Extremely conservative escape analysis. (#212)

2017-02-08 19:15:55 +03:00
parent a856e16d2f
commit 4b27074979
9 changed files with 571 additions and 68 deletions
@@ -0,0 +1,481 @@
+package org.jetbrains.kotlin.backend.konan
+
+import org.jetbrains.kotlin.backend.konan.descriptors.allValueParameters
+import org.jetbrains.kotlin.backend.konan.llvm.Lifetime
+import org.jetbrains.kotlin.backend.konan.llvm.RuntimeAware
+import org.jetbrains.kotlin.backend.konan.ir.getArguments
+import org.jetbrains.kotlin.backend.konan.ir.ir2string
+import org.jetbrains.kotlin.backend.konan.llvm.isObjectType
+import org.jetbrains.kotlin.descriptors.*
+import org.jetbrains.kotlin.ir.IrElement
+import org.jetbrains.kotlin.ir.declarations.IrField
+import org.jetbrains.kotlin.ir.declarations.IrFunction
+import org.jetbrains.kotlin.ir.declarations.IrModuleFragment
+import org.jetbrains.kotlin.ir.declarations.IrVariable
+import org.jetbrains.kotlin.ir.expressions.*
+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.types.KotlinType
+import org.jetbrains.kotlin.types.typeUtil.isNothing
+import org.jetbrains.kotlin.types.typeUtil.isUnit
+
+val DEBUG = false
+
+// Roles in which particular object reference is being used. Lifetime is computed from
+// all roles reference.
+internal enum class Role {
+    // If reference is created as call result.
+    CALL_RESULT,
+    // If reference is created as allocation call result.
+    ALLOC_RESULT,
+    // If reference is being returned.
+    RETURN_VALUE,
+    // If reference is being thrown.
+    THROW_VALUE,
+    // If reference's field is being read.
+    FIELD_READ,
+    // If reference's field is being written to.
+    FIELD_WRITTEN,
+    // If reference is being read from the field.
+    READ_FROM_FIELD,
+    // If reference is being written to the field.
+    WRITTEN_TO_FIELD,
+    // If reference is being read from the gloabl.
+    READ_FROM_GLOBAL,
+    // If reference is being written to the global.
+    WRITTEN_TO_GLOBAL,
+    // Outgoing call argument.
+    CALL_ARGUMENT
+}
+
+internal class RoleInfoEntry(val data: Any? = null)
+
+internal open class RoleInfo {
+    val entries = mutableListOf<RoleInfoEntry>()
+    open fun add(entry: RoleInfoEntry) = entries.add(entry)
+}
+
+private fun RuntimeAware.isInteresting(type: KotlinType) : Boolean =
+        !type.isUnit() && !type.isNothing() && isObjectType(type)
+
+internal class Roles {
+    val data = HashMap<Role, RoleInfo>()
+
+    fun add(role: Role, info: RoleInfoEntry?) {
+        val entry = data.getOrPut(role, { RoleInfo() })
+        if (info != null) entry.add(info)
+    }
+
+    fun add(roles: Roles) {
+        roles.data.forEach { role, info ->
+            info.entries.forEach { entry ->
+                add(role, entry)
+            }
+        }
+    }
+
+    fun remove(role: Role) = data.remove(role)
+
+    fun has(role: Role) : Boolean = data[role] != null
+
+    fun escapes() : Boolean {
+        return has(Role.WRITTEN_TO_FIELD) || has(Role.WRITTEN_TO_GLOBAL) ||
+                has(Role.CALL_ARGUMENT) || has(Role.THROW_VALUE)
+    }
+
+    fun pure() : Boolean = !escapes() && has(Role.RETURN_VALUE)
+
+    fun info(role: Role) : RoleInfo? = data[role]
+
+    override fun toString() : String {
+        val builder = StringBuilder()
+        data.forEach { t, u ->
+            builder.append(t.name)
+            builder.append(": ")
+            builder.append(u.entries.joinToString(", "))
+            builder.append("; ")
+        }
+        return builder.toString()
+    }
+}
+
+internal class VariableValues {
+    val elementData = HashMap<ValueDescriptor, MutableSet<IrExpression>>()
+
+    fun addEmpty(variable: ValueDescriptor) =
+            elementData.getOrPut(variable, { mutableSetOf<IrExpression>() })
+    fun add(variable: ValueDescriptor, element: IrExpression) =
