From 9ffa464dfb6a3f3fc7f8daed527e1a213ac74baa Mon Sep 17 00:00:00 2001
From: Simon Giesecke <sgiesecke@mozilla.com>
Date: Fri, 29 Nov 2019 10:40:55 +0000
Subject: [PATCH] Bug 1596395 - Avoid copying of tokenizer token sub-strings.
 r=dom-workers-and-storage-reviewers,edenchuang

Differential Revision: https://phabricator.services.mozilla.com/D53013

--HG--
extra : moz-landing-system : lando
---
 dom/indexedDB/ActorsParent.cpp | 5 ++---
 dom/indexedDB/KeyPath.cpp      | 8 ++++----
 2 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/dom/indexedDB/ActorsParent.cpp b/dom/indexedDB/ActorsParent.cpp
index 48948b4812c8..c527d7fdc713 100644
--- a/dom/indexedDB/ActorsParent.cpp
+++ b/dom/indexedDB/ActorsParent.cpp
@@ -8564,7 +8564,7 @@ class MOZ_STACK_CLASS FileHelper final {
 bool TokenizerIgnoreNothing(char16_t /* aChar */) { return false; }
 
 nsresult DeserializeStructuredCloneFile(const FileManager& aFileManager,
-                                        const nsString& aText,
+                                        const nsDependentSubstring& aText,
                                         StructuredCloneFile* aFile) {
   MOZ_ASSERT(!aText.IsEmpty());
   MOZ_ASSERT(aFile);
@@ -8634,11 +8634,10 @@ nsresult DeserializeStructuredCloneFiles(
   nsCharSeparatedTokenizerTemplate<TokenizerIgnoreNothing> tokenizer(aText,
                                                                      ' ');
 
-  nsAutoString token;
   nsresult rv;
 
   while (tokenizer.hasMoreTokens()) {
-    token = tokenizer.nextToken();
+    const auto& token = tokenizer.nextToken();
     MOZ_ASSERT(!token.IsEmpty());
 
     auto* const file = aResult.EmplaceBack(StructuredCloneFile::eBlob);
diff --git a/dom/indexedDB/KeyPath.cpp b/dom/indexedDB/KeyPath.cpp
index 95fa325a0b25..37a943494476 100644
--- a/dom/indexedDB/KeyPath.cpp
+++ b/dom/indexedDB/KeyPath.cpp
@@ -36,13 +36,13 @@ bool IsValidKeyPathString(const nsAString& aKeyPath) {
   KeyPathTokenizer tokenizer(aKeyPath, '.');
 
   while (tokenizer.hasMoreTokens()) {
-    nsString token(tokenizer.nextToken());
+    const auto& token = tokenizer.nextToken();
 
     if (!token.Length()) {
       return false;
     }
 
-    if (!JS_IsIdentifier(token.get(), token.Length())) {
+    if (!JS_IsIdentifier(token.Data(), token.Length())) {
       return false;
     }
   }
@@ -76,7 +76,7 @@ nsresult GetJSValFromKeyPathString(
   JS::Rooted<JSObject*> obj(aCx);
 
   while (tokenizer.hasMoreTokens()) {
-    const nsDependentSubstring& token = tokenizer.nextToken();
+    const auto& token = tokenizer.nextToken();
 
     NS_ASSERTION(!token.IsEmpty(), "Should be a valid keypath");
 
@@ -472,7 +472,7 @@ KeyPath KeyPath::DeserializeFromString(const nsAString& aString) {
       // There is a trailing comma, indicating the original KeyPath has
       // a trailing empty string, i.e. [..., '']. We should append this
       // empty string.
-      keyPath.mStrings.AppendElement(nsString{});
+      keyPath.mStrings.EmplaceBack();
     }
 
     return keyPath;