Bug 1846695 - Have a trivially move assignable and constructible StartupCacheEntry::KeyValuePair. r=xpcom-reviewers,emilio

Depends on D182731

Differential Revision: https://phabricator.services.mozilla.com/D185065

startupcache/StartupCache.cpp

@@ -520,11 +520,12 @@ Result<Ok, nsresult> StartupCache::WriteToDisk() {
   MOZ_TRY(mFile->OpenNSPRFileDesc(PR_WRONLY | PR_CREATE_FILE | PR_TRUNCATE,
                                   0644, &fd.rwget()));
 
-  nsTArray<std::pair<const nsCString*, StartupCacheEntry*>> entries;
+  nsTArray<StartupCacheEntry::KeyValuePair> entries(mTable.count());
   for (auto iter = mTable.iter(); !iter.done(); iter.next()) {
     if (iter.get().value().mRequested) {
-      entries.AppendElement(
-          std::make_pair(&iter.get().key(), &iter.get().value()));
+      StartupCacheEntry::KeyValuePair kv(&iter.get().key(),
+                                         &iter.get().value());
+      entries.AppendElement(kv);
     }
   }
 
@@ -535,8 +536,8 @@ Result<Ok, nsresult> StartupCache::WriteToDisk() {
   entries.Sort(StartupCacheEntry::Comparator());
   loader::OutputBuffer buf;
   for (auto& e : entries) {
-    auto key = e.first;
-    auto value = e.second;
+    auto* key = e.first;
+    auto* value = e.second;
     auto uncompressedSize = value->mUncompressedSize;
     // Set the mHeaderOffsetInFile so we can go back and edit the offset.
     value->mHeaderOffsetInFile = buf.cursor();

startupcache/StartupCache.h

@@ -113,8 +113,18 @@ struct StartupCacheEntry {
         mRequestedOrder(0),
         mRequested(true) {}
 
+  // std::pair is not trivially move assignable/constructible, so make our own.
+  struct KeyValuePair {
+    const nsCString* first;
+    StartupCacheEntry* second;
+    KeyValuePair(const nsCString* aKeyPtr, StartupCacheEntry* aValuePtr)
+        : first(aKeyPtr), second(aValuePtr) {}
+  };
+  static_assert(std::is_trivially_move_assignable<KeyValuePair>::value);
+  static_assert(std::is_trivially_move_constructible<KeyValuePair>::value);
+
   struct Comparator {
-    using Value = std::pair<const nsCString*, StartupCacheEntry*>;
+    using Value = KeyValuePair;
 
     bool Equals(const Value& a, const Value& b) const {
       return a.second->mRequestedOrder == b.second->mRequestedOrder;