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

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/optimizations.kt

@@ -11,6 +11,8 @@ import org.jetbrains.kotlin.backend.common.phaser.invokeToplevel
 import org.jetbrains.kotlin.ir.backend.js.dce.DceDumpNameCache
 import org.jetbrains.kotlin.ir.backend.js.dce.eliminateDeadDeclarations
 import org.jetbrains.kotlin.ir.backend.js.transformers.irToJs.JsIrProgramFragment
+import org.jetbrains.kotlin.ir.backend.js.utils.JsStaticContext
+import org.jetbrains.kotlin.ir.backend.js.utils.getVoid
 import org.jetbrains.kotlin.ir.declarations.IrModuleFragment
 import org.jetbrains.kotlin.js.backend.ast.JsClass
 import org.jetbrains.kotlin.js.backend.ast.JsFunction
@@ -35,11 +37,13 @@ fun optimizeProgramByIr(
     }
 }
 
-fun optimizeFragmentByJsAst(fragment: JsIrProgramFragment) {
+fun optimizeFragmentByJsAst(fragment: JsIrProgramFragment, context: JsStaticContext) {
+    val voidName = context.backendContext.intrinsics.void.owner.backingField?.let(context::getNameForField)
+
     val optimizer = object : RecursiveJsVisitor() {
         override fun visitFunction(x: JsFunction) {
             super.visitFunction(x)
-            FunctionPostProcessor(x).apply()
+            FunctionPostProcessor(x, voidName).apply()
         }
 
         override fun visitClass(x: JsClass) {

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/IrDeclarationToJsTransformer.kt

@@ -10,6 +10,7 @@ import org.jetbrains.kotlin.ir.backend.js.utils.JsGenerationContext
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.util.hasAnnotation
 import org.jetbrains.kotlin.js.backend.ast.*
+import org.jetbrains.kotlin.js.backend.ast.metadata.constant
 
 @Suppress("PARAMETER_NAME_CHANGED_ON_OVERRIDE")
 class IrDeclarationToJsTransformer : BaseIrElementToJsNodeTransformer<JsStatement, JsGenerationContext> {

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/IrModuleToJsTransformer.kt

@@ -471,7 +471,7 @@ class IrModuleToJsTransformer(
         result.computeAndSaveDefinitions(definitionSet, fileExports)
 
         if (optimizeGeneratedJs) {
-            optimizeFragmentByJsAst(result)
+            optimizeFragmentByJsAst(result, staticContext)
         }
 
         return JsIrProgramFragments(result, exportFragment)

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/JsNameLinkingNamer.kt

@@ -13,6 +13,7 @@ import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
 import org.jetbrains.kotlin.ir.types.IrSimpleType
 import org.jetbrains.kotlin.ir.util.*
 import org.jetbrains.kotlin.js.backend.ast.*
+import org.jetbrains.kotlin.js.backend.ast.metadata.constant
 import org.jetbrains.kotlin.utils.DFS
 import org.jetbrains.kotlin.utils.addToStdlib.safeAs
 
@@ -50,7 +51,11 @@ class JsNameLinkingNamer(
             }
         }
 
-        return declaration.getName()
+        return declaration.getName().also {
+            if (declaration == context.intrinsics.void.owner.backingField) {
+                it.constant = true
+            }
+        }
     }
 
     override fun getNameForMemberFunction(function: IrSimpleFunction): JsName {

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/utils/serialization/JsIrAstDeserializer.kt

@@ -459,6 +459,7 @@ private class JsIrAstDeserializer(private val source: ByteArray) {
         } ?: JsDynamicScope.declareName(identifier)
         ifTrue { name.localAlias = readLocalAlias() }
         ifTrue { name.imported = true }
+        ifTrue { name.constant = true }
         ifTrue { name.specialFunction = specialFunctionValues[readInt()] }
         return name
     }

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/utils/serialization/JsIrAstSerializer.kt

@@ -605,6 +605,7 @@ private class JsIrAstSerializer {
             writeBoolean(name.isTemporary)
             ifNotNull(name.localAlias) { writeLocalAlias(it) }
             writeBoolean(name.imported && name !in importedNames)
+            writeBoolean(name.constant)
             ifNotNull(name.specialFunction) { writeByte(it.ordinal) }
         }
         nameMap.size