Optimize control-flow analysis by use of persistent maps

The case that it's worth to optimize is functions
with a lot of variables.

After debugging it's recovered that control-flow works nearly
O(n * m) where n is pseudocode size and m is a number of variables:
the algorithm performs O(n) copies of hashmap of size O(m)

Persistent maps should help because we don't need to perform a
copy of them, so the expected performance after the change is applied
is O(n log m)

We've tried pcollections and javaslang, and the latter one has demonstrated
better results

See results before and after optimizations
before:
https://github.com/dzharkov/kotlin-compiler-benchmarks/blob/3da7ba45a704969653d70b50995f730e968540d8/reports/benchmarks-many-vars-2017-03-14.txt

after with pcollections:
https://github.com/dzharkov/kotlin-compiler-benchmarks/blob/3da7ba45a704969653d70b50995f730e968540d8/reports/benchmarks-many-vars-persistent-optimizations-2017-03-17.txt

after with javaslang:
https://github.com/dzharkov/kotlin-compiler-benchmarks/blob/d22a871b175b291fb337b51ef6465ba70bbfd96c/reports/benchmarks-many-vars-javaslang-2017-04-07.txt

.idea/libraries/javaslang.xml

@@ -0,0 +1,11 @@
+<component name="libraryTable">
+  <library name="javaslang">
+    <CLASSES>
+      <root url="jar://$PROJECT_DIR$/dependencies/javaslang-2.0.6.jar!/" />
+    </CLASSES>
+    <JAVADOC />
+    <SOURCES>
+      <root url="jar://$PROJECT_DIR$/dependencies/javaslang-2.0.6-sources.jar!/" />
+    </SOURCES>
+  </library>
+</component>

build.xml

@@ -60,6 +60,7 @@
         <fileset dir="${basedir}/lib" includes="**/*.jar"/>
         <fileset dir="${dependencies}" includes="jansi.jar"/>
         <fileset dir="${dependencies}" includes="jline.jar"/>
+        <fileset dir="${dependencies}" includes="javaslang-2.0.6.jar"/>
         <fileset dir="${basedir}/ideaSDK/jps" includes="jps-model.jar"/>
     </path>
 
@@ -369,6 +370,7 @@
                 <zipfileset src="${idea.sdk}/lib/oromatcher.jar"/>
                 <zipfileset src="${idea.sdk}/jps/jps-model.jar"/>
                 <zipfileset src="${dependencies}/jline.jar"/>
+                <zipfileset src="${dependencies}/javaslang-2.0.6.jar"/>
                 <zipfileset src="${protobuf.jar}"/>
 
                 <manifest>
@@ -728,7 +730,7 @@
             <fileset dir="${basedir}/plugins/source-sections/source-sections-compiler/src" includes="META-INF/services/**"/>
         </jar>
     </target>
-    
+
     <target name="annotation-processing">
         <cleandir dir="${output}/classes/annotation-processing"/>
 

compiler/compiler.pro

@@ -49,6 +49,8 @@ messages/**)
 -dontwarn org.apache.xerces.dom.**
 -dontwarn org.apache.xerces.util.**
 -dontwarn org.w3c.dom.ElementTraversal
+-dontwarn javaslang.match.annotation.Unapply
+-dontwarn javaslang.match.annotation.Patterns
 
 -libraryjars '<rtjar>'
 -libraryjars '<jssejar>'

compiler/frontend/frontend.iml

@@ -17,5 +17,6 @@
     <orderEntry type="module" module-name="resolution" exported="" />
     <orderEntry type="library" exported="" name="kotlin-script-runtime" level="project" />
     <orderEntry type="module" module-name="script.runtime" />
+    <orderEntry type="library" name="javaslang" level="project" />
   </component>
 </module>

