatement> = ArrayList(2)
 
-    fun addStatement(statement: IrStatement) {
-        statement.setTreeLocation(this, statements.size)
+    override fun addStatement(statement: IrStatement) {
         statements.add(statement)
     }
 
-    fun addAll(newStatements: List<IrStatement>) {
-        val originalSize = this.statements.size
-        this.statements.addAll(newStatements)
-        newStatements.forEachIndexed { i, irStatement ->
-            irStatement.setTreeLocation(this, originalSize + i)
+    override fun addAll(statements: Collection<IrStatement>) {
+        this.statements.addAll(statements)
+    }
+
+    override fun putStatement(index: Int, statement: IrStatement) {
+        statements[index] = statement
+    }
+
+    override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
+        statements.forEach { it.accept(visitor, data) }
+    }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        statements.forEachIndexed { i, irStatement ->
+            statements[i] = irStatement.transform(transformer, data)
         }
     }
-
-    override fun getChild(slot: Int): IrElement? =
-            statements.getOrNull(slot)
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        if (slot < 0 || slot >= statements.size) throwNoSuchSlot(slot)
-
-        statements[slot].detach()
-        statements[slot] = newChild.assertCast()
-        newChild.setTreeLocation(this, slot)
-    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrDoWhileLoopImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrDoWhileLoopImpl.kt
index 3e202927c21..478b2e4c4ec 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrDoWhileLoopImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrDoWhileLoopImpl.kt
@@ -18,8 +18,8 @@ package org.jetbrains.kotlin.ir.expressions.impl
 
 import org.jetbrains.kotlin.ir.expressions.IrDoWhileLoop
 import org.jetbrains.kotlin.ir.expressions.IrExpression
-import org.jetbrains.kotlin.ir.expressions.impl.IrLoopBase
 import org.jetbrains.kotlin.ir.expressions.IrStatementOrigin
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.KotlinType
 
@@ -41,4 +41,9 @@ class IrDoWhileLoopImpl(startOffset: Int, endOffset: Int, type : KotlinType, ori
         body?.accept(visitor, data)
         condition.accept(visitor, data)
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        body = body?.transform(transformer, data)
+        condition = condition.transform(transformer, data)
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrEmptyBlockImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrEmptyBlockImpl.kt
deleted file mode 100644
index 284620d75ec..00000000000
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrEmptyBlockImpl.kt
+++ /dev/null
@@ -1,44 +0,0 @@
-/*
- * Copyright 2010-2016 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.jetbrains.kotlin.ir.expressions.impl
-
-import org.jetbrains.kotlin.ir.IrElement
-import org.jetbrains.kotlin.ir.IrStatement
-import org.jetbrains.kotlin.ir.expressions.IrBlock
-import org.jetbrains.kotlin.ir.expressions.IrStatementOrigin
-import org.jetbrains.kotlin.ir.throwNoSuchSlot
-import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
-import org.jetbrains.kotlin.types.KotlinType
-
-class IrEmptyBlockImpl(startOffset: Int, endOffset: Int, type: KotlinType, override val origin: IrStatementOrigin? = null) :
-        IrExpressionBase(startOffset, endOffset, type), IrBlock {
-    override val statements: List<IrStatement> get() = emptyList()
-
-    override fun getChild(slot: Int): IrElement? = null
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        throwNoSuchSlot(slot)
-    }
-
-    override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R {
-        return visitor.visitBlock(this, data)
-    }
-
-    override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
-        // no children
-    }
-}
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrErrorCallExpressionImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrErrorCallExpressionImpl.kt
index c3c78ddb119..1ba811b8b48 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrErrorCallExpressionImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrErrorCallExpressionImpl.kt
@@ -16,9 +16,9 @@
 
 package org.jetbrains.kotlin.ir.expressions.impl
 
-import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.expressions.IrErrorCallExpression
 import org.jetbrains.kotlin.ir.expressions.IrExpression
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.KotlinType
 import org.jetbrains.kotlin.utils.SmartList
@@ -30,16 +30,9 @@ class IrErrorCallExpressionImpl(
         override val description: String
 ) : IrExpressionBase(startOffset, endOffset, type), IrErrorCallExpression {
     override var explicitReceiver: IrExpression? = null
-        set(value) {
-            field?.detach()
-            field = value
-            value?.setTreeLocation(this, DISPATCH_RECEIVER_SLOT)
-        }
-
     override val arguments: MutableList<IrExpression> = SmartList()
 
     fun addArgument(argument: IrExpression) {
-        argument.setTreeLocation(this, arguments.size)
         arguments.add(argument)
     }
 
@@ -52,14 +45,10 @@ class IrErrorCallExpressionImpl(
         arguments.forEach { it.accept(visitor, data) }
     }
 
-    override fun getChild(slot: Int): IrElement? =
-            arguments.getOrNull(slot)
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        if (slot < 0 || slot >= arguments.size) throwNoSuchSlot(slot)
-
-        arguments[slot].detach()
-        arguments[slot] = newChild.assertCast()
-        newChild.setTreeLocation(this, slot)
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        explicitReceiver = explicitReceiver?.transform(transformer, data)
+        arguments.forEachIndexed { i, irExpression ->
+            arguments[i] = irExpression.transform(transformer, data)
+        }
     }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrErrorExpressionImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrErrorExpressionImpl.kt
index 8151924b1d8..b4662c97431 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrErrorExpressionImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrErrorExpressionImpl.kt
@@ -31,10 +31,6 @@ class IrErrorExpressionImpl(
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
             visitor.visitErrorExpression(this, data)
 
-    override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
-        // No children
-    }
-
     override fun copy(): IrErrorExpressionImpl =
             IrErrorExpressionImpl(startOffset, endOffset, type, description)
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrExpressionBodyImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrExpressionBodyImpl.kt
index 0b83613c367..e35ae21f89c 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrExpressionBodyImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrExpressionBodyImpl.kt
@@ -19,6 +19,7 @@ package org.jetbrains.kotlin.ir.expressions.impl
 import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrExpressionBody
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
 class IrExpressionBodyImpl(startOffset: Int, endOffset: Int) : IrElementBase(startOffset, endOffset), IrExpressionBody {
@@ -26,27 +27,7 @@ class IrExpressionBodyImpl(startOffset: Int, endOffset: Int) : IrElementBase(sta
         this.expression = expression
     }
 
-    private var expressionImpl: IrExpression? = null
-    override var expression: IrExpression
-        get() = expressionImpl!!
-        set(newValue) {
-            expressionImpl?.detach()
-            expressionImpl = newValue
-            newValue.setTreeLocation(this, CHILD_EXPRESSION_SLOT)
-        }
-
-    override fun getChild(slot: Int): IrElement? =
-            when (slot) {
-                CHILD_EXPRESSION_SLOT -> expression
-                else -> null
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            CHILD_EXPRESSION_SLOT -> expression = newChild.assertCast()
-            else -> throwNoSuchSlot(slot)
-        }
-    }
+    override lateinit var expression: IrExpression
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
             visitor.visitExpressionBody(this, data)
@@ -54,4 +35,8 @@ class IrExpressionBodyImpl(startOffset: Int, endOffset: Int) : IrElementBase(sta
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         expression.accept(visitor, data)
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        expression = expression.transform(transformer, data)
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrFieldExpressionBase.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrFieldExpressionBase.kt
index cf15b62177c..a552c254f2f 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrFieldExpressionBase.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrFieldExpressionBase.kt
@@ -30,22 +30,4 @@ abstract class IrFieldExpressionBase(
         override val superQualifier: ClassDescriptor? = null
 ) : IrDeclarationReferenceBase<PropertyDescriptor>(startOffset, endOffset, type, descriptor), IrFieldAccessExpression {
     override final var receiver: IrExpression? = null
-        set(value) {
-            field?.detach()
-            field = value
-            value?.setTreeLocation(this, BACKING_FIELD_RECEIVER_SLOT)
-        }
-
-    override fun getChild(slot: Int): IrElement? =
-            when (slot) {
-                BACKING_FIELD_RECEIVER_SLOT -> receiver
-                else -> null
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            BACKING_FIELD_RECEIVER_SLOT -> receiver = newChild.assertCast()
-            else -> throwNoSuchSlot(slot)
-        }
-    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrGeneralCallBase.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrGeneralCallBase.kt
index caf1436230b..96114c34dc5 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrGeneralCallBase.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrGeneralCallBase.kt
@@ -16,15 +16,13 @@
 
 package org.jetbrains.kotlin.ir.expressions.impl
 
-import org.jetbrains.kotlin.ir.IrElement
-import org.jetbrains.kotlin.ir.assertCast
-import org.jetbrains.kotlin.ir.detach
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrGeneralCall
-import org.jetbrains.kotlin.ir.expressions.impl.IrMemberAccessExpressionBase
 import org.jetbrains.kotlin.ir.expressions.IrStatementOrigin
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.KotlinType
+import java.lang.AssertionError
 
 abstract class IrGeneralCallBase(
         startOffset: Int, endOffset: Int, type: KotlinType,
@@ -41,31 +39,22 @@ abstract class IrGeneralCallBase(
         if (index >= argumentsByParameterIndex.size) {
             throw AssertionError("$this: No such argument slot: $index")
         }
-        argumentsByParameterIndex[index]?.detach()
         argumentsByParameterIndex[index] = valueArgument
-        valueArgument?.setTreeLocation(this, index)
     }
 
     override fun removeArgument(index: Int) {
-        argumentsByParameterIndex[index]?.detach()
         argumentsByParameterIndex[index] = null
     }
 