+            elementData.get(variable)?.add(element)
+    fun add(variable: ValueDescriptor, elements: Set<IrExpression>) =
+            elementData.get(variable)?.addAll(elements)
+    fun get(variable: ValueDescriptor) : Set<IrExpression>? =
+            elementData[variable]
+
+    fun computeClosure() {
+        elementData.forEach { key, _ ->
+            add(key, computeValueClosure(key))
+        }
+    }
+
+    // Computes closure of all possible values for given variable.
+    fun computeValueClosure(value: ValueDescriptor): Set<IrExpression> {
+        val result = mutableSetOf<IrExpression>()
+        val workset = mutableSetOf<ValueDescriptor>(value)
+        val seen = mutableSetOf<IrGetValue>()
+        while (!workset.isEmpty()) {
+            val value = workset.first()
+            workset -= value
+            val elements = elementData[value] ?: continue
+            for (element in elements) {
+                if (element is IrGetValue) {
+                    if (!seen.contains(element)) {
+                        seen.add(element)
+                        workset.add(element.descriptor)
+                    }
+                } else {
+                    result.add(element)
+                }
+            }
+        }
+        return result
+    }
+}
+
+internal class ParameterRoles {
+    val elementData = HashMap<ParameterDescriptor, Roles>()
+
+    fun addParameter(parameter: ParameterDescriptor) {
+        elementData.getOrPut(parameter) { Roles() }
+    }
+
+    fun add(parameter: ParameterDescriptor, role: Role, roleInfoEntry: RoleInfoEntry?) {
+        val roles = elementData.getOrPut(parameter, { Roles() });
+        roles.add(role, roleInfoEntry)
+    }
+
+    fun canEliminateCallArgument(info: RoleInfo): Boolean {
+        for (call in info.entries) {
+            val entry = call.data as Pair<ParameterDescriptor, CallableDescriptor>
+            val argument = entry.first
+            val callee = entry.second
+            // Virtual dispatch.
+            if (callee is FunctionDescriptor && callee.isOverridable) return false
+            if (DEBUG) println("passed as ${argument}")
+            val rolesInCallee = elementData[argument] ?: return false
+            if (DEBUG) println("In callee is: $rolesInCallee")
+            // TODO: make recursive computation here.
+            if (rolesInCallee.escapes()) return false
+        }
+        return true
+    }
+
+    fun propagateCallArguments(roles: Roles): Boolean {
+        val info = roles.info(Role.CALL_ARGUMENT) ?: return false
+        if (canEliminateCallArgument(info)) {
+            roles.remove(Role.CALL_ARGUMENT)
+            return true
+        }
+        return false
+    }
+
+    fun propagateCallArguments(expressionToRoles: MutableMap<IrExpression, Roles>) {
+        expressionToRoles.forEach {
+            if (propagateCallArguments(it.value) && DEBUG)
+                println("unescaped expression ${it.key}")
+        }
+        elementData.forEach {
+            if (propagateCallArguments(it.value) && DEBUG)
+                println("unescaped paramater ${it.key}")
+        }
+    }
+}
+
+internal fun rolesToLifetime(roles: Roles) : Lifetime {
+    val roleSetSize = roles.data.keys.size
+    return when {
+        // If reference is stored to global or generic field - it must be global.
+        roles.escapes() ->
+            Lifetime.GLOBAL
+         // If we pass it to unknown methods or throw - it must be global.
+        roles.has(Role.CALL_ARGUMENT) || roles.has(Role.THROW_VALUE) ->
+            Lifetime.GLOBAL
+        // If reference is only obtained as call result and never used - it can be local.
+        roleSetSize == 1 && roles.has(Role.CALL_RESULT) ->
+            Lifetime.LOCAL  // throw Error()
+        // If reference is obtained as some call result and returned - we can use return.