compiler/frontend/src/org/jetbrains/kotlin/cfg/ConstructorConsistencyChecker.kt

@@ -26,8 +26,8 @@ import org.jetbrains.kotlin.cfg.pseudocode.instructions.eval.ReadValueInstructio
 import org.jetbrains.kotlin.cfg.pseudocodeTraverser.TraversalOrder
 import org.jetbrains.kotlin.cfg.pseudocodeTraverser.traverse
 import org.jetbrains.kotlin.descriptors.*
-import org.jetbrains.kotlin.psi.*
 import org.jetbrains.kotlin.lexer.KtTokens
+import org.jetbrains.kotlin.psi.*
 import org.jetbrains.kotlin.psi.psiUtil.getStrictParentOfType
 import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlin.resolve.BindingTrace
@@ -117,7 +117,7 @@ class ConstructorConsistencyChecker private constructor(
 
             fun firstUninitializedNotNullProperty() = propertyDescriptors.firstOrNull {
                 !it.type.isMarkedNullable && !KotlinBuiltIns.isPrimitiveType(it.type) &&
-                !it.isLateInit && !(enterData[it]?.definitelyInitialized() ?: false)
+                !it.isLateInit && !(enterData.getOrNull(it)?.definitelyInitialized() ?: false)
             }
 
             fun handleLeakingThis(expression: KtExpression) {
@@ -197,4 +197,4 @@ class ConstructorConsistencyChecker private constructor(
             else -> expression
         }
     }
-}
+}

compiler/frontend/src/org/jetbrains/kotlin/cfg/ControlFlowInfo.kt

@@ -16,36 +16,56 @@
 
 package org.jetbrains.kotlin.cfg
 
+import javaslang.Tuple2
 import org.jetbrains.kotlin.descriptors.VariableDescriptor
-import java.util.*
 
-open class ControlFlowInfo<D> internal constructor(protected val map: MutableMap<VariableDescriptor, D> = hashMapOf()) :
+typealias ImmutableMap<K, V> = javaslang.collection.Map<K, V>
-        MutableMap<VariableDescriptor, D> by map {
+typealias ImmutableHashMap<K, V> = javaslang.collection.HashMap<K, V>
-    open fun copy() = ControlFlowInfo(HashMap(map))
 
-    fun retainAll(predicate: (VariableDescriptor) -> Boolean): ControlFlowInfo<D> {
+abstract class ControlFlowInfo<S : ControlFlowInfo<S, D>, D>
-        map.keys.retainAll(predicate)
+internal constructor(
-        return this
+        protected val map: ImmutableMap<VariableDescriptor, D> = ImmutableHashMap.empty()
+) : ImmutableMap<VariableDescriptor, D> by map {
+    abstract protected fun copy(newMap: ImmutableMap<VariableDescriptor, D>): S
+
+    override fun put(key: VariableDescriptor, value: D): S = put(key, value, this[key].getOrElse(null as D?))
+
+    /**
+     * This overload exists just for sake of optimizations: in some cases we've just retrieved the old value,
+     * so we don't need to scan through the peristent hashmap again
+     */
+    fun put(key: VariableDescriptor, value: D, oldValue: D?): S {
+        @Suppress("UNCHECKED_CAST")
+        // Avoid a copy instance creation if new value is the same
+        if (value == oldValue) return this as S
+        return copy(map.put(key, value))
     }
 
-    override fun equals(other: Any?) = map == (other as? ControlFlowInfo<*>)?.map
+    fun retainAll(predicate: (VariableDescriptor) -> Boolean): S = copy(map.removeAll(map.keySet().filterNot(predicate)))
+
+    override fun equals(other: Any?) = map == (other as? ControlFlowInfo<*, *>)?.map
 
     override fun hashCode() = map.hashCode()
 
