When by String constants:

Generate TABLESWITCH/LOOKUPSWITCH bytecode operation for when operator by String constants

compiler/testData/codegen/boxWithStdlib/whenStringOptimization/expression.kt

@@ -0,0 +1,20 @@
+import kotlin.test.assertEquals
+
+fun foo(x : String) : String {
+    return when (x) {
+        "abc", "cde" -> "abc_cde"
+        "efg", "ghi" -> "efg_ghi"
+        else -> "other"
+    }
+}
+
+fun box() : String {
+    assertEquals("abc_cde", foo("abc"))
+    assertEquals("abc_cde", foo("cde"))
+    assertEquals("efg_ghi", foo("efg"))
+    assertEquals("efg_ghi", foo("ghi"))
+
+    assertEquals("other", foo("xyz"))
+
+    return "OK"
+}