[K/JS] feat: eliminate usage of kotlin.reflection if there is just raw js class usage.

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

@@ -734,10 +734,18 @@ private val blockDecomposerLoweringPhase = makeBodyLoweringPhase(
     prerequisite = setOf(typeOperatorLoweringPhase, suspendFunctionsLoweringPhase)
 )
 
+private val jsClassUsageInReflectionPhase = makeBodyLoweringPhase(
+    ::JsClassUsageInReflectionLowering,
+    name = "JsClassUsageInReflectionLowering",
+    description = "[Optimization] Eliminate ClassReference and GetClassExpression usages in a simple case of usage raw js constructor",
+    prerequisite = setOf(functionInliningPhase)
+)
+
 private val classReferenceLoweringPhase = makeBodyLoweringPhase(
     ::ClassReferenceLowering,
     name = "ClassReferenceLowering",
-    description = "Handle class references"
+    description = "Handle class references",
+    prerequisite = setOf(jsClassUsageInReflectionPhase)
 )
 
 private val primitiveCompanionLoweringPhase = makeBodyLoweringPhase(
@@ -845,6 +853,7 @@ val loweringList = listOf<Lowering>(
     innerClassesLoweringPhase,
     innerClassesMemberBodyLoweringPhase,
     innerClassConstructorCallsLoweringPhase,
+    jsClassUsageInReflectionPhase,
     propertiesLoweringPhase,
     primaryConstructorLoweringPhase,
     delegateToPrimaryConstructorLoweringPhase,

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/dce/Dce.kt

@@ -29,8 +29,8 @@ fun eliminateDeadDeclarations(
         context.configuration.getBoolean(JSConfigurationKeys.PRINT_REACHABILITY_INFO) ||
                 java.lang.Boolean.getBoolean("kotlin.js.ir.dce.print.reachability.info")
 
-    val usefulDeclarations = JsUsefulDeclarationProcessor(context, printReachabilityInfo, removeUnusedAssociatedObjects)
+    val usefulDeclarationProcessor = JsUsefulDeclarationProcessor(context, printReachabilityInfo, removeUnusedAssociatedObjects)
-        .collectDeclarations(allRoots)
+    val usefulDeclarations = usefulDeclarationProcessor.collectDeclarations(allRoots)
 
     val uselessDeclarationsProcessor =
         UselessDeclarationsRemover(removeUnusedAssociatedObjects, usefulDeclarations, context, context.dceRuntimeDiagnostic)
@@ -38,7 +38,7 @@ fun eliminateDeadDeclarations(
     modules.forEach { module ->
         module.files.forEach {
             it.acceptVoid(uselessDeclarationsProcessor)
-            context.polyfills.saveOnlyIntersectionOfNextDeclarationsFor(it, usefulDeclarations)
+            context.polyfills.saveOnlyIntersectionOfNextDeclarationsFor(it, usefulDeclarationProcessor.usefulPolyfilledDeclarations)
         }
     }
 }

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/dce/JsUsefulDeclarationProcessor.kt

@@ -15,6 +15,7 @@ import org.jetbrains.kotlin.ir.backend.js.utils.getJsNameOrKotlinName
 import org.jetbrains.kotlin.ir.backend.js.utils.invokeFunForLambda
 import org.jetbrains.kotlin.ir.declarations.*
 import org.jetbrains.kotlin.ir.expressions.IrCall
+import org.jetbrains.kotlin.ir.expressions.IrGetObjectValue
 import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
 import org.jetbrains.kotlin.ir.types.classOrNull
 import org.jetbrains.kotlin.ir.types.classifierOrFail
@@ -109,6 +110,7 @@ internal class JsUsefulDeclarationProcessor(
                 }
             }
         }
+
     }
 
     override fun processClass(irClass: IrClass) {

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/dce/UsefulDeclarationProcessor.kt

@@ -52,8 +52,10 @@ abstract class UsefulDeclarationProcessor(
 
         override fun visitBlock(expression: IrBlock, data: IrDeclaration) {
             super.visitBlock(expression, data)
-            if (expression !is IrReturnableBlock) return
+
-            expression.inlineFunctionSymbol?.owner?.enqueue(data, "inline function usage")
+            if (expression is IrReturnableBlock) {
+                expression.inlineFunctionSymbol?.owner?.addToUsefulPolyfilledDeclarations()
+            }
         }
 
         override fun visitFieldAccess(expression: IrFieldAccessExpression, data: IrDeclaration) {
@@ -111,6 +113,14 @@ abstract class UsefulDeclarationProcessor(
         if (this !in result) {
             result.add(this)
             queue.addLast(this)
+
+            addToUsefulPolyfilledDeclarations()
+        }
+    }
+
+    private fun IrDeclaration.addToUsefulPolyfilledDeclarations() {
+        if (hasJsPolyfill() && this !in usefulPolyfilledDeclarations) {
+            usefulPolyfilledDeclarations.add(this)
         }
     }
 