     override fun toString() = map.toString()
 }
 
-class InitControlFlowInfo(map: MutableMap<VariableDescriptor, VariableControlFlowState> = hashMapOf()) :
+operator fun <T> Tuple2<T, *>.component1(): T = _1()
-        ControlFlowInfo<VariableControlFlowState>(map) {
+operator fun <T> Tuple2<*, T>.component2(): T = _2()
-    override fun copy() = InitControlFlowInfo(HashMap(map))
+
+fun <K, V> ImmutableMap<K, V>.getOrNull(k: K): V? = this[k].getOrElse(null as V?)
+
+class InitControlFlowInfo(map: ImmutableMap<VariableDescriptor, VariableControlFlowState> = ImmutableHashMap.empty()) :
+        ControlFlowInfo<InitControlFlowInfo, VariableControlFlowState>(map) {
+    override fun copy(newMap: ImmutableMap<VariableDescriptor, VariableControlFlowState>) = InitControlFlowInfo(newMap)
 
     // this = output of EXHAUSTIVE_WHEN_ELSE instruction
     // merge = input of MergeInstruction
     // returns true if definite initialization in when happens here
     fun checkDefiniteInitializationInWhen(merge: InitControlFlowInfo): Boolean {
-        for ((key, value) in entries) {
+        for ((key, value) in iterator()) {
             if (value.initState == InitState.INITIALIZED_EXHAUSTIVELY &&
-                merge[key]?.initState == InitState.INITIALIZED) {
+                merge.getOrNull(key)?.initState == InitState.INITIALIZED) {
                 return true
             }
         }
@@ -53,9 +73,9 @@ class InitControlFlowInfo(map: MutableMap<VariableDescriptor, VariableControlFlo
     }
 }
 
-class UseControlFlowInfo(map: MutableMap<VariableDescriptor, VariableUseState> = hashMapOf()) :
+class UseControlFlowInfo(map: ImmutableMap<VariableDescriptor, VariableUseState> = ImmutableHashMap.empty()) :
-        ControlFlowInfo<VariableUseState>(map) {
+        ControlFlowInfo<UseControlFlowInfo, VariableUseState>(map) {
-    override fun copy() = UseControlFlowInfo(HashMap(map))
+    override fun copy(newMap: ImmutableMap<VariableDescriptor, VariableUseState>) = UseControlFlowInfo(newMap)
 }
 
 enum class InitState(private val s: String) {

compiler/frontend/src/org/jetbrains/kotlin/cfg/ControlFlowInformationProvider.kt

@@ -274,8 +274,8 @@ class ControlFlowInformationProvider private constructor(
 
         pseudocode.traverse(TraversalOrder.FORWARD, initializers) {
             instruction: Instruction,
-            enterData: Map<VariableDescriptor, VariableControlFlowState>,
+            enterData: ImmutableMap<VariableDescriptor, VariableControlFlowState>,
-            exitData: Map<VariableDescriptor, VariableControlFlowState> ->
+            exitData: ImmutableMap<VariableDescriptor, VariableControlFlowState> ->
 
             val ctxt = VariableInitContext(instruction, reportedDiagnosticMap, enterData, exitData, blockScopeVariableInfo)
             if (ctxt.variableDescriptor == null) return@traverse
@@ -532,7 +532,7 @@ class ControlFlowInformationProvider private constructor(
         val declaredVariables = pseudocodeVariablesData.getDeclaredVariables(pseudocode, false)
         for (variable in declaredVariables) {
             if (variable is PropertyDescriptor) {
-                if (initializers.incoming[variable]?.definitelyInitialized() ?: false) continue
+                if (initializers.incoming.getOrNull(variable)?.definitelyInitialized() ?: false) continue
                 trace.record(BindingContext.IS_UNINITIALIZED, variable)
             }
         }
@@ -548,8 +548,8 @@ class ControlFlowInformationProvider private constructor(
         val usedValueExpressions = hashSetOf<KtExpression>()
         pseudocode.traverse(TraversalOrder.BACKWARD, variableStatusData) {
             instruction: Instruction,
-            enterData: Map<VariableDescriptor, VariableUseState>,
+            enterData: ImmutableMap<VariableDescriptor, VariableUseState>,
-            _: Map<VariableDescriptor, VariableUseState> ->
+            _: ImmutableMap<VariableDescriptor, VariableUseState> ->
 