+        roleSetSize == 2 && roles.has(Role.CALL_RESULT) && roles.has(Role.RETURN_VALUE) ->
+            Lifetime.RETURN_VALUE
+        // Otherwise, say it is global.
+        else ->
+            Lifetime.GLOBAL
+    }
+}
+
+internal class ElementFinderVisitor(
+        val context: RuntimeAware,
+        val expressionToRoles: MutableMap<IrExpression, Roles>,
+        val variableValues: VariableValues,
+        val parameterRoles: ParameterRoles)
+    : IrElementVisitorVoid {
+
+    fun isInteresting(element: IrExpression) : Boolean {
+        return (element is IrMemberAccessExpression && context.isInteresting(element.type)) ||
+                (element is IrGetValue && context.isInteresting(element.type))
+    }
+
+    fun isInteresting(variable: ValueDescriptor) : Boolean {
+        return context.isInteresting(variable.type)
+    }
+
+    override fun visitElement(element: IrElement) {
+        if (element is IrExpression && isInteresting(element)) {
+            expressionToRoles[element] = Roles()
+        }
+        element.acceptChildrenVoid(this)
+    }
+
+    override fun visitTypeOperator(expression: IrTypeOperatorCall) {
+        super.visitTypeOperator(expression)
+        if (expression.operator == IrTypeOperator.IMPLICIT_COERCION_TO_UNIT) {
+            expressionToRoles.remove(expression.argument)
+        }
+    }
+
+    override fun visitFunction(declaration: IrFunction) {
+        declaration.descriptor.allValueParameters.forEach {
+            if (isInteresting(it))
+                parameterRoles.addParameter(it)
+        }
+        super.visitFunction(declaration)
+    }
+
+    override fun visitVariable(expression: IrVariable) {
+        if (isInteresting(expression.descriptor))
+            variableValues.addEmpty(expression.descriptor)
+        super.visitVariable(expression)
+    }
+}
+
+//
+// elementToRoles is filled with all possible roles given element can play.
+// varValues is filled with all possible elements that could be stored in a variable.
+//
+internal class RoleAssignerVisitor(
+        val expressionRoles: MutableMap<IrExpression, Roles>,
+        val variableValues: VariableValues,
+        val parameterRoles: ParameterRoles,
+        val useVarValues: Boolean) : IrElementVisitorVoid {
+
+    fun assignExpressionRole(expression: IrExpression, role: Role, infoEntry: RoleInfoEntry?) {
+        if (!useVarValues)
+            expressionRoles[expression]?.add(role, infoEntry)
+    }
+
+    fun assignValueRole(value: ValueDescriptor, role: Role, infoEntry: RoleInfoEntry?) {
+        if (!useVarValues) return
+        // Whenever we see variable use in certain role - we propagate this role
+        // to all possible expression this variable can be assigned to.
+        val possibleValues = variableValues.get(value)
+        if (possibleValues != null) {
+            for (possibleValue in possibleValues) {
+                expressionRoles[possibleValue]?.add(role, infoEntry)
+            }
+        }
+        if (value is ParameterDescriptor) {
+            parameterRoles.add(value, role, infoEntry)
+        }
+    }
+
+    // Here we handle variable assignment.
+    fun assignVariable(variable: VariableDescriptor, value: IrExpression) {
+        if (useVarValues) return
+        // Sometimes we can assign value to Unit variable (unit4.kt) - we don't care.
+        if (value.type.isUnit()) return
+        when (value) {
+            is IrContainerExpression -> assignVariable(variable, value.statements.last() as IrExpression)
+            // is IrVararg -> value.elements.forEach { assignVariable(variable, it as IrExpression) }
+            is IrWhen -> value.branches.forEach { assignVariable(variable, it.result) }
+            is IrMemberAccessExpression -> variableValues.add(variable, value)
