JS: improve dead code elimination to handle switch case bodies

Author: Alexey Andreev

js/js.inliner/src/org/jetbrains/kotlin/js/inline/clean/DeadCodeElimination.kt

@@ -56,10 +56,14 @@ internal class DeadCodeElimination(private val root: JsStatement) {
 
         override fun visitBlock(x: JsBlock) {
             canContinue = true
-            for ((index, statement) in x.statements.withIndex()) {
+            visitStatements(x.statements)
+        }
+
+        private fun visitStatements(statements: MutableList<JsStatement>) {
+            for ((index, statement) in statements.withIndex()) {
                 accept(statement)
                 if (!canContinue) {
-                    val removedStatements = x.statements.subList(index + 1, x.statements.size)
+                    val removedStatements = statements.subList(index + 1, statements.size)
                     if (removedStatements.isNotEmpty()) {
                         hasChanges = true
                         removedStatements.clear()
@@ -174,7 +178,7 @@ internal class DeadCodeElimination(private val root: JsStatement) {
 
             for (caseBlock in x.cases) {
                 canContinue = true
-                caseBlock.statements.forEach { accept(it) }
+                visitStatements(caseBlock.statements)
 
                 if (!canContinue && localBreakExists) {
                     canContinue = true

js/js.tests/test/org/jetbrains/kotlin/js/test/optimizer/DeadCodeEliminationTest.kt

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2010-2016 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jetbrains.kotlin.js.test.optimizer
+
+import org.junit.Test
+
+class DeadCodeEliminationTest : BasicOptimizerTest("dead-code-elimination") {
+    @Test fun switchCases() = box()
+}

js/js.translator/testData/js-optimizer/dead-code-elimination/switchCases.optimized.js

@@ -0,0 +1,35 @@
+function test(x) {
+    var log = "";
+    switch (x) {
+        case 0:
+            log += "0;";
+            break;
+        case 1:
+            return "one";
+        case 2:
+            log += "2;";
+        case 3:
+            log += "3;";
+            break;
+        default:
+            if (x == 4) {
+                log += "four;";
+                break;
+            }
+            else {
+                return "default";
+            }
+    }
+    return log;
+}
+
+function box() {
+    if (test(0) != "0;") return "fail1";
+    if (test(1) != "one") return "fail2";
+    if (test(2) != "2;3;") return "fail3";
+    if (test(3) != "3;") return "fail4";
+    if (test(4) != "four;") return "fail5";
+    if (test(5) != "default") return "fail5";
+
+    return "OK";
+}

js/js.translator/testData/js-optimizer/dead-code-elimination/switchCases.original.js

@@ -0,0 +1,40 @@
+function test(x) {
+    var log = "";
+    switch (x) {
+        case 0:
+            log += "0;";
+            break;
+            log += "00;";
+            break;
+        case 1:
+            return "one";
+            return "uno";
+        case 2:
+            log += "2;";
+        case 3:
+            log += "3;";
+            break;
+        default:
+            if (x == 4) {
+                log += "four;";
+                break;
+            }
+            else {
+                return "default";
+            }
+            log += "!";
+            return "!" + log;
+    }
+    return log;
+}
+
+function box() {
+    if (test(0) != "0;") return "fail1";
+    if (test(1) != "one") return "fail2";
+    if (test(2) != "2;3;") return "fail3";
+    if (test(3) != "3;") return "fail4";
+    if (test(4) != "four;") return "fail5";
+    if (test(5) != "default") return "fail5";
+
+    return "OK";
+}