-    override fun getChild(slot: Int): IrElement? =
-            if (0 <= slot)
-                argumentsByParameterIndex.getOrNull(slot)
-            else
-                super.getChild(slot)
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        if (0 <= slot)
-            putArgument(slot, newChild.assertCast())
-        else
-            super.replaceChild(slot, newChild)
-    }
-
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         super.acceptChildren(visitor, data)
         argumentsByParameterIndex.forEach { it?.accept(visitor, data) }
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        super.transformChildren(transformer, data)
+        argumentsByParameterIndex.forEachIndexed { i, irExpression ->
+            argumentsByParameterIndex[i] = irExpression?.transform(transformer, data)
+        }
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrGetClassImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrGetClassImpl.kt
index d13c63c461e..1c88b3f1963 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrGetClassImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrGetClassImpl.kt
@@ -16,10 +16,9 @@
 
 package org.jetbrains.kotlin.ir.expressions.impl
 
-import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrGetClass
-import org.jetbrains.kotlin.ir.expressions.impl.IrExpressionBase
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.KotlinType
 
@@ -28,27 +27,7 @@ class IrGetClassImpl(startOffset: Int, endOffset: Int, type: KotlinType) : IrExp
         this.argument = argument
     }
 
-    private var argumentImpl: IrExpression? = null
-    override var argument: IrExpression
-        get() = argumentImpl!!
-        set(value) {
-            argumentImpl?.detach()
-            argumentImpl = value
-            value.setTreeLocation(this, CHILD_EXPRESSION_SLOT)
-        }
-
-    override fun getChild(slot: Int): IrElement? =
-            when (slot) {
-                CHILD_EXPRESSION_SLOT -> argument
-                else -> null
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            CHILD_EXPRESSION_SLOT -> argument = newChild.assertCast()
-            else -> throwNoSuchSlot(slot)
-        }
-    }
+    override lateinit var argument: IrExpression
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R {
         return visitor.visitGetClass(this, data)
@@ -58,4 +37,7 @@ class IrGetClassImpl(startOffset: Int, endOffset: Int, type: KotlinType) : IrExp
         argument.accept(visitor, data)
     }
 
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        argument = argument.transform(transformer, data)
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrGetFieldImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrGetFieldImpl.kt
index 7b121997a26..62af0c76861 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrGetFieldImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrGetFieldImpl.kt
@@ -22,6 +22,7 @@ import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrGetField
 import org.jetbrains.kotlin.ir.expressions.IrStatementOrigin
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
 class IrGetFieldImpl(
@@ -37,13 +38,6 @@ class IrGetFieldImpl(
         this.receiver = receiver
     }
 
-    override fun getChild(slot: Int): IrElement? =
-            super.getChild(slot)
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        super.replaceChild(slot, newChild)
-    }
-
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R {
         return visitor.visitGetField(this, data)
     }
@@ -51,4 +45,8 @@ class IrGetFieldImpl(
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         receiver?.accept(visitor, data)
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        receiver = receiver?.transform(transformer, data)
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrIfThenElseImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrIfThenElseImpl.kt
index 105e74cea48..3fb78d5f1e5 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrIfThenElseImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrIfThenElseImpl.kt
@@ -16,10 +16,10 @@
 
 package org.jetbrains.kotlin.ir.expressions.impl
 
-import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrStatementOrigin
 import org.jetbrains.kotlin.ir.expressions.IrWhen
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.KotlinType
 
@@ -47,49 +47,21 @@ class IrIfThenElseImpl(
     override fun getNthResult(n: Int): IrExpression? =
             if (n == 0) thenBranch else null
 
-    private var conditionImpl: IrExpression? = null
-    var condition: IrExpression
-        get() = conditionImpl!!
-        set(value) {
-            value.detach()
-            conditionImpl = value
-            value.setTreeLocation(this, IF_CONDITION_SLOT)
-        }
+    override fun putNthCondition(n: Int, expression: IrExpression) {
+        if (n == 0) condition = expression
+        else throw AssertionError("No such branch $n")
+    }
 
-    private var thenBranchImpl: IrExpression? = null
-    var thenBranch: IrExpression
-        get() = thenBranchImpl!!
-        set(value) {
-            value.detach()
-            thenBranchImpl = value
-            value.setTreeLocation(this, IF_THEN_SLOT)
-        }
+    override fun putNthResult(n: Int, expression: IrExpression) {
+        if (n == 0) thenBranch = expression
+        else throw AssertionError("No such branch $n")
+    }
+
+    lateinit var condition: IrExpression
+
+    lateinit var thenBranch: IrExpression
 
     override var elseBranch: IrExpression? = null
-        set(value) {
-            value?.detach()
-            field = value
-            value?.setTreeLocation(this, IF_ELSE_SLOT)
-        }
-
-    override fun getChild(slot: Int): IrElement? =
-            when (slot) {
-                IF_CONDITION_SLOT -> condition
-                IF_THEN_SLOT -> thenBranch
-                IF_ELSE_SLOT -> elseBranch
-                else -> null
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            IF_CONDITION_SLOT ->
-                condition = newChild.assertCast()
-            IF_THEN_SLOT ->
-                thenBranch = newChild.assertCast()
-            IF_ELSE_SLOT ->
-                elseBranch = newChild.assertCast()
-        }
-    }
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
             visitor.visitWhen(this, data)
@@ -99,4 +71,10 @@ class IrIfThenElseImpl(
         thenBranch.accept(visitor, data)
         elseBranch?.accept(visitor, data)
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        condition = condition.transform(transformer, data)
+        thenBranch = thenBranch.transform(transformer, data)
+        elseBranch = elseBranch?.transform(transformer, data)
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrLoopBase.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrLoopBase.kt
index b8f9243c3ff..30171a14e38 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrLoopBase.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrLoopBase.kt
@@ -31,34 +31,7 @@ abstract class IrLoopBase(
 ) : IrExpressionBase(startOffset, endOffset, type), IrLoop {
     override var label: String? = null
 
-    private var conditionImpl: IrExpression? = null
-    override var condition: IrExpression
-        get() = conditionImpl!!
-        set(value) {
-            conditionImpl?.detach()
-            conditionImpl = value
-            value.setTreeLocation(this, LOOP_CONDITION_SLOT)
-        }
+    override lateinit var condition: IrExpression
 
     override var body: IrExpression? = null
-        set(value) {
-            field?.detach()
-            field = value
-            value?.setTreeLocation(this, LOOP_BODY_SLOT)
-        }
-
-    override fun getChild(slot: Int): IrElement? =
-            when (slot) {
-                LOOP_BODY_SLOT -> body
-                LOOP_CONDITION_SLOT -> condition
-                else -> null
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            LOOP_BODY_SLOT -> body = newChild.assertCast()
-            LOOP_CONDITION_SLOT -> condition = newChild.assertCast()
-            else -> throwNoSuchSlot(slot)
-        }
-    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrMemberAccessExpressionBase.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrMemberAccessExpressionBase.kt
index 0a3ebee3ad8..82ae3f045e4 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrMemberAccessExpressionBase.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrMemberAccessExpressionBase.kt
@@ -16,10 +16,9 @@
 
 package org.jetbrains.kotlin.ir.expressions.impl
 
-import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrMemberAccessExpression
-import org.jetbrains.kotlin.ir.expressions.impl.IrExpressionBase
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.KotlinType
 
@@ -29,36 +28,15 @@ abstract class IrMemberAccessExpressionBase(
         type: KotlinType
 ) : IrExpressionBase(startOffset, endOffset, type), IrMemberAccessExpression {
     override var dispatchReceiver: IrExpression? = null
-        set(newReceiver) {
-            field?.detach()
-            field = newReceiver
-            newReceiver?.setTreeLocation(this, DISPATCH_RECEIVER_SLOT)
-        }
-
     override var extensionReceiver: IrExpression? = null
-        set(newReceiver) {
-            field?.detach()
-            field = newReceiver
-            newReceiver?.setTreeLocation(this, EXTENSION_RECEIVER_SLOT)
-        }
-
-    override fun getChild(slot: Int): IrElement? =
-            when (slot) {
-                DISPATCH_RECEIVER_SLOT -> dispatchReceiver
-                EXTENSION_RECEIVER_SLOT -> extensionReceiver
-                else -> null
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            DISPATCH_RECEIVER_SLOT -> dispatchReceiver = newChild.assertCast()
-            EXTENSION_RECEIVER_SLOT -> extensionReceiver = newChild.assertCast()
-            else -> throwNoSuchSlot(slot)
-        }
-    }
 