+            is IrGetValue -> variableValues.add(variable, value)
+            is IrGetField -> variableValues.add(variable, value)
+            is IrConst<*> -> { }
+            is IrTypeOperatorCall -> {
+                when (value.operator) {
+                    IrTypeOperator.IMPLICIT_CAST, IrTypeOperator.CAST ->
+                        assignVariable(variable, value.argument)
+                    else -> TODO(ir2string(value))
+                }
+            }
+            is IrTry -> (value.catches + value.tryResult).forEach {
+                if (it is IrExpression) assignVariable(variable, it)
+            }
+            is IrThrow -> { /* Do nothing, error path in an assignment. */ }
+            is IrGetObjectValue -> { }
+            // TODO: is it correct?
+            is IrReturn -> { /* Do nothing, return path in an assignment. */ }
+            else -> TODO(ir2string(value))
+        }
+    }
+
+    // Here we assign a role to expression's value.
+    fun assignRole(expression: IrExpression, role: Role, infoEntry: RoleInfoEntry?) {
+        if (expression.type.isUnit()) return
+        when (expression) {
+            is IrContainerExpression -> assignRole(expression.statements.last() as IrExpression, role, infoEntry)
+            is IrVararg -> expression.elements.forEach { assignRole(it as IrExpression, role, infoEntry) }
+            is IrWhen -> expression.branches.forEach { assignRole(it.result, role, infoEntry) }
+            is IrMemberAccessExpression -> assignExpressionRole(expression, role, infoEntry)
+            is IrGetValue -> assignValueRole(expression.descriptor, role, infoEntry)
+            // If field plays certain role - we cannot use this info now.
+            is IrGetField -> {}
+            // If constant plays certain role - this information is useless.
+            is IrConst<*> -> {}
+            is IrTypeOperatorCall -> {
+                when (expression.operator) {
+                    IrTypeOperator.IMPLICIT_CAST, IrTypeOperator.CAST ->
+                        assignRole(expression.argument, role, infoEntry)
+                    // No info from those ones.
+                    IrTypeOperator.INSTANCEOF, IrTypeOperator.NOT_INSTANCEOF,
+                    IrTypeOperator.IMPLICIT_COERCION_TO_UNIT -> {}
+                    else -> TODO(ir2string(expression))
+                }
+            }
+            is IrThrow -> { /* Do nothing, error path in an assignment. */ }
+            is IrGetObjectValue -> { /* Shall we do anything here? */ }
+            // TODO: is it correct?
+            is IrReturn -> { /* Do nothing, return path in an assignment. */ }
+            else -> TODO(ir2string(expression))
+        }
+    }
+
+    override fun visitElement(element: IrElement) {
+        element.acceptChildrenVoid(this)
+    }
+
+    override fun visitCall(expression: IrCall) {
+        assignRole(expression, Role.CALL_RESULT, RoleInfoEntry(expression))
+        for (argument in expression.getArguments()) {
+            assignRole(argument.second, Role.CALL_ARGUMENT,
+                    RoleInfoEntry(Pair(argument.first, expression.descriptor)))
+        }
+        super.visitCall(expression)
+    }
+
+    override fun visitSetField(expression: IrSetField) {
+        assignRole(expression.value, Role.WRITTEN_TO_FIELD, RoleInfoEntry(expression))
+        super.visitSetField(expression)
+    }
+
+    override fun visitField(declaration: IrField) {
+        val initializer = declaration.initializer
+        if (initializer != null) {
+            assignRole(initializer.expression,
+                    Role.WRITTEN_TO_FIELD, RoleInfoEntry(declaration))
+        }
+        super.visitField(declaration)
+    }
+
+    override fun visitSetVariable(expression: IrSetVariable) {
+        assignVariable(expression.descriptor, expression.value)
