From 7aaba3b78add36e0d5f1d1fbbcc58e9beaa15bed Mon Sep 17 00:00:00 2001
From: deotime <89555032+DeoTimeTheGithubUser@users.noreply.github.com>
Date: Wed, 5 Apr 2023 13:18:11 -0500
Subject: [PATCH] [KT-57607] Fix performance of ArrayList.addAll methods in JS
 stdlib (#5116)

* Fix performance of ArrayList.addAll methods in JS stdlib: extend the backing array and copy elements manually
* Update expected reachable nodes after DCE in test data

---------

Co-authored-by: Ilya Gorbunov <ilya.gorbunov@jetbrains.com>
---
 .../multiModule/privateInterfaceNameClash.kt  |  2 +-
 .../js/src/kotlin/collections/ArrayList.kt    | 22 ++++++++++++++-----
 2 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/js/js.translator/testData/box/multiModule/privateInterfaceNameClash.kt b/js/js.translator/testData/box/multiModule/privateInterfaceNameClash.kt
index dab0b9f07c6..e2d89a0cbe6 100644
--- a/js/js.translator/testData/box/multiModule/privateInterfaceNameClash.kt
+++ b/js/js.translator/testData/box/multiModule/privateInterfaceNameClash.kt
@@ -1,6 +1,6 @@
 // IGNORE_FIR
 // KJS_WITH_FULL_RUNTIME
-// EXPECTED_REACHABLE_NODES: 1819
+// EXPECTED_REACHABLE_NODES: 2002
 // MODULE: lib1
 // FILE: lib1.kt
 package lib1
diff --git a/libraries/stdlib/js/src/kotlin/collections/ArrayList.kt b/libraries/stdlib/js/src/kotlin/collections/ArrayList.kt
index 9689eaaf13a..fddcc6dce76 100644
--- a/libraries/stdlib/js/src/kotlin/collections/ArrayList.kt
+++ b/libraries/stdlib/js/src/kotlin/collections/ArrayList.kt
@@ -67,11 +67,20 @@ public actual open class ArrayList<E> internal constructor(private var array: Ar
         modCount++
     }
 
+    private fun increaseLength(amount: Int): Int {
+        val previous = size
+        array.asDynamic().length = size + amount
+        return previous
+    }
+
     actual override fun addAll(elements: Collection<E>): Boolean {
         checkIsMutable()
         if (elements.isEmpty()) return false
 
-        array += elements.toTypedArray<Any?>()
+        val offset = increaseLength(elements.size)
+        elements.forEachIndexed { index, element ->
+            array[offset + index] = element
+        }
         modCount++
         return true
     }
@@ -82,10 +91,13 @@ public actual open class ArrayList<E> internal constructor(private var array: Ar
 
         if (index == size) return addAll(elements)
         if (elements.isEmpty()) return false
-        when (index) {
-            size -> return addAll(elements)
-            0 -> array = elements.toTypedArray<Any?>() + array
-            else -> array = array.copyOfRange(0, index).asDynamic().concat(elements.toTypedArray<Any?>(), array.copyOfRange(index, size))
+
+        val tail = array.asDynamic().splice(index).unsafeCast<Array<E>>()
+        addAll(elements)
+
+        val offset = increaseLength(tail.size)
+        repeat(tail.size) { tailIndex ->
+            array[offset + tailIndex] = tail[tailIndex]
         }
 
         modCount++