[K/JS] Add VOID optimization on object properties + align with the optimization the JS Plain Object plugin

js/js.ast/src/org/jetbrains/kotlin/js/backend/ast/metadata/metadataProperties.kt

@@ -77,6 +77,7 @@ var JsFunction.functionDescriptor: FunctionDescriptor? by MetadataProperty(defau
  */
 var JsReturn.returnTarget: FunctionDescriptor? by MetadataProperty(default = null)
 
+var HasMetadata.constant: Boolean by MetadataProperty(default = false)
 var HasMetadata.synthetic: Boolean by MetadataProperty(default = false)
 
 var HasMetadata.isInlineClassBoxing: Boolean by MetadataProperty(default = false)

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

@@ -17,8 +17,9 @@
 package org.jetbrains.kotlin.js.inline.clean
 
 import org.jetbrains.kotlin.js.backend.ast.JsFunction
+import org.jetbrains.kotlin.js.backend.ast.JsName
 
-class FunctionPostProcessor(val root: JsFunction) {
+class FunctionPostProcessor(val root: JsFunction, private val voidName: JsName? = null) {
     val optimizations = listOf(
         { RedundantLabelRemoval(root.body).apply() },
         { EmptyStatementElimination(root.body).apply() },
@@ -32,7 +33,8 @@ class FunctionPostProcessor(val root: JsFunction) {
         { RedundantStatementElimination(root).apply() },
         { CoroutineStateElimination(root.body).apply() },
         { BoxingUnboxingElimination(root.body).apply() },
-        { MoveTemporaryVariableDeclarationToAssignment(root.body).apply() }
+        { MoveTemporaryVariableDeclarationToAssignment(root.body).apply() },
+        { voidName?.let { VoidPropertiesElimination(root.body, voidName).apply() } ?: false }
     )
     // TODO: reduce to A || B, A && B if possible
 

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

@@ -17,10 +17,7 @@
 package org.jetbrains.kotlin.js.inline.clean
 
 import org.jetbrains.kotlin.js.backend.ast.*
-import org.jetbrains.kotlin.js.backend.ast.metadata.SideEffectKind
-import org.jetbrains.kotlin.js.backend.ast.metadata.imported
-import org.jetbrains.kotlin.js.backend.ast.metadata.sideEffects
-import org.jetbrains.kotlin.js.backend.ast.metadata.synthetic
+import org.jetbrains.kotlin.js.backend.ast.metadata.*
 import org.jetbrains.kotlin.js.inline.util.collectFreeVariables
 import org.jetbrains.kotlin.js.inline.util.collectLocalVariables
 import org.jetbrains.kotlin.js.translate.context.Namer
@@ -481,8 +478,8 @@ internal class TemporaryVariableElimination(private val function: JsFunction) {
 
         override fun visitNameRef(nameRef: JsNameRef) {
             val name = nameRef.name
-            if (name != null && name in localVariables) {
-                if (name !in namesToSubstitute && shouldConsiderTemporary(name)) {
+            if (name != null && (name in localVariables || name.constant)) {
+                if (name.constant || (name !in namesToSubstitute && shouldConsiderTemporary(name))) {
                     if (!sideEffectOccurred) {
                         substitutableVariableReferences += name
                     }
@@ -637,16 +634,18 @@ internal class TemporaryVariableElimination(private val function: JsFunction) {
     private fun isTrivial(expr: JsExpression): Boolean = when (expr) {
         is JsNameRef -> {
             val qualifier = expr.qualifier
-            if (expr.sideEffects == SideEffectKind.PURE && (qualifier == null || isTrivial(qualifier))) {
-                expr.name !in temporary
-            }
-            else {
-                val name = expr.name
-                name in localVariables && when (definitions[name]) {
-                    // Local variables with zero definitions are function parameters. We can relocate and copy them.
-                    null, 0 -> true
-                    1 -> name !in namesToSubstitute || definedValues[name]?.let { isTrivial(it) } ?: false
-                    else -> false
+            when {
+                expr.name?.constant == true -> true
+                expr.sideEffects == SideEffectKind.PURE && (qualifier == null || isTrivial(qualifier)) ->
+                    expr.name !in temporary
+                else -> {
+                    val name = expr.name
+                    name in localVariables && when (definitions[name]) {
+                        // Local variables with zero definitions are function parameters. We can relocate and copy them.
+                        null, 0 -> true
+                        1 -> name !in namesToSubstitute || definedValues[name]?.let { isTrivial(it) } ?: false
+                        else -> false
+                    }
                 }
             }
         }

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

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2010-2017 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 org.jetbrains.kotlin.js.backend.ast.*
+import org.jetbrains.kotlin.js.backend.ast.metadata.isInlineClassBoxing
+import org.jetbrains.kotlin.js.backend.ast.metadata.isInlineClassUnboxing
+
+// Replaces { a: 2, b: VOID, c: VOID } with { a: 2 }
+class VoidPropertiesElimination(private val root: JsBlock, private val voidName: JsName) {
+    private var changed = false
+
+    fun apply(): Boolean {
+        val visitor = object : JsVisitorWithContextImpl() {
+            override fun endVisit(x: JsPropertyInitializer, ctx: JsContext<JsNode>) {
+                super.endVisit(x, ctx)
+                if ((x.valueExpr as? JsNameRef)?.name === voidName) {
+                    ctx.removeMe()
+                    changed = true
+                }
+            }
+        }
+
+        visitor.accept(root)
+
+        return changed
+    }
+}