+        super.visitSetVariable(expression)
+    }
+
+    override fun visitVariable(expression: IrVariable) {
+        val initializer = expression.initializer
+        if (initializer != null) {
+            assignVariable(expression.descriptor, initializer)
+        }
+        super.visitVariable(expression)
+    }
+
+    override fun visitReturn(expression: IrReturn) {
+        assignRole(expression.value, Role.RETURN_VALUE, RoleInfoEntry(expression))
+        super.visitReturn(expression)
+    }
+
+    override fun visitThrow(expression: IrThrow) {
+        assignRole(expression.value, Role.THROW_VALUE, RoleInfoEntry(expression))
+        super.visitThrow(expression)
+    }
+}
+
+internal class ContextFinderVisitor(val needle: IrElement) : IrElementVisitorVoid {
+    val stack = mutableListOf<IrElement>()
+    var found = false
+
+    override fun visitElement(element: IrElement) {
+        if (found) return
+        stack.add(element)
+        if (element == needle) {
+            found = true
+        }
+        element.acceptChildrenVoid(this)
+        if (found) return
+        stack.removeAt(stack.size - 1)
+    }
+
+    override fun visitModuleFragment(module: IrModuleFragment) {
+        module.acceptChildrenVoid(this)
+    }
+}
+
+private fun findContext(irModule: IrModuleFragment, element: IrElement) : String {
+    val visitor = ContextFinderVisitor(element)
+    irModule.acceptVoid(visitor)
+    val result = StringBuilder()
+    if (visitor.found) {
+        visitor.stack.forEach {
+            result.append(ir2string(it))
+            result.append(" -> ")
+        }
+    } else {
+        result.append("<not found>")
+    }
+    return result.toString()
+}
+
+//
+// Analysis we're implementing here is as following.
+//  * compute roles IR value nodes can play
+//  * merge role information with all methods being called
+//  * squash set of roles to conservatively estimated lifetime
+//
+fun computeLifetimes(irModule: IrModuleFragment, context: RuntimeAware,
+                     lifetimes: MutableMap<IrElement, Lifetime>) {
+    assert(lifetimes.size == 0)
+
+    val expressionToRoles = mutableMapOf<IrExpression, Roles>()
+    val variableValues = VariableValues()
+    val parameterRoles = ParameterRoles()
+    irModule.acceptVoid(ElementFinderVisitor(
+            context, expressionToRoles, variableValues, parameterRoles))
+    // On this pass, we collect all possible variable values and assign roles
+    // to expressions.
+    irModule.acceptVoid(RoleAssignerVisitor(
+            expressionToRoles, variableValues, parameterRoles, false))
+    // Compute transitive closure of possible values for variables.
+    variableValues.computeClosure()
+    // On this pass, we use possible variable values to assign roles to expression.
+    irModule.acceptVoid(RoleAssignerVisitor(
+            expressionToRoles, variableValues, parameterRoles, true))
+    parameterRoles.propagateCallArguments(expressionToRoles)
+
+    expressionToRoles.forEach { expression, roles ->
+        if (DEBUG)
+            println("for ${expression} roles are ${roles.data.keys.joinToString(", ")}")
+        var role = rolesToLifetime(roles)
+        if (role == Lifetime.LOCAL) {
+            println("arena alloc for ${ir2string(expression)} in ${findContext(irModule, expression)}")
+            // Not yet enabled.
+            role = Lifetime.GLOBAL
+        }
+        lifetimes[expression] = role
+    }
+    if (DEBUG) {
+        variableValues.elementData.forEach { variable, expressions ->
+            println("variable $variable could be ${expressions.joinToString(", ")}") }
+        parameterRoles.elementData.forEach { parameter, roles ->
+            println("parameter $parameter could be $roles") }
+    }
+}
@@ -29,7 +29,7 @@ internal enum class SlotType {
 }