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         dispatchReceiver?.accept(visitor, data)
         extensionReceiver?.accept(visitor, data)
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        dispatchReceiver = dispatchReceiver?.transform(transformer, data)
+        extensionReceiver = extensionReceiver?.transform(transformer, data)
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrPrimitiveCall.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrPrimitiveCall.kt
index 5394670ccd5..08ca6cfe0e6 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrPrimitiveCall.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrPrimitiveCall.kt
@@ -22,8 +22,8 @@ import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.expressions.IrCall
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrStatementOrigin
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
-import java.lang.AssertionError
 import java.lang.UnsupportedOperationException
 
 abstract class IrPrimitiveCallBase(
@@ -35,17 +35,17 @@ abstract class IrPrimitiveCallBase(
     override val superQualifier: ClassDescriptor? get() = null
     override var dispatchReceiver: IrExpression?
         get() = null
-        set(value) = throw UnsupportedOperationException("Operator call expression can't have a receiver")
+        set(value) {
+            if (value != null)
+                throw UnsupportedOperationException("Operator call expression can't have a receiver")
+        }
 
     override var extensionReceiver: IrExpression?
         get() = null
-        set(value) = throw UnsupportedOperationException("Operator call expression can't have a receiver")
-
-    override fun getArgument(index: Int): IrExpression? = getChild(index)?.assertCast()
-
-    override fun putArgument(index: Int, valueArgument: IrExpression?) {
-        replaceChild(index, valueArgument ?: throw AssertionError("Operator call expression can't have a default argument"))
-    }
+        set(value) {
+            if (value != null)
+                throw UnsupportedOperationException("Operator call expression can't have a receiver")
+        }
 
     override fun removeArgument(index: Int) {
         throw AssertionError("Operator call expression can't have a default argument")
@@ -54,19 +54,28 @@ abstract class IrPrimitiveCallBase(
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R {
         return visitor.visitCall(this, data)
     }
+
+    companion object {
+        const val ARGUMENT0 = 0
+        const val ARGUMENT1 = 1
+    }
 }
 
 class IrNullaryPrimitiveImpl constructor(startOffset: Int, endOffset: Int, origin: IrStatementOrigin, descriptor: CallableDescriptor) :
         IrPrimitiveCallBase(startOffset, endOffset, origin, descriptor) {
-    override fun getChild(slot: Int): IrElement? = null
+    override fun getArgument(index: Int): IrExpression? = null
 
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        throwNoSuchSlot(slot)
+    override fun putArgument(index: Int, valueArgument: IrExpression?) {
+        throw UnsupportedOperationException("Nullary operator $descriptor doesn't have arguments")
     }
 
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         // no children
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        // no children
+    }
 }
 
 class IrUnaryPrimitiveImpl private constructor(startOffset: Int, endOffset: Int, origin: IrStatementOrigin, descriptor: CallableDescriptor) :
@@ -77,31 +86,29 @@ class IrUnaryPrimitiveImpl private constructor(startOffset: Int, endOffset: Int,
         this.argument = argument
     }
 
-    private var argumentImpl: IrExpression? = null
-    var argument: IrExpression
-        get() = argumentImpl!!
-        set(value) {
-            argumentImpl?.detach()
-            argumentImpl = value
-            value.setTreeLocation(this, ARGUMENT0_SLOT)
+    lateinit var argument: IrExpression
+
+    override fun getArgument(index: Int): IrExpression? {
+        return when (index) {
+            ARGUMENT0 -> argument
+            else -> null
         }
+    }
 
-    override fun getChild(slot: Int): IrElement? =
-            when (slot) {
-                ARGUMENT0_SLOT -> argument
-                else -> null
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            ARGUMENT0_SLOT -> argument = newChild.assertCast()
-            else -> throwNoSuchSlot(slot)
+    override fun putArgument(index: Int, valueArgument: IrExpression?) {
+        when (index) {
+            ARGUMENT0 -> argument = valueArgument ?: throw AssertionError("Primitive call $descriptor argument is null")
+            else -> throw AssertionError("Primitive call $descriptor: no such argument index $index")
         }
     }
 
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         argument.accept(visitor, data)
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        argument = argument.transform(transformer, data)
+    }
 }
 
 class IrBinaryPrimitiveImpl(startOffset: Int, endOffset: Int, origin: IrStatementOrigin, descriptor: CallableDescriptor) :
@@ -114,36 +121,23 @@ class IrBinaryPrimitiveImpl(startOffset: Int, endOffset: Int, origin: IrStatemen
         this.argument1 = argument1
     }
 
-    private var argument0Impl: IrExpression? = null
-    var argument0: IrExpression
-        get() = argument0Impl!!
-        set(value) {
-            argument0Impl?.detach()
-            argument0Impl = value
-            value.setTreeLocation(this, ARGUMENT0_SLOT)
+    lateinit var argument0: IrExpression
+    lateinit var argument1: IrExpression
+
+    override fun getArgument(index: Int): IrExpression? {
+        return when (index) {
+            ARGUMENT0 -> argument0
+            ARGUMENT1 -> argument1
+            else -> null
         }
+    }
 
-    private var argument1Impl: IrExpression? = null
-    var argument1: IrExpression
-        get() = argument1Impl!!
-        set(value) {
-            argument1Impl?.detach()
-            argument1Impl = value
-            value.setTreeLocation(this, ARGUMENT1_SLOT)
-        }
-
-    override fun getChild(slot: Int): IrElement? =
-            when (slot) {
-                ARGUMENT0_SLOT -> argument0
-                ARGUMENT1_SLOT -> argument1
-                else -> null
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            ARGUMENT0_SLOT -> argument0 = newChild.assertCast()
-            ARGUMENT1_SLOT -> argument1 = newChild.assertCast()
-            else -> throwNoSuchSlot(slot)
+    override fun putArgument(index: Int, valueArgument: IrExpression?) {
+        val argument = valueArgument ?: throw AssertionError("Primitive call $descriptor argument is null")
+        when (index) {
+            ARGUMENT0 -> argument0 = argument
+            ARGUMENT1 -> argument1 = argument
+            else -> throw AssertionError("Primitive call $descriptor: no such argument index $index")
         }
     }
 
@@ -151,4 +145,9 @@ class IrBinaryPrimitiveImpl(startOffset: Int, endOffset: Int, origin: IrStatemen
         argument0.accept(visitor, data)
         argument1.accept(visitor, data)
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        argument0 = argument0.transform(transformer, data)
+        argument1 = argument1.transform(transformer, data)
+    }
 }
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrPropertyAccessorCall.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrPropertyAccessorCall.kt
index 3a721f964f3..b10f750d74c 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrPropertyAccessorCall.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrPropertyAccessorCall.kt
@@ -18,12 +18,12 @@ package org.jetbrains.kotlin.ir.expressions.impl
 
 import org.jetbrains.kotlin.descriptors.CallableDescriptor
 import org.jetbrains.kotlin.descriptors.ClassDescriptor
-import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.expressions.IrCall
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrStatementOrigin
-import org.jetbrains.kotlin.ir.expressions.impl.IrMemberAccessExpressionBase
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
+import java.lang.AssertionError
+import java.lang.UnsupportedOperationException
 
 abstract class IrPropertyAccessorCallBase(
         startOffset: Int, endOffset: Int,
@@ -34,6 +34,10 @@ abstract class IrPropertyAccessorCallBase(
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R {
         return visitor.visitCall(this, data)
     }
+
+    companion object {
+        const val SETTER_ARGUMENT_INDEX = 0
+    }
 }
 
 class IrGetterCallImpl(startOffset: Int, endOffset: Int, descriptor: CallableDescriptor,
@@ -83,28 +87,12 @@ class IrSetterCallImpl(startOffset: Int, endOffset: Int, descriptor: CallableDes
             if (index == SETTER_ARGUMENT_INDEX) argumentImpl!! else null
 
     override fun putArgument(index: Int, valueArgument: IrExpression?) {
-        if (index != SETTER_ARGUMENT_INDEX) return
-        argumentImpl?.detach()
+        if (index != SETTER_ARGUMENT_INDEX) throw AssertionError("Property setter call $descriptor has no argument $index")
         argumentImpl = valueArgument
-        valueArgument?.setTreeLocation(this, SETTER_ARGUMENT_INDEX)
     }
 
     override fun removeArgument(index: Int) {
-        if (index != SETTER_ARGUMENT_INDEX) return
-        argumentImpl?.detach()
+        if (index != SETTER_ARGUMENT_INDEX) throw AssertionError("Property setter call $descriptor has no argument $index")
         argumentImpl = null
     }
-
-    override fun getChild(slot: Int): IrElement? =
-            when (slot) {
-                SETTER_ARGUMENT_INDEX -> argumentImpl
-                else -> super.getChild(slot)
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            SETTER_ARGUMENT_INDEX -> putArgument(slot, newChild.assertCast())
-            else -> super.replaceChild(slot, newChild)
-        }
-    }
 }
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrReturnImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrReturnImpl.kt
index f01ca05f425..dd51dbec2ed 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrReturnImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrReturnImpl.kt
@@ -17,10 +17,9 @@
 package org.jetbrains.kotlin.ir.expressions.impl
 
 import org.jetbrains.kotlin.descriptors.CallableDescriptor
-import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrReturn
-import org.jetbrains.kotlin.ir.expressions.impl.IrExpressionBase
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.KotlinType
 
