From 0d60cf211dc81cf2787a68e90d0e950165063aa2 Mon Sep 17 00:00:00 2001
From: Andreas Kling <kling@serenityos.org>
Date: Sat, 5 Feb 2022 17:59:14 +0100
Subject: [PATCH] LibJS: Cache valid indices in IndexedPropertyIterator

Refetching the list of indices every time we increment the iterator was
showing up hot & heavy in a profile of Discord.
---
 Userland/Libraries/LibJS/Runtime/IndexedProperties.cpp | 7 ++++---
 Userland/Libraries/LibJS/Runtime/IndexedProperties.h   | 1 +
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/Userland/Libraries/LibJS/Runtime/IndexedProperties.cpp b/Userland/Libraries/LibJS/Runtime/IndexedProperties.cpp
index b8bef63734..1d7bd301e5 100644
--- a/Userland/Libraries/LibJS/Runtime/IndexedProperties.cpp
+++ b/Userland/Libraries/LibJS/Runtime/IndexedProperties.cpp
@@ -177,8 +177,10 @@ IndexedPropertyIterator::IndexedPropertyIterator(const IndexedProperties& indexe
     , m_index(staring_index)
     , m_skip_empty(skip_empty)
 {
-    if (m_skip_empty)
+    if (m_skip_empty) {
+        m_cached_indices = m_indexed_properties.indices();
         skip_empty_indices();
+    }
 }
 
 IndexedPropertyIterator& IndexedPropertyIterator::operator++()
@@ -203,8 +205,7 @@ bool IndexedPropertyIterator::operator!=(const IndexedPropertyIterator& other) c
 
 void IndexedPropertyIterator::skip_empty_indices()
 {
-    auto indices = m_indexed_properties.indices();
-    for (auto i : indices) {
+    for (auto i : m_cached_indices) {
         if (i < m_index)
             continue;
         m_index = i;
diff --git a/Userland/Libraries/LibJS/Runtime/IndexedProperties.h b/Userland/Libraries/LibJS/Runtime/IndexedProperties.h
index db9777369e..53792f5746 100644
--- a/Userland/Libraries/LibJS/Runtime/IndexedProperties.h
+++ b/Userland/Libraries/LibJS/Runtime/IndexedProperties.h
@@ -106,6 +106,7 @@ private:
     void skip_empty_indices();
 
     const IndexedProperties& m_indexed_properties;
+    Vector<u32> m_cached_indices;
     u32 m_index;
     bool m_skip_empty;
 };