             val ctxt = VariableUseContext(instruction, reportedDiagnosticMap)
             val declaredVariables = pseudocodeVariablesData.getDeclaredVariables(instruction.owner, false)
@@ -560,7 +560,7 @@ class ControlFlowInformationProvider private constructor(
                 || !ExpressionTypingUtils.isLocal(variableDescriptor.containingDeclaration, variableDescriptor)) {
                 return@traverse
             }
-            val variableUseState = enterData[variableDescriptor]
+            val variableUseState = enterData.getOrNull(variableDescriptor)
             when (instruction) {
                 is WriteValueInstruction -> {
                     if (trace.get(CAPTURED_IN_CLOSURE, variableDescriptor) != null) return@traverse
@@ -1017,8 +1017,8 @@ class ControlFlowInformationProvider private constructor(
     private inner class VariableInitContext(
             instruction: Instruction,
             map: MutableMap<Instruction, DiagnosticFactory<*>>,
-            `in`: Map<VariableDescriptor, VariableControlFlowState>,
+            `in`: ImmutableMap<VariableDescriptor, VariableControlFlowState>,
-            out: Map<VariableDescriptor, VariableControlFlowState>,
+            out: ImmutableMap<VariableDescriptor, VariableControlFlowState>,
             blockScopeVariableInfo: BlockScopeVariableInfo
     ) : VariableContext(instruction, map) {
         internal val enterInitState = initialize(variableDescriptor, blockScopeVariableInfo, `in`)
@@ -1027,9 +1027,9 @@ class ControlFlowInformationProvider private constructor(
         private fun initialize(
                 variableDescriptor: VariableDescriptor?,
                 blockScopeVariableInfo: BlockScopeVariableInfo,
-                map: Map<VariableDescriptor, VariableControlFlowState>
+                map: ImmutableMap<VariableDescriptor, VariableControlFlowState>
         ): VariableControlFlowState? {
-            val state = map[variableDescriptor ?: return null]
+            val state = map.getOrNull(variableDescriptor ?: return null)
             if (state != null) return state
             return PseudocodeVariablesData.getDefaultValueForInitializers(variableDescriptor, instruction, blockScopeVariableInfo)
         }

compiler/frontend/src/org/jetbrains/kotlin/cfg/PseudocodeTraverser.kt

@@ -55,7 +55,7 @@ fun <D> Pseudocode.traverse(
     }
 }
 
-fun <I : ControlFlowInfo<*>> Pseudocode.collectData(
+fun <I : ControlFlowInfo<*, *>> Pseudocode.collectData(
         traversalOrder: TraversalOrder,
         mergeEdges: (Instruction, Collection<I>) -> Edges<I>,
         updateEdge: (Instruction, Instruction, I) -> I,
@@ -75,7 +75,7 @@ fun <I : ControlFlowInfo<*>> Pseudocode.collectData(
     return edgesMap
 }
 
-private fun <I : ControlFlowInfo<*>> Pseudocode.collectDataFromSubgraph(
+private fun <I : ControlFlowInfo<*, *>> Pseudocode.collectDataFromSubgraph(
         traversalOrder: TraversalOrder,
         edgesMap: MutableMap<Instruction, Edges<I>>,
         mergeEdges: (Instruction, Collection<I>) -> Edges<I>,
@@ -138,7 +138,7 @@ private fun getPreviousIncludingSubGraphInstructions(
     return result
 }
 
-private fun <I : ControlFlowInfo<*>> updateEdgeDataForInstruction(
+private fun <I : ControlFlowInfo<*, *>> updateEdgeDataForInstruction(
         instruction: Instruction, previousValue: Edges<I>?, newValue: Edges<I>?, edgesMap: MutableMap<Instruction, Edges<I>>, changed: BooleanArray) {
     if (previousValue != newValue && newValue != null) {
         changed[0] = true

compiler/frontend/src/org/jetbrains/kotlin/cfg/PseudocodeVariableDataCollector.kt