 // Lifetimes class of reference, computed by escape analysis.
-internal enum class Lifetime(val slotType: SlotType) {
+enum class Lifetime(val slotType: SlotType) {
    // If reference is frame-local (only obtained from some call and never leaves).
    LOCAL(SlotType.ARENA),
    // If reference is only returned.
@@ -4,6 +4,7 @@ import llvm.*
 import org.jetbrains.kotlin.backend.konan.ValueType
 import org.jetbrains.kotlin.backend.konan.isRepresentedAs
 import org.jetbrains.kotlin.types.KotlinType
+import org.jetbrains.kotlin.types.typeUtil.isNothing
 import org.jetbrains.kotlin.types.typeUtil.isUnit

 private val valueTypes = ValueType.values().associate {
@@ -38,4 +39,6 @@ internal fun RuntimeAware.getLLVMReturnType(type: KotlinType): LLVMTypeRef {
        // KotlinBuiltIns.isNothing(type) -> LLVMVoidType()
        else -> getLLVMType(type)
    }
-}
+}
+
+fun RuntimeAware.isObjectType(type: KotlinType) : Boolean = isObjectType(getLLVMType(type))
@@ -1,38 +0,0 @@
-package org.jetbrains.kotlin.backend.konan.llvm
-
-import org.jetbrains.kotlin.ir.IrElement
-import org.jetbrains.kotlin.ir.declarations.IrModuleFragment
-import org.jetbrains.kotlin.ir.expressions.IrMemberAccessExpression
-import org.jetbrains.kotlin.ir.visitors.IrElementVisitorVoid
-import org.jetbrains.kotlin.ir.visitors.acceptChildrenVoid
-import org.jetbrains.kotlin.ir.visitors.acceptVoid
-
-// Analysis we're implementing here is as following.
-// We build graph with the following nodes:
-//    * allocation set, keeping tuple of [local, ctor call, owner function], AS
-//    * local store set, keeping pair [local, stored], LSS
-//    * field store set, keeping tuple [local, object to store, stored field id], FSS
-//    * global store set, [local, stored global address], GSS
-// Function we're trying to compute is the following:
-//   for each element of AS, could it be referred by someone, whose value is
-//   alive on return from function, where element was allocated.
-// Each element in RS is associated with few elements in AS, which it could refer to.
-//
-internal class EscapeAnalyzerVisitor(
-        val lifetimes: MutableMap<IrMemberAccessExpression, Lifetime>) : IrElementVisitorVoid {
-
-    override fun visitElement(element: IrElement) {
-        element.acceptChildrenVoid(this)
-    }
-
-    override fun visitModuleFragment(module: IrModuleFragment) {
-        module.acceptChildrenVoid(this)
-    }
-}
-
-internal fun computeLifetimes(irModule: IrModuleFragment,
-                              lifetimes: MutableMap<IrMemberAccessExpression, Lifetime>) {
-    assert(lifetimes.size == 0)
-
-    irModule.acceptVoid(EscapeAnalyzerVisitor(lifetimes))
-}
@@ -168,7 +168,7 @@ internal interface CodeContext {
 internal class CodeGeneratorVisitor(val context: Context) : IrElementVisitorVoid {

