JS: translate when to JsSwitch when possible

See KT-21160

compiler/testData/codegen/box/when/stringOptimization/duplicatingItems.kt

@@ -1,4 +1,6 @@
 // WITH_RUNTIME
+// CHECK_CASES_COUNT: function=foo count=3
+// CHECK_IF_COUNT: function=foo count=0
 
 import kotlin.test.assertEquals
 

compiler/testData/codegen/box/when/stringOptimization/expression.kt

@@ -1,4 +1,6 @@
 // WITH_RUNTIME
+// CHECK_CASES_COUNT: function=foo count=4
+// CHECK_IF_COUNT: function=foo count=0
 
 import kotlin.test.assertEquals
 

compiler/testData/codegen/box/when/stringOptimization/nullability.kt

@@ -1,4 +1,8 @@
 // WITH_RUNTIME
+// CHECK_CASES_COUNT: function=foo1 count=2
+// CHECK_IF_COUNT: function=foo1 count=1
+// CHECK_CASES_COUNT: function=foo2 count=4
+// CHECK_IF_COUNT: function=foo2 count=0
 
 import kotlin.test.assertEquals
 

compiler/testData/codegen/box/when/stringOptimization/statement.kt

@@ -1,4 +1,8 @@
 // WITH_RUNTIME
+// CHECK_CASES_COUNT: function=foo1 count=4
+// CHECK_IF_COUNT: function=foo1 count=0
+// CHECK_CASES_COUNT: function=foo2 count=4
+// CHECK_IF_COUNT: function=foo2 count=0
 
 import kotlin.test.assertEquals
 

compiler/testData/codegen/box/when/switchOptimizationDense.kt

@@ -1,4 +1,6 @@
 // WITH_RUNTIME
+// CHECK_CASES_COUNT: function=dense count=10
+// CHECK_IF_COUNT: function=dense count=0
 
 fun dense(x: Int): Int {
     return when (x) {

compiler/testData/codegen/box/when/switchOptimizationMultipleConditions.kt

@@ -1,4 +1,6 @@
 // WITH_RUNTIME
+// CHECK_CASES_COUNT: function=foo count=9
+// CHECK_IF_COUNT: function=foo count=0
 
 fun foo(x: Int): Int {
     return when (x) {

compiler/testData/codegen/box/when/switchOptimizationSparse.kt

@@ -1,4 +1,6 @@
 // WITH_RUNTIME
+// CHECK_CASES_COUNT: function=sparse count=3
+// CHECK_IF_COUNT: function=sparse count=0
 
 fun sparse(x: Int): Int {
     return when ((x % 4) * 100) {

compiler/testData/codegen/box/when/switchOptimizationStatement.kt

@@ -1,4 +1,8 @@
 // WITH_RUNTIME
+// CHECK_CASES_COUNT: function=exhaustive count=3
+// CHECK_IF_COUNT: function=exhaustive count=0
+// CHECK_CASES_COUNT: function=nonExhaustive count=3
+// CHECK_IF_COUNT: function=nonExhaustive count=0
 
 fun exhaustive(x: Int): Int {
     var r: Int

compiler/testData/codegen/box/when/switchOptimizationTypes.kt

@@ -1,4 +1,12 @@
 // WITH_RUNTIME
+// CHECK_CASES_COUNT: function=intFoo count=3
+// CHECK_IF_COUNT: function=intFoo count=0
+// CHECK_CASES_COUNT: function=shortFoo count=3
+// CHECK_IF_COUNT: function=shortFoo count=0
+// CHECK_CASES_COUNT: function=byteFoo count=3
+// CHECK_IF_COUNT: function=byteFoo count=0
+// CHECK_CASES_COUNT: function=charFoo count=3
+// CHECK_IF_COUNT: function=charFoo count=0
 
 fun intFoo(x: Int): Int {
     return when (x) {

compiler/testData/codegen/box/when/switchOptimizationUnordered.kt

@@ -1,4 +1,6 @@
 // WITH_RUNTIME
+// CHECK_CASES_COUNT: function=foo count=3
+// CHECK_IF_COUNT: function=foo count=0
 
 fun foo(x: Int): Int {
     return when (x) {

compiler/testData/codegen/box/when/switchOptimizationWithGap.kt

@@ -0,0 +1,31 @@
+// WITH_RUNTIME
+// CHECK_CASES_COUNT: function=foo count=4
+// CHECK_IF_COUNT: function=foo count=1
+
+var log = ""
+
+fun foo(x: Int): String {
+    log += "foo($x);"
+    return when (x) {
+        1 -> "one"
+        2 -> "two"
+        three(x) -> "three"
+        4 -> "four"
+        5 -> "five"
+        else -> "many"
+    }
+}
+
+fun three(x: Int): Int {
+    log += "three($x);"
+    return 3
+}
+
+fun box(): String {
+    var result = (1..7).map(::foo).joinToString()
+
+    if (result != "one, two, three, four, five, many, many") return "fail1: $result"
+    if (log != "foo(1);foo(2);foo(3);three(3);foo(4);three(4);foo(5);three(5);foo(6);three(6);foo(7);three(7);") return "fail2: $log"
+
+    return "OK"
+}