@@ -41,24 +40,6 @@ class IrReturnImpl(
     }
 
     override var value: IrExpression? = null
-        set(newValue) {
-            field?.detach()
-            field = newValue
-            newValue?.setTreeLocation(this, CHILD_EXPRESSION_SLOT)
-        }
-
-    override fun getChild(slot: Int): IrElement? =
-            when (slot) {
-                CHILD_EXPRESSION_SLOT -> value
-                else -> null
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            CHILD_EXPRESSION_SLOT -> value = newChild.assertCast()
-            else -> throwNoSuchSlot(slot)
-        }
-    }
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
             visitor.visitReturn(this, data)
@@ -67,5 +48,7 @@ class IrReturnImpl(
         value?.accept(visitor, data)
     }
 
-
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        value = value?.transform(transformer, data)
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrSetFieldImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrSetFieldImpl.kt
index dadab958c3e..932000e87bb 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrSetFieldImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrSetFieldImpl.kt
@@ -23,6 +23,7 @@ import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrStatementOrigin
 import org.jetbrains.kotlin.ir.expressions.IrSetField
 import org.jetbrains.kotlin.ir.expressions.impl.IrFieldExpressionBase
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.typeUtil.builtIns
 
@@ -43,27 +44,7 @@ class IrSetFieldImpl(
         this.value = value
     }
 
-    private var valueImpl: IrExpression? = null
-    override var value: IrExpression
-        get() = valueImpl!!
-        set(value) {
-            valueImpl?.detach()
-            valueImpl = value
-            value.setTreeLocation(this, CHILD_EXPRESSION_SLOT)
-        }
-
-    override fun getChild(slot: Int): IrElement? =
-            when (slot) {
-                CHILD_EXPRESSION_SLOT -> value
-                else -> super.getChild(slot)
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            CHILD_EXPRESSION_SLOT -> value = newChild.assertCast()
-            else -> super.replaceChild(slot, newChild)
-        }
-    }
+    override lateinit var value: IrExpression
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R {
         return visitor.visitSetField(this, data)
@@ -73,4 +54,9 @@ class IrSetFieldImpl(
         receiver?.accept(visitor, data)
         value.accept(visitor, data)
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        receiver = receiver?.transform(transformer, data)
+        value = value.transform(transformer, data)
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrSetVariableImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrSetVariableImpl.kt
index 9377e75c7d4..fd3e392f78b 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrSetVariableImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrSetVariableImpl.kt
@@ -22,6 +22,7 @@ import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrStatementOrigin
 import org.jetbrains.kotlin.ir.expressions.IrSetVariable
 import org.jetbrains.kotlin.ir.expressions.impl.IrExpressionBase
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.resolve.descriptorUtil.builtIns
 
@@ -38,27 +39,7 @@ class IrSetVariableImpl(
         this.value = value
     }
 
-    private var valueImpl: IrExpression? = null
-    override var value: IrExpression
-        get() = valueImpl!!
-        set(value) {
-            valueImpl?.detach()
-            valueImpl = value
-            value.setTreeLocation(this, ARGUMENT0_SLOT)
-        }
-
-    override fun getChild(slot: Int): IrElement? =
-            when (slot) {
-                ARGUMENT0_SLOT -> value
-                else -> null
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            ARGUMENT0_SLOT -> value = newChild.assertCast()
-            else -> throwNoSuchSlot(slot)
-        }
-    }
+    override lateinit var value: IrExpression
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R {
         return visitor.visitSetVariable(this, data)
@@ -67,4 +48,8 @@ class IrSetVariableImpl(
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         value.accept(visitor, data)
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        value = value.transform(transformer, data)
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrSpreadElementImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrSpreadElementImpl.kt
index f8dfef5efe5..19979234fe2 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrSpreadElementImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrSpreadElementImpl.kt
@@ -19,6 +19,7 @@ package org.jetbrains.kotlin.ir.expressions.impl
 import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrSpreadElement
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
 class IrSpreadElementImpl(
@@ -29,28 +30,7 @@ class IrSpreadElementImpl(
         this.expression = expression
     }
 
-    private var expressionImpl: IrExpression? = null
-    override var expression: IrExpression
-        get() = expressionImpl!!
-        set(value) {
-            expressionImpl?.detach()
-            expressionImpl = value
-            value.setTreeLocation(this, CHILD_EXPRESSION_SLOT)
-        }
-
-
-    override fun getChild(slot: Int): IrElement? =
-            when (slot) {
-                CHILD_EXPRESSION_SLOT -> expression
-                else -> null
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            CHILD_EXPRESSION_SLOT -> expression = newChild.assertCast()
-            else -> throwNoSuchSlot(slot)
-        }
-    }
+    override lateinit var expression: IrExpression
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R {
         return visitor.visitSpreadElement(this, data)
@@ -60,5 +40,7 @@ class IrSpreadElementImpl(
         expression.accept(visitor, data)
     }
 
-
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        expression = expression.transform(transformer, data)
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrStringConcatenationImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrStringConcatenationImpl.kt
index c9ce78ceab8..a22f0ffe699 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrStringConcatenationImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrStringConcatenationImpl.kt
@@ -20,6 +20,7 @@ import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrStringConcatenation
 import org.jetbrains.kotlin.ir.expressions.impl.IrExpressionBase
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.KotlinType
 import java.util.*
@@ -32,25 +33,19 @@ class IrStringConcatenationImpl(
     override val arguments: MutableList<IrExpression> = ArrayList()
 
     override fun addArgument(argument: IrExpression) {
-        argument.setTreeLocation(this, arguments.size)
         arguments.add(argument)
     }
 
-    override fun getChild(slot: Int): IrElement? =
-            arguments.getOrNull(slot)
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        if (slot < 0 || slot >= arguments.size) throwNoSuchSlot(slot)
-
-        arguments[slot].detach()
-        arguments[slot] = newChild.assertCast()
-        newChild.setTreeLocation(this, slot)
-    }
-
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
             visitor.visitStringConcatenation(this, data)
 
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         arguments.forEach { it.accept(visitor, data) }
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        arguments.forEachIndexed { i, irExpression ->
+            arguments[i] = irExpression.transform(transformer, data)
+        }
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrSyntheticBodyImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrSyntheticBodyImpl.kt
index 64fdacec2ca..67bb7015c1f 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrSyntheticBodyImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrSyntheticBodyImpl.kt
@@ -16,11 +16,10 @@
 
 package org.jetbrains.kotlin.ir.expressions.impl
 
-import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.IrElementBase
 import org.jetbrains.kotlin.ir.expressions.IrSyntheticBody
 import org.jetbrains.kotlin.ir.expressions.IrSyntheticBodyKind
-import org.jetbrains.kotlin.ir.throwNoSuchSlot
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 
 class IrSyntheticBodyImpl(startOffset: Int, endOffset: Int, override val kind: IrSyntheticBodyKind) : IrElementBase(startOffset, endOffset), IrSyntheticBody {
@@ -32,9 +31,7 @@ class IrSyntheticBodyImpl(startOffset: Int, endOffset: Int, override val kind: I
         // no children
     }
 
-    override fun getChild(slot: Int): IrElement? = null
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        throwNoSuchSlot(slot)
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        // no children
     }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrTerminalDeclarationReferenceBase.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrTerminalDeclarationReferenceBase.kt
index d96adf7a603..70b65a72374 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrTerminalDeclarationReferenceBase.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrTerminalDeclarationReferenceBase.kt
@@ -17,9 +17,7 @@
 package org.jetbrains.kotlin.ir.expressions.impl
 
 import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
-import org.jetbrains.kotlin.ir.IrElement
-import org.jetbrains.kotlin.ir.expressions.impl.IrDeclarationReferenceBase
-import org.jetbrains.kotlin.ir.throwNoSuchSlot
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.KotlinType
 