@@ -17,20 +17,17 @@
 package org.jetbrains.kotlin.cfg
 
 import org.jetbrains.kotlin.cfg.pseudocode.Pseudocode
-import org.jetbrains.kotlin.cfg.pseudocode.instructions.Instruction
 import org.jetbrains.kotlin.cfg.pseudocode.instructions.BlockScope
+import org.jetbrains.kotlin.cfg.pseudocode.instructions.Instruction
 import org.jetbrains.kotlin.cfg.pseudocode.instructions.special.VariableDeclarationInstruction
 import org.jetbrains.kotlin.cfg.pseudocodeTraverser.Edges
 import org.jetbrains.kotlin.cfg.pseudocodeTraverser.TraversalOrder
 import org.jetbrains.kotlin.cfg.pseudocodeTraverser.collectData
 import org.jetbrains.kotlin.cfg.pseudocodeTraverser.traverse
-import org.jetbrains.kotlin.descriptors.ClassDescriptor
 import org.jetbrains.kotlin.descriptors.VariableDescriptor
 import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlin.resolve.BindingContextUtils
-import org.jetbrains.kotlin.resolve.calls.tower.getFakeDescriptorForObject
+import java.util.*
-import java.util.ArrayList
-import java.util.HashMap
 
 class PseudocodeVariableDataCollector(
         private val bindingContext: BindingContext,
@@ -38,7 +35,7 @@ class PseudocodeVariableDataCollector(
 ) {
     val blockScopeVariableInfo = computeBlockScopeVariableInfo(pseudocode)
 
-    fun <I : ControlFlowInfo<*>> collectData(
+    fun <I : ControlFlowInfo<*, *>> collectData(
             traversalOrder: TraversalOrder,
             initialInfo: I,
             instructionDataMergeStrategy: (Instruction, Collection<I>) -> Edges<I>
@@ -51,7 +48,7 @@ class PseudocodeVariableDataCollector(
         )
     }
 
-    private fun <I : ControlFlowInfo<*>> filterOutVariablesOutOfScope(
+    private fun <I : ControlFlowInfo<*, *>> filterOutVariablesOutOfScope(
             from: Instruction,
             to: Instruction,
             info: I
@@ -63,7 +60,7 @@ class PseudocodeVariableDataCollector(
         // Variables declared in an inner (deeper) scope can't be accessed from an outer scope.
         // Thus they can be filtered out upon leaving the inner scope.
         @Suppress("UNCHECKED_CAST")
-        return info.copy().retainAll { variable ->
+        return info.retainAll { variable ->
             val blockScope = blockScopeVariableInfo.declaredIn[variable]
             // '-1' for variables declared outside this pseudocode
             val depth = blockScope?.depth ?: -1

compiler/frontend/src/org/jetbrains/kotlin/cfg/PseudocodeVariablesData.kt

@@ -20,7 +20,10 @@ import com.google.common.collect.Maps
 import org.jetbrains.kotlin.cfg.pseudocode.Pseudocode
 import org.jetbrains.kotlin.cfg.pseudocode.PseudocodeUtil
 import org.jetbrains.kotlin.cfg.pseudocode.instructions.Instruction
-import org.jetbrains.kotlin.cfg.pseudocode.instructions.eval.*
+import org.jetbrains.kotlin.cfg.pseudocode.instructions.eval.MagicInstruction
+import org.jetbrains.kotlin.cfg.pseudocode.instructions.eval.MagicKind
+import org.jetbrains.kotlin.cfg.pseudocode.instructions.eval.ReadValueInstruction
+import org.jetbrains.kotlin.cfg.pseudocode.instructions.eval.WriteValueInstruction
 import org.jetbrains.kotlin.cfg.pseudocode.instructions.special.VariableDeclarationInstruction
 import org.jetbrains.kotlin.cfg.pseudocodeTraverser.Edges
 import org.jetbrains.kotlin.cfg.pseudocodeTraverser.TraversalOrder
@@ -28,7 +31,7 @@ import org.jetbrains.kotlin.descriptors.VariableDescriptor
 import org.jetbrains.kotlin.psi.KtProperty
 import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlin.resolve.BindingContextUtils.variableDescriptorForDeclaration
-import java.util.Collections
+import java.util.*
 
