JS: prevent generation of excessive updates of state fields

js/js.inliner/src/org/jetbrains/kotlin/js/coroutine/CoroutineBodyTransformer.kt

@@ -123,14 +123,18 @@ class CoroutineBodyTransformer(val program: JsProgram, val scope: JsScope, val t
                 if (target != null) {
                     val lhs = JsNameRef(stateFieldName, JsLiteral.THIS)
                     val rhs = program.getNumberLiteral(blockIndexes[target]!!)
-                    ctx.replaceMe(JsAstUtils.assignment(lhs, rhs).makeStmt())
+                    ctx.replaceMe(JsExpressionStatement(JsAstUtils.assignment(lhs, rhs)).apply {
+                        targetBlock = true
+                    })
                 }
 
                 val exceptionTarget = x.targetExceptionBlock
                 if (exceptionTarget != null) {
                     val lhs = JsNameRef(exceptionStateName, JsLiteral.THIS)
                     val rhs = program.getNumberLiteral(blockIndexes[exceptionTarget]!!)
-                    ctx.replaceMe(JsAstUtils.assignment(lhs, rhs).makeStmt())
+                    ctx.replaceMe(JsExpressionStatement(JsAstUtils.assignment(lhs, rhs)).apply {
+                        targetExceptionBlock = true
+                    })
                 }
 
                 val finallyPath = x.finallyPath
@@ -138,7 +142,9 @@ class CoroutineBodyTransformer(val program: JsProgram, val scope: JsScope, val t
                     if (finallyPath.isNotEmpty()) {
                         val lhs = JsNameRef(finallyPathFieldName, JsLiteral.THIS)
                         val rhs = JsArrayLiteral(finallyPath.map { program.getNumberLiteral(blockIndexes[it]!!) })
-                        ctx.replaceMe(JsAstUtils.assignment(lhs, rhs).makeStmt())
+                        ctx.replaceMe(JsExpressionStatement(JsAstUtils.assignment(lhs, rhs)).apply {
+                            this.finallyPath = true
+                        })
                     }
                     else {
                         ctx.removeMe()
@@ -623,7 +629,3 @@ private fun CoroutineBlock.collectFinallyPaths(): List<List<CoroutineBlock>> {
     })
     return finallyPaths
 }
-
-private var JsDebugger.targetBlock: CoroutineBlock? by MetadataProperty(default = null)
-private var JsDebugger.targetExceptionBlock: CoroutineBlock? by MetadataProperty(default = null)
-private var JsDebugger.finallyPath: List<CoroutineBlock>? by MetadataProperty(default = null)

js/js.inliner/src/org/jetbrains/kotlin/js/coroutine/CoroutineMetadataProperties.kt

@@ -0,0 +1,29 @@
+/*
+ * 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.js.coroutine
+
+import com.google.dart.compiler.backend.js.ast.JsDebugger
+import com.google.dart.compiler.backend.js.ast.JsExpressionStatement
+import com.google.dart.compiler.backend.js.ast.metadata.MetadataProperty
+
+var JsDebugger.targetBlock: CoroutineBlock? by MetadataProperty(default = null)
+var JsDebugger.targetExceptionBlock: CoroutineBlock? by MetadataProperty(default = null)
+var JsDebugger.finallyPath: List<CoroutineBlock>? by MetadataProperty(default = null)
+
+var JsExpressionStatement.targetBlock by MetadataProperty(default = false)
+var JsExpressionStatement.targetExceptionBlock by MetadataProperty(default = false)
+var JsExpressionStatement.finallyPath by MetadataProperty(default = false)

js/js.inliner/src/org/jetbrains/kotlin/js/inline/clean/CoroutineStateElimination.kt

@@ -0,0 +1,87 @@
+/*
+ * 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.js.inline.clean
+
+import com.google.dart.compiler.backend.js.ast.*
+import org.jetbrains.kotlin.js.coroutine.finallyPath
+import org.jetbrains.kotlin.js.coroutine.targetBlock
+import org.jetbrains.kotlin.js.coroutine.targetExceptionBlock
+
+class CoroutineStateElimination(private val body: JsBlock) {
+    fun apply(): Boolean {
+        var changed = false
+
+        body.accept(object : RecursiveJsVisitor() {
+            override fun visitBlock(x: JsBlock) {
+                visitStatements(x.statements)
+                super.visitBlock(x)
+            }
+
+            override fun visitCase(x: JsCase) {
+                visitStatements(x.statements)
+                super.visitCase(x)
+            }
+
+            private fun visitStatements(statements: MutableList<JsStatement>) {
+                class IndexHolder {
+                    var value: Int? = null
+                }
+
+                val indexesToRemove = mutableSetOf<Int>()
+                val lastTargetBlockIndex = IndexHolder()
+                val lastTargetExceptionBlockIndex = IndexHolder()
+                val lastFinallyPathIndex = IndexHolder()
+
+                for ((index, statement) in statements.withIndex()) {
+                    val indexesToUpdate = mutableListOf<IndexHolder>()
+                    if (statement is JsExpressionStatement) {
+                        if (statement.targetBlock) {
+                            indexesToUpdate += lastTargetBlockIndex
+                        }
+                        if (statement.targetExceptionBlock) {
+                            indexesToUpdate += lastTargetExceptionBlockIndex
+                        }
+                        if (statement.finallyPath) {
+                            indexesToUpdate += lastFinallyPathIndex
+                        }
+                    }
+
+                    if (indexesToUpdate.isNotEmpty()) {
+                        for (indexToUpdate in indexesToUpdate) {
+                            indexToUpdate.value?.let { indexesToRemove += it }
+                            indexToUpdate.value = index
+                        }
+                    }
+                    else {
+                        lastTargetBlockIndex.value = null
+                        lastTargetExceptionBlockIndex.value = null
+                        lastFinallyPathIndex.value = null
+                    }
+                }
+
+                for (index in indexesToRemove.sorted().reversed()) {
+                    statements.removeAt(index)
+                }
+                if (indexesToRemove.isNotEmpty()) {
+                    changed = true
+                }
+            }
+        })
+
+        return changed
+    }
+}

js/js.inliner/src/org/jetbrains/kotlin/js/inline/clean/FunctionPostProcessor.kt

@@ -29,7 +29,8 @@ class FunctionPostProcessor(root: JsFunction) {
         { IfStatementReduction(root.body).apply() },
         { DeadCodeElimination(root.body).apply() },
         { RedundantVariableDeclarationElimination(root.body).apply() },
-        { RedundantStatementElimination(root).apply() }
+        { RedundantStatementElimination(root).apply() },
+        { CoroutineStateElimination(root.body).apply() }
     )
     // TODO: reduce to A || B, A && B if possible