@@ -29,13 +27,11 @@ abstract class IrTerminalDeclarationReferenceBase<out D : DeclarationDescriptor>
         type: KotlinType,
         descriptor: D
 ) : IrDeclarationReferenceBase<D>(startOffset, endOffset, type, descriptor) {
-    override fun getChild(slot: Int): IrElement? = null
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        throwNoSuchSlot(slot)
-    }
-
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         // No children
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        // No children
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrTerminalExpressionBase.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrTerminalExpressionBase.kt
index 1ca486fb6c2..19a384212c1 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrTerminalExpressionBase.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrTerminalExpressionBase.kt
@@ -16,9 +16,7 @@
 
 package org.jetbrains.kotlin.ir.expressions.impl
 
-import org.jetbrains.kotlin.ir.IrElement
-import org.jetbrains.kotlin.ir.expressions.impl.IrExpressionBase
-import org.jetbrains.kotlin.ir.throwNoSuchSlot
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.KotlinType
 
@@ -27,13 +25,11 @@ abstract class IrTerminalExpressionBase(
         endOffset: Int,
         type: KotlinType
 ) : IrExpressionBase(startOffset, endOffset, type) {
-    override fun getChild(slot: Int): IrElement? = null
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        throwNoSuchSlot(slot)
-    }
-
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         // No children
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        // No children
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrThisReferenceImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrThisReferenceImpl.kt
index 77fd1a40430..748a630e3b2 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrThisReferenceImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrThisReferenceImpl.kt
@@ -18,7 +18,6 @@ package org.jetbrains.kotlin.ir.expressions.impl
 
 import org.jetbrains.kotlin.descriptors.ClassDescriptor
 import org.jetbrains.kotlin.ir.expressions.IrThisReference
-import org.jetbrains.kotlin.ir.expressions.impl.IrTerminalExpressionBase
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.KotlinType
 
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrThrowImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrThrowImpl.kt
index a310284a1d4..8bb5a5d2bb3 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrThrowImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrThrowImpl.kt
@@ -16,10 +16,9 @@
 
 package org.jetbrains.kotlin.ir.expressions.impl
 
-import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrThrow
-import org.jetbrains.kotlin.ir.expressions.impl.IrExpressionBase
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.KotlinType
 
@@ -37,27 +36,7 @@ class IrThrowImpl(
         this.value = value
     }
 
-    private var valueImpl: IrExpression? = null
-    override var value: IrExpression
-        get() = valueImpl!!
-        set(newValue) {
-            valueImpl?.detach()
-            valueImpl = newValue
-            newValue.setTreeLocation(this, CHILD_EXPRESSION_SLOT)
-        }
-
-    override fun getChild(slot: Int): IrElement? =
-            when (slot) {
-                CHILD_EXPRESSION_SLOT -> value
-                else -> null
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            CHILD_EXPRESSION_SLOT -> value = newChild.assertCast()
-            else -> throwNoSuchSlot(slot)
-        }
-    }
+    override lateinit var value: IrExpression
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
             visitor.visitThrow(this, data)
@@ -66,5 +45,7 @@ class IrThrowImpl(
         value.accept(visitor, data)
     }
 
-
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        value = value.transform(transformer, data)
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrTryCatchImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrTryCatchImpl.kt
index f2fc11806f4..a2b5e8d2258 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrTryCatchImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrTryCatchImpl.kt
@@ -17,27 +17,16 @@
 package org.jetbrains.kotlin.ir.expressions.impl
 
 import org.jetbrains.kotlin.descriptors.VariableDescriptor
-import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrTryCatch
-import org.jetbrains.kotlin.ir.expressions.impl.IrExpressionBase
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.KotlinType
 import org.jetbrains.kotlin.utils.SmartList
 
-class IrTryCatchImpl(
-        startOffset: Int,
-        endOffset: Int,
-        type: KotlinType
-) : IrExpressionBase(startOffset, endOffset, type), IrTryCatch {
-    private var tryResultImpl: IrExpression? = null
-    override var tryResult: IrExpression
-        get() = tryResultImpl!!
-        set(value) {
-            tryResultImpl?.detach()
-            tryResultImpl = value
-            value.setTreeLocation(this, TRY_RESULT_SLOT)
-        }
+class IrTryCatchImpl(startOffset: Int, endOffset: Int, type: KotlinType) :
+        IrExpressionBase(startOffset, endOffset, type), IrTryCatch {
+    override lateinit var tryResult: IrExpression
 
     private val catchClauseParameters = SmartList<VariableDescriptor>()
     private val catchClauseResults = SmartList<IrExpression>()
@@ -45,7 +34,6 @@ class IrTryCatchImpl(
     override val catchClausesCount: Int get() = catchClauseResults.size
 
     fun addCatchClause(parameter: VariableDescriptor, result: IrExpression) {
-        result.setTreeLocation(this, catchClausesCount)
         catchClauseParameters.add(parameter)
         catchClauseResults.add(result)
     }
@@ -56,44 +44,15 @@ class IrTryCatchImpl(
     override fun getNthCatchResult(n: Int): IrExpression? =
             catchClauseResults.getOrNull(n)
 
+    override fun putNthCatchParameter(n: Int, variableDescriptor: VariableDescriptor) {
+        catchClauseParameters[n] = variableDescriptor
+    }
+
+    override fun putNthCatchResult(n: Int, expression: IrExpression) {
+        catchClauseResults[n] = expression
+    }
+
     override var finallyExpression: IrExpression? = null
-        set(value) {
-            field?.detach()
-            field = value
-            value?.setTreeLocation(this, FINALLY_EXPRESSION_SLOT)
-        }
-
-    override fun getChild(slot: Int): IrElement? =
-            when {
-                slot == TRY_RESULT_SLOT ->
-                    tryResult
-                slot >= 0 ->
-                    catchClauseResults.getOrNull(slot)
-                slot == FINALLY_EXPRESSION_SLOT ->
-                    finallyExpression
-                else -> null
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when {
-            slot == TRY_RESULT_SLOT ->
-                tryResult = newChild.assertCast()
-            slot >= 0 ->
-                putCatchClauseElement(catchClauseResults, newChild, slot)
-            slot == FINALLY_EXPRESSION_SLOT ->
-                finallyExpression = newChild.assertCast()
-            else ->
-                throwNoSuchSlot(slot)
-        }
-    }
-
-    private inline fun <reified T : IrElement> putCatchClauseElement(list: MutableList<T>, newChild: IrElement, slot: Int) {
-        if (slot < 0 || slot >= list.size) throwNoSuchSlot(slot)
-
-        list[slot].detach()
-        list[slot] = newChild.assertCast()
-        newChild.setTreeLocation(this, slot)
-    }
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R {
         return visitor.visitTryCatch(this, data)
@@ -101,9 +60,14 @@ class IrTryCatchImpl(
 
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         tryResult.accept(visitor, data)
-        for (index in 0 ..catchClausesCount - 1) {
-            catchClauseResults[index].accept(visitor, data)
-        }
+        catchClauseResults.forEach { it.accept(visitor, data) }
         finallyExpression?.accept(visitor, data)
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        tryResult = tryResult.transform(transformer, data)
+        catchClauseResults.forEachIndexed { i, irExpression ->
+            catchClauseResults[i] = irExpression.transform(transformer, data)
+        }
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrTypeOperatorCallImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrTypeOperatorCallImpl.kt
index 125d2722b48..32cca7352c7 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrTypeOperatorCallImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrTypeOperatorCallImpl.kt
@@ -21,6 +21,7 @@ import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrTypeOperator
 import org.jetbrains.kotlin.ir.expressions.IrTypeOperatorCall
 import org.jetbrains.kotlin.ir.expressions.impl.IrExpressionBase
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.KotlinType
 
@@ -42,27 +43,7 @@ class IrTypeOperatorCallImpl(
         this.argument = argument
     }
 
-    private var argumentImpl: IrExpression? = null
-    override var argument: IrExpression
-        get() = argumentImpl!!
-        set(value) {
-            argumentImpl?.detach()
-            argumentImpl = value
-            value.setTreeLocation(this, ARGUMENT0_SLOT)
-        }
-
-    override fun getChild(slot: Int): IrElement? =
-            when (slot) {
-                ARGUMENT0_SLOT -> argument
-                else -> null
-            }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            ARGUMENT0_SLOT -> argument = newChild.assertCast()
-            else -> throwNoSuchSlot(slot)
-        }
-    }
+    override lateinit var argument: IrExpression
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
             visitor.visitTypeOperator(this, data)
@@ -71,5 +52,7 @@ class IrTypeOperatorCallImpl(
         argument.accept(visitor, data)
     }
 