 class PseudocodeVariablesData(val pseudocode: Pseudocode, private val bindingContext: BindingContext) {
     private val pseudocodeVariableDataCollector: PseudocodeVariableDataCollector
@@ -105,39 +108,39 @@ class PseudocodeVariablesData(val pseudocode: Pseudocode, private val bindingCon
             blockScopeVariableInfo: BlockScopeVariableInfo): InitControlFlowInfo {
         if (instruction is MagicInstruction) {
             if (instruction.kind === MagicKind.EXHAUSTIVE_WHEN_ELSE) {
-                val exitInstructionData = enterInstructionData.copy()
+                return enterInstructionData.iterator().fold(enterInstructionData) {
-                for ((key, value) in enterInstructionData) {
+                    result, (key, value) ->
                     if (!value.definitelyInitialized()) {
-                        exitInstructionData.put(key, VariableControlFlowState.createInitializedExhaustively(value.isDeclared))
+                        result.put(key, VariableControlFlowState.createInitializedExhaustively(value.isDeclared))
                     }
+                    else result
                 }
-                return exitInstructionData
             }
         }
         if (instruction !is WriteValueInstruction && instruction !is VariableDeclarationInstruction) {
             return enterInstructionData
         }
         val variable = PseudocodeUtil.extractVariableDescriptorIfAny(instruction, bindingContext) ?: return enterInstructionData
-        val exitInstructionData = enterInstructionData.copy()
+        var exitInstructionData = enterInstructionData
         if (instruction is WriteValueInstruction) {
             // if writing to already initialized object
             if (!PseudocodeUtil.isThisOrNoDispatchReceiver(instruction, bindingContext)) {
                 return enterInstructionData
             }
 
