[IR][Native] Fix invalid IR return statement generation

^KT-46836

kotlin-native/backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/lower/ReturnsInsertionLowering.kt

@@ -16,6 +16,7 @@ import org.jetbrains.kotlin.ir.declarations.IrFile
 import org.jetbrains.kotlin.ir.declarations.IrFunction
 import org.jetbrains.kotlin.ir.expressions.*
 import org.jetbrains.kotlin.ir.expressions.impl.IrBlockBodyImpl
+import org.jetbrains.kotlin.ir.types.isNullableNothing
 import org.jetbrains.kotlin.ir.util.isSimpleTypeWithQuestionMark
 import org.jetbrains.kotlin.ir.visitors.IrElementVisitorVoid
 import org.jetbrains.kotlin.ir.visitors.acceptChildrenVoid
@@ -46,7 +47,8 @@ internal class ReturnsInsertionLowering(val context: Context) : FileLoweringPass
                             } else if (declaration.returnType.isSimpleTypeWithQuestionMark) {
                                 // this is a workaround for KT-42832
                                 val typeOperatorCall = body.statements.lastOrNull() as? IrTypeOperatorCall
-                                if (typeOperatorCall?.operator == IrTypeOperator.IMPLICIT_COERCION_TO_UNIT) {
+                                if (typeOperatorCall?.operator == IrTypeOperator.IMPLICIT_COERCION_TO_UNIT
+                                        && typeOperatorCall.argument.type.isNullableNothing()) {
                                     body.statements[body.statements.lastIndex] = irReturn(typeOperatorCall.argument)
                                 }
                             }

kotlin-native/backend.native/tests/build.gradle

@@ -533,6 +533,12 @@ standaloneTest("function_nothingN_returning_safe_call") {
     source = "codegen/function/nothingNReturningSafeCall.kt"
 }
 
+standaloneTest("unreachable_statement_after_return") {
+    flags = ["-g", "-entry", "codegen.function.unreachable_statement_after_return.main"]
+    source = "codegen/function/unreachableStatementAfterReturn.kt"
+    goldValue = "1\n2\n3\n4\n"
+}
+
 task codegen_controlflow_for_loops(type: KonanLocalTest) {
     source = "codegen/controlflow/for_loops.kt"
     goldValue = "01234\n0123\n43210\n\n024\n02\n420\n\n036\n03\n630\n\n024\n02\n420\n\n"

kotlin-native/backend.native/tests/codegen/function/unreachableStatementAfterReturn.kt

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2010-2021 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 codegen.function.unreachable_statement_after_return
+
+fun test1(): Any? {
+    return 1
+    42
+}
+
+fun test2(): Int? {
+    return 2
+    42
+}
+
+fun test3(): Any {
+    return 3
+    42
+}
+
+fun test4(): Int {
+    return 4
+    42
+}
+
+fun main() {
+    println(test1())
+    println(test2())
+    println(test3())
+    println(test4())
+}
+