-
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        argument = argument.transform(transformer, data)
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrVarargImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrVarargImpl.kt
index 65e28aad647..d3b2f16ecd7 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrVarargImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrVarargImpl.kt
@@ -16,10 +16,9 @@
 
 package org.jetbrains.kotlin.ir.expressions.impl
 
-import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.expressions.IrVararg
 import org.jetbrains.kotlin.ir.expressions.IrVarargElement
-import org.jetbrains.kotlin.ir.expressions.impl.IrExpressionBase
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.KotlinType
 import org.jetbrains.kotlin.utils.SmartList
@@ -33,19 +32,11 @@ class IrVarargImpl(
     override val elements: MutableList<IrVarargElement> = SmartList()
 
     fun addElement(varargElement: IrVarargElement) {
-        varargElement.setTreeLocation(this, elements.size)
         elements.add(varargElement)
     }
 
-    override fun getChild(slot: Int): IrElement? =
-            elements.getOrNull(slot)
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        if (slot < 0 || slot >= elements.size) throwNoSuchSlot(slot)
-
-        elements[slot].detach()
-        elements[slot] = newChild.assertCast()
-        newChild.setTreeLocation(this, slot)
+    override fun putElement(i: Int, element: IrVarargElement) {
+        elements[i] = element
     }
 
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R {
@@ -55,4 +46,10 @@ class IrVarargImpl(
     override fun <D> acceptChildren(visitor: IrElementVisitor<Unit, D>, data: D) {
         elements.forEach { it.accept(visitor, data) }
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        elements.forEachIndexed { i, irVarargElement ->
+            elements[i] = irVarargElement.transform(transformer, data) as IrVarargElement
+        }
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrWhenImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrWhenImpl.kt
index 8e9369691fe..da70a5f4f9d 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrWhenImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrWhenImpl.kt
@@ -16,11 +16,10 @@
 
 package org.jetbrains.kotlin.ir.expressions.impl
 
-import org.jetbrains.kotlin.ir.*
 import org.jetbrains.kotlin.ir.expressions.IrExpression
 import org.jetbrains.kotlin.ir.expressions.IrStatementOrigin
 import org.jetbrains.kotlin.ir.expressions.IrWhen
-import org.jetbrains.kotlin.ir.expressions.impl.IrExpressionBase
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.KotlinType
 import java.util.*
@@ -34,38 +33,11 @@ class IrWhenImpl(
     private val branchParts = ArrayList<IrExpression>()
 
     fun addBranch(condition: IrExpression, result: IrExpression) {
-        condition.setTreeLocation(this, branchParts.size)
         branchParts.add(condition)
-        result.setTreeLocation(this, branchParts.size)
         branchParts.add(result)
     }
 
     override var elseBranch: IrExpression? = null
-        set(value) {
-            value?.detach()
-            field = value
-            value?.setTreeLocation(this, IF_ELSE_SLOT)
-        }
-
-    override fun getChild(slot: Int): IrElement? {
-        return when (slot) {
-            IF_ELSE_SLOT -> elseBranch
-            else -> branchParts.getOrNull(slot)
-        }
-    }
-
-    override fun replaceChild(slot: Int, newChild: IrElement) {
-        when (slot) {
-            IF_ELSE_SLOT -> elseBranch = newChild.assertCast()
-            in branchParts.indices -> {
-                branchParts[slot].detach()
-                branchParts[slot] = newChild.assertCast()
-                newChild.setTreeLocation(this, slot)
-            }
-            else ->
-                throwNoSuchSlot(slot)
-        }
-    }
 
     override val branchesCount: Int get() = branchParts.size / 2
 
@@ -75,6 +47,14 @@ class IrWhenImpl(
     override fun getNthResult(n: Int): IrExpression? =
             branchParts.getOrNull(n * 2 + 1)
 
+    override fun putNthCondition(n: Int, expression: IrExpression) {
+        branchParts[n * 2] = expression
+    }
+
+    override fun putNthResult(n: Int, expression: IrExpression) {
+        branchParts[n * 2 + 1] = expression
+    }
+
     override fun <R, D> accept(visitor: IrElementVisitor<R, D>, data: D): R =
             visitor.visitWhen(this, data)
 
@@ -82,4 +62,11 @@ class IrWhenImpl(
         branchParts.forEach { it.accept(visitor, data) }
         elseBranch?.accept(visitor, data)
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        branchParts.forEachIndexed { i, irExpression ->
+            branchParts[i] = irExpression.transform(transformer, data)
+        }
+        elseBranch = elseBranch?.transform(transformer, data)
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrWhileLoopImpl.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrWhileLoopImpl.kt
index d825c58c849..46a62946bfe 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrWhileLoopImpl.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/expressions/impl/IrWhileLoopImpl.kt
@@ -18,6 +18,7 @@ package org.jetbrains.kotlin.ir.expressions.impl
 
 import org.jetbrains.kotlin.ir.expressions.IrStatementOrigin
 import org.jetbrains.kotlin.ir.expressions.IrWhileLoop
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformer
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
 import org.jetbrains.kotlin.types.KotlinType
 
@@ -31,4 +32,9 @@ class IrWhileLoopImpl(startOffset: Int, endOffset: Int, type: KotlinType, origin
         condition.accept(visitor, data)
         body?.accept(visitor, data)
     }
+
+    override fun <D> transformChildren(transformer: IrElementTransformer<D>, data: D) {
+        condition = condition.transform(transformer, data)
+        body = body?.transform(transformer, data)
+    }
 }
\ No newline at end of file
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/RenderIrElement.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/RenderIrElement.kt
index eb2d56d9eea..a44e93ecf59 100644
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/RenderIrElement.kt
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/RenderIrElement.kt
@@ -162,10 +162,10 @@ class RenderIrElementVisitor : IrElementVisitor<String, Nothing?> {
             "DO_WHILE label=${loop.label} origin=${loop.origin}"
 
     override fun visitBreak(jump: IrBreak, data: Nothing?): String =
-            "BREAK label=${jump.label} loop.label=${jump.loop.label} depth=${jump.getDepth()}"
+            "BREAK label=${jump.label} loop.label=${jump.loop.label}"
 
     override fun visitContinue(jump: IrContinue, data: Nothing?): String =
-            "CONTINUE label=${jump.label} loop.label=${jump.loop.label} depth=${jump.getDepth()}"
+            "CONTINUE label=${jump.label} loop.label=${jump.loop.label}"
 
