Mark only unreachable parts of element if it has reachable parts

like for 'return todo()' mark only 'return'

compiler/testData/diagnostics/tests/controlFlowAnalysis/deadCode/deadCodeInLoops.kt

@@ -0,0 +1,21 @@
+fun testFor() {
+    fun Nothing.iterator() = (0..1).iterator()
+
+    <!UNREACHABLE_CODE!>for (i in<!> todo()<!UNREACHABLE_CODE!>) {}<!>
+}
+
+fun testWhile() {
+    <!UNREACHABLE_CODE!>while (<!>todo()<!UNREACHABLE_CODE!>) {
+    }<!>
+}
+
+fun testDoWhile() {
+    do {
+
+    } while(todo())
+
+    <!UNREACHABLE_CODE!>bar()<!>
+}
+
+fun todo() = throw Exception()
+fun bar() {}