-            val enterInitState = enterInstructionData[variable]
+            val enterInitState = enterInstructionData.getOrNull(variable)
             val initializationAtThisElement = VariableControlFlowState.create(instruction.element is KtProperty, enterInitState)
-            exitInstructionData.put(variable, initializationAtThisElement)
+            exitInstructionData = exitInstructionData.put(variable, initializationAtThisElement, enterInitState)
         }
         else {
             // instruction instanceof VariableDeclarationInstruction
-            var enterInitState: VariableControlFlowState? = enterInstructionData[variable]
+            var enterInitState: VariableControlFlowState? = enterInstructionData.getOrNull(variable)
             if (enterInitState == null) {
                 enterInitState = getDefaultValueForInitializers(variable, instruction, blockScopeVariableInfo)
             }
             if (!enterInitState.mayBeInitialized() || !enterInitState.isDeclared) {
                 val variableDeclarationInfo = VariableControlFlowState.create(enterInitState.initState, isDeclared = true)
-                exitInstructionData.put(variable, variableDeclarationInfo)
+                exitInstructionData = exitInstructionData.put(variable, variableDeclarationInfo, enterInitState)
             }
         }
         return exitInstructionData
@@ -154,34 +157,35 @@ class PseudocodeVariablesData(val pseudocode: Pseudocode, private val bindingCon
                 enterResult = incomingEdgesData.single()
             }
             else {
-                enterResult = UseControlFlowInfo()
+                enterResult = incomingEdgesData.fold(UseControlFlowInfo()) { result, edgeData ->
-                for (edgeData in incomingEdgesData) {
+                    edgeData.iterator().fold(result) {
-                    for ((variableDescriptor, variableUseState) in edgeData) {
+                        subResult, (variableDescriptor, variableUseState) ->
-                        enterResult.put(variableDescriptor, variableUseState.merge(enterResult[variableDescriptor]))
+                        subResult.put(variableDescriptor, variableUseState.merge(subResult.getOrNull(variableDescriptor)))
                     }
                 }
             }
+
             val variableDescriptor = PseudocodeUtil.extractVariableDescriptorFromReference(instruction, bindingContext)
             if (variableDescriptor == null || instruction !is ReadValueInstruction && instruction !is WriteValueInstruction) {
                 Edges(enterResult, enterResult)
             }
             else {
-                val exitResult = enterResult.copy()
+                val exitResult =
-                if (instruction is ReadValueInstruction) {
+                    if (instruction is ReadValueInstruction) {
-                    exitResult.put(variableDescriptor, VariableUseState.READ)
+                        enterResult.put(variableDescriptor, VariableUseState.READ)
-                }
-                else {
-                    var variableUseState: VariableUseState? = enterResult[variableDescriptor]
-                    if (variableUseState == null) {
-                        variableUseState = VariableUseState.UNUSED
                     }
-                    when (variableUseState) {
+                    else {
-                        VariableUseState.UNUSED, VariableUseState.ONLY_WRITTEN_NEVER_READ ->
+                        var variableUseState: VariableUseState? = enterResult.getOrNull(variableDescriptor)
-                            exitResult.put(variableDescriptor, VariableUseState.ONLY_WRITTEN_NEVER_READ)
+                        if (variableUseState == null) {
-                        VariableUseState.WRITTEN_AFTER_READ, VariableUseState.READ ->
+                            variableUseState = VariableUseState.UNUSED
-                            exitResult.put(variableDescriptor, VariableUseState.WRITTEN_AFTER_READ)
+                        }
+                        when (variableUseState) {
+                            VariableUseState.UNUSED, VariableUseState.ONLY_WRITTEN_NEVER_READ ->
+                                enterResult.put(variableDescriptor, VariableUseState.ONLY_WRITTEN_NEVER_READ)
+                            VariableUseState.WRITTEN_AFTER_READ, VariableUseState.READ ->
+                                enterResult.put(variableDescriptor, VariableUseState.WRITTEN_AFTER_READ)
+                        }
                     }
-                }
                 Edges(enterResult, exitResult)
             }
         }
@@ -202,23 +206,25 @@ class PseudocodeVariablesData(val pseudocode: Pseudocode, private val bindingCon
             return VariableControlFlowState.create(isInitialized = declaredOutsideThisDeclaration)
         }
 
+        private val EMPTY_INIT_CONTROL_FLOW_INFO = InitControlFlowInfo()
+
         private fun mergeIncomingEdgesDataForInitializers(
                 instruction: Instruction,
                 incomingEdgesData: Collection<InitControlFlowInfo>,
                 blockScopeVariableInfo: BlockScopeVariableInfo
         ): InitControlFlowInfo {
             if (incomingEdgesData.size == 1) return incomingEdgesData.single()
+            if (incomingEdgesData.isEmpty()) return EMPTY_INIT_CONTROL_FLOW_INFO
             val variablesInScope = linkedSetOf<VariableDescriptor>()
             for (edgeData in incomingEdgesData) {
-                variablesInScope.addAll(edgeData.keys)
+                variablesInScope.addAll(edgeData.keySet())
             }
 
-            val enterInstructionData = InitControlFlowInfo()
+            return variablesInScope.fold(EMPTY_INIT_CONTROL_FLOW_INFO) { result, variable ->
-            for (variable in variablesInScope) {
                 var initState: InitState? = null
                 var isDeclared = true
                 for (edgeData in incomingEdgesData) {
-                    val varControlFlowState = edgeData[variable]
+                    val varControlFlowState = edgeData.getOrNull(variable)
                                               ?: getDefaultValueForInitializers(variable, instruction, blockScopeVariableInfo)
                     initState = initState?.merge(varControlFlowState.initState) ?: varControlFlowState.initState
                     if (!varControlFlowState.isDeclared) {
@@ -228,9 +234,8 @@ class PseudocodeVariablesData(val pseudocode: Pseudocode, private val bindingCon
                 if (initState == null) {
                     throw AssertionError("An empty set of incoming edges data")
                 }
-                enterInstructionData.put(variable, VariableControlFlowState.create(initState, isDeclared))
+                result.put(variable, VariableControlFlowState.create(initState, isDeclared))
             }
-            return enterInstructionData
         }
     }
 }