     override fun visitThrow(expression: IrThrow, data: Nothing?): String =
             "THROW type=${expression.type.render()}"
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/ValidateIrTree.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/ValidateIrTree.kt
deleted file mode 100644
index dc767c141a5..00000000000
--- a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/ValidateIrTree.kt
+++ /dev/null
@@ -1,40 +0,0 @@
-/*
- * Copyright 2010-2016 JetBrains s.r.o.
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-package org.jetbrains.kotlin.ir.util
-
-import org.jetbrains.kotlin.ir.IrElement
-import org.jetbrains.kotlin.ir.visitors.IrElementVisitor
-
-inline fun IrElement.validateTree(crossinline onFailBody: (IrElement, IrElement) -> Unit) {
-    accept(object : IrTreeValidationVisitor() {
-        override fun onFail(irElement: IrElement, expectedParent: IrElement) {
-            onFailBody(irElement, expectedParent)
-        }
-    }, null)
-}
-
-abstract class IrTreeValidationVisitor : IrElementVisitor<Unit, IrElement?> {
-    override fun visitElement(element: IrElement, data: IrElement?) {
-        if (data != null && element.parent != data) {
-            onFail(element, data)
-        }
-        element.acceptChildren(this, element)
-    }
-
-    protected abstract fun onFail(irElement: IrElement, expectedParent: IrElement)
-}
-
diff --git a/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/visitors/IrElementTransformer.kt b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/visitors/IrElementTransformer.kt
new file mode 100644
index 00000000000..dbb6faf92c2
--- /dev/null
+++ b/compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/visitors/IrElementTransformer.kt
@@ -0,0 +1,119 @@
+/*
+ * Copyright 2010-2016 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jetbrains.kotlin.ir.visitors
+
+import org.jetbrains.kotlin.ir.IrElement
+import org.jetbrains.kotlin.ir.declarations.*
+import org.jetbrains.kotlin.ir.expressions.*
+
+interface IrElementTransformer<in D> : IrElementVisitor<IrElement, D> {
+    override fun visitElement(element: IrElement, data: D): IrElement {
+        element.transformChildren(this, data)
+        return element
+    }
+
+    override fun visitModuleFragment(declaration: IrModuleFragment, data: D): IrModuleFragment {
+        declaration.transformChildren(this, data)
+        return declaration
+    }
+
+    override fun visitFile(declaration: IrFile, data: D): IrFile {
+        declaration.transformChildren(this, data)
+        return declaration
+    }
+
+    override fun visitDeclaration(declaration: IrDeclaration, data: D): IrDeclaration {
+        declaration.transformChildren(this, data)
+        return declaration
+    }
+
+    override fun visitClass(declaration: IrClass, data: D) = visitDeclaration(declaration, data)
+    override fun visitTypeAlias(declaration: IrTypeAlias, data: D) = visitDeclaration(declaration, data)
+    override fun visitFunction(declaration: IrFunction, data: D) = visitDeclaration(declaration, data)
+    override fun visitConstructor(declaration: IrConstructor, data: D) = visitFunction(declaration, data)
+    override fun visitProperty(declaration: IrProperty, data: D) = visitDeclaration(declaration, data)
+    override fun visitField(declaration: IrField, data: D) = visitDeclaration(declaration, data)
+    override fun visitLocalDelegatedProperty(declaration: IrLocalDelegatedProperty, data: D) = visitDeclaration(declaration, data)
+    override fun visitEnumEntry(declaration: IrEnumEntry, data: D) = visitDeclaration(declaration, data)
+    override fun visitAnonymousInitializer(declaration: IrAnonymousInitializer, data: D) = visitDeclaration(declaration, data)
+    override fun visitVariable(declaration: IrVariable, data: D) = visitDeclaration(declaration, data)
+
+    override fun visitBody(body: IrBody, data: D): IrBody {
+        body.transformChildren(this, data)
+        return body
+    }
+
+    override fun visitExpressionBody(body: IrExpressionBody, data: D) = visitBody(body, data)
+    override fun visitBlockBody(body: IrBlockBody, data: D) = visitBody(body, data)
+    override fun visitSyntheticBody(body: IrSyntheticBody, data: D) = visitBody(body, data)
+
+    override fun visitExpression(expression: IrExpression, data: D): IrExpression {
+        expression.transformChildren(this, data)
+        return expression
+    }
+
+    override fun <T> visitConst(expression: IrConst<T>, data: D) = visitExpression(expression, data)
+    override fun visitVararg(expression: IrVararg, data: D) = visitExpression(expression, data)
+    override fun visitSpreadElement(spread: IrSpreadElement, data: D): IrSpreadElement = spread
+
+    override fun visitContainerExpression(expression: IrContainerExpression, data: D) = visitExpression(expression, data)
+    override fun visitBlock(expression: IrBlock, data: D) = visitContainerExpression(expression, data)
+    override fun visitComposite(expression: IrComposite, data: D) = visitContainerExpression(expression, data)
+    override fun visitStringConcatenation(expression: IrStringConcatenation, data: D) = visitExpression(expression, data)
+    override fun visitThisReference(expression: IrThisReference, data: D) = visitExpression(expression, data)
+
+    override fun visitDeclarationReference(expression: IrDeclarationReference, data: D) = visitExpression(expression, data)
+    override fun visitSingletonReference(expression: IrGetSingletonValue, data: D) = visitDeclarationReference(expression, data)
+    override fun visitGetObjectValue(expression: IrGetObjectValue, data: D) = visitSingletonReference(expression, data)
+    override fun visitGetEnumValue(expression: IrGetEnumValue, data: D) = visitSingletonReference(expression, data)
+    override fun visitVariableAccess(expression: IrVariableAccessExpression, data: D) = visitDeclarationReference(expression, data)
+    override fun visitGetVariable(expression: IrGetVariable, data: D) = visitVariableAccess(expression, data)
+    override fun visitSetVariable(expression: IrSetVariable, data: D) = visitVariableAccess(expression, data)
+    override fun visitFieldAccess(expression: IrFieldAccessExpression, data: D) = visitDeclarationReference(expression, data)
+    override fun visitGetField(expression: IrGetField, data: D) = visitFieldAccess(expression, data)
+    override fun visitSetField(expression: IrSetField, data: D) = visitFieldAccess(expression, data)
+    override fun visitGetExtensionReceiver(expression: IrGetExtensionReceiver, data: D) = visitDeclarationReference(expression, data)
+    override fun visitGeneralCall(expression: IrGeneralCall, data: D) = visitDeclarationReference(expression, data)
+    override fun visitCall(expression: IrCall, data: D) = visitGeneralCall(expression, data)
+    override fun visitDelegatingConstructorCall(expression: IrDelegatingConstructorCall, data: D) = visitGeneralCall(expression, data)
+    override fun visitEnumConstructorCall(expression: IrEnumConstructorCall, data: D) = visitGeneralCall(expression, data)
+    override fun visitGetClass(expression: IrGetClass, data: D) = visitExpression(expression, data)
+
+    override fun visitCallableReference(expression: IrCallableReference, data: D) = visitGeneralCall(expression, data)
+    override fun visitClassReference(expression: IrClassReference, data: D) = visitDeclarationReference(expression, data)
+
+    override fun visitInstanceInitializerCall(expression: IrInstanceInitializerCall, data: D) = visitExpression(expression, data)
+
+    override fun visitTypeOperator(expression: IrTypeOperatorCall, data: D) = visitExpression(expression, data)
+
+    override fun visitWhen(expression: IrWhen, data: D) = visitExpression(expression, data)
+    override fun visitLoop(loop: IrLoop, data: D) = visitExpression(loop, data)
+    override fun visitWhileLoop(loop: IrWhileLoop, data: D) = visitLoop(loop, data)
+    override fun visitDoWhileLoop(loop: IrDoWhileLoop, data: D) = visitLoop(loop, data)
+    override fun visitTryCatch(tryCatch: IrTryCatch, data: D) = visitExpression(tryCatch, data)
+
+    override fun visitBreakContinue(jump: IrBreakContinue, data: D) = visitExpression(jump, data)
+    override fun visitBreak(jump: IrBreak, data: D) = visitBreakContinue(jump, data)
+    override fun visitContinue(jump: IrContinue, data: D) = visitBreakContinue(jump, data)
+
+    override fun visitReturn(expression: IrReturn, data: D) = visitExpression(expression, data)
+    override fun visitThrow(expression: IrThrow, data: D) = visitExpression(expression, data)
+
+    override fun visitErrorDeclaration(declaration: IrErrorDeclaration, data: D) = visitDeclaration(declaration, data)
+    override fun visitErrorExpression(expression: IrErrorExpression, data: D) = visitExpression(expression, data)
+    override fun visitErrorCallExpression(expression: IrErrorCallExpression, data: D) = visitErrorExpression(expression, data)
+}
diff --git a/compiler/testData/ir/irText/expressions/breakContinue.txt b/compiler/testData/ir/irText/expressions/breakContinue.txt
index 40e86a3c20b..19f3bcbfc6c 100644
--- a/compiler/testData/ir/irText/expressions/breakContinue.txt
+++ b/compiler/testData/ir/irText/expressions/breakContinue.txt
@@ -4,18 +4,18 @@ FILE /breakContinue.kt
       WHILE label=null origin=WHILE_LOOP
         condition: CONST Boolean type=kotlin.Boolean value='true'
         body: BLOCK type=kotlin.Nothing origin=null
