Fix incorrect code generation for Nothing-returning suspend calls

#KT-30642 Fixed

backend.native/compiler/ir/backend.native/src/org/jetbrains/kotlin/backend/konan/llvm/IrToBitcode.kt

@@ -2148,7 +2148,7 @@ internal class CodeGeneratorVisitor(val context: Context, val lifetimes: Map<IrE
     private fun call(function: IrFunction, llvmFunction: LLVMValueRef, args: List<LLVMValueRef>,
                      resultLifetime: Lifetime): LLVMValueRef {
         val result = call(llvmFunction, args, resultLifetime)
-        if (function.returnType.isNothing()) {
+        if (!function.isSuspend && function.returnType.isNothing()) {
             functionGenerationContext.unreachable()
         }
 

backend.native/tests/build.gradle

@@ -1543,6 +1543,11 @@ task coroutines_controlFlow_while2(type: RunKonanTest) {
     source = "codegen/coroutines/controlFlow_while2.kt"
 }
 
+task coroutines_returnsNothing1(type: RunKonanTest) {
+    goldValue = "OK\n"
+    source = "codegen/coroutines/returnsNothing1.kt"
+}
+
 task coroutines_returnsUnit1(type: RunKonanTest) {
     goldValue = "117\ns1\n0\n"
     source = "codegen/coroutines/returnsUnit1.kt"

backend.native/tests/codegen/coroutines/returnsNothing1.kt

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2010-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the LICENSE file.
+ */
+
+package codegen.coroutines.returnsNothing1
+
+import kotlin.test.*
+
+import kotlin.coroutines.*
+import kotlin.coroutines.intrinsics.*
+
+open class EmptyContinuation(override val context: CoroutineContext = EmptyCoroutineContext) : Continuation<Any?> {
+    companion object : EmptyContinuation()
+    override fun resumeWith(result: Result<Any?>) { result.getOrThrow() }
+}
+
+suspend fun suspendForever(): Int = suspendCoroutineUninterceptedOrReturn {
+    COROUTINE_SUSPENDED
+}
+
+suspend fun foo(): Nothing {
+    suspendForever()
+    throw Error()
+}
+
+suspend fun bar() {
+    foo()
+}
+
+fun builder(c: suspend () -> Unit) {
+    c.startCoroutine(EmptyContinuation)
+}
+
+@Test fun runTest() {
+    builder {
+        bar()
+    }
+    println("OK")
+}