    val codegen = CodeGenerator(context)
-    val resultLifetimes = mutableMapOf<IrMemberAccessExpression, Lifetime>()
+    val resultLifetimes = mutableMapOf<IrElement, Lifetime>()

    //-------------------------------------------------------------------------//

@@ -237,7 +237,7 @@ internal class CodeGeneratorVisitor(val context: Context) : IrElementVisitorVoid
    override fun visitModuleFragment(module: IrModuleFragment) {
        context.log("visitModule                  : ${ir2string(module)}")

-        computeLifetimes(module, resultLifetimes)
+        computeLifetimes(module, this.codegen, resultLifetimes)

        module.acceptChildrenVoid(this)
        appendLlvmUsed(context.llvm.usedFunctions)
@@ -476,11 +476,11 @@ internal class CodeGeneratorVisitor(val context: Context) : IrElementVisitorVoid
     */
    private fun bindParameters(descriptor: FunctionDescriptor?): Map<ParameterDescriptor, LLVMValueRef> {
        if (descriptor == null) return emptyMap()
-        val paramDescriptors = descriptor.allValueParameters
-        return paramDescriptors.mapIndexed { i, paramDescriptor ->
-            val param = codegen.param(descriptor, i)
-            assert(codegen.getLLVMType(paramDescriptor.type) == param.type)
-            paramDescriptor to param
+        val parameterDescriptors = descriptor.allValueParameters
+        return parameterDescriptors.mapIndexed { i, parameterDescriptor ->
+            val parameter = codegen.param(descriptor, i)
+            assert(codegen.getLLVMType(parameterDescriptor.type) == parameter.type)
+            parameterDescriptor to parameter
        }.toMap()
    }

@@ -1081,7 +1081,7 @@ internal class CodeGeneratorVisitor(val context: Context) : IrElementVisitorVoid
        }


-        assert (loop.type.isUnit())
+        assert(loop.type.isUnit())
        return codegen.theUnitInstanceRef.llvm
    }

@@ -1104,7 +1104,7 @@ internal class CodeGeneratorVisitor(val context: Context) : IrElementVisitorVoid
            codegen.positionAtEnd(loopScope.loopExit)
        }

-        assert (loop.type.isUnit())
+        assert(loop.type.isUnit())
        return codegen.theUnitInstanceRef.llvm
    }

@@ -1119,11 +1119,11 @@ internal class CodeGeneratorVisitor(val context: Context) : IrElementVisitorVoid

    private fun evaluateSetVariable(value: IrSetVariable): LLVMValueRef {
        context.log("evaluateSetVariable        : ${ir2string(value)}")
-        val ret = evaluateExpression(value.value)
+        val result = evaluateExpression(value.value)
        val variable = currentCodeContext.getDeclaredVariable(value.descriptor)
-        codegen.vars.store(ret, variable)
+        codegen.vars.store(result, variable)

-        assert (value.type.isUnit())
+        assert(value.type.isUnit())
        return codegen.theUnitInstanceRef.llvm
    }

@@ -1131,8 +1131,8 @@ internal class CodeGeneratorVisitor(val context: Context) : IrElementVisitorVoid

    private fun generateVariable(value: IrVariable) {
        context.log("generateVariable           : ${ir2string(value)}")
-        val ret = value.initializer?.let { evaluateExpression(it) }
-        currentCodeContext.genDeclareVariable(value.descriptor, ret)
+        val result = value.initializer?.let { evaluateExpression(it) }
+        currentCodeContext.genDeclareVariable(value.descriptor, result)
    }

    //-------------------------------------------------------------------------//
@@ -1454,7 +1454,7 @@ internal class CodeGeneratorVisitor(val context: Context) : IrElementVisitorVoid
                }
            }

-            assert (value.type.isUnit())
+            assert(value.type.isUnit())
            return codegen.theUnitInstanceRef.llvm
        }
    }
@@ -1621,8 +1621,8 @@ internal class CodeGeneratorVisitor(val context: Context) : IrElementVisitorVoid
    }

    //-------------------------------------------------------------------------//
-    private fun resultLifetime(callee: IrMemberAccessExpression): Lifetime {
-        return resultLifetimes.getOrElse(callee) { Lifetime.GLOBAL }
+    private fun resultLifetime(callee: IrElement): Lifetime {
+        return resultLifetimes.getOrElse(callee) { /* TODO: make IRRELEVANT */ Lifetime.GLOBAL }
    }

    private fun evaluateConstructorCall(callee: IrCall, args: List<LLVMValueRef>): LLVMValueRef {
@@ -2,6 +2,9 @@ package org.jetbrains.kotlin.backend.konan.llvm

 import kotlinx.cinterop.*
 import llvm.*
+import org.jetbrains.kotlin.types.KotlinType
+import org.jetbrains.kotlin.types.typeUtil.isNothing
+import org.jetbrains.kotlin.types.typeUtil.isUnit

 interface RuntimeAware {
    val runtime: Runtime
@@ -70,17 +70,13 @@ internal class VariableManager(val codegen: CodeGenerator) {
    }