-          BREAK label=null loop.label=null depth=0
+          BREAK label=null loop.label=null
       DO_WHILE label=null origin=DO_WHILE_LOOP
         body: BLOCK type=kotlin.Unit origin=null
-          BREAK label=null loop.label=null depth=0
+          BREAK label=null loop.label=null
         condition: CONST Boolean type=kotlin.Boolean value='true'
       WHILE label=null origin=WHILE_LOOP
         condition: CONST Boolean type=kotlin.Boolean value='true'
         body: BLOCK type=kotlin.Nothing origin=null
-          CONTINUE label=null loop.label=null depth=0
+          CONTINUE label=null loop.label=null
       DO_WHILE label=null origin=DO_WHILE_LOOP
         body: BLOCK type=kotlin.Unit origin=null
-          CONTINUE label=null loop.label=null depth=0
+          CONTINUE label=null loop.label=null
         condition: CONST Boolean type=kotlin.Boolean value='true'
   FUN public fun test2(): kotlin.Unit
     BLOCK_BODY
@@ -25,18 +25,18 @@ FILE /breakContinue.kt
           WHILE label=INNER origin=WHILE_LOOP
             condition: CONST Boolean type=kotlin.Boolean value='true'
             body: BLOCK type=kotlin.Nothing origin=null
-              BREAK label=INNER loop.label=INNER depth=0
-              BREAK label=OUTER loop.label=OUTER depth=1
-          BREAK label=OUTER loop.label=OUTER depth=0
+              BREAK label=INNER loop.label=INNER
+              BREAK label=OUTER loop.label=OUTER
+          BREAK label=OUTER loop.label=OUTER
       WHILE label=OUTER origin=WHILE_LOOP
         condition: CONST Boolean type=kotlin.Boolean value='true'
         body: BLOCK type=kotlin.Nothing origin=null
           WHILE label=INNER origin=WHILE_LOOP
             condition: CONST Boolean type=kotlin.Boolean value='true'
             body: BLOCK type=kotlin.Nothing origin=null
-              CONTINUE label=INNER loop.label=INNER depth=0
-              CONTINUE label=OUTER loop.label=OUTER depth=1
-          CONTINUE label=OUTER loop.label=OUTER depth=0
+              CONTINUE label=INNER loop.label=INNER
+              CONTINUE label=OUTER loop.label=OUTER
+          CONTINUE label=OUTER loop.label=OUTER
   FUN public fun test3(): kotlin.Unit
     BLOCK_BODY
       WHILE label=L origin=WHILE_LOOP
@@ -45,13 +45,13 @@ FILE /breakContinue.kt
           WHILE label=L origin=WHILE_LOOP
             condition: CONST Boolean type=kotlin.Boolean value='true'
             body: BLOCK type=kotlin.Nothing origin=null
-              BREAK label=L loop.label=L depth=0
-          BREAK label=L loop.label=L depth=0
+              BREAK label=L loop.label=L
+          BREAK label=L loop.label=L
       WHILE label=L origin=WHILE_LOOP
         condition: CONST Boolean type=kotlin.Boolean value='true'
         body: BLOCK type=kotlin.Nothing origin=null
           WHILE label=L origin=WHILE_LOOP
             condition: CONST Boolean type=kotlin.Boolean value='true'
             body: BLOCK type=kotlin.Nothing origin=null
-              CONTINUE label=L loop.label=L depth=0
-          CONTINUE label=L loop.label=L depth=0
+              CONTINUE label=L loop.label=L
+          CONTINUE label=L loop.label=L
diff --git a/compiler/testData/ir/irText/expressions/breakContinueInLoopHeader.txt b/compiler/testData/ir/irText/expressions/breakContinueInLoopHeader.txt
index 5c41ba57148..6f6c4edf929 100644
--- a/compiler/testData/ir/irText/expressions/breakContinueInLoopHeader.txt
+++ b/compiler/testData/ir/irText/expressions/breakContinueInLoopHeader.txt
@@ -12,7 +12,7 @@ FILE /breakContinueInLoopHeader.kt
                 if: CALL 'EQEQ(Any?, Any?): Boolean' type=kotlin.Boolean origin=EQEQ
                   arg0: GET_VAR 'tmp0_elvis_lhs: Boolean?' type=kotlin.Boolean? origin=null
                   arg1: CONST Null type=kotlin.Nothing? value='null'
-                then: BREAK label=null loop.label=L depth=1
+                then: BREAK label=null loop.label=L
                 else: GET_VAR 'tmp0_elvis_lhs: Boolean?' type=kotlin.Boolean? origin=null
   FUN public fun test2(c: kotlin.Boolean?): kotlin.Unit
     BLOCK_BODY
@@ -27,7 +27,7 @@ FILE /breakContinueInLoopHeader.kt
                 if: CALL 'EQEQ(Any?, Any?): Boolean' type=kotlin.Boolean origin=EQEQ
                   arg0: GET_VAR 'tmp0_elvis_lhs: Boolean?' type=kotlin.Boolean? origin=null
                   arg1: CONST Null type=kotlin.Nothing? value='null'
-                then: CONTINUE label=null loop.label=L depth=1
+                then: CONTINUE label=null loop.label=L
                 else: GET_VAR 'tmp0_elvis_lhs: Boolean?' type=kotlin.Boolean? origin=null
   FUN public fun test3(ss: kotlin.collections.List<kotlin.String>?): kotlin.Unit
     BLOCK_BODY
@@ -44,7 +44,7 @@ FILE /breakContinueInLoopHeader.kt
                     if: CALL 'EQEQ(Any?, Any?): Boolean' type=kotlin.Boolean origin=EQEQ
                       arg0: GET_VAR 'tmp0_elvis_lhs: List<String>?' type=kotlin.collections.List<kotlin.String>? origin=null
                       arg1: CONST Null type=kotlin.Nothing? value='null'
-                    then: CONTINUE label=null loop.label=L depth=0
+                    then: CONTINUE label=null loop.label=L
                     else: GET_VAR 'tmp0_elvis_lhs: List<String>?' type=kotlin.collections.List<kotlin.String>? origin=null
             WHILE label=null origin=FOR_LOOP_INNER_WHILE
               condition: CALL 'hasNext(): Boolean' type=kotlin.Boolean origin=FOR_LOOP_HAS_NEXT
@@ -68,7 +68,7 @@ FILE /breakContinueInLoopHeader.kt
                     if: CALL 'EQEQ(Any?, Any?): Boolean' type=kotlin.Boolean origin=EQEQ
                       arg0: GET_VAR 'tmp0_elvis_lhs: List<String>?' type=kotlin.collections.List<kotlin.String>? origin=null
                       arg1: CONST Null type=kotlin.Nothing? value='null'
-                    then: BREAK label=null loop.label=L depth=0
+                    then: BREAK label=null loop.label=L
                     else: GET_VAR 'tmp0_elvis_lhs: List<String>?' type=kotlin.collections.List<kotlin.String>? origin=null
             WHILE label=null origin=FOR_LOOP_INNER_WHILE
               condition: CALL 'hasNext(): Boolean' type=kotlin.Boolean origin=FOR_LOOP_HAS_NEXT
diff --git a/compiler/testData/ir/irText/expressions/forWithBreakContinue.txt b/compiler/testData/ir/irText/expressions/forWithBreakContinue.txt
index 22ef064dfc5..9371b7ebad6 100644
--- a/compiler/testData/ir/irText/expressions/forWithBreakContinue.txt
+++ b/compiler/testData/ir/irText/expressions/forWithBreakContinue.txt
@@ -13,7 +13,7 @@ FILE /forWithBreakContinue.kt
               CALL 'next(): String' type=kotlin.String origin=FOR_LOOP_NEXT
                 $this: GET_VAR 'tmp0_iterator: Iterator<String>' type=kotlin.collections.Iterator<kotlin.String> origin=null
             BLOCK type=kotlin.Nothing origin=null
-              BREAK label=null loop.label=null depth=0
+              BREAK label=null loop.label=null
   FUN public fun testForBreak2(ss: kotlin.collections.List<kotlin.String>): kotlin.Unit
     BLOCK_BODY
       BLOCK type=kotlin.Unit origin=FOR_LOOP
@@ -40,10 +40,10 @@ FILE /forWithBreakContinue.kt
                       CALL 'next(): String' type=kotlin.String origin=FOR_LOOP_NEXT
                         $this: GET_VAR 'tmp1_iterator: Iterator<String>' type=kotlin.collections.Iterator<kotlin.String> origin=null
                     BLOCK type=kotlin.Nothing origin=null
-                      BREAK label=OUTER loop.label=OUTER depth=1
-                      BREAK label=INNER loop.label=INNER depth=0
-                      BREAK label=null loop.label=INNER depth=0
-              BREAK label=OUTER loop.label=OUTER depth=0
+                      BREAK label=OUTER loop.label=OUTER
+                      BREAK label=INNER loop.label=INNER
+                      BREAK label=null loop.label=INNER
+              BREAK label=OUTER loop.label=OUTER
   FUN public fun testForContinue1(ss: kotlin.collections.List<kotlin.String>): kotlin.Unit
     BLOCK_BODY
       BLOCK type=kotlin.Unit origin=FOR_LOOP
@@ -58,7 +58,7 @@ FILE /forWithBreakContinue.kt
               CALL 'next(): String' type=kotlin.String origin=FOR_LOOP_NEXT
                 $this: GET_VAR 'tmp0_iterator: Iterator<String>' type=kotlin.collections.Iterator<kotlin.String> origin=null
             BLOCK type=kotlin.Nothing origin=null
-              CONTINUE label=null loop.label=null depth=0
+              CONTINUE label=null loop.label=null
   FUN public fun testForContinue2(ss: kotlin.collections.List<kotlin.String>): kotlin.Unit
     BLOCK_BODY
       BLOCK type=kotlin.Unit origin=FOR_LOOP
@@ -85,7 +85,7 @@ FILE /forWithBreakContinue.kt
                       CALL 'next(): String' type=kotlin.String origin=FOR_LOOP_NEXT
                         $this: GET_VAR 'tmp1_iterator: Iterator<String>' type=kotlin.collections.Iterator<kotlin.String> origin=null
                     BLOCK type=kotlin.Nothing origin=null
-                      CONTINUE label=OUTER loop.label=OUTER depth=1
-                      CONTINUE label=INNER loop.label=INNER depth=0
-                      CONTINUE label=null loop.label=INNER depth=0
-              CONTINUE label=OUTER loop.label=OUTER depth=0
+                      CONTINUE label=OUTER loop.label=OUTER
+                      CONTINUE label=INNER loop.label=INNER
+                      CONTINUE label=null loop.label=INNER
+              CONTINUE label=OUTER loop.label=OUTER