JVM IR: add lowering to remove calls to KFunction{n}.invoke

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmLower.kt

@@ -192,6 +192,7 @@ private val jvmFilePhases =
         jvmBuiltinOptimizationLoweringPhase then
         additionalClassAnnotationPhase then
         typeOperatorLowering then
+        replaceKFunctionInvokeWithFunctionInvokePhase then
 
         recordNamesForKotlinTypeMapperPhase then
 

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/GenerateMultifileFacades.kt

@@ -220,6 +220,7 @@ private class UpdateFunctionCallSites(
     override fun visitCall(expression: IrCall): IrExpression {
         val newFunction = functionDelegates[expression.symbol] ?: return super.visitCall(expression)
         return expression.run {
+            // TODO: deduplicate this with ReplaceKFunctionInvokeWithFunctionInvoke
             IrCallImpl(startOffset, endOffset, type, newFunction).apply {
                 copyTypeArgumentsFrom(expression)
                 extensionReceiver = expression.extensionReceiver?.transform(this@UpdateFunctionCallSites, null)

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/lower/ReplaceKFunctionInvokeWithFunctionInvoke.kt

@@ -0,0 +1,61 @@
+/*
+ * Copyright 2010-2019 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.backend.jvm.lower
+
+import org.jetbrains.kotlin.backend.common.FileLoweringPass
+import org.jetbrains.kotlin.backend.common.phaser.makeIrFilePhase
+import org.jetbrains.kotlin.backend.jvm.JvmBackendContext
+import org.jetbrains.kotlin.ir.declarations.IrClass
+import org.jetbrains.kotlin.ir.declarations.IrFile
+import org.jetbrains.kotlin.ir.declarations.IrSimpleFunction
+import org.jetbrains.kotlin.ir.expressions.IrCall
+import org.jetbrains.kotlin.ir.expressions.IrExpression
+import org.jetbrains.kotlin.ir.expressions.copyTypeArgumentsFrom
+import org.jetbrains.kotlin.ir.expressions.impl.IrCallImpl
+import org.jetbrains.kotlin.ir.util.defaultType
+import org.jetbrains.kotlin.ir.util.isKFunction
+import org.jetbrains.kotlin.ir.util.isKSuspendFunction
+import org.jetbrains.kotlin.ir.visitors.IrElementTransformerVoid
+import org.jetbrains.kotlin.ir.visitors.transformChildrenVoid
+import org.jetbrains.kotlin.util.OperatorNameConventions
+
+internal val replaceKFunctionInvokeWithFunctionInvokePhase = makeIrFilePhase<JvmBackendContext>(
+    { ReplaceKFunctionInvokeWithFunctionInvoke() },
+    name = "ReplaceKFunctionInvokeWithFunctionInvoke",
+    description = "Replace KFunction{n}.invoke with Function{n}.invoke"
+)
+
+/**
+ * This lowering replaces calls to `KFunction{n}.invoke` with `Function{n}.invoke`, and calls to `KSuspendFunction{n}.invoke`
+ * with `SuspendFunction{n}.invoke`. This is needed because normally the type e.g. `kotlin.reflect.KFunction2` is mapped to
+ * `kotlin.reflect.KFunction` (a real class, without arity), which doesn't have the corresponding `invoke`.
+ */
+private class ReplaceKFunctionInvokeWithFunctionInvoke : FileLoweringPass, IrElementTransformerVoid() {
+    override fun lower(irFile: IrFile) {
+        irFile.transformChildrenVoid(this)
+    }
+
+    override fun visitCall(expression: IrCall): IrExpression {
+        val callee = expression.symbol.owner
+        if (callee !is IrSimpleFunction || callee.name != OperatorNameConventions.INVOKE) return super.visitCall(expression)
+
+        val parentClass = callee.parent as? IrClass ?: return super.visitCall(expression)
+        if (!parentClass.defaultType.isKFunction() && !parentClass.defaultType.isKSuspendFunction()) return super.visitCall(expression)
+
+        // The single overridden function of KFunction{n}.invoke must be Function{n}.invoke.
+        val newCallee = callee.overriddenSymbols.single()
+        return expression.run {
+            IrCallImpl(startOffset, endOffset, type, newCallee).apply {
+                copyTypeArgumentsFrom(expression)
+                dispatchReceiver = expression.dispatchReceiver?.transform(this@ReplaceKFunctionInvokeWithFunctionInvoke, null)
+                extensionReceiver = expression.extensionReceiver?.transform(this@ReplaceKFunctionInvokeWithFunctionInvoke, null)
+                for (i in 0 until valueArgumentsCount) {
+                    putValueArgument(i, expression.getValueArgument(i)?.transform(this@ReplaceKFunctionInvokeWithFunctionInvoke, null))
+                }
+            }
+        }
+    }
+}