@@ -128,6 +138,8 @@ abstract class UsefulDeclarationProcessor(
     protected val result = hashSetOf<IrDeclaration>()
     protected val classesWithObjectAssociations = hashSetOf<IrClass>()
 
+    public val usefulPolyfilledDeclarations = hashSetOf<IrDeclaration>()
+
     protected open fun processField(irField: IrField): Unit = Unit
 
     protected open fun processClass(irClass: IrClass) {

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/lower/JsClassUsageInReflectionLowering.kt

@@ -0,0 +1,83 @@
+/*
+ * Copyright 2010-2022 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.ir.backend.js.lower
+
+import org.jetbrains.kotlin.backend.common.BodyLoweringPass
+import org.jetbrains.kotlin.ir.IrElement
+import org.jetbrains.kotlin.ir.UNDEFINED_OFFSET
+import org.jetbrains.kotlin.ir.backend.js.JsIrBackendContext
+import org.jetbrains.kotlin.ir.backend.js.JsStatementOrigins
+import org.jetbrains.kotlin.ir.backend.js.ir.JsIrBuilder
+import org.jetbrains.kotlin.ir.declarations.IrDeclaration
+import org.jetbrains.kotlin.ir.expressions.*
+import org.jetbrains.kotlin.ir.expressions.impl.IrConstImpl
+import org.jetbrains.kotlin.ir.expressions.impl.IrDynamicMemberExpressionImpl
+import org.jetbrains.kotlin.ir.symbols.IrClassSymbol
+import org.jetbrains.kotlin.ir.util.defaultType
+import org.jetbrains.kotlin.ir.util.fqNameWhenAvailable
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformerVoid
+import org.jetbrains.kotlin.ir.visitors.transformChildrenVoid
+import org.jetbrains.kotlin.name.FqName
+
+private val JS_CLASS_GETTER = FqName("kotlin.js.<get-js>")
+
+class JsClassUsageInReflectionLowering(val backendContext: JsIrBackendContext) : BodyLoweringPass {
+    override fun lower(irBody: IrBody, container: IrDeclaration) {
+        irBody.transformChildrenVoid(object : IrElementTransformerVoid() {
+            override fun visitCall(expression: IrCall): IrExpression {
+                if (expression.origin != IrStatementOrigin.GET_PROPERTY || !expression.isGetJsCall()) {
+                    return super.visitCall(expression)
+                }
+
+                return when (val extensionReceiver = expression.extensionReceiver) {
+                    is IrClassReference -> extensionReceiver.generateDirectValueUsage() ?: super.visitCall(expression)
+                    is IrGetClass -> extensionReceiver.generateDirectConstructorUsage()
+                    else -> super.visitCall(expression)
+                }
+            }
+
+        })
+    }
+
+    private fun IrClassReference.generateDirectValueUsage(): IrExpression? {
+        return with(backendContext) {
+            when(val classSymbol = symbol as? IrClassSymbol ?: return null) {
+                irBuiltIns.nothingClass -> null
+                irBuiltIns.anyClass ->
+                    JsIrBuilder.buildCall(intrinsics.jsCode).apply {
+                        putValueArgument(
+                            0,
+                            IrConstImpl.string(
+                                UNDEFINED_OFFSET,
+                                UNDEFINED_OFFSET,
+                                irBuiltIns.stringType,
+                         "Object"
+                            )
+                        )
+                    }
+
+                else ->
+                    JsIrBuilder.buildCall(intrinsics.jsClass, origin = JsStatementOrigins.CLASS_REFERENCE).apply {
+                        putTypeArgument(0, classSymbol.owner.defaultType)
+                    }
+            }
+        }
+    }
+
+    private fun IrGetClass.generateDirectConstructorUsage(): IrDynamicMemberExpression {
+        return IrDynamicMemberExpressionImpl(
+            startOffset,
+            endOffset,
+            backendContext.dynamicType,
+            "constructor",
+            argument
+        )
+    }
+
+    private fun IrCall.isGetJsCall(): Boolean {
+        return symbol.owner.fqNameWhenAvailable == JS_CLASS_GETTER
+    }
+}

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

@@ -128,8 +128,9 @@ class IrElementToJsExpressionTransformer : BaseIrElementToJsNodeTransformer<JsEx
 
     override fun visitGetObjectValue(expression: IrGetObjectValue, context: JsGenerationContext): JsExpression {
         val obj = expression.symbol.owner
-        assert(obj.kind == ClassKind.OBJECT)
+
-        assert(obj.isEffectivelyExternal()) { "Non external IrGetObjectValue must be lowered" }
+         assert(obj.kind == ClassKind.OBJECT)
+         assert(obj.isEffectivelyExternal()) { "Non external IrGetObjectValue must be lowered" }
 
         return context.getRefForExternalClass(obj).withSource(expression, context)
     }