    // Creates anonymous mutable variable.
-    fun createAnonymousMutable(type: KotlinType, value: LLVMValueRef? = null) : Int {
-        return createAnonymousMutable(codegen.getLLVMType(type), value)
-    }
-
    // Think of slot reuse.
    fun createAnonymousSlot(value: LLVMValueRef? = null) : LLVMValueRef {
        val index = createAnonymousMutable(codegen.kObjHeaderPtr, value)
        return addressOf(index)
    }

-    fun createAnonymousMutable(type: LLVMTypeRef, value: LLVMValueRef? = null) : Int {
+    private fun createAnonymousMutable(type: LLVMTypeRef, value: LLVMValueRef? = null) : Int {
        val index = variables.size
        val slot = codegen.alloca(type)
        if (value != null)
@@ -91,9 +87,8 @@ internal class VariableManager(val codegen: CodeGenerator) {

    fun createImmutable(scoped: Pair<ValueDescriptor, CodeContext>, value: LLVMValueRef) : Int {
        val scopedVariable = ScopedVariable(scoped)
-        if(contextVariablesToIndex.containsKey(scopedVariable))
+        if (contextVariablesToIndex.containsKey(scopedVariable))
            throw Error("${scopedVariable.descriptor} is already defined")
-        assert(!contextVariablesToIndex.containsKey(scopedVariable))
        val index = variables.size
        variables.add(ValueRecord(value, scopedVariable.descriptor.name))
        contextVariablesToIndex[scopedVariable] = index
@@ -0,0 +1,58 @@
+fun foo1(arg: String) : String = arg
+
+/*
+fun foo2(arg: String) : String = arg + " foo2"
+
+fun bar(arg1: String, arg2: String) : String  = arg1 + " bar " + arg2
+
+fun zoo1() : String {
+    var x = foo1("")
+    var y = 4
+    return x
+}
+
+fun zoo2() : String {
+    val x = foo1("")
+    var y = 5
+    return x
+}
+
+class Node(var previous: Node?)
+
+fun zoo3() : Node {
+    var current = Node(null)
+    for (i in 1 .. 5) {
+        current = Node(current)
+    }
+    return current
+}
+
+fun zoo4(arg: Int) : Any {
+    var a = Any()
+    var b = Any()
+    var c = Any()
+    a = b
+    val x = 3
+    a = when {
+        x < arg -> b
+        else -> c
+    }
+    return a
+} */
+
+fun zoo5(arg: String) : String {
+    return arg + foo1(arg)
+}
+
+fun zoo6(arg: Any) : Any {
+    return zoo7(arg, "foo", 11)
+}
+
+fun zoo7(arg1: Any, arg2: Any, selector: Int) : Any {
+    return if (selector < 2) arg1 else arg2;
+}
+
+fun main(args : Array<String>) {
+    val z = zoo7(Any(), Any(), 1)
+    //println(bar(foo1(foo2("")), foo2(foo1(""))))
+}
@@ -11,8 +11,9 @@ public abstract class AbstractCollection<out E> protected constructor() : Collec

    override fun isEmpty(): Boolean = size == 0

-    /*
-    override fun toString(): String = joinToString(", ", "[", "]") {
-        if (it === this) "(this Collection)" else it.toString()
-    } */
+
+    @Fixme
+    override fun toString(): String = TODO() // joinToString(", ", "[", "]") {
+    // if (it === this) "(this Collection)" else it.toString()
+    // }
 }