re-apply "Improve nsHtml5AtomTable performance (#693)" (#695)"

This reverts commit ca87455cc5880897c8b921077819988feede90bd.

1 files changed, 14 insertions, 0 deletions

diff --git a/parser/html/nsHtml5AtomTable.cpp b/parser/html/nsHtml5AtomTable.cpp
index d523f58b0..d9c18485d 100644
--- a/parser/html/nsHtml5AtomTable.cpp
+++ b/parser/html/nsHtml5AtomTable.cpp
@@ -31,7 +31,11 @@ nsHtml5AtomTable::nsHtml5AtomTable()
 }
 
 nsHtml5AtomTable::~nsHtml5AtomTable()
+  : mRecentlyUsedParserAtoms{}
 {
+#ifdef DEBUG
+  NS_GetMainThread(getter_AddRefs(mPermittedLookupThread));
+#endif
 }
 
 nsIAtom*
@@ -44,13 +48,23 @@ nsHtml5AtomTable::GetAtom(const nsAString& aKey)
     NS_ASSERTION(mPermittedLookupThread == currentThread, "Wrong thread!");
   }
 #endif
+
+  uint32_t index = mozilla::HashString(aKey) % RECENTLY_USED_PARSER_ATOMS_SIZE;
+  nsIAtom* cachedAtom = mRecentlyUsedParserAtoms[index];
+  if (cachedAtom && cachedAtom->Equals(aKey)) {
+    return cachedAtom;
+  }
+
   nsIAtom* atom = NS_GetStaticAtom(aKey);
   if (atom) {
+    mRecentlyUsedParserAtoms[index] = atom;
     return atom;
   }
   nsHtml5AtomEntry* entry = mTable.PutEntry(aKey);
   if (!entry) {
     return nullptr;
   }
+
+  mRecentlyUsedParserAtoms[index] = entry->GetAtom();
   return entry->GetAtom();
 }