compiler/tests/compiler-tests.iml

@@ -35,5 +35,6 @@
     <orderEntry type="module" module-name="ir.psi2ir" scope="TEST" />
     <orderEntry type="module" module-name="ir.ir2cfg" scope="TEST" />
     <orderEntry type="library" name="idea-full" level="project" />
+    <orderEntry type="library" name="javaslang" level="project" />
   </component>
 </module>

compiler/tests/org/jetbrains/kotlin/cfg/AbstractDataFlowTest.java

@@ -18,6 +18,7 @@ package org.jetbrains.kotlin.cfg;
 
 import com.google.common.collect.Lists;
 import com.intellij.openapi.util.text.StringUtil;
+import javaslang.Tuple2;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.kotlin.cfg.pseudocode.PseudocodeImpl;
 import org.jetbrains.kotlin.cfg.pseudocode.instructions.Instruction;
@@ -79,21 +80,22 @@ public abstract class AbstractDataFlowTest extends AbstractPseudocodeTest {
                 maxWidth = length;
             }
         }
+
         return maxWidth;
     }
 
     @NotNull
-    private static <S, I extends ControlFlowInfo<S>> String dumpEdgesData(String prefix, @NotNull Edges<I> edges) {
+    private static <S, I extends ControlFlowInfo<?, S>> String dumpEdgesData(String prefix, @NotNull Edges<I> edges) {
         return prefix +
                " in: " + renderVariableMap(edges.getIncoming()) +
                " out: " + renderVariableMap(edges.getOutgoing());
     }
 
-    private static <S> String renderVariableMap(Map<VariableDescriptor, S> map) {
+    private static <S> String renderVariableMap(javaslang.collection.Map<VariableDescriptor, S> map) {
         List<String> result = Lists.newArrayList();
-        for (Map.Entry<VariableDescriptor, S> entry : map.entrySet()) {
+        for (Tuple2<VariableDescriptor, S> entry : map) {
-            VariableDescriptor variable = entry.getKey();
+            VariableDescriptor variable = entry._1;
-            S state = entry.getValue();
+            S state = entry._2;
             result.add(variable.getName() + "=" + state);
         }
         Collections.sort(result);

ultimate/.idea/libraries/javaslang.xml

@@ -0,0 +1,9 @@
+<component name="libraryTable">
+  <library name="javaslang">
+    <CLASSES>
+      <root url="jar://$PROJECT_DIR$/../dependencies/javaslang-2.0.6.jar!/" />
+    </CLASSES>
+    <JAVADOC />
+    <SOURCES />
+  </library>
+</component>

ultimate/kotlin-ultimate.iml

@@ -30,5 +30,6 @@
     <orderEntry type="library" scope="PROVIDED" name="intellij-core" level="project" />
     <orderEntry type="library" name="idea-full" level="project" />
     <orderEntry type="library" name="protobuf" level="project" />
+    <orderEntry type="library" name="javaslang" level="project" />
   </component>
 </module>

update_dependencies.xml

@@ -236,6 +236,9 @@
         <!-- Rhino -->
         <get-maven-library prefix="org/mozilla" lib="rhino" version="1.7.6"/>
 
+        <!-- Javaslang -->
+        <get-maven-library prefix="io/javaslang" lib="javaslang" version="2.0.6"/>
+
         <!-- Uast -->
         <property name="uast.server" value="http://dl.bintray.com/kotlin/uast"/>
         <get-maven-library prefix="org/jetbrains/uast" lib="uast-common" version="${uast.version}" target.jar.name.base="uast-common" server="${uast.server}"/>