JVM_IR: keep suspend fun return type in IrCalls

Otherwise:

  * should the dispatch receiver of a call be another call to a `suspend
    fun` wrapped in something that is optimized away later, the owner of
    the method will be incorrect;

  * references to functions returning non-Unit but casted to `() ->
    Unit` (allowed by new inference) might in fact not return Unit after
    tail call optimization.

compiler/testData/codegen/box/coroutines/suspendImplBridge.kt

@@ -0,0 +1,45 @@
+// IGNORE_BACKEND_FIR: JVM_IR
+// TARGET_BACKEND: JVM
+// WITH_RUNTIME
+// WITH_COROUTINES
+
+import kotlin.coroutines.*
+import kotlin.coroutines.intrinsics.*
+
+var result: String = ""
+var proceed: (() -> Unit)? = null
+
+fun box(): String {
+    async {
+        O().foo(1)
+        O().foo(2)
+    }
+    while (proceed != null) {
+        result += "--;"
+        proceed!!()
+    }
+    if (result != "begin(1);--;end(1);begin(2);--;end(2);done;") return result;
+    return "OK"
+}
+
+open class O {
+    open suspend fun foo(x: Int) {
+        result += "begin($x);"
+        sleep()
+        result += "end($x);"
+    }
+}
+
+suspend fun sleep(): Unit = suspendCoroutine { c ->
+    proceed = { c.resume(Unit) }
+}
+
+fun async(f: suspend () -> Unit) {
+    f.startCoroutine(object : Continuation<Unit> {
+        override fun resumeWith(x: Result<Unit>) {
+            result += "done;"
+            proceed = null
+        }
+        override val context = EmptyCoroutineContext
+    })
+}

compiler/testData/codegen/box/coroutines/suspendReturningPlatformType.kt

@@ -0,0 +1,31 @@
+// IGNORE_BACKEND_FIR: JVM_IR
+// TARGET_BACKEND: JVM
+// WITH_RUNTIME
+// WITH_COROUTINES
+
+// FILE: I.kt
+
+open class A<T> {
+    suspend fun id(x: T): T = x
+}
+
+class B {
+    fun ok() = "OK"
+}
+
+// FILE: JavaClass.java
+
+public class JavaClass extends A<B> {}
+
+// FILE: main.kt
+import helpers.*
+import kotlin.coroutines.*
+import kotlin.coroutines.intrinsics.*
+
+fun box(): String {
+    var result = "fail"
+    suspend {
+        result = JavaClass().id(B()).ok()
+    }.startCoroutine(EmptyContinuation)
+    return result
+}

compiler/testData/codegen/box/coroutines/tailCallOptimizations/unit/functionReference.kt

@@ -0,0 +1,24 @@
+// !LANGUAGE: +NewInference
+// IGNORE_BACKEND_FIR: JVM_IR
+// TARGET_BACKEND: JVM
+// WITH_RUNTIME
+// WITH_COROUTINES
+
+import helpers.*
+import kotlin.coroutines.*
+import kotlin.coroutines.intrinsics.*
+
+object Dummy
+
+suspend fun suspect(): Dummy = suspendCoroutineUninterceptedOrReturn {
+    x -> x.resume(Dummy)
+    COROUTINE_SUSPENDED
+}
+
+fun box(): String {
+    var res: Any? = null
+    suspend {
+        res = (::suspect as suspend () -> Unit)()
+    }.startCoroutine(EmptyContinuation)
+    return if (res != Unit) "$res" else "OK"
+}