[JS IR BE] Fix @DoNotIntrinsify processing. Reuse it for compareTo

libraries/stdlib/js/irRuntime/charSequence.kt

@@ -10,7 +10,7 @@ internal annotation class DoNotIntrinsify
 @PublishedApi
 @DoNotIntrinsify
 internal fun charSequenceGet(a: CharSequence, index: Int): Char {
-    return  if (a is String) {
+    return if (isString(a)) {
         Char(a.asDynamic().charCodeAt(index).unsafeCast<Int>())
     } else {
         a[index]
@@ -20,8 +20,8 @@ internal fun charSequenceGet(a: CharSequence, index: Int): Char {
 @PublishedApi
 @DoNotIntrinsify
 internal fun charSequenceLength(a: CharSequence): Int {
-    return if (a is String) {
-        a.asDynamic().length.unsafeCast<Int>()
+    return if (isString(a)) {
+        js("a.length").unsafeCast<Int>()
     } else {
         a.length
     }
@@ -30,9 +30,12 @@ internal fun charSequenceLength(a: CharSequence): Int {
 @PublishedApi
 @DoNotIntrinsify
 internal fun charSequenceSubSequence(a: CharSequence, startIndex: Int, endIndex: Int): CharSequence {
-    return if (a is String) {
+    return if (isString(a)) {
         a.asDynamic().substring(startIndex, endIndex).unsafeCast<String>()
     } else {
         a.subSequence(startIndex, endIndex)
     }
 }
+
+// Keeping this function as separate non-inline to intrincify `is` operator
+internal fun isString(a: CharSequence) = a is String

libraries/stdlib/js/irRuntime/compareTo.kt

@@ -23,7 +23,7 @@ fun compareTo(a: dynamic, b: dynamic): Int {
     return compareToDoNotIntrinsicify(a, b)
 }
 
-// TODO: Use @DoNotIntrincify annotation
+@DoNotIntrinsify
 private fun <T : Comparable<T>> compareToDoNotIntrinsicify(a: Comparable<T>, b: T) =
     a.compareTo(b)